EFFECT OF CARBON TO NITROGEN RATIO ON THE COMPOSTING OF CASSAVA PULP WITH SWINE MANURE

This research investigated the composting process of cassava pulp and swine manure at various initial C/N ratios of 20/1, 30/1, and 40/1 and the effect of microbial activator, p.d.1, on composting process. Compost with an initial C/N ratio of 30/1 seeded with p.d.1 showed the highest maximum temperature (63.5°C), the lowest number of faecal coliform (2.87 Log10 MPN g-1), and the shortest time (around day 42) to reach maturity, suggesting a suitable initial C/N ratio

EFFECT OF CARBON TO NITROGEN RATIO

ON THE COMPOSTING OF CASSAVA PULP WITH

Nattipong Kamolmanit*, and Alissara Reungsang**

*Department of Biotechnology, Graduate School, Khon Kaen University A.Muang, Khon Kaen 40002 THAILAND

**Research Centre for Environmental and Hazardous Substance

Management and Department of Biotechnology, Faculty of Technology, Khon Kaen University, A.Muang, Khon Kaen 40002 THAILAND

E-mail: alissara@kku.ac.th; Correspondence author

ABSTRACT

This research investigated the composting process of cassava pulp and swine manure at various initial C/N ratios of 20/1, 30/1, and 40/1 and the effect of microbial activator, p.d.1,

on composting process Compost with an initial C/N ratio of 30/1 seeded with p.d.1 showed the highest maximum temperature (63.5°C), the lowest number of faecal coliform (2.87 Log10 MPN g-1), and the shortest time (around day 42) to reach maturity, suggesting

a suitable initial C/N ratio

KEYWORDS: Cassava pulp, C/N ratio, Compost, Swine Manure

INTRODUCTION

Cassava (Manihot esculenta Crantz) is one of the most important crops in Thailand

Approximately 40 percent of the cassava produced in Thailand is converted into starch Domestic demand for cassava starch is as high as 1.3-1.7 million tons per year (Thai Tapioca starch Association, 2005) The cassava processing industry produces solid residues known as “pulp” Cassava pulp contains a large amount of carbohydrate (up to 50-60% dry weight basis), fiber and minerals such as Cu, Zn, Mn, Fe and Mg (Penuliar,

1940) and has a moisture content of about 60-70 % (Sriroth et al, 2000) Cassava pulp is

commonly used as organic soil amendment and bulking agent for composting Some researches focused on the utilization of cassava pulp as a single cell protein and as a raw material for ethanol production (Boonyakamol, 2003; Potisung, 2003) However, since cassava pulp has high carbon content, its value can be enhanced if mixed with other organic waste of high nitrogen content and used as soil amendment

Composting is a biological decomposition process, wherein organic matter is degraded to achieve inorganic nutrients and stable organic material (compost) at the end Composting

is generally used for the treatment of organic wastes such as sewage sludge and animal manure It is also used in agro-industrial process to obtain products which can be applied

to soil to increase soil organic matter content as well as enhance soil structure and cation

exchange capacity (Contreras-Ramos et al, 2004) During the decomposition process,

initial carbon to nitrogen ratio (C/N) in compost material is the major controllable factor indicating the digestion process which include enzymatic activity by microorganisms

(Bertoldi et al, 1983) The C/N ratio can be used as an indicator for compost maturity The initial C/N ratio in compost affects the quality of mature products (Heerden et al, 2002; Huang et al, 2004) It is reported that an initial C/N ratio of 25-30 is suitable for

microbial activities during the nitrification process (Alexander, 1961)

Animal manure such as pig manure, spent pig manure, cow manure, and solid poultry

manure had been used for adjusting C/N levels in composting pile (Tiquia et al, 1996; Guerra-Rodriguez et al., 2001; Contreras-Ramos, 2004; Huang et al, 2004) Swine

manure is one promising N-source because it contains 70 % water, 36.6 % total organic

carbon, 3.24 % total nitrogen and 1.72 % total phosphorus (Tiquia and Tam, 1998; Huang

et al, 2004) Furthermore, the pH and C/N ratio of swine manure are 8.12 and 11.3,

respectively, (Huang et al, 2004) which makes it suitable as supplement for C/N ratio

adjustment in composting

Composting process can be accelerated through the addition of microbial activators such

as LD-1, F-60, Bionic, and p.d.1 (Subjarearn et al, 2002) A commercial microbial product

is often added to the compost mixture to ensure the establishment of initial microbial

population and enhance the composting process (Tiquia et al, 1997a; Subjarearn et al,

