Waste Management 33 (2013) 2328–2340
Contents lists available at SciVerse ScienceDirect
Waste Management
journal homepage: www.elsevier.com/locate/wasman
Review
Recycling and recovery routes for incinerated sewage sludge ash (ISSA):
A review
Shane Donatello a,⇑, Christopher R. Cheeseman b
a
b
Department of Cement and Material Recycling, Eduardo Torroja Institute of Construction Sciences (CSIC), C/Serrano Galvache 4, 28033 Madrid, Spain
Department of Civil and Environmental Engineering, Imperial College London, South Kensington SW7 2AZ, London, UK
a r t i c l e
i n f o
Article history:
Received 4 December 2012
Accepted 29 May 2013
Available online 29 June 2013
Keywords:
Sewage sludge incineration
Ash characteristics
Pozzolanic cements
Phosphate recovery
Ceramics
Sintered brick and tile
a b s t r a c t
The drivers for increasing incineration of sewage sludge and the characteristics of the resulting incinerated sewage sludge ash (ISSA) are reviewed. It is estimated that approximately 1.7 million tonnes of ISSA
are produced annually world-wide and is likely to increase in the future. Although most ISSA is currently
landfilled, various options have been investigated that allow recycling and beneficial resource recovery.
These include the use of ISSA as a substitute for clay in sintered bricks, tiles and pavers, and as a raw
material for the manufacture of lightweight aggregate. ISSA has also been used to form high density
glass–ceramics. Significant research has investigated the potential use of ISSA in blended cements for
use in mortars and concrete, and as a raw material for the production of Portland cement. However,
all these applications represent a loss of the valuable phosphate content in ISSA, which is typically comparable to that of a low grade phosphate ore. ISSA has significant potential to be used as a secondary
source of phosphate for the production of fertilisers and phosphoric acid. Resource efficient approaches
to recycling will increasingly require phosphate recovery from ISSA, with the remaining residual fraction
also considered a useful material, and therefore further research is required in this area.
Ó 2013 Elsevier Ltd. All rights reserved.
Contents
1.
2.
3.
4.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.
Sewage sludge disposal practices in the EU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.
Mono-combustion of sewage sludge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Incinerated sewage sludge ash (ISSA) characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Recycling and recovery options for ISSA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.
Sintered materials containing ISSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.1.
Sintering studies using ISSA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.2.
Bricks, tiles and pavers containing ISSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.3.
Manufacture of lightweight aggregates from ISSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.
Glass–ceramics containing ISSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3.
Lightweight aerated cementitious materials containing ISSA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.
Use of ISSA in cementitious materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.1.
Use of ISSA in the Portland cement manufacturing process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.2.
Use of ISSA as an additive to Portland cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4.3.
Pozzolanic activity of ISSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5.
Phosphate recovery from ISSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5.1.
Recovery of P by acid leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5.2.
Recycling of acid insoluble ISSA residue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5.3.
Thermal methods of P recovery from ISSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.6.
Other recycling and recovery options for ISSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
⇑ Corresponding author. Tel.: +34 913 020 440; fax: +34 913 020 700.
E-mail address: [email protected] (S. Donatello).
0956-053X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.wasman.2013.05.024
2329
2329
2329
2331
2331
2331
2331
2332
2332
2333
2333
2333
2333
2334
2334
2335
2336
2337
2337
2338
2338
2338
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
1. Introduction
1.1. Sewage sludge disposal practices in the EU
The application of sewage sludge to agricultural land is generally considered to be the ‘‘Best Practical Environmental Option’’ because the N, P and K content of sludge provides high fertiliser value
and the organic matter acts as a useful soil conditioner. However, a
number of factors are making land-spreading of sewage sludge
increasingly difficult. For example, the transport time and distances between utilities producing sludge and suitable agricultural
land are generally increasing and this is increasing costs. While
sludge disposal to land is regulated by the EU Sludge Directive
(86/278/EC), many countries have applied tighter limits because
of public concerns associated with pathogen transfer to crops
and the accumulation of heavy metals in agricultural soils. For
example, in the UK a voluntary code of conduct known as the ‘‘Safe
Sludge Matrix’’ has been introduced and this only permits limited
application of pre-treated sewage sludge under specific conditions
(ADAS, 2001). However, it should also be noted that sewage sludge
is exempt from controls and charges for the land disposal of other
wastes levied via the UK Environmental Permitting scheme. In the
Netherlands, the Flemish region of Belgium and regions of Germany that have sandy soils, land-spreading has effectively been
banned due to the adoption of prohibitively restrictive heavy metal
limits for sewage sludge and sludge treated soils (Milieu et al.,
2010). In other countries such as Greece, Italy, Malta and Iceland,
landfill remains the major disposal route for sewage sludge. This
will become difficult to justify in the EU as the EU Landfill Directive
(99/31/EC) places increasing restrictions on the quantities of biodegradable waste that can be landfilled due to concerns over methane generation under anaerobic conditions. An alternative to these
options was sea disposal of sewage sludge but this has been
banned in EU countries since 1999 following the implementation
of the EU Urban Wastewater Treatment Directive (1991). The differences in current sewage sludge disposal practices in EU countries from data available via Eurostat are shown in Fig. 1.
The major alternative to land-spreading and landfill are thermal
treatment processes. It can clearly be seen from Fig. 1 that the
countries with low levels of land-spreading have invested significantly in incineration. An important advantage of incineration is
the degree of control this provides to sewage sludge managers.
Fig. 1. Sewage sludge disposal management practices in EU countries in 2009 or in
the year of latest available data on Eurostat. Data expressed as % of total sludge
mass produced in each country. Note that data for Portugal and Denmark was not
available.
2329
Poor weather, changes in landowner attitudes and unexpected
occurrences such as the foot and mouth disease outbreak in the
UK in 2001 can have a dramatic effect on land disposal capacity.
Such impacts do not normally affect sewage sludge disposal using
thermal treatment technologies. For an excellent review of thermal
treatment options of sewage sludge the reader is directed to work
by Werther and Ogada (1999) and Fytili and Zabaniotou (2008).
Outside of the EU, there is a long history of sewage sludge incineration in the USA and Japan. Densely populated regions such as
those in Japan have the double problem of high quantities of sludge
production and low land availability. The largest sewage sludge
incineration plant in the world is currently under construction in
Hong Kong and is expected to produce around 240,000 tonnes of
ISSA per year from 2013 onwards.
1.2. Mono-combustion of sewage sludge
During incineration, organic matter is combusted to CO2 and
other trace gases, with water removed as vapour. The process cannot be considered as a complete disposal option because significant quantities of inorganic incinerated sewage sludge ash (ISSA)
remain. This is removed from flue gases and requires further
management.
This paper focuses on the ISSA generated by conventional
mono-combustion of sewage sludge. Although there are some
examples of co-combustion of sewage sludge with coal (Ireland
et al., 2004; Leckner et al., 2004; Wolski et al., 2004), there are
important legal issues that need to be overcome involving both
the definition of sewage sludge as a waste or fuel and standards
for the use of subsequent co-combustion ashes (Cenni et al.,
2001; EN 197-1). These issues also apply to ISSA despite the fact
that mono-combustion of sewage sludge has been widely practised
at an industrial scale in many dedicated plants across the world
over several decades (Werther and Ogada, 1999).
An overview of a typical modern fluidised bed sewage sludge
mono-combustion process is given in Fig. 2. Primary and secondary
sewage sludge typically consists of 1–4 wt.% solids and this is
pumped to tanks for further treatment. Fig. 2 shows a thickening
stage where sludge settles and the supernatant is removed. This
raises the solids content to 3–8 wt.% solids. Thickened sludge is
then dewatered typically using plate or belt presses. At this stage
organic or inorganic additives can be employed to improve dewatering. For incineration there is an obvious incentive to optimise
dewatering using organic additives as there are dual advantages
of improving sludge calorific value and reducing inorganic ash content. The solids content of dewatered sludge typically varies from
18 to 35 wt.%.
Although the calorific value of sewage sludge is often regarded
as similar to that of brown coal, this is somewhat misleading. The
calorific value of the solid organic matter present in sewage sludge
does have similar calorific value to brown coal, but when sewage
sludge is considered as a potential fuel, consideration has to be given to the accompanying inorganic solids, which have no calorific
value. In addition, the water content consumes heat as it is vapourised. Sewage sludge typically has to be at least 28–33 wt.% solids to
burn auto-thermically, with no requirement for external fuel to
maintain the incineration process. Some researchers have examined the combustion of sewage sludge with significantly higher
solids content, with the aim of minimising supplementary fuel
requirements (Sanger et al., 2001). However, any gain in energy
output must be balanced against the energy input required for drying the feed sludge to higher solids content.
Sludge and hot compressed air (ca. 500–600 °C) are fed to the
combustion chamber. The sand bed temperature is typically
750 °C and the overhead freeboard zone at 800–900 °C. Guidance
on good operation is provided by technical documents (PD CEN,
2330
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
Fig. 2. Overview of the sewage sludge incineration process (adapted from Arundel (2000)).
Fig. 3. A breakdown of likely physicochemical processes occurring to a sludge floc upon entering a sewage sludge incinerator and heat exchanger (from Donatello (2009)).
2004; USEPA, 2003). Temperatures can be finely controlled by the
injection of water or liquefied gas oil. The sand bed acts as a ‘‘thermal fly wheel’’ and helps stabilise temperature fluctuations in the
incinerator. Particle residence times in the combustion chamber
are typically only 1–2 s (Arundel, 2000) and during this time water
is evaporated, volatile metals vapourise and organic compounds
are combusted completely to gases, either directly or via the formation of an intermediate char. The remaining inorganic material
is carried out of the chamber as fine particulates with the exhaust
gases. The ash is generally removed by bag filters, electrostatic pre-
cipitators or cyclones after passing through a heat exchanger. The
flue gas is then treated using a wet scrubber with acid, alkali and
possibly activated carbon dosing to comply with emission limits,
as required by EU Waste Incineration Directive (2000/76/EC). The
scrubbing process produces an additional waste sludge, which is
dewatered and normally disposed of in hazardous waste landfill.
