TOC Testing Services

Disinfection Byproducts Testing

The water treatment industry constantly tests water quality, and at times it is impractical to test for several species of interest at once. One solution is to test for the concentration of one element in several species. One of the most common reporting terms to this industry is the total concentration of carbon of the organic compounds present. The method for testing organically bound carbon - or Natural Organic Matter (NOM) - in water is called Total Organic Carbon (TOC) Testing (Benjamin, 2002).

Natural Organic Matter (NOM), which is found in all natural water sources, is produced by the breakdown of plant and animal material in the environment. Its chemical and physical characteristics vary according to environmental source (Aiken et al., 1995).

total organic carbon testing

Typically, NOM comprises compounds ranging from proteins and amino acids to humic and fulvic acids. A range of functional groups can be associated with NOM, including carboxyl groups, carbonyl groups, phenolics, ethers, and esters (Snoeyink et al., 1980). It is the carboxyl and phenolic groups that render the NOM negatively charged at typical water pH values. Neutralization of the negative charge surface is desired in order to get the particles to coagulate or attach to filter media during water treatment operations (Benjamin, 2002).

With these vast characteristics of NOM, it is easy to realize the importance of studying their relevance to activated carbon adsorption during water treatment.

Detecting Disinfection Byproducts with TOC Testing

Removal of NOM in water treatment plants has become extremely important in the last few decades, because NOM serves as the precursor for many disinfection byproducts that are produced in the plants as well as in water distribution systems.

Two sets of disinfection byproducts that are currently regulated by the EPA are Trihalomethanes (THMs) & Haloacetic Acids (HAAs). THMs and HAAs have both been shown to be carcinogens. Removal of the disinfection byproduct precursors prior to chemical disinfection can be enhanced by adsorption onto activated carbon. This can be achieved with PAC in mixing basins or pipes or with granular activated carbon (GAC) in filter beds or adsorbers.

Each method has advantages and disadvantages. PAC has a lower cost, strong kinetics and is adaptable to variance in NOM levels. However, since PAC is typically added prior to conventional treatment, it encounters the highest levels of NOM and high doses are necessary for effective removal.

GAC is gaining popularity as a treatment method for lowering disinfection byproducts and disinfection byproduct precursors. GAC is commonly used after sedimentation so NOM levels are lower and therefore the carbon can lower the Total Organic Carbon concentration of the effluent to below desired levels for many months before being replaced. Another advantage is that GAC can then be reactivated after it becomes spent and then reused. The disadvantages with GAC are higher capital and material costs, as well as additional maintenance.

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