Decomposing plant and animal life (organics) are prevalent in surface water. Organics can affect the taste, odor and color of water, and these organics have shown themselves to be precursors of disinfection byproducts. Organics can also accelerate corrosion rates and greatly increase treatment requirements and associated costs. For these reasons, we try to limit the amount of them that enter the raw water source or we remove them with our treatment process before disinfection.
The first option, limiting the amount of organic material that enters the source water, may be accomplished using a watershed management approach. More information about this approach may be found at the following link:
The second option, removal of organics using a treatment process is a better choice since the watershed approach does not remove all of the organics from the source water. If the removal process is not complete, the finish water may have taste and odor problems and color issues. The most important reason to remove these organics from the raw water is to reduce the precursors for the formation of trihalomethanes.
Trihalomethanes are the byproducts of the chemical reaction between chlorine and the natural-occurring organics in drinking water. These naturally occurring carbon compounds are not hazardous by themselves, but when combined with chlorine, produce byproduct reactants, which have a health concern.
Normally, we think of three different treatment methods to remove the organics from the raw water: aeration, oxidation and activated carbon absorption.
Aeration treatment consists of passing large amounts of air through the contaminated water. The efficiency of the device is improved by breaking up the water flow into many small droplets. The goal is to maximize the water’s surface area to allow the contaminants to volatilize into the air stream.
Oxidation is the reaction of a chemical with oxygen or oxygen-like compounds. Some of the chemicals that are used for oxidation include ozone, potassium permanganate, sodium permanganate, hydrogen peroxide and hypochlorite. Further treatment may be required to completely remove any residual amount of organics left after treatment.
Activated carbon is carbon that has been exposed to very high temperatures, creating a vast network of internal pores. Two types of activated carbon, granular and powdered, have been used widely in drinking water treatment. Powdered activated carbon (PAC), which is most often used for taste and odor control, is added directly to the raw water and removed by settling in sedimentation basins. GAC removes many organic contaminants, as well as taste and odor from water supplies.
The removal of organics from source water is one of the important duties associated with being the operator of a water plant. In fulfilling this duty you as an operator reduce the number of complaints about the flavor, smell or appearance of the water, and through this removal process, you also reduce the concentration of potential cancer-causing chemicals, trihalomethanes.