Oxygen transfer capability in sfs-h natural wwt studied on engineering-unibo pilot plant

The increasing interest on natural wastewater treatment systems implementation for large flow rates involves to study in detail the process features. Recently, the full scale implementation of horizontal sub-surface flow (SFS-H) phytotreatment systems in irrigation channels is studied. Biological processes in SFS-H phytotreatment systems for wastewater treatment are regulated by vertical profiles of dissolved oxygen which balance and distribute the aerobic/anoxic/anaerobic conditions in filtration bed. Nitrification in horizontal flow systems is strongly influenced by the limited oxygen transfer capability so hybrid systems (vertical and horizontal flow) are frequently implemented to improve the nitrification/denitrification rates. Consequently, the oxygen transfer capability in SFS-H natural ponds is a key point for their efficient implementation. Thus, a monitoring study has been carried on the Engineering-UNIBO pilot plant in order to measure and improve the oxygen transfer capability in SFS-H natural pond. The pilot plant consists of two tanks with the same sand bed and one of them also contain plants (Phragmites Australis). The pilot plant was alternatively fed by clean water and wastewater from the University sewage system. Consequently, four work conditions were studied and compared: 1) clean water and tank without plants 2) clean water and tank with plants 3) wastewater and tank without plants 4) wastewater and tank with plants. The Dissolved Oxygen (DO) and Temperature (T) were measured at two levels corresponding to surface and bottom of the tank in order to evaluate the horizontal and vertical variations. As expected, the monitoring results show that in case of clean water inlet the DO variations are very low even if an increase was observed when the hydraulic retention time was 30 h, while in case of wastewater inlet DO increase reach around 30%.