Monitoring the effects of wastewater treatment strategies
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Wastewater disposal in coastal waters causes widespread environmental problems. Secondary treatment is expected to reduce the adverse effects of insufficiently treated wastewater. The environmental impact of sewage disposal via 18 wastewater treatment plants was analysed using the benthic opportunistic polychaetes and amphipods (BOPA) index. In previous studies this index proved to be an effective tool for monitoring sewage pollution. The impact of these discharges was highly related to treatment level, which ranged from pre-treatment to biological, as well as to flow rates and outfall position. Locations affected by pre-treated wastewater showed environmental degradation, especially marked near outfalls with higher flow rates. At most locations, biologically treated wastewater did not cause a significant impact and an improvement in ecological integrity was detected after this secondary treatment had been implemented. The impact of discharge was highly related to chemical oxygen demand (COD), suspended solids and nutrient concentrations, which are all lower in biologically treated wastewater. A ‘moderate’ ecological status was observed not only near sewage outfalls with high wastewater flow rates (>1,500,000 m3/month) with a COD over 200 mg/l but also near those with lower flow rates but with a COD over 400 mg/l. To reduce the impact of sewage disposal, it is necessary to carry out adequate treatment, have site outfalls deep enough, and implement water recycling.
KeywordsWastewater treatment Mediterranean Sewage Benthos BOPA index Pre-treatment Biological treatment
We gratefully acknowledge CONSOMAR S.A. and Entitat de Sanejament d’Aigües for their financial contribution to this project. We also thank the staff of the Department of Marine Sciences and Applied Biology of University of Alicante, especially Y. Mugica, M. Diaz-Valdes and C. Celdrán for their invaluable collaboration. Thanks to Guido Jones for revising the English text.
Compliance with ethical standards
This article complies with editorial and publication policies as well as ethical standards of environmental monitoring and assessment. All procedures performed were in accordance with the ethical standards of the University of Alicante. Informed consent was obtained from all individual participants included in the study.
Conflict of interest
The authors declare that they have no conflicts of interest, and funding agencies are informed.
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