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\rj ~ 0"':1' 0J Evaporation Ponds c......' G The use of solar evaporation ponds for final disposal of power plant was- tewaters is commercially proven technology in areas where positive annual average net evaporation rates are present. For the study, evaporation ponds are appl icable to all wastewater disposal options. The design of evaporation ponds Is highly site specific. Design of the pond liner Includes considera- tion of local soil permeabil ity, depth and quality of underlying aquiflers and qual ity of fluid to be contained. Liner requirements can range from a single clay or membrane I iner to multiple liners with interdrain and monitoring sys- tems. For util ity power plant wastes the choice between membrane and clay I iners is usually economics. For this study a single membrane liner was selected. ,;. " Chemical Treatment Chemical treatment is not a treatment option by itself. Inherent with the proper operation of each of the technologies Is the application of a proper chemical treatment program to maintain the cleanliness of the circulating water system and assure optimum heat transfer coefficients. '.: Utility station circulating water systems dissipate heat by evaporating a por- tion of the circulating water. The remaining water recirculates, causing a buildup of dissolved solids In the system. Eventually, the solubll ity of one or more salts Is exceeded, and precipitation ( e.g. scaling of heat transfer surfaces) wil I occur unless a portion of the circulating water Is removed by blowdown to balance the salt concentration. ~:, , , ;,'; ~-r >.' -.-'" The general trend has been to use scale inhibitors as "insurance policies" against deviations from the standard solubil ity limits. However, as water/wastewater conservation continues to assume a higher priority, more utll itles are using these Inhibitors to set their operatlng'cycies at levels above conventionally accepted solubil ities. A broad spectrum of scale in- hibitors are available today including polyphosphates, phosphonates, polyacry- lates, and others. Although available generically, most of these chemicals are sold as proprietary blends of chemical compounds marketed by water treat- ment chemical suppliers. :' '\. l: Corrosion control is achieved by proper selection of the materials of con- struction and Inhibitor addition. Historically chromate-based InhIbitors have been the most popular and cost effective. However, current regulations severely restrict the discharge of chromates. Chromate recovery or removal processes are available, but the costs are relatively high and other disposal problems are created. These problems with chromate disposal have created development of a family of environmentally acceptable Inhibitors. Included In these are polyphosphates, sil icates, organic-based compounds, and proprietary combinations. ...' Control of biological organisms In cooling tower systems is commonly achieved with oxidizing agents such as chlorine. Chlorine Is usually appl ied on a "shock" basis to circulating water systems. The presence of nitrates, phos- ". :~5~ 4-7