Anaerobic Co-digestion Research Articles

Utilization of Anaerobic Co-Digestion for Biogas Production for Institutional Cooking: A Case of Nkumbi International College

Studies have linked the use of wood fuel to deforestation leading to greenhouse gas emissions which cause climate change. Despite these concerns, some institutions located in the rural areas of Zambia like boarding schools and colleges still use firewood as a fuel for cooking and heating. Additionally, electricity, where available, is usually based on fossil fuel combustion, and often has high tariffs if connected to the national electricity grid and is also unreliable. On the other hand, biogas produced from animal and other organic wastes has demonstrated to be a cleaner alternative source of energy that can be used for cooking and supply of heat. A case of Nkumbi international college was selected to consider the economic viability of using the animal and agriculture waste from the institutional farm as a feedstock in an anaerobic co-digester to generate biogas for use as fuel for cooking to replace firewood and grid electricity, the current sources of energy for cooking. Results showed that installing a biogas system at the college and using the biogas to replace a combination of firewood and electricity is highly viable with a positive net present value of USD 19,747, a payback period of 3.1 years, and an internal rate of return of 35.5% over a period of 20 years.

Anaerobic Co-Digestion of Cattle Manure with Ruminal Waste to Increase Biogas Production

Cattle manure (CM) is mostly used as an inoculum in order to start-up of agricultural biogas plants or as a co-substrate in the anaerobic digestion of lignocellulosic content. Rumen fluid microbiota is also considered to be effective in lignocellulose digestion. It is known that microorganisms in the ruminal waste facilitate the hydrolysis of lignocellulosic structures. However, there are few studies on the inoculum effect of rumen microorganisms on bioreactor performances when rumen content is used as co-substrate and inoculum together with cattle manure, and it is not clear how rumen waste can be used in various anaerobic digestion systems. In this study, biogas production efficiencies obtained from lignocellulosic content in mono and cosubstrate (1:1 and 1:2 Volatile Solids) bioreactors formed by using ruminal waste (RW) and CM microbial communities were investigated. In order to determine the biogas production efficiencies, biomethane potential (BMP) experiments that simulate anaerobic digestion process conditions in a laboratory environment were applied. Treatment with 50% application of RW cosubstrate, 65.51% biogas and 70.64% methane production efficiency increases were achieved compared to monosubstrate CM bioreactor.

Anaerobic Co-Digestion of Food Waste and Microalgae at Variable Mixing Ratios: Enhanced Performance, Kinetic Analysis, and Microbial Community Dynamics Investigation

There is an urgent need for clean recycling strategies to address the increase in food waste (FW) and the harvesting of microalgae (MA). In this study, biogas production potential and operational stability were evaluated by testing combinations of FW and MA mixed at five different ratios. Co-digestion of FW and MA improved substrate biodegradability, achieving a decomposition rate of 0.45/d (FW/MA = 1:1), which is 1.25 to 1.55 times higher than that of MA or FW alone. Co-digestion of FW and MA resulted in a synergistic effect, improving biogas yield by 2.04–26.86%. Four mathematical models were applied to estimate biological degradation and biogas production kinetics, and the Cone model performed better than the other models in terms of reliability and accuracy. The abundance of Bacteroidetes, Firmicutes, and Synergistetes peaked at FW/MA = 1:1. At the same ratio, the genera Methanospirillum, Methanocorpusculum, and Methanomethylovorans were also found to have increased in abundance. The optimal ratio was found to be 1:1 for co-digestion of FW and MA, which is a feasible approach for simultaneous bioenergy production and biomass waste co-disposal.

