Urban Wastewater Disposal and Eutrophication Risk Assessment in the Coastal Zone

The main objective of this paper is to evaluate the possible relationship between urban wastewater disposal and eutrophication in the coastal zone. Firstly, nutrient loadings are studied in raw and treated sewages coming from physical-chemical and biological wastewater treatment plants. Secondly biological responses of coastal ecosystems to overenrichment are considered in term of macroalgal or phytoplanktonic proliferations. Finally it can be deduced that to assess the risk of eutrophication due to urban wastewater disposal, it is necessary a) to evaluate the form and the respective importance of urban and riverine nutrient loadings into the site, b) to determine the physical sensitivity of the disposal area by evaluating the morphological or hydrodynamical entrapment of water masses, c) to point out possible nitrogen or phosphorus limitation for primary production in a potentially eutrophicated site. All these evaluations may help optimizing a reduction strategy of nutrient coastal discharge by urban wastewater, and finding the limiting nutrient that must be controlled in the sewage treatment plant.