Spatial Variability in Methane Generation and Methane Oxidation Potential of Excavated Waste Residue: Implications for Landfill Gas Modeling and Waste Valorization

Estimation of gas emission and derived electrical power generation from landfills. Trinidad and Tobago as study case

Landfills are one of the major sources of greenhouse gas emissions worldwide. Over the past few decades, gas collection and energy conversion systems have been increasingly implemented in landfills to enhance sustainability and profitability. Accurate methane (CH4) generation rate estimates are essential for designing and optimizing these systems. However, due to the heterogeneity of waste properties, site-specific conditions, and the complex interrelated thermo-hydro-bio-mechanical processes involved, obtaining precise CH4 generation predictions is challenging. Although laboratory and field monitoring data provide valuable insights, obtaining such data is expensive and is often site-specific and non-generalizable. Process-based numerical models, such as the coupled thermo-hydro-bio-mechanical (CTHBM) model developed at the University of Illinois Chicago, offer reliable estimates but are computationally intensive for optimization tasks. Recent advancements in machine learning (ML) based data-driven modeling show promise in handling complex nonlinear datasets. This study evaluates the effectiveness of several ML models, including random forests (RF), extreme gradient boosting (XGB), multi-layer perceptron (MLP), and linear regression (LR), in predicting landfill CH4 generation rates. The data used to train these ML models is generated using the CTHBM model by varying several waste properties. Results indicate that during the rapid methane generation phase, the MLP model demonstrated excellent performance, while XGB also showed reasonable accuracy. In contrast, RF and LR models did not accurately predict methane generation rates during this phase. This study is a preliminary proof of concept for applying ML techniques in landfill CH4 prediction. Further exploration of advanced techniques, such as physics-informed ML, is recommended for scalable and generalizable predictions.

Recent advances in anaerobic digestion has resulted in expansion of sustainable methods for use of waste as energy resources. Conventional methods prove to be uneconomical and environmentally impractical. Moreover, the microbial consortia in anaerobic digestion are temperature dependent and therefore requires investigations on temperature optimization. Therefore, the recent experimental study is being undertaken with the objective in order to assess the effect of temperature on anaerobic biodegradation of food wasted from a hostel campus. The effect of temperature on methane generation rate has also been investigated. The anaerobic digestion study under psychrophilic, mesophilic and thermophilic temperature conditions has been carried out and compared in order to assess the optimum methane production conditions. All the experimental study for anaerobic digestion of food waste has been carried out at optimum F/M (food to mass) ratio of 0.75. The cumulative highest methane production is observed to be 33, 50 and 65 mL of CH4 in reactor R1, R2 and R3 with initial food waste COD dosage of 100, 150 and 200 mg, respectively under mesophilic temperature conditions. The highest biochemical methane potential (BMP) value of 0.94, 0.95 and 0.93 gCH4-COD/gCOD fed in reactor R1, R2 and R3 respectively, under mesophilic temperature conditions. It been observed that for maximum methane generation rate constant of 0.62 d-1 were observed under thermophilic conditions thus has to be highly accelerative process but overall conversion of organic matter to methane is less as compared to mesophilic temperature conditions, this is because free ammonia concentration increases with increasing temperature, by influencing the equilibrium. However, mesophilic conditions provide a more stable environment for the anaerobic digestion process. This may be due to the fact that temperature fluctuations can disrupt the microbial activity and slow down the process, but mesophilic conditions provide a stable environment for the microorganisms to thrive. Therefore, the mesophilic temperature range provides a balance between high reaction rates, stability, and cost-effectiveness, making it the optimal temperature range for anaerobic digestion of food waste. The obtained results in present study will be helpful in implementing on full-scale anaerobic solid waste digesters for enhancing the methane generation under mesophilic temperature conditions with high organic matter removal. Also, under thermophilic conditions the energy requirement for heating proves to be uneconomical.

