Application of Humic Substances in Environmental Remediation

Humic substances are generally seen as important soil and natural water components. They are formed during humification of organic matter by soil microorganisms. Humic substances are a mixture of complex organic compounds that are usually separated into three fractions: humic acids, fulvic acids and humins. The properties of humate products on the market depend on the ratios between these fractions as well as on the content of inorganic ballast. Interactions of humic substances with environmental chemicals have long been studied. It has been found that humic substances can enhance biotic and abiotic degradation of phenols, polyaromatic hydrocarbons (PAH) and pesticides in the aquatic environment. They are generally recognized to be responsible for the binding of major parts of the available metal ions in water and soil. Interaction between humic substances and hazardous wastes chemicals is most likely to occur when such chemicals have been disposed of underground. High adsorption capacity, high ion exchange capacity and environmental compatibility makes humic substances an attractive material for environmental remediation. Conestoga-Rovers & Associates (CRA) recently initiated treatability studies on the application of humates in environmental remediation. The studies included biochemical and chemical tests with various heavy metals and organic pollutants. The results of biochemical studies indicate that humates can detoxify organic and inorganic inhibitors of biological processes. Humates also enhance biodegradation of toxic organic substances (phenols, formaldehyde, mineral oil) thus make their treatment more efficient. The results of chemical studies demonstrate that humates can be successfully used for immobilization of heavy metals (copper, iron, manganese). Thus humates can potentially be used as a filling material for barrier walls to prevent transport and bioavailability of heavy metals in soil. INTRODUCTION Properties of Humic Substances Humic substances (HS) are present in all soils and natural waters. Their abundance in soils is of the order of two to three times greater than the living mass of organic matter on and above the surface of earth (1). HSs are believed to be a product of transformations (humification) of organic residues of plants and animals by soil microorganisms. The properties of HSs depend on the properties of the soil, vegetation and weather conditions. Therefore there are distinct differences between HSs from different sources, soil types and climates. Nethertheless, some general reactivity, regardless of source, are broadly similar (2). WM’01 Conference, February 25-March 1, 2001, Tucson, AZ According to the classical definition (3) HSs are "a general category of naturally occurring heterogeneous organic substances that can generally be characterized as being yellow to black in color, of high molecular weight and refractory". HSs are a mixture of complex organic compounds that are usually separated into three fractions based on aqueous solubility: Humic acids The fraction of humic substances that is not soluble in water under acidic conditions (pH < 2) but is soluble at higher pH values;