Impact of coal combustion waste on the microbiology of a model aquifer

Abstract

Abstract. The effects of water infiltration into an alkaline coal combustion waste burial site on the chemical and microbiological aspects of a meso-scale (2.44 m diameter • 4.6 m, height, 65 tonne) model aquifer were analyzed. The spatial and temporal effects of the alkaline leachate on microbial activity, numbers and diversity were examined in the model and compared with uncontaminated control materials. Within the saturated zone below the waste there was a pH gradient from 12.4 at the water table, immediately below the waste, to 6.0 at 3.5 meters from the waste, and elevated levels of arsenic and strontium in the pore waters. Microtox testing of the contaminated pore waters indicated high toxicity (a gamma value of 1 at dilutions of 45 to 110 fold). The leachate contamination was associated with a reduction in bacterial [3H] leucine incorporation from a high of 267 fmol g-1 h-' in sediments below the contaminant plume to undetectable in the contaminated zone. In comparison, leucine incorporation rates in control column sediments were 899 fmol g-i h-'. Similar toxic effects were evident in reduced total direct and culturable counts of bacteria. Observations also indicated a reduction in microbial diversity and development of alkaline-tolerant microbial communities. These results indicated that any failure of confinement technologies at disposal sites would adversely affect both the chemistry and microbiology of the underlying saturated zone.

Chemistry of fly ash and cyclone ash leachate from waste materials and effects of ash leachates on bacterial growth, nitrogen-transformation activity, and metal accumulation

“…The leachates were all alkaline (10.4-13.2). Because pH is known to be one of the most important factors determining the toxicity of coal combustion waste on microorganisms [13], the pH of the leachates were adjusted to 6.8 by adding HCl such that non-pH factors could be examined. The leachates were then filtered again with a 0.22-m polycarbonate filter, and were used in the chemical and microbiological experiments described below.…”