Algae growth in the operating area of UV systems

Pipeline with algae biofilm in the inlet of a UV medium pressure system

A growth of algae biofilms was observed in the operating area of UV plants responsible for UV disinfection as part of drinking water treatment. This study is used to gain an overview of the frequency and extent of algae biofilm formation and consequently to assess the relevance for drinking water supply.

Mercury vapour lamps are generally used for the UV disinfection of drinking water. In addition to UV radiation that is effective for disinfection, these also emit visible radiation. However, the short-waved UV radiation, effective in disinfecting penetrate less deeply in water than visible radiation. At certain distances away from UV plants, it is therefore possible to have areas with zero effective disinfection but still with visible radiation, which can encourage algae growth.

In this review and by identifying affected water supply companies, the influence of raw water quality, preliminary treatment and the used UV device type on the presence of algae biofilms should be established.

In about 50 % of cases, it was possible to verify the development of a phototropic biofilm in the effective zone of a UV plant. Water supply companies that treat surface water or water influenced by surface water, are increasingly affected by algae biofilms. Besides the type of raw water, the type of UV device used (low pressure or medium pressure lamps) appears to significantly influence algae growth. For instance, algae biofilms were noted in about 35 % of cases for water supply companies using UV low pressure systems and in about 80 % of cases for water supply companies using UV medium pressure systems.

At present no guide parameter is available for raw water and no measurement or testing methods are available that could be used to estimate the likelihood of a phototropic biofilm forming.

If there are any uncertainties ahead of a large-scale implementation of UV disinfection, then according to the findings obtained, small-scale UV pilot trials should be conducted over a representative time frame. Based on current knowledge, operating a UV pilot plant offers the most-promising way of estimating the algae formation potential at the UV disinfection site.

The results are incorporated in the revised DVGW worksheet DVGW W294-1.

Publications

J. Eggers, UV Disinfection in Drinking Water Treatment: May Visible Emission from UV Lamps Cause Algal Growth?. IUVA World Congress, Vancouver, February 2016.

Final report W 201516 (2018-12): Bestandsaufnahme zum Wachstum von Algen im äußeren Wirkbereich von UV-Anlagen [Survey on algae growth in the outer effective zone of UV plants]
DVGW Regelwerk plus

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