75    PILOT PLANT COMPARISON OF EXTENDED AERATION
AND PACT® FOR TOXICITY REDUCTION IN
REFINERY WASTEWATER
Joseph M. Wong, Project Manager
Patrick M. Maroney, Principal-in-Charge
Brown and Caldwell Consulting Engineers
Pleasant Hill, California 94596
INTRODUCTION
During the 1970s, water pollution regulations focused primarily on controlling conventional
pollutants —oxygen-demanding materials, heat, and suspended solids. These pollutants had caused
severe degradation of rivers, lakes, and streams. In response to these regulations, industries and
municipalities spent billions of dollars constructing facilities to control the discharge of these pollutants. By the mid-1980s, regulators considered conventional pollution problems to be largely under
control. Their focus shifted to the control of toxic chemicals and toxicity in general. The case study
described here is an example of how one petroleum refinery is dealing with the need industrial waste
managers are facing today —controlling toxicity in wastewater treatment plant effluent.
The state regulatory agency ordered a major West Coast petroleum refinery to upgrade its wastewater treatment plant (WWTP) to meet new toxicity-based discharge requirements. The refinery's
existing WWTP has the capacity to treat 2,500 gallons per minute (gpm) of combined process and rain
water flows. The previous permit had allowed emergency bypassing when wet weather flows exceeded
retention basin capacity. The new order required the refinery to treat all process water and rain water
flows and to upgrade the treatment process to meet newly adopted effluent toxicity requirements.
The oil company retained Brown and Caldwell to conduct a comprehensive wastewater treatment
study for the upgrade. The objectives of the study were to: 1) identify waste constituents and the
refinery operations that contribute to effluent toxicity; 2) test the treated effluent to identify a
treatment process that could meet a toxicity standard of 50% survival of test species (both three-
spined stickleback and trout), after 96 hours in undiluted effluent (continuous flow-through bioas-
says); 3) plan expansion of the existing biological treatment facilities to process all combined process
and rainwater flows; and 4) determine the treatment process configuration needed to meet other
discharge limits, operating requirements, and site and economic constraints.
This chapter describes the upstream and effluent characterization, the toxicity screening and the
pilot plant testing of PACT* and extended aeration processes.
EXISTING REFINERY WASTEWATER SYSTEM
The refinery sewer system collects rain water and wastewater from all process streams. Streams that
are high in phenolic contents are collected separately and then processed in a sour water stripper, an
oxidizing tower, a trickling filter, and an activated sludge (phenolic) unit. All other process wastewaters and rain water are collected together and conveyed to a diversion structure. Figure 1 shows a
schematic of the existing system.
During dry weather, general process wastewater flows directly to an API separator and a dissolved
air flotation (DAF) unit. It is then blended with effluent from the phenolic activated sludge unit and
conveyed to the main biological treatment system. That system has an aeration tank and a clarifier
with a capacity of 2,500 gpm. Settled sludge from the clarifier is recycled to both the main aeration
tank and the phenolic activated sludge unit. Wet weather flows in excess of the capacity of the API
separator and the DAF unit, are diverted to retention basins and held for subsequent treatment at the
WWTP.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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