2002) The commercial bacterial product that has been used to enhance the composting process in Thailand is a microbial activator p.d.1 (Subjarearn et al, 2002) The p.d.1 consists of various degrading lignocellulolytic microorganisms such as bacteria, actinomycetes and fungi that can accelerate the decomposition rate when seeded to the compost (Land Development Department, 2003) Cassava pulp and swine manure composting processes with and without p.d.1 and the quality of the final compost products are worth investigated Several studies reported the use of animal manure compost for plant production in agricultural farm due to its low cost as compared to inorganic fertilisers (Stephanon et al., 1990; Gajalakshini and Abbasi, 2002; Ta-oun, 2003) However, there is a very limited information on the use of cassava pulp as raw material in composting process Thus, in this study, cassava pulp and swine manure were used as raw materials for compost production with and without microbial activator (p.d.1)

MATERIALS AND METHODS

Raw materials

Cassava pulp

Cassava pulp was collected from Takul Lek Tapioca Flour Factory Co., Ltd Mahasarakham, Thailand The pulp was air-dried for 3 weeks prior to usage

Swine manure

Swine manure (a mixture of liquid and solid forms) was obtained from the pig farm located at the Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand Sub-samples of swine manure were air dried at 80 °C for 24 h, ground and passed through a 2.0

mm sieve The samples were then stored in desiccator for further analysis and usage

p.d 1

Microbial activator (p.d.1) was obtained from the Land Development Department, Khon

Kaen, Thailand The p.d.1 consists of 2 strains of bacteria in Genus Bacillus sp., 2 strains

of Actinomyces in Genus Streptomyces sp., and 4 strains of fungi that include

Scopulariopsis sp., Helicomyces sp., Chaetomium sp., and Trichoderma sp

(Sunanthapongsuk, 2001) These commercial microbial products are often added to the

compost mixture to enhance the composting process in Thailand (Subjarearn et al,

2002;Land Development Department, 2003)

Composting pile establishment

The first set of composting piles was prepared as follows :

Pile 1: Cassava pulp and swine manure at an initial C:N ratio of 20:1 (dw/dw)

Pile 2: Cassava pulp and swine manure at an initial C:N ratio of 30:1 (dw/dw)

Pile 3: Cassava pulp and swine manure at an initial C:N ratio of 40:1 (dw/dw)

Each pile contained 20 kg of mixture The dimension of each pile was approximately 50

cm (width) X 50 cm (length) X 50 cm (height) Every seven days, the moisture content in each pile was adjusted to 60 % before and during the composting process until the temperature in compost reached the ambient temperature

The second set of composting piles (pile 4, pile 5 and pile 6) was prepared in a similar manner as the first set but the seeding microbial activator (p.d.1) was added to each pile in

a p.d.1/composting pile ratio of 10 ml:500 g of compost Every seven days, the moisture content of the mixture was also adjusted to 60% through the addition of water before and during the composting process When the temperature in compost piles reached the ambient temperature, addition of water was stopped although the composting process

continued Each compost pile was manually mixed with a shovel for about 10 minutes to

turn the pile and provide aeration This was done every 3-4 days until the compost piles

reached maturity The ambient temperature and the temperature within each pile at a depth

of 15 cm from the surface of the piles were determined using a thermometer At days 14,

28, 42, 56, 70 and 84, after turning the compost piles, a 50 g sub-sample was randomly

collected from the compost pile and analyzed using some physical and biological

parameters (Table 1)

Table 1 Physicochemical and biological parameters used for analyses of samples

(1998)

(1998) Moisture content (%) Oven dry method Every 7 day Page et al (1982)

Total organic carbon (%) Walkley and Black method Every 14 day Walkley and

Black (1934) Total Nitrogen (%) Micro-kjeldahl method Every 14 day Black (1965)

Total Phosphorus (%) Spectrophotometric method Every 14 day Black (1965)

Total Potassium (%) Atomic absorption technique

method

Every 14 day Black (1965) Faecal coliforms Most Probable Number Every 14 day AOAC (2000)

Statistical analysis

Mean and standard deviation values were reported for all parameters measured Analysis

of variance (ANOVA) and Duncan’ s multiple range test were performed using SPSS v

11 statistical software for windows One-way ANOVA was carried out to compare the

means of different treatments where significant F-values at p≤ 0.05 were obtained

Differences between individual means were tested using the least significant difference

test

RESULTS AND DISCUSSION

Main characteristics of cassava pulp and swine manure

Analysis of cassava pulp revealed that it had high carbon content but low nitrogen thus giving a high C/N ratio (Table 2) The pH of cassava pulp indicated that it was slightly acidic

Although the carbon content of swine manure was twice as low as that of cassava pulp, its nitrogen content was about five times higher This caused the C/N ratio of the former to

be 10 times higher than that of the latter (Table 2) indicating that swine manure was suitable for the adjustment of C/N ratio in composting

