| Nitrate contamination in drinking water becomes severe and presents a threat to human health. To solve this problem, hydrogenotrophic denitrification was employed to remove high concentration nitrate from drinking water. Gas-permeable membrane served as hydrogen diffuser in the denitrification process. Denitrification performance of three hydrogenotrophic biofilm reactors, integrated gas-permeable membrane biofilm reactor (IGM-BR), apart gas-permeable membrane biofilm reactor (AGM-BR) and apart biofilm reactor (A-BR), used to remove high concentration nitrate from drinking water, was investigated as a reference for wide practical application of hydrogenotrophic denitrification.A double Mechaelis-Menten form was employed to describe the hydrogenotrophic denitrification kinetics. Kinetic parameters, mainly the saturation constants of nitrate (KN1), nitrite (KN2) and hydrogen (KH1 and KH2), were measured by batch tests in an attached-growth denitrification system. The results showed that KN1 was 2.09 mg/L, KN2 was 1.55 mg/L, KH1 was 0.059 mg/L and KH2 was 0.006 mg/L.The denitrification performance of IGM-BR was not so good with high concentration nitrate and nitrite in the effluent. Lower than 60% of nitrate and 40% of total nitrogen were removed, respectively, and nitrate reducing rate (NRR) and total nitrogen removal rate (TNRR) were less than 200 g/(m3·d) and 150 g/(m3·d), respectively. AGM-BR and A-BR performed better than IGM-BR in the term of good nitrate removal and less nitrate in the effluent. The effluent total nitrogen was below 10 mg/L, satisfying the requirement of this study. In the continuous experiments, NRRs of AGM-BR and A-BR could achieve above 300 g/(m3·d), and TNRRs were about 250 g/(m3·d). The maximum NRR and TNRR of AGM-BR appeared in batch test, 471.36 g/(m3·d) and 443.52 g/(m3·d), respectively, indicating that improvement of denitrification capacity was available for the reactor. Nitrate loading and dissolved hydrogen (DH) concentration were the main factors influencing denitrification performance.Incomplete denitrification occurred in all of the three reactors. Although the effluent total nitrogen was less than 10 mg/L, the effluent nitrite concentration was more than the standards required. Nitrite could be oxidized to nitrate by sodium hypochlorite. The tests results showed that the kinetics of nitrite oxidation by hypochlorite followed the first-order form. The reaction rate was influenced by nitrite concentration and pH value, and the stoichiometric relationship between nitrite and hypochlorite was unrelated with the organics in the water.The organics in the effluent increased after hydrogenotrophic denitrification treatment, and the increasing amount depended on the nitrate loading of the reactor. Under low nitrate loading, denitrifying bacteria lacked substrates and self-hydrolysis occurred. Thus, the organics concentration in the effluent was relatively high. Under high nitrate loading, the organics in the effluent was low, and the measured total organic carbon (TOC) was 0.23-0.87 mg/L higher than that in the influent Coagulation with ferrous-coagulant had no obvious effect on organics removal.Under the influence of many factors, such as hydrogen pressure, nitrate loading and temperature, the effluent water quality of IGM-BR fluctuated and IGM-BR was in an unstable running state. Compared with that, AGM-BR and A-BR worked stably. It was found that clogging was the main factor influencing the stability of the reactor for long time operation.In conclusion, although some problems had arisen during the application of hydrogenotrophic reactors, they were resolved gradually as the investigation went on. Moreover, hydrogenotrophic denitrification exhibited some advantages for the removal of high concentration nitrate from drinking water. It is believed that hydrogenotrophic denitrification will have an extensive future in the field of drinking water treatment as it is improved.
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