title: Elimination of enteric bacteria in biological-chemical wastewater treatment and tertiary filtration units.
abstract: The occurrence and removal of salmonellae and faecal indicators in four conventional municipal wastewater treatment plants (MWTP) were investigated. In addition, we tested the efficiency of a semi-technical scale biological nutrient removal process and three pilot-scale tertiary filtration units in microbial removal. All influent samples collected from MWTPs contained salmonellae from 93 to 11,000 MPN/100 ml and indicator bacteria from about 10(7) to 10(8) CFU/100 ml. The reductions in salmonella numbers achieved in full-scale biological-chemical wastewater treatment and semi-technical scale biological nutrient removal processes were usually between 94% and virtually 100% (99.9%) and indicator bacteria reductions between 2 and 3 log units. Microbial numbers in MWTP effluents could be modelled as a function of effluent residual organic matter, suspended solids and total phosphorus concentrations. Pilot-scale tertiary treatment by rapid sand contact filter, chemical contact filter and biological-chemical contact filter reduced salmonella numbers below the detection limit and faecal coliform numbers on average by 99%, 39% and 71%, respectively. A total of 32 Salmonella serovars were identified among 197 Salmonella isolates from municipal wastewaters. Of the isolates, 32% were resistant to nalidixic acid, indicating reduced sensitivity to ciprofloxacin, the drug of choice in the treatment of salmonellosis. In addition, 18% of the isolates were multiresistant. Our results, especially antibiotic resistant Salmonella strains, indicate that conventional municipal wastewater treatment without efficient tertiary treatment, like filtration or disinfection, may constitute a risk for public health.
authors.affiliation: Department of Environmental Sciences, University of Kuopio, POB 1627, FIN-70211 Kuopio, Finland. jari.koivunen@uku.fi
authors.forename: Jari
authors.initials: J
authors.lastname: Koivunen
authors.forename: Anja
authors.initials: A
authors.lastname: Siitonen
authors.forename: Helvi
authors.initials: H
authors.lastname: Heinonen-Tanski
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology; D002939:Ciprofloxacin / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D004755:Enterobacteriaceae / Q000302:isolation & purification*; D005243:Feces / Q000382:microbiology; D006801:Humans; D011634:Public Health; D018570:Risk Assessment; D012475:Salmonella / Q000187:drug effects / Q000302:isolation & purification* / Q000472:pathogenicity; D014865:Waste Disposal, Fluid / Q000379:methods*; D014871:Water Microbiology
chemical_list: D000890:Anti-Infective Agents; D002939:Ciprofloxacin