In municipal wastewater treatment plants (WWTPs), algae could be utilised for cleaning the water and, at the same time, produce a biomass that can be used for energy. Through anaerobic digestion, microalgae can contribute to biogas production when co-digested with sewage sludge. In this paper, previous published results on the co-digestion of sewage sludge and microalgae are summarised and reviewed, and any remaining knowledge gaps are identified. The batch tests currently documented in literature mostly concern digestion under mesophilic conditions, and studies investigating thermophilic conditions are less common. The average biochemical methane potential (BMP) for 29 different mixtures co-digested under mesophilic conditions is 317 ± 101 N cm³ CH₄ gVS⁻¹ while the result for 12 different mixtures investigated under thermophilic conditions is a BMP of 318 ± 60 N cm³ CH4 gVS⁻¹. An evaluation of the heat required for increasing the temperature from mesophilic to thermophilic conditions shows that increased methane production under thermophilic conditions can be enough to create a positive energy balance. For a full-scale WWTP, using thermophilic digestion on sludge, or a combination of sludge and microalgae could therefore be of interest. This is dependent on the demands on sanitation of the sludge and the possibilities for heat recovery.

Most of the mesophilic investigations indicate a synergetic effect for co-digestion, with enhancements of up to almost 70%. However, the results are uncertain since the standard deviations for some of the BMP tests are in the same order of magnitude as the identified enhancement. Neither of the presented publications provide an understanding of the basic mechanisms that led to higher or lower BMP when microalgae were mixed with wastewater sludge. We, therefore, call for care to be taken when assuming any effects related to the specification of substrates. Microalgae and wastewater sludge have several similarities, and the specific results of BMP in the mixtures relate more to the specifics of the respective materials than the materials themselves.

Investigations into semi-continuous processes of co-digestion of microalgae and sludge are scarce. The yields for three co-digestion studies show high variation, with an average of 293 ± 112 N cm³ gVS_in⁻¹. The available results show strong potential for co-digestion of sewage sludge and microalgae. Further investigations are required to identify optimal conditions for biogas production, and analysis of microalgae implementation on wastewater treatment at a system level is also needed to identify the total mass balance of substrate and nutrient recovery.

在市政废水处理厂（WWTP）中，藻类可用于清洁水，同时生产可用于能源的生物质。通过厌氧消化，微藻类与污水污泥共同消化可促进沼气生产。在本文中，总结并回顾了以前发表的关于污水污泥和微藻类共消化的结果，并找出了任何剩余的知识空白。目前在文献中记录的批量测试主要涉及在嗜温条件下的消化，而研究嗜热条件的研究则较少见。在中温条件下共同消化的29种不同混合物的平均生物化学甲烷势（BMP）为317±101 N cm ³ CH ₄ gVS ^-1在高温条件下研究的12种不同混合物的BMP为318±60 N cm ³ CH4 gVS ^-1。对将温度从嗜温条件提高到嗜热条件所需热量的评估表明，在嗜热条件下增加的甲烷产量足以产生正能量平衡。对于大规模污水处理厂，对污泥或污泥与微藻的组合使用嗜热消化法可能会引起人们的兴趣。这取决于对污泥的卫生要求和热回收的可能性。

大多数嗜温性研究表明，共同消化作用具有协同作用，最多可提高70％。但是，由于某些BMP测试的标准偏差与确定的增强值处于相同的数量级，因此结果不确定。所提供的出版物均未提供对将微藻类与废水污泥混合时导致BMP升高或降低的基本机理的理解。因此，我们在假定与基材规格有关的任何影响时都应格外小心。微藻类和废水污泥有一些相似之处，混合物中BMP的具体结果比材料本身更与各自材料的特性有关。

对微藻类和污泥共消化的半连续过程的研究很少。三个共消化研究的产量显示出高的变异性，平均值为293±112 N cm ³ gVS _in ^-1。现有结果表明，有很大的潜力可以共同消化污水污泥和微藻。需要进行进一步的调查以确定沼气生产的最佳条件，还需要在系统水平上分析微藻在废水处理中的实施情况，以确定基质和营养物回收的总质量平衡。