New Methods for the Treatment of
Oily Wastewater Streams
ROSS NEBOLSINE, President
Hydrotechnic Corporation
Consulting Engineers
641 Lexington Avenue
New York, New York
INTRODUCTION
The largest oil and waste streams are generated by refineries, petrochemical
complexes, steel finishing mills and machine shops. The volume of effluents from
different parts of such plants range from a few gal per min to many thousands per
min. The oil content in these streams can vary from as low as 100 mg/l to over
100,000 mg/l for some of the more concentrated waste discharge or blow-downs.
Until recently, the water quality regulations merely called for effluents to be
"substantially" free from visible floating oil. For coastal waters this has meant keeping oil concentrations below 30 to 40 mg/l and in the case of rivers or lakes to 15 to
30 mg/l.
Under such conditions, few plants with oil carrying wastewater discharges had
to face very complicated pollution control problems. When secondary treatment was
needed, floatation, flocculator clarifiers, or some form of bio-oxidation was usually
found to be sufficient. Processes, equipment selection and design of treatment facilities were ordinarily based on previous experience, API manuals, and recommendations of equipment manufacturers.
Conditions have changed. Industry must now anticipate that oil concentrations
will frequently have to be kept to 5 mg/l or less. Moreover, strict limitations for
BOD, COD, taste and odor causing and toxic substances as well as petroleum ether
extractable materials are being sought. This will mean that more complicated
multistep systems analogous to tertiary type treatment for sewage will be increasingly required.
The most common basic processes are as follows.
For treating the main effluents: chemical coagulation and
gravity separation (with or without flotation), biological
oxidation, chemical oxidation.
For treating skimmings and sludges: gravity thickeners, precoat
vacuum filtration, filtration, centrifuging, wet oxidation,
incineration.
To effect these various forms of treatment, there are less than one dozen basic
equipment modules to choose from. The performance of every one of them has a
definite range and has certain specific economic or operational limitations. These
may consist of high initial or operating cost, the large amount of chemicals required
or the extent of supervision and skilled labor needed. Other constraints may be
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