Bioresource Technology 96 (2005) 1584–1591

Chemical and biological changes during compostingof different organic wastes and assessment of compost maturity

Sneh Goyal *, S.K. Dhull, K.K. Kapoor

Department of Microbiology, CCS Haryana Agricultural University, Hisar 125 004, India

Received 31 August 2004; received in revised form 25 October 2004; accepted 20 December 2004

Available online 29 March 2005

Abstract

Changes in organic C, total N, C:N ratio, activities of cellulase, xylanase and protease, and microbial population were deter-

mined during composting of different organic wastes such as mixture of sugarcane trash and cattle dung, press mud, poultry waste

and water hyacinth biomass. There were losses of N in poultry waste and water hyacinth with the effect an initial increase in C:N

ratio was observed which decreased later on due to decomposition. The activities of cellulase, xylanase and protease were maximum

between 30 and 60 days of composting in various wastes. Similar trend was observed with respect to mesophilic bacterial and fungal

population. Various quality parameters like C:N ratio, water soluble C (WSC), CO2 evolution and level of humic substances were

compared after 90 day composting. There was statistically significant correlation between C:N ratio and CO2 evolution, WSC and

humic substances. Significant correlation between CO2 evolved and level of humic substances was also observed. The study shows

that no single parameter can be taken as an index of compost maturity. However, C:N ratio and CO2 evolved from finished compost

can be taken as the most reliable indices of compost maturity.

� 2005 Elsevier Ltd. All rights reserved.

Keywords: Composting; Organic wastes; Enzyme activities; C:N ratio; Water soluble carbon; Humic substances

1. Introduction

The use of organic manures as amendments to im-

prove soil organic matter level and long term soil fertil-

ity and productivity is gaining importance. The benefits

of composted organic wastes to soil structure, fertility as

well as plant growth have been increasingly emphasized

(Chen et al., 1992; Murwira et al., 1995; Esse et al.,

2001). Composting is a widely used method for disposalof organic wastes. Application of undecomposed wastes

or non-stabilized compost to land may lead to immobi-

lization of plant nutrients and cause phytotoxicity

(Butler et al., 2001; Fuchs, 2002; Cambardella et al.,

2003). Mesophilic and thermophilic microorganisms

0960-8524/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.biortech.2004.12.012

* Corresponding author. Tel.: +91 1662 243065; fax: +91 1662

234952.

E-mail address: snehgoyal@hau.ernet.in (S. Goyal).

are involved in the composting and their succession isimportant in the effective management of composting

process (Beffa et al., 1996; Ishii et al., 2000). The heat

generated during composting helps in destruction of

pathogens (Golueke, 1977). Different hydrolytic enzymes

are released by microorganisms, which are involved in

the depolymerization of different constituents of organic

wastes (Kandeler et al., 1999; Marx et al., 2001). Impor-

tant enzymes involved in the composting process includecellulases, hemicellulases, proteases, lipases, phospha-

tases and arlylsulphatases. High levels of protease, lipase

and cellulase activities have been detected throughout

the active phase of composting (Herrman and Shann,

1993; Cunha Queda et al., 2002; Mondini et al., 2004).

The composts prepared from different organic wastes

differ in their quality and stability, which further de-

pends upon the composition of raw material used forthe compost production (Poincelot, 1974; Gaur and

S. Goyal et al. / Bioresource Technology 96 (2005) 1584–1591 1585

Singh, 1995; Ranalli et al., 2001). Compost quality is

closely related to its stability and maturity. The abun-

dance of chemical and biological changes that occur

during composting, and the range of methods suggested

in literature, has made it difficult to agree on methods

for the practical assessment of maturity (Itavaaraet al., 2002; Wang et al., 2004). Various parameters that

have been used to assess the quality and maturity of

composts include the C:N ratio of the finished product,

water soluble carbon, cation exchange capacity, humus

content, and the carbon dioxide evolution from the fin-

ished compost (Garcia et al., 1992; Huang et al., 2001;

Wu and Ma, 2002). Germination index, which is a mea-

sure of phytotoxicity, has been considered as a reliableindirect quantification of compost maturity (Cunha

Queda et al., 2002). However, it is difficult to apply these

parameters across a wide range of composts prepared

from different organic wastes (Roletto et al., 1985;

Saviozsi et al., 1988; Benito et al., 2003).

