To define the problem, existing system elements were reviewed (Figure 8.1.3). The original design specified a once-through system capable of processing an existing flow of 3500 gpm with the capability to handle 7000 gpm in the future. Effluent quality was to meet stringent state requirements for discharge to the waterway. Applying knowledge of stream quality to the original design requirements raised question about the once-through concept. It was noted that if process utilization of this water did not require a higher quality supply than the polluted raw river water presently used, the need for a once-through system was questionable.
A system to treat this wastewater to meet stage discharge standards would be very expensive. However, it cost much less to treat this wastewater only to the extent required by the process. Historically, this requirement was met by the quality of a badly polluted stream. The cost difference between a reuse system and a once-through discharge system is substantial. Water quality design standards were key factors in system cost.
Table 8.1.5 lists the design parameters. Provisions were also made for sludge and recovered oil handling with minimal expense and minimal personnel time required. The original process flowsheet is shown in Figure 8.1.4. A closed system of this type is susceptible to three primary problems: algal accumulation, dissolved solids buildup, and heat buildup.
Solving these problems requires bactericide and/or al-gicide additives, blowdown and addition of makeup water, and a system cooling tower. The original design included a cooling tower hookup, if required, together with a chemical feed system. However, makeup water from the
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