Phosphorus recovery from sludge by rusty scrap iron enhanced anaerobic digestion and vivianite crystallization

Phosphorus (P) scarcity is a global problem. On the other hand, sludge is a rich second source of phosphorus. A new approach for recovering P from waste activated sludge using rusty scrap iron (RSI) adjustment-enhanced anaerobic digestion and vivianite crystallization was devised in this work. The findings suggest that acidic environments favor P removal by RSI. The clearance rate of total phosphorus (TP) declined from 18.30% to 0.81% when the pH climbed from 3 to 10. Raising the Fe/P ratio (β) in a particular range promotes anaerobic digestion of sludge. The elimination rate of TP rose from 10.44% to 51.37% when it was raised from 1.0 to 8.0. The temperature has little influence on phosphorus removal effectiveness in the range of 15–45 °C. The theoretical optimal procedure in the orthogonal test of three components and four levels is that the temperature is 35 °C, the β is 2.5, and the pH is 4.