Nitrogen removal from wastewater plant secondary effluent in a compound natural treatment system

A method for removal of low concentrations of nitrogen in the secondary effluent from a wastewater plant was evaluated. The method can be summarized as follows: Primary Subsurface Vertical Flow Wetland (PSVFW). Submerged Macrophyte Oxidation Ponds (SMOPs). Secondary Subsurface Vertical Flow Wetland (SSVFW). Pilot experiments were conducted to assess the efficiency of total nitrogen (TN) removal from secondary effluent from the Chengjiang Wastewater Treatment Plant, China. At a total hydraulic retention time (HRT) of 21.38 days and a hydraulic loading (HL) of 0.024 m(3) m(-2) d(-1), the average TN concentration in the influent decreased from 6.60 mg L-1 in the influent to 0.87 mg L-1 in the effluent, thus meeting the Class-III surface water standards. PSVFW mediated the ammonification of organic nitrogen (ORG-N) and the nitrification of NH3-N (ammonia), resulting in a TN reduction of 7.58%. In the SMOPs, the concentration of NH3-N was further reduced, and most NO3--N (nitrate nitrogen) was denitrified under aerobic conditions, resulting in a 63.18% TN reduction. In the SSVFW, the concentrations of the remaining NO3--N and ORG-N declined even further so that the whole process accounted for an 86.82% TN removal efficiency relative to the influent TN concentrations. (C) 2013 Elsevier B. V. All rights reserved.