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.

Smart technological options in collection and transportation of municipal solid waste in urban areas: A mini review.

The rapid increase in quantities and the mismanagement of municipal solid waste (MSW) in developing countries are increasing the environmental impacts such as air, water and soil contamination. The present scenario of MSW management deals with numerous issues such as lack of technological resources, strategical management, social awareness, public participation, etc. Globally, numerous efforts in the form of new policies, schemes and regulatory acts have been made to develop a systematic collection and transportation (C&T) method using advanced, integrated technologies. However, very few studies have addressed this issue for low- and middle-income countries due to the lack of availability of reliable resources and data sets. This paper addresses the present challenges in C&T methods and highlights the application of information communication technology in monitoring, capturing, data management, planning, live tracking and communication. This systematic mini-review is based on the availability of technical resources, consumer acceptance and cost-effectiveness of different technologies in managing the processes. The study revealed that the C&T methods in most developed countries are designed based on their geographical stretch, climatic factors, waste characteristics and compatible technology, resulting in sustainable MSW management. However, developing countries have followed the same monotonous approach in managing their MSW, which fails in C&T process. The case study provides a valuable resource for researchers and policymakers to frame a better C&T process based on the recent technological interventions, infrastructure development, and social and economic status.

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.

Estimation of spontaneous waste ignition time for prevention and control of landfill fire.

Openmunicipal solid waste(MSW) dumpsites in India are significant hotspots of spontaneous fire and associated air and ground water pollution. Unscientific dumping of MSW poses a major threat to the surrounding environment and human health. One-year-old biodegradable waste components comprised of paper, cardboard, newspaper, textile, wood, grass leaves and coconut shell were analyzed for the determination of the moisture content (MC), smoldering temperature, ignition temperature, and ignition time. Principal component analysis of the old waste components revealed that cardboard, paper, newspaper and leaves are most susceptible waste components for spontaneous ignition. In contrast, MC was the most influential parameter for resulting changes in ignition temperature (0C) on ignition time (min). A numerical equation was developed to estimate the time required for the spontaneous waste ignition at MSW dumpsite. The results of the study showed that the aged waste (age ≥ 3 year) having MC below 6 % and initial surface temperature of 78 0C might smolder and ignite during the hottest time of the day in âˆ¼ 6 and âˆ¼ 26 days, respectively. Estimates showed that the time required for spontaneous waste ignition of aged waste is moderately dependent on waste MC (∼5-55 %), surface temperature (∼40-100 0C), monthly pattern of average high temperature (∼36.6-42.6 0C), biodegradable waste components having smoldering temperature ≤ 150 0C and ignition temperature ≤ 270 0C. The present study also showed that the occurrence of landfill fire events at MSW dumpsites is more prominent during the pre-monsoon season i.e. during the elevated temperature level.

Determination of risk of spontaneous waste ignition and leachate quality for open municipal solid waste dumpsite.

The waste receiving capacity of most municipal solid waste (MSW) landfill sites in India is exhausted, resulting in the formation of larger waste heaps. In the majority of Indian cities, these old waste heaps are prone to frequent smoldering and ignition resulting into fires. In this study, the potential risk of spontaneous ignition of landfilled waste at landfill surface was analyzed based on the physico-chemical characteristics of waste, carbon monoxide (CO) levels, landfill surface temperature (LST). The leachate pollution index was also determined to analyze the leachate quality for three different seasons (monsoon, pre-monsoon and post-monsoon). The regression analysis was carried out to understand the thermal properties (smoldering temperature, smoldering time, ignition temperature etc.) of MSW. The results showed that old waste has a higher tendency to undergo ignition compared to fresh waste. It has also been observed that the lower MC of old waste samples in the range of 3.4% and 18.2% is the most likely cause of early smoldering (106.6-109.5 °C) and ignition (198.6-208.4 °C) of old waste. In pre-monsoon season, CO concentrations for sub-surface (10-30 cm depth) smoldering events (SSE) were observed to be between âˆ¼ 150 to 200 ppm. This CO level substantially dropped to 10 ± 1 ppm in the post-monsoon season. The estimation of the leachate pollution index (LPI) showed an index score of 27.35, 30.47 and 10.71 for pre-monsoon, monsoon and post-monsoon seasons, respectively. The determination of CO levels, increased LST and physico-chemical properties of landfilled waste will greatly assist in the abatement of environmental pollution arising from landfill fires.

Determination of landfill gas generation potential from lignocellulose biomass contents of municipal solid waste.

The presence of heat, methane (CH4) and oxygen in landfill sub-surface causes initiation of spontaneous waste ignition posing severe environmental impacts. A municipal solid waste (MSW) reactor (trough) was designed to monitor landfill gases (LFGs) i.e., CH4 and CO2 and its potential from different waste categories (synthetic waste, fresh waste, 3-month, 6-month, 3-year and 5-year-old waste) collected from open MSW dumpsite. The quantity of cellulose (C), hemicellulose (H) and lignin (L) contents (C + H: L) present in organic waste fraction of each waste category was determined. Results showed that fresh waste which has higher ratio of C + H: L is responsible for maximum CH4 and CO2 generation i.e., 31,660 and 46,078 ml/g of volatile solid, respectively. The ratio of C + H: L observed in fresh waste, 3-month, 6-month, 3-year and 5-year-old waste was 2.62, 1.70, 1.32, 1.21 and 1, respectively. The study also showed that LFG generation is directly proportional to lignocellulose biomass contents present in MSW. Artificial neural network (ANN) modelling was used for the cross validation of CH4 yield (valuable product) which showed ±4% error between experimental and predicted data.