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Tobago, a small island off the coast of South America, relies heavily on tourism tokeep its economy afloat. Along with its exceptional beaches, Tobago's main touristattraction is the Buccoo Reef. However, land activities, run off, andimproper treatment of wastewater have contributed to degrading the coral reef. Tocounter this, the government has chosen to retrofit two existing wastewatertreatment plants (WWTP) with membranes. The effluent from these two WWTPs is sent to a stream that makes its way out to sea adjacent to theBuccoo Reef.The two existing treatment plants are located in the Bucco and Bon Accordcommunities. The pre-modified plants consist of two circular tanks. Each tankcontains an outside and center portion. The outside portion was used as anactivated sludge system where nitrification and oxidation of BOD took place. Theinfluent wastewater has the typical characteristics of 44.1 mg/L suspended solids,129.7 mg/L BOD and 21.7 mg/L free ammonia. Mixed liquor from the aeratedsection of the tank was transferred to the center ring which acted as a clarifier.Effluent leaving the clarifier had averages of 16.5 mg/L suspended solids, 63 mg/LBOD, 17.3 mg/L free ammonia, and faecal coliforms in excess of 60,000 cfu/100 mL.Four membranes were placed in the aeration tank of only one circular tank at eachlocation, which allowed the plants to treat all of the 30,000 gallonsthat flow into the plant on a daily basis. The clarifier was eliminated and is nowbeing used for sludge holding and aerobic digestion. The second circular tank isbeing utilized as a flow equalization tank. The Membrane Bioreactor systems (MBR)have significantly improved the quality of effluent now being discharged to the sea.The effluent quality now leaving the plant has the following average data: 2.4 mg/Lsuspended solids; 2.4 mg/L BOD; 0.6 mg/L free ammonia; and, 0 cfu/100 mL counts of faecal coliforms. Though the first plant has only been in operation for the past year, lab results show an effluent that has little or no effect on the reef. Includes 2 references, tables, figures.

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Edition: Vol. - No. Published: 03/01/2005 Number of Pages: 13File Size: 1 file , 520 KB