Coliforms as indicators of efficiency of wastewater treatment plants

Indicator microorganisms are used to evaluate the water quality and in wastewaters the most used indicator bacteria are the total and fecal coliforms. The main objective of the present work was to verify if the treated wastewater had sufficient quality, regarding the chosen parameters, to be discharged in receiving natural waters. In the present work 660 residual water samples from 9 sewage treatment plants located in the Algarve region had been analyzed. The performance of these treatment plants in the removal of fecal and total coliforms was studied. The obtained results showed that 78% of the wastewater treatment plants had levels of removal of faecal coliforms up to 90%, what indicates that they had a proper functioning. Plants that showed very low efficiencies of removal were 22%. The last mentioned plants presented a very high number of coliforms, what could be harmful for the public health if these waters will be discharged at the environment in inadequate sites. Faecal coliforms maximum concentration observed in this study in final effluent was 6.7x 10(8).