Utilization strategy for algal bloom waste through co-digestion with kitchen waste: Comprehensive kinetic and metagenomic analysis

Anaerobic co-digestion (AcoD) with kitchen waste (KW) is an alternative utilization strategy for algal bloom waste (AW). However, the kinetic characteristic and metabolic pathway during this process need to be explored further. This study conducted a comprehensive kinetic and metagenomic analysis for AcoD of AW and KW. A maximum co-digestion performance index (CPI) of 1.13 was achieved under the 12% AW addition. Co-digestion improved the total volatile fatty acids generation and the organic matter transformation efficiency. Kinetic analysis showed that the Superimposed model fit optimally (R2Adj = 0.9988–0.9995). The improvement of the kinetic process by co-digestion was mainly reflected in the increase of the methane production from slowly biodegradable components. Co-digestion enriched the cellulolytic bacterium Clostridium and the hydrogenotrophic methanogenic archaea Methanobacterium. Furthermore, for metagenome analysis, the abundance of key genes concerned in cellulose and lipid hydrolysis, pyruvate and methane metabolism were both increased in co-digestion process. This study provided a feasible process for the utilization of AW produced seasonally and a deeper understanding of the AcoD synergistic mechanism from kinetic and metagenomic perspectives.

Use of Continuous Stirred Tank Reactors for Anaerobic Co-Digestion of Dairy and Meat Industry By-Products for Biogas Production

The dairy and meat industries generate thousands of tons of organic waste and by-products each year, making them two of the least environmentally sustainable sectors. Typical waste includes not only processing by-products such as curds but also commercial products that are defective or unsaleable due to expiration or damaged packaging. This study aimed to evaluate the methanogenic potential of a mixture of 80% inedible curds and 20% expired sausages, as a substrate, using two continuously stirred tank reactors (CSTR). The reactors were fed daily with increasing doses of the 80–20% mixture and an organic loading rate ranging from 0.31 gVS/litre/day at the beginning of the trials to 7.20 gVS/litre/day toward the end. The produced biogas was continuously analysed from both quantitative and qualitative point of view. Also, the process was continuously monitored by withdrawing samples from each reactor during the whole process, to analyse their physical–chemical parameters, including pH, total solids (TS), total volatile solids (TVS), chemical oxygen demand (COD), ammonium nitrogen (NH4+-N), total Kjeldahl nitrogen (TKN) and total volatile fatty acids (VFA). The results of this study show a promising increase in biogas production with the increase in feed. In terms of biogas production, organic waste from the dairy and meat industry shows the potential to be exploited as a substrate to produce biomethane. Indeed, in this study, biomethane cumulative production reached 410.86 NLCH4∙gTVS−1 using an 8 L capacity reactor filled up to 6 L. This makes the tested by-products usable as a renewable energy source in the future, particularly within a circular economy approach, helping to mitigate the effects of global warming and addressing sustainable development goals.

Efficient methane production from anaerobic co-digestion of lignin-based feedstock and waste plastic: Digester performance and microbial community structures

Waste plastic (WP) and lignocellulosic biomass (LCB) are both refractory polymers that can provide feedstocks for the production of fuels. Anaerobic digestion (AD) is a widely recognized technology utilized in waste management and renewable energy production. It involves the utilization of microorganisms to decompose organic matter into methane (CH4). Nevertheless, mono-digestion, which refers to AD utilizing a single feedstock, encounters difficulties related to the properties of the feedstock. Therefore, the utilization of co-digestion with multiple feedstocks provides the potential to overcome these limitations. This study might be the first to examine the impact of co-digestion of low-density polyethylene (LDPE) with rice straw (RS) for biogas and CH4 production. The cumulative CH4 production for AD-1, AD-2, AD-3, AD-4, AD-5, and AD-6 was 154.9, 177.4, 52.0, 81.2, 98.43, and 135.15 NmL/g VS. The methane energy yields varied between 2.29 and 7.64 MJ/m3, while their respective βece values spanned from 17.6 to 58.8 %. Volatile solid removal was enhanced for the treated RS-LDPE mixture, as demonstrated in AD-6, in comparison to the untreated substrate in the AD-2 digester. There is a notable disparity in the composition of bacterial communities within the bioreactors that were constructed prior to and subsequent to the AD process. The proliferating Firmicutes, Bacteroidetes, and Protobacteria were crucial to the AD of RS and LDPE. The three predominant methanogenic genera present in the constructed digesters and inoculum were Methanobacterium, Methanolinea, and Methanosarcina, each with a distinct abundance level. The findings open up the possibility of better understanding the effect of co-digestion of WP and LCB on enhancing CH4 production, which is critical for developing strategies for bioremediation and waste valorization simultaneously with biofuel production.

