PHILIPP AGRIC SCIENTIST
Vol. 94 No. 3, 292-300
September 2011
ISSN 0031-7454
Bench-Scale Composting of Recycled Paper Mill Sludge Using
Chicken Manure + Duck Manure, Kitchen Wastes and Agricultural
Wastes as Nitrogen Amendments
Jurex Gallo*, Jose Naraval, Jr. and Susan Gallardo
Asian Regional Research Programme on Environmental Technology – De La Salle University, Room 217, Science and
Technology Research Center, De La Salle University, 1004 Manila, Philippines
*
Author for correspondence; e-mail: [email protected], [email protected]; Tel.: + 63 (02) 524 4611 local
214/215; Fax: + 63 (02) 524 0563
The study determined the effect of carbon to nitrogen ratio (C/N) and N amendments in bench-scale
composting of recycled paper mill sludge. N amendments used in the study included mixed chicken
manure + duck manure, kitchen wastes and agricultural wastes. Experiments were conducted in
three bench-scale reactors designed to simulate a composting system. Mixed chicken manure + duck
manure as N amendment was used to adjust the C/N of composting feedstock to 20:1 and 30:1. Test
parameters included temperature, free air space (FAS), pathogens and nutrient content of compost
products. Feedstock amended with mixed chicken manure + duck manure with initial C/N of 30 was
favorable and results are in agreement with the findings of previous studies. Although the initial
feedstock with C/N=20 had the highest reduction in volatile solids, it emitted foul odor due to
ammonia emission all throughout the composting process. The total NPK in composts produced by
manure-amended feedstocks passed the requirements of the Fertilizer and Pesticide Authority;
however, pathogens present in compost exceeded the United States Environmental Protection
Agency standards. Further investigations were also conducted using kitchen wastes and agricultural
wastes as N amendments for composting recycled paper mill sludge at initial C/N of 30. Based on
composting performances and quality of compost products, results of treatments using kitchenwaste-amended feedstock and agricultural-waste-amended feedstock were outweighed by the results
of treatment using mixed chicken manure + duck manure as N amendment. High ammonia emission
was observed in kitchen-waste-amended feedstock while the FAS of agricultural-waste-amended
feedstock significantly dropped in the early stage of composting.
Key Words: C/N, composting, nitrogen amendments, recycled paper mill sludge
Abbreviations: APHA – American Public Health Association, ARRPET–DLSU – Asian Regional Research
Programme on Environmental Technology – De La Salle University, C/N – carbon to nitrogen ratio, DPS – de-inking
paper sludge, FAS – free air space, FPA – Fertilizer and Pesticide Authority, FS – fixed solids, MC – moisture content,
OC – organic carbon, TKN – total Kjeldahl N, USEPA – United States Environmental Protection Agency, VS –
volatile solids
INTRODUCTION
In the Philippines, there has been a growing concern on
the sludge generated by the pulp and paper industry. In
2002, an assessment of the industry showed an average
rate of 100 metric tons of sludge generated daily by pulp
and paper mills (Gallo 2002). An increase in the demand
for paper and other paper-based products has led the pulp
and paper industry to increase its production of paper,
thereby increasing the amount of solid waste that requires
management. The country‟s stringent environmental laws
and regulations such as the Clean Air Act of 1999 and the
292
Ecological Solid Waste Management Act of 2000 have
until recently discouraged mills from focusing only on
landfilling and incineration as means of sludge disposal;
other alternatives include recycling and reuse. Alternative
sludge management is thus necessary to address the
problem of solid waste disposal in pulp and paper mills.
In 2003, the Asian Regional Research Programme on
Environmental Technology – De La Salle University
(ARRPET-DLSU)
conducted
heavy
metal
characterization of sludge from a recycled paper mill in
the Philippines (Carillo and Gallardo 2005). Results of
the study showed the presence of heavy metals (Cr, Cd,
The Philippine Agricultural Scientist Vol. 94 No.3 (September 2011)
Bench-Scale Composting of Recycled Paper Mill Sludge
Ni, Cu, Zn and Pb) in recycled paper mill sludge in
concentrations way below the Part 503 Standard provided
by the United States Environmental Protection Agency
(USEPA) (http://yosemite.epa.gov) for sludge and by the
Department of Agriculture (DA) in the Philippines
standard for fortified fertilizers (FPA 1996). These
findings have led ARRPET-DLSU to embark on
composting as an alternative process for the management
of recycled paper mill sludge in the country.
