Study on the Removal of Phosphorus from Aquaculture Tail Water of Litopenaeus Vannamei by Magnesium Hydroxide and Calcium Hydroxide

By using the different concentrations of magnesium hydroxide and calcium hydroxide to treat the tail water of prawn culture, the effects of the concentrations of calcium hydroxide and magnesium hydroxide, stirring time and settling time on the phosphorus removal were studied. The concentrations of total phosphorus, soluble total phosphate and soluble orthophosphate in water samples were determined by the ammonium molybdate spectrophotometric method in GB11893-89 determination of total phosphorus in water quality. The results showed that when the concentration of magnesium hydroxide was 3 000 mg·L^-1, the stirring time was 15 min, and the settling time was 15 min, the removal rates of total phosphorus, soluble total phosphate and soluble orthophosphate in the tail water of prawn culture reached the highest value, being 96.29%, 93.29% and 95.56% respectively, while when the concentration of calcium hydroxide was 400 mg·L^-1, the stirring time was 10 min, and the settling time was 15 min, the removal rates of total phosphorus, soluble total phosphate and soluble orthophosphate in the tail water of prawn culture reached the highest value, being 98.80%、93.89%、95.56% respectively. The phosphorus content in water samples treated with magnesium hydroxide and calcium hydroxide conforms to the first-level discharge standard of phosphate (≤ 0.5 mg·L^-1) in GB8978-1996 comprehensive discharge standard of waste water, and the pH value of the treated water samples was 8.88 and 8.60, respectively. The total phosphorus and pH value were both consistent with the discharge standard of aquaculture tail water, namely SC/T9101-2007 discharge requirements of aquaculture water in freshwater ponds. These two kinds of reagent had the characteristics of low price, no secondary pollution and easy operation, so they were very ideal "green safe water treatment agent", which could provide help for the treatment of aquaculture tail water in prawn pond.