Chemical Precipitation Removal Of Ammonia Nitrogen In The Coke Plant Wastewater

Existing technologies for treating with wastewater containing ammonia nitrogen are reviewed in the paper. According to existing technologies for treating with coking wastewater and present situation on which ammonia nitrogen can' t meet the need of discharging standard, chemical precipitation used to improve the technology and solve the ammonia nitrogen problem is developed.Using coking wastewater from WISCO, various factors affecting on ammonia nitrogen removal rate such as chemical precipitators, pH value, reaction temperature, dosages etc. are researched. The possibility of application the chemical precipitation to industry production is investigated.Research results have shown that, three sets of chemical precipitators (MgCl2 6H20 and Na2HP04 12H20,MgO and H3P04, Mg(OH)2 and H3P04)can be used to remove the ammonia nitrogen effectively, but when MgCl2 6H20 and Na2HP04 12H20 are used, removal rate of ammonia nitrogen is highest.Theoretical analyses and calculation show that, optimum pH for removing ammonia nitrogen is 8. 89, besides the pH is independent of original concentration of ammonia nitrogen, but applicable range of the PH become broader with increase of original concentration of ammonia nitrogen. Experimentation shows that the range of optimum pH for removing ammonia nitrogen is 8. 5-9. 5.Reaction temperature has effect on removal of ammonia nitrogen. The reaction temperature rises, removal rate of ammonia nitrogen lowers.When the dosage of chemical precipitators is according to stoichiometric coefficient n(Mg2+) : n(NH4+) : n (P043-) =1 : 1 : 1, removal rate of ammonia nitrogen is highest. If increasing the dosage, operation cost would increase and secondary contamination of phosphorus would be produced.On the condition of pH 8.5-9.5, dosage n(Mg2+) : n(NH4+) : n (P043-) =1 : 1 : 1 and room temperature, ammonia nitrogen of coking wastewater from settling pond and from regulating pond with concentration less than 500mg/L can be lowered to less than 15mg/L and discharged on meeting the discharge standard, and the removal rate of ammonia nitrogen is up to more than 95%. But the removal rate of wastewater from distillation of ammonia is only 75%.Investigation and discussion show that the chemical precipitation is an effective means to improve the existing technologies for treating with coking wastewater, the chemical precipitators are added into regulating pond or settlingpond to cause the index of ammonia nitrogen to meet the discharge standard.