Biological treatment was chosen because some oils float, some sink, some are "soluble," and some saponifiable. Thus, a broad-spectrum treatment was required. No municipal sewerage system was available, therefore the effluent had to meet waterway discharge requirements. This specified effluent concentration limits (mg/l): including biological oxygen demand (BOD) of 20 or less; hexane solubles of 15 or less; suspended solids of not over 25; and a pH range of 6 to 10. In addition, effluent had to be substantially color free. Influent characteristics were as follows:
Average daily flow 20 gpm
Average BOD 400 ppm
Average hexane solubles 300 ppm
Average suspended solids 100 ppm Average pH range 5 to 12
Maximum aeration requirements were calculated to provide (1) sufficient flexibility to vary input air in response to extreme pollutant load variations; and (2) excess hydraulic mixing capacity to increase suspended solids oxidation and reduce the volume of sludge accumulating in the system.
The use of 3-5 hp floating aerators provides a total available oxygen transfer rate of 7.5 lb oxygen per lb of
BOD, according to the manufacturer. Under most terminal operating conditions, only two aerators were required to provide 95% BOD removal. Sludge accumulation was below 350 lb wet sludge (7 lb dry) per day. The system has never had an odor problem.
A recirculating system was established for peak waste loads in oil handling terminal operations (Figure 8.2.7). The 800,000 gal ballast tank gives an additional ten days of holding time for recirculation when pollutant loadings far exceed design capacity.
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