Summary
Slow filtration is a drinking water treatment method which, in addition to the low energy consumption, maintenance costs and waste production, has been demonstrated to be advantageous in terms of its adaptability to individual requirements and conditions. While the cost-effective method is already established in moderate climatic zones, the possibilities for using it in (semi) arid regions are still unclear.
Thus, the project partners are studying the influence of extreme climatic conditions on the mechanisms of slow filtration and treatment of very highly polluted untreated water. The tests were carried out on a semi-industrial scale system, and the effects of different operating conditions, different overlays (gravel, pumice, coconut fibres) and the influence of light on the filtering time and elimination capacity of the slow filters were determined.
Results:
- Because evaporation losses under extreme climatic conditions are <10%, no additional construction measures are normally required to reduce them.
- To treat heavily anthropogenically polluted untreated water with a high biochemical oxygen requirement, continuous operation with a slow filter speed appears to be the most suitable method.
- The filtering time can be significantly extended with overlays, with coconut fibres achieving the best results.
- If the particulate substances accumulated in the overlay are biodegradable, this leads to additional oxygen consumption. As this affects other aerobic degradation processes in the filter, overlays are primarily suitable if mineral particulate substances are present in the supply.
- Different light incidence on the slow filters did not appear to have any influence on the filtering time or its retention and degradation capacity.
- The use of activated carbon significantly reduces the filtering time.
