Pilot-scale struvite recovery from anaerobic digester supernatant at an enhanced biological phosphorus removal wastewater treatment plant

Abstract

Pilot testing of a fluidized bed reactor used to recover phosphate, in the form of struvite, from anaerobic digester supernatant was conducted at the Advanced Wastewater Treatment Plant, City of Penticton, British Columbia. The main objective of this study was to demonstrate the ability of the reactor to remove at least 70% of the phosphate in the supernatant from a digester fed with a combination of primary and secondary sludge. It was found that the operation of the reactor could be controlled to achieve any desired level of phosphorus removal up to 90%. Analysis of the recovered struvite crystals showed essentially pure struvite (>99% by weight) with small amounts of calcium (<0.5% by weight) and traces of potassium and iron. The recovered crystals had mean diameters increasing from 0.5 to 1.8 mm over the course of the study. The increasing diameters are believed to be the result of changes in the crystal structures that caused them to become stronger over the course of the study.Key words: crystallization, nutrient removal, phosphorus recovery, struvite, sludge treatment, wastewater.