| Statistics show that the serious water pollution problems and water shortages have created contradictions between water quality protection and water supply in our country. Water problems have became a major obstacle of achieving sustainable development for our country at present stage. Traditional thermal power plants is one of the main industrial water consumers, which uses about a fifth of the industrial water use, meanwhile four-fifths of it is used for circulating cooling water. So used effluent from MWTP as reused water for circulating cooling water in thermal power plants after further treatment has a great significance in both environmental and economic aspects.In this Paper, according to the engineering design method, using a technique which combined laboratory scale test with pilot scale experiment based on a thermal power plants of Shenyang, the hereinafter study was done in this paper as follows:(1) Monitoring and analysis the circulating water depth treatment process composed of biological aerated filter, mechanical stirring clarification pool and variable pore filter, the optimized research is according to the analysis results, in order to achieve the purpose of high efficiency and energy saving.(2)Because the water quality of the field is not suitable for mechanical agitation settling process, this process is cancelled. In order to avoid the influence of the subsequent reverse osmosis desalination system after adjusting the process, the study on the effect of flocculation and sedimentation treatment process on the fouling of reverse osmosis membrane is carried out to provide a basis for process change.Experiment results show that:(1) Aiming at the secondary effluent from wastewater treatment plant, the optimal operating parameters of biological aerated filter are:gas-water ratio 3:1, hydraulic load 4 m3/m2-h, method of backwash:"first gas scour, second air-water combination, last water wash", intensity of gas scour:9-11 L/(m2·s), intensity of water scour:6L/(m2·s), backwash cycle:24-36h; Dosage of flocculation deposition is changed according to the content of TP in water turbidity. When the total phosphorus content is less than 2mg/L, dosage of PAC is 13mg/L (calculated by alumina), dosage of PAM is 0.5mg/L. The optimum operating parameters of variable pore filter are:2.5% volume of fine sand ratio, filtrating speed 16m/h, intensity of gas scour:14 L/(m2·s), intensity of water scour:5.04 L/(m2·s), backwash cycle: 20h.(2) The secondary effluent is desalinated by reverse osmosis, after treatment of biochemistry, flocculation, filtration and ultrafiltration. As the running time increases, the pollution of reverse osmosis membrane is changed from single organic pollution to the combination of organic pollution and inorganic fouling pollution. The organic pollutant is in gel layer state, which is mainly composed of carbohydrate and protein. the main component of inorganic scale substances is silicon scale, and there are many complicated forms.(3)Directly using the effluent of biochemistry, filtration and ultrafiltration treatment wit hout flocculation treatment, the process of reverse osmosis membrane fouling and the main p ollutants are the same as the flocculation treatment, but the pollution is lighter in water sampl es with flocculation treatment. The degree of organic pollution of reverse osmosis membrane in initial stage is 16.4% higher in water samples with flocculation treatment than those with out flocculation treatment(calculated by membrane flux). And the inorganic scaling pollution formed in long-term operation is also more serious. The reason for this phenomenon is the r esidue of flocculant. |
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