Study On The Effects Of Humic Acid On Trichloroethylene Removal In Groundwater By Zero-valent Iron

Groundwater is an important water source of human life, however, with therapid development of social economy, the influence of human activities haveresulted in the increasingly serious contamination of groundwater. The leakage ofindustrial wastewater containing Trichloroethylene (TCE), which was widely usedas an organic solvent in industries, is one source of groundwater contamination.Permeable reactive barrier (PRB) technology, has been widely used to removeinorganic and organic pollutants from contaminated groundwater due to its highefficiency and low cost, etc. zero-valent iron (Fe0) based PRB system have showngreat potential for removing TCE pollutants from contaminated groundwater as anin situ remediation technology. However, uncertainties remain concerning theeffectiveness of Fe0PRB in complicated water quality of the subsurface water.Among the numerious effects, the ubiquitous presence of humic substances insubsurface water is an important issue that might influence the performance of Fe0PRB. Thus, the project of this paper was to study the effects of humic acid on TCEremoval in groundwater by Fe0and the behavior of humic acid in Fe0system underdifferent conditions.This study investigated the effects of humic acid on TCE removal by Fe0inlaboratory batch settings and continuous flow column systems with the presence ofvarious geochemical constituents, such as Ca2+. It also studied the interactions ofhumic acid, Fe0, TCE, and Ca2+.Humic acid showed no significant effect on the removal of TCE within40days,which indicated that the direct reduction effect of humic acid on the removal of TCEcould be negligible in Fe0PRB system. It was found that humic acid could bequickly adsorbed on the surface of Fe0, and the adsorption rate of humic acid ontoFe0was faster with the presence of Ca2+.The existence of humic acid showed a significant inhibitory effect on thereduction reaction between TCE and Fe0with the presence of Ca2+whether or not.In addition, the inhibition of humic acid on TCE removal would be faster with thepresence of Ca2+.The pretreatment was conducted between humic acid and Fe0contacting for24h with the presence of Ca2+whether or not. At the absence of Ca2+, the addition ofhumic acid onto Fe0showed no siginificant effect on TCE removal. There was ahydrophobic interaction between humic acid and TCE, which would promote theTCE removal. However, humic acid would compete with TCE of the reaction points on the surface of Fe0, leading to the inhibition of TCE removal. The negligible effectof humic acid on TCE degradation by Fe0was caused by the above comprehensiveeffects. At the presence of Ca2+, humic acid showed a significant inhibition effect onTCE removal.The results of continuous flow column test showed that Ca2+had noeffect on TCE removal in Fe0column at the absence of humic acid. Humic acidshowed a significant inhibition effect on TCE removal in Fe0column with thepresence of Ca2+whether or not. When Ca2+coexist with humic acids, the inhibitioneffect was also obvious and porosity of Fe0media was significantly reduced, whichsignificantly shortened the life of Fe0media in the column.