Digestion Of Municipal Solid Waste Research Articles

Anaerobic digestion of municipal solid waste produced by the city of Algiers using life cycle assessment

This study analyses the life cycle assessment of anaerobic digestion process of municipal solid waste management (MSWM) produced by Algiers city. Some keys parameters of the processes are then modified to analyze the "hot spots" and perform a sensitivity analysis to identify their influence on the results. Data for the inventory came from actual city facilities, and background process information came from Eco invent version 3.1 of SimaPro 8.1 software. The analyzed process contribution indicates that the global warming potential is affected by the anaerobic digestion because of the NOx and CO emissions from the thermal processes of biogas burning and fuel oil combustion for digesters heating. Furthermore, plastics recycling is environmentally beneficial because of net savings. The energy valorization of biogas produces the least amount of environmental damage, eliminating 403.06 kg CO2 eq/ton of waste, saving 18.2 E+09 MJ/ton of fossil fuels, and producing 2.8 E+08 kWhel/year, or 6% of the city's annual electricity consumption.

Optimizing Biogas Production and Digestive Stability through Waste Co-Digestion

This study aimed to enhance the nutrient balance of municipal solid waste (MSW), characterized by a high carbon-to-nitrogen (C/N) ratio, which is a critical factor in the anaerobic digestion process. The investigation involved the addition of MSW, which is rich in carbon content, to food waste (FW) with high nitrogen content. The goal was to determine an optimal co-substrate mixing ratio of MSW and FW for anaerobic co-digestion at mesophilic temperatures, aiming to improve process stability and performance to achieve higher biogas yield. The co-digestion experiments encompassed five mixing ratios of MSW and FW with C/N ratios of 20, 25, 30, 35, and 40 under mesophilic conditions in a laboratory. The results indicated that the highest specific biogas yield, reaching 827 L/kg VS, was attained when the co-substrate feedstock had a balanced C/N ratio of 20, surpassing the 520 L/kg vs. obtained from MSW digestion alone. As the proportion of MSW increased in the co-substrate mixing feedstock, the biogas production rate decreased. Additionally, the study explored the optimal substrate-to-inoculum (S/I) ratio, focusing on the co-substrate feedstock with a C/N ratio of 20. Four S/I ratios (0.5, 1.0, 1.5, and 2.0) were examined, revealing that the highest specific biogas yield, at 642 L/kg VS, occurred at an S/I ratio of 0.5. An accumulation in volatile fatty acids (VFAs) was observed at higher S/I ratios, attributed to the lower abundance of inoculum microorganisms in the anaerobic digestion process. Overall, the findings suggested that the optimum C/N ratio for co-digestion of MSW and FW falls within the range of 20–25/1, while the preferred S/I ratio is 0.5.

Meso- and thermophilic posttreatment of press water coming from a thermophilic municipal solid waste digester.

An efficient biogas production out of organic (waste) materials is important to contribute to a carbon-neutral future. In this study, thermophilic press water (PW) coming from an organic fraction of the municipal solid waste digester was further digested in a thermo- and mesophilic posttreatment approach using two semicontinuous 14 L digesters. The results showed that the PW can still have considerable high biogas potential-at least during the touristic high season in central Europe. The change in temperature led to an increase in volatile fatty acid concentrations and a decrease in biogas production in the mesophilic approach in the first days. However, the losses in biogas production at the beginning could be compensated thus there were no considerable differences in biogas production between thermo- and mesophilic posttreatment at the end of incubation. This can most probably be contributed to a change in the microbial community, and potentially problematic intermediates like valerate could be better degraded in the mesophilic reactor. Especially the abundanceof representatives of the phylum Bacteroidota, like Fermentimonas spp., increased during mesophilic anaerobic digestion.