Development of a fed-batch-scale anaerobic co-digestion control system based on multivariable output error state space and model predictive control

This paper describes a feeding control system for fed-batch-scale anaerobic co-digestion. The proposed system is based on the multivariable output error state space and uses model predictive control to regulate the biogas flow output of anaerobic co-digestion. This control system combines predictive modeling, receding-horizon optimization, and state feedback. An accurate linear model of anaerobic co-digestion is obtained through the multivariable output error state space method using experimental data, and the accuracy of the model is evaluated using a goodness-of-fit index and the root mean square error. After augmenting the model, a predictive control system is established. The system states are observed through a Kalman filter, and the constrained receding-horizon optimization problem is solved using quadratic programming. Finally, the stability of the control system is demonstrated from both open- and closed-loop perspectives. The control system is then constructed and used in actual experiments, with the target flow output set at 100 NmL/h. The final flow output indicates that the control system achieves good control performance. This research enables the biogas output of anaerobic co-digestion to be controlled from a linear perspective through a concise control algorithm with strong practical application prospects.

Anaerobic Co-Digestion of Fish Sludge Originating from a Recirculating Aquaculture System

Anaerobic co-digestion (AcoD) of fish sludge (FS) with food waste (FW), and fruit and vegetable waste (FVW) for biogas and methane production was optimised in small-scale bioreactors, and batch and semi-continuous pilot-scale digesters, under mesophilic (37 ℃) conditions. An experimental mixture design was first applied to small-scale biomethane potential (BMP) tests, to determine the optimal mixture proportions of the AcoD of FS, FW, and FVW that maximise the specific methane yield (SMY in NmLCH4 gVS−1). The optimal mixture proportion was 67%FS:18%FW:19%FVW (w/w), producing 401 mLCH4 gVS−1, which was 8 times higher than the SMY when FS was mono-digested (48 mLCH4 gVS−1). The SMY achieved in batch pilot-scale digesters were 70–82% of methane yields obtained in BMP tests under the same operating conditions, with stable biogas production and no apparent inhibition during the batch run. Semi-continuous operation of the pilot-scale digester was undertaken with organic loading rates (OLRs) of 1, 2, and 3 gVSL-1d-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$gVS{L}^{-1}{d}^{-1}$$\\end{document}, provided intermittently. However, the digester did not achieve stable biogas production at all of the evaluated OLRs, due to the intermittent feeding and accumulation of volatile fatty acids (VFAs): Improved process stability was achieved at an OLR of 2 gVSL-1d-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$gVS{L}^{-1}{d}^{-1}$$\\end{document}, compared to OLRs of 1 and 3 gVSL-1d-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$gVS{L}^{-1}{d}^{-1}$$\\end{document}. Optimisation of the AcoD process resulted in attractive biomethane yields from FS with FW and FVW co-feeds, indicating that producing biogas from co-digestion of FS with relevant substrates is a valuable managing tool for FS, while simultaneously providing renewable energy. The work provides novel data that elucidated optimal proportions in which to combine FS, FW and FVW to obtain optimal biogas production, and provided important new information relevant for the scale up and continuous operation of an AD process for treating FS.Graphical

Potential of Biogas Production from Anaerobic Co-digestion of Hydrothermal Pre-treated OPEFB and Digested Sludge

Potential of Biogas Production from Anaerobic Co-digestion of Hydrothermal Pre-treated OPEFB and Digested Sludge

Effect of Biochar on Anaerobic Co-Digestion of Untreated Sewage Sludge with Municipal Organic Waste under Mesophilic Conditions