Present work was conducted to monitor the chemical

and biological changes during composting of various or-

ganic wastes with particular reference to microflora andenzyme activities. The maturity parameters to determine

quality of compost were also analyzed to select suitable

parameters, which can be used for evaluation of com-

posts prepared from different organic wastes.

2. Methods

The composting mixtures were prepared in the fol-

lowing proportions.

1. Sugarcane trash (ST) + cattle dung (CD) (4:1) dry

weight basis;

2. Sugarcane trash (ST) + cattle dung (CD) (1:1) dry

weight basis;

3. Press mud (PM);4. Poultry waste (PW);

5. Water hyacinth (WH).

Since sugarcane trash is a waste of high C:N ratio, it

was mixed with cattle dung to narrow down the C:N

ratio. Press mud is a waste generated during clarification

of sugarcane juice during manufacturing of cane sugar.

Water hyacinth (Ecchornia crassipes) an aquatic weedwas collected from the village pond. Poultry waste was

collected from the local farmers who use litter method

of rearing using wheat straw as a bedding material

and the amount of straw in poultry waste was about

40%. Ten kilograms of compostable material on dry

weight basis for each treatment was thoroughly mixed

and moisture was adjusted to 60% of water holding

capacity (WHC). The material was put in cemented pits(60 · 60 · 60 cm) and allowed to decompose. The con-

tents were turned after 14, 30, 45, 60 and 90 days and

moisture was maintained to 60% of WHC throughout

the experiment. Compost samples were drawn at 30 days

interval upto 90 days and analyzed for organic C by dry

combustion (Nelson and Sommers, 1982), and total N

by Kjeldahl method (Bremner and Mulvaney, 1982).

To measure water soluble C in water extract; 5 g of ovendried and sieved (2 mm) compost was suspended in

50 ml of distilled water in a 250 ml Erlenmayer flask

and shaken for 30 min on rotary shaker at 160 rpm

and filtered through Whatman No. 1 filter paper. Total

C in compost water extract was measured by the titri-

metric method of Kalembasa and Jenkinson (1973). Dif-

ferent enzyme activities were estimated at 0, 30, 60 and

90 days. The cellulase and xylanase activities were esti-mated by the method of Schinner and Von Mersi

(1990) using carboxymethyl cellulose and birch wood

xylan, respectively as substrates. Protease activity was

estimated by measuring hydrolysis of casein by method

of Ladd and Butler (1972). Carbon dioxide evolution

in the compost was measured by trapping the CO2 in

0.5 N NaOH solution and titrating it with 0.5 N HCl

after addition of saturated barium chloride (Garcia etal., 1992). During the composting of different organic

wastes the changes in the microflora of composting sys-

tem at various stages of decomposition was also esti-

mated. A standard procedure for sampling and suitable

media were used for the enumeration of the different

groups of microorganisms (Wollum II, 1982). Bacteria

and fungi were counted by plating on nutrient agar and

Martin�s rose begal medium, respectively. The incuba-tion temperature was 30 �C for mesophilic and 45 �Cfor thermophilic microorganisms. Humic substances in

compost were determined according to method outlined

by Kononova (1961).

All determinations were carried out in triplicate and

LSD values at P = 0.05 were used to determine the

significant differences between treatment means. Linear

correlations between compost maturity parameters weredetermined.

3. Results and discussion

Changes in temperature at various stages of decom-

position of different organic wastes is shown in Fig. 1.

Initial temperature of 28–30 �C was recorded at the startof composting and highest temperature was observed at

14 days of composting which rose up to 46 �C in treat-

ment with water hyacinth and then declined gradually.

Table 1 shows the changes in total organic carbon

content during the composting of different organic

wastes. The initial organic carbon in different treatments

varied from 40.7% to 48.0%. The content of organic car-

bon decreased as the decomposition progressed. At theend of the experiment, the lowest organic carbon

was observed in the treatment with water hyacinth and

0

5

10

15

20

25

30

35

40

45

50

Tem

pera

ture

(ºC

)

0 7 14 21 30 60 90Days

ST+CD (4:1)

ST+CD (1:1)PM

PWWH

Fig. 1. Changes in temperature during composting of different wastes.

1586 S. Goyal et al. / Bioresource Technology 96 (2005) 1584–1591

highest was present in sugarcane trash plus cattle dung

(4:1) treatment. This was mainly due to the presence

of more recalcitrant carbon compounds such as lignin

in sugarcane trash than water hyacinth, press mud and

poultry waste. Atkinson et al. (1996) reported that dur-

ing composting of poultry litter with saw dust about29% of carbon was lost as carbon dioxide and it was

having large amount of carbon in the form of lignin

which is decomposed slowly. The poultry waste during

the present study consisted of a mixture of wheat straw

(40%) and poultry excreta. Wheat straw decomposes

more quickly compared to saw dust, hence its decompo-

sition occurred fast.