Modification and extension of the anaerobic model N°2 (AM2) for the simulation of anaerobic digestion of municipal solid waste

Anaerobic digestion is a complex process whose understanding, optimization, and development require mathematical modeling to simulate digesters' operation under various conditions. Consequently, the present work focuses on developing a new and improved model called "AM2P" derived from the AM2 model. This new model incorporates surface-based kinetics (SBK) into the overall simulation process to transform the system into three stages: hydrolysis, acidogenesis, and methanogenesis. Experimental data from our previous work were used to identify the AM2 and AM2P models' parameters. Simulations showed that the AM2P model satisfactorily represented the effect of the hydrolysis phase on the anaerobic digestion process, since simulated values for acidogenic (X1) and methanogenic (X2) biomass production revealed an increase in their concentration as a function of particle size reduction, with a maximum concentration of the order of 5.5 g/l for X1 and 0.8 g/l for X2 recorded for the case of the smallest particle size of 0.5 cm, thus accurately representing the effect of substrate particle disintegration on biomass production dynamics and enabling the process of anaerobic digestion to be qualitatively reproduced. The AM2P model also provided a more accurate response, with less deviation from the experimental data; this was the case for the evolution of methane production, where the coefficient of determination (R2) was higher than 0.8, and the root-mean-square error (RMSE) was less than 0.02.

Enhancing biogas production in anaerobic digestion of MSW with addition of bio-solids and various moisture sources

This study aimed to investigate the influence of moisture content on the anaerobic digestion of municipal solid waste (MSW) with the addition of leachate, tap water, wastewater, and sewage sludge. To accomplish this, ten sets of batch experiments were conducted to examine the impact of these various moisture sources on the rate of degradation, indicated by cumulative biogas yield, volatile solids (VS) and total solids (TS) removal. The addition of sludge with leachate and wastewater to MSW resulted in biogas yields that were approximately 30 % higher than the biogas yield from MSW and wastewater alone. Based on the observations of VS removal, it was observed that the addition of sludge degraded about half of the substrate. Therefore, it was observed that the addition of 10 % sludge with leachate and wastewater to MSW provides the best outcomes. The lowest biogas yield was observed with the mixing of tap water with MSW. Further, it was determined that the optimal moisture content for MSW degradation should be greater than 75 % of field capacity (FC). The cumulative biogas yield decreased by more than 50 % when the moisture contents decreased from 100 % to 50 % of FC. The reduction in biogas production at low moisture contents is attributed to limited mass transfer, and the hydrolysis rate also slightly decreases with an increase in total solids. The kinetic study was also carried out using the first order, modified Gompertz, Transference, and Logistic models, and the predicted cumulative biogas yield was compared with the experimental data. The modified Gompertz and Logistic models showed the best fit (R2 ≥ 0.994) with the experimental data for all the sets. The sludge, leachate, and wastewater are produced in large quantities in developing countries, and this study may provide a possible utilization strategy of these wastes for accelerated degradation of MSW.

Application of the AM2 Model to Simulate Anaerobic Digestion of Municipal Solid Waste

Anaerobic digestion is a promising technology due to its significant economic and environmental potential. Nevertheless, its development is a substantial challenge for researchers since this biochemical process is difficult to predict due to the many reactions involved. Thus, mathematical modeling becomes necessary to analyze the fermentation process and determine the complex kinetic parameters to identify and predict the system's performance under the most varied conditions. This research aims to apply the AM2 model to simulate the anaerobic digestion process of municipal solid waste. The experimental results obtained from our previous research work were used for identifying the parameters of the AM2 model and for its validation by the cross-validation method. Simulations showed that the model could effectively reproduce the dynamics of the evolution of the anaerobic digestion process with reasonable accuracy.

Design, multi-aspect analyses, and multi-objective optimization of a novel trigeneration system based on geothermal and municipal solid waste energies

The study of multi-source energy systems, due to higher performance and producing various products, is an interesting subject. The current study designs a multi-source system including a gas turbine cycle with CH4 and municipal solid waste digester, a geothermal system with an organic Rankine, organic flash, and a double-effect absorption refrigeration subsystem to produce power, cooling, and heating loads simultaneously. The thermodynamic and economic analyses are utilized to estimate the system’s performance and multi-objective optimization has been applied to define the optimum state of the system concerning two scenarios. The results indicate that the system provides 423.4 kW net power, 384.7 kW heating load, and 106.3 kW cooling load with 39.28% exergetic efficiency and 6.67 years payback period. These values are improved to 664.9 kW net power, 446.5 heating load, 42.01% exergetic efficiency, and 6.05 years payback period at the best optimum scenario. The sensitivity analysis reveals that the air compressor’s pressure ratio mainly impacts the net power, heating load production, and net present value. The cooling load production and exergetic efficiency are mainly affected by the air preheater effectiveness variation.

