REGULATIONS COMPLIANCE Many of these elements or compounds may be introduced by process conditions. For example, on an increasing basis, treated municipal wastewater is the choice for industrial plant makeup. This water often contains elevated concentrations of ammonia and phosphorus. Copper might be released from copper-alloy heat exchangers. Copper also has been used as a preservative in the wood of cooling towers constructed from that material. Sulfate poses a conundrum because a common method to mitigate calcium carbonate scaling in cooling towers is feed of sulfuric acid (H2SO4) to eliminate bicarbonate alkalinity. Depending on the method of wastewater treatment allowed or available, this issue can range from straightforward to exceedingly complex. Some plants are permitted to discharge spent water to a local municipal wastewater treatment plant, provided the industrial water does not contain excessive concentrations of harmful impurities such as heavy metals. At plants in arid regions of the country, evaporation ponds might serve the purpose. However, these ponds must be permitted and installed in a proper manner. Lined ponds are de rigueur in today’s strident environmental climate. If none of the above options are available, mechanical-thermal evaporation of the waste stream might be the only choice. Accurate determination of influent water chemistry is vital for design and selection of evaporator/crystallizers, as hardness, alkalinity and silica can cause severe scaling. Crystal seeding is often necessary to mitigate scaling. A common seed crystal is
gypsum, which provides a more thermodynamically stable site for precipitation of such minerals as calcium sulfate and silicates. For ammonia and phosphorus removal, a biological process might be the best option. Both chemicals are primary nutrients for microbiological growth, and these properties are used to obvious advantage in a bioreactor or membrane bioreactor. Alternatively with regard to phosphorus, which has been noted exists as phosphate in wastewaters, precipitation in clarifiers or reactors may be a good alternative. Phosphate reacts readily with iron or aluminum and can be reduced to low concentration in a reactor. A problem we encounter with increasing frequency is a limit on the quantity of discharge. In arid locations, but sometimes in other areas also, a limit might be placed on discharge volume, or even at times the minimum cooling tower cycles of concentration (COC) might be mandated. However, as many readers will plainly see, increasing COC to reduce discharge volume increases the concentration of impurities in the water. This has impacts on cooling tower operation and might make wastewater treatment much more complicated. ~
References 1. Federal Register, Vol. 78, No. 110, June 7, 2013, Environmental Protection Agency, 40 CFR Part 423 Effluent Limitations Guidelines and Standards for the Steam Electric Generating Point Source Category; Proposed Rule.
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Brad Buecker serves as a process specialist in the Process Engineering and Permitting group of Kiewit Engineering and Design Company, Lenexa, Kan. The group provides water and wastewater engineering and consulting to the power and chemical industries. Buecker has more than 34 years of experience in, or affiliated with, the power industry, much of it in chemistry, water treatment, air quality control and results engineering positions with City Water, Light & Power in Springfield, Ill., and Kansas City Power & Light Company’s La Cygne, Kan., station. He has a bachelor’s degree in chemistry from Iowa State University, with additional course work in fluid mechanics, energy and materials balances, and advanced inorganic chemistry. You may contact him by emailing email@example.com. Michael McMenus graduated from Missouri University of Science and Technology (Rolla) with a bachelor’s degree in Life Science in 1981. He obtained his master’s degree in Environmental Management from University of Maryland University College in 2010 and has more than 30 years of experience in the environmental management field as a regulator, consultant and industrial facility environmental compliance manager. He is currently the manager of Process Engineering and Permitting for Kiewit Engineering Design Co. You may contact him by emailing firstname.lastname@example.org.
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