A regular supply of nutrients such as nitrogen and phosphorus to agriculture is needed for global food security, and increased recycling of nutrients back to agriculture from organic waste streams is necessary for increased rural–urban sustainability. Anaerobic digestion of sewage sludge and agricultural wastes is widely applied to stabilize the substrate and capture some of its energetic value via biogas production. Anaerobic digestate is a concentrated source of nutrients to which nutrient recovery technologies can be applied. By combining anaerobic digestion and nutrient recovery technologies on the digestate, both energy and nutrient recovery can be achieved. Two promising technologies that could increase nutrient recycling from different types of wastewater are struvite precipitation and ammonia stripping. This review examined the effectiveness of these ecotechnologies for the recovery of nitrogen and phosphorus from anaerobic digestate with the aim of reducing the impact of waste on the environment. We searched for academic and grey literature published after 2013. Searches were performed in 5 bibliographic databases in English, in the search engine Google Scholar in English, Swedish, Finnish and Polish, and across a range of organisational websites in English, Swedish, Finnish and Polish. Eligibility screening was conducted at two levels: ‘title and abstract’ and ‘full text’. Included eligible studies were subject to a critical appraisal that assessed external and internal study validity. We extracted information on study characteristics, intervention, comparators, effect modifiers, and measured outcomes. Data synthesis included narrative synthesis of each study of sufficient validity. We performed quantitative synthesis on a subset of studies. The review included 30 studies on struvite precipitation and 8 studies on ammonia stripping. Both pH and Mg:PO4 ratio were found to have a clear influence on the effectiveness of struvite precipitation process (and thus nutrient removal rates). The response to pH was found to be non-linear, resembling a bell curve with a maximum around pH 9.5. Mg:PO4 ratio was found to have a positive effect on removal up to a ratio as high as 4:1. However, it should be noted that high removal efficiencies were sometimes achieved at a ratio as low as 1:1 as well. Although the effects of pH and Mg:PO4 ratio were clear, the model developed could not accurately predict removal based on these two parameters alone. Studies on ammonia stripping were relatively heterogeneous. Due to the small size of the evidence base, and the heterogeneity between studies, no conclusions are presented regarding the influence of different process parameters on the outcome of ammonia stripping. In conclusion, when performed under the right conditions (i.e. pH around 9.5 and Mg:PO4 ratio of at least 1:1), available evidence suggests that struvite precipitation is an effective technology for the recovery of nutrients from the liquid phase of anaerobic digestate. The evidence base is limited for ammonia stripping. We provided suggestions of which data to report in future studies.

中文翻译：

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鸟粪石沉淀和氨气去除从厌氧消化物中回收磷和氮的有效性：系统综述

为了全球粮食安全，需要定期向农业供应氮和磷等养分，为提高城乡可持续性，必须增加从有机废物流向农业的养分循环利用。污水污泥和农业废料的厌氧消化被广泛用于稳定基质并通过沼气生产来获取其高能价值。厌氧消化物是营养物的集中来源，可以应用营养物回收技术。通过将厌氧消化和养分回收技术相结合，可以实现能量和养分的回收。鸟粪石沉淀和氨汽提是可以增加不同类型废水的养分循环利用的两项有前途的技术。这篇综述检查了这些生态技术从厌氧消化物中回收氮和磷的有效性，目的是减少废物对环境的影响。我们搜索了2013年之后出版的学术和灰色文献。搜索在5个英语书目数据库中，在搜索引擎Google Scholar中以英语，瑞典语，芬兰语和波兰语进行搜索，以及在一系列组织网站中用英语，瑞典语，芬兰语和抛光。资格筛选分为两个级别：“标题和摘要”以及“全文”。纳入的合格研究均经过严格评估，以评估外部和内部研究的有效性。我们提取了有关研究特征，干预措施，比较者，效果修正剂和测量结果的信息。数据综合包括每个研究的叙述性综合，具有足够的有效性。我们对一部分研究进行了定量合成。审查包括鸟粪石沉淀的30项研究和氨汽提的8项研究。发现pH和Mg：PO4的比例均对鸟粪石沉淀过程的有效性（以及因此的营养去除率）有明显的影响。发现对pH的响应是非线性的，类似于钟形曲线，其最大值约为pH 9.5。发现Mg：PO4比例高达4：1时对去除具有积极作用。但是，应注意的是，有时也以低至1：1的比例获得高去除效率。尽管pH和Mg：PO4比例的影响很明显，但是仅基于这两个参数，开发的模型无法准确预测去除量。关于氨汽提的研究相对而言是异质的。由于证据基础的规模小，以及研究之间的异质性，因此没有得出关于不同工艺参数对氨汽提结果的影响的结论。总之，在正确的条件下（即pH值约为9.5，Mg：PO4的比例至少为1：1）时，现有证据表明鸟粪石沉淀是一种从厌氧消化液液相中回收营养物的有效技术。氨气汽提的证据基础有限。我们提供了有关在以后的研究中报告哪些数据的建议。没有给出关于不同工艺参数对氨汽提结果的影响的结论。总之，在正确的条件下（即pH值约为9.5，Mg：PO4的比例至少为1：1）时，现有证据表明鸟粪石沉淀是一种从厌氧消化液液相中回收营养物的有效技术。氨气汽提的证据基础有限。我们提供了有关在以后的研究中报告哪些数据的建议。没有给出关于不同工艺参数对氨汽提结果的影响的结论。总之，在正确的条件下（即pH值约为9.5，Mg：PO4的比例至少为1：1）时，现有证据表明鸟粪石沉淀是一种从厌氧消化液液相中回收营养物的有效技术。氨气汽提的证据基础有限。我们提供了有关在以后的研究中报告哪些数据的建议。氨气汽提的证据基础有限。我们提供了有关在以后的研究中报告哪些数据的建议。氨气汽提的证据基础有限。我们提供了有关在以后的研究中报告哪些数据的建议。