Medium chain length polyhydroxyalkanoate produced from ethanol by Pseudomonas putida grown in liquid obtained from acidogenic digestion of organic municipal solid waste

Production of medium chain length polyhydroxyalkanoate (mcl-PHA) up to about 6 g.L−1 was obtained by feeding ethanol to Pseudomonas putida growing in liquid obtained from acidogenic digestion of organic municipal solid waste. Washing the wet, heat-inactivated Pseudomonas cells at the end of the fermentation with ethanol obviated the need of drying the biomass and enabled the removal of contaminating lipids before solvent-mediated extraction of PHA. Using ‘green’ solvents, 90 to near 100% of the mcl-PHA was extracted and purities of 71–78% mcl-PHA were reached already by centrifugation and decantation without further filtration for biomass removal. The mcl-PHA produced in this way consists of 10–18% C8, 72–78% C10 and 8–12% C12 chains (entirely medium chain length), has a crystallinity and melting temperature of ∼13% and ∼49 °C, respectively, and is a stiff rubberlike, colourless material at room temperature.

Experimental and modelling optimisation of sustainable techniques for the pre-treatment of the organic fraction municipal solid waste to improve anaerobic digestion

The study investigated and compared the anaerobic digestion (AD) of real organic fraction municipal solid waste (OFMSW) prior pre-treated with four types of pre-treatments: mechanical, thermal, hydrodynamic-cavitation (HC), and ultrasound (US). The tested pre-treatments and AD configurations were selected through Design of Experiments and then regression models were built to find the most promising configurations in terms of biogas production and energetic sustainability of the whole process. The novelty of the research is the simultaneously study of the working conditions of the pre-treatments; and AD parameters like the two origins of the inoculum, its incubation time, and the substrate: inoculum ratio (SI).The results demonstrated that the best configurations of pre-treatments and AD were the ones performed with thermal pre-treatment at 120 °C for 45 min (with inoculum incubation of 10 d at substrate: inoculum (SI) ratio of 2:1) and HC at 55 °C (with inoculum incubation of 10 d at SI of 3:1). The thermal, and to some extent the mechanical pre-treatment, evidenced as significant the interaction between the pre-treatment time and the inoculum incubation time. AD of US-OFMSW achieved the lowest performances since inhibition occurred, probably due to the lignocellulosic inhibitors release after ultrasound pre-treatment.

Techno-economic analysis of a biogas-to-methanol process: Study of different process configurations and conditions

Bio-methanol produced from renewable resources, such as biogas, represents an interesting low carbon energy carrier due to its versatility. Few publications are available on the topic and techno-economic assessments focusing on the production of renewable methanol are needed to properly design such plants and understand their potential. To this purpose, a detailed techno-economic analysis of a 20 MWLHV biogas to methanol process via steam reforming is presented in this work. The process was designed to treat biogas produced via anaerobic digestion of municipal solid waste and be autonomous from a thermal viewpoint. The analysis included the comparison of three different process configurations, differing in the presence and position of the carbon dioxide separation unit. Sensitivity analyses were carried out on key process parameters, namely MeOH synthesis loop Recycle Ratio (RR, in the interval 3−7), methanol reactor pressure (pMeOH; 50–95bar) and Gas Hourly Space Velocity (GHSV,4000−8000; Nm3h·mCAT3). The best plant configuration was achieved when carbon dioxide separation was performed upstream of the reformer, which allowed to achieve higher carbon and fuel efficiencies. In the base case (RR=5, pMeOH=95bar, and GHSV=4000Nm3h·mCAT3), such configuration produced 2480kg/h of methanol, with a carbon and fuel efficiency equal to 51.4% and 72.2% respectively and a levelized cost of methanol of 378.0€/t. Reactor pressure considerably affected process profitability, whereas GHSV and RR had little impact on process economics. When methanol reactor pressure was decreased to 50bar, methanol production kept almost constant, but overall costs were remarkably lower. This led to a higher profitability, with a levelized cost of methanol of about 357.7€/t.

