Performance evaluation of a newly developed flow diverted bed system for stream restoration

The flow diverted bed (FDB) system was developed to improve the stream water quality. This system (Run 2) had two wetlands where the flow from the upper layer (aerobic) in the first wetland could be redirected to the lower layer (anaerobic) in the second wetland by the flow diverter, and vice versa. In addition, the yellow-soil media placed at the bottom layer allowed a larger influx in the lower layer and had a sorption capacity of phosphate ions. The removal efficiencies of COD and TN at Run 2 [hydraulic loading rate (HLR) = 177 cm/d] was 1.7–3.6 times higher than that at Run 1 (HLR = 192 cm/d) without the diverter. The values of void fraction, dimensionless variance, dispersion number, Peclet number and velocity for this system were found to be 0.6637, 0.2847, 0.1717, 5.8241, and 53.2 m/d, respectively. The reducing trend of each pollutant was exponentially decreased along the overall length of this system. Also, the transport was dominated by convection (plug flow) rather than dispersion (complete mix). The volumetric removal rate constants for COD, SS, TKN, TN, and TP were found to be 4.854, 7.988, 1.388, 1.625, and 1.767 d−1 via the first-order rate model. Consequently, the flow diverter and yellow-soil media in this system played an important role in enhancing the treatability of pollutants and operating at a higher HLR.