Parameters Influencing Nitrite Generation in Drinking Water MBBR Denitrification

Biological denitrification of contaminated drinking water is a promising and cost effective treatment method. A central challenge in biological nitrate removal is incomplete denitrification, and a concomitant production of nitrites (NO2). Since nitrites are considered more dangerous for human consumption than nitrates (NO3), restrictions on allowable nitrite concentrations are substantially more severe than on nitrate, thereby greatly complicating the purification challenge (Kim Shapiro et al., EPA 2007).The objective of this study was to use a Moving Bed Biofilm Reactor (MBBR) in a biological denitrification process that consistently meets nitrate drinking water requirements while also minimizing nitrite production. Drinking water contaminated with nitrate was treated in a 10-month bench scale pilot test involving an anoxic denitrification stage followed by an aerobic polishing stage. The subsequent full-scale pilot system treated well water with a nitrate level of ca. 120 mg NO3/l and consisted of only an anoxic stage followed by complementary physical filtration stage.Nitrate load; the carbon source used (ethanol & citric acid); temperature and HRT were each evaluated for their influence on effectiveness of nitrate removal rates and on nitrite production. The correlation between parameters such as Dissolved Oxygen (DO), ORP levels and the acclimation period was also studied. Results showed that the nitrate removal rates were higher and nitrite production was completely absent with the use of ethanol when compared to citric acid. Nitrate removal rates increased further with increasing temperatures. Good correlation was found between nitrite levels and operational parameters such as DO, ORP and acclimation period. Nitrate and nitrite concentrations in treated water met stringent regulations.