| Along with the rapid growth of world economy, the impact of environmental pollution on water resources is getting more and more serious, which leads to an urgent question in protection of water resources and control of water quality to the world and particularly to our country. Apart from their high cost in construction and operation, the sewage treatment technologies commonly applied do not well meet the market demands due to unsolved technical problems in several aspects, which gives direct and indirect influences on planning, construction, operation and management of sewage treatment systems.Improvement of present sewage treatment techniques and development of new methods are thus of high significance in related fields.Immobilization of microorganisms, as a new method to deal with wastewater, is a hot research area in bioengineering, which has been used in chemical industry and drug industry successfully. So many researchers make emphasis on immobilization of activated-sludge, such as pure bacteria abstracted from activated-sludge to treat special wastewater including ammonia nitrogen wastewater and wastewater with hard-degrade organic pollutant. As there are very few reports concerning application of immobilized activated-sludge in sewage treatment, the present trials are conducted to study the processing of activated sludge immobilization with PVA (Polyvinyl Alcohol); the formation of PVA-immobilized activated sludge membrane-cell layers and their effect in reactor, and as well, in improved reaction system. The method gives satisfactory results shown as follows:(1) The method, using circulatory freezing and thawing to prepare immobilized-cell membrane with Polyvinyl Alcohol (PVA), is simpler and easier to operate than the method making it particle, and avoids the particles' inter-adhesion and brokenness.(2) In the sequence of process, the best technological condition is that aeration time approaches 6h and the rate of aeration is 16L/min. under this condition sludge load is 0.13KgCODCT/KgMLSS.d, and volume load can reach 2. \9KgCODJm*.d, then the concentration of CODo- and NHs-N in effluent attains the second grade discharge standard of GB8978-1996, which is hard to achieve by the normal activated-sludge process.(3) After immobilization, activated-sludge's adaptive range to pH and temperature of wastewater becomes wider.(4) After immobilization, there is little excess activated-sludge left.(5) During the experiment, the concentration of COD^ in inflow has littleinfluences on the effect of treatment, but there is a decline in the removal rate of CODCT when its concentration reaches 900mg/l owing to the bad character of PVA that affects the intra-transmission of high-concentration substrate. So in the aerobic condition, immobilized activated-sludge does not appear to be a proper method for high concentration sewage treatment.(6)Improvement of the process by addition of filtration using sands and slags, enhanced significantly the treatment efficiency. At a flow rate IL/h, the removal rate of CODcr reaches the first grade discharge standard (GB8978-1996), with an average removal rate of T-P 70.77% and that of NH3-N 72.59%, which meet the discharge standard grade 2 (GB8978-1996).(7) In comparison with those of contact oxidation method, the tested method has special advantages, such as higher removal rate, more economical, easier to operate and so on.In conclusion, this method is more feasible than method commonly applied. |
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