DENITRIFICATION WITH EXTERNAL CARBON SOURCE UTILIZING ADSORPTION AND DESORPTION CAPABILITY OF ACTIVATED CARBON

The adsorption-desorption capability of activated carbon was incorpora ted into biological denitrification process with the addition of exter nal carbon source for nitrogen removal in water and wastewater treatme nt. Laboratory scale column packed with granular activated carbon (GAC ) was fed with nitrate and sucrose in various modes. Other than contin uous organic carbon addition (continuous mode), two different dynamic feeding modes, namely intermittent and injection modes were investigat ed. Under intermittent mode, organic carbon source was added in accord ance with cycles consisting of two stages: an organic carbon feeding s tage 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 c olumns for 10 min at frequencies of 1, 2 or 3 times per day. With subs trate 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 ove rall N removal efficiencies ranging from 89 to 95% which are comparabl e with levels attainable under continuous mode. Injection mode achieve d slightly lower but reasonably high denitrification efficiencies. Und er the conditions employed, once per day organic substrate injection w as 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 perfo rmed equally well under continuous mode where organic carbon source wa s 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 9 0% obtained in GAC media. The adsorption and desorption property of ac tivated carbon was also applied in denitrification process for the tre atment of water or wastewater with fluctuating influent NO3- concentra tion levels. Two cases of NO3- fluctuation were examined and in both c ases, overall N removal efficiencies of more than 93% were achieved.