2
Nitrogen recovery and reuse
M. Maurer, J. Muncke and T.A. Larsen T.A.
2.1 INTRODUCTION
2.1.1 Chemical properties
Nitrogen gas comprises 78.3% of the earth's atmosphere by volume and
75.5% by mass. N has two stable isotopes, 14N and 15N. The lighter isotope is
272 times as abundant as the heavier one.
N is present in many chemical species. The following list contain inorganic
species relevant in microbes and aquatic systems (in brackets formula and oxidation state of nitrogen): Nitrate (NO3-, +V), nitrite (NO2-, +III) , nitric oxide
(NO, +II), nitrous oxide (N2O, +I), elemental nitrogen (N2, 0), ammonium
(NH4+, -III) and ammonia (NH3, -III). Besides organically bound N, elemental
nitrogen, nitrate and ammonium (respectively ammonia) are the most common
N-forms dissolved in water.
[1]
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2.1.2 Availability of nitrogen
The availability of elemental nitrogen (N2) is very high. Our atmosphere consists
of 78% of N2.Due to its gaseous nature N2 is easily accessible all over the worlds
surface. However, elemental nitrogen is kinetically inert and not reactive because of the strong bond between the nitrogen atoms (three electron pairs,
bonding energy: 924 kJ⋅mol-1N2). For this reason N2 hardly engages in any
chemical reactions and is therefore biologically not relevant. Yet, nitrogen is of
essential importance to living organisms: DNA, RNA, proteins and structural
components in all living cells contain nitrogen.
In contrary to other nutrients like phosphorus or potassium there are not many
exploitable natural sources of fixed nitrogen. In the 19th -century the availability
of human and animal waste was the main limitation for crop production. The use
of soluble inorganic nitrates like rock deposits found in Chilean deserts and organic guano from the excrement left by birds on Peru's rainless Chincha Islands
provided a temporary reprieve for some farmers. It was not until the invention of
the ammonia synthesis in 1913, that broke this limitation and enabled industrial
food production and disastrous warfare.
2.1.3 Nitrogen fixation
There are three major ways[1] to convert N2 into a chemically more reactive
species:
• Biological fixation: Some bacteria (associated with certain plants, leguminosae) and certain blue-green algae are able to fix nitrogen and assimilate it as organic nitrogen
• Technical N-fixation: In the Haber-Bosch process N2 is converted together with hydrogen gas (H2) into ammonia (NH3).
• Combustion of gasoline and fossil fuel (automobile engines and thermal
power plants)
Table 2.1. Global nitrogen flux and reservoirs. The values are estimated magnitudes and
vary in different sources significantly (Kümmel and Papp, 1988; Jaffe, 1992; Soderlund
and Svensson, 1976). 1012 gN = 1 MtoN.
Turnover Rates
Process
[1012 gNa-1]
Biological fixation
200
Technical fixation
90
Combustion
20
1
Reservoirs
Compartment
[1012 gN]
Atmosphere
3.9⋅109
Biomass
0.9⋅106
Dissolved (oceans)
2.2⋅107
Important for the atmospheric chemistry, but not for the nitrogen turnover on earth, are also the
formation of NO from N2 and O2 due to photons and lightning.
Nitrogen recovery and reuse
Denitrification
Deposition
Biomass turnover
3
210
20
6000
2.1.4 Antropogenic interference with the N-flux
The Table 2.1 shows that fixation of nitrogen due to human activity is about
the same magnitude as the natural one. This also means that we heavily interfere
with the natural nitrogen cycle. Massive introduction of reactive nitrogen into
soils and waters has many unfavourable consequences for the environment.
Problems range from local health to global changes. Examples for adverse effects in the hydrosphere are: Nitrate in drinking water can cause life-threatening
methemoglobinemia ('blue baby' symptoms) in infants, and it is linked epidemiologically to some cancers. Excessive nitrogen compounds in certain lakes,
ocean bays and estuaries can cause eutrophication. Ammonia and nitrite are
toxic to aquatic organisms.
2.1.5 Urban wastewater system
Parallel to the technical development of N-fixation the urban wastewater system was established. The water closet uses water as a transport medium to remove human waste from urban areas. This improved the hygienic conditions in
the cities significantly and was an important prerequisite for the development of
many European cities. However, the use of flushing toilets and sewer systems
made it impossible to continue with the traditional recycling of human excreta.
