Influence of Humic Substance Alteration during Soil Passage on their Treatment Behaviour

Abstract

Humic substances are not major objectives of water treatment in drinking water supply. But, as they often influence the treatment efficiency or participate in treatment reactions, their behaviour in the treatment process can significantly determine the process design. A very effective pretreatment step can be achieved by soil passage (e. g. bank filtration or slow sand filtration) which is usually involved in German surface water treatment processes. In this study transport phenomena of humic matter during underground passage are investigated with special attention to the alteration of their treatment behavior. In a fundamental work the deposition of humic substances was studied in a model system. Transport phenomena could mathematically be described by a filtration theory of colloidal transport. From the results of these calculations the collision efficiencies of humic substances on clean and coated surfaces can be derived. The humic substance deposition on subsurfaces is accompanied by a classification based on molecular weight. An additional alteration of dissolved humic matter due to microbiological degradation and partial resolvation of deposited humic matter was observed by passage of river water through columns containing actual soil. The alteration of dissolved organic matter during soil passage is finally characterized by its adsorption and chlorination precursor behaviour. All results confirm that bank filtration is an effective pretreatment step particulary due to the decrease in connection with improvement in treatability of humic matter.

Peer Reviewed: The Promise of Bank Filtration

“…Different components of NOM exhibit different transport behavior during surface water infiltration. Several studies have indeed demonstrated that the mobility of NOM in the subsurface increases with decreasing molecular weight and hydrophobicity (20)(21)(22). These results suggest that the smaller and more hydrophilic fraction of NOM may dominate the NOM-facilitated transport of contaminants in groundwater.…”

Natural Organic Matter Removal During Riverbank Filtration: Current Knowledge and Research Needs

“…The aromatic carbon of these isolates decreased significantly only during long travel times (2 to 8 years of transport) with relatively small changes in DOC concentration. Kivimaeki et al (1998) and Gerlach and Gimbel (1999) also observed that the highest molecular weight fractions of organic matter were removed during the initial phase of infiltration because the collision efficiencies greatly increased with increasing molecular weight. These findings point to the long-term transformation of remaining organic matter during travel through the subsurface towards well-aged fulvic acids, while non-humic material is biodegraded and humic substances are adsorbed during the initial phase of infiltration.…”

“…These findings point to the long-term transformation of remaining organic matter during travel through the subsurface towards well-aged fulvic acids, while non-humic material is biodegraded and humic substances are adsorbed during the initial phase of infiltration. A fundamental understanding of the removal mechanisms for humic substances in RBF systems is still missing, although most studies suggest a combination of initial adsorption followed by biodegradation (Sontheimer, 1991;Gerlach and Gimbel, 1999). The accumulation of organic matter in RBF systems due to the continuous deposition of humic substances usually does not occur due to microbiologically induced degradation of sorbed humic substances (Gerlach and Gimbel, 1999).…”

“…A fundamental understanding of the removal mechanisms for humic substances in RBF systems is still missing, although most studies suggest a combination of initial adsorption followed by biodegradation (Sontheimer, 1991;Gerlach and Gimbel, 1999). The accumulation of organic matter in RBF systems due to the continuous deposition of humic substances usually does not occur due to microbiologically induced degradation of sorbed humic substances (Gerlach and Gimbel, 1999). Gerlach (1998) reported that the oxygen consumption in RBF is two to three times greater than the stoichiometric oxygen requirements for DOC and ammonium ion mineralization.…”

Effects of Urbanization on Groundwater

“…Different components of NOM can have a substantial effect on its treatability, and its mobility in the subsurface, its reactivity with chlorine, and the speciation of the DBPs formed as a result of this reaction (Aiken and Cotsaris 1995; Croue et al 1999). The mobility of NOM in the subsurface increases with decreasing molecular weight and hydrophobicity, which suggests that smaller and more hydrophilic fraction of NOM may dominate NOMfacilitated transport of contaminants in groundwater (McCarthy et al, 1993;Ludwig et al, 1997;Gerlach and Gimbel, 1999). While the overall concentrations of organic DBP precursors are effectively reduced during bank filtration, the reductions appear to be largely the result of the reduction in NOM concentration rather than a consistent change in NOM character (Weiss et al, 2004).…”