Removal of nitrate from water by modified activated carbon

NUNELL, G.V.; FERNANDEZ, M.E.; BONELLI, P.R.; CUKIERMAN, A.L.

Rosario, Argentina

Workshop; 1st Argentinian Workshop in Environmental Science / Taller Argentino en Ciencia Mediambiental; 2009

Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario

Nitrate contamination in surface and ground water has become an increasingly important problem all over the world. High levels in ground waters mainly result from human and animal waste, and excessive use of chemical fertilizers. Nitrates are extremely soluble in water and can move easily through soil into drinking water supplies. The high concentration of nitrate in drinking water can cause several environmental problems, and have also been linked to outbreaks of different diseases. Due to its versatility and wide range of applications activated carbon is widely used as a contaminant removal medium. Although this adsorbent has proved effective in the removal of several different organic and inorganic pollutants from water, its effectiveness in nitrate uptake is particularly low. Recent research in the literature has focused on enhancing activated carbon effectiveness by modifying specific properties in order to enable the carbon to develop affinity for certain contaminants. Within this context, in the present work, the effect of modifying a commercially available activated carbon on its performance in nitrate removal is examined. For this purpose, the commercial sample was subjected to thermal treatment under N2 flow (100 mL/min) for 60 min at 550ºC. Both the raw and treated activated carbons were comparatively tested in batch mode for nitrate removal from dilute solutions used as model. The treatment effect on textural characteristics was examined from comparative analysis of N2 (77 K) adsorption isotherms determined for the two carbons. Surface chemistry of the samples was mainly characterized by determination of the point of zero charge (pHZC), quantification of surface acidic oxygen groups (carbonyls, phenols, lactones, carboxyls) by the titration method of Boehm using bases of different strength, and elemental compositions. To evaluate the pH effect on the removal of nitrate ions from dilute solutions, batch experiments at 25 ºC were first carried out. Then, nitrate adsorption capability for both activated carbons was assessed by determination of equilibrium isotherms, which were properly described by the Freundlich model. Model parameters indicated that the thermal treatment led to enhance nitrate removal, without considerably affecting the original textural properties of the carbon (BET area 1360 m2/g; total pore volume 1 cm3/g). However, a reduction in the total content of surface functional groups and modification of the amounts of individual functionalities were evidenced. Accordingly, present results suggest that thermal treatment of activated carbons under N2 flow could be applied to improve their performance for nitrate removal from aqueous media by targeting their surface chemistry, which plays a key role in the uptake of nitrate anions.