Microbial inoculants for small scale composting of putrescible kitchen wastes
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Onsite small scale composting of organic waste is encouraged asan effective solution to reduce the wasteglobally and several processes and techniqposting have been discussed in the literatucomposting process to produce good quaon the type of waste and size of the systeare adopted to accelerate composting proof the product.
clude Bacillus species. It was reported that 87% of bacteria in ther-mophilic composts is of genus Bacillus (Strom, 1985b). Thermus sp.can tolerate as high temperatures as 6582 C (Beffa et al., 1996).Actinomycetes are also thermophilic bacteria with genus Nocardia,Streptomyces, Thermoactinomyces andMicromonospora as represen-tative forms isolated from compost (Waksman et al., 1939; Strom,1985a), and identied as important agents of ligno-cellulose degra-
hemicelluloses, facilitating compost stabilization and accelerate
The waste materials for the premix for composting were se-lected based on the generation from domestic sources and consid-ering the need for sufcient quantities of bulking agent to treatputrescible kitchen waste. It has been observed that compost canbe a good starting material for a fresh batch of composting process.Therefore in this experiment, the premix contained compost from aprevious trial using kitchen waste. The compost premix was pre-pared by mixing compost (30%), sawdust (16%) paper/cardboard(4%), grass clippings (20%) and kitchen waste (30%). Paper/card-board included shredded ofce paper, card board, and news paper
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Waste Management 30 (2010) 977982
Contents lists availab
elsE-mail address: email@example.com (J. Nair).able period of time. Inoculation with bacteria and fungi which canbreakdown ligno-cellulolytic material has been reported to beeffective in composting (Tiquia et al., 1997; Bolta et al., 2003).For example inoculation of complex microorganisms such as Bacil-lus casei, Lactobacillus buchnei and Candida rugopelliculosa and lig-no-cellulolytic fungi (Trichoderma sp. and white-rot fungi)accelerate humication and maturation in composting process(Wei et al., 2007). Bacteria that are the dominant in the process in-
study is therefore to test the impact of bacterial inoculum, EMand a fungal inoculum, Trichoderma sp. on the thermo and vermi-composting of household organic waste.
2. Materials and methods
2.1. MethodologyThe ligno-cellulose content of wsuch as wood and straw which has2030% hemicelluloses and lignin (breakdown in a normal composting p0956-053X/$ - see front matter 2010 Elsevier Ltd. Adoi:10.1016/j.wasman.2010.02.016management problemues for effective com-re. The duration of thelity end product variesm. Different processescesses and maturation
articularly of biomassximately 40% cellulose,m, 1993) is difcult toand can take consider-
composting process of the waste material (Singh and Sharma,2002; Pramanik et al., 2007, 2009).
The best way to combine high-temperature microbial compost-ing (called thermo composting in this paper) with vermicompo-sting has been a subject of recent research (Nair et al., 2006). Nowork has been conducted on how inoculants could help or hindera combined thermo/vermicomposting system. It was consideredimportant to understand whether inoculation of bacteria or fungiis essential for treatment of normal household wastes and/orwhether inoculation will improve the quality of a vermicompostproduct in terms of stability and maturity. The objective of thiscommon fungi in soil (Leandro et al., 2007) and known to degradeMicrobial inoculants for small scale com
J. Nair *, K. OkamitsuEnvironmental Technology Centre, Murdoch University, Perth, Western Australia 6150,
a r t i c l e i n f o
Article history:Accepted 6 February 2010Available online 6 March 2010
a b s t r a c t
This research looked at thsmall to medium scale coprised of kitchen waste, ptions of thermo compostintotal of 28 days. The resulprocess of composting forence was observed betweeratio of the nal product.earthworms, and so probab
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ed for ligno-cellulolytic inoculants (EM bacteria and Trichoderma sp.) insting of household wastes. A mixture of household organic waste com-, grass clippings and composted material was subjected to various dura-llowed by vermicomposting with and without microbial inoculants for avealed that ligno-celluloytic inoculants are not essential to speed up theite small scale household organic waste treatment as no signicant differ-e control and those inoculated with Trichoderma and EM in terms of C:Never, it was observed that EM inoculation enhanced reproductive rate ofreated the best environment for vermicomposting, in all treatment groups.
