Section 5. REFINERY WASTES
STARTUP AND OPERATION OF A REFINERY
ACTIVATED SLUDGE PLANT
A. J. Reitano, Jr., Staff Engineer
Exxon Research and Engineering Company
Florham Park, New Jersey 07932
The activated sludge process continues to be the preferred secondary wastewater treatment method for removal of biodegradable, soluble, organic matter. The mode of operation
consists of contacting the substrate organic matter with a large population of viable microorganisms in an aerobic environment. The development of this mixed liquor population
during startup of activated sludge plants can sometimes prove to be a laborious task affected
by the seeding method employed. Factors which influence the microbial growth rate and,
therefore, the length of time required to attain an acclimated mixed liquor culture, are
temperature, organic loading, dissolved oxygen concentration and nutrient levels.
This chapter reports on the startup of an activated sludge plant using enriched dried
cultures at an Exxon refinery. Performance data during the startup period and typical
operating data after attainment of a stable mixed liquor are included. The effect of phenol
loadings of up to 200 mg/l on the activated sludge operation three weeks after wastewater
in is reported. Operator training for the activated sludge plant is also discussed.
TREATMENT PLANT DESCRIPTION
The activated sludge plant and upstream equalization tankage commissioned in 1979
were the second phase of wastewater treatment facilities constructed at the refinery. In
1975 advanced primary treatment equipment was installed for oil removal from gravity
separator effluent as part of the phase one facilities.
The refinery wastewater treatment plant is shown schematically in Figure 1. The total
refinery wastewater flows by gravity to a bank of API separators for primary oil and suspended solids removal. The separator effluent is pumped to a 20,000-m tank for flow and
contaminant equalization for downstream equipment. This tank provides a hydraulic retention time of 19.5 hours at maximum flow and 28.5 hours at average flow. The equalized
effluent flows by gravity to a 20-m-diameter dissolved air flotation (DAF) unit for additional
oil removal.
The DAF effluent flows by gravity to the activated sludge plant which was designed
similar to a step feed mode. The aeration basin contains four inlet points for the feed along
the length of the basin. The feed lines are turned up under each of four 2-speed, floating,
mechanical aerators. The recycle sludge from the clarifier can enter the basin at three positions; between the back wall and the first aerator, the first and second aerators, and the
second and third aerators. Each feed and recycle line entering the basin contains an annu-
bar station for measuring flow to split the feed or recycle as desired. Dissolved oxygen and
Figure 1. Wastewater treatment plant schematic.
310