Industrial Wastewater Treatment by the Combination of Chemical Precipitation and Immobilized Microorganism Technologies

Abstract

The combined technology consisting of chemical precipitation and microorganism immobilization was employed for removal of ammonium (NH₄⁺-N) and chemical oxygen demand (COD_Cr) in rare-earth smelting wastewater. The influencing factors to the chemical precipitation based on the precipitation of magnesium ammonium phosphate (MAP), such as pH, precipitation reagents and feed ratio, precipitation time, as well as composition of the precipitation, were investigated systematically. The optimal experimental conditions in this process were: Na₂HPO₄ as the phosphorous source, NH₄⁺:Mg²⁺:HPO₄²⁻ = 1.0:1.2:1.3 (molar ratio), pH = 11.10–11.20, precipitation time 90 min. The remained contaminants after the chemical precipitation were decontaminated continuously by the microorganism immobilization through the simultaneous nitrification and denitrification (SND). For the wastewater with concentrations of NH₄⁺-N = 1,540 mg/L, COD 1,088 mg/L, the overall removal ratios of them were 99.27% and 95.14%, respectively. This showed the possibility and advantage of the combined technology in purifying industrial wastewater containing high concentrations of NH₄⁺-N, COD_Cr, and metal ions. Additionally, the possibility of employing calcium phosphate as an alternative precipitation agent for NH₄⁺-N removal was also investigated in this paper.