At the beginning of composting the total N contentof different organic wastes varied from 0.93% to 3.16%

and lowest N was recorded in sugarcane trash plus cattle

dung (4:1) and highest in poultry waste (Table 1). The

total N in sugarcane trash plus cattle dung and press

mud treatments increased with time. In case of poultry

waste and water hyacinth a decrease in total N at

30 day sampling was observed due to N losses. Later

on increase in total N was observed in case of waterhyacinth only. The decrease in total N content at early

stages of decomposition was due to losses of N in the

form of ammonia which in turn depends upon the type

of material and its C:N ratio. The composting of mate-

rials with low C:N ratio result in more N losses than in

high C:N ratio wastes (Reddy et al., 1979; Sanchez-

Monedero et al., 2001).

Table 1

Changes in organic carbon, total N and C:N ratio during composting of diff

Treatments Organic C (%) (days) T

0 30 60 90 0

Sugarcane trash + cattle dung (4:1) 47.5 44.1 43.0 41.3 0

Sugarcane trash + cattle dung (1:1) 48.0 44.7 43.8 38.9 1

Press mud 40.7 40.6 40.4 38.0 2

Poultry waste 43.9 41.8 38.8 36.2 3

Water hyacinth 41.8 39.3 30.2 28.2 2

LSD (P = 0.05) 1.2 1.3 1.6 2.1 0

The initial C:N ratio of the wastes used for compo-

sting ranged from 13.9 to 51.1 (Table 1). As the decom-

position progressed due to losses of carbon mainly as

carbon dioxide, the carbon content of the compostable

material decreased with time and N content per unit

material increased, which resulted in the decrease ofC:N ratio. At 30 day sampling the C:N ratio decreased

with time in sugarcane trash plus cattle dung and

press mud but it increased in case of poultry waste.

The increase in C:N ratio of poultry waste was due

to the N losses mainly through ammonia volatilization.

The C:N ratio also increased upto 30 days in water

hyacinth due to N loss but decreased later on as the

decomposition progressed. After 90 days of compostingof different organic wastes the C:N ratio of end product

varied from 11.7 to 28.3 which was lowest in case of

press mud and highest in sugarcane trash plus cattle

dung (4:1).

Various hydrolytic enzymes are believed to control

the rate at which various substrates are degraded.

Enzymes are the main mediators of various degradative

processes (Mckinley et al., 1985; Tiquia et al., 1996;Tiquia, 2002). So the changes in the activities of three

important enzymes; cellulase, xylanase and protease

which are responsible for hydrolysis of cellulose, hemi-

cellulose and proteins, respectively, were studied to

understand the degradation of various organic wastes.

The cellulase activity increased during decomposition

and was maximum at 30 days in all the treatments and

declined further at 60 and 90 days (Table 2). At 30 daysmaximum cellulase activity was observed with water

hyacinth followed by sugarcane trash plus cattle dung

(1:1), press mud and poultry waste. Cellulase activity

is dependent on the types of cellulolytic microorganisms

which develop on the organic waste. Cattle dung did

not contain bedding material such as straw. It supplied

nutrients for the growth of microorganism which re-

sulted in more cellulase activity. At 90 days samplinglowest cellulase activity was observed in sugarcane trash

plus cattle dung (4:1) and highest in water hyacinth

treatment. Cellulases are the enzymes involved in the

degradation of cellulose present in the composting mate-

rial. Sugarcane trash has more recalcitrant carbon due

to presence of large amount of lignin and have low

erent wastes

otal N (%) (days) C:N ratio (days)

30 60 90 0 30 60 90

.93 1.22 1.42 1.46 51.1 36.1 30.3 28.3

.50 1.53 1.71 1.90 32.0 29.2 25.6 20.5

.81 2.82 3.10 3.24 14.5 14.1 13.0 11.7

.16 2.26 1.71 1.74 13.9 18.5 22.7 20.8

.31 1.58 1.70 1.75 18.1 24.9 17.8 16.1

.41 0.28 0.27 0.13 2.9 4.0 2.8 3.2

Table 2

Changes in cellulase, xylanase and protease activity during composting of different wastes

