Funding:

Project management / project work:

Dr.-Ing. Barbara Wendler, Jakob Kämmler

Situation:

Many groundwaters exhibit a coloration caused by organic components due to regional deposits of peat or lignite sands in the aquifers.

• The coloration of drinking water is limited by German Drinking Water Ordinance (spectral absorption coefficient, SAC436 = color, < 0.5 m-1).
• Though increased coloration by humic substances is typically non-hazardous, it might cause aesthetic problems, leading to complaints by consumers.
• Increased concentrations of humic substances are undesired, as they increase the bioavailability of the DOC and may be initiators in the formation of disinfection by-products.
• Groundwaters with high coloration values are typically anaerobic and contain high concentrations of iron and manganese.  Presence of organic components in water may negatively affect removal of iron and manganese

Currently, the DVGW set of rules does not contain any information on process selection to achieve decolorization in the context of groundwater treatment, in a sustainable and cost-efficient manner.

Both in the laboratory and at selected waterworks sites, three technologies (flocculation / precipitation, oxidation, adsorption) are examined for their decolorization efficiency and the respective performance limits. As an innovative method, ozonation with downstream biofiltration is used. This technique is used almost exclusively in surface waters for other treatment purposes (disinfection, odorants, pre-flocculation). Ozone selectively attacks chromophoric molecules and is therefore well suited for decolorization. In contrast to other technologies, no residues (sludge, concentrates) are generated. However, questions about the resulting DOC bioavailability and the formation of bromate depending on technical parameters and water quality have to be answered.

The participating water suppliers offer access to their plants and previous experience in dealing with the problem. Thus, the application possibilities and limitations of the considered methods become clear.

The evaluation of the results of the analyzed treatment processes is carried out with the aim of developing recommendations for action in the DVGW set of rules, as well as minimizing the use of energy and chemicals and the entire life cycle costs.