Best Management Practice and Guidance Manual for Cooling Towers

Best management practices (BMP) are designed to help facilities comply with environmental regulations and prevent pollution. This best management practice contains a set of recommended operating procedures and guidelines designed to reduce the amount of pollutants discharged to the JEA Publicly Owned Treatment Works (POTW). The development of this BMP is intended to protect the POTW and environment without unduly burdening facilities that utilize cooling towers.

As part of the Clean Water Act, the National Pretreatment Regulation (40CFR 403) was established to protect POTWs and the waterways in which they discharge. The Environmental Protection Agency (EPA) delegates this responsibility to the State of Florida Department of Environmental Protection (DEP). In Jacksonville, Fl, the State has delegated local authority to JEA (an electric, water, and sewer utility). It is the responsibility of the JEA Industrial Pretreatment (IP) program to regulate discharges to the POTW.
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Background

Many industries, hospitals, institutions, and office buildings utilize some type of cooling tower. Open recirculating cooling water systems utilize cooling towers to reject heat through the process of evaporation. Cooling tower evaporation transfers heat from HVAC systems and other processes into the atmosphere.

As evaporation occurs, the concentration of mineral salts increases in open recirculating cooling water systems (cooling towers). When the concentration of mineral salts exceed their solubility, fouling and scale formation on heat exchange surfaces may occur. Cooling systems control the level of dissolved solids (mineral salts) by discharging part of the recirculating water in the system and replenishing this volume with fresh make up water. Cooling towers can cycle water numerous times before the water becomes saturated and must be discharged out of the system. Blow down is a term for water that is removed from the recirculated cooling water to reduce contaminant buildup in the tower water. Management of cooling tower blow down is necessary to prevent fouling and efficiently use the makeup water resource. This water is often discharged to the sanitary sewer system. 

In addition to blow down, most recirculating cooling water system maintenance plans include controlled additions of conditioning chemicals. Chemical additions are made for the purposes of microbiological control, corrosion protection, and to increase the solubility of mineral salts. Scale and bacterial growth may reduce the operating efficiency of heat exchange devices like cooling towers, condensers and heat exchangers.

One common constituent of cooling tower chemicals is molybdenum (Mo). It is used in cooling tower treatment chemicals for corrosion inhibition or as a tracer to determine the concentration of treatment chemical present. Molybdenum has been used for corrosion inhibition in cooling water systems for many years because of its ability to passivate cathodic surfaces. Frequently, molybdenum is used in combination with other corrosion inhibitors like organic phosphates and aromatic azoles.
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