Anaerobic digestion (AD) is a biological process that occurs in the limited presence of oxygen. This process involves various difficulties during the operation, such as acidification and increased concentration of volatile fatty acids, which can inhibit methane production. Therefore, in this work, the impact of biochar on the co-digestion of untreated sludge and residual biomass under mesophilic conditions was studied. For the production of biochar, the gasification process was used at different temperatures: 759 °C (BL), 798 °C (BM), and 888 °C (BH). This biochar was added in concentrations of 0 g/L, 3.33 g/L, and 6.67 g/L at the beginning of the co-digestion process. The results showed that a concentration of 6.67 g/L with BH biochar increased the PBM by 18% compared to the control sample and reduced the chemical oxygen demand (COD) by 88%. In addition, there was a reduction of volatile fatty acids (VFA) of 42.75%. Furthermore, FTIR analysis demonstrated that biochar has appropriate functional groups for this process. These data suggest a good interaction of biochar with the mixture of sludge and municipal waste, indicating that biochar can improve the anaerobic co-digestion of untreated sludge and municipal waste.

The effects of microalgae use as a biofertilizer on soil and plant before and after its anaerobic (co-)digestion with food waste

The increase in food waste generation has resulted in significant challenges for its sustainable management. Anaerobic digestion coupled with microalgae-based ponds for digestate treatment can be used as a low-cost eco-friendly technology approach. In this case, microalgal biomass harvested from the ponds may be valorized into bioenergy (biogas) and soil conditioner and/or biofertilizers. The aim of the present study was to evaluate the microalgal biomass produced from a food waste digestate treatment ponds as agricultural fertilizer. For this purpose, microalgal biomass was tested before and after anaerobic digestion and co-digestion with food waste, exploring its potential for valorization. The inorganic fertilizer urea and soil with no fertilization were also used as treatments. The experimental design consisted of applying the treatments in pots cultivated with hybrid grass Brachiaria cv. Sabiá and distributed in randomized blocks in a controlled greenhouse. Microalgal biomass was mainly composed by Scenedesmus sp.. The assessed parameters showed comparable results on plant growth (i.e. number of tillers, fresh and dry matter and Chlorophyll content index) for fresh and digested microalgal biomass and inorganic fertilizer. Furthermore, it was observed that fresh microalgae provided the highest Phosphorus content in the leaf (21 %). Additionally, there were increases of 9 % in Nitrogen and 12 % in organic matter in the soil after applying digested microalgae compared to the control group without any fertilization. Finally, experimental data obtained suggests that microalgae-based biofertilizer holds the potential to replace inorganic fertilizer as a nutrient source. Moreover, it contributes to the valorization of by-products from organic waste treatment.

Study on the Environmental Impact and Benefits of Incorporating Humus Composites in Anaerobic Co-Digestion Treatment.

This study evaluated the environmental impact and overall benefits of incorporating humus composites in the anaerobic co-digestion of kitchen waste and residual sludge. The life cycle assessment method was used to quantitatively analyze the environmental impact of the entire anaerobic co-digestion treatment process of waste, including garbage collection, transportation, and final product utilization. Moreover, the comprehensive assessment of the environmental impact, energy-saving and emission-reduction abilities, and economic cost of using humus composites in the anaerobic co-digestion treatment process was conducted using a benefit analysis method. The results showed that the anaerobic co-digestion of kitchen waste and residual sludge significantly contributed to the mitigation of global warming potential (GWP), reaching -19.76 kgCO2-eq, but had the least impact on the mitigation of acidification potential (AP), reaching -0.10 kgSO2-eq. In addition, the addition of humus composites significantly increased the production of biogas. At a concentration of 5 g/L, the biogas yield of the anaerobic co-digestion process was 70.76 m3, which increased by 50.62% compared with the blank group. This amount of biogas replaces ~50.52 kg of standard coal, reducing CO2 emissions by 13.74 kg compared with burning the same amount of standard coal. Therefore, the anaerobic co-digestion treatment of kitchen waste and residual sludge brings considerable environmental benefits.

