Transitions of microbial communities in the solid and liquid phases during high-solids anaerobic digestion of organic fraction of municipal solid waste

Effects of seasonal variations of the physio-chemical properties of municipal solid waste on effective materials and resources recovery

Municipal solid waste (MSW) generation rate is on the rise as it is estimated to reach 3,539 million tonnes by 2050 from the 1,999 million tonnes in 2015. The seasonal variations of the physio-chemical properties of the MSW among others exacerbates its management challenges. This study aimed to conduct in-depth investigations on the seasonal variations of physio-chemical properties of the MSW generated in Kabale Municipality, southwestern Uganda to inform sustainable MSW management systems. This study revealed that this MSW is majorly plastics, with concentrations of 21.45% and 26.94% in the dry and wet seasons, respectively, which presents a more recycling potential for these plastics in the wet season. The biodegradable MSW fraction (food, paper, cardboard and garden trimming wastes), which were 35.6% and 35.34% for the dry and wet seasons, respectively, supports energy recovery from the waste in the form of biogas, with a higher potential in the wet season as supported by its higher volatile solid content for the same of 48.92% as compared to that of the dry season of 34.92%. Based on these findings, it is recommended among others that the masses be sensitized on how to generate biogas from the biodegradable fraction of this MSW.

Tackling municipal solid waste crisis in India: Insights into cutting-edge technologies and risk assessment

Municipal Solid Waste (MSW) management is a pressing global concern, with increasing interest in Waste-to-Energy Technologies (WTE-T) to divert waste from landfills. However, WTE-T adoption is hindered by financial uncertainties. The economic benefits of MSW treatment and energy generation must be balanced against environmental impact. Integrating cutting-edge technologies like Artificial Intelligence (AI) can enhance MSW management strategies and facilitate WTE-T adoption. This review paper explores waste classification, generation, and disposal methods, emphasizing public awareness to reduce waste. It discusses AI's role in waste management, including route optimization, waste composition forecasting, and process parameter optimization for energy generation. Various energy production techniques from MSW, such as high-solids anaerobic digestion, torrefaction, plasma pyrolysis, incineration, gasification, biodegradation, and hydrothermal carbonization, are examined for their advantages and challenges. The paper emphasizes risk assessment in MSW management, covering chemical, mechanical, biological, and health-related risks, aiming to identify and mitigate potential adverse effects. Electronic waste (E-waste) impact on human health and the environment is thoroughly discussed, highlighting the release of hazardous substances and their contribution to air, soil, and water pollution. The paper advocates for circular economy (CE) principles and waste-to-energy solutions to achieve sustainable waste management. It also addresses complexities and constraints faced by developing nations and proposes strategies to overcome them. In conclusion, this comprehensive review underscores the importance of risk assessment, the potential of AI and waste-to-energy solutions, and the need for sustainable waste management to safeguard public health and the environment.

Low-temperature thermal hydrolysis for enhancing sludge anaerobic digestion and antibiotic resistance management: Significance of digester solids retention time

Recently, there has been a growing inclination towards utilizing primary sludge (PS) fermentation prior to anaerobic digestion (AD) in water resource recovery facilities (WRRFs), where sludge liquor containing volatile fatty acids is used for biological nutrient removal. Nevertheless, using a low-temperature thermal hydrolysis process (THP) to improve AD in WRRFs adopting PS fermentation remains an area that has received limited research attention. Here, we studied the impact of THP (90 °C, 90 min) on anaerobic co-digestion of thickened waste activated sludge (TWAS) and fermented primary sludge (FPS) under varying solids retention times (SRTs) in semi-continuous mode. The study involved two THP schemes: scheme 1, where THP was done for both TWAS and FPS, and scheme 2, where THP was applied to TWAS only. The results demonstrated that reducing SRT from 20 to 15 and 10 d leads to decreased methane yield in both schemes. However, THP significantly enhances methane production, showing improvements of up to 37.9 % (scheme 1) and 31.2 % (scheme 2) under a 15-d SRT. Furthermore, while decreasing SRT increased the proliferation of antibiotic resistance genes (ARGs), thermal hydrolysis could effectively reduce most ARGs, indicating its potential to mitigate antibiotic resistance in the AD process. Overall, these results provide useful perceptions regarding the potential adoption of low-temperature THP in WRRFs with PS fermentation.

