Sorption of nitrates to activated carbon

Abstract

Stormwater is an increasing global threat to water quality in water bodies. Urbanization is expanding, and so is the amount of impermeable surfaces that prevents water seepage into the ground. This is disturbing the natural water cycle and is leading to increased surface runoff. Waters that receives this runoff are exposed to rapid shock concentrations of pollutants. Nitrate is such a pollutant. High concentrations of nitrate lead to several adverse effects on human health and nature, like methaemoglobinaemia in infants and eutrophication of water bodies. In this study, batch experiments were performed on synthetic stormwater with commercial activated carbon added to investigate the sorption of nitrate. Synthetic stormwater samples contained various concentrations of nitrate-nitrogen. The activated carbon used as sorbents were Hydrodarco 3000 and the Sub-bituminous CR830A . Sampling was performed at specific time intervals and analyzed by an ion chromatograph for anion concentrations. Freundlich and Langmuir adsorption models were investigated for their prediction to explain the experimental data. Between 49 - 95% of the nitrate-nitrogen was removed from the samples to which the sub-bituminous carbon was added, with an average percent removal of 75%. Adsorption capacity was determined to be between 11.662 - 2363.814 mg/kg. None of the adsorption models were found suitable. Samples with added Hydrodarco carbon had an nitrate-nitrogen removal between 31 - 93 % , and the average percent removal was 67%. Adsorption capacity was found to be between 32.547 - 5192.875 mg/kg. The Freundlich isotherm was found to be the most suitable model. Adsorption occurring in this study were found to be quick, where equilibrium was reached rapidly after activated carbon was added to the synthetic stormwater samples. Sulfate release was observed at high amounts in equilibrium samples containing activated carbon.