A comparative study on the removal of several pathogenic bacteria and their indicators was carried out at three natural wastewater treatment systems: stabilisation pond, high-rate algal pond and a free-water macrophyte system, retention times being 24, 5 and 3 days respectively. The macrophyte system showed higher removal efficiency for most of the groups, followed by stabilisation pond and high rate algal pond. All systems showed their highest efficiencies in the reduction of total coliforms, ranging from 98.68% for the stabilisation pond to 99.48% for the macrophyte process. Highly significant differences were found between the systems for bifidobacteria, C. perfringens and total coliforms removal. Pathogens and their indicators showed a different behaviour in their daily removal rate depending on the treatment plant.

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