Wastewater finishing by facultative biomass in estuarine channels of Cesenatico (I)

The present work describes effects on water quality of the more internal part of the channels in an open sea drainage system where variations in depth are provided by tide but prevalent freshwater conditions are maintained by high rate of upstream discharged treated wastewater.The research is carried out by a multiparameter probe into an internal channel of Cesenatico harbour basin at the limits of the transition area, at four kilometres from sea outlet. Along his length (3500 m) this tract receives, in dry water conditions, only residual organic loading from Cesena municipal wastewater treatment plant (180.000 AE) and presents low average depth (max 0,8-1 m) and almost constant width (8m). Unsteady flow conditions regulated by downstream level, according with tidal oscillations and wastewater input, are schematized for water quality calculation as four sequencing daily cycles of storage and discharge. Wastewater finishing effects provided by channel are described by classic facultative lagoon biological processes applied to a plug flow reactor scheme. In three different tidal conditions are measured water depth , velocity, temperature, salinity, pH, redox, oxygen, suspended solids and nitrate nitrogen. Data permit a quantification of combined productive and consumer activities sustained by microalgal and bacterial populations during the day and a balance between oxidizing and anoxic bacterial phases during the night.