Effect of leachate recycle and inoculation on microbial characteristics of municipal refuse in landfill bioreactors.

ABSTRACT

Population development of key groups of anaerobic and aerobic bacteria involved in municipal refuse decomposition under laboratory landfill bioreactors with and without leachate recycle and inoculation was measured since modeling municipal refuse was landfilled in bioreactors for about 210 days. Hydrolytic fermentative bacteria (HFB), hydrogen-producing acetogenic bacteria (HPAB), methane-producing bacteria (MPB), sulfate-reducing bacteria (SRB), anaerobic and aerobic cellulolytic bacteria and denitrabacteria were enumerated by the most probable number technique. The results showed that the dominant microorganism groups were the methanogenic bacteria including hydrolytic fermentative, hydrogen-producing acetogenic and methane-producing bacteria. They were present in fresh refuse but at low values and positively affected by leachate recycle and refuse inoculation. The amounts of HFB or HPAB in digesters D4 and D5 operated with inoculation and leachate recycle reached their maximum values of 10(10)-10(12) cells/g dry refuse for HFB or 10(5)-10(6) cells/g dry refuse for HPAB on day 60, in digester D3 operated with leachate recycle on day 120 for HFB (10(9) cells/g dry refuse) or on day 90 for HPAB (10(5) cells/g dry refuse), and in digesters D1 and D2 on day 210 for HFB (10(9) cells/g dry refuse) or on day 90 for HPAB (10(4)-10(6) cells/g dry refuse). The population of methane-producing bacteria in digesters D4 and D5 sharply increased on days 60 and 90 respectively, however in digesters D1, D2 and D3 on day 120. Leachate recycle and inoculation changed the cellulolytic microorganisms composition of refuse ecosystem, the higher amounts of anaerobic cellulolytic bacteria were measured in digesters D4 and D5 (10(7) cells/g dry refuse), followed by digesters D3 (10(6) cells/g dry refuse), D2 or D1(10(4) cells/g dry refuse). However, the amounts of aerobic cellulolytic bacteria were much lower than that of anaerobic cellulolytic bacteria. And it was higher in digester D3 than those in digesters D1, D2, D4 and D5. The amounts of SRB and denitrabacteria were also higher in digester D5 than those in digesters D1, D2, D3 and D4. Refuse decomposition could be accelerated by leachate recycle and inoculation in the view of microorganism development.