Especially urine contains up to 11 gNd-1 per inhabitant, which makes wastewater
to one of the major sources of N-pollution in urban freshwater bodies. Nowadays
the conversion of fishtoxic ammonia to nitrate (nitrification) and the removal of
nitrogen (denitrification) are the most costly part of modern wastewater treatment plants.
2.1.6 Conclusions
The conclusions that can be drawn from this introduction are:
• The natural resources for nitrogen are extensive and universally accessible. However, in order to be accessible to plants and most microorganisms nitrogen has to be converted to ammonia or nitrate; either industrially by the Haber-Bosch process or naturally by N-fixing organisms. Haber-Bosch process requires an input of fossil fuel for energy
supply. The technical production of ammonia by the Haber-Bosch proc-
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Maurer & Muncke
ess is of the same magnitude as the natural nitrogen fixation, or even
greater. Mankind is intervening heavily in the natural N-cycle.
• In reality we have to protect our environment from excessive nitrogen
loads. This is mostly done by conversion of a toxic species into a less
hazardous one (ammonia to nitrate) or by conversion into gaseous nitrogen (N2). Recycling is only common in economically poor areas. In
Europe, nitrogen rich resources like manure are usually treated as waste
and handled accordingly.
The following chapters focus mainly on municipal wastewater. This is one of
the biggest point sources of nitrogen and has a major impact on aquatic systems
in many areas. For N-containg liquid industrial waste (e.g. pig manure or food
processing waste) treatment options are very similar.
2.2 WASTEWATER
2.2.1 Municipal Wastewater
2.2.1.1 Wastewater Characteristics
Wastewater contains significant amounts of nitrogen. The German guideline
for designing wastewater treatment plants assumes 11 gNd-1 per person, also
called 'population equivalent' (PE). At the wastewater treatment plant (WWTP)
the biggest fraction is ammonium and the rest is mainly organically bound nitrogen. Figure 2.1 shows that in reality the average daily load of a WWTP is not
constant and can vary significantly. As we later will see this is an important
point for the design and operation of the WWTP, because the detoxification of
ammonium is one of the most critical steps in wastewater treatment.
Besides the load variations during the year there is also a very pronounced
daily concentration profile. In Figure 2.2. it can be shown that the influx of ammonium has a clear daily peak after noon. This reflects one of the most important human activities after getting up in the morning: Going to the bathroom. The
released urine contains urea that is hydrolysed in the sewer system. As a consequence, the hydrolisation product, ammonium, arrives at the WWTP in high
concentrations. Ammonium peak shape, size and incidence can vary in different
catchment areas, depending on population size and wastewater flowtime.
Nitrogen recovery and reuse
5
1.0
0.9
Ammonium
Cumulative %
0.8
0.7
0.6
Total Nitrogen
0.5
0.4
0.3
0.2
0.1
0.0
0
50
100
150
200
Nitrogen-Load [kgNd-1]
Figure 2.1. Nitrogen and ammonium load of a smaller wastewater treatment plant in
Switzerland with about 80'000 population equivalent (water inflow: 32'000 m3d-1) in the
catchment area. The wastewater has mainly a municipal character with a minor fraction
industry.
Maurer & Muncke
Deviation from Ntot-load
6
1.5
1.3
Total Nitrogen
1.1
0.9
0.7
Ammonium
0.5
0.3
part. Nitrogen
0.1
0
3
6
9
12
15
18
21
24
Time of the day
Figure 2.2. Example for daily variations of the nitrogen load (workday) of the WWTP
described in Figure 2.1. 69% of the total nitrogen after the primary settler is ammonium,
mostly from urine.
Denitrification
Primary
settling tank
10-50%
Nitrification
Settling tank
100%
10-20%
Supernatant
20%
15-20%
Sludge
Digestor
15-20%
Sludge thickening
Figure 2.3. Flowscheme of a wastewater treatment plant with nitrification, biological
denitrification and a sludge treatment. The numbers give the flow of nitrogen through the
WWTP, relative to the N-load in the input.
