Phosphate removal from food industry wastewater by chemical precipitation treatment with biocalcium eggshell

The physicochemical treatment (PT) of food industry wastewater was investigated. In the first stage, calcium magnesium acetate (CaMgAc₄) was synthesized using eggshell (biocalcium), magnesium oxide and acetic acid in a 1:1:1 stoichiometric ratio. In the synthesis process, the thermodynamic parameters (ΔH, ΔS and ΔG) indicated that the reaction was endothermic and spontaneous. The samples were characterized by infrared spectroscopy (IR), scanning electronic microscopy (SEM), X-ray diffraction (XRD) and electron X-ray dispersive spectroscopy (EDS). CaMgAc₄ was used to precipitate the phosphate matter. IR analysis revealed that the main functional groups were representative of the acetate compounds and the presence of OH^- groups and carbonates. In the physicochemical treatment, a response surface design was used to determine the variables that influence the process (pH, t, and concentration), and the response variable was phosphorus removal. The treatments were carried out in the wastewater industry with an initial concentration of 658 mg/L TP. The optimal conditions of the precipitation treatment were pH 12, time 12 min, and a CaMgAc₄ concentration of 13.18 mg/L. These conditions allowed the total elimination (100%) of total phosphorus and phosphates, 81.43% BOD₅ and 81.0% COD, 98.9% turbidity, 95.01% color, and 92% nitrogen matter.