Supersaturation control of struvite growth by operating pH

Abstract

Struvite crystallization has attracted more and more attention as it is a promising strategy to recover phosphorus and nitrogen from wastewater and simultaneously produce a valuable fertilizer. However, the fine crystals formed during the process make the liquid–solid separation difficult which impedes its industrial application. This paper aims to produce struvite crystals with bigger sizes through the modification of crystal growth process. In this study, the metastable zone defined by pH was determined and pH of the solution was employed to modify the driving force of struvite crystallization process. With the aid of real time solution information, the continuous feed back control of pH-supersaturation was put forward and conducted to regulate the growth of struvite crystals. Secondary nucleation during the growth process was effectively inhibited which enhanced the final crystal size, and the settling velocity was improved about 10 times compared with those without growth regulation. The results showed that the crytallization technology with pH-supersaturation control might be a good solution to the problem of struvite separation.