Tham khảo tài liệu 'water conservation part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 126 Water Conservation 4. Conclusions Petroleum refining industry has a high potential for implementation of water conservation strategies. After a suitable treatment the totality of the petroleum refining wastewaters can be reused obtaining therefore the protection of the receiving water bodies and reducing the fresh water demand. The performed study of the water management systems in two refineries allowed the development of alternatives which could provide fresh water savings of 51-59 . It is possible to obtain high quality treated water not only for reuse in the cooling towers but also for the production processes and auxiliary services. The pretreatment of the oily wastewaters using primary oil gravitational separators and chemically enhanced separation processes allows a successful implementation of biological treatment followed by advanced processes. The use of reclaimed municipal wastewater in the cooling towers make-up allows further fresh water saving opportunity. The waste management has to consider separate treatment of sour waters and for the spent caustics as well as a pretreatment of all effluents whose main pollutants are oil solids and sulfides. Cleaner production actions have to be implemented for the reduction of the pollutants in the wastewater. The preliminary separation of the free oil by natural flotation allows 90-95 O G removal efficiency with surface loading rates of . As the floatation velocity of the oil droplets depend of the oil characteristics which are different for each refinery the performance of experimental tests are highly recommended for the obtaining of reliable design parameters. The TSS and COD removals obtained in the performed treatability tests were of 62-72 and 34-39 . The increase of the hydraulic retention time in the range h improves the TSS and COD removal in the separators. The effluents from the separators had low O G concentration 47-62 mg L however the remained COD was higher than 340
