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Coupling of phosphorus recovery to an enhanced biological phosphorus removal process through a sidestream : a pilot scale study Srinivas, Hemanth Kumar

Abstract

This research was initiated with the purpose to remove and recover phosphorus simultaneously, by coupling a sidestream for phosphorus recovery to an enhanced biological phosphorus removal (EBPR) process. Sidestream process comprised of a phosphorus release unit along with a clarifier connected to the MAP (magnesium ammonium phosphate) crystallizer. To understand the sidestream process and to investigate the optimum operating conditions, the configuration was simulated using ASM2-Delft metabolic bio-P model on AQUASIM platform. The simulation exercise revealed that anoxic is the best zone to take sidestream when taken individually and anoxic/anaerobic when taken in combination. In both the cases N: P molar ratio of the supernatant was more than 1:1 which is essential for the recovery of phosphorus as struvite. The minimum hydraulic retention time required in the phosphate release unit was found to be around one to two hours, above which there was no considerable amount of phosphate released. Potentially, up to 78% of the incoming phosphorus is estimated to be recovered by implementing sidestream technology. Based on the simulation results, sidestream process was successfully implemented at UBC pilot plant for both membrane and conventional enhanced biological phosphorous removal processes (MEBPR and CEBPR). The MAP crystallizer was used to recover phosphorus as struvite. Although, the recovery efficiency obtained was not very high (approximately 60%), the refined conditions as suggested should yield better results. Sidestream wasting method to control the solid retention time of the process indicated selective increase of phosphorus accumulating organisms in the main EBPR process. Sidestream wasting also reduced the phosphorus rich sludge wasting from the aerobic zone of the EBPR process. Magnesium (Mg) was added to the influent of the process to increase the Mg²⁺ concentration in the sidestream supernatant to provide better conditions for struvite formation. The CEBPR and MEBPR processes experienced poor phosphorus removal after Mg addition was started. More detailed investigation is suggested to look in to the effects of magnesium on the EBPR process along with potassium.

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