Nitrogen recovery and reuse
7
2.2.1.2 Flowscheme of a WWTP
Figure 2.3 shows a denitrifying wastewater treatment plan (WWTP), typical
for central Europe (e.g. Germany, Netherlands or Switzerland). Of course there
are many existing variation of this flowscheme, but figure 2.3 illustrates the most
important features.
Two different sections can easily be identified:
• Wastewater treatment (the upper flow line in the figure): After the mechanical removal of the solids the wastewater undergoes a biological purification. In this specific example small immersed microbially active
colonies, known as activated sludge flocs, are used. These flocs are
mixed together with the wastewater after the primary clarifier, and are
exposed to anoxic and aerobic condition. At the end they are separated
from each other, the purified water is discharged and the activated
sludge is recycled. The following paragraphs are discussing the two
biological processes relevant for nitrogen conversion: nitrification and
denitrification.
• Sludge treatment (the lower flow line in the figure): An often used system is the anaerobic mesophilic sludge treatment (or digestion). Slowly
biodegradable substances like fat, proteins or hydrocarbons are degraded anerobically typically at about 35 °C. This reduces the amount of
solids and renders methane for energy production. An other side product
which is of special importance is the digester supernatant that contains
high concentrations of ammonium.
2.2.1.3 Nitrification
Nitrification converts ammonia/ammonium to nitrate, usually in a two step
process. The responsible organisms, also referred to as nitrifiers, are mainly
chemoautotrophs, meaning that they use carbon dioxide (CO2) as main carbon
source. Nitrifiers gain energy by oxidation of ammonia to nitrite or nitrate. The
nitrification is a prerequisite for denitrification and a way to eliminate the fishtoxine ammonia.
The growth rate of the nitrifiers is relatively small, much smaller than typical
heterotrophic micro-organisms that are responsible for the degradation of Ccompounds. As a consequence nitrifying WWTP are designed to meet the criteria of the slow-growing nitrifiers and are therefore significantly larger than other
WWTP.
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2.2.1.4 Denitrification
Denitrification refers to the process in which nitrate is converted to gaseous
compounds, mainly nitrogen gas. In wastewater treatment two very different
processes are used:
• Heterotrophic denitrification: Many types of micro-organisms are capable to use nitrate as a terminal electron acceptor when growing on organic matter("CH2O" stands for biodegradable organic compound, e.g.
carbohydrates):
5 "CH2O" + 4 NO3- + 4 H+ → 5 CO2 + 2 N2 + 7 H2O
This reaction is mostly inhibited under aerobic condition. Thus, the environmental conditions in which we find denitrification are characterised
by a supply of oxidisable organic matter (e.g. "CH2O"), absence of oxygen, availability of reducible nitrogen, and of course denitrifying microorganisms.
• Autotrophic denitrification: In recent years a new process for denitrification was discovered and investigated. Under anoxic conditions certain
chemoautotrophic organisms are capable of breathing by oxidising
ammonium with nitrite to nitrogen gas2. Technically the N-removal can
be achieved in a thick biofilm, where in the aerobic top layer of the film
parts of the ammonium is converted to nitrite. In the deeper anoxic layers nitrite and ammonium are converted to N2. An other established process is the ANAMMOX-process where the required nitrite is produced in
a first step and consequently denitrification is accomplished in a second
step.
Both denitrification processes are technically well established and relatively
successful in removing nitrogen from diluted aqueous solutions. Any other solution for removal and recycling of N has to compete against these technically easy
options of 'recycling nitrogen back to the atmosphere'.
2.2.1.5 Other removal techniques
In the literature other N-removal techniques are described. Huang et al (2001)
presented a catalytic oxidation of ammonia to N2-gas at high concentrations and
temperatures. Other possibilities are electrochemical approaches (e.g. Juttner et
al., 2000). These usually produce in-situ chlorine and hypochlorite which both
are capable to oxidise NH4+ to N2.