New insights on ecological roles of waste activated sludge in nutrient-stressed co-digestion

There have been extensive applications of waste activated sludge (WAS) in anaerobic co-digestion (AcoD). Nonetheless, mechanisms through which AcoD systems maintain stability, particularly under nutrient-stressed conditions, are under-appreciated. In this study, the role of WAS in a nutrient-stressed WAS-food waste AcoD system was re-evaluated. Our findings demonstrated that WAS-based co-digestion increased methane production (by 20–60%) as WAS bolsters such systems’ resilience via establishing a core niche-based microbial balance. The carbon utilization investigation suggested a microbial niche balance is attainable if two conditions are satisfied: 1) hydrolysis efficiency is greater than 50%; and 2) both the acidogenesis-to-hydrolysis and acetogenesis-to-hydrolysis efficiencies surpass 0.5. Metagenomic assembly genome (MAG) analysis indicated that the versatile metabolic characteristics strengthened the microbial niche balance, rendering the system resilient and efficient through a syntrophic mode, contributing to both acidogenesis and acetogenesis. The findings of this study provide new insights into the ecological effects of WAS on AcoD.

Unlocking potential: Exploring the methane production potential in anaerobic co-digestion of cassava wastewater and glycerol

This study aimed at evaluating the feasibility of CH4 production in a mesophilic (30 °C) single-stage anaerobic co-digestion of cassava wastewater (CW) and glycerol in an anaerobic fluidized bed reactor (AFBR) with mixing ratio of 50 % / 50 % CW/Gly on a (chemical oxygen demand)COD basis. Thus, the following strategy was used: increasing the organic loading rate (OLR) (1–20 g COD.L−1.d−1) by increasing the substrate concentration (1–20 g COD.L−1) and applying a hydraulic detention time (HRT) of 24 h. The AFBR presented a maximum methane (CH4) content of 88.38±1.94 % and a CH4 yield (MY) of 293.48±18.37 mL of CH4.mL−1CODrem in the OLR of 1 g COD.L−1.d−1 and the maximum methane production rate (MPR) of 62.09±2.75 mL of CH4.L−1.h−1 in the OLR of 20 g COD.L−1.d−1. The conversion of glycerol and carbohydrates remained above 91±0.54 % and 82±2.79 %, respectively, and the COD conversion was above 80±0.65 %. The main metabolites were HAc, HPr, HBu, EtOH and HVa. The most abundant genera identified in the AFBR were Izemoplasmatales and Enterobacteriaceae for the bacteria domain, and Methanosaeta, Methanobacterium for the archaea domain. The single-stage system is robust and can operate with higher OLR without reducing the efficiency of wastewater treatment and CH4 production.

Enhanced anaerobic co-digestion of cattle manure with food waste and pig manure: Statistical optimization of pretreatment condition and substrate mixture ratio

This study investigated the optimal pretreatment condition and mixture ratio of cattle manure (CM) for its efficient anaerobic co-digestion (AcoD) with food waste (FW) and pig manure (PM). The pretreatment performances of thermal (TM), microwave (MW), and ultrasound (US) technologies and the AcoD performance were statistically and experimentally evaluated at various mixture ratios of CM, FW, and PM. The results revealed that the most effective pretreatment condition with the TM, MW, and US pretreatments was 129.3 °C for 49.6 min, 824.2 W for 7.3 min, and 418.0 W for 36.3 min, respectively. The best AcoD performance of optimally pretreated CM (PCM) was achieved when 30.5 % PCM was mixed with 42.5 % FW and 27.0 % PM. A long-term evaluation showed that the start-up rate for the anaerobic mono-digestion of PCM was 2.3 times faster than that of CM and the amount of methane produced was 4.7 times higher; process stability was thus preferentially maintained under a higher organic loading rate (OLR) (2.0 kg-VS/m3∙d). The start-up rate for the AcoD of PCM with FW and PM was 1.2 times higher than that of the AcoD of CM with FW and PM. Although the performance gap between the AcoD reactors after steady state was not significantly different, the PCM AcoD reactor provided a more stable operation under a higher OLR (5.0 kg-VS/m3∙d). This study demonstrates that the pretreatment and co-digestion of CM could significantly enhance the production of biogas and improve process stability.