Treatments Cellulase activity

(mg reducing sugar kg�1

dry matter h�1) (days)

Xylanase activity

(mg sugar kg�1 dry

matter h�1) (days)

Protease activity

(mg tyrosine kg�1 dry

matter h�1) (days)

0 30 60 90 0 30 60 90 0 30 60 90

Sugarcane trash + cattle dung (4:1) 8 103 81 36 22 42 53 30 159 1030 1520 1183

Sugarcane trash + cattle dung (1:1) 26 197 123 51 16 65 83 51 309 717 1524 1198

Press mud 41 143 141 54 58 71 111 71 530 1240 1194 907

Poultry waste 30 124 99 60 10 17 56 32 552 562 954 797

Water hyacinth 12 277 157 63 19 108 127 67 467 797 1966 811

LSD (P = 0.05) 3 11 13 5 2 5 8 4 21 67 76 71

S. Goyal et al. / Bioresource Technology 96 (2005) 1584–1591 1587

cellulose contents as compared to water hyacinth, so the

activity of cellulase was found to be highest in the water

hyacinth treatment.

The initial xylanase activity varied from 10 to 58 mg

reducing sugar released kg�1 dry mater h�1 (Table 2).

The activity increased with increase in composting peri-

od up to 60 days and declined later on. The activities of

both cellulase and xylanase showed that cellulose andhemicellulose are actively degraded during first 60 days

of composting. At the start of composting, protease

activity was highest in poultry waste followed by press

mud and water hyacinth and increased up to 60 days

in all the treatments and then declined further (Table

2). Cunha Queda et al. (2002) determined activities of

cellulase, protease and lipase in composts prepared from

pig slurry and straw; horse manure and residue fromcorrugated cardboard production; and vegetables, resi-

dues from cardboard production and straw. The cellu-

Table 3

Population of mesophilic and thermophilic bacteria during composting of d

Treatments Mesophilic bacterial population

(·107 g�1 material) (days)

0 14 30 6

Sugarcane trash + cattle dung (4:1) 13.8 24.0 207.0

Sugarcane trash + cattle dung (1:1) 9.8 21.2 215.0 1

Press mud 5.6 15.6 37.8

Poultry waste 5.0 19.1 81.0

Water hyacinth 12.0 25.5 164.5

LSD (P = 0.05) 1.2 2.6 21.2

Table 4

Changes in mesophilic and thermophilic fungal population during composti

Treatments Mesophilic fungal population

(·107 g�1 dry material) (days)

0 14 30 6

Sugarcane trash + cattle dung (4:1) 2.0 25.0 144.0 4

Sugarcane trash + cattle dung (1:1) 5.4 29.1 150.5 2

Press mud 13.0 32.1 64.8 3

Poultry waste 0.6 1.2 6.6

Water hyacinth 17.8 39.2 94.1 1

LSD (P = 0.05) 3.2 8.2 9.5

lase and protease activities reported were lower than

those observed in the present experiment. This may be

due to differences in the substrates used for compost

preparation.

The population of mesophilic and thermophilic bac-

teria and fungi at various stages of composting process

were determined. Population of mesophilic bacteria

was found to be highest at 30 days of composting andwas highest in both mixture of sugarcane trash with cat-

tle dung and water hyacinth pile (Table 3). The popula-

tion of mesophilic bacteria declined with time and was

not lowest at 90 days of decomposition. Similarly, the

highest mesophilic fungal population was observed at

30 days of composting and then declined (Table 4).

The population of thermophilic bacteria was maximum

at 14 days of composting and then decline was observed(Table 3). The count of thermophilic bacteria was max-

imum in sugarcane trash + cattle dung (1:1) followed by

ifferent wastes

Thermophilic bacterial population

(·105 g�1 material) (days)

0 90 0 14 30 60 90

75.0 72.0 6.0 50.4 8.0 1.8 0.6

14.0 84.0 2.0 88.2 24.0 2.4 1.2

27.0 24.0 1.0 61.0 36.0 3.6 1.0

30.0 12.0 2.0 61.0 36.0 3.6 1.0

52.5 30.0 4.5 24.6 10.5 1.2 0.3

11.8 5.3 1.8 6.8 5.9 1.2 0.8

ng of different wastes

Thermophilic fungal population

(·105 g�1 dry material) (days)

0 90 0 14 30 60 90

2.0 24.0 0.0 36.2 16.6 12.3 8.6

7.0 6.2 0.4 38.3 15.7 11.2 6.6

8.0 36.0 0.3 21.4 12.6 11.1 6.1

3.6 1.6 0.3 19.2 11.2 10.1 6.6

0.5 6.5 0.2 38.1 12.9 10.1 5.2

3.8 2.9 0.3 3.2 4.8 1.2 1.6

0

1

2

3

4

5

6

7

8

9

10

0 30 60 90Days

Wat

er s

olub

le C

in th

e co

mpo

st

(% to

tal o

rgan

ic c

arbo

n)

ST+CD(4:1)

ST+CD(1:1)

PM

PW

WH

Fig. 2. Changes in organic carbon in compost water extract during

composting of different wastes.

