Professor POU/POE
This month’s topics:
AC & sulfur, high hardness & H2S, whole-house RO, rainwater, db
Activated carbon and hydrogen sulfide I recently had my water softener rebedded with gravel, resin and car- bon. After a three-week vacation we came home to very bad smelling water. It seems to be mostly the cold water for the first minute or so. The odor is very rotten egg smelling, like sulfur well water. We live in the Orlando, Florida, area and have city water. One water treatment system guy told me he thinks it is hydrogen sulfide being exposed from the new bedding doing so good a job removing all the chlo- rine. What do you think? He told me that he could put a post tank on with carbon and a couple other things to remove the hydrogen sulfide. — Florida The “water treatment system guy” could be partially right. If your city source has hydrogen sulfide (rotten egg smell), the city chlorina- tion would probably be destroying it. Activated carbon is a very efficient remover of chlorine but not very good at removing hydrogen sulfide. But, I strongly dislike the placement of a few inches of carbon on top of water softener resin. There is almost always too little carbon for it to last very long before it becomes exhausted. Also, when the softener backwashes the car- bon becomes mixed with the softening resin and cannot be separated for replacement purposes. If there is hydrogen sulfide in the city water, the chlorine should have destroyed it before it reached your house. If the purpose of the carbon was to rid your water of chlorine taste, I’d recommend that you install a full size catalytic activated carbon tank before the softener (chlorine is harmful to the softening resin) or use activated carbon cartridges wherever you draw drinking water. I’m also thinking that the three-week sitting period was part of the problem, but I can’t be sure without more information. QA
High hardness
I have a customer with water that is 100 gpg total hardness, 2. 5 ppm iron and 1270 ppm TDS. There are sulfates along with hydrogen sulfide. I am treating it presently with a hydrogen peroxide filter with activated carbon fol- lowed by two water softeners. The second one is set on a low salt dose. I am not happy with the results, but the customer is not complaining at this time. I am interested in a comment on this to see if you have any suggestions for treat- ment or if we should run a line from a bottled water company 100 miles away. It might be cheaper. — Michigan Q
I don’t see why this water could- n’t be treated satisfactorily. My cal- culations show that this hardness, with a factor included for ferrous iron (Fe2) and at a salt dose of 15 lbs. per cubic foot of resin, should yield softened water containing about 3-4 gpg of hardness and no iron. This should be a very acceptable amount of hardness under the circumstances and the 15 lb. salt dose should give you a capacity of about 20,000 grains per cubic foot. Remember that ferrous iron is more strong- ly attracted to softening resin than is hard- ness. The important thing is to get the iron off the resin during regeneration. In addition to the hydrogen peroxide and carbon filter, the hydrogen sulfide (H2S) can be removed by preceding the sof- tener with a tank of catalytic activated car- bon or a system that includes an empty tank with compressed air introduction and air relief, followed by a catalytic activated carbon filter. You didn’t specify the level of sulfate but the US EPA Secondary Drinking Water Standards recommends (not mandates) a maximum level of 250 ppm. You might want to check the sulfate concentration. A
(Concluded on page 24)
