A Comparative kinetic modelling for biogas yield assessment from food waste valorisation

This work investigated the potential of generating biogas from mono-digestion of various substrates such as food and fruit waste (e.g., durian shell, dragon fruit peel and pineapple peel) and co-digestion in different combinations of a co-substrate as food waste as well as different types of fruit waste (durian shell, dragon fruit peel and pineapple peel). The mixture of food waste and fruit waste ratio varied as follows: 75:25, 50:50 and 25:75, which was based on weight. The batch experiments were carried out using 125 ml anaerobic digesters and were incubated for 50 days. For a mono-substrate, food waste produced the highest amount of methane gas (60.63 ± 1.02 ml/gvs) followed by durian shell (34.93 ± 1.30 ml/gvs), pineapple peel (31.70 ± 1.60 ml/gvs), and dragon fruit peel (30.12 ± 1.20 ml/gvs), respectively. The highest amount of methane gas came from food waste mixed with durian shell (FW75:D25), and it was on a higher level than food waste mixed with dragon fruit peel (FW75:DF25) and pineapple peel (FW75:P25). The highest methane gas production of co-digestion which was observed at the proportion of food waste and durian shell was 75:25 and produced higher content of methane gas than the highest methane gas production of mono-digestion (food waste) according to the high organic compound and optimum pH value in the system. The results showed that the co-digestion of durian shell and food waste improved methane production and reduced the startup time compared with their mono-digestion. On the other hand, pineapple peel was not suitable for co-digestion with food waste due to a decreasing pH value in the system.

Codigestion of food waste and dairy manure in a mesophilic, completely mixed anaerobicdigester was studied in the laboratory. Two mixtures of food waste and dairy manure were testedwith the first mixture composed of 32% food waste (based on VS content) and 68% dairy manureand the second mixture composed of 48% food waste and 52% dairy manure. For each mixture, theperformance of the anaerobic digester was evaluated at two different organic loading rates (2 and 4gVS/L.day). The results showed that at 2 gVS/L.day, the digesters fed with both mixtures werestable. The digester fed with the second mixture had higher biogas yield and production rate (504mL/gVS and 1.01 L/L.day, respectively) than the digester fed with the first mixture (398 mL/gVS and0.78 L/L.day, respectively). At 4 gVS/L.day, the digester fed with the first mixture had stableperformance but the digester fed with the second mixture had variable performance as shown bylarge fluctuation in daily biogas production. The average biogas yield was 476 and 504 mL/gVS,respectively, and biogas production rate was 1.91 and 2.02 L/L.day. No significant differences werefound for VS removals between different conditions tested. Based on the measurement data, theenergy generation potential of a farm digester was calculated for co-digestion of different amounts ofmanure and food waste.

Biogas production from co-digestion of dairy manure and food waste

The potential of biogas production by the anaerobic codigestion (AcoD) of canteen food waste and animal manure was investigated using the biochemical methane potential assay (BMP). The BMP assay was conducted under thermophilic temperature of 35 °C in a batch process at digestion time of 40 d. Waste substrate mixture was digested at a fixed proportion of 1:1 with different animal manure as co-substrate. Maximum cumulative biogas production (418 ml g-1 VS) was achieved during codigestion of food waste with pig manure > chicken manure (408 ml g-1 VS) > goat manure (319 ml g-1 VS). Generally, all manure codigested reactors produced 1.01 to 1.34 times more biogas than food waste alone indicating the synergistic effect of codigestion on overall biogas productivity. With analogous increase in biogas production, manure amendment produced significant (p<0.05) substrate biodegradation in terms of total and volatile solids loss. The microbial load profile prior and post-AD revealed significant reduction (p<0.05)in microbial species suggestion that anaerobic digestion can be adopted as a method of waste treatment and hygienization.

Livestock manure treatments have become a more serious problem because massive environmental pollutions such as green and red tides caused by non-point pollution sources from livestock manures have emerged as a serious social issue. In addition, more food wastes are being produced due to population growth and increased income level. Since the London Convention has banned the ocean dumping of wastes, some other waste treatment methods for land disposal had to be developed and applied. At the same time, researches have been conducted to develop alternative energy sources from various types of wastes. As a result, anaerobic digestion as a waste treatment method has become an attractive solution. In this study has three objectives: first, to identify the physical properties of the mixture of livestock wastewater and food waste when combining food waste treatment with the conventional livestock manure treatment based on anaerobic mesophilic digestion; second, to find the ideal ratio of waste mixture that could maximize the collection efficiency of methane (CH4) from the anaerobic digestion process; and third, to promote CH4 production by comparing the biodegradability. As a result of comparing the reactors R1, R2, and R3, each containing a mixture of food waste and livestock manure at the ratio of 5:5, 7:3, and 3:7, respectively, R2 showed the optimum treatment efficiencies for the removal of Total Solids (TS) and Volatile Solids (VS), CH4 production, and biodegradability.

