Anyone know the answers: 1) Chlorides and sulfates. Chlorides also are noted for breaking down corrosion protective films on ferrous metals and alloys and is one of the main causes of pitting of stainless steels. 2) Measured as CaCO3: Soft < 75 mg/liter Moderately hard = 75 – 150 mg/l Hard = 150 – 300 mg/l Very hard > 300 mg/l 3) SeaQuest
10	Phosphate Performance vs. New Drinking Water Regulations

Over the past decade, federal regulations on drinking water quality have been promulgated at a pace that is outstripping the ability of water systems to deal with both efficiently and economically. Many water managers have become frustrated at laws which, for all their good intentions to improve water quality, seem to be contradictory in their recommended solutions using best available treatment technologies.

One good example of this paradox is the lead and copper rule versus the new mcls for THMs (trihalomethanes). The lead and copper rule states that the mcl for lead is now 0.015 ppm and for copper is now 1.3 ppm. When exceeding these levels, the industry recommended answer was to raise pH treatment alone or in combination with a variety of other treatments. Now comes the new mcls for THM levels to 80 ppb down from 100 ppb (and eventually will go down to 40 ppb). The industry recommended answer to bring THMs down is to lower pH (so chlorine becomes more stable and less is required resulting in lower THM formation). Both solutions are diametrically opposed to one another, one solution saying raise pH and the other saying lower pH. Alternatively, other solutions such as ozone and chloramine treatment have been implemented, but can be expensive, difficult to control, and cause taste problems for some systems.

A second good example is regulations governing general corrosion control (red water, tuberculation build up, etc.) versus new regulations being promulgated for turbidity. The industry recommended answer to optimize general corrosion control is to add lime (calcium hydroxide) to raise alkalinity and pH to affect a Langlier index as close to zero as possible. The industry recommended standard for lowering turbidity is to stop liming and alternatively use sodium carbonate, sodium silicate, or very corrosive and expensive sodium hydroxide all of which have proven to have numerous expensive problems associated with successful application. Both solutions are diametrically opposed to one another, one solution saying add lime and the other saying stop liming.

One recommended approach has been to use orthophosphate technology either with metals (zinc) or without metals. This approach has been found to require use of very high (expensive) treatments rates up to 4 ppm along with even higher pH levels up to 9+ in order to treat lead/copper and corrosion control, but still negatively effecting mcls for THMs and DBP regulations...while doing nothing for turbidity. Too, the zinc alternative is usually counterproductive to waste water requirements and regulations by raising zinc levels in wastewater sludge. The end result is spending a lot of money with more problems to solve.

Another approach recommended is to use polyphosphate technology either with metals (zinc) or without metals. Although this approach has been found to require more economically manageable treatment rates, it still does not deal with THM and DBP regulations as well as the problem of zinc in wastewater sludge. Also, the stability of these compounds to temperature, time, and pH is extremely limited resulting in reversion within the distribution system causing additional deposit problems as well as increased lead/copper levels as suggested by published AWWA studies.

This has lead to the advent of blended phosphates (combinations of ortho and polyphosphates) in order to provide the best benefits of all types of phosphates without the negative aspects of any particular phosphate component. However, this technology has been very elusive in that it requires a total understanding of phosphate chemistry, water chemistry, interfacial surface chemistry, and biological chemistry. Many products making many beneficial claims have turned out to be nothing more than a simple blend of one or two orthophosphates and a polyphosphate (i.e. phosphoric acid and sodium hexametaphosphate). None of these products have been found to adequately control lead/copper or corrosion. Also, they all still require pH control, the presence of calcium (or magnesium) in the water, and do not deal with THM or DBP regulations.

SeaQuest

One blended phosphate, SeaQuest, which does incorporate all the above technologies overcomes reversion problems, deals with lead/copper problems all the way to the tap, is independent of calcium water levels, and provides optimum corrosion control without the need for additional pH control. At the same time, SeaQuest slowly removes existing corrosion/scale deposits, sequesters iron/manganese (minimizing red/black water complaints), and eliminates the negative effects of hardness. Because SeaQuest does not require pH control (either as lime, sodium carbonate, sodium silicate, or sodium hydroxide), a water system using SeaQuest can be operated at lower pH levels. This is known to result in more stable chlorine residuals out in distribution, which in turn requires less chlorine to be added. Because of this, the potential formation of THMs and DBPs are reduced considerably.

Editor’s Note: We have attempted to provide our readers with topics we believe to be of interest based on numerous questions and responses which have been posted on the AWWA Discussion Forum, Water Technology Forum, and other drinking water forums. We welcome all responses, recommendations, and suggestions on related topics you wish to see discussed.
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