Application of coagulation and full-membrane process in municipal reclaimed water in northern China: an optimized process

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Abstract
Lime coagulation and the full-membrane process are sharply being used in wastewater treatment as the technology is cost-effective. This paper studies the water treatment system in thermal power plants located in northern China. The municipal reclaimed water is processed by lime coagulation and full-membrane technique and it is the main water supply source of this power plant. An analysis is established to affirm the operation status of lime coagulation and full-membrane systems. The response surface Box-Behnken central composite design method was used to optimize the lime coagulation system to achieve the desired results. The optimal conditions are obtained by the response surface method and combine with the actual situation. In conclude, the polymerized ferrous sulfate (PFS) dosage (30 mg/L), the NaClO dosage (4.5 mg/L), the stirring rate (300 rpm), temperature (20 degrees C), pH of flocculant area adjusted by adding calcium hydroxide (10.1), inlet flow (800 t/h) and pH of effluent adjusted by adding H2SO4 (6.5). Under these conditions, chemical oxygen demand and NH3-N removal rate is 84.72%, 88.25%, and 87.74%, respectively. After the effluent passes through DMF, ultrafiltration, primary, and secondary reverse osmosis, and EDI, the effluent finally meets the requirements of high-purity water in the thermal power plants. Any problems associated with the process and solutions of corresponding problems are also discussed in this paper. All the requirements desired from lime coagulation and full-membrane technique are successfully achieved and save a large amount of freshwater resources. The annual savings for the thermal power plant is about 7.63 million USD and also there is no acid-base wastewater drainage that needs to be treated. The payback period of the project investment is 33 months. The research results provide technical support for the water treatment process upgrade of the thermal power plant.