Sewage sludge combustion is different from normal fuel combustion due to the high quantity of water present (Solimene
et al., 2010; Urciuolo et al., 2012). The characteristics of the ashes
resulting from sewage sludge combustion differ significantly from
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
those of, for example, coal fly ash. Coal fly ashes contain different
amorphous and crystalline aluminosilicate phases due to the much
higher temperatures involved in coal combustion (1500–1700 °C
versus 800–900 °C) and coal is generally poor in nutrients such
as P, which are concentrated in sewage sludge ash.
2. Incinerated sewage sludge ash (ISSA) characteristics
A schematic diagram is given in Fig. 3 that highlights the rapid
physical and chemical processes that occur to sewage sludge particles in the combustion chamber and the flue gas heat exchangers
of a sludge incinerator. Approximately one third of the solids content of sewage sludge consists of inorganic matter which forms
ISSA particles during combustion. Typical removal efficiencies of
ash particles suspended in the flue gas are 95–99%. This translates
to an estimated global ISSA production of 1.7 mt per year, mainly
from the USA, the EU and Japan, which are the main regions operating sewage sludge incinerators (Cyr et al., 2007; Murakami et al.,
2009).
The general characteristics of ISSA have been reported in the literature (Cyr et al., 2007) and this shows that the major elements in
ISSA are Si, Al, Ca, Fe and P. Crystalline forms of these elements are
invariably quartz (SiO2), whitlockite (Ca3(PO4)2) and hematite
(Fe2O3). Aluminium is typically present in feldspar and XRD amorphous glassy phases (Mahieux et al., 2010). These authors report
that the amorphous glassy phase content can vary considerably between ISSA samples. This is an important characteristic when considering ISSA as a potential pozzolanic additive in blended
cements. The ISSA particle size distribution is also important. A
literature review by Cyr et al., (2007) and data from samples from
different UK incinerators reported by Donatello (2009) showed
that mean particle diameters can range from 8 to 263 lm with
particle sizes ranging from submicron to around 700 lm. The exact
contents of the major elements depend on the sludge treatment
processes applied at wastewater plants and other factors, such as
the level of industrial activity in the catchment area and whether
or not the sewerage system is combined (collecting storm-water)
(Wiebusch and Seyfried, 1997). The choice of sludge dewatering
aid will affect the ISSA composition. If tertiary sludge is included
in the feed, then the precipitation salt used to remove P (typically
FeCl3 or Al2(SO4)3 are used) will increase the Fe or Al content in
ISSA respectively. Even in a plant operating under steady conditions, the major elements in ISSA can vary (Anderson and Skerratt,
2003; Wiebusch and Seyfried, 1997). Loss on ignition values for
ISSA, which is essentially a measure of unburned carbon content,
are typically below 3 wt.%, which is indicative of efficient combustion of the feed sludge.
Minor elements present in ISSA are much more variable and can
be strongly influenced by the degree and nature of industrial activity within the catchment area of the wastewater treatment plant.
Metals such as Hg, Cd, Sb, As and Pb are expected to be volatilised
during combustion (Elled et al., 2007). However, in an industrial
scale study run over 1 year, it was found that 20% of Hg, 93% of
As and almost 100% of Cd and Pb were retained in the ISSA (Van
de Velden et al., 2008). These findings support the theory that volatile trace metals condense on ash surfaces as temperatures fall
during flue gas heat recovery, as illustrated in Fig. 3. A laboratory
scale study by Corella and Toledo (2000) revealed that thermodynamic predictions of the fate of heavy metal during fluidised bed
sewage sludge combustion were not accurate because metal
behaviour is controlled by fluid dynamics and kinetic factors associated with the limited residence time in the combustion chamber.
Ecotoxicity is a relatively new hazardous property used to classify wastes (EU Hazardous Waste Directive, 91/689/EC). As far as
the authors are aware, only two papers have been published to
2331
date regarding the ecotoxicity of ISSA from the mono-combustion
of sewage sludge. A study by Lapa et al. (2007) focused on both
ecotoxicological and chemical methods to analyse leachates, prepared according to EN 12457-3. Results were inconsistent and
there was poor correlation between the methods used. In work
published by Donatello et al. (2010a), the chemical method was
followed according to UK Environment Agency guidance (Environment Agency, 2011), and revealed that the major element of concern was Zn. Several compounds that contain Zn have been
assigned ecotoxicological risk phrases (R50-53). If these compounds can be assumed to exceed a combined concentration of
2500 mg/kg, in the EU at least, the ash would be classified as hazardous waste via the H14 ecotoxic category. If all Zn is assumed to
exist as ZnO, total Zn concentrations of 2009 mg/kg would reach
the H14 threshold. If assuming all Zn to be present as other compounds where Zn constitutes a smaller% mass, such as ZnCl2 or
Zn3(PO4)2, the total Zn level permitted would be even lower,
around 1200 mg/kg (Donatello et al., 2010a). There is a need to better understand to real Zn speciation in ISSA. Geochemical modelling could be particularly beneficial although the very short
residence times in modern incinerators mean that kinetic factors
are likely to be more important than thermodynamic ones. When
disposing ISSA to landfill in the EU, it is the level of soluble heavy
metals that is considered important rather than total metal content. Comparing soluble metal levels from EN 12457-3 leaching
tests with ISSA, it was found that levels of Sb, Mo and Se were of
most concern when comparing results to landfill waste acceptance
criteria (Donatello et al., 2010a).
In Japan, the use of temperature resistant ceramic filters to remove ISSA prior to heat recovery has been investigated (Kataoka
et al., 2006). By removing the ash at high temperature, when the
volatile metals are present as vapours (see Fig. 3), a greater degree
of separation of ash from volatile species can be achieved, with volatile metals later being recovered during gas scrubbing. Retrofitting of ceramic filters on flue gas treatment systems could
potentially prevent ISSA from retaining relatively high levels of soluble Mo, Sb and Se, and this would reduce the cost of landfill
disposal.
Further research is needed to determine the most likely speciation of metals in ISSA to support a robust waste classification
exercise.
3. Recycling and recovery options for ISSA
A wide variety of potential reuse applications have been reported in the literature for ISSA and each of these is discussed in
the following sections.
3.1. Sintered materials containing ISSA
Sintering is a process in which a relatively weak compacted
material consisting of discrete particles is consolidated into a
strong material. Sintering occurs when particles bond together
after exposure to sufficiently high temperatures to promote atomic
diffusion between neighbouring particles. The driving force causing this effect is the reduction in particle surface energy by the
reduction in vapour–solid surface area. Sintering is essential to
the ceramics industry involved in the production of bricks, tiles
and lightweight aggregate.
3.1.1. Sintering studies using ISSA
The elemental composition of ISSA favours the formation of a liquid phase during sintering, which greatly reduces the temperature and time required to form sintered products. Sintering
causes shrinkage of the as-formed ‘‘green’’ sample along with den-
2332
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
sification due to the elimination of porosity. This is also associated
with significant improvements in physical properties including
strength and hardness. Decomposition reactions that involve gaseous products, such as the reduction of Fe3+ in Fe2O3, can create
a high degree of porosity in sintered materials. Results reported
by Cheeseman et al. (2003) showed that for samples of ISSA
pressed into cylindrical specimens and heated in the range of
980–1080 °C, maximum sample density, maximum shrinkage and
minimum water absorption were achieved after treatment at
1000–1020 °C for 1 h. Heating above this temperature resulted in
a decrease of sample density associated with the formation of
spherical pores from the decomposition of trace inorganic components in the ISSA matrix. Heating above 1080 °C caused the ISSA to
soften significantly and samples were deformed. Although heat
treatment generally reduced metal solubility, significant leaching
was still demonstrated under acidic (pH 3.6) conditions. The
authors reported no changes in the major crystalline phases present (quartz (SiO2), whitlockite (Ca9(MgFe)(PO4)6PO3OH) and hematite (Fe2O3)) as a result of sintering.
Similar studies by Lin et al. (2006) using pressed ISSA cylinders
concluded that significant sintering of ISSA occurred between 900
and 1000 °C. Merino et al. (2005) reported large increases in the
density of ISSA specimens between 1100 and 1200 °C. The same
authors also highlighted the great stability of calcium-magnesium
phosphate minerals in ISSA even up to 1300 °C. When blending
ISSA with 25% glass powder, Merino et al. (2007) showed that maximum sample density, maximum compressive strength and minimum water absorption resulted from heating to 1125 °C.
Different optimum temperatures were found when the type of
additive (powdered glass, kaolin, illite and montmorillonite) and
the percentage addition (12.5–75 wt.%) were varied.
3.1.2. Bricks, tiles and pavers containing ISSA
ISSA consists predominantly of Si, Al, Ca and Fe and therefore
one of the earliest uses investigated was as raw material for the
manufacture of bricks and tiles (Anderson, 2002; Anderson et al.,
1996; Chen and Lin, 2009a; Liew et al., 2004; Lin et al., 2008; Lin
and Weng, 2001; Schirmer et al., 1999; Tay, 1987a,b: Tay and
Show, 1992; Trauner, 1991; Wiesbusch et al., 1998; Wiebusch
and Seyfried, 1997).
When manufacturing glazed tiles at laboratory scale, the substitution of 30 wt.% of clay by ISSA was shown to increase tile water
absorption and decrease bending strength, irrespective of the glaze
used after firing tiles at 1050 °C (Lin et al., 2008). These authors
showed that tile warp increased progressively as ISSA content increased. An assessment of tile properties made from two different
types of clay substituted by 0–50 wt.% ISSA and fired at either 1000
or 1100 °C showed that while bending strengths slightly decreased
as ISSA content increased, the firing temperature ultimately determined tile properties such as shrinkage, water absorption, abrasion
resistance and bending strength (Chen and Lin, 2009a).
The substitution of clay with ISSA by Tay (1987a,b) caused a
slight but continual reduction in the compressive strength of bricks
as the weight percentage of ISSA increased. Generally satisfactory
results of 71 MPa for 50 wt.% ISSA bricks were reported, which
compared well with those of 87 MPa for 100% clay bricks. However, disappointing results were reported by Trauner (1991), where
adding 30 wt.% ISSA to the raw brick mix caused compressive
strengths to reduce from around 46 to 20 MPa. Other effects of partial clay replacement by ISSA reported are an increase in ‘‘gauging
water’’ content, an increase in brick water absorption, a decrease in
bulk density and a decrease in sintering temperature (Wiebusch
and Seyfried, 1997). Whether or not the overall effects of ISSA addition are beneficial or detrimental depend on the replacement level
and the specific Si, Ca, P and Fe content in the ISSA.
