Dynamics of pollution-indicator and pathogenic bacteria in high-rate oxidation wastewater treatment ponds

The spatio-temporal dynamics and removal efficiency of pollution-indicator (total coliforms, fecal coliforms and fecal streptococci) and some opportunistic pathogenic bacteria (Pseudomonas aeruginosa and Aeromonas spp.) were studied in two high-rate oxidation ponds (HROP) A and B pilot-plants. The more evident component of the pollution-indicator bacteria dynamics in HROP effluents was an annual periodicity, based on higher concentrations in winter than in summer. The temporal dynamics of opportunistic pathogenic bacteria studied in HROP effluents was more complex than that of fecal-indicator bacteria. While a 6- or 4-month periodicity appeared, respectively, in the effluents of HROP A and B for Aeromonas spp. abundance, no particular trends were highlighted by chronological analyses for Pseudomonas aeruginosa. Removal efficiency of fecal-indicator bacteria by HROP reached a maximum in summertime and a minimum in wintertime. On the other hand, for each season, removal efficiency was always higher when the retention time is the longest. The relatively low removal of Pseudomonas aeruginosa and Aeromonas spp. showed that HROP efficiency should be improved. When HROP sanitary performance was compared to that of conventional wastewater treatment lagoons (CTL) located in the same area, it appears that HROP is the most efficient treatment system. On the other hand, HROP operates with specific load of 500 kg COD/ha/day (vs 100 kg COD/ha/day for CTL). Thus, the required surface area is five times smaller for HROP than for CTL.