Importance of TOC Reduction in Surface Water Treatment
Written by AOS Treatment Solutions on April 4, 2017
The deployment of disinfectants is an essential step in surface water treatment. However, with the process comes the potential for undesirable disinfection byproducts (DBPs). Natural organic matter (NOM) interacts with DBPs to increase total organic carbon (TOC), often to unacceptable levels.
What Is TOC in Water?
The measure of total organic carbon (TOC) in water indicates the level of contaminants or organic molecules present. Measuring TOC in water helps organizations understand whether or not water is safe for their specific needs. TOC will not determine which compounds are present, but only the amount of compounds.
TOC Water Treatment and DBPs
When this occurs, TOC reduction is necessary to meet federal and/or state standards. Using TOC removal methods is particularly vital because certain DBPs, such as haloacetic acids and trihalomethanes, can cause cancer. Concentrations of haloacetic acids cannot exceed 40 parts per billion, and trihalomethane concentrations cannot exceed 80 ppb.
The most common steps in surface water treatment in municipal systems are:
- Coagulation and flocculation
- Sedimentation
- Filtration
- Disinfection
First, positively charged chemicals neutralize negatively charged dirt and other dissolved solids. The chemicals and particles bind together, forming floc. Their combined weight causes them to sink during the sedimentation process. Clearer water at the top is then filtered through substances with different pore sizes to progressively remove most remaining dust, chemicals, bacteria, viruses and parasites.
However, these disinfectants tend to increase DBPs. A 2013 study highlighted the impact different disinfectant types and dosages have on DBPs. It also drew attention to the vast array of potential DBPs. Researchers accumulated their data by studying four surface water treatment plants in Sweden. Water quality was compared before and after treatment. Researchers identified 499 DBPs, including 230 byproducts not previously reported.
TOC Treatment Methods
There are a variety of TOC reduction methods used to reduce total organic carbon, including ultraviolet (UV) light, advanced oxidation, ion exchange and membrane filtration.
TOC Reduction With UV (Ultraviolet Light)
UV light promotes free radical formation, resulting in oxidation of organics into water and carbon dioxide. UV light with a wavelength of 254 nanometers (nm) is commonly used in water treatment operations. The power of the oxidation process may be amplified through the addition of persulfate compounds.
Advanced Oxidation
Advanced oxidation requires hydroxyl radicals in proportion to the contaminants being removed, so the cost of required chemical reagents can escalate. However, the hydroxyl radicals are among the strongest antioxidants around. They are generated by precisely introducing hydrogen peroxide, ozone or oxygen into the water treatment process. The process is capable of eliminating certain organic compounds rather than simply transferring them to another phase. In ideal conditions, contaminant levels are reduced from hundreds of parts per billion to less than five ppb.
Membrane Filtration
When it comes to membranes used in water treatment, there are both low-pressure and high-pressure versions. Reverse osmosis (RO) and nanofiltration (NF) are high-pressure systems, while microfiltration (MF) and ultrafiltration (UF) are low-pressure systems. The differences are substantial. Low-pressure membranes commonly operate at between 10 and 30 psi, while high-pressure membranes typically operate at 75-250 psi.
Ion Exchange
TOC removal water treatment is also possible through the introduction of styrenic and acrylic strong base anion resins. The large pores in these resins capture large organic molecules. After a brine solution removes the organic compounds from the resin, it can be reused year after year. Another method makes use of an iron-impregnated anion resin that can be regenerated. The use of such resins may be economically viable in larger municipal water treatment plants.
Let us show you the methods that our AOS industrial water treatments offer to reduce the compound levels in your TOC water testing samples. It is possible to deal with disinfection byproducts is an efficient and effective manner. Our state-of-the-art testing equipment accurately assesses TOC levels so the right solutions are deployed.