2
NH4+ + NO2- à N2 + 2H2O
Nitrogen recovery and reuse
9
2.2.2 Possible techniques to recycle N from wastewater
2.2.2.1 Biosolids
One very common way to reuse nitrogen from wastewater is the use of the
biosolids (sludge from the WWTP) in agriculture (examples in Chambers and
Smith, 1998; Cogger et al., 1999). About 20% of the total nitrogen load can be
found in the solid fraction of the WWTP output at a concentration of roughly 30
gNkg-1DRY MATTER (see also Figure 2.3). Depending on the regulations this sludge
has to undergo a thermal treatment to minimise the hygienic risks. The problematic aspect of this approach is that the sludge adsorbs many potentially hazardous compounds like heavy metals. In Europe this pathway is becoming more and
more questionable and it can be expected that in the near future biosolids are not
allowed to be used as a fertiliser anymore.
2.2.2.2 Adsorption
Zeolites and other minerals like clay or tuff have ion exchange properties and
are used to adsorb ammonium. A common approach is to pump wastewater
through columns packed with zeolite. Ammonia concentrations of 25 to 50 gNH4-3
-3
Nm can be lowered to levels around 1 gNH4-Nm (zeolites: Booker et al., 1996;
Nishimura et al., 1996; Nguyen and Tanner, 1998; Komarowski and Yu, 1997;
Cooney et al., 1999; Lahav and Green, 2000; tuff: Ibrahim, 2001; clay: Gisvold
et al., 2000).
Buday (1994) used cation exchange resins to reuse ammonia from wastewater
of an ammonium nitrate fertiliser plant. The exhausted resins were regenerated
with nitric acid, gaining an ammonium nitrate solution that is recycled into the
fertiliser production. Chen et al. (1999) successfully tested the use of different
cellulose acetate fibrets for the adsorption and recovery of proteins.
Kioussis et al. (2000) developed polymer hydrogels that remove nitrate, nitrite and phosphate from aquaculture wastewater. They claim to achieve following effluent qualities: 10 gNm-3 for nitrate and 0.08 gNm-3 for nitrite. Gel regeneration is accomplished with 1 M sodium hydroxide solution.
2.2.2.3 Stripping
The stripping of ammonia requires a high pH (around 10 to 12), which is usually achieved by addition of base in significant amounts:
NH4+ + NaOH
-> NH3 + H2O + Na+
+
NH4 + Ca(OH)2 + HCO3 -> NH3 + CaCO3 + 2 H2O
Per kilogram nitrogen about 7.2 kg NaOH or 7 kg Ca(OH)2 is required. There
are two ways to strip the ammonia out of the water:
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•
Steam stripping: Steam is blown through the water and after condensation a concentrated ammonia solution is produced.
• Air stripping (Thorndale, 1993): Air is bubbled through the wastewater
and takes up the gaseous ammonia. This has to be washed out in a second reactor under acidic conditions. Usually sulphuric acid (H2SO4) is
used, so that the product is an ammonium sulfate solution, 40% strong.
2 NH3 + H2SO4
-> (NH4)2SO4
The stripping process is not applicable for wastewater of low strength. Certain wastewaters, like from manure, from the production of PU-foams or the
digester supernatant in municipal WWTP can be treated economically.
2.2.2.4 Chemical Precipitation
Ammonium forms together with magnesium and phosphate the relatively insoluble complex struvite or ammonium magnesium phosphate (AMP or MAP).
The formation reaction is well known for analysing magnesium:
NH4+ + PO43- + Mg2+ + 6 H2O -> NH4MgPO4⋅6H2O
The reaction is strongly pH-dependent, due to the equilibrium constants for
the species NH4+ and PO43-. Figure 2.4. shows that the optimal pH-range is
around 10. However, in reality a pH over 9.5 leads to odour problems, because
of ammonia evaporation.
In soil, MAP has a similar availability of magnesium, phosphate and nitrogen
like for commercial fertilisers. Without drying it can be used as additive to compost or garden soil; after drying it could replace organic-mineral fertilisers based
on peat (Moll, 1991).
Nitrogen recovery and reuse
11
Concentration [log(M)]
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
5
6
7
8
9
10
11
12
pH
Figure 2.4. Solubility of struvite at different pH-values. The curve represents the concentration of Mg2+ after the dissolution of struvite at 25 °C. KS(MgNH4PO4) = 10-12.6
(Sillen and Martell, 1964); matrix: wastewater with no Mg2+, NH4+/NH3 and phosphate;
ionic strength: 0.01.