The feasibility of composting pulp and paper mill
sludge has been studied in the past by various
researchers. Sesay et al. (1997) provided information
about the process and the changes in the physical,
chemical and biological characteristics of sludge during
composting. Most organic matter was found to be stable
within 2 wk of composting; more than 30% of the initial
volatile solid content was decomposed and the respiration
rate dropped by more than 80%. Sesay et al. (1997)
hypothesized that subsequent storage for 4–5 wk would
improve the quality and maturation of compost with no
need for further aeration. Jackson and Line (1997)
investigated the feasibility of composting pulp and paper
mill sludge in large-scale periodically turned windrows.
Results of their study showed a decrease of 45% in pile
volume and production of a well-humified material in the
absence of phytotoxicity at termination. In a study by
Beauchamp et al. (2002) of raw and composting deinking paper sludge (DPS), raw de-inking paper sludge
and its young compost did not represent a major threat to
the environment. In the same year, Charest and
Beauchamp (2002) conducted a study to determine the
behavior of physico-chemical parameters during
composting of de-inking paper sludge using mechanical
turning with poultry manure as N amendment. Results of
their study showed that the best composting performance
was observed in 0.6% N treatment compared with 0.7%
N and 0.9% N treatments; however, a period of more
than 24 wk was required for compost product of 0.6% N
treatment to reach maturity. Marche et al. (2003)
investigated the chemical changes during composting of
a paper mill sludge and hardwood sawdust mixture.
Composting was conducted in a vessel with 2-h interval
mixing using an electro-mechanical turner. Increase in
carbohydrates and decreases in parafinnic C,
proteinacious C and C in methoxy (O-CH3) groups
appeared to influence the increase in microbial activity.
At biomaturity, the compost material consisted primarily
of polysaccharide/carbohydrate materials, specifically
cellulose and acidic polysaccharides (uronic acids) in
combination with smaller quantities of lignin.
Composting of de-inking sludge from a recycled paper
mill was also investigated by Gea et al. (2005).
Respiration tests on compost materials produced after 40
d of composting showed complete stabilization with final
values of the static respiration index in the range of 1.1–
The Philippine Agricultural Scientist Vol. 94 No.3 (September 2011)
Jurex Gallo et al.
2.8 mg O2 per gram of total organic matter content per
hour. They recommended composting as a suitable
technology for effective recycling of this type of sludge
from the recycled paper manufacturing industry.
Beauchamp et al. (2006) also conducted a study on
isolation of free-living N2-fixing bacteria and their
activity in compost containing DPS and suggested that
this type of compost supports N2-fixing bacteria and that
N2-fixing activity is dependent on a usable carbohydrate
source.
Our study evaluated the effect of the initial C/N of
the composting feedstock (20:1, 30:1, 92:1) and the effect
of N amendments (kitchen wastes, agricultural wastes
and mixed chicken manure + duck manure) on the
composting performance of recycled paper mill sludge.
Nowadays, the use of low-cost N amendments to
complement an organic material is significant because
wastes that are normally dumped or incinerated are
utilized in a composting process. The use of kitchen
wastes, agricultural wastes and mixed chicken litter +
duck manure has not yet been investigated as N
amendments in composting recycled paper mill sludge.
Results of the study will provide understanding on the
performances of the different N amendments available
and determine their suitability for composting recycled
paper mill sludge.
MATERIALS AND METHODS
The study was conducted at the Environmental
Engineering and Biochemical Process Laboratories
located at the Science and Technology Research building
of De La Salle University in Manila from June 2004 to
December 2007.
Materials
The paper mill sludge used was a mixture of primary and
secondary treatment sludge (95:5 in volume) from the
wastewater treatment facility of a recycled paper mill in
Bundagul, Mabalacat, Pampanga in the Philippines.
