Pilot-scale study of phosphorus recovery through struvite crystallization - examining the process feasibility

The suitability of a new pilot-scale reactor to recover phosphorus through struvite crystallization was examined. Based on the similar principles previously tested in bench-scale reactors and scaled up to overcome operating problems encountered in earlier work, the pilot-scale crystallizer was used to effectively remove-recover phosphorus from synthetic wastewaters. Ortho-P removal rates as high as 90% were obtained for low (similar to50-70 mg/L P) and medium (similar to70-100 mg/L P) strength wastewaters. To achieve these removal rates, a relatively high pH value of 8.3 was required. Over 90% of the removed phosphates could be recovered in the form of harvestable struvite crystals with a mean size of 2.5-3.5 mm and sufficient mechanical strength to permit harvesting-reuse. A new concept of crystal retention time (CRT) has been developed, which is used to make estimates of the struvite crystal age. Results of this study indicate that CRT is one of the main factors affecting the mean crystal size.