Section 2. COAL, COKE AND POWER PLANT WASTES
SINGLE-STAGE BIOLOGICAL TREATMENT OF
COKE-PLANT WASTEWATERS WITH A HYBRID
SUSPENDED-GROWTH-FIXED-FILM REACTOR
Bernard W. Medwith, Processing Technologist
John F. Lefelhocz, Supervisor, Chemical Processing
Research Center
Republic Steel Corporation
Independence, Ohio 44131
Metallurgical coal is transformed into blast furnace coke by destructive distdlation.
The coal volatdes and moisuture are collected and processed in the coke by-product plant
into clean coke oven gas, coal chemicals and wastewater. The steel industry may have to
treat these wastewaters after 1984 for greater removal of phenol, ammonia-nitrogen, cyanide, suspended solids, oils and grease, and several priority pollutants.
Our review of operating laboratory and fud-scale biological coke plant wastewater treatment systems revealed that phenolics are consistently biooxidized; but nitrification is at
best sporadic. The difficulty in achieving stable biooxidation of ammonia was theorized
to be due to: (1) the presence of inhibitory refractories; and (2) inadequate biosolids residence time. We decided to investigate biophysical treatment, where contaminants are removed by combining physical adsorption onto powdered activated carbon with biological
oxidation, as the treatment process to overcome these difficulties. The objective was to
reach a 10 mg/1 ammonia-nitrogen effluent concentration.
This goal was reached after six months of study with two biophysical treatment systems:
(1) a rotating biological surface with powdered activated carbon (RBS-PAC); and (2) a
suspended growth system with powdered activated carbon (SG-PAC) (Table I). The capital
cost of a full-scale single-stage SG-PAC system was estimated to be approximately 20% less
than for the RBS-PAC system. Estimated maintenance and operating costs for both were
about equal.
The high capital and operating costs associated with the continuous use and regeneration
of powdered activated carbon (PAC) prompted us to investigate further the necessity of
adding PAC. This paper describes our development of a single-stage hybrid suspended-
growth-fixed-fdm bioreactor that treats coke plant wastewater by using finely ground
coke breeze or coal dust as the fixed-fdm support.
BIOLOGICAL TEST REACTORS
Rotating Biological Surface
The specifications and operating parameters for the four-foot diameter pilot unit are
listed in Table II. Temperature control was maintained by heating the wastewater feed
and ddution water in a feed premix tank. The unit was covered to minimize heat loss by
evaporation. A 5% (wt) sodium hydroxide solution was metered into the first RBS cell
to control basin pH. Dry PAC was added to the first cell at a rate of 0.2 g virgin PAC per
mg of applied COD per day.
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