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Urban wastewater reuse for landscape irrigation in a seaside resort: microbial requirements.

IWRA World Water Congress 2008 Montpellier France
6. Water Conservation and Demand Management
Author(s): Eric Blin
Philippe Blatière
François Brissaud
Eric Blin, SDEI, route de Bessan, BP 86, 34340 Marseillan, France. E-mail : eric.blin@lyonnaise-des-eaux.fr Philippe Blatière, Communauté de Communes Terre de Camargue, 13 rue du Port, 30220 Aigues Mortes, E-mail: ccterredecamargue@wanadoo.fr

AbstractDue to recent droughts, increasing public awareness of water being a limited resource and to ever more stringent requirements on the disposal of wastewater treatment effluents, many municipalities are planning to reuse municipal wastewater. Protecting bathing places, shellfish farms and sensitive receiving water bodies has led to the implementation of tertiary wastewater treatments, the cost of which municipalities would like to recover through treated water reuse for the irrigation of landscaped and recreational areas. However inappropriate or too strict regulations may hamper the development of water reuse, which would result in a waste of fresh water resource. The investigation aims at evaluating the health related risks due to sprinkler irrigation of urban landscaped areas with the effluents of Le Grau du Roi wastewater treatment plant (WWTP). Based on the microbial quality of the effluents, the appropriateness of the current French regulations, which prohibits spraying treated wastewater in the vicinity of houses, buildings, roads and recreational areas whatever the quality of the treated water, will be assessed and adaptations of the regulations suggested. Le Grau du Roi, 100,000 p.e. WWTP, encompasses an activated sludge system achieving high dephosphatation, nitrification and denitrification, and a 20 hectares waste stabilization pond system. The microbial quality of the WWTP effluents was monitored from April to September 2006. Effluents of the activated sludge facility and the ponds were analysed for faecal contamination indicators, E. coli and Streptococci, helminth eggs, Salmonella, enteroviruses, Legionella spp and Legionella pneumophila. Faecal indicator bacteria were efficiently removed from the very outlet of primary ponds. Effluents of the waste stabilization pond system complied with the “excellent quality” criteria defined by the European Directive 2006/7/EC (EC, 2006) for coastal bathing waters. Helminth eggs, salmonellae and enteroviruses were never detected neither in the ponds nor at the outlet of the activated sludge treatment. Legionella spp content was found to be slightly higher or of the order of magnitude of contents often observed in river waters, e.g. the Rhône water. Legionella pneumophila was detected in the activated sludge effluents, several times at the outlet of primary ponds and in April only at the outlet of the ponds system using PCR method; however, contents were not high enough for quantification. Regarding this criterion, effluents of the WWTP did not differ from the Rhône water. The microbial quality of the effluents of the waste stabilization pond system appeared to be virtually pathogen free and, whatever the criterion considered, similar to the quality of the Rhône water which is currently used for spray irrigation of the green spaces of the resort. Therefore, substituting waste stabilization pond effluents to Rhône River water is unlikely to alter health risks related to spray irrigation. In this particular situation, enforcing a buffer zone seems to be short of rational support. Adding a chlorination of pond effluents is envisaged in order to secure the microbial quality of the irrigation water.
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