Anaerobic co-digestion of food waste and excess sludge by humus composites: Characteristics and microbial community structure
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Humus
Food Waste
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Published national and state reports have revealed that Australia deposits an average of 16 million Mg of solid waste into landfills yearly, of which approximately 12.6% is comprised of food. Being highly biodegradable and possessing high energy content, anaerobic digestion offers an attractive treatment option alternative to landfilling. The present study attempted to identify the theoretical maximum benefit of food waste digestion in Australia with regard to energy recovery and waste diversion from landfills. The study also assessed the scope for anaerobic process to utilize waste for energy projects through various case study scenarios. Results indicated anaerobic digestion of total food waste generated across multiple sites in Australia could generate 558 453 dam(3) of methane which translated to 20.3 PJ of heating potential or 1915 GWe in electricity generation annually. This would contribute to 3.5% of total current energy supply from renewable sources. Energy contribution from anaerobic digestion of food waste to the total energy requirement in Australia remains low, partially due to the high energy consumption of the country. However its appropriateness in low density regions, which are prevalent in Australia, may allow digesters to have a niche application in the country.
Food Waste
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This study has established that the use of a computer model, the Anaerobic Digestion Model 1, is suitable for investigation of the stability and energy balance of the anaerobic digestion of food waste. In simulations, digestion of undiluted food waste was less stable than that of sewage sludge or mixtures of the two, but gave much higher average methane yields per volume of digester. In the best case scenario simulations, food waste resulted in the production of 5.3 Nm3 of methane per day per m3 of digester volume, much higher than that of sewage sludge alone at 1.1 Nm3 of methane per day per m3. There was no substantial difference in the yield per volatile solids added. Food waste, however, did not sustain a stable digestion if its cation content was below a certain level. Mixing food waste and sewage sludge allowed digestion with a lower cation content. The changes in composition of food waste feedstock caused great variation in biogas output and even more so volatile fatty acid concentration, which lowered the digestion stability. Modelling anaerobic digestion allowed simulation of failure scenarios and gave insights into the importance of the cation/anion balance and the magnitude of variability in feedstocks.
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In spite of global efforts to reduce the generation of food waste, overwhelming quantities are still generated annually. In the United Kingdom for example, a third of the food crops produced annually for consumption end up in the bins. Anaerobic digestion (AD) is currently the most suitable technology for treating food waste, providing energy in the form of methane. However, the highly organic nature of food waste enriches the release of nutrients up to levels, which can be toxic or inhibitory to the acting microorganisms. As a result, the biomethane yields are much lower than the theoretical potential. This study investigates the possibility of improving the stability of AD and enhancing biomethane yield from mono-digestion of food waste, by a sequential optimisation of the biomethane production process.
The first level of optimisation was to identify suitable combinations of food waste particle size and microbial availability (inoculum-to-substrate ratio – ISR), to improve the process stability and biomethane yield. This investigation revealed that PS reduction (≤ 3 mm) resulted in a rapid digestion of food waste, and while this is expected to result in higher rates of acidification within the system, the variation in ISR helped to reduce such effects. Hence, an optimum condition of 1 mm PS and 3:1 ISR was determined; resulting in 38% increase in methane, and was used henceforth.
The second level of optimisation explored the potential for incorporating biomethanation into food waste AD. To optimise the conversion of the injected hydrogen to biomethane, three hydrogen injection points were investigated. As a result, 12.1%, 4% and 9.6% increases in biomethane yield were achieved, when hydrogen was added before hydrolysis, at the peak of acidification and during active methanogenesis respectively.
The third level of optimisation adopted the principle of acclimation to further improve the biomethane yield and explore the possibility of using formic acid (FA) as an alternative source of H2. The H2-acclimated systems performed better than the FA-acclimated systems, and yielded up to 81% biomethane against 65% without acclimation. Based on the results obtained in this study, it is possible to obtain up to 98% biomethane content, with continuous hydrogen acclimation. This reveals that the energy and revenue potential of food waste AD can be improved, by opening up multiple end uses beyond combined heat and power, such as gas-to-grid injection and vehicle fuel.