Purpose: Methane production potential in aerobic digestion was assessed according to feed to inoculum (F/I) ratio for food waste only, and mixing ratio of two materials for food waste and swine manure to give a basic data for the design of anaerobic digestion system. Methods: Anaerbic digestion test was performed using a lab scale batch reactor at <TEX>$35^{\circ}C$</TEX> for six different feed to inoculum (F/I) ratios (0.50, 0.72, 1.14, 1.50, 2.14 and 3.41), three food waste to swine manure ratios (100:0, 60:40 and 40:60) with two different loading concentrations (10g VS/L and 30g VS/L). Results: For food waste only, the highest biogas yield of 1008 mL/gVS was obtained at 0.50 of F/I. For the co-digestion of food waste and swine manure mixture, the highest biogas yield of 1148 mL/gVS was obtained at a mixing ratio of 40:60 with loading concentration of 10g VS/L. Conclusions: F/I ratio for the food waste only, mixing ratio of food waste and swine manure, and co-substrate loading rate affected the biogas production rate. For the low loading rate, there was not so much difference according to the mixing ratio of food waste and swine manure, but for the high loading rate higher biogas yield was acquired for the co-digestion of food waste and swine manure than for the food waste alone (mixing ratio, 100:0).

Enhancement of biogas production in anaerobic co-digestion of food waste and waste activated sludge by biological co-pretreatment

Every day, a large amount of food waste (FW) is generated that causes serious environmental problems such as the production of greenhouse gases and leachate. A possible treatment for this waste is anaerobic digestion (AD), but there are several problems associated with the accumulation of volatile fatty acids (VFA), foaming, or low buffer capacity. In order to resolve or mitigate this problem, FW was mixed with cabbage and cauliflower (CCF) leaves and stalks at different carbon/nitrogen ratios (C/N) to add value to this agricultural waste and benefit from the advantages of co-digestion. Under the study conditions, promising results were obtained during the co-digestion of FW and agricultural wastes at C/N = 45. These include a high biodegradability (98%), a methane yield of 475 mLSTP CH4/g VS, and an organic loading rate (OLR) of 0.06 kg of VS/m3 h for the CCF and FW mixture (CCF + FW). Anaerobic co-digestion of CCF + FW might be an interesting option for the simultaneous treatment of these types of organic waste, with the consequent social and environmental benefits.

ABSTRACTBiopower can diversify energy supply and improve energy resiliency. Increases in biopower production from sustainable biomass can provide many economic and environmental benefits. For example, increasing biogas production through anaerobic digestion of food waste would increase the use of renewable fuels throughout California and add to its renewables portfolio. Although a biopower project will produce renewable energy, the process of producing bioenergy should harmonize with the goal of protecting public health. Meeting air emission requirements is paramount to the successful implementation of any biopower project. A case study was conducted by collecting field data from a wastewater treatment plant that employs anaerobic codigestion of fats, oils, and grease (FOG), food waste, and wastewater sludge, and also uses an internal combustion (IC) engine to generate biopower using the biogas. This research project generated scientific information on (a) quality and quantity of biogas from anaerobic codigestion of food waste and municipal wastewater sludge, (b) levels of contaminants in raw biogas that may affect beneficial uses of the biogas, (c) removal of the contaminants by the biogas conditioning systems, (d) emissions of NOx, SO2, CO, CO2, and methane, and (e) types and levels of air toxics present in the exhausts of the IC engine fueled by the biogas. The information is valuable to those who consider similar operations (i.e., co-digestion of food waste with municipal wastewater sludge and power generation using the produced biogas) and to support rulemaking decisions with regards to air quality issues for such applications.Implications: Full-scale operation of anaerobic codigestion of food waste with municipal sludge is viable, but it is still new. There is a lack of readily available scientific information on the quality of raw biogas, as well as on potential emissions from power generation using this biogas. This research developed scientific information with regard to quality and quantity of biogas from anaerobic co-digestion of food waste and municipal wastewater sludge, as well as impacts on air quality from biopower generation using this biogas. The need and performance of conditioning/pretreatment systems for biopower generation were also assessed.

Exploring feedstock proportions in anaerobic co-digestion of food and green waste for enhancing methane yield and process stability.