Kitchen waste as N amendment was collected from the
canteen located in the premises of the mill and owned by
the milling company. Kitchen waste included kitchen
refuse, leftover food and other food wastes. Agricultural
wastes and mixed chicken manure + duck manure were
collected from the agricultural section within the mill
complex also owned by the milling company. The
percentage volume of chicken manure and duck manure
used in the manure amendment was not evaluated.
Agricultural wastes included mixed grass clippings, fruit
and vegetable leaves and other plant residues available in
the area. Sawdust as bulking agent was collected from a
local sawmill near the area. Sawdust is currently used by
the recycled paper mill in their mushroom production
293
Bench-Scale Composting of Recycled Paper Mill Sludge
located in the mill‟s agricultural section. Sawdust and N
amendments were mixed with the sludge at weight ratios
of 8:93:50, 16:61:100, 16:77:100 and 16:215:100 for
mixed chicken manure + duck manure amended at C/
N=20, mixed chicken manure + duck manure amended at
C/N=30, kitchen waste amended at C/N=30 and
agricultural waste amended at C/N=30, respectively,
designed to optimize the moisture content of the mixture
at >50%. This weight ratio followed the input material
provided in Table 1.
Paper sludge samples were collected during
newsprint production. Collected sludge samples were
preserved at 4 °C and 500 mg sample of paper sludge
was brought to CRL Environmental Corporation for
heavy metal analysis. Another 500 mg of paper sludge
sample was brought to the Science and Technology
Research Center of De La Salle University to verify the
results of heavy metal analysis. Heavy metal analyses for
sludge include Cu, Zn, Pb, Cd, Cr and Ni determination
using Atomic Absorption Spectroscopy methods (Flame
AAS) (Skoog et al. 2004). Analysis of the results was
compared with the standards provided by the Fertilizer
and Pesticide Authority (FPA) for fortified fertilizers in
the Philippines (FPA 1996) and with the United States
Environmental Protection Agency (USEPA) Part 503
standard for sludge (www.yosemite.epa.gov). Feedstock
materials were also analyzed for total solids (TS) and
volatile solids (VS) using APHA standard methods
2540B and 2540E. Moisture content (MC) and fixed
solids (FS) were obtained from these results. Total
Kjeldahl N (TKN) was determined using the Modified
Kjeldahl Method (PCARRD 1991). Wet (Dwb) and dry
(Ddb) bulk densities of the feedstock were determined
using the core method while particle density was
determined by the pycnometer method (PCARRD 1991).
In the latter method, particle density of the soil is
calculated from the mass and the density of water or
other liquid displaced by the sample. VS and TKN values
and compaction data were used to calculate organic
carbon (OC) (McCartney and Chen 2000). Compaction
data were derived from the estimated volume reduction
of the composting feedstock. C/N and free air space
(FAS) values were calculated from the following data:
TS, MC, VS, FS, TKN, OC, bulk density and particle
density of the raw materials (McCartney and Chen 2000).
A
commercially
available
“Effective
Microorganism” (EM) from Larutan Resources
Incorporated - Philippines was used as inoculant to
ensure the presence of the specific microorganism that is
responsible for the biodegradation of organic matter
during the composting process. EM inoculant has ray
fungi or actinomycetes and other microflora that include
lactic acid bacteria, yeasts and mold fungi (Xu 2001).
294
Jurex Gallo et al.
Composting
Preliminary composting runs were conducted to evaluate
the effect of C/N at various levels: 20, 30 and control (no
N amendment with C/N = 92). Results of this preliminary
run provided a basis for determining the suitable C/N of
initial feedstocks used in the succeeding study. Further
investigation determined the effect of other N
amendments. In this study, treatments evaluated include
the control feedstock, the kitchen-waste-amended
feedstock (C/N=30) and the agricultural-waste-amended
feedstock (C/N=30). Amounts of raw material input for
all treatments are presented in Table 1. The compost
produced from these waste-amended feedstock and their
performance were compared with results obtained by
composting manure-amended feedstock (C/N=30).
