Drinking water treatment plant with high level of residual manganese after sand filtration
asked 17 January 2017 asked by edv (420 points)
The solution would be to reproduce oxidation either by upping the pH or the redox potential (permanganate, bleach) until you recreate initial filtration conditions. What's the pH of the water that goes through the filter? Preventing a filter from becoming anaerobic during extended inactivity might be difficult. On the other hand, conditioning with a static mixer prior to restarting the filter, as described above with large doses of reagents, may decrease the observed water loss.
Thanks for your reply; I will try chlorination on the filter. As for the pH of the water, it's between 7.5 and 7.8.
Hi, In order to avoid anaerobic conditions, it would be best to first wash and then dry out the filter before stoppage. If that’s not possible, then at least regular cleaning while it is out of service.
Hi, We were faced with this type of situation in a plant about 10 years ago. The only solution we found, after restarting the filter after a prolonged shutdown, was contact with a dose of coagulant <5ppm commercial product (FeCl3 for example).
Hi, We are experiencing the same issue in our plant for the very first time. Usually we shut down in winter and all tanks are emptied, but the filters remain submerged. This time, the temperature of the water was at 25 °C, but the tanks were not emptied. I would like to have some feedback on this phenomenon and whether adding bleach helped? Thanks in advance.
Testing a filter aid polymer such as DADMAC might help gather the precipitated manganese. Usually low dosages which can be anywhere from 0.1 ppm to 2-3 ppm depending on application. Pre and post filtration via 0.45 micron filter paper should give the fraction of dissolved versus precipitated manganese.