Study of pig manure digestate pretreatment - Results and Figures

This work evaluates the release of phosphorus contained in the digestate from the anaerobic digestion of pig manure, through an acidification process. The objective of this acidification is to increase the amount of phosphorus available in the digestate liquid fraction and, subsequently, recover this element by chemical precipitation in the form of struvite or calcium phosphate. Two digestate samples (one fresh and one old) were studied and treated by adding various amounts of sulphuric acid to the different digestate fractions (raw digestate, solid fraction and liquid fraction). For the raw digestate, phosphorus releases higher than 95% were obtained for pH 4.0. In the last part of the experiment, the influence of acid pre-treatment on the reaction yield of phosphorus precipitation, in the form of struvite or calcium phosphate, was determined. Improvements in reaction yield were obtained up to 15% for struvite and 80% for calcium phosphate, increasing also in 7.5 times the amount of phosphorus available in the digestate liquid fraction, for both cases.本研究通过酸化工艺，评估猪粪厌氧消化消化出料（digestate）中所含磷的释放特性。本次酸化的目标为提升消化出料液相组分中的有效磷含量，后续再通过化学沉淀法，以鸟粪石（struvite）或磷酸钙（calcium phosphate）的形式回收该磷元素。本研究选取两份消化出料样品（一份新鲜样品与一份陈化样品），针对原始消化出料、固相组分与液相组分三类不同的消化出料组分，通过添加不同剂量的硫酸开展处理实验。实验结果显示，对于原始消化出料，当pH值为4.0时，磷释放率可达95%以上。在实验的最后阶段，本研究测定了酸化预处理对以鸟粪石或磷酸钙形式进行的磷沉淀反应产率的影响。结果表明，两种沉淀形式的反应产率均得到提升：鸟粪石的产率提升幅度可达15%，磷酸钙的产率提升幅度可达80%；且两种工况下，消化出料液相组分中的有效磷含量均提升了7.5倍。