Phosphorus reclamation by end-of-pipe recovery as calcium phosphate from effluent of wastewater treatment plants of agroindustry

Phosphorus is essential for live and must be recovered from all possible secondary resources. One of these secondary resources may be the effluent of a wastewater treatment plant in which no obvious measures are taken to remove or recover the phosphorus. Effluent water of the wastewater treatment facility of a potato processor was spiked with 40-50 mg phosphate-P.L-1 to simulate such a water that can be subjected to an end-of-pipe recovery of phosphate. Simulations with PHREEQC were calculated and batch experiments were performed. Continuously stirred tank reactors (CSTR) were fed with P-spiked effluent. Increasing the Ca/P ratio promoted calcium phosphate precipitation but increased also the calcium carbonate contamination. With calcium added in fourfold excess relative to endogenous phosphate-P concentration, 90 % removal can be obtained. For the recovery of phosphorus from this purified effluent the same Ca/P ratio is necessary than in the case where phosphorus is recovered from nitrified UASB effluent. The recovery is stimulated by aeration, which however should not be continuous and by the addition of 5 g L(-1 )hydroxyapatite and reaches up to 95 %. In contrast to what was expected based upon the batch experiments, but in agreement with the simulations, the precipitates contained up to 6 m% magnesium phosphate, which probably can further be reduced by using shorter hydraulic retention times in the reactor.