Co-digestion of cow manure and food waste for biogas enhancement and nutrients revival in bio-circular economy

Determinant and Characterization of Biogas Product at Different Agroecological Zones of Ethiopia

Biogas production uses microorganisms to degrade organic material in the absence of oxygen to produce CH4, CO2, and other residual gases. Anaerobic digestion of cattle manure and human feces for biogas production is an important technology in Ethiopia's National Energy Strategy. Thus, this study aimed to analyze determinants and characteristic composition of biogas product at different agroecological zones in Southern Ethiopia. In this study, biogas plants were categorized based on agroecology, size, age, and design type. A total of 32 biogas plants were included and their gas composition were analyzed using OPTIMA Biogas Analyzer. One-way ANOVA and paired-wise comparison were widely used for data analysis. ANOVA results for CH4 revealed that agroecology, temperature, and biogas plant design were statistically significant whereas biogas plant size and age of biogas plants were not statistically significant. From this study, the authors concluded that agroecology, biogas plant design, and temperature significantly affect biogas yield quality. Future research needs to focus on seasonal variation of biogas product at different agroecological zones and evaluation of the rural household biogas plants' performance.

Alkaline catalytic liquefaction of pig manure fermentation residue in ethanol solvent for the production of high-quality biocrude oil

The widespread application of biogas projects generates substantial amounts of waste fermentation residue. Further treatment of fermentation residues facilitates resource utilization, ensures safe disposal, and is anticipated to enhance the economic returns of biogas projects. Herein, catalytic liquefaction of pig manure fermentation residue to produce biocrude oil was investigated using various alkaline catalysts at 340 ℃ with ethanol as the solvent. Biocrude oils were analyzed by elemental analysis, gas chromatography-mass spectrometry (GC-MS), thermogravimetric analysis, and kinetic analysis. The maximum biocrude oil yield (45.24 wt%) was obtained with the KOH catalyst. Additionally, the biocrude oil produced by the catalysis of CaO exhibited the maximum higher heating value at 44.18 MJ/kg. GC-MS results showed that KOH and K2CO3 considerably increased the content of phenols and hydrocarbons in the biocrude while reducing nitrogenous compounds. All alkaline catalysts effectively reduced the activation energy of biocrude oil compared to biocrude oil without catalyst. The maximum reduction in activation energy (18.73 %) was achieved with the addition of Na2CO3. More importantly, adding CaO not only increased the yield and higher heating value of biocrude oil but also reduced nitrogenous compounds and activation energy, improving the overall yield and quality. Overall, this work provides an effective and promising method to convert pig manure fermentation residue into green high-quality biocrude oil, simultaneously providing an economical and environmentally friendly waste management strategy for the fermentation industry.

Rice straw co-digestion potential with cow dung and poultry droppings for maximizing biogas production in Bangladesh

Rice is the staple food of the people of Bangladesh. Burning and landfilling of carbon-rich rice straw (RS) causes greenhouse gas emissions. On the other hand, cow dung (CD) and poultry droppings (PD) produced from the livestock sector in Bangladesh could be a potential threat to the environment if the wastes are not properly managed. However, anaerobic co-digestion of RS with CD and PD could be an effective means of biogas generation. Therefore, co-digestion of CD and PD with carbon-rich RS was conducted in batch assay at seven different mixing ratios (100:0, 90:10, 70:30, 50:50, 30:70, 10:90, 0:100) separately. Mesophilic condition (35 °C) was maintained for 92 days of digestion time to investigate biogas production potential and find out optimal mixing ratios of both co-digestion sets. Co-digestion of CD and RS at 70:30 ratio significantly showed maximum biogas yield (441.7 ± 54.1 ml/gVS). Additionally, an increase in biogas yield in this ratio was 212.11 % and 38.10 % compared to mono-digestion of CD and RS, respectively. Another co-digestion set of PD with RS showed highest biogas yield (344.8 ± 22.3 ml/gVS) at 90:10 ratio. The 90:10 ratio of PD and RS improved biogas yield by 173.16 % and 7.8 % as compared to mono-digestion of PD and RS, respectively. Co-digestion of RS with CD and PD had a statistically significant effect (P ≤ 0.05) on biogas production. Furthermore, kinetic modelling outcomes suggested the modified Gompertz model as ideal for forecasting biomethane production over time in both cases. The findings of this study will help in the implementation of ACoD at the field level.

Deciphering cleaner and sustainable frontiers in scientific cow waste valorization: a review

The forecasted global population growth is poised to create a greater exigency for livestock-derived food production, leading to a significant waste generation from the industrial-scale livestock operations, which necessitates to develop sustainable waste management solutions. The heightened demand for livestock and dairy products has driven a surge in cow waste (CW) production. While CW is typically used as organic fertilizer or solid fuel, improper disposal poses potential environmental hazards. Anaerobic digestion and composting transform CW into valuable products, such as biofuels and organic fertilizers, with the potential for electricity and heat generation, biochar production, and advanced friction materials. The CW contains essential inorganic and organic compounds vital for plant functions, including lignin, cellulose, hemicellulose, nitrogen, and minerals such as potassium, sulfur, iron, magnesium, copper, cobalt, and manganese. Additionally, the rich microbial diversity in cow dung drives the production of bioenergy carriers like biomethane and biohydrogen, promoting cost-effective energy generation and environmental sustainability. This review employs bibliometric analysis to explore the latest trends in CW applications, with a particular focus on innovative applications such as cellulose extraction, biochar production, microbial fuel cells, and nanoparticle synthesis. It further evaluates the environmental impacts of these technologies and assesses their potential to advance sustainable and cleaner frontiers in the valorization of CW.