A strategic review on sustainable approaches in municipal solid waste management andenergy recovery: Role of artificial intelligence,economic stability andlife cycle assessment

The consumption of energy levels has increased in association with economic growth and concurrently increased the energy demand from renewable sources. The need under Sustainable Development Goals (SDG) intends to explore various technological advancements for the utilization of waste to energy. Municipal Solid Waste (MSW) has been reported as constructive feedstock to produce biofuels, biofuel carriers and biochemicals using energy-efficient technologies in risk freeways. The present review contemplates risk assessment and challenges in sorting and transportation of MSW and different aspects of conversion of MSW into energy are critically analysed. The circular bioeconomy of energy production strategies and management of waste are also analysed. The current scenario on MSW and its impacts on the environment are elucidated in conjunction with various policies and amendments equipped for the competent management of MSW in order to fabricate a sustained environment.

Potential of hydrochar/pyrochar derived from sawdust of oriental plane tree for stimulating methanization by mitigating propionic acid inhibition in mesophilic anaerobic digestion of swine manure

VFAs accumulation in anaerobic digestion systems can lead to disturbance of the acid base balance, which has brought major challenges for methane production. Meanwhile, less research explored the potential of biochar derived from wood wastes of oriental plane tree (Platanus orientalis L.) for stimulating methanization in mesophilic anaerobic digestion. In this study, the effects of pyrochar and hydrochar derived from sawdust of oriental plane tree on mesophilic anaerobic digestion of swine manure were compared for the first time. Fourier infrared transform analysis indicated that more functional groups existed on the surface of hydrochar, whereas higher ash content and BET specific surface area were found in pyrochar. The maximum methane production rate during anaerobic digestion was observed in the pyrochar treatment, which increased by 59.5% compared with the control without biochar. Although stimulative effects on dissolved organic carbon and volatile fatty acids production were both observed in the pyrochar and hydrochar treatments, the pyrochar treatment was much easier to trigger multipath methanogenesis and direct interspecific electron transport and subdue propionic acid accumulation compared to the hydrochar treatment. Moreover, redundancy analysis indicated that the variations in acetic acid and dissolved organic carbon were mostly associated with microbial succession. These results suggest that pyrochar has better promoting effects than HC in terms of methane generation and propionic acid inhibition alleviation owing to its special porous structures, functional groups (e.g., C=O, C-O and O-H), and physicochemical properties. These excellent properties play a greater role in recruiting functional archaea and bacteria to regulate the levels of volatile fatty acids and dissolved organic carbon to enhance the methane yield of anaerobic digestion. This study provides novel and valuable information for further engineering applications of pyrochar and hydrochar derived from sawdust of oriental plane tree in energy production and environmental waste treatment.

Carbon cloth amendment for boosting high-solids anaerobic digestion with percolate recirculation: Spatial patterns of microbial communities

The addition of conductive materials in anaerobic digestion (AD) is a promising method for boosting biomethane recovery from organic waste. However, conductive additives have rarely been investigated for the high-solids anaerobic digestion (HSAD). Here, the impact of adding carbon cloth in the solid phase of an HSAD system with percolate recirculation was investigated. Furthermore, spatial patterns of microbial communities in suspended biomass, percolate, and carbon cloth attached biofilm were assessed. Carbon cloth increased biomethane yield from source-separated organics (SSO) by 20% more than the unamended control by shortening the lag phase (by 15%) and marginally improving the methanogenesis rate constant (by ∼8%) under a batch operation for 50 days. Microbial community analysis demonstrated higher relative abundances of the archaeal population in the carbon cloth amended reactor than in unamended control (12%-21% vs. 5%-15%). Compared to percolate and suspension, carbon cloth attached microbial community showed higher enrichment of known electroactive Pseudomonas species along with Methanosarcina and Methanobacterium species, indicating the possibility of DIET-based syntrophy among these species.

