Pilot plant experiences on nutrients and E. coli removal in aerobic layer of WW finishing ponds

Circular economy model encourages to develop new strategies in the wastewater treatment plants (WWTPs) management. The implementation of good practices in WWTPs management allows to reach different goals (wastewater reuse, energy production and raw material reservoir). At the same time, water scarcity has become more prominent in the last decades and reuse and valorization of water from WWTPs can help solving the problem. The implementation of natural system as finishing treatment for wastewater reuse could be a smart alternative in existing urban WWTPs. In this context this study focuses on the processes occurring in the aerobic layer of a hybrid natural treatment plant : aerobic lagoon/Phytotreatment FWS with Lemna. This layer is crucial to reduce the concentrations under the legal thresholds of the following parameters: 1) Escherichia coli 2) Nitrogen Ammonia 3)Total Nitrogen(TN). The aim of the study is to verify the disinfection and nitrification capacity in this layer to suggest more efficient management policies in terms of ratio between surface occupied (phytotreatment) and not occupied (lagoon) by Lemna. To this aim, a pilot plant was built in the Santerno WWTP area (Imola, Italy). The influent flow comes from the outlet of the full scale plant pumped using a peristaltic pump (QIN = 0.03 l/s). The retention time is similar to a real lagoon and to obtain an adequate turbolent flow the output is recirculated with 0.55 kW pump in the inlet section (QREC = 1.03 l/s). The monitoring results show the role of Lemna to guarantee the phosphorus (from 15% to 30%) and nitrogen (from 10% to 20%) compounds removal. The influence of algal photosyntesys to the dissolved oxygen concentration in water column has been observed. In those cases interesting nitrification and nitrogen extraction removal rates were measured (from 15% to 40 %). Moreover, an E.coli removal efficiency around 90% was obtained.