Evaluation of flue gas desulfurization gypsum as a low-cost precipitant for phosphorus removal from anaerobic digestion effluent filtrate

Land application of anaerobic digestion (AD) effluent as a fertilizer is desirable for nutrient recycle, but often supplies excess phosphorus (P), which contributes to surface water eutrophication. Reducing the P content in AD effluent using calcium treatment prior to land application is a potential strategy for improving effluent disposability. In order to solve the problems of low phosphorus removal efficiency and high operating cost in wastewaters, this study took flue gas desulphurization (FGD) gypsum, a by-product of coal-fired power plants, as a low-cost calcium source, and combined with traditional phosphorus removal agents to achieve high phosphorus removal efficiency with less chemical inputs. As the results showed, FGD gypsum dosages of 20 mM Ca (3.44 g/L) and 40 mM Ca (6.89 g/L) removed up to 97.1% of soluble P (initially 102.8 mg/L) within 60-90 minutes. Combining FGD gypsum treatment with traditional chemical treatments using Ca(OH)2 or FeCl3 could achieve >99% P removal with reduced chemical costs. This study demonstrated that FGD gypsum is an effective calcium precipitant for phosphorus removal.