Study On Removal Of Ammonia-nitrogen From Coking Wastewater And Its Mechanism By Chemical Precipitation

The removal of ammonia nitrogen by chemical precipitation is a new-type method with simple technology,fast reaction speed and high removal efficiency,especially for getting rid of high concentration of ammonia nitrogen from wastewater and it can become complementarity of biodenitrification.Using simulative wastewater from laboratory and coking wastewater from WISCO, MgCl2·6H2O and Na2HPO4·12H2O were added into these kinds of wastewater as precipitator, and precipitation occured at an optimal condition to produce magnesium-ammonium-phosphate that is an insoluble compound,which carried the ends of eliminating ammonia nitrogen in wastewater.Based on a amount of experiments,the paper studied several kinetic parameters and summarized the relationship among pH value,reaction temperature and reaction ratio.By orthogonal and optimized experiments the paper drew an optimal reaction condition.The research results shows that:at room temperature,when pH is controlled 9~11,the mol ratio of PO43- /NH4+ is 1.3/1, Mg2+ /NH4+ is (1.2~1.5)/1,the ammonia nitrogen concentration decreases from 1100 mg/L to 15 mg/L,the removal rate of ammonia nitrogen is up to 98% meeting the discharge standard.The theoretical calculation shows that the optimal pH is 10.8 by chemical precipitation for high concentration of ammonia nitrogen(>500mg/L).The testing experiment also confirms that the maximum removal rate comes into being at condition of pH=11.The main mechanism of removing ammonia nitrogen by chemical precipitation finally includes chemical equilibrium, the principles of solubility product,acid effect,etc.Chemical equilibrium,common-ion effect can make an good explanation for the effect of ratio on the removal of ammonia nitrogen.The principles of solubility product shows that it is more favorable to precipitate in alkaline condition for MgNH4PO4·6H2O;The mechanism of the influence of pH on removing ammonia nitrogen can be illuminated with acid effect.The chemical precipitation provides a new way to treat wastewater with high strength ammonia nitrogen,and it can be used as a composite fertilizer,So chemical precipitation has a very bright future.