Struvite production from dairy processing wastewater: Optimizing reaction conditions and effects of foreign ions through multi-response experimental models.

Struvite is the preferred form of phosphorus recovery for fertilizer by chemical precipitation. The concentration of phosphorus in raw wastewater from dairy processing is higher than acceptable values for prevention of water pollution. Along with phosphorus, potassium and calcium are its main counterions with high concentration. Thus, calcium phosphate salts are prompt to precipitate and decrease struvite production. The effect of such phosphate counter-ions were optimized using design of experiments and desirability function to maximize both phosphorus recovery and struvite production. Under optimum conditions, the yields were 98.6 ± 1.1 and 85.7 ± 2.5 percent for phosphorus recovery and struvite precipitation, respectively. Factors optimization was achieved with desirability D = 0.995. By in-vitro assay of nutrients release, the product demonstrated better phosphorus availability than the one obtained with high calcium dose in reactor. The obtained molar ratios of dose can serve in wastewater treatment coupled to phosphorus precipitation with a fertilizer value product. Image, graphical abstract • P recovery from whey was achieved to 98.6 ± 1.1% using design of experiments. • PO 4 ^3- counterions mainly Ca²⁺ inhibited struvite precipitation before optimization. • The optimum were pH 8.9, n:n P of 1.21Mg, 0.26Ca, and 2.69NH 4 ⁺to desirability 0.995. • The product struvite content improved from 23% to 89% by optimum conditions. • The in vitro assay indicated that the product provide efficiently both P and nitrogen. [ABSTRACT FROM AUTHOR]