Struvite precipitation within wastewater treatment: A problem or a circular economy opportunity?

Enhanced biological phosphorus removal at wastewater treatment plants that use anaerobic digesters for sludge treatment have historically encountered phosphate precipitation problems in the form of struvite. Literature on struvite is thin which is surprising given it can foul/block the sludge return lines and associated pumps and valves, causing significant operational problems. This study has evaluated if a typical large wastewater treatment plant can overcome this problem by adopting circular economy thinking. The struvite profile based on the supersaturation ratio of (Mg:NH₄:PO₄ ^2-), pH and temperature demonstrates the potential operational hotspots that can present uncontrolled struvite formation. Based on current struvite monitoring technologies and a cost-benefit analysis, the controlled struvite recovery via an Ostara crystallization reactor has been demonstrated to be economically viable with a pay-back period of less than a decade. An integrated evaluation illustrates the positive environmental impact arising from the utilisation of the recovered product. Economic viability and payback periods will vary according to circumstances, but we recommend that WWTP operators globally consider fitting a crystallisation reactor to appropriate plants, The outcomes and recommendation from this study are particularly timely given the global fertiliser shortage (2022) that is driving up food prices and reducing crop sizes.