Study Of The Aerobic Composting And The Communities Of Thermophilic Microorganisms In Compost Of Municipal Solid Waste

Aerobic composting is the natural process of the strengthening of microbial degradation and relies on the widely distributed nature of the bacteria,fungi,actinomycetes. Microorganisms are key organisms in the composting systems. Moreover,the thermophilic phases is a key stage with a quick degradation of organic materials. Studying the changes of microbial communities and the degradation of the organic materials in composting system is of great importance for technique improvement and efficiency enhancement. In this paper , a culture - dependent approach and molecular thechnologies polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) were chosen to study the succession profiles of thermophilic microorganisms communities during the thermophilic composting phases.In this paper,two aerobic composting were separately processed with garden waste and kitchen trash for 20 days going through mesophilic phase,thermophilic phase and cooling phase. And the thermophilic period of the two composting (≥50℃) lasted 10d and 8d respectively. The final pH value maintained at 7.5～8.0 in a tiny alkalescence environment. The reduce rate of water content and organic materials were 38.5% and 40.5%,46.3% and 44.6%, While in the thermophilic phases the reduce rate of degradation of organic materials taked up 58.3% and 48.0%. The final C/N ratio was close to 20. Considering all the indicators,we inferred that the two composting piles satisfied with the demand of composting stabilization. Besides,the degradation percentage of cellulose,hemicellulose and lignin of the two piles were 45.0% and 41.0%,33.9% and 32.3% and both of 27.0%,respectively. And the degradation rate of the three indicators in thermophilic phases accounting for the total degradation quantity were 49.0% and 48.0%,68.0% and 54.0%,65.0% and 52.0%. All the datas showed that the degradation of cellulose and hemicellulose were bigger than that of lignin.The mixed bacteria,fungi and actinomycetes in samples during thermophilic phases of two piles were cultured by plate count,and the result was that the total population of bacteria,fungi and actinomycetes showed a wave-like curve,i.e"up-down","down-up"and"up-down- up",which showed close relationship with the degradation of organic materials with a change of"down-up-down-up". And the total microbial DNA was extracted from samples by method of Protein K-CTAB. PCR amplifications were performed with primers GC-341F and 907R targeting the V3 region of bacteria 16 S rRNA,GC-NS7 and NS8 targrting the V8-V9 region of fungal 18S rRNA and primers F243 and GC-R513 targeting the V3 region of 16S rRNA genes of actinomycetes. And the PCR products were separated by DGGE for a segment of 630bp,340bp and 270bp,respectively. The results of culture-dependent approach and DGGE profiles showed that the population of the thermophilic bacteria were more than that of fungi and actinomycetes during thermophilic phase in the two piles,while the predominant kinds of the themophilic actinomycetes were less than that of fungi and bacteria. A total of 28 DGGE single bands were isolated from the profiles by cloning. The obtained sequences of these clones showed similarity to some known organisms in a range of 91% to 100%. The clones identified as Bacillus spp.,Aspergillus spp., Penicillium spp., Stretomyces spp. and Nocardioides spp. are characterized as cellulose and lignin-degrading bacteria,fungi and actinomycetes. The bacteria,fungi and actinomycetes composition for different composting materials processes similarly. This study would be beneficial for definituding the thermophilic microorganisms of thermophilic phases in aerobic composting. The clustering analysis indicated that themophilic fungi and actinomycetes in high temperature stages of composting can be divided into two phases,the dividing lines were temperature of 56℃and 58℃,when heating up,respectively. But there was no exact rules for the changes of thermophilic bacteria. The clustering relation in phrases were close to each other,while between phrases was distant. Temperature played a great role in sieving thermophilic fungi and actinomycetes of high temperature stage in composting.