Hello, I want to use BAC filtration in a treatment line (surface water -direct filtration - ozonation - BAC filtration) but want to treat only small part of water (25 m3/h) by BAC and this water will be chlorinated (0,4 mg/l of free Cl2), pH 8. Main purpose is to reduce BDOC to prevent regrowth in distribution. Currently, there is no other possibility to take non-chlorinated water. Will the BAC filter work properly even with chlorine on the inlet or should I place some smaller dechlorination filter upstream. Thank you for your comments.
It is necessary to remove free chlorine for the Ozone/BAC process to be effective. Ozone breaks down complex organic matter (humic and fulvic acids and also blue green algae toxins) forming simpler compounds (eg acetates). Bacteria grow in the media to "activate" the filters so that they can oxidise these simple organic compounds. It is these simple RBCOD compounds that cause biological film growths in distribution pipework. Chlorine would prevent bacterial growth in the BAC filters and the removal of the simple breakdown products. The bacteria in the BAC filters also help to regenerate the adsorbtion capacity of the carbon. It is still necessary to chlorinate the filtered water but the chlorine demand will be less and therefore lower concentrations of THMs will be produced.
Thank you for your answers guys. I have additional question. What is your opinion on chlorinated water backwash? It looks I will have to use the same water for backwash. Opinion of researchers on this topic often differs.
Can't use chlorinated backwash as this will kill off all the bacteria in the BAC filters and there would be no bacterial activity.
you can chlorinate the treated water, but I don't recommend the chlorination of the filter influent and the filter backwash water as well.
Did someone test it by pilot or fullcale? I would like to know how big is the influence of chlorine on BAC filter performance. We can count that if we have chlorinated inlet the chlorine will be removed in upper 20 cm of GAC and the rest of media bed should be ok for bacteria growth at least since I exhaust the capacity of GAC. I know that best way is operation without chlorinated inlet and BW. But I did not have opportunity to test something like this so I am curious. Thanks for your answers.
Backwashing with chlorinated water will kill and washout all the bacteria, in effect sterilizing the entire BAC filter. Efficient removal of the Ozone decomposition products requires a temperature dependant minimum critical mass of bacteria. Typically BAC filters require backwashing every 1 to 3 days to manage head loss and filtered water turbidity. However, if the backwash frequency is too high, the time period for bacterial growth required to achieve the critical mass may be too small. This growth period will be longer starting with a bacterial population of zero. Backwash frequency is the key operating variable.
- Badges
- Science topic
- Similar topics
- Engineering
- Electrical Engineering
- Electrodes