COLOR REMOVAL Why? and How?

WHERE DOES “COLOR”COME FROM?  For the purpose of this discussion, we will stick totally to organic color, since organics are the primary source of color in the groundwater in Mississippi.  Color is often caused by dissolved organic matter, e.g. humic and fulvic acids (organic decomposition products from vegetation).  The color level can often be a good indicator of the organic content of water. If color is caused by organic matter, there is often a relation between color intensity and the level of organic content.  Color is caused by the refraction of light by the double bonds which are almost always encountered in long-chain organic molecules.

WHY SHOULD WE REMOVE COLOR? Aesthetics Disinfection Byproducts

AESTHETICS  Sometimes it is necessary to remove color from our drinking water, even though we are in complete compliance with the EPA and MSDH.  Commercial Laundries, Hotels and Casinos often find colored water a problem.

DISINFECTION BYPRODUCTS  Sometimes we must remove the “color” (organics) because the reaction of these organics with chlorine forms disinfection byproducts which are not allowed by USEPA and MSDH standards. The chief example of such a disinfection byproduct is Trihalomethane, or THM.

DISINFECTION BYPRODUCTS  Sometimes we must remove the “color” (organics) because the reaction of these organics with chlorine forms disinfection byproducts which are not allowed by USEPA and MSDH standards. The chief example of such a disinfection byproduct is Trihalomethane, or THM.  We can do things to avoid the actual removal of the organics. We can implement alternate disinfection processes like chloramines or UV, which minimizes or eliminates free chlorine and the subsequent DBP formation.

HOW DO WE REMOVE COLOR FROM WATER?  Chemical Precipitation, followed by filtration  Ozonation  Ion Exchange  Carbon Adsorption  Nanofiltration

CHEMICAL PRECIPITATION/FILTRATION  The addition of an iron salt (alum or ferric), along with pH adjustment and flocculation by a polymer, creates a “floc” that can be direct filtered if low enough in concentration, or clarified then filtered if higher in concentration.  This coagulation process usually brings the organic content low enough to be able to disinfect with chlorine. Sometimes, however, alternate disinfection is still required.  The best example of color removal using this process is the Culkin Water District, which has been using this method since 1992.

OZONATION  Ozone cleaves the organic double bonds which cause the organic molecules to appear colored.  Even though the color goes away, the organic fragments remain and should be removed, lest they react and form disinfection byproducts as well.  Common methods for the removal of this type of residual dissolved organics are biologically active filters or carbon adsorption.  There are a couple of water systems in MS using ozone for color removal on groundwater; Fisher Ferry and South Hinds County.

ION EXCHANGE  Negatively charged organic molecules cling to positively charged resin sites. Sometimes it works; sometimes it doesn’t.  An Ion Exchange plant is starting up now in Gautier.

CARBON ADSORPTION  Carbon adsorption functions in much the same manner as ion exchange, in that charged organic molecules cling to naturally positively charged sites on the activated carbon.  Unlike ion exchange, the activated carbon cannot be reactivated on site. It must, rather, be returned to the manufacturer, where impurities are baked off.  The life of a carbon filter is based upon mass loading.  There are no municipal carbon adsorption plants in MS at this time.

NANOFILTRATION  Nanofiltration is a filtration process in which a fluid is forced through a membrane which acts almost like a sieve to separate out impurities. The membrane blocks impurities in the fluid, allowing only the fluid and certain monovalent ions to pass through, while trapping undesirable materials on the other side.  Organic molecules are too large to pass through the pores and are thus “rejected”.  This “reject” water can be as much as 20% of the raw water feed and will be highly colored and high in TSS. Disposal can be an issue.  The raw water must be almost totally free of silt.  No nano plants currently operate in Mississippi for color removal.

CONCLUSION  As regulations tighten on disinfection byproducts, systems with colored groundwater sources will come under more and more pressure to comply.  Stopgap methods which tweek chemicals fed and disinfectants applied can sometimes avoid or delay expensive treatment and removal systems.  Once all other options are exhausted, the removal of the organics at the root of the problem will be required for many systems.  There are many options to be considered.  Retaining a consulting engineer who is knowledgeable in all of the available technology is critical in the effective selection of your treatment process.

QUESTIONS?