In composting experiments, three identical benchscale reactors were placed inside a styropor box as
composting chamber. The reactor used in the study is
shown in Figure 1. The design of the biocell reactor and
the procedure followed in composting were adapted from
McCartney and Chen (2000). The reactor is a 2.7-L
acrylic airtight cylinder (6.4 mm thick, 107 mm inside
diameter and 300 mm total height with a perforated plate
placed 15 mm from the bottom of the reactor). Another
perforated plate was attached to the stainless steel rod
and was used in exerting load on the composting
feedstock. The perforated plates were 6.4 mm thick
complete with 6.4-mm diameter holes. A stainless steel
screen with 1-mm diameter opening was fastened with
the perforated plate to contain all the feedstock materials
inside the reactor (Fig. 2).
All three reactors were placed inside an insulating
box measuring 53 cm x 36 cm x 43 cm to minimize heat
loss in the environment. The insulating box was filled
with water at a volume half of its capacity. The water
temperature was adjusted from time to time at 1 °C lower
than the lowest temperature of any reactor inside the
insulating box. A 5-kg load was attached to each reactor,
simulating compression during actual composting. Air at
5.4 x 104 mL h-1 was pumped to each reactor using an air
compressor to supply oxygen needed by the
microorganism. This procedure was adapted from Larsen
(2000). Temperature and free air space of each feedstock
were recorded twice daily to monitor the progress of
composting. Temperature of the feedstock was monitored
using a temperature fluke and was measured only at the
core of the organic matrix. Measurement of FAS was
based on the compressive settlement of the feedstock
based on the equation:
FAS f 
FAS iVi  (Vi  V f )
Vi
where
FASf = free air space after incremental loading (cm3 cm-3)
FASi = initial free air space (cm3 cm-3)
Vf = volume after load increment (cm3) and
Vi = initial volume (cm3)
The Philippine Agricultural Scientist Vol. 94 No.3 (September 2011)
Bench-Scale Composting of Recycled Paper Mill Sludge
Jurex Gallo et al.
Table 1. Amount of raw material inputs (kg) in composting experiment.
C/N= 92
C/N = 30
Raw Materials
(Wet Basis,
Chicken Manure +
Kitchen
Control
kg)
Duck Manure
Waste
Paper sludge
1.00
0.66
0.60
Chicken manure
0.40
+ duck manure
Kitchen waste
Agricultural
waste
Sawdust
Inoculant
Agricultural
Waste
0.36
-
C/N= 20
Chicken Manure +
Duck Manure
0.38
0.71
-
-
0.46
-
0.74
-
0.16
0.12
0.10
0.12
0.10
0.12
0.06
0.12
0.06
0.12
Fig. 2. Experimental setup for bench-scale composting.
Analysis of Compost
Compost products were air dried for a week prior to
determining their physical and chemical characteristics
(weight, bulk density, particle density, volatile solids,
C/N, Ni, Cd, Cr, Zn, Cu, Pb, total NPK, FAS and
moisture content). Microbial analyses were also
conducted to determine the population count of fecal
streptococci and total coliform on compost materials
using APHA 9221B and APHA 9221E methods (APHA
1998).
Fig. 1. Bench-scale composting reactor.
Statistical analyses were conducted to determine the
significant difference of each parameter (FAS and
temperature)
profiled
by different
treatments.
Experimental runs were conducted in duplicate and
analyses of variance (ANOVA) were tested at a
significance level of 0.05.
The Philippine Agricultural Scientist Vol. 94 No.3 (September 2011)
RESULTS AND DISCUSSION
Feedstock Characterization
Physical and chemical properties of feedstock materials
are presented in Table 2. N amendments showed the high
N content needed in adjusting the initial C/N of feedstock
to 20:1 and 30:1. A C/N of 30:1 for initial composting
feedstock is recommended by Haug (1993). The
combined manure required to achieve C/N ratios of 20
and 30 were 0.56 kg and 1.61 kg, respectively, of the
control mixture (wet basis). Further, heavy metal
295
Bench-Scale Composting of Recycled Paper Mill Sludge
Jurex Gallo et al.
Table 2. Physical and chemical properties of feedstock materials.
