Water. desalination + reuse

PROJECTS August-September 2014 | Desalination & Water Reuse | 23 | 15 days before the performance test. This was to acclimatize the biomass to the caustic waste by increasing flow rate slowly. The average spent caustic characteristics were: 83,040 ppm COD; 35,536 ppm sulphides; 2,938 ppm TKN and 1,240 ppm phenols. These were different to the pilot plant characteristics. The 30-day maximum load performance test began in late November. A total flow of 4,000 gpm of process wastewater was fed to the plant for treatment to meet effluent discharge limits. During the performance test, process data were monitored daily to maintain the plant's treatment performance and uphold effluent water quality. For the test, a four-stage configuration was used. The SRT was 35 – 40 days; the sludge was recycled from the membrane tank to the first aerobic stage at a ratio of three, while nitrates were recycled from the first aerobic stage to the first anoxic stage at a ratio of two. During the performance test, spent caustic was also fed to the first biological anoxic cells according to the design data. The plant was able to treat the maximum loads and meet the effluent discharge limits. WaTER RE-uSE STudy CH2M Hill evaluated options for re-using permeate to replace totally or partially the present sources of sea water and brackish water from wells for the barometric condensers and the cooling tower. Results confirmed that the re-use of permeate in this way was limited by the build up of TDS and refractory COD/TKN. So permeate can be used to replace seawater in the barometric condenser but replacing brackish water in the cooling tower is only partially feasible. In a second set of scenarios CH2M Hill considered installing treatment units on the recycle line (oxidation process and nanofiltration membranes) to control COD, TKN and TDS concentration and to increase the overall re-use factor in the future. COnCluSiOnS Refinery, chemical and petrochemical wastewaters may contain a great variety of macro- and micro pollutants, requiring differing treatments for their removal. More stringent regulatory limits for discharge quality have meant that many existing wastewater treatment plants have needed to be upgraded. BAPCO's new MBR-based wastewater treatment plant at its refinery demonstrates a state-of-the-art plant capable of achieving complete nitrification/ denitrification and degradation, as well as bioaccumulation and mineralization of recalcitrant compounds to meet strict discharge limits. BAPCO also sets an example of how to deal with extreme operational conditions and the best way to manage specific toxic wastewater streams with proper plant design, start-up, and acclimatization procedures. l Table 3. Wastewater loads during maximum load performance test. Figure 5. Simplified block flow diagram of the water re-use study.

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