Abatement efficiency of municipal wastewater treatment plants using different technologies (Orbetello Lagoon, Italy)

Two small-scale municipal wastewater treatment plants (Neghelli and Terrarossa) discharging effluents into a lagoon of great environmental interest and highly stressed by tourism (Orbetello, Italy) were monitored over the year 2001. We evaluated plants' performances developing a general efficiency indicator of removal to select the suitable purification technology (activated sludge, Neghelli vs. rotating biodisc reactor, Terrarossa). Unexpected, conventional technologies (activated sludge) had best performances (84% vs. 62%) with higher removal efficiencies for dissolved nutrients producing, on average, better final effluents. Even if Terrarossa showed a great improvement in summertime, during winter it seemed to be considerably affected by sea aerosol. Before the final discharge in lagoon, effluents were phytodepurated in a pond to reduce their nutrient load. Although data showed that the pond had further abatement efficiency over 80%, final outlet water represented a dangerous input for the lagoon ecosystem.