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Discharge of waste in general, and food waste, in particular, is considered one of the major environmental problems today, as waste generation increases continuously, reaching values of 32% of all food produced worldwide. There are many different options that can be applied to the management and evaluation of waste treatment, and Anaerobic Digestion seems to be one of the most suitable solutions because of its benefits, including renewable energy generation in form of biogas. Moreover, if FW (food waste) is digested in anaerobic digesters from Waste Water Treatment Plants, a common solution is provided for both residues. Furthermore, co-digestion of food waste and sewage sludge provides benefits in terms of anaerobic process stability enhancing the buffer capacity of ammonia (for example) and biogas formation, which can be increased up to 80% when compared with monodigestion. The present paper reviews food waste anaerobic digestion from its generation, characteristics and different options for its management, and it does focus specifically on the anaerobic digestion and co-digestion process, stages, limiting rates and parameters, utilizing numerous experiences, strictly related to food waste. Pre-treatments are also considered as they are important and innovative for enhancing biogas production and its methane yield. The paper shows an extensive collection of pre-treatments, its basics, improving factors, and numerical data of biogas formation improvements that are related both to substrate modification and to the synergistic effect of co-digestion, which could lead to an increase of methane production from 11% to 180%.
Food Waste
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Sewage sludge
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Anaerobic respiration
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Abstract Currently, sustainable societies require a reduction in general and food waste discharge, which is a major environmental problem. As food waste contains a high moisture content, anaerobic digestion is an effective way to recycle food waste that contains large amounts of moisture. While 70% of industrial food waste is recycled, only approximately 20% of household waste is recycled in Japan. In this study, we developed a micro anaerobic digestion system with a capacity of 30 L and evaluated its basic performance by simulating a daily use situation. Biogas was produced, containing the same amount of methane as other systems. Although no mixing in the fermenter was done, the production efficiency of methane reached approximately at least 60% of the theoretical value of methane gas production for the chemical oxygen demand of the input food waste.
Food Waste
Biogas
Biogas Production
Industrial fermentation
Biodegradable waste
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Food Waste
Biogas
Hydraulic retention time
Anaerobic respiration
Biodegradable waste
Biogas Production
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Food Waste
Digestate
Biogas
Biogas Production
Digestion
Biodegradable waste
Green waste
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Food Waste
Digestion
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Food waste is one of the major problems contributing to the degradation of the environment, and thus needs serious attention. Among different options, anaerobic digestion is possibly the most effective technique for managing degradable waste, and produce renewable energy and fertilizer. Despite multiple-use and benefits of the technology, its application is limited due to a few technical challenges. This study focuses on the anaerobic digestion of food waste with the addition of different percentages of digested cow manure as inoculum to it, at different total solid content in ambient temperature. Anaerobic digestion of food waste in batch and semi-continuous processes were carried out in three different trials at an average temperature range of 20-26℃: Food waste with 20% inoculum, food waste with 50%, 100%, and 200% inoculum and 10% total solid content in batch process and food waste with 20% inoculum with 6% and 10% total solids content in the semi-continuous process. During each trial, some amount of gas production was observed, however, the gas composition showed a negligible amount of methane production (maximum 13% of CH4). There were two common problems detected in each trial: the inability to complete the methanogenesis process, and instability of the overall process due to the high degradability and acidic nature of food waste. Therefore, this study suggests that the mono digestion of food waste is not a suitable option. However, anaerobic co-digestion of food waste with different organic substrate might provide a favorable condition for stable anaerobic digestion as seen from preliminary results.
Food Waste
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Biodegradable waste
Green waste
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Food waste is an inevitable type of waste in every city, and its treatment technology evolves with time. Due to the high organic content and high biodegradability of food waste, anaerobic digestion becomes a commonly accepted treatment method to deal with it. This review article summarizes key factors for anaerobic digestion and provides useful information for successful anaerobic digestions. Reasonable temperature and pH are essential for a successful and productive anaerobic digestion process. A good inoculum to substrate ratio triggers a profitable food waste digestion. Good mixing and small particle sizes are important factors too. In addition, the pros and cons of different reactors to food waste digestion are highlighted. Moreover, co-digestion of food waste with animal manures, sewage sludge, and green waste were introduced.
Food Waste
Biogas
Sewage sludge
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Biodegradable waste
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