Study On The Advanced Treatment Of Dying-printing & Polyester Deweighting Secondary Effluent By BAC Process

With increasing application of polyester deweighting techniques in Chinese textile plants, a great deal of alkali-peeling waste streams containing high strength of recalcitrant organic matters and waste alkali are discharged. These alkali-peeling waste streams are normally treated with dying-printing wastewater by hydrolysis-acidification-aerobic bio-treatment processes. But effluents emitted by these conventional bioprocesses are always beyond discharging standards and need urgent further-treatment.Physicochemical advanced treatment methods are operational complicated and high cost, and biological processes are still simple and cost-saving ways. But existence of inhibitory compounds, inadequate biodegradable organic matters and inert active microbial population are all unfavorable factors for further bio-treatment of these notorious textile dying-printing & polyester deweighting secondary effluents (TSE). Granular activated carbon (GAC) has advantages over other bio-media in supplying microbe abundant inhabitation surface area and possessing strong adsorption capacity of micro-inhibitory matters. In this study, we employed up-flow-biofilter and used GAC as support media forming up-flow aerated bio-activated-carbon-filter (UABACF) to treat TSE. In view of the characteristics of TSE, such as low level of biodegradable organic matter, nitrogen nutrition and high content of refractory organics, we attempted to adjust the influent NH₄⁺-N with NH₄HCO₃ to induce excess nitrifiers growth in the reactor. Therefore, the recalcitrant organics can be removed by activated carbon adsorption, co-metabolism with heterotrophs/nitrifiers, catalyzed oxidization with ammonia mono-oxygenase (AMO). The experimental results demonstrated that the pollutants in the studied streams were effectively removed by UABACF, and high quality effluents were produced during almost 1.5 years of its operation. Therefore, UABACF was the simple, sound and solid process in advanced treatment of TSE.The paper studied the main operational influence factors of the UABACF, such as molecular weight distribution and adsorption/biodegradation characteristics of TSE pollutants, applied organic, hydraulic and nitrogen load, dissolved oxygen(DO), back-wash styles. The reactor performance was optimized when the key controlling factors were understood.The paper also studied the distribution of residual adsorption capacities of activated carbons, the biomass and bioactivities in the reactor. The changing rules of DO and pH values along the height of the reactor, their influencing factors as well as the relationship of pollutants removal to the above-mentioned parameters.The study applied Triphenyl tetrazolium chloride - Dehydrogenase activity (TTC-DHA) assays to measure the activities of attached biofilm on bio-activated carbon (BAC) samples in the reactor. The influences of pre-separation of biofilm from the media surface to the magnitude of attached bioflm activities were discussed and the new TTC-DHA monitoring method of attached biofilm activities of BAC samples were provided. The new method was applied to detect the captured/attached biomass bioactivity distribution along the height of BAC reactor. The relations between bioactivities to pollutants removal, activated carbon adsorption and backwash flush were also analyzed.On the basis of UBACF, we configured pressurized Enriched Oxygen Biological Activated Carbon reactor (PRBAC) which simply increased reactor pressure to create an enriched dissolved oxygen (DO) environment to improve activated biomass within the reactor, leading to pollutant removal enhancement in the reactor. The study evaluated the function of enhanced oxygen level in BAC through comparisons of UABACF and PRBAC in the scope of substrate removal rate, differences of influent/effluent pH values, different molecular size organic matter removal rate, biomass activities and activated carbon residual adsorption capacities.In addition, the study also analyzed the activated carbon adsorption capacities of COD, color, UV₂₅₄ surrogated pollutants in the wastewater with tumbling bottle adsorption and dynamic adsorption method. Differences between GAC sole adsorption and BAC treatment capacities were calculated. The essential operational controlling parameters in BAC to achieve high pollutant removal and prevent the GAC saturation during long-term performance were also concluded.Conclusions of the research provide reliable operational data on UABACF treatment capacities, activated carbon residual adsorption capacities in the reactor in advanced treatment of the TSE.