Biological Treatability of In Situ Coal Gasification Wastewater

Abstract

Wastewater from an underground coal‐gasification (UCG) pilot facility is degraded aerobically in laboratory chemostats for a period of seven months. Pretreatment includes only dilution and phosphorous addition. The experimental design includes solids retention times from 10 to 30 days and dilution rates of 25% and 50%. Aerobic biological treatment provides removal of 83–91% COD, 82–90% TOC, and 56–87% ammonia. The results extend the range of UCG wastewater strength to be effectively treated by biological processes. Air stripping is not a significant mechanism for carbon removal, but is estimated to have removed from 0% to 68% of the ammonia, depending upon operating conditions. The suitability of attached growth systems for treatment of this wastewater is indicated by: (1) Solids settling properties that would require very long clarification times in a full‐scale, activated sludge system; and (2) the enhanced COD‐removal filamentous organisms in one reactor.