Constructed wetland for the treatment of anaerobic digester effluent: experimental design

Constructed wetlands have been studied by many research groups during over 40 years, but few aspects remain to be better understood as numerous information must be deeper verified. In the last years, aside the related research activity, also the efficiency aspects of this subject is becoming more and more important. For this reasons the authors decided to build inside our academic department courtyard an hybrid constructed wetland system (CW), using the most recent guidelines available at design time (Brix, 2005). The overall aim of this research was to investigate the CW system to the treatment of anaerobic digester outlet, modifying it to produce effluents that conform to Italian regulations for wastewater reuse. The tests also aim to verify the removal efficiency under increasing organic and hydraulic loading rate. The constructed plant consists in two parallel cells of subsurface vertical flow (V-SF), and one of horizontal subsurface flow (H-SF) of 1 m3 each. The constant inflow, needed to feed the H-SSF pool, has been realized by gravity using a modified Mariotte bottle. In the V-SSF the water flow is vertical and intermittent and it is been allowed using electric pumps managed by pre-programmed timers. The system can work with a direct and inverse mode flow, with three different streams, one of 50 l/day (related with the initial physical model), one of 594 l/day (related with the second physical model) and a last one of 200 l/day that seems to be the most efficient.