Towards eliminating systematic errors caused by the experimental conditions in Biochemical Methane Potential (BMP) tests

Environmental methane emissions from seagrass wrack and evaluation of salinity effect on microbial community composition

The main object of this study was to offer information about incoming waste in landfill and to evaluate biochemical methane and hydrogen sulfide potentials of landfill wastes. We examined brick, soil, mixed waste (C&D waste and MSW) samples for the study. The leaching experiments showed that BOD, COD and sulfate were determined in the range of 0~18,816 mg/kg, 85~21,100 mg/kg and 160~1,205 mg/kg, respectively in 6hr extraction test. An accumulated extraction tests for 140day were determined BOD 226~197,219 mg/kg, COD 436~242,588 mg/kg and Sulfate 1,090~25,140 mg/kg. Also, BMP (biochemical methane potential) tests were carried out to examine methane and hydrogen sulfide yields for the 3 different wastes. As a result, methane yield was determined to 262.68 mL <TEX>$CH_4/g$</TEX> VS of MSW and 0~17.75 mL <TEX>$CH_4/g$</TEX> VS in brick, soil and C&D waste. Higher hydrogen sulfide yield was observed to 0.079mL <TEX>$H_2S/g$</TEX> VS in C&D waste. This result indicate that brick and soil could be sources of sulfate, and higher production of hydrogen sulfide could be odor problem and inhibitor of methane production.

International audience

Accelerating the waste mineralization is of great significance to control the settlement of transportation facilities nearby landfills. Mineralized waste can also be used as road construction materials to recycle waste resources and reduce the construction cost of transportation facilities. A biochem‐hydro‐mechanical‐solute migration‐coupled model for describing complex interactions in landfills with high kitchen waste content has been developed. The proposed model can consider large leachate production and landfill gas entrapment due to the fast degradation of kitchen waste. The quantitative effects of three leachate recirculation conditions are investigated in this article via a typical landfill cell. According to the simulation results, introducing methanogen into landfills with leachate recirculation can relieve acidification caused by fast hydrolysis of kitchen waste and speed up the mineralization process of landfills with high kitchen waste content significantly. Furthermore, landfill gas generation potential loss and fast degradation compression should be considered in the implementation of leachate recirculation in landfills with high kitchen waste content, which helps to maintain the operation of transportation facilities nearby landfills and improve the economic and environmental benefits of leachate treatment.

An inventory of agro-food industry organic waste streams with a high potential for biogas transformation was studied in a logistically viable area (Cider Region, Asturias, Spain). Three industries were selected as the most viable ones: livestock, dairy and beverage. The potential for methane production from six wastes (beverage waste, BW; milled apple waste, MA; milk waste, MK; yogurt waste, YG; fats and oils from dairy wastewater treatment, F&O and cattle manure, CM) at five different substrate:inoculum ratios (0.25, 0.50, 0.75, 1.00 and 1.50) was evaluated in laboratory batch assays. Obtained methane yields ranged from 202-549 mL STP CH(4)·g VS waste(-1), and the methane content in biogas ranged from 58-76%. The ultimate practical biochemical methane potentials were slightly affected by the substrate:inoculum ratio. The estimation of the regional fluxes of waste and methane potentials suggests anaerobic digestion as a sustainable solution for the valorization of the organic wastes generated in this Region.

Past research has shown that waste degradation in landfills could be affected by augmenting with manganese peroxidase (MnP) enzyme via increased hydrolysis of organic waste. However, at pr...

