Water and wastewater monitoring of Guia Submarine Outfall–an 11 year survey

摘要

SANEST is a public sanitation company that manages a wastewater treatment plant located atrnGuia, on the west coast of Lisbon, Portugal. This company collects and treats the sewage of fourrnmunicipalities with an estimated 750 000 population equivalent, thus being one of the biggestrnsanitation companies in Portugal.rnA Decision of the Commission 2001/720/CE conceded SANEST derogation, exempting it to applyrnless than secondary treatment to wastewaters discharged into the Atlantic Ocean from the fourrnagglomerations. This decision was supported on a large monitoring program, presented to the EU,rnand set up by SANEST. It surveys the impact of the effluent disposal and includes measurementsrnof physical, chemical, biological and microbiological properties in the effluent and in the receivingrnwaters. This paper presents methods and results for the effluent chemical and microbiologicalrnquality as well as for the receiving waters and an ichthyofauna survey, and resumes an elevenrnyear situation, with the preliminary wastewater treatment before effluent disposal. The WWTPrnresults correspond to medium load urban effluents without treatment with temporal variabilityrnrelated to flood fluctuations. In the receiving waters almost legal values are respected and thernplume of the outfall is only identifiable by faecal bacteria in the vicinity of the discharge.rnThe fish community, in particular benthic species, has revealed a slight degradation probably duernto the fact that pollutants tend preferentially to accumulate on sediment.rnThe treatment plant is being upgraded to fulfil, by May 2009, an advanced primary treatmentrnlevel that includes disinfection during the bathing season to fully observe the EuropeanrnCommission Decision 2001/720/EC.