Laboratory scale manufacture of bricks containing 5 wt.% of clay
substituted by ISSA revealed a number of positive results, despite
the fact that ‘‘gauging water’’ content was increased from 4 to
9 wt.% (Anderson, 2002). In 5 wt.% ash containing bricks, unfired
strengths were increased by up to 29%, fired strengths increased
by 51% or 54% and water absorption of fired bricks decreased by
25% or 78% depending on whether the bricks were fired at a maximum temperature of 1050 or 1070 °C.
Arguably the most ambitious and advanced application of ISSA
in brick manufacture was presented by Okuno and Takahashi
(1997). These authors reported commercial scale manufacture of
bricks consisting of 100 wt.% ISSA. They stated that important
parameters for the starting ash were an average particle size
<30 lm, loss on ignition <1 wt.% and CaO content <15 wt.%. These
requirements could potentially impact on process decisions made
by water utilities. Fluidised bed incinerators tend to give finer
ash compared to multiple heath type furnaces and the use of Fe
or Al salts or organic polymers may be preferred to Ca salts during
sludge dewatering prior to incineration. The authors also described
the optimisation of the dry pressing and firing process, which has
an optimum maximum temperature of 1070–1080 °C but which
can vary depending on the P2O5 content of the ISSA. The bricks
complied with all relevant Japanese standards. However, during
service life, problems with moss growth, efflorescence and ice formation were observed that were linked to water absorption. The
authors applied a silicon-resin coating that eliminated these performance problems. Unfortunately the coating resulted in a significant increase in manufacturing costs compared to conventional
clay bricks. It is not clear the extent to which the ‘‘avoided costs’’
of ISSA disposal to landfill in Japan would positively contribute
to making the ISSA brick product economically feasible. As landfill
costs continue to increase, this will become an ever more important factor in determining the economic viability of ISSA based
products.
Leaching tests on ISSA containing bricks revealed concerns over
the leaching of Cl, SO2
4 and certain heavy metals. This led authors
to increasing the brick firing temperature from 1000–1060 °C to
1100–1200 °C (Wiesbusch et al., 1998).
3.1.3. Manufacture of lightweight aggregates from ISSA
Research investigating sintering of ISSA pellets to form lightweight aggregates has been reported by a number of authors
(Bhatty and Reid, 1989a; Cheeseman and Virdi, 2005; Chiou
et al., 2006; Wainwright and Cresswell, 2001; Yip and Tay, 1999).
Lightweight aggregates (LWA) are relatively high value due to
the scarcity of suitable natural lightweight aggregates in many
countries and the beneficial impact LWA can have on reducing concrete density and improving thermal insulating properties. Using
ISSA combined with 1–16% clay as a pelletising aid, Cheeseman
and Virdi (2005) showed that the optimum sintering temperature
ranged between 1050 and 1070 °C when considering water absorption, density and aggregate strength. The ISSA LWA formed compared well to commercially available LWA based on sintered coal
fly ash. Work carried out by Chiou et al. (2006) showed that combining ISSA with limited amounts of sewage sludge (<30 wt.%) favoured formation of lower density aggregates after sintering in
the temperature range 1050–1150 °C. The authors attributed this
effect to bloating caused by decomposition of the organic matter
present in the blended sewage sludge. Work carried out by Wainwright and Cresswell (2001) showed that ternary mixtures of ISSA,
clay and sewage sludge containing 64 wt.% ISSA produced low density aggregate with properties comparable to commercially available Lytag. These authors emphasised the importance of
incorporating a preliminary ‘‘burnout’’ stage when using mixes
with high organic content. The aim was to reduce the organic matter content to <4 wt.%. This involved preliminary firing of pellets to
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
700–800 °C to reduce the organic matter while avoiding sintering.
This research also investigated the performance of ISSA based LWA
in lightweight concrete (LWC) and found that 28 day strength compared well to control concretes, but that LWA performance was improved by increasing the clay content in the blend by 10 wt.% at the
expense of the sewage sludge component.
The key to successful lightweight aggregate manufacture is the
formation of gaseous products from the decomposition of components at temperatures where the gas bubbles are trapped in a viscous pyro-plastic mass and remain as isolated pores upon cooling
to room temperature. Obvious factors affecting this process are the
sintering temperature and exposure time. However, the SiO2–Al2O3
ratio is also important (Tsai et al., 2006). These authors varied the
SiO2–Al2O3 ratio of ISSA pellets by blending with glass cullet, alumina or municipal solid waste fly ash and found that adding
Al2O3 greatly improved the strength and density of pellets and that
adding glass cullet decreased aggregate density and also resulted
in higher water absorption. This was attributed to the influence
of glass cullet on the ‘‘bloating effect’’.
2AlðsÞ þ CaðOHÞ2ðaqÞ þ 2H2 OðlÞ ! CaðAlO2 Þ2ðsÞ þ 3H2ðgÞ
2333
ð1Þ
Work in Taiwan has focused on using this reaction to produce
lightweight foamed materials using an ISSA–Portland cement mix
(Chen et al., 2006; Wang et al., 2005a,b). Initial results showed that
visible foaming occurred within 5 min of mixing ISSA–cement–Al
metal blends with water, and that visible signs of reaction only
lasted for 10–20 min (Wang et al., 2005a). Optimum conditions
of 70–80 wt.% ISSA, 0.5–0.7 water–solids ratio and 0.1–0.2 wt.%
fine Al metal powder were found based on the strength, water
absorption, density and thermal conductivity of the aerated pastes
formed. Further work with similar samples exposed to temperatures up to 1000 °C showed that foamed pastes containing 70 or
80 wt.% ISSA by dry mass underwent gradual sintering above
600 °C (Chen et al., 2006). The improvement in sample density
and compressive strength of high temperature exposed foamed
ISSA pastes was in stark contrast to results for control Portland cement pastes, which were greatly deteriorated.
3.4. Use of ISSA in cementitious materials
3.2. Glass–ceramics containing ISSA
Glass–ceramics are a formed by controlled crystallisation of a
glass. They can exhibit very useful combinations of properties such
as high strength, high chemical durability and high temperature
resistance. The manufacture of glass–ceramics from ISSA was reported by Suzuki et al. (1997) who combined ISSA with an optimal
quantity of limestone (40–60%) and melted the mixture at 1450 °C.
A nucleation pre-treatment at 800 °C for 1 h was then applied to
the melt before heating to 1100 °C for 2 h to initiate anorthite crystallisation. The Fe and S in the ISSA formed FeS during the nucleation treatment under reducing conditions (crucible lid closed),
but under oxidising conditions (crucible lid open) FeS nucleation
was inhibited and this adversely affected anorthite crystallisation
and limited the physical properties of the glass–ceramics formed.
The conversion of ISSA samples involving pre-treatment at
1500 °C prior to a controlled heat treatment to form glass–ceramics was reported by Park et al. (2003). These authors showed that
combining ISSA with 10 wt.% CaO prior to melting produced diopside or anorthite based glass–ceramics depending on the heat
treatment applied. The excellent physical properties of the resulting glass–ceramics were attributed to the interlocking diopside
crystals formed.
Interesting results have been obtained from fusion analysis of
three different ISSA samples (Wang et al., 2012). This work identified the initial deformation temperature (IDT), the softening temperature (ST), the hemisphere temperature (HT) and the flowing
temperature (FT) of ISSA. The results showed clear differences in
the thermal behaviour of different ISSA samples which correlated
strongly with the relative Al2O3 and Fe2O3 contents. Samples rich
in Al2O3 were poor in Fe2O3 and required much higher temperatures to undergo sintering and eventual melting. The sample rich
in Fe2O3 began to sinter and later melted at much lower temperatures, and this was attributed to the formation of Fe-silicates and
Fe-aluminosilicates. The relative Fe and Al contents of ISSA are
strongly influenced by the choice of dewatering aids and, where
tertiary treatment is applied to wastewater, the choice of phosphate precipitation agent.
3.3. Lightweight aerated cementitious materials containing ISSA
Low density, aerated cementitious materials can be formed
using air entraining agents such as Zn or Al during mixing (Du
and Folliard, 2005). The proposed reaction for in situ gas formation
associated with Al addition is given in the following equation (Pera
et al., 1997):
The cement industry has three main options for using waste
materials. These are the beneficial recycling of wastes as alternative raw materials to form clinker, use of wastes as alternative fuels
and use of wastes as supplementary materials in blended cements,
effectively substituting for Portland cement. Given that ISSA possesses no calorific value, use as an alternative fuel is not appropriate. The major elements present in Portland cement are Ca, Si, Al
and Fe. These compare reasonably well to the major elements in
ISSA, with the notable exception of P. Thus ISSA could be used to
a limited extent as an alternative raw material for cement manufacture. It is worth noting that the use of dried or even dewatered
sewage sludge has received considerable attention in the literature, as this can simultaneously use the calorific value of sewage
sludge to reduce fuel requirements and the inorganic content of
the sludge to reduce cement raw material requirements (Husillos
et al., 2013; Stasta et al., 2006; Zabaniotou and Theofilou, 2008).
3.4.1. Use of ISSA in the Portland cement manufacturing process
Cement is manufactured by firing a combination of limestone
(80 wt.%) and clay (20 wt.%). Small amounts of quartz sand,
bauxite and/or hematite may be added to optimise the Si, Al and
Fe contents. In the cement kiln, all organic material is combusted
and inorganic compounds, including those from any ISSA used as
an alternative raw material, fuse into molten clinker phases at
around 1450 °C, with flame temperatures reaching 1800–2000 °C.
In cement raw meal blended with ISSA it was shown that when
the P2O5 content increased above 0.46 wt.%, the belite content of
clinkers increased at the expense of alite and this caused longer
setting times and lower strength development in cement pastes
(Lin et al., 2009, 2005). Lam et al. (2010) showed that clinkers produced containing 2 wt.% ISSA were satisfactory but that when the
ISSA content increased to 8 wt.%, a significant reduction in alite
content and increase in free lime content was observed. This was
attributed to the elevated phosphate and possibly sulphate contents of ISSA inhibiting alite formation. Pre-treatment of ISSA to remove phosphates prior to use as a raw material in the production
of cement clinker was suggested.
