Groundwater is often contaminated by ammonium and nitrate, causing problems in developing countries such as Thailand and Nepal. Therefore, development of new methods for removing contaminants from groundwater is necessary. In this study, we investigated the effectiveness of a new treatment system for simultaneous removal of ammonium and nitrate by anaerobic ammonium oxidation (ANAMMOX) and hydrogenotrophic denitrification. Enriched ANAMMOX sludge was cultivated under two conditions (20 mL/min

more »

... drogen gas flow rate to investigate the effectiveness of ANAMMOX and hydrogenotrophic denitrification; and 60 mL/min hydrogen gas flow rate to examine the effect of the presence of nitrite on the activities of both microbes). Simultaneous removal of ammonium and nitrate was successfully detected using the former condition, and 95% of ammonium and 90% of nitrate were successfully removed. Additionally, the maximum nitrogen removal rate was 0.25 kg-N/m 3 /d, and 89% of the total dissolved nitrogen was removed. Using the latter condition, increases in nitrite removal were observed only during the supply of hydrogen gas. These results showed that a hydrogenotrophic denitrifier coexisted with ANAMMOX bacteria in our enriched sludge and that ANAMMOX and hydrogenotrophic denitrification removed ammonium and nitrate simultaneously. Therefore, this method may represent a novel efficient technique for the removal of contaminants from groundwater.