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dation (Crawford, 1983; Godden et al., 1992). Trichoderma sp. is asting of putrescible kitchen wastes
le at ScienceDirect
evier .com/locate /wasman
organic matter followed by a general drop to around 600 lS/cm
inoculums. There was no difference noted in volume reduction,
anaand kitchen waste, consisted of vegetable scraps, coffee grinds andfood leftovers. Therefore it can be considered that for composting a30% putrescible waste, a total of 70% of other ingredients wereused as bulking agents and as carbon sources. The control is thepremix by itself and the tests were the premix with EM and Trich-oderma sp. inoculated. Each waste component was tested for pH,conductivity, moisture content, total carbon and total nitrogen(TKN).
2.2. Inoculants used
A commercially available microbial seeding agent known as EM,procured from VRM Pty Ltd., Australia (www.vrm.com.au), is amixture of different bacterial species made for accelerating thecomposting process. EM culture was prepared according to themanufacturers instruction. The 500 ml culture was mixed with500 ml sterile distilled water. The Trichoderma sp. culture was pre-pared in potato dextrose agar and the inoculation material wasprepared from the pure culture. The 1 l inoculum was then sprin-kled onto the material in the compost barrel, rolling regularly foreven mixing. The inoculum was added on days 7, 14 and 21. After28 days, samples from all trials were tested for the total bacterialcount (CFU/g) using a pour plate method with nutrient agar andfungal count was tested using the potato dextrose agar.
2.3. Thermo composting and vermicomposting sequence
The two tests conducted compared: (1) composting efciency ofthe control with the bacterial and fungal inoculated systems and(2) complete thermo composting (TC) with the combination ofthermo composting and vermicomposting (VC). The dual process(TC + VC) is a 721 days of TC followed by the remainder of the28-day period of VC. The total treatment period in all the trialswas 28 days as it has been found (Nair et al., 2006) that the com-bination of TC + VC can produce a stable compost by 21 days. Ther-mo composting was conducted in compost barrels of 230 l capacityusing the compost premix. Three trials (control and 2 inoculants)were conducted in triplicate. Inoculations were done on the rstday of the experiment and then every 7, 14 and 21st day in the testbarrels. The barrels were rolled 10 every day for mixing and aer-ation. The moisture content was maintained between 53% and 61%throughout the experiment in the TC barrels. Reducing the mois-ture content was necessary when having putrescible kitchen wastein the premix and in this experiment, around 70% of bulking agents(sawdust, compost, lawn clippings, paper and cardboard) wereused to reduce the high moisture content of kitchen waste. Thetemperature, pH, conductivity and moisture content were mea-sured daily after rolling the barrels. Moisture content was mea-sured by drying samples in the oven at 105 C for 48 h and otherparameters using HACH portable probes of the supernatant ofthe sample made after mixing 1 g of sample in 10 ml of distilledwater.
For VC set ups where parallel TC and VC trials were conductedfor a total of 28 days starting from the same premix of ingredients,on every seventh day, 2 l of materials from the barrels were trans-ferred to 2 l containers with perforated lids, in which 10 red worms(L. rubellus) were released for further processing of the partiallycomposted material. Bed height for volume reduction, pH, and to-tal number of adult worms, juveniles and cocoons in each con-tainer were counted weekly for 28 days.
2.4. Chemical analyses
978 J. Nair, K. Okamitsu /Waste MWeekly samples were collected from the TC barrels and VC con-tainers for testing pH, total carbon and total Kjehldahl nitrogen. To-tal carbon was tested using high temperature non-dispersivepH, temperature, total carbon content and TKN in the inoculatedsystems compared to the control. From Table 1 it can be seen thatthe TKN of the initial ingredients was low which could have af-fected the TKN of the nal product. The initial C:N ratio of 79.1(Fig. 3) which could be attributed to the precipitation of mineralsalts and volatilization of ammonia (Huang et al., 2006). Volumeof compost (l) decreased during the experiment and reached themean volumes between 54% and 56% of the initial volume in thethree treatments (Fig. 4).
Inoculations did not augment TC process as all the physical andchemical parameters tested were similar to the control having noinfrared gas analyser and total nitrogen as per APHA (2005). Atthe end of the experiment nal samples were analyzed for totalcarbon, total Kjehldahl nitrogen, nitrate as well as total phosphorusand orthophosphate using an autoanalyser.
2.5. .Statistical analyses
One-way ANOVA (SPSS ver. 15.0) was used to nd out whetherthere was a signicant difference (p < 0.05) between the treatmentgroups. For those normally distributed data sets, LSD was used, andfor not normally distributed data sets Tamhanes T2 was used.
