Experimental Research On Treatment Of Coking Wastewater With Anaerobic-Aerobic Fixed Bed Biofilm Reactor

Coking wastewater is a nonbiodegradable industrial wastewater with high ammonia-nitrogen. In order to improve the biological treatment effect of the coking wastewater, the coking wastewater was treated by anaerobic-aerobic biofilm process and anaerobic-aerobic pressurized biofilm process separately using spherical pumice biocarrier as carriers in this paper. The main factors that influence the treatment effect of reactor were explored, and the best conditions for each process were obtained.meanwhile, the bioflim of carrier was observed and analyzed. In addition, a brief analysis on dynamics process of ammonia-nitrogen degradation in anaerobic-aerobic pressurized biofilm process was proposed.(1) The effect of hydraulic retention time, reflux ratio and dissolved oxygen were mainly investigated during the process of coking wastewater treatment by anaerobic-aerobic biofilm method. It is shown that when the hydraulic retention time was more than 48 hours, the reflux ratio was 2, and the dissolved oxygen in the oxidation pond was greater than 2mg/L, the mean COD removal rate was 15.15%, the ammonia-nitrogen removal rate was nearly zero even increased in the effluent in the anaerobic process.Meanwhile, the total nitrogen removal rate was unstable with the mean value of 22.74%. The turbidity of the effluent was about 40NTU for the anaerobic process. The effluent COD was less than 260mg/L, the turbidity was less than 5NTU, the total nitrogen removal rate was about 50.53%, and the concentration of ammonia-nitrogen less than 15mg/L in aerobic zone. The removal rate of ammonia-nitrogen matches the effluent standard of coking wastewater as required in the document The Effluent Standard of Pollutants in Iron and Steel Industry Wastewater (GB 13456-92).(2) The effect of the pressure, pH values, and aeration amount on the treatment techniques were observed during the coking wastewater treated by anaerobic-aerobic pressurized biofilm process. The best results were obtained when the pressure was 0.15 MPa, reactor pH value rangd from 7.5 to 8.0, the aeration amount reached to 25L/h, and the hydraulic retention time kept for 40 hours. After the treatment, the average COD of effluent was 314mg/L, and the ammonia-nitrogen was 6.55mg/L with the removal rate of 97.4%, which enhances by 9.4% compared to the removal rate of the normal pressure, and the total average removal rate of nitrogen was 31.67%.(3) Optical microscope was applied to observe the biofilm on the carrier, It was found that the surface of the biofilm was relatively thick, and was abundant in protozoa and metazoan when the biofilm formation forms in mature. After the completion of acclimation of the coking wastewater, the biofilm turns thin, living things becomes less and the biofilm was mainly made up of zoogloea The result of Scanning Electron Microscope shows that both the stage of membrane-formation of the nutrient solution on the carrier and the stage of acclimation of the coking wastewater were cellular structure on the pumice stone covered by extracellular polymeric substance, meanwhile wrapped by Corynebacterium sp and brevibacterium sp. But vorcticella did not be observed after the acclimation of the coking wastewater. In the process of pressurizing treatment, the biofilm was mainly bacillus and zoogloea, and just a small amount of colpidium. Finally the Monod model was used to make a brief dynamics analysis on the process of ammonia-nitrogen degradation.