Enhanced nitrate removal by micro-electrolysis using Fe0 and surfactant modified activated carbon

This paper investigated the enhancement of nitrate removal by micro-electrolysis using Fe0 and surfactant modified activated carbon (ACs). Effects of various parameters such as AC types, Fe0 to ACs mass ratio, initial pH and initial DO concentration were studied. The results indicate that the application of hexadecyltrimethylammonium chloride (CTAC) modified ACs is an alternative path to achieve higher nitrate removal even at neutral and basic pH conditions, while the most suitable AC is the AC modified by 25 mmol/L of cationic surfactant CTAC. Final removal of nitrate is increased with the Fe0 to AC mass ratio increasing from 1:1 to 3:1, and further increase of the mass ratio results a decline of the removal. pH is found to be a key parameter affecting micro-electrolysis, and it is found that the nitrate removal declines with pH increase, and an accepted removal about 72.0% can be observed at neutral and 58.0% at even basic pH conditions in the system of Fe0/surfactant modified ACs. The DO concentration of the solution is found to have dramatically effect on Fe0 reduction, and the increase of DO concentration will bring significant reduction in nitrate removal. Mechanism of the reaction was investigated through monitoring the concentrations of both ferrous ion and ammonia, as well as establishment an adsorption-reduction model. The results show that the nitrate was removed by the co-effect of electrochemical reduction and ACs adsorption, while the adsorption effect has played a significant part in nitrate removal. The fitting adsorption/reduction kinetic model indicate that fast reduction of nitrate commonly occurred at the acidic pH conditions with absence of DO, while the adsorption effect dominated in neutral or basic pH conditions.