Chemical Precipitation Pretreatment Of High Concentrations Of Ammonia Wastewater

With the agriculture and industry development, the pollution sources of wastewater with ammonia nitrogen become more and more, arid does the amount of discharge, which are from all types of industrial wastewaters, such as, metallurgical plant wastewater and petroleum refinery plant wastewater and landfill leachate, besides domestic wastewater and animal excrement. The key reason of eutrophication is ammonia nitrogen. How to remove ammonia nitrogen from wastewater is an important problem for environment researchers.Most researchers attach importance on biodenitrification, but nitrifying bacteria needs a favorable environment, which is not easy to be controlled. Especially nitrifying bacteria can't grow in the high strength ammonia nitrogen wastewater. It is studied in this paper how to remove high strength ammonia nitrogen from wastewater by chemical precipitation, that is, magnesium salt and phosphate salt are added into this kind of wastewater, and precipitation occurs at an optimal condition, to produce magnesium-ammonium-phosphate which is an insoluble compound and contains only three nutrients of phosphorus, nitrogen and magnesium. These nutrients are valuable to plants. It is introduced artificial wastewater with high strength ammonia nitrogen is treated by chemical precipitation in the first part of the research, which has several steps: firstly, the sequence of factors is determined by orthogonal experiment, secondly, the effects of the factors are analyzed, at last, ammonia nitrogen removal rate of artificial wastewater is above 90% at pH between 9 and 10, magnesium, ammonium and phosphate molar ratios of (1.1-1.2): 1:1. However, there is residual phosphate in the treated wastewater. The percentage of N, P, Mg in the precipitate are 4.7%(N), 32.4%(P2O5) and 18.0%(MgO) respectively. High strength ammonia nitrogen wastewater from manganese plant is treated by chemical precipitation in the second part. The result is that the removal rate of high strength ammonia nitrogen from wastewater is above 95% at the optimal precipitation condition which is pH between 9 and 10, magnesium, ammonium and phosphate molar ratios of (1.1-1.2):1:1. The percentage of N, P, Mg in the precipitate are 5.2%(N), 34.5% (P2O5) and 19.4%(MgO) respectively.The research shows that the technique removing high strength ammonia nitrogenfrom wastewater by chemical precipitation can be put into practice, and the precipitate is a composite fertilizer.