The MAP-process was developed for the fixation of ammonium in digester
supernatant. Prior to the actual precipitation step the remaining suspended solids
have to be eliminated (e.g. by flocculation) and carbon dioxide needs to be
stripped by adding acids, preferably phosphoric acid. In a next step magnesium
oxide (MgO) is added and the pH is adjusted to 9.0 with sodium hydroxide
(NaOH). A stoichiometric surplus of 20% to 30% (molar base) magnesium relative to ammonium is used to optimise the process. The precipitation of 1 kg nitrogen requires between 9.5 kg to 7.1 kg H3PO4, 4.0 kg MgO and 1.2 kg NaOH
(Siegrist, 1996; Munch and Barr, 2001).
To reduce the consumption of magnesium and phosphate the CAFR-process
recycles the magnesium and phosphate (Janus and Van der Roest, 1997). Struvite is treated thermally under basic conditions:
NH4MgPO4 + NaOH
-> MgNaPO4 + NH3 + H2O
The resulting MgNaPO4 can be reused in the precipitation process and the
nitrogen is collected as a concentrated ammonia solution.
Struvite formation is also used as a method to eliminate phosphorus from
high strength wastewater, like digester supernatant or manure. Wastewater from
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human or animal wastes usually contains much more nitrogen than phosphate.
The exclusive P removal requires only the addition of magnesium and typically
removes about 20% of the ammonium.
2.2.2.5 Other approaches
Bilstad (1995) used reverse osmosis to eliminate nitrogen from industrial and
municipal wastewater. The concentrated retentate can be used as input for struvite formation or ammonia stripping.
A completely different approach to recycle nitrogen is the direct use of
wastewater or purified wastewater as a nutrient solution for plant growth. Besides the use for irrigation purposes, there is a vast variety of aquacultures to
produce higher plants (e.g. tomatoes or duckweed) or algae for fish production
(Oron, 1990; Guterstam, 1996; Redding et al., 1997; Adamsson, 2000). There is
a wide field of different possible techniques, from simple fish ponds to combined wastewater treatment and food production facilities. Hygienic aspects are
of major concern when recycling nutrients in this form.
2.3 URINE SOURCE SEPARATION
2.3.1 Motivation
2.3.1.1 Introduction
All the efforts made at wastewater treatment plants are end-of pipe solutions.
The performance of these kind of processes depends, besides the process specific efficiency, heavily on the transport system. Both sewer system and WWTP
are burdened with pollutant loads they were never intended to manage[3] (Larsen
et al., 2001). As shown in the previous chapters the removal or recycling of nitrogen from wastewater is complicated, expensive[4] and often not very efficient.
An alternative is the removal of urine before it gets diluted in the sewer system. As already mentioned (Figure 2.2), urine constitutes major amountsof the
3
Municipal wastewater treatment is expected to eliminate phosphorus, nitrogen, micropollutants (heavy metals, pharmaceuticals, hormones,...), and various bulk chemicals
like NTA or LAS. However, WWTP are only partially capable of dealing with all these
substances. What is more, only a part of the total wastewater actually arrives in a
WWTP, due to incomplete sewer systems, storm water overflow or leaks.
4
Siegrist (1996) reports the following costs (in Euro) for the removal of one kg N:
Denitrification in a nitrifying WWTP: 3.4 to 7.3; struvite formation: 14.5; stripping:
11.2
Nitrogen recovery and reuse
13
WWTP nitrogen load. Urine typically contributes around 80% of the nitrogen,
50% of the phosphorus, 90% of the potassium, and a major part of the pharmaceutic and hormone residues. In order to reduce the burden of wastewater treatment it would be very efficient to collect urine separately at the source – per
person around 1.5 L⋅d-1 are produced.
2.3.1.2 History
Urine source separation was practised all over the world for many centuries,
before it got displaced by modern wastewater treatment. On one hand it was
recognised as a very good and effective fertiliser (molar nutrient ratio of N:P:K
= 30:1:2.5). On the other hand urine was an important raw chemical, e.g. for
dye-works or tanneries.
Urine (and faeces) separation is required if you would like to reuse the water.
Both urine and faeces are very concentrated and are potentially a health risk. For
the international space station (ISS) the urine is collected separately, stabilised
with acid to prevent hydrolysis and then distilled. This makes it possible to recycle the rest of the wastewater (also called grey water) with a reasonable effort.
