Study On Treatment Of Thermophilc PVC Wastewater In Aerobic Moving Bed Biofilm Reactor

Industry wastewater intensive treatment and recycle are becoming one of most important research hotpoints in re-utilization of the water resource. Although industry wastewater intensive treatment and reuse has a wide potential market, this technique is still under the development. It takes a long way to industrialize the recycle loop of industrial wastewater. Many important problems which haven't been solved restrict the industrialization process. The incease of the treatment efficiency of wastewater, the stable operation of treatment system and reducing the purification cost are essential to realize the industrialization.The industry in China is putting a lot of effort in closing the water cycle systems of the production process resulting in the so-called Zero Discharge Mills. Application of these Zero Discharge Mills is possible in PVC industry but requires an in-line treatment system to prevent effect of bad water quality on the endproducts.As one of the most relevant polymers for construction and commodities, PVC is a thoroughly investigated material, with polyethylene (PE) and polypropylene (PP).China has the most production capacity in the world. PVC industry can generated a great deal wastewater, whose treatment and reuse is a new domain of water treatment.This experiment was conducted in three phases moving bed biofilm reactors to investigate effects of operation condition on the formation of biofilm on polypropylene ball carriers, for treating the PVC wastewater contrast to other processes. Application of MBBR fills up the blank in terms of the expanding and modification to the existing old wastewater treatment plants and it is helpful for increasing wastewater quality as well as reducing treatment costs, possessing significant meaning for the development of environmental undertaking. Predominance bacteria were achieved after domestication, and play an important role in the quick start-up of laboratory set-up. Results show that, under the condition of the HRT of 16~24 h and the organic volume load rate of 0.23~0.47kg COD/(m3·d), the biofilm could form steadily on the carriers surface and reaches more than 100μm in thickness after 35 days. When the organic volume load rate is 0.46kgCOD/(m3·d), the biofilm of 160μm thickness has the best activity and the highest removal rate of COD. With enough supply of oxygen, the biofilm can form steadily on the carriers surface for the organic volume load rate of 0.23~0.46kgCOD/(m3·d) and although different in thickness, achieve COD removal rate of more than 85%.A disadvantage of these classic bio-treatment processes is the necessary cooling stage of the process water to mesophilic conditions prior to biological treatment and subsequent heating afterwards. The process water needs to be reheated since the optimal temperature for PVC production is approximately 70oC. The current research project aims at a complete aerobic treatment under thermophilic conditions (45±55oC) of paper process water in a closed cycle mill. Regarding the post treatment step, it is believed that thermophilic aerobic treatment may be limited by a poor oxygen transfer due to the lower oxygen saturation concentrations at higher temperatures. The goal of this study is to determine the OTR under mesophilic and thermophilic conditions in tapwater and process water.This paper summarizes the relationship between biofilm characteristic in MBBR and efficiency of reactors in the process of PVC wastewater treatment. Key points include these factors influencing biofilm formation, the biofilm activity, the variables such as temperature, biofilm thickness, substrate concentration and distribution of different microorganism species influencing biofilm activity, mass transfer in biofilm, the relationship between biofilm thickness and efficiency of reactors, and biofilm detachment. The research for further development of MBBR is also pointed out.A new method for PVC wastewater treatment with MBBR was presented. A novel type of ball carrier was applied, which achieved high treatment efficiency. The research method of cultivating mesophilic bacteria to avtive under thermophilc condition gave foundation of derect treatment of PVC thermopilic wastewater. The success of full-scale experiment and the outlet meeting the criterion of industry circulating cooling water had practical significance in the PVC wastewater treatment, and shown the possibility to reuse PVC wastewater and cut discharge for PVC industry.