Removal of Microbiological Contaminants in a Sewage Treatment System with Constructed Wetlands as Tertiary Treatment

Microbiological investigation into the fate of indicator and pathogenic microorganisms in wastewater was carried out in a full-scale sewage treatment system with constructed wetlands as tertiary treatment. In this study, the concentration of indicator and pathogenic microorganisms were determined in the various stages of the system. The investigated systems showed a high removal rate for indicator organisms (a log removal rate of 5.48 for total coliforms and faecal coliforms, 4.80 for E. coli and 4.26 for fecal streptococci was observed). The pathogenic microorganisms removal efficiency was relatively low (a log removal rate of 1.81 for Salmonella spp. and 1.56 for C. perfringens was observed). The performance of secondary treatment in removing indicator and pathogenic microorganisms was superior to that of primary and tertiary treatment. Removal of indicator and pathogenic microorganisms was 0.16-1.18 log units for primary treatment, 1.70-3.33 log units for secondary treatment, and -2.00-1.76 log units for tertiary treatment. The indicator and pathogenic microorganisms studied behaved differently during the treatment process, and Clostridium perfringens and salmonellae were more resistant to wastewater treatment than the indicator microorganisms.