For the same reason urine separation toilets were installed in 'ecological villages' built during the 90s in Sweden and Denmark (Hanæus et al., 1997; Jonsson et al., 1997). Urine is collected and directly used as a fertiliser, faeces go
through a septic tank and the sludge is composted.
2.3.2 System mechanics
2.3.2.1 NoMix toilets
Urine separating or NoMix toilets have one compartment for faeces and one
for urine. The urine flows through separate pipes to a storage tank. Then there
are several options to choose from, most of them are concepts and not yet applied in practice. Any of these possibilities can be combined with each other and
will increase the effectiveness of the wastewater treatment system.
2.3.2.2 Direct use as fertiliser
In Sweden the urine was stored for about 6 months and then directly applied
onto fields. Currently field investigations are carried out to compare the effectiveness of urine compared to conventional use of mineral fertiliser (JTI, 2000).
Empirical experience with urine as fertiliser is present world-wide; however only
few scientific studies are currently done in this field. Problems associated with
the direct use of urine as fertiliser are micropollutants, loss of nitrogen and high
salt concentrations that might disturb plant growth.
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2.3.2.3 Controlled release into the sewer system
Deviation from Ntot-load
Here several different approaches are possible. A continuous release into the
sewer system would smoothen the pronounced effect on the maximum daily load
and an even performance for ammonia (and micropollutants) could be achieved.
Already a storage volume as small as 0.5 L per inhabitant should have significant effects on the N-load (see Figure 2.5).
1.5
1.3
Total Nitrogen
1.1
0.9
0.7
Ammonium
0.5
0.3
part. Nitrogen
0.1
0
3
6
9
12
15
18
21
24
Time of the day
Figure 2.5. Expected nitrogen load under the assumption that all the ammonium from
urine is buffered locally and released evenly to the sewer system. The data is taken from
Figure 2.2.
Further possible control strategies are thinkable. Release could also be controlled to withhold urine when combined sewer overflows are likely to occur,
thus reducing the adverse effects of raw sewage emission to rivers and lakes.
Modelling of this option shows that it could successfully compete with the more
traditional approach of enlarging storm water storage capacity (Larsen et al.,
2001b).
An other approach would be the timed sudden release of all tanks in order to
create a concentrated wave of urine. Somewhere along the sewer line the wave
could be captured and processed separately (Huisman et al., 2000).
Nitrogen recovery and reuse
15
2.3.2.4 Processing of urine
There are several goals that can be achieved with a processing of urine:
• Stabilisation: Urine is a highly concentrated solution that changes its
properties rapidly after being excreted. Due to the biologically catalysed
decomposition of urea to ammonia the pH rises from originally about
6.8 to 9.5, at which ammonia evaporates into the gas phase. In addition
there are a lot of biodegradable carbon compounds present that enhance
the growth of microorganisms.
Experiments were performed to decrease the high pH by nitrifying a part
of the ammonia to nitrate in a biofilm reactor (Johansson and Hellström,
1999). Other approaches try to prevent the hydrolysis of urea by adding
acids (Hellstrom, 1999).
• Decrease of volume: In order to simplify storage and transport several
works are done in order to decrease the volume. Destillation is the
choice in space (Budininkas et al., 1986; Miernik et al., 1991). Johansson and Hellstrom (1999) tested a combination of partial nitrification
and drying. Another method is dry-freezing (Holland et al., 1992) or the
probably more feasible technique for volume reduction and nutrient
concentration by partial freezing (Lind et al., 2001).
• Production of a solid fertiliser: Of course there is also the possibility to
recycle ammonia by stripping and precipitation. Especially the formation
of struvite is investigated in several publications (Boistelle et al., 1984;
Grases et al., 1997; Lind et al., 2000).
2.3.3 Waste design
Closed material cycles are a basic principle of our naturally evolved environment. Mankind has interfered with many closed cycles and is creating waste
problems that influence large parts of our environment. In order to meet the requirements necessary for safeguarding the future closing of cycles is necessary.
In many countries this has successfully been implemented for solid wastes.
