My water is tinted yellowish

There are multiple reasons why your water is tinted. In surface water there are natural organic matters that produce a yellowish tint or color. By adding disinfectant chemicals, carcinogenic Disinfection By-Products (DBPs) can be formed.

Why is my water tinted yellow or brownish?

In surface water, natural organic matter exists in either non-dissolved or dissolved form. The dissolved forms of matter are known as Dissolved Organic Carbon (DOC), while the sum of dissolved and non-dissolved carbon is known as Total Organic Carbon (TOC).

The DOC in water is what produces the yellowish tint or color, and is measured in Color Units (CU). If this type of discoloration is present in the water, then adding disinfectant chemicals such as chlorine, bromine, or bleach will create Disinfectant By-Products (DBPs), which are carcinogenic.

Since these chemicals are commonly used in disinfecting water supplies, water discoloration presents a significant health risk to drinking water usage.

What are Disinfection By-Products (DBPs) exactly?

Disinfection by-products (DBPs) are a class of chemical by-products known as trihalomethanes (THMs). They are formed when chlorine or bromine interacts with the natural organic materials found in water. DBPs also include other formed products, such as haloacetic acids, haloacetonitriles, haloketones, and chlorophenols. The composition and levels of specific DBPs are determined by water quality, water treatment conditions, and disinfectant type.

Primary sources of DBPs are chlorinated drinking water and recreational water bodies, such as swimming pools. A 2005 article from Environmental Health Perspectives showed that you don’t just have to drink the water, either: hot showers, washing dishes and washing clothes in DBP-filled water directly correlated with higher concentrations of THMs in people’s blood. Additionally, the article showed that THMs are absorbed through the skin as well as by ingestion.

How to remove discoloration from water and avoid DBPs

Two different methods can be used to remove discoloration from water and, therefore, reduce the level of DBPs.

1. Flocculation of DOC and filtration through membrane filters

Flocculant is added into the feed-stream of a membrane filtration unit, such as a Virex Pro Connect of a Phoenix system. The DOC attaches to the flocculant, making it large enough to be filtered out, and then it is removed by the membrane filter. Typically, color can be removed significantly, although not completely, using this method.

2. Filtration through Granular Activated Carbon (GAC)

GAC has the ability to remove DOC fully from water, but to do so, a typical contact-time between water and GAC of 10 minutes (!) is required. When fully loaded, the GAC filters have to be exchanged or re-loaded with fresh-carbon.

Using flocculation-filtration to remove the discoloration from water

For larger scale projects, such a municipal water production, Seccua recommends the flocculation-filtration method. Seccua has installed hundreds of these types of public water systems world-wide; most of them are in Germany, the United States, and Canada.

Using activated carbon filtration to remove the discoloration from water

Seccua offers its Seccua Biofilter to remove DOC from water. Seccua recommends activated-carbon filtration for residential use, due to the lower volumes of water that have to be processed compared to commercial water consumption. Whoever designs the system must make sure that the contact time between the activated-carbon filter and the water is at least 10 minutes.

Case Study

Optimizing the flocculation-filtration method

Most recently, Seccua partnered with the Minnesota Department of Public Health to try and optimize the flocculation-filtration method for the removal of discoloration and disinfection by-products from drinking water. In extensive tests, performed on lakes in Ely, Minnesota by the Minnesota Department of Public Health, all of those goals were achieved.

Goals

  • Optimizing the removal of color and ultimately the reduction of DBPs
  • Minimizing the number of harsh-chemical cleanings required by the filtration system
  • Maximizing the life-time of the filtration equipment
  • Defining a straightforward, easy-to-use, operating procedure

System set-up

The feed-water to the Virex Pro Connect system was taken in from Lake Ely, Minnesota. Feed-water showed Color of 60 CU. Flocculant was added upstream the Virex Pro Connect system (please get back to Seccua for further information on type and concentration of flocculant added).

The Virex Pro filtered at a flow of 2.8 gpm. The Virex Pro Connect system controlled an automated hourly back-wash with filtered water through a back-wash pump. Also the feed-pump was connected to the system, no additional control was required.

As required per U.S. EPA Filtration Guidance manual for membrane filters applied in filtration of surface water or surface influenced water, the Virex Pro Connect performed a daily, fully automated Direct-Membrane-Integrity test.

Test results

  • The filtrate of the Seccua Virex Pro showed no yellow tint any more, Color was removed by two-thirds to 20 CU (feed: 60 CU).
  • The filter membrane of the Virex Pro did not loose any permeability during the test period of one week, so a very sustainable state-of-operation was achieved.
  • The removal of 27% of TOC also leads to a significant reduction in Disinfection-by-Products (DBP).

Study report

Seccua has many more data available, which will help you to design your color- and DBP-removal process. Please feel free to get in touch with us and we will send you further information.