Phosphorus has long been recognized as the controlling factor in plant and algae growth for many lakes and streams. A minor increase in phosphorus can fuel substantial increases in both aquatic plant and algae growth which can have severe impacts on a community. Phosphorus can originate from municipal and industrial facilities that discharge water as well as runoff from agricultural areas that makes its way into local water sources. Restrictive phosphorus discharge limits are being enacted or proposed in many geographies of the United States where the receiving water streams are particularly sensitive to changes in phosphorus levels.
For example, the Wisconsin State Department of Natural Resources (DNR) made the determination to reduce allowable phosphorus limits to 0.075 parts per million, or 75 ppb (parts per billion) and as low as 0.04 ppm as P for facilities who discharge to more stressed waterways. When a Wisconsin ethanol producer using traditional phosphorus based cooling water treatment attempted to renew their NPDES discharge permit, they were informed that they would be required to meet the new 0.075 ppm phosphorus limit.
The use of phosphorus bearing compounds in industrial cooling and boiler water treatment programs has been commonplace since it replaced chromate in the early 70's. Typical alkaline all–organic cooling water programs can have phosphorus levels from 0.3-2.5 ppm as P while stabilized phosphate programs can have phosphorus levels as high as 6.0-7.0 ppm. With the tightening restrictions now surrounding phosphorus treatments, other corrosion inhibitor options were not a viable recourse for this Wisconsin ethanol producer as most of the alternative programs available are primarily metal based utilizing metals such as Zinc (Zn) or Molybdenum (Mo), which are also being closely regulated in terms of acceptable discharge levels. Without an effective corrosion and deposit (scale) control program in place, the plant's cooling system could be compromised in a relatively short period of time. The plant could experience significantly higher operating costs as well as product loss due to overheating in the fermentation and distillation areas as a consequence of reduced heat transfer efficiency from scale deposits forming on the heat exchanger tubes. With few options available to them, the ethanol plant turned to U.S. Water for help.
In anticipation of the tightening restrictions on P and many of the metal bearing compounds currently used in industrial cooling treatment, U.S. Water recently developed a “green” corrosion and scale inhibition technology branded E-FeX™ Technology. This program contains no phosphorus while providing corrosion and scale control performance at least equivalent to traditional cooling water treatment. Corrosion protection is achieved through the development of protective iron oxide layer.
When presented with this new technology, the plant agreed to allow U.S. Water to trial this new product at their facility. The plant employs induced draft counter flow cooling towers, a four cell distillation tower and three cell fermentation tower. The fermentation tower, comprised of mild steel, copper and 304 stainless steel metallurgies, ran for six months from May-October at an estimated 18,000 GPM recirculation rate. The distillation tower ran year round at an estimated 12,600 GPM recirculation rate and was comprised of mild steel and 304 stainless steel.
U.S. Water's PhosZero™ program was implemented at the plant. In order to ensure the new technology would protect the cooling system from corrosion better than the existing technology, corrosion rates were carefully monitored using corrators and corrosion coupons.
Additionally, an online monitoring solution, U.S. Water Reports™, was installed in order to verify performance and track the systems progress 24/7.
- PhosZero's low aquatic toxicity profile and use of non-phosphorus bearing compounds allowed plant to be compliant with discharge restrictions.
- Plant received better corrosion protection with PhosZero than its existing program was able to provide, even after 51 days of exposure (see Figure 4).
- Cooling system, which had significant scale potential, showed no indication of scale formation while utilizing PhosZero.