TREATABILITY OF A COAL GASIFICATION WASTEWATER USING THE
POWDERED ACTIVATED CARBON/ACTIVATED SLUDGE PROCESS
Joseph Janeczek, Jr., Design Engineer
O'Brien & Gere Engineers
White Plains, New York 10601
James C. Lamb III, Professor
Department of Environmental Sciences and Engineering
University of North Carolina
Chapel Hill, North Carolina 27514
Because of limited oil reserves, the United States is studying various methods to meet
energy needs. One alternative is to manufacture synthetic fuel through coal gasification,
which produces concentrated and potentially hazardous wastewaters. Most of the few
investigators of methods for treating gasification wastewaters have only studied biological
processes [1-8] or biological treatment preceded or followed by treatment using activated
carbon. Treatment by combining powdered activated carbon and activated sludge (PAC/
AS process) has been studied by Luthy et al. [3].
The overall goal of this investigation was to evaluate the effects of PAC additions on
performance of the AS process in treating a coal gasification wastewater. Specific objectives were: (1) to evaluate the effect of powdered activated carbon on biotreatability by
activated sludge; (2) to evaluate the effects of powdered activated carbon on biological
activity in activated sludge systems; and (3) to conduct a preliminary study comparing
performance of the PAC/AS process with that of PAC treatment or activated sludge treatment alone.
CHARACTERISTICS OF THE WASTEWATER
Wastewater compositions from several coal conversion processes have been shown to
be relatively uniform from one process to another [11). Wastewater used in this study
was obtained from a Chapman-Wilputte Gasifier located at an army ammunitions plant
in Kingsport, Tennessee [9,10]. It contains very high concentrations of organics, sulfur,
chloride and ammonia. The major organic constituent is phenol, consisting of monohydric,
dihydric and polyphenols, which comprise 60-80% of the total organic carbon [11]. Wastewater used in these studies was diluted to one-quarter strength, at which its BOD5 was
2000 mg/1, its COD 4425 mg/1, its TOC 2000 mg/1, and its pH between 7.8 and 7.9. Several
sources have reported that the wastewater contains harmful constituents [9,10,12,13];
bioassays have shown that it could have a harmful effect on biological life in streams if
discharged without treatment [8,11 ].
Earlier studies by Singer et al. [4] found that a similar wastewater was biologically
treatable at one-quarter strength. These studies also showed that biological treatment tended
to reduce the wastewater pH and inhibit growth of some organisms. To prevent this a
phosphate buffer was added to keep pH in the reactors between 6.3 and 7.9, and to supply
nutrients needed by the organisms. The wastewater gradually undergoes some type of oxidation when exposed to the atmosphere, changing from a clear liquid, to a dark brown-
amber color. Accordingly, to minimize changes during storage, the reactor feed was made
up in batches only large enough to last for 2-3 days.
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