Treatment of Coal Mine Drainage With
The Rotating Biological Contactor
HARVEY OLEM, Graduate Assistant
RICHARD F. UNZ, Associate Professor
Department of Civil Engineering
The Pennsylvania State University
University Park, Pennsylvania 16802
INTRODUCTION
Coal mine drainage is a highly mineralized water resulting from exposure of puritic
materials contained in coal seams and surrounding strata to air and water during mining.
The water discharging from these areas is characteristically low in pH and high in dissolved
iron. In 1966, coal mine drainage from all coal mining operations in Appalachia contributed over 6,000 tons of acidity per day and affected more than 10,000 miles of streams
(1). Drastic alteration of pH and the deposition of iron precipitates most seriously
challenges the survival of aquatic life and economic value of streams polluted with mine
drainage. Mine drainage does not cease to flow when the mining operation terminates.
Although methods have been devised to reduce the magnitude of the problem, no feasible
means currently exist to prevent formation of mine drainage.
The U.S. Environmental Protection Agency recognizes coal mine drainage as a
wastewater of the coal mining industry and has proposed effluent discharge limitations for
iron, acidity, suspended solids and pH to be adopted under the National Pollution Discharge Elimination System (NPDES).
Treatment of coal mine drainage to meet effluent requirements essentially involves
three unit process operations: acid neutralization, ferrous iron oxidation, and solid-liquid
separation. In order to precipitate iron at the pH of neutralized mine water, soluble ferrous
iron must be converted to the insoluble ferric state. Techniques for ferrous iron oxidation
have been applied prior to or following acid neutralization. Contemporary chemical
treatment processes employ aeration following neutralization since ferrous iron oxidation
in an acid medium is extremely slow. The half time for ferrous iron oxidation in a sterile
solution of pH 3.5 has been estimated to be 2,000 days (2).
Several systems have been devised which include ferrous iron oxidation before acid
neutralization (3, 4, 5,6). In principal, these systems appear easier to control since iron oxidation after neutralization generates a quantity of free acid which must be accounted for in
a determination of the total requirement for alkaline chemical dosage.
It is well known that acid mine waters contain populations of autotrophic, acidophilic
thiobacilli. Certain species of the genus Thiobacillus oxidize ferrous iron, reduced sulfur
forms, or both for energy. Attempts have been made to utilize the biochemical faculties of
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