From a practical point of view, significant quantities of ISSA
could in theory be diverted from landfill by use in cement kilns
without reaching the problematic P levels reported by various
authors (Halicz et al., 1984; Nastac et al., 2007). Global cement production was estimated at 3.6 billion tonnes in 2011 (CEMBUREAU
website, 2012) whereas a reasonable estimate of global ISSA
production is approximately 1.7 million tonnes, over 2000 times
less. However, where sewage sludge is not incinerated, the direct
2334
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
mal history to the ash and may affect the physical and chemical
properties of the ISSA formed.
Regardless of the combustion history of ISSA, the irregular particle morphology causes a decrease in workability when replacing
cement, even at low percentage additions. To some extent, poor
workability can be overcome by milling (Pan et al., 2003a), addition of plasticising agents (Monzo et al., 2003) or by incorporation
of coal fly ash into the mortar mix (Paya et al., 2002). The results of
Monzo et al. (1999, 1997 and 1996) stand out due to the moderate
increase in compressive strength shown in ISSA mortars when
compared to control samples. They showed increases in average
strengths of 8.3–15.3% when replacing 15 wt.% of Portland cement
with ISSA in 3:1 mortars. These samples were cured by water
immersion at 40 °C and the moderately elevated curing temperature may well explain the unusual results reported by these
authors.
Fig. 4. Representation of trends reported by various authors upon increasing
cement replacement rates with ISSA, of using milled ISSA and of acid washing and
milling ISSA. (Numbers denoted above data points represent the % cement replaced
by ISSA).
3.4.3. Pozzolanic activity of ISSA
Despite the generally negative effects on compressive strength
of ISSA in blended cements, many authors have attributed a certain
degree of ‘‘pozzolanic activity’’ to ISSA. The definition of a ‘‘pozzolanic’’ material as given in (ASTM C618, 2008) is:
use of dried sewage sludge in the cement industry is generally preferred because this avoids the need for investment in a dedicated
mono-incineration plant for sewage sludge, although investment
would still be required in a thermal drying facility. The use of dried
sewage sludge instead of ISSA allows the calorific value of the organic matter to be exploited, reducing kiln fuel requirements
(Husillos et al., 2013; Lin et al., 2012).
A siliceous and aluminous material which, in itself, possesses little
or no cementitious value but which will, in finely divided form in
the presence of moisture, react chemically with calcium hydroxide
at ordinary temperature to form compounds possessing cementitious properties.
3.4.2. Use of ISSA as an additive to Portland cement
Wastes can be recycled in cement based materials as either active pozzolanic materials, partially replacing cement, or as inert filler, replacing sand and/or aggregates. A considerable number of
papers have reported the use of ISSA as a partial replacement for
Portland cement and the effect on the workability and strength
development of pastes, mortars and/or concretes (Bhatty and Reid;
1989b; Cyr et al., 2007; Donatello et al., 2010b,c; Garces et al.,
2008; Lisk, 1989; Luo et al., 2004; Monzo et al., 2003, 1999,
1997, 1996; Pan et al., 2003a, 2002; Pan and Tseng, 2001; Pinarli
and Kaymal, 1994; Tay and Show, 1994, 1992; Tay, 1987a,b, 1986).
The data up to 2007 has been summarised by Cyr et al. (2007),
and a selection of the data available in the literature is presented in
Fig. 4. Two clear trends are evident within any given data set:
increasing ISSA contents causes a decrease in compressive strength
and milling of ISSA generally improves strengths at a given percentage of ISSA addition. When attempting to compare results
from different authors using the same cement replacement rate,
it is clear that large differences in relative strengths exist. For
example, when replacing 20% of Portland cement with ISSA, reductions in mortar compressive strengths of 5% (Pinarli and Kaymal,
1994), 24% (Donatello et al., 2010b), 32% (Tay, 1986), 51% (Lisk,
1989) or 52% (Pan et al., 2003a,b) have been reported. While obvious differences will arise due to factors such as mortar specimen
dimensions and water/binder ratio used, an important factor not
generally considered has been the processes used to produce the
ISSA. For example, the pioneering work of Tay (1986) was carried
out using a dewatered digested sludge fired in a laboratory oven
at 550 °C for an unspecified period. Lisk (1989) used ash produced
by a multiple hearth furnace. Pan et al. (2003a) used dewatered
primary sludge fired at 700 °C for 3 h and the ISSA used by Donatello et al. (2010a–c) was sourced from industrial scale fluidised
bed incinerators where ash residence times in the combustion
zone were of the order of seconds at 800–900 °C. Each of the aforementioned methods of ash preparation will impart a specific ther-
The requirement of significant SiO2 and Al2O3 content suggest
that ISSA may have potential as a pozzolan. Another important
consideration is that any clay present in sludge fed to the incinerator may be thermally activated and this can contribute pozzolanic
properties to ISSA. Such a phenomenon is well known in paper
sludge ash in which kaolin may be converted to pozzolanic metakoalinite (Fernandez et al., 2010; Frias et al., 2010, 2008).
Many methods are available to determine the pozzolanic activity of a material. These can be broadly classified as either direct or
indirect methods. The pozzolanic reaction involves Ca(OH)2 reacting with silicate or aluminosilicate phases to form amorphous C–
S–H or C–A–S–H type gel products. Thus direct methods measure
the change in Ca(OH)2 concentration as the pozzolanic reaction
proceeds. Examples of direct methods are the Frattini test (EN
196-5), the saturated lime test (Fernández et al., 2010) and TGDTA analysis of pastes with hydration reactions being inhibited
after specific times. Indirect methods measure a physical property
of pastes that is linked to the pozzolanic reaction. Examples of indirect methods are the strength activity index (ASTM C311, 2007)
and electrical conductivity methods (McCarter and Tran, 1996;
Paya et al., 2001).
The majority of work involving the assessment of ISSA pozzolanic activity has used indirect methods, monitoring the effect of
replacing cement with ISSA on compressive strength of pastes
and mortars. Effects were generally negative but this could be
strongly influenced by the increased water demand caused by
the irregular particle morphology of ISSA. In a comprehensive
assessment of ISSA pozzolanic activity by Donatello et al. (2010b)
and 2009), it was found that ISSA gave highly positive results in
the saturated lime test, negative results in the strength activity index test and positive or negative results depending on the percentage cement replacement in the Frattini test. The authors concluded
that ISSA was not pozzolanic but instead possessed a limited affinity for Ca2þ
ðaqÞ ions via an ion exchange mechanism. They also concluded that the saturated lime test method was biased in favour
of positive results with ISSA due to the lower total quantity of
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
Ca2þ
ðaqÞ present in this system compared to the Frattini or strength
activity index tests.
Increasing the fineness of ISSA has also been shown to increase
setting times, which was attributed by Pan et al. (2003a) to the improved ability of finer ISSA to adsorb Ca2+ ions from the liquid
phase during cement hydration, inhibiting the massive precipitation of C–S–H gel responsible for setting of Portland cement (Chen
and Odler, 1992).
Given the general lack of pozzolanic activity of ISSA, another option for recycling in cement-based materials is as a fine aggregate.
Very little work has been presented on this aspect. In one set of
experiments, concretes containing up to 30% replacement of sand
by ISSA showed a 22% reduction in 28 day compressive strength
(Khanbilvardi and Afshari, 1995). The increased water requirement
due to the porous nature of ISSA relative to sand is likely to limit
sand replacement rates to <5–10 wt.%.
3.5. Phosphate recovery from ISSA
A major disadvantage of using ISSA in construction materials in
general is that it represents a loss of potentially valuable P. Phosphate is essentially a finite material in the sense that all phosphate
ore is mined from a limited number of geological reserves and once
P enters rivers, lakes or seas it can no longer be economically
recovered. The major demand for phosphate is in the manufacture
of agricultural fertilisers (ca. 80%), animal feed (ca. 12%) and detergents (ca. 5%) (Smil, 2000; C.E.E.P, 2012). No alternative to phosphate is feasible in fertilisers or animal feeds since phosphate is
an essential element in the structures of DNA, bone, cell membranes and energy carrying molecules. At current rates of consumption, it is estimated that only 50–100 years of economically
viable phosphate reserves remain (Cordell et al., 2009; Franz,
2008; Steen, 1998).
The 2010 output from mining of phosphate rock reserves is depicted in Fig. 5. It is apparent that no economically viable phosphate reserves exist within the EU. Consequently, the use of
recovered phosphates is a priority for the European phosphate
industry (Levlin et al., 2002). One of the most promising opportunities to recover phosphate is from sewage sludge collected at
large centralised wastewater treatment plants. There are various
options for recovering P from sewage sludge but the disadvantages
are the relatively high water and organic matter contents, which
2335
increase the processing capacities required. One well known example of phosphate recovery from sewage is controlled struvite precipitation but this is a complex process dependent on many
factors such as pH, Mg2+ and NH4+ concentrations (Doyle and Parsons, 2002). Phosphate is thermally stable and does not volatilise
during sludge drying or incineration at 800–900 °C. Instead phosphate is concentrated in the ISSA as whitlockite type, tri-calcium
phosphates (Ca3(PO4)2). Some evidence has suggested that in ISSA,
Ca2+ in whitlockite may be partially substituted by Mg2+, Fe3+ or
Al3+ (Adam et al., 2009; Biswas et al., 2009; Donatello, 2009; Petzet
et al., 2012; Wzorek et al., 2006). Phosphate contents in ISSA are
typically 10–25 wt.% as P2O5, while phosphate rock ore can consist
of 5–40 wt.% P2O5 (Steen, 1998). The fact that ISSA is a dry and free
flowing powder greatly simplifies processing operations for subsequent phosphate extraction when compared to either phosphate
rock or liquid and dilute sewage sludge.
The conversion of phosphate ore to phosphorus at an industrial
scale uses thermal methods in which Ca3(PO4)2 is reacted with
coke and quartz at 1200–1500 °C in an electric arc furnace. The
reaction is given in the following equation:
2Ca3 ðPO4 Þ2 þ 6SiO2 þ 10C ! 6CaSiO3 þ 4P þ 10CO
ð2Þ
Schipper et al. (2001) examined the feasibility of ISSA as an
alternative source of Ca3(PO4)2 for the thermal process and it was
concluded that the use of ISSA is limited due to the need to maintain maximum Fe content of the phosphate feed at less than
10,000 mg/kg to minimise the formation of unwanted FeP byproducts.
