Nitrification of polluted urban river waters using zeolite-coated nonwovens

Presence of ammonium nitrogen in small urban rivers in Japan due to domestic sewage inflow can lead to eutrophication of receiving lakes and can cause toxicity in aquatic systems, thus, emphasizing the need for direct purification of river waters until sewage treatment is provided. In this study, nitrification of small, polluted urban rivers in areas without centralized sewage works was experimentally examined using zeolite coated nonwovens (ZCN). NH4-N adsorption by ZCN could be described by Freundlich adsorption isotherm with k and 1/n values to be 0.28 and 1.17, respectively. The capacity of nonwovens to retain nitrifying activated sludge was determined to be 208 g-MLSS/m(2) and the effluent from the nitrifying reactor packed with nonwovens was free of SS. The effectiveness of the zeolite coating on nonwovens was verified through two months of continuous nitrification treatment and it was found that the reactor packed with ZCN showed stable treatment at about 90% removal while the reactor packed with only nonwovens showed large fluctuations. The maximum allowable NH4-N loading rate for 90 % removal of NH4-N was determined to be 50 mg/L/d. Experimental results illustrated that this system was also capable of reducing TOC from 10 mg/L to less than 2 mg/L indicating that efficient simultaneous removal of TOC and NH4-N is possible with ZCN. A protocol for culturing nitrifying microorganisms on nonwovens was also established.