Global perspective of municipal solid waste and landfill leachate: generation, composition, eco-toxicity, and sustainable management strategies

Globally, more than 2 billion tonnes of municipal solid waste (MSW) are generated each year, with that amount anticipated to reach around 3.5 billion tonnes by 2050. On a worldwide scale, food and green waste contribute the major proportion of MSW, which accounts for 44% of global waste, followed by recycling waste (38%), which includes plastic, glass, cardboard, and paper, and 18% of other materials. Population growth, urbanization, and industrial expansion are the principal drivers of the ever-increasing production of MSW across the world. Among the different practices employed for the management of waste, landfill disposal has been the most popular and easiest method across the world. Waste management practices differ significantly depending on the income level. In high-income nations, only 2% of waste is dumped, whereas in low-income nations, approximately 93% of waste is burned or dumped. However, the unscientific disposal of waste in landfills causes the generation of gases, heat, and leachate and results in a variety of ecotoxicological problems, including global warming, water pollution, fire hazards, and health effects that are hazardous to both the environment and public health. Therefore, sustainable management of MSW and landfill leachate is critical, necessitating the use of more advanced techniques to lessen waste production and maximize recycling to assure environmental sustainability. The present review provides an updated overview of the global perspective of municipal waste generation, composition, landfill heat and leachate formation, and ecotoxicological effects, and also discusses integrated-waste management approaches for the sustainable management of municipal waste and landfill leachate.

Materials and energy recovery at six European MBT plants

Mechanical Biological Treatment (MBT; called "dirty" Materials Recovery Facilities in the U.S.) is a waste management method, developed mostly in Europe, which combines sorting of recyclable materials (metals, paper, plastics, glass) with composting/digestion of green/ food wastes and, in some cases production of a fuel material. In 2018-19, the authors visited six MBT facilities in Europe that use different approaches for the recovery of materials and energy from mixed MSW. These plants were studied with respect to feedstock composition, operating conditions, capital expenditure, financial viability and environmental impacts. The compost product of most facilities examined did not comply with agricultural standards and, therefore, it was classified as compost-like output (CLO) and used as daily cover in landfills. The best composting practice used source separated organic materials (yard and other green wastes) and yielded a marketable compost. MBT plants that did not include the recovery of fuel materials had lower landfill diversion rates and, also, lower capital and operating costs. It was concluded that an MBT plant must include a very efficient sorting and recyclables recovery line and charge a sufficient gate fee. Also, in addition to the recycled products, there should be a stream to recover fuel materials sent to a power plant or cement plant, thus increasing revenue, and landfill diversion, and maximizing greenhouse gas (GHG) savings.

System integration of hydrothermal liquefaction and anaerobic digestion for wet biomass valorization: Biodegradability and microbial syntrophy

Sewage sludge treatment & disposal pose environmental challenges in populated-dense urban environments. Due to its poor digestibility and dewaterability, sewage sludge contains high water content and concentrated nutrients (carbon, nitrogen, and phosphorus) even after conditioning and mechanical thickening. Regarding this, a pretreatment step and downstream anaerobic digestion (AD) are often required. To meet our societal goal towards a circular economy, system integration of hydrothermal pretreatment and AD now present an attractive approach for recovering resources from the wet sewage sludge biomass. In this study, such system integration together with struvite precipitation was applied for valorizing sewage sludge. Firstly, hydrothermal conditions of different temperatures (160 °C-230 °C) and duration (2 h-12 h) were compared to their performance of nutrients solubilization. Subsequently, the hydrothermal condition of 220°C-3 h was selected for further investigations of struvite recovery and bioenergy production. Through AD comparisons, the integrated process improved the ultimate biomethane yield by 38%. Interestingly, a lag phase occurred in the midst of the AD, which indicated the need for microbial acclimatization after the hydrothermal process. The long-term microbial monitoring revealed the efficient biomethane re-generation was closely related to the late enrichment of Syntrophus for potential H₂-syntrophy. Therefore, on one hand, this study investigated an efficient and integrated approach of sewage sludge valorization. On other hand, it uncovered the microbial bottlenecks and potential biotechnological means for further system improvement. Further research about nutrients speciation in the integrated system would be desired.