Chicken
Manure +
Kitchen
Sludge
Duck
Wastes
Manure
Moisture content (%)
Volatile solids (%)
Total Kjeldahl nitrogen (%)
Total organic carbon (%)
Bulk density (wb)
Bulk density (db)
Free air space (mL mL-1)
C/N
61.34 ± 0.10
44.25 ± 0.83
0.31 ± 0.02
25.00 ± 0.47
1.395 ± 0.00
0.662 ± 0.02
0.195 ± 0.02
80.64 ± 3.02
39.88 ± 0.25
47.38 ± 0.09
1.98 ± 0.02
26.77 ± 0.05
1.001 ± 0.01
0.795 ± 0.00
0.493 ± 0.00
13.52 ± 0.11
concentrations (except Cd) of recycled paper mill sludge
(Table 3) were way below the standards provided by the
USEPA. Meanwhile, results of heavy metal analyses of
the compost product from manure-amended feedstock
also passed the standards set by the FPA and the USEPA.
Cu had the highest concentration in the control feedstock
(without N amendment). The increase of Zn content in
manure-amended feedstock is due to heavy metal
concentrations in manure. Rodriguez et al. (2006)
reported Zn concentration of 2134 mg kg-1 in poultry
manure, hence, manure as nitrogen amendment could add
up to the heavy metal content in composting feedstock.
Chicken Manure + Duck Manure as N Amendment
A change in temperature during composting indicates an
active composting feedstock since composting is related
to microbial activity. The temperature of the composting
feedstocks increased during the first 8 d of composting as
shown by the temperature profiles of the mixed chicken +
duck-manure-amended feedstocks (C/N=20 and C/N=30)
and the control (Fig. 3). This increase in temperature is
due to the exothermic respiratory metabolism of the
microorganism. Heat is produced, raising the temperature
of the mixture, followed by a drop in temperature toward
the end of the composting phase. Mixed chicken manure
+ duck-manure-amended feedstock was observed to have
the highest peak temperatures of 53 °C and 52 °C for the
initial feedstock‟s C/N=20 and C/N=30, respectively.
This result shows that narrower C/N ratios relative to the
control (C/N=92) achieved higher temperatures. At
C/N=20, the maximum temperature attained was roughly
19% higher than the peak temperature achieved by the
control (43.5 °C). The ANOVA on the temperature
means, measured until 15 d, showed that although there
was a significant difference in temperature profiles
among the treatments (P=0.048), there was no significant
difference (P=0.66) between performances of the
compost at initial C/N=20 and C/N=30. Temperature
monitoring results also showed that the decrease in the
C/N ratio of the composting feedstock led to the decrease
in the composting time. Composting time fell from 23 d
in the control to 18 and 19 d in the treatments with
296
62.27 ± 0.29
85.73 ± 0.95
2.89 ± 0.01
48.44 ± 0.04
1.120 ± 0.00
0.441 ± 0.02
0.491 ± 0.00
16.76 ± 0.10
Agricultural
Wastes
90.12 ± 0.25
24.26 ± 0.09
2.33 ± 0.02
13.71 ± 0.06
0.421 ± 0.01
0.141 ± 0.01
0.551 ± 0.01
5.88 ± 0.07
Sawdust
17.36 ± 0.01
97.58 ± 0.03
0.43 ± 0.01
55.13 ± 0.01
0.151 ± 0.01
0.138 ± 0.01
0.909 ± 0.00
128.6 ± 3.02
C/N=20 and C/N=30, respectively. The thermophilic
temperatures were observed in 4 and 5 d in the treatments
with C/N=20 and C/N=30, respectively, and stayed
within this range (45–70 °C) for about 7–8 d. The control
temperature has only stayed within the mesophilic range
(25–40 °C) throughout the composting period.
On the other hand, the compaction of feedstock
materials during their biodegradation is very important
due to their effect on the movement of air in the pile.
