Impact of municipal solid waste landfill leachate on biogas production rate

Promoting synergy among environmental and economic performances in food waste treatment by optimizing biogas residue management practices

Improper management of biogas residue (BR) can reduce sustainability in the food waste treatment industry. To address this issue, a comprehensive evaluation framework, based on emergy analysis, carbon emissions and economic analysis, is proposed in this study, to explore how different BR disposal practices affect the comprehensive performance of the industry. A food waste treatment plant in Henan Province, China (anaerobic digestion (AD) + BR landfilling: Scenario 1 [S1]), and two alternative scenarios (S2: AD + BR incineration; S3: AD + BR composting) are investigated as a case study. Compared with S1, S2 and S3 reduce carbon emission intensity by 16.93 % and 22.92 %, respectively; S2 enhances environmental sustainability by 48.63 % while S3 reduces the environmental sustainability by 11.64 %. Furthermore, S2 and S3 improve economic benefits by 8.70 % and 43.48 %, respectively. Generally, S2 and S3 increase the system coordination degree by 9.35 and 9.52 times, respectively. Therefore, BR management should be devoted to improving the resource structure in the future.

Composting of organic fraction of municipal solid waste in a three-stage biodegradable composter

The increase in municipal solid waste (MSW) generation rate has been a growing concern for the modern-day era. On-site composting has been the promising clean-tech alternative to managing biodegradable organic waste (BOW) in MSW. It allows sustainable and compact solutions for the in-house treatment of MSW, reducing the overall burden on landfill and treatment facilities. In this manuscript, a batch and pilot scale performance assessment study were conducted for BOW using a three-stage vertical drum composter (R1, R2, R3). The study aims to determine the impact of aeration, turning mechanisms, bulking agents, degradation rate, and process parameters on compost quality. It was found that physical-chemical properties such as bulk density (0.3 g/cm3), pH (∼7), temperature (<50 °C), moisture content (<20 %), total volatile solids (33 %), electrical conductivity (<4 dS/m) and carbon/nitrogen ratio (∼16) of final compost was under the prescribed limit. We conclude that the provision for aeration via perforated vents and regular turning mechanisms substantially impacted the quality of compost. Compost maturity was determined using humic to fulvic acid (HA/FA) ratio and germination index (GI). The HA/FA and GI of final compost in R1, R2, and R3 were found to be 6.21, 7.22, and 6.90; and 85.3 %, 90.4 %, and 87.6 %, respectively. During the degradation process, the increasing trend of HA/FA ratio (5-8) and GI (>85 %) showed that the compost quality was rich in nutrients and soil-conditioning properties. Based on the kinetic study, it was conclusive that adding bulking agents in R3 (0.0078 day-1) and R4 (0.0098 day-1) contributed to high degradation rates, underlining the value of creating a porous structure that enhances microbial activity. The findings can be a resource for waste generators, managers, technocrats, and policymakers to tackle the issues related to in-house management and treatment of MSW.

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.

Enhancing biomethanation performance through co-digestion of diverse organic wastes: a comprehensive study on substrate optimization, inoculum selection, and microbial community analysis

A blend of organic municipal solid waste, slaughterhouse waste, fecal sludge, and landfill leachate was selected in different mixing ratios to formulate the best substrate mixture for biomethanation. Individual substrates were characterized, and the mixing ratio was optimized with the help of a response surface methodology tool to a value of 1:1:1:1 (with a C/N ratio of 28±0.769 and total volatile fatty acid (VFA) concentration of 2500±10.53 mg/L) to improve the overall biomethanation. The optimized blend (C/N ratio: 28.6, VFA: 2538 mg/L) was characterized for physicochemical, biological, and microbial properties and subjected to anaerobic digestion in lab-scale reactors of 1000 mL capacity with and without the addition of inoculum. The biogas yield of individual substrates and blends was ascertained separately. The observed cumulative biogas yield over 21 days from the non-inoculated substrates varied between 142±1.95 mL (24.6±0.3 ml/gVS) and 1974.5±21.72 mL (270.4±3.1 ml/gVS). In comparison, the addition of external inoculation at a 5% rate (w/w) of the substrate uplifted the minimum and maximum cumulative gas yield values to 203±9.9 mL (35.0±1.6 mL/gVS) and 3394±13.4 mL (315.3±1.2 mL/gVS), respectively. The inoculum procured from the Defence Research and Development Organisation (DRDO) was screened in advance, considering factors such as maximizing VFA production and consumption rate, biogas yield, and digestate quality. A similar outcome regarding biogas yield and digestate quality was observed for the equivalent blend. The cumulative gas yield increased from 2673±14.5 mL (373.7±2.2 mL/gVS) to 4284±111.02 mL (391.47±20.02 mL/gVS) over 21 days post-application of a similar dosage of DRDO inoculum. The 16S rRNA genomic analysis revealed that the predominant bacterial population belonged to the phylum Firmicutes, with the majority falling within the orders Clostridiales and Lactobacillales. Ultimately, the study advocates the potential of the blend mentioned above for biomethanation and concomitant enrichment of both biogas yield and digestate quality.