Sustainable municipal waste management strategies through life cycle assessment method: A review

Increasing amounts of municipal solid waste (MSW) has gained widely concern on reduction, utilization and minimizing environmental impacts associated with waste management. Life cycle assessment (LCA) has been used to evaluate total environmental impact of municipal waste management (MSWM) options in strategy-planning and decision-making process. The exiting LCA studies have covered a large range of detailed focus from waste treatment technology to applied modelling methods in LCA of MSWM, yet an important concern for stakeholders, the relationship between practical management strategies and their LCA results, has not been comprehensively summarized. This paper reviews recent LCA studies focusing on MSWM system in 45 cases from both developing and developed regions to promote evolution of the MSWM system through modification of waste management strategies. Selected literatures conducted LCA with system boundary covering the whole MSWM system rather than single treatment process or specific type of waste. This review has explored distribution and evolution of LCA studies in waste management field and summarized critical parameters (system boundary, functional unit, assessment approach and data uncertainty) for conducting LCA of MSWM system. Comparison results from 45 worldwide cases indicated 33%-154% environmental benefit in Global warming potential (GWP) impact with implement of integrated solid waste management system to replace single landfill, incineration, or open dumping treatment. Key issues with upgrading of MSWM system have been highlighted to raise concern, i.e., the importance of targeted management strategy on organic and recyclable waste, the growing contribution of waste collection and transportation to the total environmental impact, as well as promoting multi-impacts assessment for MSWM system to achieve environmentally effective, economically affordable, and socially acceptable. Rather than focus on technical factors, results from this study indicated the key influences from understanding local limitation, environmental concern, management chain and comprehensive impact, providing useful strategies on improving MSWM with generalization results of LCA studies.

Improvement of waste management practices in a fast expanding sub-megacity in Pakistan, on the basis of qualitative and quantitative indicators

This paper deals with an analysis of waste management practices in the fast-growing city of Gujranwala with 2.6 million inhabitants, with a fast growing middle income group of 56%, and an urbanization rate of 3.49% per annum. This city is like many other cities in the developing world, characterised by hardly any waste management infrastructure. The study comprises: (1) an inventory of current waste flows, per income group as well as per season, (2) an inventory of waste management shortcomings, (3)) a what-if analysis on the carbon footprint of three waste treatment techniques. The inventory of current waste flows is based on a comprehensive site study involving 776 samples in total. The waste management shortcomings have been qualitatively analysed by Wasteaware model, which deals with physical aspects (public health, environmental control, resource management) as well as governance factors (user & provider inclusivity, financial stability, institutions & policies). The what-if analysis of the carbon footprint has been based on an LCA-based tool. The findings of this study are that: (1) the optimum choice of waste treatment scenario differs for the seasons, (2) the high and middle income groups have nearly half of the share of the waste (3) the Wasteaware system appears to be a powerful tool to communicate the weak spots and to make stakeholders aware of the opportunities for improvement. The novelty of this paper is that it focused on the impact of household income groups in combination with seasonal differences while comparing different waste disposal scenarios.

Life cycle assessment for solid waste management in Lebanon: Economic implications of carbon credit

Solid waste management has witnessed much progress in recent years with considerable efforts targeting the reduction of associated impacts and carbon emissions. Such efforts remain relatively limited in developing economies due to inefficient management practices. In this study, a life cycle assessment (LCA) approach is adopted to identify integrated systems with minimal impacts and reduced emissions in a developing context coupled with an economic valuation and sensitivity analysis to assess the effect of varying influencing parameters individually. The results showed that the highest impact arises from landfilling with minimal material recovery for recycling and composting, while incineration coupled with energy recovery contributed to the least equivalent emissions (-111% with respect to baseline scenario) at a varying cost of -70% to +93% depending on the selected technology and the value of carbon credit. Optimizing material recycling, composting and landfilling with energy recovery contributed to 98% savings in emissions (with respect to baseline scenario) and remained economically attractive irrespective of the carbon credit exchange rate of 0.5-50 US$/MTCO₂E. The sensitivity analysis showed that an improvement in landfill gas collection efficiency (up to 60%) can contribute to major savings in emissions (58%). The application of the LCA-based approach supports the development of integrated viable plans while quantifying advantages and disadvantages towards decision-making and policy-planning.

Environmental sustainability assessment of a microalgae raceway pond treating aquaculture wastewater: From up-scaling to system integration

The environmental sustainability of aquaculture wastewater treatment by microalgal bacterial flocs (MaB-flocs) in an outdoor raceway pond was analyzed using life cycle assessment. Pikeperch aquaculture wastewater treated at pilot scale (Belgium; 28m(2)) and industrial scale (hypothetical up-scaling; 41 ponds of 245m(2)) were compared. The integration of the MaB-floc raceway pond in a broader aquaculture waste treatment system was studied, comparing the valorisation of MaB-flocs as shrimp feed and as biogas. Up-scaling improves the resource footprint of the plant (848MJex,CEENEkg(-1) MaB-floc TSS at pilot scale and 277MJex,CEENEkg(-1) MaB-floc TSS at industrial scale) as well as its carbon footprint and eutrophication potential. At industrial scale, the valorisation of MaB-flocs as shrimp feed is overall more sustainable than as biogas but improvements should be made to reduce the energy use of the MaB-floc raceway pond, especially by improving the energy-efficiency of the pond stirring system.