The other major phosphate ore processing technique is known
as the ‘‘wet process’’ and involves dissolution of phosphate rock
in concentrated sulphuric acid to form phosphoric acid. Gypsum
is formed as a by-product. The general chemical reactions in the
continuous process are given in the following equations:
2Ca3 ðPO4 Þ2ðsÞ þ 4H3 PO4ðaqÞ ! 3CaðH2 PO4 Þ2ðaqÞ
ð3Þ
CaðH2 PO4 Þ2ðaqÞ þ 3H2 SO4ðaqÞ ! 3CaSO4ðsÞ þ 6H3 PO4ðaqÞ
ð4Þ
The above reactions form slurry which is filtered to separate the
phosphoric acid product from the calcium sulphate crystals.
Whether the precipitate is anhydrite (CaSO4), hemihydrate (CaSO40.5H2O) or dehydrate (CaSO42H2O) will depend on the reaction
Fig. 5. Global phosphate rock output per country in millions of tonnes. The data is for 2010 and totalled around 181 million tonnes (data from USGS, 2012).
2336
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
Fig. 6. Summary of some experimental processes for P recovery from ISSA reported in the literature; (a) Takahashi et al. (2001), (b) Franz (2008) and (c) Petzet et al. (2011).
temperature (typically in the range 70–105 °C). The phosphoric
acid filtrate can then be used to manufacture fertiliser or be further
purified for technical grade applications.
3.5.1. Recovery of P by acid leaching
Naturally occurring phosphate ores are of relatively similar
composition and phosphate is extracted on an industrial scale by
acid washing. The acid of choice is invariably H2SO4 due to low
cost, wide availability and ability to easily remove unwanted
Ca2+ from mixtures by controlled precipitation of gypsum (CaSO42H2O). Calculations to identify the minimum quantity of acid required for maximum phosphate extraction by acid leaching have
been presented in the literature (Franz, 2008; Petzet et al., 2012).
A number of papers have been published on the recovery of
phosphate from ISSA using a wet acid leaching process (Biswas
et al., 2009; Donatello et al., 2010d; Franz, 2008; Oliver and Carey,
1976; Petzet et al., 2012; Stark et al., 2006; Takahashi et al., 2001;
Wzorek et al., 2006) and selected experimental approaches are
compared in Fig. 6.
Early work by Oliver and Carey (1976) showed that averages of
76 and 61 wt.% of total P present in ISSA were recovered from eight
ash samples from different plants when washed with H2SO4 or HCl
respectively (both acids at pH 1.5). They concluded that recovery
was not economically feasible based on market prices for acids
and phosphate in 1976. Phosphate prices have increased considerably since then and there is added environmental awareness
amongst governments and companies which is a significant driver
for phosphate recovery (Cordell et al., 2009; Driver et al., 1999;
Levlin et al., 2002; Schipper et al., 2001).
A problem with acid leaching of P from ISSA is that a number of
other metals simultaneously dissolve. An interesting solution,
demonstrated by Takahashi et al. (2001) was to break up the dissolution process into three separate stages. In the first stage, sulphuric acid (pH 2) was added and the soluble P and heavy metals
separated from the insoluble ISSA residue. In the second stage,
the pH was raised to around 4 by the addition of sodium bicarbonate. At this pH, and with a very specific amount of Al2(SO4)3 added,
phosphate was selectively precipitated as AlPO4 and separated
from the solution by filtration. The third and final stage involved
adjustment of the pH of the remaining heavy metal rich liquid
phase to 10 by the addition of NaOH or Ca(OH)2, causing the precipitation of many heavy metals as insoluble hydroxides. One potential limitation of the process used by Takahashi is the
marketability of the AlPO4 product. High purity applications tend
to work with concentrated H3PO4 and the release of soluble Al3+
would be a concern in any lower grade fertiliser application.
The SESAL process presented by Petzet et al. (2012) is an interesting alternative to the process used by Takahashi, as this ultimately produces a solid Ca-phosphate precipitate and soluble
AlCl3 solution. The latter by-product can be recycled in wastewater
treatment plants for tertiary treatments involving chemical precipitation of P from sewage effluent, potentially representing a closed
loop for Al cycling. In the SESAL process, a pH of 3 is carefully maintained with HCl, under which conditions the authors claim that
Ca–P compounds dissolve and Al–P compounds simultaneously
precipitate (Petzet et al., 2011). Existing and newly formed Alphosphates are retained on the filter along with acid insoluble ISSA
residues, while soluble heavy metals and Ca2+ pass to the filtrate.
The solid fraction is then treated with NaOH at pH 13, where the
Al-phosphate is dissolved and separated from the insoluble silicate,
aluminosilicate and hematite components of ISSA. Finally the Alphosphate filtrate is treated with CaCl2 to precipitate P as Ca-phosphate and the soluble Al passes to the filtrate as AlCl3(aq).
The effect of laboratory scale incineration of small sewage
sludge samples at different temperatures on P recovery from the
resulting ISSA by leaching with nitric acid has been reported by
Wzorek et al. (2006). The authors suggested an optimum incineration temperature of 950 °C, although this is perhaps too close to
the sintering point of ISSA to be advisable in an industrial scale
incinerator, which is generally operated at 780–880 °C. Results
presented by Stark et al. (2006) showed that over 80% of P could
be extracted by shaking with 1 M HCl for 2 h. The authors also
showed that extraction with 1 M NaOH was significant (ca. 70%),
but less than with HCl. The very high liquid to solid ratios used
(ca. 50 g acid: 1 g ISSA) are unlikely to be economically viable at
an industrial scale. These authors also reported significant co-dissolution of Ca2+. This highlights a clear advantage of H2SO4 over
HCl to remove Ca2+ via the precipitation of CaSO42H2O.
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
An alternative approach to converting P from ISSA into plant
fertiliser was reported by Franz (2008). The process involved dissolving P in H2SO4. As with other researchers, co-dissolution of
heavy metals occurred. The paper by Franz investigated the ability
of ion exchange and sulphide treatment to selectively remove heavy metals and reported that both processes were suitable for this
purpose. Phosphate was then precipitated out of the purified solution following lime addition and the precipitate dried, ground and
used in plant trials along with a commercial phosphate fertiliser.
The ISSA derived P fertiliser was found to perform satisfactorily
over a 6 week fertiliser trial.
The paper by Biswas et al. (2009) reported on the recovery of P
from ISSA via leaching with NaOH HCl or H2SO4 and then recovery
of P via adsorption onto an unusual ‘‘saponified orange waste’’
(SOW) gel loaded with Zr(IV). Using a 0.1 M concentrated leachant,
the authors found that alkali leaching of P from ISSA was poor compared to acid leaching under the same conditions. The dissolution
of P from ISSA was relatively unaffected by increasing the acid
temperature from 30 to 70 °C. Recovery of P from acidic leachate
was found to be around 100% when adding 100 mg SOW adsorbent
per 10 ml of leachate. The authors reported the successful elution
of most of the adsorbed P from the SOW gel by rinsing with
0.2 M NaOH, implying that the gel could be reused. The authors
did not elaborate on potential uses for the P rich alkaline eluate.
Given that the total P potentially recoverable from ISSA is relatively small compared to the global phosphate market, Donatello
et al. (2010d) investigated the potential to produce a high value
technical grade phosphoric acid from ISSA via an optimised sulphuric acid leaching process, followed by cation exchange to remove impurities and evaporation of excess water to produce a
ca. 80% H3PO4 product. The final product had acceptable levels of
heavy metals but needed more turbulent mixing conditions to reduce the liquid to solid ratio and minimise evaporation energy
costs. The need to remove SO2
4 from the leachate was also identified by the authors.
3.5.2. Recycling of acid insoluble ISSA residue
Of the two general methods investigated for recovering P from
ISSA, the acid washing process is the simplest and cheapest option.
However, one major consideration that has not been adequately
addressed in the literature to date concerns the remaining acid
Fig. 7. The effect of milling or acid washing in 0.19 M H2SO4 and milling on the
28 day SAI value of mortars. Note that all mortars used a water/binder ratio of 0.5
and a standard flowability due to super-plasticiser addition where necessary. In all
cases 20% of cement was substituted for ISSA. The control mortar (0% ISSA) had an
average 28 d strength of 42.8 MPa (SAI = 1.00). Results are averages of 3 measurements ± 1 standard deviation. Data obtained from Donatello (2009).
2337
Fig. 8. The effect of milling or acid washing and milling of ISSA on Frattini test
Ca(OH)2 removal results after 8 d at 40 °C. Paste mixtures were 20% ISSA–80% OPC
and results were averages of duplicate analyses. Data taken from Donatello (2009).
insoluble ISSA residue generated. This acid treated ISSA will contain low concentrations of P. The concentrations of other major elements will also be altered. If H2SO4 is used in the acid treatment,
gypsum crystals may be present. The only work that has investigated the potential recycling of this acid insoluble ISSA residue
was published by Donatello (2009) and Donatello et al. (2010c).
When blended with Portland cement, it was shown that after
milling, the acid insoluble ISSA residue produced considerable increases in mortar compressive strengths when compared to both
untreated ISSA and milled but not acid washed ISSA, as is shown
in Fig. 7.
To investigate whether or not the improved strengths were due
to improved pozzolanic activity in acid washed ISSA, Frattini tests
were applied to untreated, milled or acid washed and milled ISSA
samples. The results in Fig. 8 clearly demonstrates that the acid
washing process was not associated with any increase in pozzolanic activity and so the improvements in compressive strengths of
acid washed ISSA mortars must be related to other factors such
as the gypsum content. Further work with acid-washed ISSA residues is required to improve understanding of this material and
why it shows particularly promising effects in blended cements.
