Sustainable solutions for municipal solid waste and leachate treatment: A circular economy approach
Abstract
India’s waste management system, largely reliant on landfilling and open dumping, is inadequate for handling rising volumes of unsegregated muncipal solid waste (MSW), causing environmental and public health risks. Addressing this challenge demands a shift toward circular economy principles, that reframe waste as a valuable resource. In this context, the thesis explores sustainable strategies for managing MSW and its leachate, emphasizing resource recovery, reuse, and recycling. The study evaluates advanced leachate treatment technologies such as the Aged Refuse Bioreactor (ARB) and Anaerobic Biomass Biofilm Reactor (ABBR) and investigates the role of additives like biochar and garbage enzymes in enhancing anaerobic digestion. Additionally, a life cycle assessment (LCA) is conducted to analyse the environmental impacts and sustainability of these approaches.
To support these evaluations, field assessments and laboratory experiments were carried out to characterize both legacy waste and leachate. The comprehensive analysis of legacy waste revealed a moderate calorific value and low concentrations of heavy metals, suggesting that, with suitable preprocessing (e.g., drying or pelletization), thermal treatment could be a feasible recovery option. Leachate characterization further indicated that compost leachate exhibited high biodegradability (BOD/COD > 0.5), making it suitable for biological treatment, whereas landfill leachate showed poor biodegradability, necessitating pre-treatment prior to conventional processes. Moreover, landfill gas monitoring identified elevated methane concentrations, underscoring the need for efficient gas capture and utilization systems to mitigate greenhouse gas emissions.
The study further evaluated the performance of ARBs in landfill leachate treatment, demonstrating high efficiency with 70–90% COD removal and 95–99% heavy metal reduction. Notably, ARBs achieved substantial biogas yields of 0.43 ± 0.12 L/g COD removed. Microbial analysis revealed the dominance of methanogens such as Methanosarcina and Methanomicrobia in aged refuse, which contributed to sustained methane production. These findings highlight the potential of ARBs as integrated systems for energy recovery and effective leachate remediation.
Composting, another prevalent waste management approach, generates compost leachate characterized by high COD and volatile fatty acid content, posing significant treatment challenges. To address this, an Anaerobic Biomass Biofilm Reactor (ABBR) was developed using natural agricultural residues—including coir, ridge gourd fibres, and dried acacia leaves—as biofilm support media. The treatment performance of ABBR was benchmarked against conventional technologies such as expanded granular sludge bed (EGSB) and up-flow anaerobic sludge blanket reactor (UASB). ABBR exhibited superior performance, achieving 93% COD removal, a biogas yield of 0.58 L/g COD removed, and reduced sludge production. The enhanced performance was attributed to the effective activity of biofilm-associated methanogens and the use of biodegradable support materials, which contributed to greater sustainability and alignment with circular economy goals.
Additionally, the research explored the use of garbage enzymes, fermented products derived from fruit waste—for enhancing the solubility and biodegradability of organic matter in landfill leachate. Four types of garbage enzymes were tested at two temperature conditions: ambient (27 ± 3 °C) and elevated (42 ± 3 °C). Enzymes derived from orange and lemon peels demonstrated the highest performance, achieving up to 68% removal of soluble COD (sCOD) at ambient temperature, with optimal efficacy observed at 10–15% concentration. However, a notable decline in performance at higher temperatures indicated thermal sensitivity. These findings suggest that garbage enzymes can serve as a sustainable, low-cost pretreatment option for improving the treatability of landfill leachate.
Anaerobic digestion, a viable approach for treating the organic fraction of MSW, was further optimized through the inclusion of sustainable additives. The effects of walnut shell biochar (WSBC) and garbage enzyme (GE) were investigated both independently and in combination. The optimal performance was achieved with 15 g/L of biochar and 15 ml/g of GE, while a higher biochar dosage (20 g/L) slightly inhibited digestion. Moreover, a 15 g/L of WSBC with 15% GE resulted in biogas and methane yields of 904 ml/g VS and 607 ml/g VS, respectively, confirming strong synergy. The study further optimized conditions using tea powder waste (TPW) as a co-substrate with different MSW:TPW ratios (1:3, 1:1, 3:1), GE concentrations (5–15 ml/g), and pH levels (5–8). The highest biogas yield (771.85 ml/g VS) was obtained at a 3:1 MSW:TPW ratio, 10% GE, and pH 8. These findings emphasize the importance of maintaining optimal pH (~8), moderate GE concentration, and a balanced substrate mix to maximize AD performance while aligning with circular economy principles.
Field data from Bengaluru showed that about 52% of MSW is still landfilled. This underscores the urgent need for decentralized treatment and improved source segregation. Therefore, LCA was carried out to assess the best MSW treatment scenario for Bengaluru with minimum environmental impact. The scenario characterized by 90% segregation efficiency and maximized resource recovery, demonstrated the lowest environmental impacts and embodied a circular economy approach. In contrast, high landfill dependency in current scenario or practice in Bengaluru led to the worst outcomes, with segregation efficiency identified as the most critical factor influencing environmental performance.
LCA of the biological reactors ABBR, UASB and EGSB was also carried out to determine the most environmentally sustainable option for compost leachate treatment. The analysis revealed that the ABBR system, particularly when coupled with fertilizer utilization of the digestate, exhibited the lowest environmental impacts across all categories, owing to its efficient methane recovery, low sludge production, and effective nutrient recycling. In contrast, UASB and EGSB exhibited higher impacts, primarily due to greater energy consumption and sludge generation, underscoring the need for improved digestate management and reactor design.
In summary, the research focused on exploring the resource recovery potential from the Bengaluru dumpsite and utilized waste products such as WSBC, TPW, and fruit waste to enhance the anaerobic digestion process for MSW and leachate. Additionally, it investigated repurposing aged refuse, agro waste, and yard waste as packing material in the reactor for leachate treatment, aiming for higher organic removal efficiency and biogas production. Thereby, this research demonstrated that the integration of bio-based additives, natural biofilm carriers, and biological treatment systems presents a viable and sustainable pathway for managing MSW and leachate within a circular economy framework.