Study On Nitrogen And Organics Removal From Nylon-6 Wastewater With A/O/O Biofilm System

At present, nylon-6 is unrivalled in its number of applications, including textiles, carpets, industrial fibers and engineering plastics. It was reported that the production of nylon in China had increased by 72.17% from 2002 to 2004. The greater production generates more industrial wastewater correspondingly and how to deal with this wastewater is increasingly becoming a source of concern in wastewater management.Organics and nitrogen removal of nylon-6 production wastewater was studied by using an A/O/O biofilm reactor. The thesis was to investigate effects of important process variables on system's performance, characterize biomass attached in different tanks, study reactor kinetics of submerged biofilms and finally evaluate the feasibility of a biological aerated filter in tertiary treatment for reuse.The A/O/O biofilm reactor was investigated at different conditions of nitrate recirculation ratio, HRT (Hydraulic retention time), DO as well as the influent COD_Cr and TN concentrations. The experimental data indicated that when the average influent COD_cr and TN were around 500mg/L and 30mg/L, under nitrate recirculation ratio of 3, HRT in each reactor of 3.9h, DO in aerobic tankâ… and aerobic tankâ…¡of about 3.0 mg/L, the removal efficiency of COD_cr and TN could reach 95% and 68%, respectively. In addition, the ammonia in the effluent was less than 1.5mg/L and the effluent quality perfectly met first discharge standard specified in GB8978-1996.Through pollutant transformation pathway investigation, bacteria activity testing and IR spectrometer analysis, we found that 2-step aerated tanks would enhance the nitrification property. The aeration stage was divided into 2 steps in space which made it possible that heterotrophic and autotrophic bacterium became dominant microorganism in aerated tankâ… andâ…¡respectively and furthermore overcame the problem of competing inferiority of nitrification bacterium to heterotrophic bacterium on DO, nutrient and living room. It proved that A/O/O biofilm system would effectively enhance nitrification process and assure high removal efficiency of COD_Cr.The performance of the whole A/O/O biofilm system was analyzed by kinetics simulation. The denitrification reactor kinetics model in anoxic tank, the organic removal reactor kinetics model in aerobic tankâ… and the nitrification reactor kinetics model in aerobic tankâ…¡were set up and used to calculate related kinetic parameters in each tank,which could be cited as technical reference during treatment facility design.The A/O/O biofilm process seemed to be a promising method for the organics and nitrogen removal of nylon-6 wastewater With good resistance to shock loads. However, during experimental results we noticed that under high TN loadings the effluent NH₄⁺-N would probably not be able to meet the stringent limitation on nitrogen discharge. Therefore a biological aerated filter (BAF) was selected for tertiary treatment of the effluent from the A/O/O biofilm reactor and effects of hydraulic loading, gas to liquid ratio and media height on the removal of organic matter and NH₄⁺-N were studied. Results showed that when the COD_Cr and NH₄⁺-N concentration of the influent was about 70mg/L and 15mg/L, under the conditions of gas to liquid ration 2 and hydraulic loading 0.13 m³/(m²Â·h), the average effluent COD_Cr and TN concentration were decreased to 30mg/L and 2.5rag/L, respectively, which met the reuse water quality standards CJ/T 48-1999.