Analysis of landfill leachate promoting efficient application of weathered coal anaerobic fermentation

This research aimed to develop a new method for clean utilization and treatment of landfill leachate and solid waste weathered coal. Landfill leachate and weathered coal were adopted for combined anaerobic fermentation for methane production. The characteristics of microbial community, mechanism of biological methane production, and utilization characteristics of fermentation broth and solid residue for co-fermentation were analyzed through metagenomics, soluble organic matter detection and thermogravimetric (TG) analysis. The obtained results revealed that combined anaerobic fermentation increased methane production by 80.1%. Syntrophomonas, Salipiger, Methanosaeta and Methanothrix were highly correlated. Gene abundances of 2-oxoacid ferredoxin oxidoreductase and enolase were increased in methane conversion pathway mainly by acetic acid. Pyruvate-ferroredoxin oxidoreductase, 2-oxoglutarate synthase and succinate dehydrogenase acetate synthase intensified electron transfer pathways among microorganisms. Fulvic acid, tyrosine and tryptophan contents were high in fermentation broth. Volatile decomposition temperature, ignition point and residual char combustion temperature of residual coal were decreased and combustion was more stable. The obtained results showed that the co-fermentation of landfill leachate and weathered coal improved biological methane gas production, degraded weathered coal and improved combustion performance, which provided a new idea for weathered coal clean utilization.

Landfill bacteriology: Role in waste bioprocessing elevated landfill gaseselimination and heat management

This study delves into the critical role of microbial ecosystems in landfills, which are pivotal for handling municipal solid waste (MSW). Within these landfills, a complex interplay of several microorganisms (aerobic/anaerobic bacteria, archaea or methanotrophs), drives the conversion of complex substrates into simplified compounds and complete mineralization into the water, inorganic salts, and gases, including biofuel methane gas. These landfills have dominant biotic and abiotic environments where various bacterial, archaeal, and fungal groups evolve and interact to decompose substrate by enabling hydrolytic, fermentative, and methanogenic processes. Each landfill consists of diverse bio-geochemical environments with complex microbial populations, ranging from deeply underground anaerobic methanogenic systems to near-surface aerobic systems. These kinds of landfill generate leachates which in turn emerged as a significant risk to the surrounding because generated leachates are rich in toxic organic/inorganic components, heavy metals, minerals, ammonia and xenobiotics. In addition to this, microbial communities in a landfill ecosystem could not be accurately identified using lab microbial-culturing methods alone because most of the landfill's microorganisms cannot grow on a culture medium. Due to these reasons, research on landfills microbiome has flourished which has been characterized by a change from a culture-dependent approach to a more sophisticated use of molecular techniques like Sanger Sequencing and Next-Generation Sequencing (NGS). These sequencing techniques have completely revolutionized the identification and analysis of these diverse microbial communities. This review underscores the significance of microbial functions in waste decomposition, gas management, and heat control in landfills. It further explores how modern sequencing technologies have transformed our approach to studying these complex ecosystems, offering deeper insights into their taxonomic composition and functionality.

Sustainable in situ ammonia recovery from municipal solid waste leachate in a single-stream microbial desalination cell

Municipal solid waste (MSW) leachate is one of the most hazardous waste streams leading to great potential risk to environment, and a renewable resource with high concentrations of organic contaminant and ammonia. High energy consumption and chemical input are still the challenges for ammonia recovery from MSW leachate. Here, a single-stream microbial desalination cell (SMDC) was successfully developed for simultaneous energy extraction from organic contaminant and in-situ energy utilization for ammonia recovery. 70% of the organic contaminant from the actual MSW leachate was removed, and 24.9% of the total ammonia was recovered as high-purity (NH4)2SO4. The additional desalination chamber introduced into the SMDC can potentially enhance the NH4+ migration that was determined by the NH4+ concentration gradient and electric field. More than 30% of the total nitrogen was lost, as revealed by nitrogen mass balance analysis, probably resulting from the anodic denitrification process driven by denitrifying microorganisms, e.g., Thauera, which thrived in the anode chamber. Concomitantly, the chemical input for ammonia stripping can be reduced by up to 68% due to the relatively low buffer capacity of the catholyte and the OH- production from the cathode reaction. This SMDC can be an effective and environmentally sustainable solution for MSW leachate treatment and resource recovery.

An investigation on mobility of heavy metals for assessing the reusability of soil-like material reclaimed from mining of municipal solid waste dumpsites

Landfill mining, often referred to as "bio-mining", enables the recovery of resources, including combustible, compostable, and recyclable fractions from landfills. However, most of the materials mined from old landfills mainly consist of soil-like materials (SLM). The reuse of SLM depends on the concentration of contaminants, such as heavy metals, soluble salts, etc. A sound risk assessment requires sequential extraction to determine the bioavailability of heavy metals. This study focuses on the mobility and chemical speciation of heavy metals in SLM from four old municipal solid waste dumpsites in India by performing selective sequential extraction. Additionally, the study compares the results with those of four previous investigations to identify international similarities. It has been observed that Zn was mainly available in the reducible phase (average 41%), whereas Ni and Cr proved to have the highest distribution in the residual phase (64% and 71%, respectively). Pb analysis showed a large portion in the oxidizable phase (39%), while Cu was mainly present in the oxidizable (37%) and residual (39%) phases. Similarities with previous investigations were observed for Zn (primarily reducible 48%), Ni (residual 52%), and Cu (oxidizable 56%). Correlation analysis showed that Ni correlated with all heavy metals (ρ = 0.71-0.78), except with Cu. The present study suggested that Zn and Pb are associated with a high risk of pollution due to their maximum distribution in the bioavailable phase. The findings of the study can be used to assess the heavy metal contamination potential of SLM prior to its reuse in offsite applications.