Optimised percolate recirculation strategy for batch dry anaerobic digestion

干批厌氧消化(AD)是一种越来越多地使用的处理城市固体废物(OFMSW)的有机部分，避免了每年数百万吨的垃圾填埋，同时允许从废物中生产可再生能源。尽管干ADS有众所周知的好处，但干ADS在固体含量为20%的情况下运行时会出现操作问题，包括抑制剂(如挥发性脂肪酸(VFA)、游离氨)的局部积累、混合不良、处理能力有限、反应动力学缓慢以及沼气产量远低于实验室规模的可获得的沼气产量。向原料中添加接种剂是试图解决抑制问题的最常见策略之一，但它会减少可用于废物处理的体积。最近的研究建议将干燥AD期间形成的渗滤液再循环作为接种添加的替代或组合。由此产生的好处受到对改进进程的机制缺乏科学理解的限制。因此，本研究旨在研究一种优化的渗滤液再循环策略，以最大限度地提高以间歇模式运行的干式消化单元的沼气产量和处理能力，并对干式AD中最常用的几种原料进行优化。实现这一目标的具体目标是：1)阐明渗滤液再循环改善干AD性能的机制2)确定渗滤液再循环对缓解氨或VFA积累引起的局部抑制的适用性3)提出渗滤液再循环策略(体积和频率)，以实现最佳的沼气生成和处理能力4)了解渗滤液再循环策略根据原料类型和膨胀剂的使用与否而有所不同5)量化动态渗滤液再循环策略的好处，该策略在间歇发酵过程中根据基质降解的演变而变化该项目是英国克兰菲尔德大学和法国UTC大学的合作项目，将要求学生在每个机构花费大约一半的博士时间。

Dry-batch anaerobic digestion (AD) is an increasingly used treatment for the organic fraction of municipal solid waste (OFMSW), avoiding disposal to landfill of millions of tonnes every year while allowing for renewable energy production from waste. Despite the well-known benefits, dry ADs are associated with operational problems resulting from operation at solids contents 20%, including localised accumulation of inhibitors (e.g. volatile fatty acids (VFA), free ammonia), poor mixing, limited treatment capacity, slow reaction kinetics and biogas yields much lower than those attainable in laboratory scale. Addition of inoculum to the feedstock is one of the most common strategies attempting to solve inhibition problems, but it reduces volume available for waste treatment. Recent studies have proposed recirculation of percolate formed during dry AD as an alternative or in combination to inoculum addition. The resulting benefits are capped by the lack of scientific understanding of the mechanisms by which process is improved. Therefore, this study aims to investigate an optimised percolate recirculation strategy that can maximise biogas production and treatment capacity in dry digestion units operated in batch mode, and to do so for the several feedstocks most commonly used in dry AD. The specific objectives to fulfil the aim are: 1) Elucidate the mechanisms by which percolate recirculation improves dry AD performance2) Determine suitability of percolate recirculation to mitigate localised inhibition due to ammonia or VFA accumulation3) Propose a percolate recirculation strategy (volume and frequency) that allows optimal biogas generation and treatment capacity4) Understand required variations on percolate recirculation strategies depending on feedstock type and use or not of bulking agents5) Quantify benefits of a dynamic percolate recirculation strategy that varies during batch fermentation according to evolution of substrate degradationThis project is a collaboration between Cranfield University (UK) and UTC (France) and will require the student to spend approximately half of the PhD time on each institution.