TOC stands for Total Organic Carbon, it includes all organics that contain carbon except for CO2, bicarbonate and carbonate. TOC is common on the NE coast of America where vegetative matter leaches tannins into the water giving it a tea like color. The naturally occurring TOC is typically negative charged colloids or suspended water. Ideally, RO feed water would have less than 3 ppm of TOC. Anthropogenic (man-made) sources of TOC can contribute significantly higher levels.
Nonspecific tests utilized to determine the organic content of water are given below:
- TOC - Total organic carbon - expressed as C
- BOD - Biochemical oxygen demand - expressed as O2
- CCE - Carbon-chloroform extract - expressed in weight
- CAE - Carbon-alcohol extract (performed after CCE)
- COD - Chemical oxygen demand - expressed as O2
- Color - Color - reported as APHA units
- IDOD - Immediate dissolved oxygen demand - expressed as O2
- LOI - Loss of ignition expressed in weight
Oxidation of TOC in potable water supply creates THM’s which is carcinogenic. Municipalities require TOC reduction before chlorination to remain under the THM target set by the EPA. There are a number of techniques for the removal or reduction of TOC including coagulation/flocculation, activated carbon, activated oxidation, ion exchange, reverse osmosis and nanofiltration.
- Coagulation/Flocculation: is a chemical treatment used before sedimentation and filtration. This treatment helps the procedure to eliminate particles.
- Activated Carbon: uses chemical adsorption to eliminate the contaminants and impurities. The surface area structure provided by the carbon allows the highest level of active site subjection to the contaminants.
- Advanced Oxidation: consists of chemical treatment methods that were created to remove organic materials. This process oxidizes through the reaction of hydroxyl radicals.
- Ion Exchange: this treatment not only eliminates the dissolved ions from the solution, but also replaces them with charged ions that are alike. Ion Exchange also softens hard water when it no longer carries calcium or magnesium ions. Nevertheless, Ion Exchange can also remove other dissolved ionic species.
- Reverse Osmosis: removes dissolved organic solids. This treatment is used to eliminate bacteria, ions, molecules, and large particles.
- Nanofiltration: this is a membrane filtration process. This filtration method is used for water with low total dissolved solids.
For low levels of TOC, RO/NF technology is ideal, with the combination of post UV treatment, TOC levels can be lowered to trace amounts. Nanofiltration (NF) membranes are well suited for TOC reduction while maintaining minerals in the water. The selection of RO or NF membranes is a function of the molecular weight (size) or the organic molecules, their distribution and rejection requirements. As a general rule, Hydranautics states a molecular weight of less than 200 are rejected at levels greater than 99%.
Features: TOC measurement is very important in the pharmaceutical industry, given the fact that high purity water is a vital component for production. The power industry also benefits from TOC removal. The boiler feed water in power plants must be free of salts and organic matter in order to function without corrosion issues and high steam conductivity.
- Power industry
Pure Aqua specializes in reverse osmosis and nanofiltration technology. To see Pure Aqua’s standard line of packaged RO equipment, visit our webpage: https://www.pureaqua.com/nanofiltration-nf-systems/