The impact of disinfection of the effluent of a wastewater treatment plant on the Mediterranean coast

Chlorination is commonly used in the disinfection of wastewater effluents, but it does present disadvantages such as the bactericide efficiency (global bacteria elimination rate and specific species resistivity rate) which is limited. The use and storage of chemical reagents is an operating constraint. The UV disinfection seems to be valid and efficient without any risk of toxicity in the effluent. This technique which does not require reagents is simple to maintain at low and medium flows; it is easily automated and continuously monitored. Firstly, this paper describes comparative results for the reduction rate of bacterial concentrations using the above mentioned two disinfection techniques: chlorination and UV. A full-scale chlorination unit has been installed at the wastewater treatment plant of Canet-en-Roussillon where the received pollution corresponds to 50,000 population equivalents in summer. Two UV pilot-scale units have also been installed on site. The effluents are discharged into the river Tet, the plant is located a few hundred meters from the outfall into the Mediterranean Sea downstream from a great urban center and close to a famous seaside resort. Secondly, a survey of the impact of wastewater disinfection on the coastal area is carried out following, in particular, the bacteriological state of the beaches. If the first step of this study is to determine the efficiency of the disinfection to improve the quality of the effluent and to obtain the levels required for a seaside resort, it is also essential, in a second step, to extend the investigation to evaluate the relative impact of the disinfection on the global quality of the natural coastal water.