Biologically mediated removal of dissolved organic carbon from coal slurry wastewater

The biologically mediated removal of dissolved organic carbon (DOC) from pipeline slurry wastewaters was examined. BOD₂₀ values for laboratory slurry wastewaters ranged from 52 to 216 mg liter^-1 indicating biological oxidation of the organic compounds. Second order kinetic rate constants (k₂) developed for DOC removal ranged from 1.39 X 10^-4 to 2.30 X 10^-4 liter day^-1 (mg of sludge)^-1 providing evidence that biological treatment was an affective mechanism for reducing the pollution potential of the slurry wastewaters.

After biological treatment a residual DOC (a mean of 33 mg of carbon liter^-1) remained and ultrafiltration studies indicated this residual carbon level was of high (>1000 MW) molecular weight. The activated sludge preferentially removed the lower (<1000 MW) molecular weight compounds with the higher molecular weight DOC being more resistant to biological attack. However, extended acclimation (greater than one month) enabled the activated sludge to remove the higher molecular weight components from the slurry wastewaters.

Chlorination of the slurry wastewaters reduced the efficiency of DOC removal. The k₂ values for the chlorinated wastewaters were 60% lower than for the unchlorinated wastewaters. Furthermore, acclimation of activated sludge to chlorinated wastewaters reduced or eliminated the ability of the microorganisms to remove DOC from the unchlorinated wastewaters.

The results of this investigation suggest that a fixed film community of microorganisms was capable of the biotransformation of the wastewater DOC. Increases in the removal and mineralization of model fulvic compounds occurred during the growth and development of the biofilm suggesting an increase in the heterotrophic potential of the microorganisms as the biofilm matures.