The separate collection of paper, metal, glass etc. is common. Household, as
well as industrial wastes are collected and waste streams are processed, turning
waste into raw material. This scheme is easily applicable to solid wastes, but
liquid wastes are less easy to separate and dispose of. However, wastewater
management is connected to a number of problems, and it is worthwhile to consider a change in paradigm. Some of the problems associated with the wastewater system in Europe according to Larsen and Gujer (2001c) are:
• Disposal of sewage sludge has become an environmental issue. Sludge
often contains heavy metals and micro-pollutants
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Maurer & Muncke
•
Micro-pollutants are in rivers and lakes. Their removal from WWTP is
incomplete
• Combined sewer overflows contribute to environmental pollution. Nutrients, micro-pollutants and heavy metals are discharged to natural aquifer
• Sewers are leaky; wastewater is lost, in certain areas groundwater infiltrates into sewers in large amounts
• Maintenance of sewer systems is costly and complicated. The system is
heterogeneous due to its gradual emergence
High costs and inflexibility make the system difficult to change. Also, awareness of the benefits of the current wastewater system is important: hygiene, comfort and easy handling are major properties that must be inherent to any new
system. Various attempts are currently being made to separate wastewater
streams at the source, like urine source separation (Larsen et al., 2001), compost
toilets or separation of grey water (Esrey et al., 1998). The same applies to industrial wastewaters. For instance, at dentist practices amalgam-containing
wastewater is treated separately on site.
2.4 REFERENCES
Adamsson, M. (2000) Potential Use of Human Urine by Greenhouse Culturing of Microalgae (Scenedesmus Acuminatus), Zooplankton (Daphnia Magna) and Tomatoes
(Lycopersicon). Ecological Engineering 16, 243-254.
Bilstad, T. (1995) Nitrogen Separation from Domestic Waste-Water by Reverse- Osmosis. Journal of Membrane Science 102, 93-102.
Boistelle, R., Abbona, F., Berland, Y., Grandvuillemin, M. and Olmer, M. (1984)
Growth and Stability of Magnesium Ammonium Phosphate (Struvite) in Acidic
Sterile Urine. Urological Research 12, 79-79.
Booker, N.A., Cooney, E.L. and Priestly, A.J. (1996) Ammonia Removal from Sewage
Using Natural Australian Zeolite. Water Science and Technology 34, 17-24.
Booker, N.A., Priestley, A.J. and Fraser, I.H. (1999) Struvite Formation in Wastewater
Treatment Plants: Opportunities for Nutrient Recovery. Environmental Technology
20, 777-782.
Buday, M. (1994) Reutilization of Ammonia from Waste-Water Using Cation-Exchange
Resins. Water Science and Technology 30, 111-119.
Budininkas, P., Rasouli, F. and Wydeven, T. (1986) Development of a Water Recovery
Subsystem Based on Vapor Phase Catalytic Ammonia Removal (Vpcar). Proceedings Society of Automotive Engineers P 177, 661-667.
Chambers, B.J. and Smith, K. (1998) Nitrogen: Some Practical Solutions for the Poultry
Industry. Worlds Poultry Science Journal 54, 353-357.
Chen, L.A., Carbonell, R.G. and Serad, G.A. (1999) Recovery of Proteins and Other
Biological Compounds Using Fibrous Materials: I. Adsorption by Salt Addition.
Journal of Chemical Technology and Biotechnology 74, 733-739.
Cogger, C.G., Sullivan, D.M., Bary, A.I. and Fransen, S.C. (1999) Nitrogen Recovery
from Heat-Dried and Dewatered Biosolids Applied to Forage Grasses. Journal of
Environmental Quality 28, 754-759.
Nitrogen recovery and reuse
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Cooney, E.L., Booker, N.A., Shallcross, D.C. and Stevens, G.W. (1999) Ammonia Removal from Wastewaters Using Natural Australian Zeolite. I. Characterization of the
Zeolite. Separation Science and Technology 34, 2307-2327.
Esrey, S.A., Gough, J., Rapaport, D., Sawyer, R., Simpson-Hébert, M., Vargas, J. and
Winblad, U. (1998) Ecological Sanitation. Sida, Stockholm.
Gisvold, B., Odegaard, H. and Follesdal, M. (2000) Enhanced Removal of Ammonium
by Combined Nitrification/Adsorption in Expanded Clay Aggregate Filters. Water
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