Feeding controls H2S production in situ in high solid anaerobic digestion

In this study, a high frequency monitoring method was used to assess how semi-continuous feeding affects H2S production in high solid anaerobic digestion. The results showed that H2S characteristics at a monitoring frequency of 1 point/3 h were different to that of 1 point/24 h, its concentration decreased from 3449 ± 227 mg/m3 at 0 h to 298 ± 45 mg/m3 at 3 h. H2S concentration was negatively correlated with volatile fatty acids (VFAs), and oxidation reduction potential (ORP). 72-82% of H2S reduction in the first 3 h resulted from the introduction of O2 during feeding, and 18-28% of that was closely related to the production of a large quantity of soluble acidic matter, such as VFAs. A more accurate H2S release model was established according to the content of VFAs. Totally, this study implies that feed carrying air is a promising method for in situ control of H2S production in anaerobic digestion.

Achieving biogas production and efficient pollutants removal from nitrogenous fertilizer wastewater using combined anaerobic digestion and autotrophic nitrogen removal process

Nitrogenous fertilizer was massively utilized during agricultural production process, which led to the discharge of large amount of nitrogenous wastewater with low C/N ratio. In this study, anaerobic digestion combined with subsequent Completely autotrophic nitrogen removal over nitrite (CANON) process was adopted for treating nitrogenous fertilizer wastewater. The reactor performances and the microbial community structure were analyzed. Results showed that COD was mainly removed by anaerobic digestion, with the COD removal efficiency as 98.4%, and nitrogen was effectively removed via CANON integrating with partial denitrification, with the removal efficiency as 96.3%. The COD, ammonia and total nitrogen in the effluent of the combined process were 3.7, 2.9 and 7.4 mg L^-1, respectively. Methanothrix (43.2%) and Methanomassiliicoccus (34.0%) were detected as the dominant methane production archaea, while Nitrosomanas (10.4%), Candidatus Kuenenia (13.8%) and Truepera (2.8%) were detected as the functional bacteria for nitrogen removal, when treated the nitrogenous fertilizer wastewater.

High-solids anaerobic digestion of organic fraction of municipal solid waste: Effects of feedstock to inoculum ratio and percolate recirculation time

The effects of feedstock to inoculum (F:I) ratio and percolate recirculation time (PRT) were studied for the high-solids anaerobic digestion (HSAD) of the organic fraction of municipal solid waste (OFMSW). Six mesophilic HSAD systems were operated at different F:I ratios (1 to 3 kg VS/kg VS; PRT = 2.5 h/d) and PRTs (1.5 to 3.5 h/d; F:I = 2 kg VS/kg VS). The F:I ratio of 1 provided up to 86% of the theoretical methane potential of OFMSW. In contrast, F:I ratio of 3 provided only 34% methane recovery due to volatile fatty acids (VFAs) accumulation and pH drop. Despite F:I ratio of 2 could provide 70% methane recovery, it could enable almost 45% higher organics processing capacity (VS basis) and lower solids washout during percolate recirculation, as compared to the F:I ratio of 1. However, different examined PRTs showed marginal impacts on methane yields with comparable changes in profiles of percolate characteristics.

