Factors contributing to phosphorus sorption reversibility from iron-desalinization treatment residue (Fe-DTR)

Phosphorus (P), a non-renewable nutrient, requires effective, innovative recycling practices, especially because of predicted future scarcity. This study focused on the adsorption-desorption of P from iron desalinization treatment residue (Fe-DTR) mixed with dairy wastewater to create an alternative fertilizer (P-Fe/O-DTR). Sequential extraction indicated that P adsorption onto Fe-DTR, at pH 3, predominantly favored adsorption onto iron oxides collected in summer (72 %) versus winter (59 %), due to the elevated use of FeCl3 coagulant in summer in the desalinization pre-treatment. Desorption experiments indicated that the irreversibility of sorption (apparent hysteresis index) was highest under aerobic conditions, using a synthetic P solution, ambient temperature and pH range of 7–3 (98.9–98.3 %). Irreversibility was lowest under anaerobic conditions, using dairy wastewater as a P source, at pH 7 and 40 °C (76.6 %). This suggests that loading settings of organic solution as a P source and high temperature at the sorption stage are favored for extracting P from P-Fe/O-DTR with the greatest potential for release and reuse. Desorption experiments of 3 d, 1 week and 9 weeks indicated that the initial equilibrium forms within 72 h, but resorption and precipitation processes establish a new equilibrium over time (week). Phosphorus desorption was strongly affected by the aeration conditions of the experiment followed by the size of the sorbed reservoir and the nature of the solution (wastewaters versus synthetic solution). Under anaerobic conditions, temperature exerted a high influence on the sorbed P available for desorption. [Display omitted] •Fe oxides-bound P was the primary P fraction in the iron sludge before and after loaded P.•Higher Fe oxides and organics in summer sludge enhance P binding and lability.•Unaerated P sorption at 40 °C and WW as P source yielded highest P desorption.•Irreversible sorption (Happ) was highest when sorption was aerated and at pH 7 and 3.