Table 2 Main characteristics of the raw materials

‡ Mean ± standard deviation

Compost characteristics

Temperature profile

The initial mean temperature of all piles was approximately 25 °C A high temperature of 63.5°C was found in Pile 5 at Day 4 High temperature continued to be observed in this pile for about 24 days (Figure 1) and then gradually dropped to 30.5 °C at Day 40 After day 40, the temperature varied within a narrow range until day 84 (Figure 1)

The other piles showed a similar pattern of temperature changes as in pile 5 except that the maximum temperatures recorded in piles 3 and 6 were lower (≈59 °C) as shown in Figure

1 The pattern of these temperatures i.e., increase to a certain temperature, remain constant

at that temperature and then decrease was a typical temperature profile of composting process especially for cow manure and wheat straw composts (Tiquia and Tam, 1998),

citrus wastes compost (Heerden et al, 2002), spent pig manure and sawdust litter composts (Huang et al, 2004) and filter cake and bagasse composts (Meunchang et al, 2005) The

levels of temperature in the compost piles increased and reached 50-60°C due to the energy released from biochemical reaction of microorganisms in the compost piles while

composting time (day)

0

20

40

60

C /N , 20 /1 no see din g ( p ile 1 )

C /N , 30 /1 no see din g ( p ile 2 )

C /N , 40 /1 no see din g ( p ile 3 )

C /N , 20 /1 see ding p d.1 ( pile 4 )

C /N , 30 /1 see ding p d.1 ( pile 5 )

C /N , 40 /1 see ding p d.1 ( pile 6 )

the temperature in compost piles tend to decrease after the thermophilic phase due to the

loss of substrate and a decrease in microbial activity (Bertoldi et al., 1983)

The level of temperature in compost piles can be used as an indicator of compost maturity

(Tiquia et al, 1997a; Tiquia et al, 1997b) Tiquia et al (1997a, 1997b) reported that a

compost material could be considered mature when the temperature in the compost reached the ambient temperature With this, the compost in pile 5 was considered matured after day 40, which was the fastest among the piles

Figure 1 Temperature profiles during composting of cassava pulp with swine manure

Changes in pH

During the composting process, the pH of all piles dropped from approximately 7.8 to 5.5 during the first 18 days of composting (Figure 2) The pH of compost in piles 3 and 6 were lower than the other piles This may be due to the higher organic carbon content (around 45%) in these piles A large pH drop in the compost piles at the initial stage of composting might be due to the fact that organic carbon was degraded to organic acid by the acid-forming bacteria existing in the compost pile (FAO, 1987) In addition, the pH drop might

be caused by the mineralization of organic acid during the composting process as well as the large quantities of carbon dioxide released during the composting process (FAO, 1987; Tiquia et al, 1996; Tiquia et al, 1997a; Tiquia and Tam, 1998; Huang et al, 2004; Meunchang et al, 2005)

Com posting time, days

5

6

7

8

9

C/N, 20/1 no seeding ( pile 1 ) C/N, 30/1 no seeding ( pile 2 ) C/N, 40/1 no seeding ( pile 3 ) C/N, 20/1 seeding p.d.1 ( pile 4 ) C/N, 30/1 seeding p.d.1 ( pile 5 ) C/N, 40/1 seeding p.d.1 ( pile 6 )

Figure 2 Changes in pH during composting of cassava pulp with swine manure

After 18 days of composting, the pH of all piles increased and pH levels remained relatively unchanged after Day 35 The increase of pH in composting piles during the composting process could be due to the production of ammonium as a result of the

ammonification process (Huang et al., 2004) The pH patterns were concomitant to the

previous studies on the composting of other organic wastes (Meunchang et al, 2005; Tiquia and Tam, 1998) Tiquia and Tam (2002) studied the changes on composting of spent pig manure and sawdust litter They reported that the changes in temperature of composting had a strong correlation with some chemical parameters such as the pH and decided to use these parameters to determine the maturity of compost

Moisture content

Moisture content at Day 0 and during the composting process in all compost piles were adjusted to 60 % because an optimum level of moisture content had strong effect on

oxygen consumption rate of aerobic heterotroph microorganisms (Tiquia et al, 1996) It

was reported that a suitable and efficient moisture content in composting of spent litter was between 50 % and 60 %

At the initial stage of composting, the moisture content of all piles was around 62-64% and dropped gradually during composting time (Figure 3) When the temperature in the compost piles reached the ambient temperature, addition of water was stopped although the composting process continued Afterwards, the moisture content of all piles decreased slowly to around 38.82-46.62 % at the end of the composting period It was considered that the piles have achieved an acceptable level of quality of mature compost, i.e., ≤50%

