Evaluation of energy recovery, pollutant removal, and microbial dynamics in aged refuse bioreactor for landfill leachate treatment.

The study evaluates the effectiveness of aged refuse bioreactors (ARBs) in treating young landfill leachate and recovering energy through biogas production. Over 90 days, duplicate reactors (ARB1 and ARB2) were operated through three 30-day recirculation cycles under anaerobic conditions, utilizing aged refuse from a closed landfill in Bangalore, India. The study was extended by an additional 900 days without further leachate addition to assess long-term gas generation potential. Cumulative gas production amounted to 1384 L in ARB1 and 1182 L in ARB2, with maximum methane production per gram of chemical oxygen demand (COD) recorded at 0.474 L and 0.387 L, respectively. Variability in biogas production was correlated with differences in volumetric moisture content, which also influenced pollutant removal and led to significant improvements in the leachate pollution index, decreasing from 24.4 to 12.84 in ARB1 and to 16.46 in ARB2. COD levels were decreased by 70-90%, and TDS by 46-63%. Heavy metal concentrations, including copper, chromium, cadmium, lead, zinc, and nickel, were reduced by 95-99% to acceptable levels, though increases in ammonia and total phosphorus were noted. Key mechanisms in the ARB included anaerobic degradation, adsorption, oxidation-reduction reactions, and precipitation. In the fourth cycle, without leachate recirculation, gas production reached 320 L in ARB1 and 358.8 L in ARB2, indicating effective conversion of carbon retained from aged refuse and leachate treatment into biogas. Microbial analysis identified dominant communities of Methanosarcina and Methanomicrobia. Overall, this study demonstrates that ARBs are effective in treating young landfill leachate and recovering energy, offering insights into sustainable waste management.