When
organic
materials
undergo
solid-phase
decomposition, their particle size decreases, making the
particles clump together and resulting in a decrease in the
FAS of the mixture (Fig. 4). Haug (1993) reported that
95% of the maximum oxygen uptake of the
microorganisms can be achieved when the FAS of the
composting mixture was maintained between 0.20 and
0.35. Although there was no significant difference (P
value of 0.145) in the FAS profiles among treatments,
only the chicken manure + duck-manure-amended
feedstock at C/N=30 maintained an FAS of 0.20–0.35
throughout the composting period. This result suggests
that sawdust showed a good bulking structure to this type
of feedstock in providing adequate FAS during active
composting. The drastic decrease in FAS during the first
day was only due to the load applied to the feedstock.
The comparison between the temperature profile (Fig. 3)
and the FAS profile (Fig. 4) of all treatments suggests
that as FAS dropped close to 0.21, the microbial activity
also declined as indicated by the decrease in temperature.
The decrease in the volatile solids content of the
feedstock materials during and after composting can be
attributed to the consumption of microorganisms of the
organic fraction of the feedstock materials, producing
gaseous products such as carbon dioxide, water and
ammonia (Haug 1993). In this study, maximum reduction
in the volatile solids of mixed chicken manure + duck
manure was 34.1% at C/N=20, which translates to about
77.9% increase in the loss of the volatile fraction
compared with the control. On the other hand, the
treatment with C/N=30 attained a 67.4% increase with
respect to the control, which indicates that the increased
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Bench-Scale Composting of Recycled Paper Mill Sludge
Jurex Gallo et al.
Table 3. Heavy metal analysis of paper sludge and compost products.
Compost (ppm)
Chicken Manure + Duck
Sludge
Analyte
Control
(ppm)
Manure-Amended Feedstock
(C/N=92)
C/N=30
C/N = 20
Cu
Zn
Pb
Cr
Ni
Cd
20
43
<0.06
3.9
<0.04
1.2
162
96
30
<0.04
33
<0.02
202
562
18
<0.04
21
<0.02
Standard (ppm)
246
359
16
<0.04
15
<0.02
FPA
USEPA
(Sludge)
300
1000
750
150
50
<0.05
2800
300
3000
420
<0.05
Values are means of three samples ± SD.
FPA – Fertilizer and Pesticide Authority (FPA 2008)
USEPA – United States Environmental Protection Agency (http://yosemite.epa.gov/)
0.4000
50.00
0.3500
C:N = 30
C:N = 20
35.00
-1
Control
40.00
FAS
45.00
ml )
(ml(ml/ml)
FAS
TEMPERATURE (°C)
55.00
0.3000
Control
C:N = 30
C:N = 20
0.2500
0.2000
30.00
25.00
0.1500
0
5
10
15
20
25
Time (days)
0
5
10
15
20
25
Time (days)
Fig. 3. Temperature profile of control and chicken manure
+ duck-manure-amended feedstocks at C/N=20
and 30.
Fig. 4. Free air space (FAS) profile of control and chicken
manure + duck-manure-amended feedstocks at
C/N=20 and 30.
concentration of N in the feedstock increased the
microbial activity in the degradation of organic materials.
It is also expected that when N is not a limiting factor,
the microbial activity can be maximized. Hence, weight
reduction is expected to be greater at lower initial
C/N as verified by the results of percentage weight
reduction of 41.8%, 38.2% and 34.5% for C/N=20,
C/N=30 and control C/N=92, respectively. The increased
concentration of N in the composting mixture may also
be a significant factor in the loss of volatile solids.
However, the increase in N amendment to the point of
excessive liberation of ammonia gas is not recommended
in this study. Adding more N amendment to lower the
C/N increases the reduction of the volatile solids fraction.
Although an increased composting performance was
observed in C/N = 20, it was not recommended in this
study due to excessive production of odor during and
after composting. The distinct odor of ammonia in the
C/N=20 compost also suggests that not all the added N
was utilized by the microorganisms.
The compost produced by the mixed chicken manure
+ duck-manure-amended feedstocks also passed the total
NPK content standard (>7%) provided by the FPA. The
total NPK content of this feedstock at C/N=20 and
C/N=30 and the control C/N=92 is also shown in Table 4.
