MICROORGANISM REMOVAL IN WASTE-WATER STABILIZATION PONDS IN MARACAIBO, VENEZUELA

Waste stabilisation ponds are an efficient means of wastewater treatme nt in many parts of the world wherever suitable land is available at r easonable cost and solar energy is an abundant energy resource. This s tudy evaluated the removal of total coliforms TC, faecal coliforms FC and coliphages C in waste stabilisation ponds functioning as a pilot s ystem in the tropical climate of Maracaibo, Venezuela. Sampling points included raw sewage and each pond effluent. 'Turbidity, pH and temper ature were recorded. The results for raw sewage show average levels of 4.1x10(6) TC, 2.8x10(6) FC and 7.0x10(5) C/100mL. Temperature, pH and turbidity ranges between 26-31 degrees C, 6.2-9.5 and 15-98 NTU respe ctively. Removal of microorganisms in the three systems ranged between 93-98%. Despite the high removal efficiency of microorganisms, the fi nal effluents showed average counts of 5.4x10(4)-1.4x10(5) TC, 5.2x10( 4)-1.3x10(5) FC and 1.6x10(4)-4.7x10(4) C/100mL. This study shows that the microbiological quality of the final effluents did not achieve th e WHO water quality requirement for FC (10(3)/100mL); therefore, they cannot be used for irrigation. Additional treatments, such as slow san d filtration, are needed in order to Improve the quality of the water. (C) 1997 IAWQ. Published by Elsevier Science Ltd.