How to strip out dissolved metals from well water, fast?

[billsreef]

I've got an interesting little salt water well dilemma to solve. I need to development a treatment plan to process well water that has a high level of dissolved iron and manganese. The well suffers from fresh water intrusion (kind of the opposite of what worries most people :lol: ), that fresh water is very acidic and laden with metals. The salinity of this well is 15ppt, which is fine for estuarine species, ph before degassing is around 6.2 and the level of Mn is 4.50 mg/l and Fe is 3.87 mg/l with a =/- 5% variance.

Now, the pH is easy to deal with, the metals on the other hand are troublesome. We need to use more water on a daily basis than can be dealt with by simply aging and aerating water for several days, so I need to come up with a faster method. My current thought is to hit the incoming well water with a high rate of ozone and long contact time to oxidize those metals and break down the organic acids in the water. The trick is, how many mg/l of ozone, how long of a contact time needed, and anything else to think of that I might be missing?

 

[Randy Holmes-Farley]

Wow, tough problem.

The product water is to be used how?

So you want to remove all the metals and not most of the salts or have the pH too high?

Maybe you could bubble hydrogen sulfide through it to precipitate metal sulfides.

The ozone part seems reasonable, but I don't really know how much it would take. Trial and error is perhaps the quickest way to a decent answer.

 

[billsreef]

Tough indeed, and funding is problematic to make it even tougher.

The water is going to be used for rearing estuarine fish, at the moment primarily silversides, stripped bass and various herring. So yes, we want to remove the metals, but not the salts. pH can go up to typical SW values. The big trick is, for the whole lab, we can run up to 20,000 gallons per day. So it's a lot of water to process. Right now we're dropping a fair amount of iron and some manganese just from recirculation and retention in our sump and running through arragonite to boost pH...the arragonite turns jet black from metals settling out :eek1:

 

[Randy Holmes-Farley]

Boosting he pH should enhance the precipitation of iron oxide/hydroxide, and best yet, sodium hydroxide or carbonate is pretty cheap and pH is easily monitored.

 

[loudell]

try a large Kold Ster-il....

 

[therealfatman]

Potassium permangenate, aeration and then flocculate, finally filter. Polymers added after aeration and before floculation would work better at forming larger floc that is easier to remove by settling tubes or plates prior to final filtration. Basically just set up a small continous run water treatment plant. you are dealing with a very common set of water conditions dealt with by many hundreds of water treatment plants. The above methodology is cheap, successful and produces good water with out long retention requirements.