Denitrification with external carbon source utilizing adsorption and desorption capability of activated carbon

The adsorption-desorption capability of activated carbon was incorporated into biological denitrification process with the addition of external carbon source for nitrogen removal in water and wastewater treatment. Laboratory scale column packed with granular activated carbon (GAC) was fed with nitrate and sucrose in various modes. Other than continuous organic carbon addition (continuous mode), two different dynamic feeding modes, namely intermittent and injection modes were investigated. Under intermittent mode, organic carbon source was added in accordance with cycles consisting of two stages: an organic carbon feeding stage and an organic carbon starvation stage. Three cycle schedules in terms of duration of feeding stage and starvation period were examined. In injection mode, concentrated organic substrate was fed into the columns for 10 min at frequencies of 1, 2 or 3 times per day. With substrate C:N ratio of 1.88, influent NO3---N level of 20 mgl−1 and empty bed contact time (EBCT) of 80 min, intermittent mode produced high overall N removal efficiencies ranging from 89 to 95% which are comparable with levels attainable under continuous mode. Injection mode achieved slightly lower but reasonably high denitrification efficiencies. Under the conditions employed, once per day organic substrate injection was sufficient to remove 87% of the influent NO3---N. The performance of anthracite media was also compared with GAC under both continuous and intermittent modes using identical set of conditions. Anthracite performed equally well under continuous mode where organic carbon source was always available. However, under intermittent mode, anthracite gave a poor N removal efficiency of 29% during the starvation period due to the lack of adsorption and desorption capability in comparison with 90% obtained in GAC media. The adsorption and desorption property of activated carbon was also applied in denitrification process for the treatment of water or wastewater with fluctuating influent NO−3 concentration levels. Two cases of NO−3 fluctuation were examined and in both cases, overall N removal efficiencies of more than 93% were achieved.