Use of humic acid solution to remove organic contaminants from hydrogeologic systems.
Experiments were carried out to evaluate the effectiveness of a 29 mg/L solution of humic acid to enhance the removal of six aromatic hydrocarbons (benzene, toluene, p-xylene, ethyltoluene, sec-butylbenzene, and tetramethylbenzene) from a sandy material. None of the compounds were completely removed from the material. Nonetheless, the compounds with the highest water solubility, benzene and toluene, were removed effectively; less than 1 mass % was retained with use of either the humic acid solution or water. For the less soluble organic compounds, removal was more difficult and was enhanced by the humic acid solution compared to water. Mass percent retained with humic acid was as follows: p-xylene, 1.4% (24% less than water); 3-ethyltoluene, 6.4% (40% less); sec-butylbenzene, 39% (14% less); and tetramethylbenzene, 43% (14% less). The positive effect of humic acid on the removal of these organics may arise from the aggregation of the humic acid molecules to form membranes and/or micelles, having hydrophilic exteriors and hydrophobic interiors. Partitioning of the hydrophobic organics from the bulk solution into the hydrophobic interior of these humic acid structures can account for their enhanced removal from the sandy material.