Manure is a livestock residue that causes high environmental burdens in different categories. Its usage in biogas production is an environmentally beneficial way not only to reduce these impacts, but also to produce energy and biofertilizers. Although manure has low energy value and low biogas conversion efficiency, it is indicated for use in co-digestion with other substrates to produce biogas. The present work provides a systematic review of studies that have analyzed the production cycle of biogas from manure around the world, to detect and compare the critical points of the life cycle assessment (LCA) steps defined by the International Standardization Organization (ISO), as well as the biogas process steps. The critical points related to LCA structure in the analyzed articles involve the different boundaries considered, since the initial stage varies from one that considers only the input of raw material in the digestion process, to the one that considers the upstream steps to obtain the substrate. Despite this, the comparison of LCA structure in the analyzed articles is possible, since the ISO standards contain well-defined parameters and steps. The critical points in biogas production processes involve different variables in regional case studies, such as climate, raw material availability, transportation distance, source of inputs and energy, plant location and technological development level, hindering comparison between studies. In relation to the level of technologies, no details of industrial steps were observed in the LCA studies of manure biogas. In spite of the difficulty, comparison between stages is developed in this work to allow careful evaluation of critical points and environmental impacts, and consequently to help establish regional sustainability strategies for the production of biogas from manure.

粪便是一种牲畜残余物，会在不同类别中造成较高的环境负担。在沼气生产中使用它是一种对环境有益的方式，不仅可以减少这些影响，而且还可以生产能源和生物肥料。尽管肥料具有低的能量值和低的沼气转化效率，但已表明可与其他基质共同消化以产生沼气。本工作提供了对研究的系统评价，这些研究分析了来自世界各地粪便的沼气生产周期，以检测和比较国际标准化组织（ISO）定义的生命周期评估（LCA）步骤的关键点，例如以及沼气处理步骤。在所分析的文章中，与LCA结构相关的关键点涉及所考虑的不同边界，因为初始阶段从只考虑消化过程中原料输入的阶段到考虑到获得底物的上游步骤的阶段有所不同。尽管如此，由于ISO标准包含定义明确的参数和步骤，因此可以在分析的文章中比较LCA结构。沼气生产过程中的关键点涉及区域案例研究中的不同变量，例如气候，原材料可用性，运输距离，投入和能源来源，工厂位置和技术发展水平，这妨碍了研究之间的比较。关于技术水平，在LCA研究粪便沼气中未观察到任何工业步骤的细节。尽管有困难，