The added N in the feedstock increased the nutrient
content available for microorganisms and also the
nutrient content in the compost products. Meanwhile,
compost products were also analyzed for pathogens to
evaluate the presence of microorganisms that may be
detrimental to human health. Pathogen analysis of
compost revealed a high colony count of fecal
streptococci species and total coliform in the feedstock at
C/N=20, exceeding the USEPA standard (Table 4).
Treatment with C/N=30 also showed total coliform count
and fecal streptococci count that were higher than the
FPA standard.
Based on composting performances and compost
products, the initial feedstock with C/N=30 was better
than the initial feedstock with C/N=20 and the control
feedstock (C/N=92). The presence of pathogens that
exceeded the standard is considerable since small-volume
composting feedstock is expected to reach lower
maximum temperatures during composting. However,
The Philippine Agricultural Scientist Vol. 94 No.3 (September 2011)
297
Bench-Scale Composting of Recycled Paper Mill Sludge
Jurex Gallo et al.
Table 4. Pathogens and total NPK content of compost products.
C/N=92
C/N=30
With
Control
Chicken
With
With
Parameter
(No N
Manure
Kitchen Agricultural
Amendment) and Duck Wastes
Wastes
Manure
Fecal
streptococci
(MPN g-1)
Total coliform
(MPN g-1)
Total NPK (%)
C/N=20
With
Chicken
Manure
and Duck
Manure
FPA*
Standard
USEPA**
Standard
7100
1.9 x 104
3.6 x 103
1.65 x 103
1.9 x 104
<5 x 103
<5 x 103
98
683
1.6 x 107
1.60 x 108
683
<5 x 102
<5 x 102
1.12
18.16
0.89
1.29
18.31
>7
>7
*
FPA – Fertilizer and Pesticide Authority (FPA 2008)
**
USEPA – United States Environmental Protection Agency (http://yosemite.epa.gov/)
future large-scale application of this composting
technology will ensure efficient heat conservation and
higher maximum temperatures, especially for largevolume composting feedstock. The succeeding
experiment determined the effect of N amendments using
kitchen wastes and agricultural wastes with an initial
C/N=30.
Comparison of Mixed Chicken Manure + Duck
Manure, Kitchen Waste and Agricultural Wastes as
Nitrogen Amendments
The maximum temperatures of the kitchen-wasteamended and agricultural-waste-amended feedstocks
were 46 °C and 47 °C, respectively (Fig. 5). However, the
heating potential was greater for feedstock amended with
mixed chicken manure + duck manure since it reached a
maximum temperature of 52 °C. High maximum
temperatures of composting feedstocks suggest good
stabilization of end-product composts. The ANOVA
showed that the temperature profile of the kitchen-wasteamended feedstock is significantly different from that of
the control (P value of 0.001) from the 13th day until the
end of composting. On the other hand, the temperature
profile of the agricultural-waste-amended feedstock was
also significantly different from that of the control (P
value of 0.043) from the 11th until the 17th day of
composting. However, there was no significant difference
in the temperature profiles between the two types of
wastes (P=0.37) until the 16th day of composting.
On the other hand, the FAS profiles presented in
Figure 6 showed that the kitchen-waste-amended
feedstock maintained a recommended FAS profile of
>0.20 (Haug 1993). However, the FAS profile of the
agricultural-waste-amended feedstock reached below
0.20 by the 10th day of the composting period, indicating
that the addition of sawdust as bulking agent to
agricultural-waste-amended feedstock was not enough to
maintain the FAS profile of >0.20 recommended by
Haug (1993). The immediate drop in FAS during the 1st
day of composting was due to the 5-kg load applied to
298
the feedstock; however, the succeeding drop of FAS
below 0.2 can be attributed to the weak structural
characteristics of agricultural wastes, resulting in the
compaction of feedstock materials during the early stage
of the composting process. According to Haug (1993),
microbial activity is reduced as FAS approaches 0.20,
given that not enough oxygen is present in feedstocks
available for the microorganisms. At this FAS, the
compaction of feedstock materials does not allow oxygen
to penetrate within the composting feedstock. Annan and
White (1998) also reported that the optimum level of
FAS is between 0.30 and 0.60. Although FAS ranges
suggested in the literature provide a guide in composting
organic materials, there is no optimal FAS for all types of
feedstock as FAS depends on the type of material used in
composting. No significant difference in FAS results was
observed between the control and the kitchen-wasteamended feedstock (P=0.34). Significant differences
were noted between the control and the agriculturalwaste-amended feedstock (P value = 1 x 10-4) as well as
between the two types of wastes (P<0.0001).
