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Report While it is well-known that the EPA is preparing new regulations, some states have already implemented stricter guidelines. Sulfate (SO4) is another constituent that is appearing in some new NPDES guidelines. This can be problematic with regard to process chemistry, as sulfuric acid feed to cooling-tower makeup has been a common method to remove bicarbonate alkalinity and thus minimize calcium carbonate (CaCO3) scaling in the condenser and cooling system. to new NPDES guidelines is not always simple or inexpensive. To make matters worse, sometimes other factors compete against any efforts. A primary example is the growing requirement to use recycle water in place of fresh water as plant makeup. Recycle water, such as tertiary-treated wastewater, can have quite variable concentrations of many impurities, in which case the wastewater discharge can also be quite variable. A snapshot analysis from a recent example shown to me by a colleague indicated 4.8 mg/L of phosphate and 15 mg/L of ammonia in that particular sample. Ammonia is appearing in discharge permits, as it can be lethal to aquatic creatures. For plants facing tight TDS restrictions, reducing the cooling tower COC is a method to lower the dissolved solids content of the waste stream, but that H2SO4 + Ca(HCO3)2 CaSO4 + 2H2O + 2CO2 Tighter regulations on sulfate in the discharge stream may eliminate this straightforward method of scale control at some plants. On a related note, phosphorus is being banned in many waste streams. Phosphorus, of course, serves as a nutrient for plant growth, and when released to open bodies of water can often initiate and propagate algae blooms. The difficulty is that a very common cooling watertreatment method relies on the use of ortho-phosphate and organic phosphates (phosphonates) for both corrosion and scale control. Heavy metals are also on the list, with a primary example being zinc. This element was once an integral part of the phosphate/ phosphonate programs mentioned above, as it assists with corrosion protection. However, zinc's use has been severely curtailed due to discharge issues. Another metal that is now appearing on NPDES permits is copper, for which the discharge limit may be below 30 or perhaps even 20 µg/L (µg/L is equivalent to parts-per-billion). At these very low limits, copper discharge can potentially be a problem from units equipped with copper-alloy condenser tubes. However, another copper source, and I am speaking here of wooden cooling towers, comes from copper compounds often utilized as a wood preservative. Control Methods As one might suspect, adjusting wateronline.com ■ Water Online The Magazine 19