This paper provides an extensive review of anaerobic digestion (AD) systems, with a specific focus on community scale digesters for urban applications, processing either municipal organic waste exclusively or as mix feed. Emphasis is placed on reducing the systems scale environmental impact of AD technologies, including pre-and post-treatment stages, alongside biogas production. Developments to-date in AD system research in Europe and in the Asia region have been compared, providing a comprehensive evaluation of current practice, elucidating the areas of further potentials.The scope of this review is two-fold -one, covering AD technologies including a cohort of simple and integrated wet and dry systems, which can be operated as continuous flow designs in single-or multi-stages. Two, focusing more on practices in digestate handling that minimise environmental impacts arising from their storage and land application. From an environmental perspective, we note the following trends emerging in the literature for processing urban waste that need further exploitation: dry AD (60-85% moisture) is suitable for low organic loads, mainly owing to resource savings in terms of water usage; co-digestion has shown better buffering capability, especially for two-stage digestion of food-based feed stocks; separating the digestate into liquid/solid fractions is effective for handling postdigestion emissions, mainly for mitigating ammonia volatilisation to air and phosphate leaching to soil.We report responses to a survey, conducted for this review, highlighting the contemporary issues and challenges -with particular focus on the operational, social and management issues from an Indian perspective. There is need for follow-up of running plants to ensure their environmental performance. Such initiatives will have to consider managing of pollution footprints from AD, alongside the current drive for its widespread implementation for two incentives: greenhouse gas mitigation and fossil-fuel independence.
Highlights:· In situ air pollution assessment of land applied digestate is performed. · Environmental burden minimisation scenarios for digestate bio fertiliser presented. · Food-based digestate show high ammonia volatilisation potential. · Soil incorporated digestate effectively reduces NH 3 but elevates N 2 O emissions. · Managing digestate emissions mitigate both climate change and air pollution. Abstract (limit 150 words only)Anaerobic digestion (AD) of putrescible urban waste for energy recovery has seen rapid growth over recent years. In order to ascertain its systems scale sustainability, however, determination of the environmental fate of the large volume of digestate generated during the process is indispensable. This paper evaluates the environmental burdens to air associated with land applied food-based digestate in terms of primary pollutants (ammonia, nitrogen dioxide) and greenhouse gases (methane and nitrous oxide). The assessments have been made in two stages -first, the emissions from surface application of food-based digestate are quantified for the business as usual (BAU). In the next step, environmental burden minimisation potentials for the following three mitigation measures are estimated -mixed waste digestate (MWD), soil-incorporated digestate (SID), and post-methanated digestate (PMD). Overall, the mitigation scenarios demonstrated considerable NH 3 , CH 4 and N 2 O burden minimisation potentials, with positive implications for both climate change and urban pollution. Keywords: anaerobic digestion; bio fertilizer; digestate; environmental burdens; OFMSWCapsule abstract: In situ monitoring and analyses demonstrate the role of post-processing in greenhouse gases and air pollution mitigation from food-based digestate use as bio fertiliser. Highlights:· In situ air pollution assessment of land applied digestate is performed. · Environmental burden minimisation scenarios for digestate bio fertiliser presented. · Food-based digestate show high ammonia volatilisation potential. · Soil incorporated digestate effectively reduces NH 3 but elevates N 2 O emissions. · Managing digestate emissions mitigate both climate change and air pollution.3
Vegetable wastes (VW) and food wastes (FW) are generated in large quantities by municipal markets, restaurants and hotels. Waste slurries (250 ml) in 300 ml BOD bottles, containing 3, 5 and 7 % total solids (TS) were hydrolyzed with bacterial mixtures composed of: Bacillus, Acinetobacter, Exiguobacterium, Pseudomonas, Stenotrophomonas and Sphingobacterium species. Each of these bacteria had high activities for the hydrolytic enzymes: amylase, protease and lipase. Hydrolysate of biowaste slurries were subjected to defined mixture of H 2 producers and culture enriched for methanogens. The impact of hydrolysis of VW and FW was observed as 2.6-and 2.8-fold enhancement in H 2 yield, respectively. Direct biomethanation of hydrolysates of VW and FW resulted in 3.0-and 1.15-fold improvement in CH 4 yield, respectively. A positive effect of hydrolysis was also observed with biomethanation of effluent of H 2 production stage, to the extent of 1.2-and 3.5-fold with FW and VW, respectively. The effective H 2 yields were 17 and 85 l/kg TS fed, whereas effective CH 4 yields were 61.7 and 63.3 l/kg TS fed, from VW and FW, respectively. This ecobiotechnological strategy can help to improve the conversion efficiency of biowastes to biofuels.
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