Phosphorus recovery from municipal wastewater through struvite biomineralization using model gram-negative and gram-positive bacterial strains

The present study investigated struvite biomineralization potential of model gram-negative (Enterobacter cloacae) and gram-positive (Bacillus pumilus) bacterial strains in synthetic municipal wastewater. Both micro-organisms were able to precipitate struvite crystals and the growth pattern, change in pH, ammonium and phosphate ion concentration for both the cultures were comparable. The pH of the medium increased from 6.4 to 8.8 after 3 days of incubation when the cultures attained the saturation phase. The ammonium concentration increased from initial concentration of 40 mg/L to nearly 200 mg/L after 3 days of incubation for both the bacterial strains, whereas phosphate concentration decreased from initial 20 mg/L to 3.4 mg/L and 0.8 mg/L for Bacillus pumilus and Enterobacter cloacae respectively. The mechanism involved in struvite biomineralization was also explained in detail for Enterobacter cloacae and Bacillus pumilus. The precipitation of struvite by Enterobacter cloacae is due to biologically controlled mineralization while Bacillus pumilus mineralized struvite crystals through biologically induced mineralization mechanism. Results were further validated in real influent collected from a sequencing batch reactor of an influent treatment plant. Results demonstrated that Bacillus pumilus was able to precipitate crystals in real influent whereas no precipitation was observed by Enterobacter cloacae in real influent. This study gives an insight into bacterial biomineralization in wastewater to enable recovery of nutrients (phosphorus and nitrogen) and circularity in treatment plants. Further utilization of the recovered product as fertilizer can play a key role in contributing towards meeting global food security.