The effectiveness of wetland treatment systems for removal of coliforms, Salmonella and viruses from municipal sewage is reviewed, based on studies carried out at the Arcata Marsh pilot plant, California. Since total coliform counts were probably unreliable as indicators of faecal contamination, faecal coliform counts were performed for several typical wetland ecosystems. A channelized marsh system with a serpentine flow path gave the highest percentage removal (more than 99 per cent) and pathogen removals by such constructed wetlands might be superior to those of conventional treatment systems, while disinfection of the final effluent could reduce levels of faecal coliforms below the levels required for bathing and water-contact recreational uses. A detailed description of the enrichment and isolation techniques employed for enumerating Salmonella in the course of studies at the Arcata Marsh pilot plant is given. Substantial, almost complete elimination of Salmonella could be realized, and rates of reduction for bacteriophages (as indicators of enteric virus contamination) were also close to 99 per cent, although this level of reduction did not necessarily eliminate the risk to health, where raw or partially treated sewage was fed to the wetland ecosystem. There are 42 references.
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