Methane production from anaerobic co-digestion of vinasse and molasses: effects of substrate proportion, COD and alkalizing agent

Methane production from anaerobic co-digestion of vinasse and molasses: effects of substrate proportion, COD and alkalizing agent

Evaluating the Environmental Impacts of Pretreatment and Nanoparticles in Solid-State Anaerobic Digestion Using Life Cycle Assessment

The yield of green energy from solid-state anaerobic co-digestion (SSAD) has recently been enhanced by incorporating innovative pretreatment methods and nanoparticles. However, the environmental consequences of employing new processes have not been fully examined. In this study, the environmental impacts of three high-methane-yielding scenarios including SSAD of corn stover blended with dairy manure (DM) denoted as (SYM1), calcium hydroxide-pretreated corn stover (CpCS) blended with DM (SYM2), and the CpCS blended with DM and nanoparticles (SYM3) were assessed and compared the baselines of solid-state and semi-solid-state anaerobic digestion using a life cycle assessment (LCA) approach. The approach investigated the best management practices that would result in high methane yield and low environmental impact. Results of the life cycle assessment indicate the inclusion of calcium hydroxide and nanoparticle has minimal negative environmental impact. There was an environmental gain in GWP when corn stover was co-digestion with DM (SYM1) relative to DM mono-digestions (baselines) and the carbon footprint of SYM1 was less by more than 85% compared to SYM2 and SYM3. However, the large volume of untreated corn stover harnessed for SYM1 scenario resulted in over 75% fossil fuel depletion compared to the other scenarios. The surplus methane from the SYM3 (at least twofold of other scenarios and baselines) in conjunction with being the least with the environmental implication makes the scenario the most attractive option for on-farm practice capable of harnessing the growing organic waste volume. These outcomes can guide trade-off between pretreatment and nanoparticle application to reduce solid-state anaerobic digestion’s negative environmental impact.

Ensemble machine learning prediction of anaerobic co-digestion of manure and thermally pretreated harvest residues

This study aimed to clarify the statistical accuracy assessment approaches used in recent biogas prediction studies using state-of-the-art ensemble machine learning approach according to 10-fold cross-validation in 100 repetitions. Three thermally pretreated harvest residue types (maize stover, sunflower stalk and soybean straw) and manure were anaerobically co-digested, measuring biogas and methane yield alongside eight thermal preprocessing and biomass covariates. These were the inputs to an ensemble machine learning approach for biogas and methane yield prediction, employing three feature selection approaches. The Support Vector Machine prediction with the Recursive Feature Elimination resulted in the highest prediction accuracy, achieving the coefficient of determination of 0.820 and 0.823 for biogas and methane yield prediction, respectively. This study demonstrated an extreme dependency of prediction accuracy to input dataset properties, which could only be mitigated with ensemble machine learning and strongly suggested that the split-sample approach, often used in previous studies, should be avoided.

Phytoremediation of laundry wastewater using Pistia stratiotes and recycling of spent plant biomass for sustainable biomethane production

This study investigates the decontamination of laundry wastewater (LWW) using Pistia stratiotes via phytoremediation and recyclability of residual macrophyte biomass for enriched bio-CH4 production. Phytoremediation was performed using a hydroponic system. The optimum phytoremediation factors were LWW concentration = 79.4 %, plant density = 4 plants/reactor, and retention time = 12.9 days. This condition offered maximum removal efficiencies of 82.32 ± 3.59 %, 67.19 ± 2.90 %, and 70.34 ± 3.56 % for NH4+, COD, and PO43−, respectively. The residual P. stratiotes biomass (RPSB) was anaerobically co-digested with buffalo dung (BD) at 1:1 (w/w, wet basis) for enriched bio-CH4 production, achieving a maximum cumulative bio-CH4 yield of 696.84 ± 35.82 mL/g-VS. The modified Gompertz kinetic model fitted well to the anaerobic co-digestion experimental data with R2-value = 94.4 %. The integrated phytoremediation/co-digestion scheme succeeded in promoting social well-being through improved water quality, clean energy recovery, and benefiting the environment through carbon footprint emission reduction. These outputs achieved multiple targets of sustainable development goals.

Effect of biochar on anaerobic co-digestion performance and microbial communities of hulless barley straw and pig manure

Effect of biochar on anaerobic co-digestion performance and microbial communities of hulless barley straw and pig manure