Insights into leachate reduction in landfill with different ventilation Rates: Balance of Water, waste physicochemical Properties, and microbial community

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.

Leachate derived humic-like substances drive the variation in microbial communities in landfill-affected groundwater

Landfills are commonly used for waste disposal in many countries, and pose a significant threat of groundwater contamination. Dissolved organic matter (DOM) plays a crucial role as a carbon and energy source, supporting the growth and activity of microorganisms. However, the changes in the DOM signature and microbial community composition in landfill-affected groundwater and their bidirectional relationships remain inadequately explored. Herein, we showed that DOM originating from more recent landfills mainly comprises microbially produced substances resembling tryptophan and tyrosine. Conversely, DOM originating from older landfills predominantly comprises fulvic-like and humic-like compounds. Leachate leakage increases microbial diversity and richness and facilitates the transfer of foreign bacteria from landfills to groundwater, thereby increasing the vulnerability of the microbial ecosystem in groundwater. Deterministic processes dominated the assembly of the groundwater microbial community, while stochastic processes accounted for an increased proportion of the microbial community in the old landfills. The dominant phyla observed in groundwater were Proteobacteria, Bacteroidota, and Actinobacteriota, and humic-like substances play a crucial role in driving the variation in microbial communities in landfill-affected groundwater. Predictions using PICRUSt2 suggested significant associations between various metabolic pathways and microbial communities, with the Kyoto Encyclopedia of Genes and Genomes pathway "Metabolism" being the most predominant. The findings contribute to advancing our understanding of the transformation of DOM and its interplay with microbial communities and can serve as a scientific reference for decision-making regarding groundwater pollution monitoring and remediation.

Changes of characteristics and disinfection by-products formation potential of intracellular organic matter with different molecular weight in metalimnetic oxygen minimum

Metalimnetic oxygen minimum (MOM) occurs in reservoirs or lakes due to stratification and algal blooms, which has low dissolved oxygen (DO) levels and leads to the deterioration of water quality. The transformation mechanism and the impact on the water quality of intracellular organic matter (IOM) derived from algae are poorly understood under MOM conditions. In this study, IOM extracted by Microcystis aeruginosa was divided into five components according to molecular weight (MW), and the changes of characteristics and correlated disinfection by-products formation potential (DBPFP) were analyzed and compared under MOM conditions. The removal efficiency of dissolved organic carbon (DOC) in the <5 kDa fraction (66.6%) was higher than that in the >100 kDa fraction (41.8%) after a 14-day incubation under MOM conditions. The same tendency also occurred in Fmax and DBPFP. The decrease in Fmax was mainly due to the decline in tryptophan-like and tyrosine-like for all IOM fractions. The diversity of microorganisms degrading the MW > 100 kDa fraction was lower than others. Besides low MW fractions, these findings indicated that more attention should be paid to high MW fractions which were resistant to biodegradation under MOM conditions during water treatment.

Numerical simulation to optimize passive aeration strategy for semi-aerobic landfill

Passive aeration has been proven to be efficient for oxygen supply in landfill. The combination of passive aeration and semi-aerobic landfill offers a cost-effective and energy-efficient approach to solid waste (SW) treatment. However, determining the optimal strategy for this combination has remained unclear. This study aimed to investigate the strategy of passive aeration in a semi-aerobic landfill using numerical simulation methods. A model coupled hydrodynamic model and compartment model for degradation of SW was implemented. The accuracy was well validated by comparing measured and simulated results in a pilot-scale landfill. Compared with natural convection, passive aeration by funnel caps could increase air input by 20 %. By simulating volumetric fraction distribution of CO2, CH4 and O2 in landfill, an orthogonal experiment including 4 factors was designed to identify that the diameter of tubes (DT), the spacing between tubes (ST) and the landfill depth (LD) have substantial impacts on aerobic zone ratio (AZR) of landfill. But the diameter of gas ports (DGP) has an indiscernible effect. The optimized factors were determined to be as follows: DT = 0.3 m, ST = 15.0 m, DGP = 0.05 m, and LD = 4.0 m, under which the semi-aerobic landfill could enhance SW degradation. Large diameter and spacing of tubes are favorable to improve the AZR at the top of the landfill, and the aerobic zone mainly exists near the ventilation tubes. These findings contribute to the development of more efficient and sustainable solid waste treatment strategies in semi-aerobic landfill.