Conference Name: Geological Society of America Annual Meeting & Exposition 2010: Reaching New Peaks in the Geosciences
The Southern Kent County Landfill is a non-hazardous waste facility with a confined drainage system, which acts as a barrier to migration of landfill leachate into the subsurface environment. Solid municipal waste (MSW) is stored at the landfill, and is located adjacent to a fly-ash pit of incinerated waste. Over time, the drainage system becomes clogged with a precipitate designated as bio-rock. Collaboration between GVSU and Kent County was initiated in order to understand and alleviate the clogging problems.
The first stage of research involved evaluating the chemical and mineralogical composition of the bio-rock. The bio-rock that clogs the pipes is constructed of layers of calcite (CaCO3) separated by algal or fungal mats (with perhaps another mineral or two that washed away during thin sectioning). The calcite formed as equant and plumose crystals: plumose morphology indicates very rapid growth. Analytical techniques used to identify the materials in bio-rock include effervescence in dilute HCl, polarizing microscopes, SEM, XRD, and EPMA.
A set of experiments was designed during the second phase of research to force precipitation of the bio-rock under controlled conditions. The genesis of the bio-rock was the focus. Experiments were guided by field observations: bio-rock forms where leachate from the fly-ash pit and the MSW landfill mix, and where a black organic slime is found. X-Ray diffraction analysis of the seven precipitate samples yielded results consistent with preliminary analysis: calcite, sylvite, and halite crystallized.
During preliminary X-ray diffraction analysis interpretation by hand, it appeared that one of the precipitates was a zeolite. Though this was an incorrect identification, it indirectly redirected the research focus. The landfill and fly-ash pit are by nature rich in Ca and CO2 and the combination of these, calcite, is almost inevitable at the Earth’s surface. Finally, we designed an experimental exchange column in which Ca-rich fly ash leachate passes through a column of Na-rich zeolites in order to induce a reaction, pulling Ca out of solution and thereby hindering the formation of bio-rock. Results are encouraging as leachate samples containing >1000ppm dissolved Ca are reduced to 0 ppm.