(Ta-oun et al., 2005) A decrease in moisture content was due to the release of moisture

Composting time (day)

0 7 14 21 28 35 42 49 56 63 70 77 84

20

30

40

50

60

70

C/N 40/1 no seeding ( pile 3 ) C/N 20/1 seeding ( pile 4 ) C/N 30/1 seeding ( pile 5 ) C/N 40/1 seeding ( pile 6 )

from the compost pile through water evaporation as a result of the heat generated from microbial activities during composting (Miller and Finstein, 1985)

Figure 3 Changes in moisture content during composting of cassava pulp with swine

manure

Total organic carbon and total nitrogen

During the composting process, total organic carbon in all piles sharply decreased in the first 28 days of composting and from 33 - 45% initial carbon content, it dropped to nearly 25% at the end of the composting period (Figure 4) Decrease in total organic carbon concentration resulted from the oxidation of carbon to carbon dioxide by microorganisms

during composting (Tiquia et al., 1996)

Throughout the composting process, total organic carbon loss in pile 1 (24.28%) and pile 4 (16.85%) was lower than those of the other piles (32% in pile 2, 39.44% in pile 3, 39.43%

in pile 5 and 39.74% in pile 6) The small decrease in total organic carbon in pile 1 and pile 4 could have resulted from a poor decomposition when the initial C/N ratio was low

(Huang et al., 2004) In addition, recalcitrant organic wastes such as cellulose and lignin may affect a degree of organic carbon loss during the decomposition process (Huang et al,

2004)

Total organic carbon in pile 3 and pile 6 was higher than those of the other piles in the first

70 days due to a larger amount of organic carbon supplied in these 2 piles, specifically, large amount of cassava pulp was added into the compost mixture prior to the composting process

Composting time, days

20

25

30

35

40

45

50

C/N, 20/1 no seeding ( pile 1 ) C/N, 30/1 no seeding ( pile 2 ) C/N, 40/1 no seeding ( pile 3 ) C/N, 20/1 seeding p.d.1 ( pile 4 ) C/N, 30/1 seeding p.d.1 ( pile 5 ) C/N, 40/1 seeding p.d.1 ( pile 6 )

Figure 4 Changes in total organic carbon during composting of cassava pulp with swine

manure

Total nitrogen increased slightly in all composting piles (Figure 5) The increase in total nitrogen during the composting process might be due to the activity of nitrogen fixing bacteria which was expected to exist in the compost pile These bacteria have the capability to fix N2 from the air to NO3 contained in the pile (Bishop and Godfrey, 1983)

Huang et al (2004) found the same results where the nitrogen content in the compost

slightly increased after 63 days of composting

At the end of composting, piles 1, 2, 4 and 5 contained higher total nitrogen content (2.33%, 2.19%, 2.46% and 2.11%, respectively) than pile 3 and 6 (1.72 % and 1.89 %, respectively) The nitrogen in the compost pile mainly came from the swine manure added Thus, the nitrogen content in pile 1, 2, 4 and 5 (where larger amount of swine manure was added) was found to be higher than in pile 3 and 6 at the end of composting

Composting tim e, days

0

1

2

3

4

5

C/N, 20/1 no seeding ( pile 1 ) C/N, 30/1 no seeding ( pile 2 ) C/N, 40/1 no seeding ( pile 3 ) C/N, 20/1 seeding p.d.1 ( pile 4 ) C/N, 30/1 seeding p.d.1 ( pile 5 ) C/N, 40/1 seeding p.d.1 ( pile 6 )

Figure 5 Changes in total nitrogen during composting of cassava pulp with swine manure Changes in total phosphorus and total potassium

The changes of total P and K followed a similar trend as total nitrogen wherein there was a gradual increase throughout the composting period Increase in total P and K may be due

to the net loss of dry mass which generally concentrated the phosphorus and potassium in

composting pile (Huang et al, 2004) In addition, Tiquia and Tam (2002) explained that

an increase in P and K during composting of poultry litter in forced-aeration piles were due to losses of organic C, H, N, and O from composting piles as CO2 and H2O

At day 84 of composting, as seen in Figure 6, total P in pile 1, 2, 4 and 5 were 2.51 %, 2.44 %, 2.52 % and 2.56 %, respectively, and were higher than pile 3 and pile 6 (1.61% and 1.97 %, respectively) The amount of swine manure added to piles 3 and 6 was lower than those added into pile 1 and pile 2 which could have resulted to a lower amount of total phosphorous detected in these compost piles since the phosphorous detected in the compost was mainly released from swine manure