“Sulfur Water.” Secondary MCL for odors: 3.0 TON
“Sulfur Water” refers to the stink of hydrogen sulfide, H2S, which is almost always derived from bacterial activity. There are several species from two different families: one family specializes in reducing sulfate ion, SO4-2, to sulfide, S-2, which then immediately acquires two hydrogen ions to become H2S. The other family consumes organic matter containing sulfur and metabolizes the sulfur to hydrogen sulfide. H2S makes the infamous “rotten egg” smell, and it is also an acid which can cause rapid corrosion of all types of plumbing materials. Therefore. it is always important to treat sulfur water, even if people get accustomed to the smell. Sulfur and iron and the bacteria that oxidize or reduce them often occur together, and when they do, the laundry and plumbing stains are black, due to black ferrous sulfide, FeS. Such bacterial mixtures often produce peculiar “septic” odors that are similar to that of hydrogen sulfide.
Analysis of water samples for hydrogen sulfide is possible, but since it is a volatile gas, a special preservative must be used at the time of sampling. However, the nose is a superior detector, and since the odor threshold is so low that even the tiniest concentrations must be removed, an accurate analysis is usually not needed. The only good remedy is chemical oxidation followed by filtration to remove the elemental sulfur. Activated carbon can remove low levels for a short time, but it is inefficient and has low capacity. New catalytic carbons are an improvement, but a long contact time (slow flow rate) is still needed. Chlorination is the preferred approach because it also disinfects, but oxidizing media such as manganese greensand and granular brass may also give satisfaction.