Bio-chelate assisted leaching for enhanced heavy metal remediation in municipal solid waste compost

Municipal solid waste compost, the circular economy's closed-loop product often contains excessive amounts of toxic heavy metals, leading to market rejection and disposal as waste material. To address this issue, the study develops a novel approach based on: (i) utilizing plant-based biodegradable chelating agent, L-glutamic acid, N,N-diacetic acid (GLDA) to remediate heavy metals from contaminated MSW compost, (ii) comparative assessment of GLDA removal efficiency at optimal conditions with conventional nonbiodegradable chelator EDTA, and (iii) enhanced pre- and post-leaching to evaluate the mobility, toxicity, and bioavailability of heavy metals. The impact of treatment variables, such as GLDA concentration, pH, and retention time, on the removal of heavy metals was investigated. The process was optimized using response surface methodology to achieve the highest removal effectiveness. The findings indicated that under optimal conditions (GLDA concentration of 150 mM, pH of 2.9, retention time for 120 min), the maximum removal efficiencies were as follows: Cd-90.32%, Cu-81.96%, Pb-91.62%, and Zn-80.34%. This process followed a pseudo-second-order kinetic equation. Following GLDA-assisted leaching, the geochemical fractions were studied and the distribution highlighted Cd, Cu, and Pb's potential remobilization in exchangeable fractions, while Zn displayed integration with the compost matrix. GLDA-assisted leaching and subsequent fractions illustrated transformation and stability. Therefore, this process could be a sustainable alternative for industrial applications (agricultural fertilizers and bioenergy) and social benefits (waste reduction, urban landscaping, and carbon sequestration) as it has controlled environmental footprints. Hence, the proposed remediation strategy, chemically assisted leaching, could be a practical option for extracting heavy metals from MSW compost, thereby boosting circular economy.

Co-digestion approach for enhancement of biogas production by mixture of untreated napier grass and industrial hydrolyzed food waste

The co-digestion of untreated Napier grass (NG) and industrial hydrolyzed food waste (FW) was carried out in the batch reactor to investigate the effect of substrate ratios on biogas production performance. Two-stage anaerobic digestion was performed with an initial substrate concentration of 5 g VSadded/L and a Food to Microorganism Ratio (F/M) of 0.84. The 1:1 ratio of the NG and FW showed the optimum performances on biogas production yield with a value of 1,161.33 mL/g VSadded after 60 days of digestion. This was followed by the data on methane yield and concentration were 614.37 mL/g VSadded and 67.29%, respectively. The results were similar to the simulation results using a modified Gompertz model, which had a higher potential methane production and maximum production rate, as well as a shorter lag phase and a coefficient of determination of 0.9945. These findings indicated that the co-digestion of Napier grass and hydrolyzed food waste can enhance biogas production in two-stage anaerobic digestion.

Moving towards the Application of Biocatalysis in Food Waste Biorefinery

Waste valorization is an important strategy to reduce environmental pollution and dependency on petroleum-based fuels. In this regard, utilization of food waste as a versatile and low-cost resource is important. Several advanced catalytic methods for the valorization of food waste have been widely investigated for the production of liquid biofuels. Along this line, chemical catalysts have been explored for the synthesis of liquid biofuels. Chemo-catalysis is mainly metal based, which requires harsh process conditions. Alternatively, biocatalysts are currently being investigated as a result of several advantages such as mild reaction conditions, recyclability, selectivity and biodegradability. In this work, recent biocatalytic technologies for the preparation of liquid biofuels through food waste valorization are discussed thoroughly. Lipases are employed for the synthesis of biodiesel and the upgradation of bio-oil, whereas methane mono-oxygenases could be explored for the production of methanol via the oxidation of methane generated from food wastes. Industrial production of ethanol from food waste using bioconversion technologies is a success story. To date, there has been no specific report on the use of food waste for propanol preparation using enzymes. The ABE process (Acetone–Butanol–Ethanol) (using suitable microorganisms) is used for butanol preparation, where the vacuum stripping system is integrated to remove butanol from the broth and circumvent inhibition. The synthesis of hydrocarbon fuels from fatty acids and triglycerides can be carried out using enzymes, such as carboxylic acid reductase and fatty acid photodecarboxylase (an algal photoenzyme). Both carboxylic acid reductase and fatty acid photodecarboxylase have not yet been applied in the direct valorization of food wastes. Furthermore, limitations of the reported methods, societal and economic aspects and a fresh perspective on the subject, along with important examples, are described.