FNA-based pre-treatment of primary, secondary and digested sludge

Landfilling is a dominant municipal solid waste (MSW) disposal method in most developing countries. In China, ∼85% of the generated MSW is being disposed of in the landfills. The amount of MSW is growing rapidly with the rate of ∼8–10% annually, which contains a high quantity of moisture and organic matters. The problems of leachate treatment and landfill gas (LFG) emissions are increasing gradually. Reducing the hazard before em-placement, pretreatment of MSW before landfilling has become very important for the conventional landfill. In this study, aerobic pretreatment of mixed MSW was used, and much attention has been given to the natural convection of air in the mixed and unshredded MSW for bioconversion of organic matter (OM). This study is an attempt to investigate aerobic pretreatment suitability for the mixed and unshredded MSW at Beijing. A pilot-scale aerobic pretreatment simulator (APS) was developed at Beishen Shu Landfill in Beijing. To work out the bio-degradation of the OM in the APS, fresh and pretreated MSW samples were collected and analyzed for OM, moisture content, temperature, chemical oxygen demand, total organic carbon, carbon, nitrogen, hydrogen, lignocelluloses, and biochemical methane potential at various stages of the pretreatment. Furthermore, results of the fresh and pretreated MSW are compared. Significant reduction in the observed parameters of the pretreated waste samples is observed. This work demonstrates that pretreatment is significantly effective in reducing the landfill emissions that is leachate and LFG.

BACKGROUNDThe use of microalgae–bacteria systems is particularly attractive for wastewater treatment, and the generated biomass can be further used for methane production. The aim of this study was to evaluate the influence of the hydraulic retention time (HRT) on the organic matter, nutrient removal, settling properties and the biochemical methane potential using a granular microalgae–bacteria system in a high rate algal pond.RESULTSThe primary microorganisms present in the system were constituted by diatoms, green filamentous microalgae and bacteria. At 2 d of HRT the system showed the lowest performance while high chemical oxygen demand (COD) (&gt;92%), ammonium (&gt;85%) and phosphorus (up to 30%) removal was observed at 6 and 10 d of HRT. High settling velocities (up to 8 m h−1) were observed due to agglomerates and granules as dominant structures. The highest methane yield and production rates (348 mL CH4 g−1 VS and 56 mL CH4 g−1 VS d−1) were observed with the biomass obtained at 10 d of HRT.CONCLUSIONFlocs and granules were the dominant structures in the system. High settling velocities and low effluent total suspended solids concentrations were obtained at higher HRT. An inverse relationship between HRT and the biochemical methane potential was observed. © 2016 Society of Chemical Industry

Effect of substrate to inoculum ratio and inoculum type on the biochemical methane potential of solid agroindustrial waste

Organic waste has the potential to produce methane gas as a substitute for petrol-based fuels, while reducing landfilling and possible environmental pollution. Generally, anaerobic digestion (AD) is used only in wastewater treatment plants as a tertiary stage of sewage sludge treatment, generating a fraction of the energy that such process plants require. In this study, four different wastes—food waste (FW), dairy industry waste (DIW), brewery waste (BW), and cardboard waste (CBW)—were tested for biogas production. The biochemical methane potential (BMP) of each sample was evaluated using an automatic methane potential system (AMPTS). Operating parameters such as pH, temperature, total solids, and volatile solids were measured. Experiments on the anaerobic digestion of the samples were monitored under mesophilic conditions (temperature 37 °C, retention time 30 days). Specific methane yields (SMYs), as well as the theoretical methane potential (BMPth), were used to calculate the biodegradability of the substrates, obtaining the highest biodegradability for BW at 95.1% and producing 462.3 ± 1.25 NmL CH4/g volatile solids (VS), followed by FW at an inoculum-to-substrate ratio (ISR) of 2 at 84% generating 391.3 NmLCH4/g VS. The BMP test of the dairy industry waste at an inoculum-to-substrate ratio of 1 was heavily inhibited by bacteria overloading of the easily degradable organic matter, obtaining a total methane production of 106.3 NmL CH4/g VS and a biodegradability index of 24.8%. The kinetic modeling study demonstrated that the best-fitting model was the modified Gompertz model, presenting the highest coefficient of determination (R2) values, the lowest root means square error (RMSE) values for five of the substrates, and the best specific biogas yield estimation with a percentage difference ranging from 0.3 to 3.6%.