Determination of the energy efficiency of a flat reflector solar air heating collector with a heat accumulator

The article presents an improved scheme and pilot-industrial copy of a flat reflector solar air heating collector with a heat accumulator. The heat balance equation of the flat reflector solar air heating collector with heat accumulator is constructed, and its energy efficiency is based on it. Considering the local climatic and meteorological characteristics of the city of Karshi, its useful performance coefficient was determined based on the experiment conducted on the flat reflector solar air heating collector with a heat accumulator. This designed device is proposed as an active solar heating system for the anaerobic digestion of municipal solid waste based on energy and resource efficiency. As a result of experimental studies, a flat reflector solar air heating collector with a heat accumulator’s high energy efficiency was determined in the heating heat carriers (air up to + 75°C and heat accumulators up to +85°C) on February 24, 2023.

Bioenergy, Electricity, Biogas Production, and Emission Reduction Using the Anaerobic Digestion of Organic Municipal Solid Waste in Campinas, One of the Largest Brazilian Cities

Anaerobic digestion (AD) is an attractive process for bioenergy production and is considered to be an alternative way to reduce landfills. AD improves municipal solid waste (MSW) management, representing a profitable application of the circular economy and could reduce environmental impact. The methane (CH4) potential of four different organic fractions of MSW—paper (PFW), garden (GFW), food (FFW), and a mixture of these three (OFMSW)—via AD was used to investigate the energy potential and the economic and environmental impact of Campinas. Theoretical and experimental biochemical methane potential (BMP) and substrate biodegradability were determined using the Buswell and Müller equation and the VDI 4630 method. The Gompertz model was used to predict the kinetics of the biochemical processes. The highest experimental BMP (410.7 NmLCH4 gVS−1) and biodegradability (86.6%) were reached with OFMSW. OFMSW can avail an energetic potential of approximately 119 GWh year−1, with a biomethane production equivalent to diesel at 49.9 × 103 m3 year−1, hence, potentially curtailing the CO2 emissions of heavy-duty vehicles by almost 133 kt year−1. The electricity demand for approximately 11% of the households in Campinas could be met by the biogas produced by OFMSW, thus increasing local energy security. The replacement of fossil diesel with biomethane to fuel garbage trucks in Campinas could reduce 25% of the diesel demand.

Co-Treatment of Landfill Leachate and Liquid Fractions of Anaerobic Digestate in an Industrial-Scale Membrane Bioreactor System

The management of the liquid fraction of digestate produced from the anaerobic digestion of biodegradable municipal solid waste is a difficult affair, as its land application is limited due to high ammonium concentrations and the municipal waste that water treatment plants struggle to treat due to high pollutant loads. The amount of leachate and the pollutant load in the leachate produced by landfills usually decreases with the time, which increases the capacity of landfill leachate treatment plants (LLTPs) to treat additional wastewater. In order to solve the above two challenges, the co-treatment of landfill leachate and the liquid fraction of anaerobic digestate in an industrial-scale LLTP was investigated along with the long-term impacts of the liquid fraction of anaerobic digestate on biocoenosis and its impact on LLTP operational expenses. The co-treatment of landfill leachate and liquid fraction of anaerobic digestate was compared to conventional leachate treatment in an industrial-scale LLTP, which included the use of two parallel lanes (Lane-1 and Lane-2). The average nitrogen removal efficiencies in Lane-1 (co-treatment) were 93.4%, 95%, and 92%, respectively, for C/N ratios of 8.7, 8.9, and 9.4. The average nitrogen removal efficiency in Lane-2 (conventional landfill leachate treatment), meanwhile, was 88%, with a C/N ratio of 6.5. The LLTP’s average chemical oxygen demand (COD) removal efficiencies were 63.5%, 81%, and 78% during phases one, two, and three, respectively. As the volume ratios of the liquid fraction of anaerobic digestate increased, selective oxygen uptake rate experiments demonstrated the dominance of heterotrophic bacteria over ammonium and nitrite-oxidising organisms. The inclusion of the liquid fraction of anaerobic digestate during co-treatment did not cause a significant increase in operational resources, i.e., oxygen, the external carbon source, activated carbon, and energy.