3.5.3. Thermal methods of P recovery from ISSA
The main alternative for P recovery from ISSA is via thermal
methods. As with acid leaching, one issue is how to separate the
valuable P from problematic heavy metals. From an industrial perspective considering the production of white phosphorus, the potential of ISSA is considerable as long as Fe contents are low. This
can be controlled to an extent by avoiding the use of Fe-salts during sludge processing at wastewater treatment plants. However,
levels of Cu and Zn are also considered to be of concern. Regarding
removal of heavy metals from ISSA, thermochemical treatment
with 5–15% of KCl or MgCl2 and heating at 900–1000 °C resulted
in high percentage removals of Pb, Cd, Cu and Zn (Mattenberger
et al., 2008). However, as much as 30% of P could also be lost in fine
ashes that were carried out of the rotary kiln with exhaust gases,
and removal percentages for Ni and Cr were unsatisfactory. To reduce the problem of P loss in fine ashes, the authors modified the
process to work with granulated ISSA pellets instead of ash (Mattenberger et al., 2010).
The effect of thermochemical treatment of ISSA on the bioavailability of P has been reported by Adam et al. (2009). This work
showed that untreated ISSA exceeded German and Austrian limits
for heavy metals and particularly Zn and Cu in fertilisers. Treat-
2338
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
ment with 15% MgCl2 at 1000 °C for 60 min was shown to remove
well over 90% of Cu and Zn from ISSA by volatilisation as CuCl2 or
ZnCl2. As the ISSA treatment temperature was increased, so did the
bio-available P content. Treatment at 800 °C resulted in similar
available-P levels to a commercial fertiliser. The changes in P availability were attributed to the conversion of whitlockite (Ca3(PO4)2)
to chlorapatite (Ca5(PO4)3Cl1x(OH)x) via an intermediary chlorspodiosite (Ca2PO4Cl) species, with the formation of new Mg-phosphates (farringtonite Mg3(PO4)2) or Mg–Ca-phosphates. The same
research group report results extending earlier research on P-fertilisers based on thermo-chemically treated ISSA to NPK fertilisers
following treatment with NH4NO3 and K2SO4 (Vogel et al., 2010).
3.6. Other recycling and recovery options for ISSA
Although the majority of research on ISSA recycling has focussed on sintered materials, cements and phosphate recovery, it
is worthwhile to mention other, more unusual recycling applications reported in the literature.
The concentration of many trace elements and minor nutrients
in ISSA has led to untreated ISSA being considered as a potential
soil amendment (Zhang et al., 2002a). A study by Escudey et al.
(2007) showed that most of the important plant nutrients in ISSA
were only slightly soluble and provided slow release of nutrients
to volcanic soils. Direct application of ISSA to soil in Japan was restricted to a maximum application of 40 tonne/ha due to high heavy metal content relative to Japanese soils (Zhang et al., 2002b).
The potential recycling of ISSA in combination with Ca(OH)2 or
cement has been reported for soil stabilisation applications (Lin
et al., 2007; Chen and Lin, 2009b). ISSA has also been used to replace limestone as mineral filler in asphalt (Al Sayed et al., 1995).
The use of ISSA as a Cu adsorbent has been investigated by Pan
et al. (2003b) and Bouzid et al. (2008). Up to 98% removal of Cu was
reported by Pan et al. (2003b) with estimated maximum Cu
adsorption capacities of 3.2–4.1 mg Cu2+/g ISSA. Bouzid et al.
(2008) used ISSA from the combined incineration of sewage sludge
cake and an olive mill waste and found that almost all Cu adsorption occurred within the first 30 min of contact between the ash
and the Cu bearing solution. These authors reported a Cu2+ adsorption capacity of 5.7 mg Cu2+/g ash, which is significantly higher
than coal fly ash, but much lower than commercial activated carbon adsorbents or other sewage sludge based adsorbents (Smith
et al., 2009). In both studies, Cu adsorption efficiency was very sensitive to the system pH.
4. Conclusions
The majority of research on recycling and recovery of ISSA has
been completed during the last 15 years, due to the increasing
attention given by water utilities to mono-incineration of sewage
sludge as traditional disposal routes become increasingly restricted. Research has focused on the use of ISSA as a clay substitute in bricks and as a partial cement replacement material. In
both applications, small additions of ISSA can be made without
detrimental effects to the final product. Larger additions require
process adjustments and may affect product performance. The
pozzolanic activity of ISSA is at best limited. These recycling applications fail to consider the potentially valuable P content of ISSA.
Recent research has recognised the potential for recovery of phosphate from ISSA using both acid leaching and thermochemical
methods. Both approaches allow ISSA to be converted into fertiliser
or phosphate rich products, with acceptably low heavy metal contamination. It is likely that these processes will become more
attractive as both phosphate prices and ISSA disposal costs continue to increase. Acid washing to recover P requires the recycling
potential of the acid-insoluble ISSA to be considered. When milled,
this acid-insoluble residue has promise as a partial cement replacement. ISSA can be successfully recycled via a number of different
routes and the main reason why this material is sent to landfill is
lack of industrial scale examples of the recycling applications already demonstrated at the laboratory scale.
References
Adam, C., Peplinski, B., Michaelis, M., Kley, G., Simon, F.G., 2009. Thermochemical
treatment of sewage sludge ashes for phosphorus recovery. Waste Manage. 29,
1122–1128.
ADAS, 2001. The safe sludge matrix. Guidelines for the application of sewage sludge
to
agricultural
land.
third
ed.
<http://www.adas.co.uk/
LinkClick.aspx?fileticket=f_CX7x_v4nY%3D&tabid=211&mid=664>.
Al Sayed, M.H., Madany, I.M., Buali, A.R.M., 1995. Use of sewage sludge ash in
asphaltic paving mixes in hot regions. Constr. Build. Mater. 9 (1), 19–23.
Anderson, M., 2002. Encouraging prospects for recycling incinerated sewage sludge
ash (ISSA) into clay-based building products. J. Chem. Technol. Biot. 77 (3), 352–
360.
Anderson, M., Skerratt, R.G., 2003. Variability study of incinerated sewage sludge
ash in relation to future use in ceramic brick manufacture. Brit. Ceram. T. 102
(3), 109–113.
Anderson, M., Skerratt, R.G., Thomas, J.P., Clay, S.D., 1996. Case study involving using
fluidised bed incinerator sludge ash as a partial substitute in brick manufacture.
Water Sci. Technol. 34, 507–515.
Arundel, J., 2000. Sewage and Industrial Effluent Treatment, second ed. Blackwell
Science.
ASTM C311, 2007. Standard test methods for sampling and testing fly ash or natural
pozzolans for use in Portland cement concrete.
ASTM C618, 2008. Standard specification of coal fly ash and raw or calcined natural
pozzolan for use in concrete.
Bhatty, J.I., Reid, K.J., 1989a. Lightweight aggregates from incinerated sludge ash.
Waste Manage. Res. 7, 363–376.
Bhatty, J.I., Reid, K.J., 1989b. Compressive strength of municipal sludge ash mortars.
ACI Mater. J. 4, 394–400.
Biswas, B.K., Inoue, K., Harada, H., Ohto, K., Kawakita, H., 2009. Leaching of
phosphorus from incinerated sewage sludge ash by means of acid extraction
followed by adsorption on orange waste gel. J. Environ. Sci. 21, 1753–1760.
Bouzid, J., Elouear, Z., Ksibi, M., Feki, M., Montiel, A., 2008. A study on the removal
characteristics of copper from aqueous solution by sewage sludge and pomace
ashes. J. Hazard. Mater. 152, 838–845.
C.E.E.P., 2012. Centre European d’Etudes des Polyphosphates. <www.ceepphosphates.org> (last accessed 10.12).
CEMBUREAU
website:
<http://www.cembureau.be/about-cement/key-factsfigures> (last accessed 09.12).
Cenni, R., Janisch, B., Spliethoff, H., Hein, K.R.G., 2001. Legislative and environmental
issues on the use of ash from coal and municipal sludge co-firing as
construction material. Waste Manage. 21, 17–31.
Cheeseman, C.R., Virdi, G.S., 2005. Properties and microstructure of lightweight
aggregate produced from sintered sewage sludge ash. Resour. Conserv. Recy. 45
(1), 18–30.
Cheeseman, C.R., Sollars, C.J., McEntee, S., 2003. Properties, microstructure and
leaching of sintered sewage sludge ash. Resour. Conserv. Recy. 40, 13–25.
Chen, L., Lin, D.F., 2009a. Applications of sewage sludge ash and nano-SiO2 to
manufacture tile as construction material. Constr. Build. Mater. 23, 3312–3320.
Chen, L., Lin, D.F., 2009b. Stabilization treatment of soft subgrade soil by sewage
sludge ash and cement. J. Hazard. Mater. 162 (1), 321–327.
Chen, Y., Odler, I., 1992. On the origin of setting time. Cem. Concr. Res. 22, 1130–
1140.
Chen, C.H., Chiou, I.J., Wang, K.S., 2006. Sintering effect on cement bonded sewage
sludge ash. Cem. Concr. Compos. 28, 26–32.
Chiou, I.J., Wang, K.S., Chen, C.H., Lin, Y.T., 2006. Lightweight aggregate made from
sewage sludge and incinerated ash. Waste Manage. 26, 1453–1461.
Cordell, D., Drangert, J.O., White, S., 2009. The story of phosphorus: global food
security and food for thought. Glob. Environ. Change 19, 292–305.
Corella, J., Toledo, J.M., 2000. Incineration of doped sludges in fluidized bed. Fate
and partitioning of six targeted heavy metals. I. Pilot plant used and results. J.
Hazard. Mater. B80, 81–105.
Cyr, M., Coutand, M., Clastres, P., 2007. Technological and environmental behaviour
of sewage sludge ash (SSA) in cement-based materials. Cem. Concr. Res. 37,
1278–1289.
Donatello, S., 2009. Characteristics of incinerated sewage sludge ashes: potential for
phosphate extraction and re-use as a pozzolanic material in construction
projects, PhD thesis, Imperial College London.
Donatello, S., Tyrer, M., Cheeseman, C.R., 2010a. EU landfill waste acceptance
criteria and EU Hazardous Waste Directive compliance testing of incinerated
sewage sludge ash. Waste Manage. 30, 63–71.
Donatello, S., Tyrer, M., Cheeseman, C.R., 2010b. Comparison of test methods to
assess pozzolanic activity. Cem. Concr. Compos. 32, 121–127.
Donatello, S., Freeman-Pask, A., Tyrer, M., Cheeseman, C.R., 2010c. Effect of milling
and acid washing on the pozzolanic activity of incinerator sewage sludge ash.
