Effect of leachate recycling and inoculation on the biochemical characteristics of municipal refuse in landfill bioreactors

Activity development of key groups of enzymes involved in municipal refuse decomposition was measured in laboratory landfill bioreactors with and without leachate recycling and inoculation for about 210 days. The results showed that the enzymes (amylase, protease, cellulase, lipase and pectinase) were present in fresh refuse but at low values and positively affected by leachate recycling and refuse inoculation. The total average of cellulase activity in digesters D3 operated with leachate recycling but no inoculation, D4 and D5 operated with leachate recycling and inoculation was much higher than that in digesters D1 and D2 without leachate recycling and inoculation by 88%—127%, 117%—162% and 64%—98%. The total average of protease activity was higher in digester D4 than that in digesters D1, D2, D3 and D5 by 63%, 39%, 24% and 24%, respectively, and the positive effect of leachate recycling and inoculation on protease activity of landfilled refuse mainly was at the first two months. The total average of amylase activity was higher in digesters D3, D4 and D5 than that in digesters D1 and D2 by 83%—132%, 96%—148% and 81%—129%. During the early phase of incubation, the stimulatory effect of inoculation on lipase activity was measured, but refuse moisture was the main factor affecting lipase activity of landfilled refuse. The inoculation, initial and continuous inoculation of microorganisms existing in leachate, was the mainly stimulatory factor affecting pectinase activity of landfilled refuse.

Comparison between controlled landfill reactor and conditioned landfill bioreactor

Bioreactor landfills allow a more active landfill management that recognizes the biological, chemical and physical processes involved in a landfill environment. The laboratory-scale simulators of landfill reactors treating municipal solid wastes were studied, the effect of solid waste size, leachate recirculation, nutrient balance, pH value, moisture content and temperature on the rate of municipal solid waste(MSW) biodegradation were determined, and it indicated the optimum pH value, moisture content and temperature decomposing MSW. The results of waste biodegradation were compared with that of the leachate-recirculated landfill simulator and conservative sanitary landfill simulator. In the control experiment the antitheses of a decreasing trend of the organic load, measured as biological oxygen demand and chemical oxygen demand, was shown. An obvious enhancement of effective disposal from conservative sanitary landfill(CSL) simulator, to the leachate-recirculated landfill(LRL) simulator and to the conditioned bioreactor landfill(CBL) simulator would be noted, through displaying the compared results of solid waste settlement, heavy metal concentration in leachate, methane production rate, biogas composition, BOD and COD as well as their ratio.

Degradation of Refuse in Hybrid Bioreactor Landfill

Objective To explore the process of refuse decomposition in hybrid bioreactor landfill. Methods The bioreactor landfill was operated in sequencing of facultative-anaerobic and aerobic conditions with leachate recirculation, pH, COD, and ammonia in the leachate and pH, biodegradable organic matter （BDM）, and cation exchange capacity （CEC） in refuse were detected. Results CEC increased gradually with the degradation of refuse, which was negatively correlated with BDM. COD and ammonia in the leachate was declined to 399.2 mg L^-1 and 20.6 mg N L^-1, respectively, during the 357-day operation. The respective concentrations of ammonia and COD were below the second and the third levels of current discharge standards in China. Conclusion The refuse is relatively stable at the end of hybrid bioreactor landfill operation. Most of the readily biodegradable organic matter is mineralized in the initial phase of refuse degradation, whereas the hard-biodegradable organic matter is mainly humidified in the maturity phase of refuse degradation.

N_2O and NH_3 emissions from a bioreactor landfill operated under limited aerobic degradation conditions

The combination of leachate recirculation and aeration to landfill may be an efficient way for in-situ nitrogen removal.However,nitrogenous substances contained in the landfill layer are concomitantly transformed into N2O and NH3,leading to increased emissions into the atmosphere.In the present study,the emissions of N2O and NH3 were measured under conditions of fresh or partially stabilized refuse with or without leachate recirculation or intermittent aeration.The results showed that the largest N2O emission（12.4 mg-N/L of the column） was observed in the aerated column loaded with partially stabilized refuse and recycled with the leachate of low C/N ratio;while less than 0.33 mg-N/L of the column was produced in the other columns.N2O production was positively correlated with the prolonged aerobic time and negatively related with the C/N ratio in the recycled leachate.NH3 volatilization increased with enhanced gas flow and concentration of free ammonia in the leachate,and the highest cumulative volatilization quantity was 1.7 mg-N/L of the column.