Manganese release in drinking water plant
First of all, slow down throughput time by performing more frequent and thorough washing of filters.
Pre-ozonation also works for oxidation of Mn, just as when a lot of oxidant is injected upstream of filtration.
What are the raw water concentrations, filter throughput, and injected reagents (air, permanganate, etc.)?
Replace 2/3 of sand with MnO2; it's simple and very effective.
I have been using this technique since 1998 and it has worked in four plants.
MnO2 works very well indeed, however you need to make sure your pH is > 7.4.
Thank you for all your feedback. I will look into these possible solutions.
Is the treatment biological or physicochemical? You have to treat the iron and the manganese.
Oxidation tank, therefore physical, so watch the pH.
Here in Canada, the ideal treatment method for manganese is ion exchange, because filtration after oxidation requires high pH (+8.2) as well as a prolonged contact time.
The parameter to monitor is the ORP, which should be measured at plant input and output. It regulates precipitation of iron (Fe2+ becomes Fe3+) and manganese. If all the iron (and all the manganese) is not oxidized before filtration, it is inefficient.
Chlorine dioxide reacts with manganese: an avenue worth exploring.
But that depends on your network and your treatment system
We use Sodium Permanganate as Pre Oxidant to control Mn and Fe along with organics and taste and odor. Do you test your raw water to see what's in it (Mn & Fe)? Our formula is taken from your raw water tests. Take the Mn plus 2x the Iron, plus a little more for organics depending on the time of year and that will get you in the ballpark to stop Mn and Fe dead in their tracks.
Permanganate has a 45 minute reaction time so that works very well with a traditional settling basin. I go by the color (light purple) at the top of the basin and the end of the flocculator (brown) to control the feed. We get very good results (0.00 - 0.01 Mn and Fe) as well as no taste and odor complaints. We also use Miox for our chlorine which helps as well.
I also make sure the turbidity is down after washing filters and they have been sufficiently rewashed before I put a filter back in service. The OP I took over for would slap them back in service as fast as he could after washing and would get complaints of brown/ black water. I haven't had complaints for almost 10 years. Makes a difference.
Wouldn't let me edit my answer.
Got my dosages backwards. Per Carus: 2x Manganese and 1x Iron.
Ex: 0.28 mg/L Mn and 0.65 Fe. (0.28 X 2) + 0.65 = 1.21 mg/L Permanganate.