Struvite recovery from anaerobically digested waste-activated sludge: A short review

Effective treatment of waste streams such as municipal waste-activated sludge (WAS) presents an opportunity for energy and nutrient recovery, water reclamation, and mitigation of climate change. WAS is a waste product of the activated sludge treatment (AST) process widely used for municipal wastewater. Currently, WAS treatment and disposal account for up to 50% of the total operation cost and 40% of the total greenhouse gas emissions from wastewater treatment plants. Anaerobic digestion (AD) is usually preferred for WAS treatment since it is more economical compared to other existing technologies. The decomposition of sludge during AD releases nutrients, which are then discharged in the anaerobic effluent, polluting recipient water bodies and increasing the nutrient burden. The nutrients, mainly nitrogen (N), phosphorus (P), and potassium (K), can be crystallised into struvite (magnesium ammonium phosphate, NH4MgPO4.6H2O) with numerous agricultural applications as fertilisers. The present review focusses on struvite recovery from anaerobically digested WAS and its potential application for crop production.