Cem. Concr. Compos. 32, 54–61.
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
Donatello, S., Tong, D., Cheeseman, C.R., 2010d. Production of technical grade
phosphoric acid from incinerator sewage sludge ash (ISSA). Waste Manage. 30,
1634–1642.
Doyle, J.D., Parsons, S.A., 2002. Struvite formation, control and recovery. Water Res.
36 (16), 3925–3940.
Driver, J., Lijmbach, D., Steen, I., 1999. Why recover phosphorus for recycling and
how? Environ. Technol. 20, 651–662.
Du, L., Folliard, K.J., 2005. Mechanisms of air entrainment in concrete. Cem. Concr.
Res. 35, 1463–1471.
Elled, A.L., Amand, L.E., Leckner, B., Andersson, B.A., 2007. The fate of trace elements
in fluidised bed combustion of sewage sludge and wood. Fuel 86, 843–852.
EN 12457-3. Characterisation of waste – leaching compliance test for leaching of
granular waste materials and sludges.
EN 196-5. Pozzolanicity test for pozzolanic cement.
EN 197-1. Compositions, specifications and conformity criteria for common
cements.EU Landfill Directive (99/31/EC).
Environment Agency, 2011. Hazardous waste – interpretation of the definition and
classification of hazardous waste. Technical Guidance WM2 (version 2.3).
<http://www.environment-agency.gov.uk/business/topics/waste/32200.aspx>.
Escudey, M., Forster, J.E., Becerra, J.P., Quinteros, M., Torres, J., Arancibia, N., Galindo,
G., Chang, A.C., 2007. Disposal of domestic sludge and sludge ash on volcanic
soils. J. Hazard. Mater. B139, 550–555.
EU Hazardous Waste Directive (91/689/EC).
EU Landfill Directive (99/31/EC).
EU Sludge Directive (86/278/EEC).
EU Urban waste-water treatment Directive (91/271/EEC).
EU Waste Incineration Directive (2000/76/EC).
Eurostat website: <http://epp.eurostat.ec.europa.eu/portal/page/portal/eurostat/
home/euonline> (last accessed 10.12). Data obtained using data code
env_watq6.
Fernandez, R., Nebreda, B., Vigil, R., Garcia, R., Frias, M., 2010. Mineralogical and
chemical evolution of hydrated phases in the pozzolanic reaction of calcined
paper sludge. Cem. Concr. Compos. 32, 775–782.
Franz, M., 2008. Phosphate fertilizer from sewage sludge ash (SSA). Waste Manage.
28 (10), 1809–1818.
Frias, M., Garcia, R., Vigil, R., Ferreiro, S., 2008. Calcination of art paper sludge waste
for the use as a supplementary cementing material. Appl. Clay Sci. 42, 189–193.
Frias, M., Rodriguez, O., Sanchez de Rojas, M.I., Ferreiro, S., Nebreda, B., Olmeda, J.,
2010. New construction materials: calcined paper sludges as active additions.
Materials Science Forum 636–637, 1222–1227.
Fytili, D., Zabaniotou, A., 2008. Utilization of sewage sludge in EU application of old
and new methods – a review. Renew. Sust. Energy Rev. 12, 116–140.
Garces, P., Perez-Carrion, M., Garcia-Alcocel, E., Paya, J., Monzo, J., Borrachero, M.V.,
2008. Mechanical and physical properties of cement blended with sewage
sludge ash. Waste Manage. 28, 2495–2502.
Halicz, L., Nathan, Y., Ben-Dor, L., 1984. The influence of P2O5 on clinker reactions.
Cem. Concr. Res. 14, 11–18.
Husillos-Rodríguez, N., Martínez-Ramírez, S., Blanco-Varela, M.T., Donatello, S.,
Guillem, M., Puig, J., Fos, C., Larrotcha, E., Flores, J., 2013. The effect of using
thermally dried sewage sludge as an alternative fuel on Portland cement clinker
production. J. Clean. Prod.. http://dx.doi.org/10.1016/j.jclepro.2013.02.026 (in
press).
Ireland, S.N., McGrellis, B., Harper, N., 2004. On the technical and economic issues
involved in the co-firing of coal and waste in a conventional pf-fired power
station. Fuel 83, 905–915.
Kataoka, S., Nagatsuka, E., Miyamoto, T., 2006. Reducing heavy metal contents in
sewage sludge incineration ash with high-temperature dust collection method.
J. Jpn. Sewage Works Assoc. 43 (527), 125–132.
Khanbilvardi, R., Afshari, S., 1995. Sludge ash as fine aggregate for concrete mix. J.
Environ. Eng-ASCE 121, 633–637.
Lam, C.H.K., Barford, J.P., McKay, G., 2010. Utilization of incineration waste ash
residues in Portland cement clinker. Chem. Eng. Trans. 21, 757–762.
Lapa, N., Barbosa, R., Lopes, M.H., Mendes, N., Abelha, P., Gulyurtlu, I., Santos
Oliveira, J., 2007. Chemical and ecotoxicological characterization of ashes
obtained from sewage sludge combustion in a fluidised-bed reactor. J. Hazard.
Mater. 147, 175–183.
Leckner, B., Amand, L.E., Lucke, K., Werther, J., 2004. Gaseous emissions from cocombustion of sewage sludge and coal/wood in a fluidized bed. Fuel 83, 477–
486.
Levlin, E., Lowen, M., Stark, K., Hultman, B., 2002. Effects of phosphorus recovery
requirements on Swedish sludge management. Water Sci. Technol. 46 (4–5),
435–440.
Liew, A.G., Idris, A., Wong, C.H.K., Samad, A.A., Noor, M.J.M.M., Baki, A.M., 2004.
Incorporation of sewage sludge in clay brick and its characterization. Waste
Manage. Res. 22, 226–233.
Lin, D.F., Weng, C.H., 2001. Use of sewage sludge ash as brick material. J. Environ.
Eng-ASCE 127, 922–927.
Lin, K.L., Chiang, K.Y., Lin, C.Y., 2005. Hydration characteristics of waste sludge ash
that is reused in eco-cement clinkers. Cem. Concr. Res. 35, 1074–1081.
Lin, K.L., Chiang, K.Y., Lin, D.F., 2006. Effect of heating temperature on the sintering
characteristics of sewage sludge ash. J. Hazard. Mater. B128, 175–181.
Lin, D.F., Lin, K.L., Hung, M.J., Luo, H.L., 2007. Sludge ash/hydrated lime on the
geotechnical properties of soft soil. J. Hazard. Mater. 145 (1–2), 58–64.
Lin, D.F., Chang, W.C., Yuan, C., Luo, H.L., 2008. Production and characterization of
glazed tiles containing incinerated sewage sludge. Waste Manage. 28,
502–508.
2339
Lin, K.L., Lin, D.F., Luo, H.L., 2009. Influence of phosphate of the waste sludge on the
hydration characteristics of eco-cement. J. Hazard. Mater. 168, 1105–1110.
Lin, Y., Zhou, S., Li, F., Lin, Y., 2012. Utilization of municipal sewage sludge as
additives for the production of eco-cement. J. Hazard. Mater. 213–214, 457–
465.
Lisk, D.J., 1989. Compressive strength of cement containing ash from municipal
refuse or sewage sludge incinerators. B. Environ. Contam. Toxicol. 42, 540–543.
Luo, H.L., Lin, D.F., Kuo, W.T., 2004. The effects of nano-materials on the behaviours
of sludge mortar specimens. Water Sci. Technol. 9, 57–65.
Mahieux, P.-Y., Aubert, J.-E., Cyr, M., Coutand, M., Husson, B., 2010. Quantitative
mineralogical composition of complex mineral wastes – contribution of the
Rietveld method. Waste Manage. 30, 378–388.
Mattenberger, H., Fraissler, G., Brunner, T., Herk, L., Hermann, I., Obernberger, I.,
2008. Sewage sludge ash to phosphorus fertiliser: variables influencing heavy
metal removal during thermochemical treatment. Waste Manage. 28 (12),
2709–2722.
Mattenberger, H., Fraissler, G., Joller, M., Brunner, T., Obernberger, I., Herk, P.,
Hermann, L., 2010. Sewage sludge ash to phosphorus fertiliser (II): influences of
ash and granulate type on heavy metal removal. Waste Manage. 30, 1622–1633.
McCarter, W.J., Tran, D., 1996. Monitoring pozzolanic activity by direct activation
with calcium hydroxide. Constr. Build. Mater. 10, 179–184.
Merino, I., Arevalo, L.F., Romero, F., 2005. Characterisation and possible uses of
ashes from wastewater treatment plants. Waste Manage. 25, 1046–1054.
Merino, I., Arevalo, L.F., Romero, F., 2007. Preparation and characterization of
ceramic products by thermal treatment of sewage sludge ashes mixed with
different additives. Waste Manage. 27 (12), 1829–1844.
Milieu Ltd., WRc and RPA, 2010. Environmental, economic and social impacts of the
use of sewage sludge on land. Final report for the European Commission. Part
III: Project Interim Reports.
Monzo, J., Paya, J., Borrachero, M.V., Corcoles, A., 1996. Use of sewage sludge ash
(SSA) – cement admixtures in mortars. Cem. Concr. Res. 26, 1389–1398.
Monzo, J., Paya, J., Borrachero, M.V., Bellver, A., Peris-Mora, E., 1997. Study of
cement-based mortars containing spanish ground sewage sludge ash. Stud.
Environ. Sci. 71, 349–354.
Monzo, J., Paya, J., Borrachero, M.V., Peris-Mora, E., 1999. Mechanical behaviour of
mortars containing sewage sludge ash (SSA) and Portland cements with
different tricalcium aluminate content. Cem. Concr. Res. 29 (1), 87–94.
Monzo, J., Paya, J., Borrachero, M.V., Girbes, I., 2003. Reuse of sewage sludge ashes
(SSA) in cement mixtures: the effect of SSA on the workability of cement
mortars. Waste Manage. 23, 373–381.
Murakami, T., Suzuki, Y., Nagasawa, H., Yamamoto, T., Koseki, T., Hirose, H.,
Okamotot, S., 2009. Combustion characteristics of sewage sludge in an
incineration plant for energy recovery. Fuel 90, 778–783.