1588 S. Goyal et al. / Bioresource Technology 96 (2005) 1584–1591

poultry waste and press mud piles. Highest number of

colony forming units of thermophilic fungi were ob-

served in case of sugarcane trash plus cattle dung (4:1)

and sugarcane trash plus cattle dung (1:1). The lowest

mesophilic and thermophilic fungal population was ob-

served in poultry waste pile. Fungi are actively involvedin the decomposition of cellulose, hemicellulose and lig-

nin present in the organic matter which was reflected by

their population of different stages of composting. Dur-

ing decomposition the temperature of the material rises

which favours the growth of thermophilic microorgan-

isms. In the present study also, the maximum rise in

temperature at 14th day of composting was observed

which is related to the presence of highest number ofthermophilic bacteria and fungi at that stage of compo-

sting. The development of mesophilic and thermophilic

microorganisms during composting are related to the

mesophilic and thermophilic stages of the composting

system (Diaz-Ravina et al., 1989; Davis et al., 1991; Ishii

et al., 2000; Riddech et al., 2002). Microbial succession

plays a key role in composting process and appearance

of some microorganisms reflects the quality of maturingcompost (Ishii et al., 2000; Ryckeboer et al., 2003). The

methods used to investigate the microorganisms during

composting include traditional dilution plating tech-

nique, measurement of ATP content, microbial biomass

and microbial community composition, and analysis of

phospholipid fatty acid patterns (Riddech et al., 2002;

Ryckeboer et al., 2003). Until now, no single method

has been proved to be most reliable. During the presentstudy dilution plating technique was used to study

microbial changes during composting and it clearly

showed succession from mesophilic to thermophilic

microflora depending on the temperature of the pile

developed during composting.

Compost stability is an important aspect of compost

quality. It relates to the degree to which the organic mat-

ter has been stabilized during the composting process(Eggen and Vethe, 2001; Weppen, 2002). Various phys-

ical, biological and chemical parameters have been used

to monitor the quality and maturity of compost. Matu-

rity of the compost has been measured by the C:N ratio,

carbon dioxide evolution, cation exchange capacity,

Table 5

Carbon dioxide evolution of 90 days old composts and amount of humic an

Treatments Cumulative CO2–C evolved

(mg 100 g�1 compost) (days)

7 14 21

Sugarcane trash + cattle dung (4:1) 22 33 46

Sugarcane trash + cow dung (1:1) 13 14 27

Press mud 10 14 22

Poultry waste 12 17 29

Water hyacinth 10 14 23

LSD (P = 0.05) 3 4 4

water soluble C and production of humic substances

in the finished product (Abd-el-Malek et al., 1976; Gar-

cia et al., 1992; Ranalli et al., 2001). Phytotoxicity mea-

sured by means of germination test with water cress

(Lipidium sativum) is also used to test compost maturity

(Cunha Queda et al., 2002). We determined the amountof CO2 evolved from the different composts prepared

from various organic wastes. The amount of CO2 evolu-

tion was lowest in composts prepared from press mud

and water hyacinth (Table 5). Higher amount of CO2

evolution occurred in the compost prepared from sugar-

cane trash plus cattle dung (4:1). Composting of sugar-

cane trash with cattle dung in (1:1) ratio resulted in

better compost from sugarcane trash compared to thatprepared from sugarcane trash plus cattle dung (4:1).

The composting of poultry waste also resulted in a prod-

uct which still evolved more CO2 because the wheat

straw used as bedding material continued to decompose

slowly even after 90 days of composting.