Development of a MSW-fueled sustainable co-generation of hydrogen and electricity plant for a better environment comparing PEM and alkaline electrolyzers

Efficient conversion of Municipal Solid Waste (MSW) into useful energy by anaerobic digestion is a sustainable method which received growing interest, particularly for small-scale decentralized energy systems. This paper aims at development of an efficient combined cogeneration cycle for production of electricity and hydrogen from biogas generated using anaerobic digestion of MSW. When it comes to the topping cycle, the proposed system makes use of a micro gas turbine, whose waste heat is converted to electricity by an absorption power cycle. This additional electricity is provided to a water electrolyzer, which uses it to generate hydrogen. Two types of electrolyzers, including the Proton Exchange Membrane Electrolyzer (PEME) and the Alkaline Electrolyzer (AE) are considered, and their performances (as a component of the overall suggested combined systems) are compared from economic and thermodynamic viewpoints. The CO2 emission index is also addressed, and tri-objective optimization based on exergy, cost, and emission indices is carried out to compare the two systems. Obtained results indicated important outcomes, including that the system integrated with PEME is superior in terms of exergetic performance and emissions, whereas the system with AE is superior in terms of economics. The former has a 3.0% greater efficiency and a 3.3% lower emissions at optimal point established by tri-objective optimization, while it has a 9.3% higher levelized product cost.

Biomethane enhancement using reduced graphene oxide in anaerobic digestion of municipal solid waste

The present research investigated the impact of reduced graphene oxide (rGO) addition on the semi-continuous anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) in the range of 0.5–10 gVolatileSolid(VS)/Lreactorday organic loading rates (OLR). Adding rGO enhanced the rate and yield of biomethane production, and the maximum biomethane increment rate was obtained as 110% at an OLR of 4.0 gVS/Lreactorday. However, after increasing the OLR to 6 gVS/Lreactorday, there was a dramatic decrease in biomethane production because of volatile fatty acid (VFA) accumulation. Methanotrix is the predominant archaeal genus at OLRs lower than 6 gVS/Lreactorday in reactors (89–97%). An increment in biomethane production was associated with the higher abundance of the Methanothrix genus in the rGO-supported reactor (rG) than in the control reactor (rC).

Effect of inoculum origin and substrate-inoculum ratio to enhance the anaerobic digestion of organic fraction municipal solid waste (OFMSW)

This study evaluated the key role of inoculum in mesophilic anaerobic digestion (AD) of Organic Fraction of Municipal Solid Waste. The effect of two different inocula, the mesophilic digestate of wastewater activated sludge (WAS) and the mesophilic digestate of cow-agriculture sludge (CAS), at three different substrate: inoculum ratios (1:2, 1:1 and 2:1) at three different incubation times (0, 5 and 10 d) were studied in batch feeding reactor for a total of 18 AD configurations. The AD configurations were study through specific biogas and methane productions, first order disintegration kinetics, Gompertz modified study and energy sustainable index. A multi criteria decision aid outranked the 18 AD configurations tested. The study proved that the AD performed with inoculum CAS incubated for 10 d at 2:1 substrate inoculum ratio reached the highest biogas yield and methene content equal to 997.81 NL/kgVS and 70.00% v/v.

Optimizing the effect of hydrochar on anaerobic digestion of organic fraction municipal solid waste for biogas and methane production.

Anaerobic digestion (AD) is the biological waste treatment method for the organic fraction of municipal solid waste (OFMSW). AD is notable for its ability to reduce volume and produce biogas from waste. However, the conventional AD of OFMSW has a low degradation rate. In recent years, some treatment method has been used to promote the biogas and methane production of AD. One of these methods is hydrothermal carbonization (HTC). This study aimed to evaluate the effect of hydrothermal carbonization (HTC) temperature and hydrochar: OFMSW ratio as factors on biogas production, methane production, and methane content of anaerobic digestion (AD) as responses was investigated. This study determined the biomethane potential of raw and pretreated OFMSW (hydrochars) in 118 ml serum glass bottles. Based on the Hansen method, all tests were conducted at mesophilic temperature (37 ± 1 °C) in an incubator for 45 days. The response surface method and central composite model were used for designing experimental conditions. Quadratic models were used to estimate the correlation between factors and responses. Also, the optimal conditions for maximizing responses were determined. Biogas production of mixing hydrochar and OFMSW was 41% more than control groups which contained OFMSW and inoculum. The optimal operating conditions to maximize all responses were applied in HTC temperature and hydrochar: OFMSW ratio of 179.366 °C and 2.406, respectively. In this condition, the maximum biogas production, methane production, and methane content were 394 mL/g VS, 284.351 mL/g VS, and 73.176%, respectively. As an OFMSW HTC pretreatment for AD, hydrochar additive has a significantly positive and negative effect on biogas production, methane production, and methane content of biogas depending on operating conditions. Therefore. It is necessary to consider the individual and interaction effects of the temperature and hydrochar: OFMSW ratio, obtain the optimal conditions and determine responses.

