Microbial Community Succession During Biowaste Composting :-Dimkpa, Chinomnso P

ABSTRACT

Microbial community succession during biowaste composting investigated the prevailing physio-chemical condition and bacterial community; bacteria and filamentous fungi present in biowaste during its processing into organic manure.Composting is viable option for minimizing recycling, incinerating and sanitary land filling of waste streams. In the present work we aimed at constructing a more complete picture of the culturable micro flora during the small-scale composting of biowaste (vegetable, fruit and garden wastes) from starting material to mature compost. Physiochemical characteristics ofthe compost were also examined. Investigations were conducted in a wooden cell consisting of Biowaste (vegetable, fruit market and garden waste). These materials were collected from the mixed municipal solid waste ofthe city of Umuahia after manual separation. The municipal solid wastes used were characterized by a large fermentable fraction (contains almost 70% biodegradable material constituting vegetable and fruit residues, waste paper, garden waste (leaves, grass, straw, wood etc).Total bacteria load was determined on nutrient Agar following the method described variously by Fawole and Oso (1998). All the bacteria and fungal isolates were subjected to characterization leading to their identification. The ambient temperature was continuously monitored every 8 days by inserting a thermometer 25cm deep into the pile. Samples were pooled from the various parts and suspended in water (w/v, 1:10), shaken for 30 minutes on rotary shaker and the pH ofthe supernatant was determined using a pH meter. Moisture content was also calculated and expressed in percentage. The CO2 librated by the microorganisms during composting of biowaste was also captured tiltrimetrically. Nutrient composition was determined by the methods described by (AOAC 2002). A total of 16 dominating colonies ofmicrobial genera were isolated at different times indicating microbial succession. These include the primary Saprophytes, Bacillus Sp., Pseudomonas Sp., Alcaligenus Sp., Micrococcus sp, Staphlococus Sp., E. Coli and Enterobacter sp. Fungal isolates also showed the same trend. Muccor Sp., Aspergillus Sp., RhizopusSp.,Cladiosporium sp. and Fusarium sp. were isolated during the first month while Penicillium sp in the second month. A number ofthese microorganisms did not grow at the thermophilic stage but grew at the cooling down stage. Microbial density showed a steady increase from 6.9 x 106 (cfu/g) to 8.30 xlO6 (cfu/g) on the 5th week and later reduced to 7.3x 106 (cfu/g) and subsequently increased to 9.0xl06 (cfu/g). CO2 evolution increased from 2.50 Cm2 /100g to 5.11 Cm2 /100g showing a positive(P < 0.05) correlation with microbial density. The result showed an increase in temperature of the compost from 20°C to 70 °Cin the 6th week which later decreased to 30 °C. During the composting process pH dropped from 8.0 to 7.3 and stabilized as the composting process progressed while there is no significant increase in moisture content of the pile. While the percentage carbon and carbon- Nitrogen ratio reduced, there is significant (P < 0.05) increase in the percentage composition of phosphorus, nitrogen and potassium. Quality compost was obtained on the 12 week. The processing of Biowaste into organic manure is a microbial process shown by the structural changes in the state ofthe biowaste and succession ofmicrobes during the process. Microbial succession was also affected by the prevailing physiochemical conditions (temperature and pH). The whole process resulted in the reduction in size of biowaste and production of compost which satisfied the major aim ofsolid waste management which include bulk reduction and reuse.