A shift from a linear economy to a circular economy of resource consumption is vital for diverting the value from lost resources to resource-efficient products towards developing a sustainable system. Household digesters provide one opportunity to create a biogas-based circular economy. Because household digesters are typically fed a wide and variable range of substrates, it is important to determine the ideal mixing ratios for them. In this study, an anaerobic digester startup process was analyzed and an assessment of anaerobic co-digestion of food waste with different livestock manures was carried out at ambient temperatures. Food waste (FW), cow manure (CM), poultry litter (PL) and goat manure (GM) were co-digested at mixing ratios (FW:PL:CM) of 2:1:1, 2:2:1, 1:1:2, 1:1:1 (wt/wt) and FW:PL:GM at mixing ratios of 2:1:1 and 1:1:2, at an organic loading rate of 1 g volatile solid (VS)/L/day, and 8% total solids. A maximum methane yield was obtained from co-digestion of FW:PL:GM at a mixing ratio of 2:1:1 in autumn-to-winter conditions, 21–10 °C, while the mixing ratio of FW:PL:CM at 2:2:1, showed negligible methane production under the same temperature condition. This study suggests that co-digestion of food waste and poultry litter with goat manure yields more biogas than other substrate combinations. Therefore, selecting suitable co-substrates with an optimized mixing ratio can promote several key indicators of a biogas-based circular economy towards achieving sustainable development goals 2, 3, 5, 6, 7, 9, 13 and 15.

Co-digestion of food waste and dairy manure in a mesophilic, completely mixed anaerobic digester was studied in the laboratory. Two mixtures of food waste and dairy manure were tested. The first mixture was composed of 32% food waste, based on volatile solids (VS) content, and 68% dairy manure; the second mixture was composed of 48% food waste and 52% dairy manure. For each mixture, the performance of the anaerobic digester was evaluated at two different organic loading rates (2 and 4 g VS L-1 d-1). The results showed that at 2 g VS L-1 d-1, the digesters were stable when fed with either mixture. The second mixture yielded a higher biogas production yield and rate (504 mL g-1 VS and 1010 mL L-1 d-1, respectively) than the first mixture (398 mL g-1 VS and 780 mL L-1 d-1, respectively). At 4 g VS L-1 d-1, the digester fed with the first mixture had stable performance, but the digester fed with the second mixture had large fluctuation in daily biogas production. The average biogas yields were 476 and 504 mL g-1 VS, respectively, and biogas production rates were 1910 and 2020 mL L-1 d-1, respectively, for the first and second mixture. No significant differences were found for VS removal between different conditions tested. Based on the measurement data, the energy generation potential of a farm digester was calculated for co-digestion of different amounts of manure and food waste.

Increasing production of food waste can lead to major environmental pollution if it is disposed without proper control in many countries. Food waste can be regarded as a resource rather than unwanted discard due to its high potential for resource recovery. Anaerobic digestion of food waste has shown promising potential for food waste treatment and valorisation by producing biogas as a renewable energy and digestate as fertiliser. Food waste has high biogas potential due to the presence of highly labile organic matter but this can lead to process instability. The process instability is often linked to the imbalance of process intermediates that affects the microbial community. Common parameters that are crucial for ensuring optimal metabolic activity of anaerobes includes temperature, pH, carbon-nitrogen ratio, organic loading rate, retention time and nutrient concentration. Co-digestion of food waste with other feedstocks are increasingly being practiced for better nutrient balance and reducing chances for rapid acidfication. The optimum conditions for the process has been shown to vary following different microbial inoculants and loadings of the respective substrates. This study aims to review only the effect of substrate and inoculum used during the AD of food waste, including the type of co-digested substrate, the mixing ratio, the microbial inoculant used and the substrate to inoculum ratio.

Background: The high cost of fossil fuels has driven the exploration of renewable energy alternatives. This study investigates the anaerobic co-digestion of waterleaf, cow dung, and food waste to optimize biogas production. Methods: Four co-digestion experiments were performed using a prototype plastic bio-digester over 50 days. The combinations tested were: waterleaf with cow dung, waterleaf with food waste, food waste with cow dung, and a mix of all three feedstocks. Results: Co-digestion of waterleaf and food waste yielded an average biogas output of 25%, with a pH of 7.2 and a carbon-to-nitrogen (C/N) ratio of 28. Combining waterleaf and cow dung produced a 31% yield, a pH of 7.2, and a C/N ratio of 29. The mixture of food waste and cow dung resulted in a 34% biogas yield, with a pH of 7.1 and a C/N ratio of 30. The highest yield, 46%, was achieved by co-digesting waterleaf, cow dung, and food waste, with a pH of 7 and a C/N ratio of 32. All feedstock combinations maintained neutral pH levels, benefiting from the unique properties of each component: waterleaf provided vitamins A and C, food waste supplied carbohydrates and proteins, and cow dung contributed anaerobic microbes essential for digestion. Additionally, temperature was a significant factor influencing biogas production. Conclusion: Co-digesting waterleaf, cow dung, and food waste maximized biogas production, demonstrating the potential for enhanced renewable energy generation through optimized anaerobic digestion processes.

Managing food waste is key to tackling climate change