From the environment to the cells: An overview on pivotal factors which affect spreading and infection in COVID-19 pandemic

Several factors ranging from environmental risks to the genetics of the virus and that of the hosts, affect the spread of COVID-19. The impact of physicochemical variables on virus vitality and spread should be taken into account in experimental and clinical studies. Another avenue to explore is the effect of diet and its interaction with the immune system on SARS-CoV-2 infection and mortality rate. Past year have witnessed extensive studies on virus and pathophysiology of the COVID-19 disease and the cellular mechanisms of virus spreading. However, our knowledge has not reached a level where we plan an efficient therapeutic approach to prevent the virus entry to the cells or decreasing the spreading and morbidity in severe cases of disease. The risk of infection directly correlates with the control of virus spreading via droplets and aerosol transmission, as well as patient immune system response. A key goal in virus restriction and transmission rate is to understand the physicochemical structure of aerosol and droplet formation, and the parameters that affect the droplet-borne and airborne in different environmental conditions. The lifetime of droplets on different surfaces is described based on the contact angle. Hereby, we recommend regular use of high-quality face masks in high temperature and low humidity conditions. However, in humid and cold weather conditions, wearing gloves and frequently hand washing, gain a higher priority. Additionally, social distancing rules should be respected in all aforementioned conditions. We will also discuss different routes of SARS-CoV-2 entry into the cells and how multiple genetic factors play a role in the spread of the virus. Given the role of environmental and nutritional factors, we discuss and recommend some strategies to prevent the disease and protect the population against COVID-19. Since an effective vaccine can prevent the transmission of communicable diseases and abolish pandemics, we added a brief review of candidate SARS-CoV-2 vaccines.

High-rate blackwater anaerobic digestion under septic tank conditions with the amendment of biosolids-derived biochar synthesized at different temperatures

Septic tanks have been widely used for blackwater treatment in developing countries, while high-rate septic tanks with improved methane recovery are yet to be achieved. This study investigated biosolids-derived biochar (synthesized at 300℃, 425℃, and 550℃) as an additive for developing high-rate septic tanks. The experiments were conducted with anaerobic bioreactors operated with synthetic blackwater under septic tank conditions. All biochar amended reactors demonstrated a steady increase in daily methane production for increasing OLR from 0.08 to 3 g COD/L/d. The control reactor showed significant process disturbances at OLRs ≥ 2 g COD/L/d with an accumulation of volatile fatty acids followed by pH drop. At OLR of 3 g COD/L/d, the daily methane production from biochar amended reactors was ~ 4.3 times higher than the control (300 vs. 70 mL per day). Biochar addition established a robust microbiome consisted of a higher abundance of hydrogenotrophic and acetoclastic methanogens and hydrogen-producing fermentative bacteria.

Fate of disposable face masks in high-solids anaerobic digestion: Experimental observations and review of potential environmental implications

Face masks became a part of our daily life amid the global COVID-19 (SARS-CoV-2) pandemic. Most of the face masks are made for single-use and primarily disposed of in garbage bins with other non-recyclable wastes. To date, little is known about how disposable face masks in municipal solid waste (MSW) would interfere with high-solids anaerobic digestion (HSAD) in waste management facilities. Here, we first report preliminary results from a lab experiment conducted with the organic fraction of municipal solid waste (OFMSW) amended with used disposable face masks. The lab-scale HSAD systems were operated with percolate recirculation comparable to commercial HSAD systems typically used for full-scale processing of OFMSW. The results suggested that the presence of face masks in OFMSW could negatively affect methane productivity and kinetics. In the digesters amended with face masks, total cumulative methane production decreased by up to 18%, along with a 12-29% decrease in maximum methane production rates than the control digester (without face masks). Moreover, lag phases increased by 7-14%. The results also suggested that the type of polymeric materials used in face masks would be more critical than their total number/loading in the digester, which warrants further investigation. The visual inspection of digestate showed that the face masks were mostly undegraded after 40 days of operation. Much remains unknown about how the undegraded face masks will affect the digestate management practices, such as composting, land application, and landfilling. However, the review of existing literature suggested that they can be a potential source of plastic and microplastic pollution and amplify transmission of antibiotic resistance genes to the ecosystem. In summary, this study underscores the importance of developing safe and reliable disposal guidelines and management plans for single-use face masks.