AWWA MTC61203

Tobago, a small island off the coast of South America, relies heavily on tourism to keep its economy afloat. Along with its exceptional beaches, Tobago's main tourist attraction is the Buccoo Reef. However, land activities, run off, and improper treatment of wastewater have contributed to degrading the coral reef. To counter this, the government has chosen to retrofit two existing wastewater treatment plants (WWTP) with membranes. The effluent from these two WWTPs is sent to a stream that makes its way out to sea adjacent to the Buccoo Reef. The two existing treatment plants are located in the Bucco and Bon Accord communities. The pre-modified plants consist of two circular tanks. Each tank contains an outside and center portion. The outside portion was used as an activated sludge system where nitrification and oxidation of BOD took place. The influent 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 aerated section 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/L BOD, 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 each location, which allowed the plants to treat all of the 30,000 gallons that flow into the plant on a daily basis. The clarifier was eliminated and is now being used for sludge holding and aerobic digestion. The second circular tank is being 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/L suspended 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.