Optimised percolate recirculation strategy for batch dry anaerobic digestion

干批式厌氧消化（AD）是一种越来越多地用于处理城市固体废物（OFMSW）有机部分的方法，每年可避免数百万吨的垃圾填埋，同时允许从废物中生产可再生能源。尽管有众所周知的好处，但干AD与在固体含量20%下操作引起的操作问题有关，包括抑制剂（例如挥发性脂肪酸（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可达到的产量。向原料中添加接种物是试图解决抑制问题的最常见策略之一，但它减少了可用于废物处理的体积。最近的研究提出了在干AD过程中形成的渗滤液的再循环，作为接种物添加的替代或组合。由于缺乏对改进过程的机制的科学理解，所产生的好处受到限制。因此，本研究的目的是调查一个优化的渗滤液再循环策略，可以最大限度地提高沼气生产和处理能力，在干消化装置在分批模式下运行，并这样做的几个原料最常用的干AD。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）确定渗滤液再循环是否适合减轻由于氨或VFA积累引起的局部抑制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产和处理能力4）了解渗滤液再循环策略所需的变化，具体取决于原料类型和是否使用填充剂5）根据基质降解的演变，量化动态渗滤液再循环策略在分批发酵期间的变化该项目是克兰菲尔德大学（英国）和UTC（法国）之间的合作，将要求学生花费大约一半的博士时间在每个机构。

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.