3. Results and discussion
All three trials (control, EM inoculated and Trichoderma inocu-lated) showed similar changes in temperature and pH throughoutthe composting period (Figs. 1 and 2). The temperature peakedover 50 C in the rst 7 days and remained between 3035 C fornext 2 weeks. By the 23rd day it dropped to 25 C which is consid-ered to have entered the maturation phase. The pH decreased inthe early stage to a slightly acidic state and towards the 20th dayit gradually increased to a neutral pH and was almost neutral inall treatment groups in all composting schedules. This is in accor-dance with the pH changes that occur in a composting system, ini-tial drop followed by pH stabilization. The process being (1) themineralization of nitrogen such as nitrates, nitrites, and other or-ganic acids, (2) the microorganisms convert organic matter, intoCO2 and humic substances releasing heat, (3) the degradation ofsoluble and easily degradable carbon sources, such as monosaccha-ride, starch and lipids increases organic acids of the material. In thenext stage proteins are degraded to ammonium and would resultin an increase in pH (Cceres et al., 2006; Paatero et al., 1984;Ndegwa and Thompson, 2001).
After the initial breakdown, larger organic compounds, such asligno-cellulose, are degraded to humic substances (Crawford,1983; Paatero et al., 1984) and this is when the inoculants were ex-pected to play their role. During this stage, the waste mixtureexperiences mass reduction, stabilization and pathogen reduction.It is also understood that compost needs to be kept at 55 C for15 days to maximize composting efciency and pathogen reduc-tion. In this study, the thermophilic phase lasted for only a week,with the maximum temperature of 55 C retained only for 2 days(treatments with Trichoderma did not reach 55 C). This is commonin systems that use smaller volume as in this experiment where itis susceptible to heat loss due to the high surfacevolume ratio(Nair et al., 2006).
Electrical conductivity increased constantly from around 400 to1200 lS/cm during the rst 12 days which could be due to releaseof mineral salts and ammonium ions through the decomposition of
gement 30 (2010) 977982was reduced to
J. Nair, K. Okamitsu /Waste M4 weeks of composting, the ratio reduced to around 23, 27 and 23in the control, EM inoculation and Trichoderma sp. inoculationgroup respectively. The overall high C:N ratio (>23:1) is attributedto the unchanged TKN during the composting process.
1 2 3 4 5 6 7 8 9 10 11 12 13 1
Fig. 1. The changes in pH in compost barrels
2 3 4 5 6 7 8 9 10 11 12 13 14D
p (o C
Fig. 2. Temperature variati
1 2 3 4 5 6 7 8 9 10 11 12 13
Fig. 3. Change of electrical conductivgement 30 (2010) 977982 979Previous studies have shown contrasting results when usingbioinoculants in the composting process (Golueke et al., 1954;Nakasaki and Akiyama, 1988; Faure and Deschamps, 1991; Elorri-eta et al., 2002; Gaind et al., 2005); however as Vargas-Garcia
4 15 16 17 18 19 20 21 22 23 24 25 26 27 28Days
(bars show standard deviations, n = 3).
15 16 17 18 19 20 21 22 23 24 25 26 27 28ays
on in compost barrels.
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
ity in compost barrels (lS SD).
inoculation also showed increase in nitrate nitrogen with the in-crease in the period of vermicomposting. This explains better min-eralization of nitrogen with vermicomposting. In contrast, EMinoculation reduced the formation of nitrate (Fig. 8).
Total phosphorus (TP) was highest in 28 days TC inoculatedwith Trichoderma (Fig. 9). There was no signicant effect onincreasing TP by adding inoculants even for the VC process. One-
Fig. 6. TKN of the in the nal sample of TC and VC substrate (mg/g SD).
980 J. Nair, K. Okamitsu /Waste Management 30 (2010) 977982(2006) suggested, the activity of various inoculants will vary withthe raw material. It seems that for composting kitchen waste, theinoculants such as EM and Trichoderma sp. are not very effective.This could also be because the premix had mature compost (30%)that normally harbors microbes that will facilitate the compostingprocess.
The addition of inoculants in sequential TC + VC seemed toaccelerate carbon degradation. Most effective reduction of totalcarbon was observed in 21 days TC followed by 7 days VC withTrichoderma inoculation. TKN was expected to increase duringthe VC process as Garg et al. (2006) reported an increase of 4.4-to 5.8-fold in 100 days. However, in the present study there wasno obvious increase in TKN (Fig. 6). TKN content is primarilydependent on the initial total nitrogen content of the organic wasteand the rate of decomposition of the waste (Crawford, 1983; Shar-ma,...