The composting process results in the production of

humic substances which are slowly degradable and

have the ability to improve soil physical and chemicalproperties (Chen et al., 1996; Chefetz et al., 1998). Mea-

surement of humic substances is also one of the para-

d fulvic acids in composts prepared from different wastes

Humic substances

(mg kg�1 compost)

28 Humic acid Fulvic acid Total

55 62 29 91

34 40 27 67

30 40 19 59

40 31 15 46

31 25 13 38

5 5 3 6

Table 6

Correlation coefficients between compost maturity parameters

C:N ratio Water soluble C CO2–C evolved Content of humic substances

C:N ratio 1.000 0.475 0.970 0.678

Water soluble C 1.000 0.113 �0.010

CO2–C evolved 1.000 0.749

Content of humic substances 1.000

The correlation coefficients with absolute value >0.444 are significant at P = 0.05; with absolute value >0.561 are significant at P = 0.01.

S. Goyal et al. / Bioresource Technology 96 (2005) 1584–1591 1589

meters which can be used to assess the maturity of com-

post. The amount of humic and fulvic acids were more

in compost prepared from sugarcane trash and cattle

dung (4:1) and was lowest in case of water hyacinth (Ta-

ble 5). So the compost prepared from sugarcane trash

plus cattle dung (4:1) can be considered a better source

of humic substances for improvement of soil properties

than prepared from other wastes.Changes in water soluble C in composts prepared

from different sources have shown that the content of

water soluble C in relation to total C decreased as the

composting process progressed (Fig. 2). At 90 days press

mud compost showed lowest water soluble C and high-

est water soluble C was observed in compost prepared

from mixture of sugarcane trash and cattle dung (1:1).

Garcia et al. (1992) studied the water soluble C contentof compost prepared from municipal wastes. They also

reported decrease in water soluble C with the increase

in time of composting and the values reached in the

range of 0.41–1.19% of total organic C in 91 days. They

proposed that water soluble C in mature municipal

waste compost should be less than 0.5%. In the present

studies, these values at 90 days composting ranged from

2.06% to 4.09%. Higher values were due to release ofwater-soluble compounds during composting of carbon

rich materials. There cannot be a single limit for water

soluble C to judging compost maturity as the amount

of water soluble C at the end of composting depends

on the raw material used for composting (Huang

et al., 2001; Charert et al., 2004).

There is no single parameter which can be used as a

suitable indicator of maturity of a wide range of com-posts prepared from different materials. One ratio,

which is frequently used as an index of maturity is

C:N ratio. When a waste is composted, generally there

is decrease in C:N ratio with time due to losses of C

as CO2 which stabilizes in the range of 15–20 (Poincelot,

1974; Golueke, 1981). In the present studies all the C:N

ratios at 90 days were in this range except sugarcane

trash plus cattle dung (4:1). There was statistically sig-nificant positive correlation between C:N ratio and

water soluble C, humic substances and CO2–C evolved

in the 90 day compost (Table 6). Significant positive

correlation was also obtained between CO2–C evolved

and humic substances.

Garcia et al. (1992) suggested that in a mature muni-

cipal compost the amount of CO2–C evolved should be

less than 500 mg CO2–C per 100 g total organic C in the

compost. More CO2 evolution indicates that compost

has not yet stabilized and needs further decomposition.

During present investigation the CO2–C evolved from

90 days old compost was less than this limit in all the

treatments, indicating that composts were stabilized in

90 day composting period. The C:N ratio below 20 is

indicative of an acceptable compost maturity. However,Hirari et al. (1983) stated that the C:N ratio cannot be

used as an absolute indicator of compost maturity, since

the values for well-composted materials present a great

maturity variability, due to characteristics of the waste

used. The compost prepared from mixture of sugarcane

trash and cattle dung (4:1) had C:N ratio of 28.3 after

90 days due to high amount lignin in the sugarcane

trash. The lignin fraction is refractory to biodegrada-tion, so the CO2–C evolved is low. Therefore, single

parameter cannot be taken as an index of compost

maturity. The C:N ratio, water soluble C, content of

humic substances and CO2–C evolution from compost

can be taken as good indices of compost maturity.

4. Conclusions

Chemical and biological changes during composting

of various organic wastes indicated that there is succes-

sion of microbial population depending on the tempera-

ture reached during composting. Maximum enzyme

activities for cellulase, xylanase and protease are mani-

fested between 30 and 60 days, which is active phase

of decomposition. Nitrogen losses occur in wastes con-taining high amount of N such as poultry waste and

water hyacinth. In general, decrease in C:N ratio can

be taken as a reliable index of compost maturity when

combined with other parameters such as CO2 evolution

from mature compost, water soluble C and content of

humic substances.

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