Section 6.
COAL, COKE, AND POWER PLANT WASTE
TREATMENT OF COAL LIQUEFACTION WASTE WITH
PAC-ENHANCED ACTIVATED SLUDGE PROCESS
Kuo-Chun Tsai, Associate Professor
Department of Chemical and Environmental Engineering
University of Louisville
Louisville, Kentucky 40292
C. Michael Folsom, Second Lieutenant Officer
Air Force Institute of Technology
Dayton, Ohio 45432
INTRODUCTION
The addition of powdered activated carbon (PAC) in activated sludge process, called PAC-
enhanced activated sludge or PACT® process, has been reported by many researchers to have several
advantages over ordinary activated sludge without PAC addition [1-4]. Notably among them are
improved organics removal, better ability to handle toxic and shock loadings, higher color removal,
more odor reduction, reduced foaming and provision of extra oxygen reservoir under anoxic
conditions. In addition, there are reports that revealed that nitrification in activated sludge was
significantly enhanced by adding PAC to the aeration tank [5-7).
The main objective of this research was to treat coal liquefaction (H-Coal®) wastewater with
PAC-enhanced activated sludge process. The treatment results were compared with those from a
parallel activated sludge unit without PAC addition to determine if the PAC-enhanced process is a
better system than non-PAC unit in treating coal liquefaction wastewater. Parameters used for
comparison included ammonia nitrogen removal (nitrification), sulfide removal, biochemical oxygen
demand (BOD) and chemical oxygen demand (COD) removals, phenol removal, and sludge characteristics such as zone settling velocity (ZSV), sludge volume index (SVI), and oxygen uptake rate
(OUR). It is hoped that the results obtained from this bench-scale study would be helpful in the design
and operation of the full-scale treatment plant.
MATERIALS AND METHOD
The Reactor
The continuous-flow bench-scale activated sludge reactor used in this study was of the sliding
baffle type with internal clarifier. Total volume of the reactor was 101 with 7.2 1 for the aeration tank
and 2.8 1 for the clarifier. The continuous feeding to the reactor was accomplished by using a peristaltic metering pump at a normal flow rate of approximately 0.70 ml/min to obtain a desired
constant food to microorganisms (F/M) ratio of about 0.16/day based on COD. Since the strength of
the wastewater received from Ashland Synthetic Fuels, Inc. (ASFI) varied from time to time, the
feeding rate to the reactor was adjusted each time according to the wastewater COD to maintain the
substrate loading rate at the desired F/M value.
Sludge Acclimation
The sludge acclimation procedure in this study was performed in two steps. The first acclimation
involved adjusting the original sewage sludge from raw sewage to a synthetic wastewater. The
synthetic waste had a COD of 640 mg/l, NH3-N of 196 mg/l, and a phenol concentration of 120 mg/l.
The second acclimation was the acclimation of the sludge to actual coal liquefaction wastewater.
Gradual acclimation technique was used for both steps.
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