Nastac, D.C., Käantee, U., Liimatainen, J., Hupa, M., Muntean, M., 2007. Influence of
P(V) on the characteristics of calcium silicates and the hydration of clinkers.
Adv. Cem. Res. 19, 93–100.
Okuno, N., Takahashi, S., 1997. Full scale application of manufacturing bricks from
sewage. Water Sci. Technol. 36 (11), 243–250.
Oliver, B.G., Carey, J.H., 1976. Acid solubilization of sewage sludge and ash
constituents for possible recovery. Water Res. 10, 1077–1081.
Pan, S.C., Tseng, D.H., 2001. Sewage sludge ash characteristics and its potential
applications. Water. Sci. Technol. 44 (10), 261–267.
Pan, S.C., Tseng, D.H., Lee, C., 2002. Use of sewage sludge ash as fine aggregate and
pozzolan in portland cement mortar. J. Solid Waste Technol. Manage. 28 (3),
121–130.
Pan, S.H., Tseng, D.H., Lee, C.C., Lee, C., 2003a. Influence of the fineness of sewage
sludge ash on the mortar properties. Cem. Concr. Res. 33, 1749–1754.
Pan, S.C., Lin, C.C., Tseng, D.H., 2003b. Reusing sewage sludge ash as adsorbent for
copper removal from wastewater. Resour. Conserv. Recy. 39, 79–90.
Park, J.P., Moon, S.O., Heo, J., 2003. Crystalline phase control of glass ceramics
obtained from sewage sludge fly ash. Ceram. Int. 29, 223–227.
Paya, J., Borrachero, M.V., Monzo, J., Peris-Mora, E., Amahjour, F., 2001. Enhanced
conductivity measurement techniques for evaluation of fly ash pozzolanic
activity. Cem. Concr. Res. 31, 41–49.
Paya, J., Monzo, J., Borrachero, M.V., Amahjour, F., Girbes, I., Velazquez, S., Ordonez,
L.M., 2002. Advantages in the use of fly ashes in cements containing pozzolanic
combustion residues: silica fume, sewage sludge ash, spent fluidized bed
catalyst and rice husk ash. J. Chem. Technol. Biot. 77 (3), 331–335.
PD CEN/TR 13767, 2004. Characterization of sludges – good practice for sludges
incineration with and without grease and screenings.
Pera, J., Coutaz, L., Ambroise, J., Chababbet, M., 1997. Use of incinerator bottom ash
in concrete. Cem. Concr. Res. 27, 1–5.
Petzet, S., Peplinski, B., Bodkhe, S.Y., Cornel, P., 2011. Recovery of phosphorus and
aluminium from sewage sludge ash by a new wet chemical elution process
(SESAL-Phos-recovery process). Water Sci. Technol. 64, 29–35.
Petzet, S., Peplinski, B., Cornel, P., 2012. On wet chemical phosphorus recovery from
sewage sludge ash by acidic or alkaline leaching and an optimized combination
of both. Water Res. 46, 3769–3780.
Pinarli, V., Kaymal, G., 1994. An innovative sludge disposal option-reuse of sludge
ash by incorporation in construction materials. Environ. Technol. 15, 843–852.
Sanger, M., Werther, J., Ogada, T., 2001. NOx and N2O emission characteristics from
fluidised bed combustion of semi-dried municipal sewage sludge. Fuel 80, 167–
177.
Schipper, W.J., Klapwijk, A., Potjer, B., Rulkens, W.H., Temmink, B.G., Kiestra, F.D.G.,
Lijmbach, A.C.M., 2001. Phosphate recycling in the phosphorus industry.
Environ. Technol. 22, 1337–1345.
2340
S. Donatello, C.R. Cheeseman / Waste Management 33 (2013) 2328–2340
Schirmer, T., Mengel, K., Wiesbusch, B., 1999. Chemical and mineralogical
investigations on clay bricks containing sewage sludge ash. Tile Brick Int. 15,
166–174.
Smil, V., 2000. Phosphorus in the environment: natural flows and human
interferences. Ann. Rev. Energy Environ. 25, 53–88.
Smith, K.M., Fowler, G.D., Pullket, S., Graham, N.J.D., 2009. Sewage sludge-based
adsorbents: a review of their production, properties and use in water treatment
applications. Water Res. 43, 2569–2594.
Solimene, R., Urciuolo, M., Cammarota, A., Chirone, R., Salatino, P., Damonte, G.,
Donati, C., Puglisi, G., 2010. Devolatilization and ash comminution of two
different sewage sludges under fluidized bed combustion conditions. Exp.
Therm. Fluid Sci. 34, 387–395.
Stark, K., Plaza, E., Hultman, B., 2006. Phosphorus release from ash, dried sludge and
sludge residue from supercritical water oxidation by acid or base. Chemosphere
62, 827–832.
Stasta, P., Boran, J., Bebar, L., Stehlik, P., Oral, J., 2006. Thermal processing of sewage
sludge. Appl. Therm. Eng. 26 (13), 1420–1426.
Steen, I., 1998. Phosphorus availability in the 21st century: management of a nonrenewable resource. British Sulphur Publishing.
Suzuki, S., Tanaka, M., Kaneko, T., 1997. Glass–ceramic from sewage sludge ash. J.
Mater. Sci. 32, 1775–1779.
Takahashi, M., Kato, S., Shima, H., Sarai, E., Takao, I., Hatyakawa, S., Miyajiri, H.,
2001. Technology for recovering phosphorus from incinerated wastewater
treatment sludge. Chemosphere 44, 23–29.
Tay, J.H., 1986. Potential use of sludge ash as construction material. Resour. Conserv.
Recy. 13, 53–58.
Tay, J.H., 1987a. Bricks manufactured from sludge. J. Environ. Eng. Div. ASCE 113,
278–283.
Tay, J.H., 1987b. Sludge ash as filler for Portland cement concrete. J. Environ. EngASCE 113, 345–351.
Tay, J.H., Show, K.Y., 1992. Utilisation of municipal wastewater sludge as building
and construction materials. Resour. Conserv. Recyc. 6, 191–204.
Tay, J.H., Show, K.Y., 1994. Municipal wastewater sludge as cementitious and
blended cement materials. Cem. Concr. Compos. 16 (1), 39–48.
Trauner, E.J., 1991. Sludge ash bricks fired to above and below ash-vitrifying
temperature. J. Environ. Eng. Div. ASCE 119, 506–519.
Tsai, C.C., Wang, K.S., Chiou, I.J., 2006. Effect of SiO2–Al2O3–flux ratio change on the
bloating characteristics of lightweight aggregate material produced from
recycled sewage sludge. J. Hazard. Mater. B134, 87–93.
Urciuolo, M., Solimene, R., Chirone, R., Salatino, P., 2012. Fluidized bed combustión
and fragmentation of wet sewage sludge. Exp. Thermal Fluid Sci. 43, 97–104.
USEPA, 2003. Use of incineration for biosolids management. Washington D.C.,
USEPA.
USGS (United States Geological Survey) Mineral Commodity Summaries, January
2012.
Report
accessed
via:
<http://minerals.usgs.gov/minerals/pubs/
commodity/phosphate_rock/mcs-2012-phosp.pdf> (last accessed in November
2012).
Van de Velden, M., Dewil, R., Baeyens, J., Josson, L., Lanssens, P., 2008. The
distribution of heavy metals during fluidized bed combustion of sludge (FBSC).
J. Hazard. Mater. 151 (1), 96–102.
Vogel, C., Adam, C., Peplinski, B., Wellendorf, S., 2010. Chemical reactions during the
preparation of P and NPK fertilizers from thermochemically treated sewage
sludge ashes. Soil Sci. Plant Nutr. 56, 627–635.
Wainwright, P.J., Cresswell, D.J.F., 2001. Synthetic aggregates from combustion
ashes using an innovative rotary kiln. Waste Manage. 21 (3), 241–246.
Wang, K.S., Chiou, I.J., Chen, C.H., Wang, D., 2005a. Lightweight properties and pore
structure of foamed material made from sewage sludge ash. Constr. Build.
Mater. 19, 627–633.
Wang, K.S., Tseng, C.J., Chiou, I.J., Shih, M.H., 2005b. The thermal conductivity
mechanism of sewage sludge ash lightweight materials. Cem. Concr. Res. 35,
803–809.
Wang, L., Skjevrak, G., Hustad, J.E., Gronli, M.G., 2012. Sintering characteristics of
sewage sludge ashes at elevated temperatures. Fuel Process. Technol. 96, 88–97.
Werther, J., Ogada, T., 1999. Sewage sludge combustion. Prog. Energy Combust. 25,
55–116.
Wiebusch, B., Seyfried, C.F., 1997. Utilization of sewage sludge ashes in the brick
and tile industry. Water Sci. Technol. 36 (11), 251–258.
Wiesbusch, B., Ozaki, M., Watanabe, H., Seyfried, C.F., 1998. Assessment of leaching
tests on construction materials made of incinerator ash (sewage sludge):
investigations in Japan and Germany. Water Sci. Technol. 38, 195–205.
Wolski, N., Maier, J., Hein, K.R.G., 2004. Fine particle formation from co-combustion
of sewage sludge and bituminous coal. Fuel Process. Technol. 85, 673–686.
Wzorek, Z., Jodko, M., Gorazda, K., Rzepecki, T., 2006. Extraction of phosphorus
compounds from ashes from thermal processing of sewage sludge. J. Loss
Prevent. Proc. 19, 39–50.
Yip, W.K., Tay, J.H., 1999. Aggregate made from incinerated sludge residue. J. Mater.
Civil Eng. 2 (2), 84–93.
Zabaniotou, A., Theofilou, C., 2008. Green energy at cement kiln in Cyprus – use of
sewage sludge as a conventional fuel substitute. Renew. Sust. Energy Rev. 12,
531–541.
Zhang, F.S., Yamasaki, S., Kimura, K., 2002a. Waste ashes for use in agricultural
production: II. Contents of minor and trace metals. Sci. Total Environ. 286, 111–
118.
Zhang, F.S., Yamasaki, S., Nanzyo, M., 2002b. Waste ashes for use in agricultural
production: I. Liming effect, contents of plant nutrients and chemical
characteristics of some metals. Sci. Total Environ. 284, 215–225.