Treatment Of COD And NH₄ -N In The Wastewater From Coke Plant By Using IMC Technology

The coking wastewater is produced in coking plant and gasworks, which is abundant in hydroxybenzene and difficult to dispose, and contains wide range of contaminants, including ammonia, cyanide, thiocyanate, and many toxic organic contaminants, such as phenols, mono- and poly-cyclic nitrogen-containing aromatics, oxygen- and sulfur-containing heterocyclic compounds and PAHs. These compounds produce long-term environmental impacts, and most of the heterocycliccompounds and PAHs are reported mutative and carcinogenic. It is therefore necessary to remove these harmful substances from coking wastewater.Recent days, extensive work has demonstrated that anaerobic- aerobic (A/O) system is an efficient and cost-effective method for the removal of nitrogen and organics. However, after a conventional. A/O biological treatment of coking wastewater, the effluent of COD and ammonia-N often could not meet the discharge standard especially for industry due to the presence of refractory and biologically inhibitory organic compounds such as PAHs and nitrogenous heterocyclic compounds in coking wastewaters. Therefore, the dispose of the coking wastewater is still a problem in the wastewater treatment.Immobilized Microbial Cell (IMC) technology is a promising method for entrapping and enhancing certain species of bacteria. Therfore, the application of IMC has been attempted in the field of wastewater treatment process. Although theapplication of IMC technology in the removal of COD or NH4-N in wastewater has been attempted, its application for the treatment of real industrial wastewater has not been well studed, especially for the simutanously removal of COD and NH4-N in coking wastewater.The purpose of this study was to asses the feasibility of the IMC for the simutanously removal of COD and NH4-N in coking wastewater to make the pollutant concentration of COD and NH4-N was up to the discharge standard GB8978-1996 (CODsSl50mg/L; ammonia-N^25mg/L) .Firstly, the preparations of immobilized cells are explored by choosing polyvinyl alcohol (PVA) as the main entrapping agent. The optimal conditions are chosen in terms of the ammonia oxidation rate, mass trasfer and mechanical stability of the beads. The immobilization process was observed with entrapping activated sludge in mixed PVA gel beads, Na-alginate (SA) and powder actived carbon. In addition, experiments on the optimal of diameter and preservation of theimmobilized cells have been investigated.In the activated sludge process, the fluctuation of influent quality and the diversity of the mixed culture in the biological system, the realitively slow-growing nitrifying bacteria are gradually washed out of thebioreactor until the nitrifying function is lost entirely. Only at low organic carbon loads or in relatively extended bioreactors, does competititive nitrification take place to any considerable extent. So, we study the immobilization process of nitrobacteria and removing ammonia-N from coke-plant wastewater by immobilized nitrobacteria. An immobilization system was obtained with entrapping cultivated nitrifying activated sludge in mixed PVA gel bead and powdered activated carbon. The influence factors of nitrification were studied. The comparison of the performances of the immobilized and the dissociated nitrobacteria shows that the former has significant advantages over the latter in the treatment of nitrogeneous-containing wastewater.Therefore, an IMC anaerobic-aerobic process was used to treat the coking wastewater. Compared with conventional A/O and immobilized nitrobacteria process, the IMC has the advantages. When the coke plant wastewater influent COD is about 1350mg/L, NH4-N is about 287mg/L, reaction time was 48h, the removal efficiency of COD was about 90.2%, the removal efficiency of NH4-N was about 91.6%. It is suggested that immobilization technique is a promising way in the coking wastewater treatment.