A sample study on nitrogen removal from polluted streams by using hybrid natural wastewater treatment systems

The ecological structure and function of the water reservoirs deteriorate dramatically because of streams fed by the excess nitrogen-containing wastewater. To protect the water reservoirs from polluted streams, structures such as natural wastewater treatment (NWT) systems to be created inside or outside streams may be a most suitable and economical solution method to overcoming the problem. In this study, a hybrid NWT system was installed to remove nitrogenous pollutants in Karasu creek (Nigde city, Turkey) in 2014. The system built near the creek consisted of feeding basin (FB), settlement basin (SB), free water surface-constructed wetland (FWS-CW), and overland flow (OF) system respectively. Despite quite high nitrogen loading rates, the system managed to reduce NH4+-N from average 29 mg/L to 12 mg/L and TN from 44 mg/L to 19 mg/L with an average removal efficiency of 57%. Results revealed that hydraulic and nitrogen loading rate, temperature and seasonal variation, BOD/TKN ratio, hydraulic residence time (HRT), and the use of the filter material were effective on nitrogen removal. The results suggest that the hybrid NWT systems can be used as a low-cost wastewater treatment alternative to improve water quality in streams contaminated by nitrogenous pollutants in the similar areas.