Optimizing alkali-pretreatment dosage for waste-activated sludge disintegration and enhanced biogas production yield.

The rapid transition towards modernization and industrialization led to an increase in urban population, resulting in paramount challenge to municipal sewage sludge management. Anaerobic digestion (AD) serves as a promising venue for energy recovery from waste-activated sludge (WAS). Addressing the challenge of breaking down floc structures and microbial cells is crucial for releasing extracellular polymeric substances and cytoplasmic macromolecules to facilitate hydrolysis and fermentation process. The present study aims to introduce a combined process of alkaline/acid pre-treatments and AD to enhance sludge digestion and biogas production. The study investigates the influence of alkali pretreatment at ambient temperature using four alkali reagents (NaOH, Ca(OH)2, Mg(OH)2, and KOH). The primary goal is to provide insights into the intricate interplay of alkali dosages (0.04-0.12 g/gTS) on key physic-chemical parameters crucial for optimizing the pre-treatment dosage. Under the optimized alkaline/acid pre-treatment condition, the TSS reduction of 18%-30% was achieved. An increase in sCOD concentration (24%-50%) signifies the enhanced hydrolysis and solubilization rate of organic substrate in WAS. Finally, the biomethane potential test (BMPT) was performed for pre-treated WAS samples. The maximum methane (CH4) yield was observed in combination A1 (244 mL/g) and D1 (253 mL/g), demonstrating the pivotal role of alkali optimization in enhancing AD efficiency. This study serves as a valuable resource to policymakers, researchers, and technocrats in addressing challenges associated to sludge management.

Impact of municipal solid waste landfill leachate on biogas production rate.

Landfills/open dump sites are the final disposal facilities for municipal solid waste (MSW). These sites undergo continuous process of biochemical reactions and anaerobic degradation, which make them prone to generation of landfill gas (LFG) and leachate. Worldwide, the quantitative and qualitative assessment for leachate treatment and management has been a growing concern. The present study investigated the physico-chemical characteristics and heavy metal parameters for fresh, 3-month, 6-month and 3-year old landfill leachate samples. The total dissolved solids (13280 mg/l), alkalinity (13000 mg/l), chemical oxygen demand (42000 mg/l) and total organic carbon (16500 mg/l) was found to be maximum in 3-year old leachate sample. While, the 3 and 6-month old leachate samples had maximum heavy metal concentration. The attempt was also made to identify the key parameters responsible to enhance biogas production yield from different ages of MSW. The substrate combinations of MSW and 3-year old leachate samples was prepared at varying proportion. The study was performed in three cycles and the volume of leachate diffused in each cycle was kept constant. The control samples with no leachate diffusion was also prepared to compare the percentage increase in biogas production rate. It was found that the cumulative methane (CH4) production from fresh (358 ml/g) and 3-month old MSW (273 ml/g) was maximum, and the overall percentage increase was 43% and 32%. It was also conclusive that the excess leachate diffusion of >15 ml results in low calcination behaviour and CH4 production rate. The response surface methodology was used to correlate and validate independent input variables (volatile solids, C/N ratio and leachate concentration) responsible for maximum CH4 yield.

Mask consumption and biomedical waste generation rate during Covid-19 pandemic: A case study of central India.

The rapid generation of biomedical waste (BMW) due to covid-19 pandemic has created burden on the existing municipal solid waste management (MSWM) system in both developed and developing countries. The substantial influx of covid patients in Maharashtra, India has influenced the pattern of BMW generation, especially for the yellow category of BMW and incineration facilities. The objective of the study was to estimate the daily face mask consumption (DFM) and BMW generation from May 2020 to August 2021 in Maharashtra, India. The study was carried out based on the confirmed covid 19 cases, population forecast, urban population (%), BMW generation rate (kg/bed/day), and so on. The data set for the each paramters were collected from web-portals, published reports based on previous studies. These data sets were further regrouped, processed and analyised using mathematical equations. The study also revealed that Mumbai, Pune, and Thane districts, India has contributed ≥ 60% of the DFM and BMW generation. It was found that the DFM by non-covid patients was higher compared to the covid patients (DCFM). Further, it was revealed that BMW generated in the months of July 2020 (152 tons/day), August 2020 (228 tons/day), September 2020 (364 tons/day), October 2020 (177 tons/day), March 2021 (405 tons/day), April 2021 (1,102 tons/day), May 2021 (705 tons/day), June 2021 (194 tons/day), and July 2021 (149 tons/day), exceeded the existing BMW treatment capcity of 132 tons/day. The sudden spike in covid-19 cases has influenced the pattern of DFM and BMW generation, espeicllay for the yellow category of BMW (BMWCY) and has increased the burden on BMW incineration facilities. The daily emission rates from BMW-incineration was in the order PM10> NO2> CO>SO2, with maximum emission of PM10 (85.61 kg of pollutant/day). The F-test was performed using one-way ANOVA to understand the influence of covid cases on daily face mask consumption. It was found that F-satistic of DCFM and BMWCY is more than the F-critical i.e., increase in covid cases had a significant effect on mass consumption rate and BMW generation.

A review on recovery processes of metals from E-waste: A green perspective.

E-waste management has become a global concern because of the enormous rise in the rate of end-of-life electrical and electronic equipment's (EEEs). Disposal of waste EEE directly into the environment leads to adverse effects on the environment as well as on human health. For the management of E-waste, numerous studies have been carried out for extracting metals (base, precious, and rare earth) following pyrometallurgy, hydrometallurgy, and biometallurgy. Irrespective of the advantages of these processes, certain limitations still exist with each of these options in terms of their adoption as treatment techniques. Several journal publications regarding the different processes have been made which aids in future research in the field of E-waste management. This review provides a comprehensive summary of the various metal recovery processes (pyrometallurgy, hydrometallurgy, and biometallurgy) from E-waste, along with their advantages and limitations. A bibliometric study based on the published articles using different keywords in Scopus has been provided for a complete idea about E-waste with green technology perspective like bioleaching, biosorption, etc. The present study also focussed on the circular economic approach towards sustainable E-waste management along with its socio-economic aspects and the economic growth of the country. The present study would provide valuable knowledge in understanding E-waste and its different treatment processes to the students, researchers, industrialists, and policymakers of the country.