An investigation for improving dry anaerobic digestion of municipal solid wastes by adding biochar derived from gasification of wood pellets

In this study, the effect of biochar addition derived from a downdraft fixed-bed gasifier on the performances of dry anaerobic digestion of the Organic Fraction of Municipal Solid Waste (OFMSW) was investigated at a high organic load of (1) the source segregated OFMSW (16 and 26% TS) and (2) the source segregated OFMSW replaced with 15% garden waste (22.2% TS). Adding biochar effectively enhanced the rate and yield of biomethane (up to 36.6%), controlled acidification, and shortened lag phase in both feedstocks at high organic loads up to 136.9 gVS/L. Execution of dry anaerobic digestion for source-separated OFMSW without acidification can only be achieved by more than 30 g/L biochar dosage, which is better to run in a semi-solid state (16% TS). However, the synergistic effects at higher biochar doses were not palpable. OFMSW with a higher C/N ratio yielded more limited benefits, as inhibitory volatile fatty acids were further controlled in the early days. This study could promise the integration of gasification and dry anaerobic digestion to enhance the biogas production efficiency at high organic loads, although more researches should be done under continuous conditions.

Life cycle assessment and life cycle costing of advanced anaerobic digestion of organic fraction municipal solid waste

The aim of this study is the evaluation of the environmental sustainability by means of Life Cycle Assessment (LCA) and economic profitability through Life Cycle Costing (LCC) of the 18 anaerobic digestion (AD) configurations carried out on Organic Fraction Municipal Solid Waste (OFMSW) at three Substrate Inoculum (S:I) ratios (1:2, 1:1 and 2:1) for three different inoculum incubation times (0, 5 and 10 d). The adopted approach was the eco-efficiency perspective, coming from the combination of technical, environmental (LCA) and economic (LCC) perspectives. The main findings of the study were that increasing both the S:I ratio and the inoculum incubation time (5 and 10 d) the environmental impacts decreased, and economic profitability increased. The lowest values of Climate Change were achieved by the AD performed with both inocula WAS and CAS for 10 d at S:I equal to 2:1: 28.67 and 27.72 kg CO2 eq respectively. The minimum AD plant size for which all the 18 AD configurations was economically profitable after 5 y of amortization was 30,000 t/y of OFMSW. Capital and operational costs decreased by increasing the incubation time of the inoculum and the S:I ratio, since higher specific biogas rate was reached, and smaller AD bio-reactor volume were adopted because hydraulic retention time decreased.The AD plant size, for which maximal revenues and minimal capital and operational costs were detected, was 50,000 t/y OFMSW. Among all the AD configurations, the environmental sustainability and economic profitability were reached by test perfomed with inocula WAS and CAS incubated for 5 and 10 d at the highest S:I ratio 2:1.

Acidogenic digestion of organic municipal solid waste in a pilot scale reactor: Effect of waste ratio and leachate recirculation and dilution on hydrolysis and medium chain fatty acid production

The purpose of this investigation is to study the effect of 1) leachate recirculation (LR) and dilution (LD), 2) the increment of the waste ratio, and 3) co-digestion using poultry waste as co-substrate for enhancing the acidogenesis process of the organic municipal solid waste (OMSW), thereby increasing the medium chain fatty acids (MCFAs) production. The results of the experiment carried in a batch pilot reactor show that LR increases hydrolysis as well as the OMSW conversion efficiency. Meanwhile, the highest total MCFA production of around 62,000 mg/L is shown for LR with a high OMSW ratio. Thus, a high concentration of hexanoic acid is shown in LR lysimeters (5475 mg/L, 6627 mg/L, and 10,889 mg/L respectively). However, a metabolic shift toward the production of heptanoic and octanoic acids is reported for LD samples. Nonetheless, the use of poultry waste as co-substrate in the co-digestion process multiplied the concentration of the produced MCFAs.