HO-2670 -- Rapid Cooling of Effluents for Bioassay Tests Using Stored Cooling Capacity of Refrigerated Brine PDF

In order to evaluate the toxicity of various effluents to aquatic life, bioassays using continuous flow live fish are performed at the Freshwater Institute. The effluents tested include wastes from mines, pulp and paper plants, oil refineries, chemical plants and municipal sewage treatment plants. The continuous flow-through system requires the storage of large volumes of effluents, because the test procedure used requires a 48-hour exploratory static toxicity test to determine the toxic range of concentrations, followed by a 96-hour test at various concentration levels throughout this range. For some effluents tested, it is neces- sary to minimize changes during the storage period which could be caused by loss of volatiles or chemical and bacterial changes. Large changes in the chemical composition of saline ground- water have been observed.'

Effects such as this can be reduced by rapidly cooling the entire batch of effluent to 40C and maintaining this temperature throughout the duration of the tests. Conventional cooling techniques required the installation of an 11.19 kW (15 hp) cooling unit and a large electrical service panel. Since high capacity is only needed for the short pull-down period, this system is more expensive to operate because of a demand charge of $4.75/kVA imposed by the power utility, based on maximum demand. It was, therefore, decided to design a system based on the "stored cold" principle. Using this system, a large amount of secondary brine refrigerant is slowly reduced in temperature over a long period of time to create a large "cold sink" into which the heat from the effluent can be rejected at a high rate for a much shorter period of time.