Enhanced Phosphate Recovery Using Crystal-Seed-Enhanced Struvite Precipitation: Process Optimization with Response Surface Methodology

Phosphate is an essential nutrient vital for the survival of living organisms. In recent years, demand for phosphate fertilizer has increased tremendously due to rapid population growth, thereby existing natural phosphate reserves become increasingly scarce. Hence, phosphate recovery from the wastewater had great significance. The present study examined the recovery of phosphate as struvite from fertilizer wastewater, and the recovery was enriched using the seeding method. The impact of different parameters pH and Mg:P molar ratio on phosphate recovery was investigated and the optimum conditions were observed as 10 and 1.6:1, respectively. The phosphate recovery corresponding to optimum pH and Mg:P molar ratio was 87.65%. In order to further enhance the phosphate recovery, seed was employed and the results indicated that steel powder improved phosphate-recovery efficiency. The presence of calcium in the solution inhibited the recovery of phosphate by struvite precipitation. Hence, calcium concentration in the solution must be controlled for recovering phosphate as struvite. In addition, the Box-Behnken design of the response surface methodology was used to optimize the phosphate-recovery process, and the interaction effect of parameters was also examined. An economic assessment revealed that the present study was economically feasible.