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

<p>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.</p>

Nitrogen removal by denitrification and annamox processes in freshwater rivers of high nitrogen loading region of China

The importance of anaerobic ammonium oxidation (anammox) – a metabolic pathway that can generate dinitrogen – remains poorly understood in freshwater river system. Using the 15N-isotope pairing technique (15N IPT) combined with membrane inlet mass spectrometry (MIMS), the potential rates of denitrification, anammox and total N removal, and their respective contributions to total N2 production were evaluated in 11 rivers in the Taihu Lake region of China. The measured potential rates of denitrification, total N removal and anammox varied from 18.9±0.3 to 70.0±11.4, 26.3±0.4 to 71.3±11.1 and 1.3±0.3 to 11.0±2.5 μmol N m-2 h-1, respectively. The relative contribution of anammox to total N2 production (ra%) ranged from 2.0±0.8% to 29.9±0.7%. The mean potential denitrification and the total N removal rates varied spatially in these 11 rivers, with the highest rates occurring in the western rivers of the region, while the mean potential anammox rates and ra% displayed the opposite trend with the highest values occurring in the southern rivers of the region. The contents of nitrate and dissolved organic carbon in sediments appeared to be the primary controlling factors for denitrification and anammox in these studied rivers. Our results indicated that the potential rates of N removal varied spatially, and denitrification is the dominant activity for removing fixed N but the role of anammox is not negligible in freshwater rivers.