Effect of Ferrous Ion Coagulation on Biological Ammonium Nitrogen Removal in Treating Coke Wastewater

Effects of ferrous ion coagulation in treating coke wastewater were examined through tests. In addition, nitrification tests using coagulated coke wastewater were carried out to evaluate the effect of ferrous ion coagulation on biological ammonium nitrogen removal. Experimental results showed that ferrous ion coagulation was very effective in terms of free cyanide (CN-) removal. The best free CN- removal was found to be 98% at a ferrous ion dosage of 242mg Fe2+ L-1. In addition, ferrous ion coagulation was also effective for the removal of turbidity. The highest turbidity removal was observed to be 88% at a ferrous ion dosage of 242mg Fe2+ L-1, where the best free CN- removal was found. This indicates that the determination of optimum ferrous ion dosage for free CN- removal could be indicated by turbidity removal. Although ferrous ion coagulation caused a decrease in total alkalinity, it did not affect nitrification. In triplicate nitrification tests, the best NH4+-N removal rate in nitrification was found to be 16.43mg NH4+-N L-1 h(-1) in residual solution, where the highest free CN- removal was observed by coagulation tests. Consequently, it was found that, in terms of biological ammonium nitrogen removal, ferrous ion coagulation contributed to 35% enhancement compared to that of noncoagulated coke wastewater by reducing the concentration of free CN- from raw coke wastewater.