Abstract

Direct landspreading of anaerobic digestates is the most common digestate management strategy. Nevertheless, digestate post-treatment can be unavoidable, especially for environmental services providers operating large-scale anaerobic digestion (AD) facilities. This review aims to assess the technical feasibility of achieving value-added products from digestates from urban and/or centralized AD plants (UC-AD). An exhaustive effort was dedicated to identifying and clarifying the available processing technologies and specific issues that can be related to UC-AD digestates. The valorization options were classified according to the final product destination. The result is a useful information source for assessing digestate valorization pathway given a local market and context. Agriculture was the first destination to be considered, as it allows a more direct closing of nutrient and carbon cycles. Several processes exist either for concentrating desirable characteristics of digestates, enhancing organic matter stability or producing pure and reformulated fertilizers. Thermal conversion processes are either under development or full-scale demonstration. They allow to valorize the solids through the production of biofuels and/or biochar and in the coming future, to start a whole biorefinery system. Similarly, biomass harvesting processes such as microalgae are under upscaling, enabling to valorize the nutrients of the digestate liquid phase while producing renewable biomass from sunlight. Several value-added products were already obtained in laboratory to pilot conditions from UC-AD digestates, for example, biopesticides, biosurfactants and composite materials. Adding to technical challenges, the quality variation of digestates, regulation barriers, public acceptance and the difficult access to new markets are among the main obstacles to UC-AD digestates valorization into value-added products.

Graphic abstract

中文翻译：

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评估城市或集中式沼气厂消化物的价值：一项重要评论

摘要

直接厌氧消化物的土地传播是最常见的消化物管理策略。然而，消化后处理是不可避免的，特别是对于操作大型厌氧消化（AD）设施的环境服务提供商而言。这篇综述旨在评估从城市和/或中央AD工厂（UC-AD）的消化物中获得增值产品的技术可行性。竭尽全力致力于识别和澄清与UC-AD摘要有关的可用处理技术和特定问题。评估选项根据最终产品目的地分类。结果是在给定本地市场和环境的情况下评估消化物增值途径的有用信息来源。农业是第一个被考虑的目的地，因为它可以更直接地关闭养分和碳循环。存在几种用于浓缩消化物的所需特性，增强有机物稳定性或生产纯肥料和重新配制肥料的方法。热转化工艺正在开发中或正在全面示范中。它们允许通过生产生物燃料和/或生物炭来增值固体，并在未来的将来启动整个生物精炼系统。类似地，诸如微藻类的生物质收获过程正在扩大规模，从而能够在利用阳光产生可再生生物质的同时，使消化液相的营养价值得到平衡。在实验室中已经从UC-AD消化物中获得了一些增值产品，以进行试验条件，例如生物农药，生物表面活性剂和复合材料。

图形摘要