One disadvantage in composting kitchen-wasteamended feedstock (C/N=30) was the high emission of
ammonia, resulting in the foul odor observed throughout
the composting process compared with the other
treatments.
Only the compost produced from manure-amended
feedstock passed the total NPK standard of the FPA and
the USEPA for compost products (Table 4). The high
NPK content of compost produced from manureamended feedstock can be attributed to the N coming
from the manure. Paper sludge has high total P and K
content (Beauchamp et al. 2002) that may also add up to
the total NPK of the compost product. The total NPK of
the composting feedstock increases as composting
progresses due to the reduction of organic matter and
other biodegradable materials present in the feedstock.
On the other hand, the choice of the type of kitchen
wastes and agricultural wastes may also explain the low
total NPK content in composts from feedstocks with
these N sources. The reduced volume of paper sludge
The Philippine Agricultural Scientist Vol. 94 No.3 (September 2011)
Bench-Scale Composting of Recycled Paper Mill Sludge
Jurex Gallo et al.
CONCLUSION
Fig. 5. Temperature profile of control feedstock and
kitchen-waste-amended and agricultural-wasteamended feedstocks at C/N=30.
Fig. 6. Free air space (FAS) profiles of control and
kitchen-waste-amended and agricultural-wasteamended feedstocks at C/N=30.
added to the kitchen-waste-amended and agriculturalwaste-amended feedstocks compared with the volume of
paper sludge added in the manure-amended feedstock
may also lower the total NPK of the resulting compost.
All compost products from the N-amended
feedstocks exceeded the FPA and the USEPA standards
for total coliform count. Also, the manure-amended
feedstock exceeded the FPA and USEPA standards for
fecal streptococci. High pathogen count in composts
could be attributed to the low maximum temperatures
attained by these treatments. It could also be due to the
type of material used as N amendment. In the case of
manure as N source, manure has a natural presence of
pathogens and although it had the highest maximum
temperature (52 °C) compared with other treatments, the
heat generated was not enough to reduce the pathogens to
meet the FPA and USEPA standards. USEPA (1998)
reported that pathogens can be destroyed when
the temperature of the composting matrix is greater than
55 °C and when it is maintained at that level for 3 d.
Lower maximum temperatures in these treatments are
expected since only small-volume composting feedstock
was used in the laboratory experiment and the intensity
of accumulated heat depends on the volume of the
feedstock.
The Philippine Agricultural Scientist Vol. 94 No.3 (September 2011)
There was no significant difference in FAS among the
three treatments (control, C/N=20 and C/N=30).
Although no significant difference was observed between
temperature profiles of C/N=20 and C/N=30, the
temperature profiles of these manure-amended feedstocks
were better than those of the control. Reduction in
volatile solids was highest in manure-amended feedstock
with initial C/N=20; however, it emitted foul odor due to
ammonia emission throughout the composting process.
Hence, manure-amended feedstock with initial C/N=30 is
recommended. Although this feedstock showed better
performance compared with the control and the treatment
with C/N=20 in composting recycled paper mill sludge,
further investigation is recommended to determine the
optimum range of C/N values in initial feedstock for
composting recycled paper mill sludge. Only the manureamended feedstocks passed the total NPK required by
FPA for composts from among other nitrogen-amended
feedstocks (kitchen waste and agricultural waste). In
general, mixed chicken manure + duck manure as N
amendment for composting recycled paper mill sludge
showed better performance and produced better quality
compost compared with kitchen and agricultural wastes
as feedstock amendments.
ACKNOWLEDGMENT
The authors acknowledge the fund support of the
Swedish International Development Cooperation Agency
(SIDA).
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