Experimental and Modeling Assessment of the Main Bio-physical-chemical Mechanisms and Kinetics in High-solids Anaerobic Digestion of Organic Waste

Download or read book Experimental and Modeling Assessment of the Main Bio-physical-chemical Mechanisms and Kinetics in High-solids Anaerobic Digestion of Organic Waste written by Vicente Pastor Poquet and published by . This book was released on 2018 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The organic fraction of municipal solid waste (OFMSW) includes readily biodegradable wastes such as food waste, and slowly biodegradable wastes such as lignocellulosic materials. Anaerobic digestion (AD) is a mature treatment biotechnology in which OFMSW is decomposed to a mixture of methane (CH4) and carbon dioxide (CO2), known as biogas. Due to the elevated CH4 content (50-70%), biogas can be used as a source of renewable energy. Moreover, AD yields a partially stabilized digestate, allowing the recycle of nutrients to agriculture. High-solids anaerobic digestion (HS-AD) is a well-suited strategy to enhance the overall AD efficiency for OFMSW treatment. HS-AD is operated at a total solid (TS) content ≥ 10%, permitting to reduce the reactor size and overall operational costs. Nonetheless, the TS increase can result into biochemical instability, and even reactor failure by acidification. Both the high organic load and the buildup of inhibitors can be responsible for the HS-AD instability. The most notable inhibitor in HS-AD of OFMSW is NH3. Therefore, a balance is often required between enhancing the HS-AD economy and the 'undesired' instability for OFMSW treatment. This PhD research investigated the main bio-physical-chemical mechanisms and kinetics in HS-AD of OFMSW, with the aim to optimize the industrial application and maximize the kinetic rates. Laboratory-scale batch and semi-continuous experiments highlighted the main strengths and weaknesses of HS-AD. Simultaneously, the development of a HS-AD model permitted to condense the experimental knowledge about the bio-physical-chemical effects occurring when increasing the TS content in HS-AD.HS-AD batch experiments required a tradeoff between the initial TS, the inoculum-to-substrate ratio (ISR), the alkalinity and the nitrogen content, to assess the effects of increasing the initial TS content upon the methane yield, TS removal and chemical oxygen demand conversion. Particularly, a low ISR led to acidification, whereas the NH3 buildup led to volatile fatty acid (VFA) accumulation, reducing the methane yield, whether or not co-digestion of OFMSW with beech sawdust was used.In semi-continuous experiments, HS-AD of OFMSW required a reduced effluent compared to the influent to counterbalance the organic mass removal associated to the biogas production. Nonetheless, mono-digestion of readily-biodegradable OFMSW could not sustain a TS ≥ 10% without exacerbating the risk of substrate overload. Overloading was associated to the high biodegradability and the NH3 buildup. Thus, adding sawdust to OFMSW permitted to operate the reactors up to 30% TS, due to the lower biodegradability and nitrogen content of lignocellulosic substrates. As the main novelty of this PhD research, a HS-AD model based on the Anaerobic Digestion Model No.1 (ADM1) was developed. This model simulates the reactor mass and TS in HS-AD, in contrast of models focusing on 'wet' AD simulations (TS