Microorganism removal in wastewater stabilisation ponds in Maracaibo, Venezuela.

Waste stabilisation ponds are an efficient means of wastewater treatment in many parts of the world wherever suitable land is available at reasonable cost and solar energy is an abundant energy resource. This study evaluated the removal of total coliforms TC, faecal coliforms FC and coliphages C in waste stabilisation ponds functioning as a pilot system in the tropical climate of Maracaibo, Venezuela. Sampling points included raw sewage and each pond effluent. 'Turbidity, pH and temperature 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 respectively. Removal of microorganisms in the three systems ranged between 93-98%. Despite the high removal efficiency of microorganisms, the final 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 the WHO water quality requirement for FC (10(3)/100mL); therefore, they cannot be used for irrigation. Additional treatments, such as slow sand filtration, are needed in order to Improve the quality of the water. (C) 1997 IAWQ. Published by Elsevier Science Ltd.