Bioremediation of Effluent Water in a Coal Ash Disposal Area: Optimizing Microbial Sulfate Reduction

Author

Ryka Shea, Stephen F Austin State UniversityFollow

Date of Award

12-2024

Degree Type

Thesis

Degree Name

Master of Science - Environmental Sciences

Department

Environmental Science

First Advisor

Mindy Faulkner

Second Advisor

Jenny Rashall

Third Advisor

Alyx Frantzen

Fourth Advisor

Kevin Stafford

Abstract

Coal combustion residues (CCR) pose a serious environmental threat, even long after they are disposed of in specialized landfills, due to their complex composition and potential for leaching into waterways. This study focuses on the issue of elevated sulfate concentrations at the Martin Lake Steam Electric Station (MLSES) A-I Disposal Area in Panola County, Texas, where CCR are disposed of in a permanent landfill. Currently, this site is exceeding its regulatory limit of sulfate concentrations in its effluent and is in need of a cost-effective and sustainable solution to this problem. This research utilized benchtop experiments to investigate sulfate reducing bacteria (SRB) mechanisms within flask wetland microcosms, simulating conditions comparable to the final pond at the disposal area. The effectiveness of acetic acid, lactic acid, mushroom compost, and cow manure were analyzed through a series of laboratory experiments treating flask wetland microcosms with varying concentrations of carbon sources to test their efficiency in improving SRB reduction. Mud substrate from an active wetland on site of the A-1 Disposal Area was used to inoculate flasks with SRB, and 1000 ppm synthetic sulfate water was created using sodium sulfate powder. Carbon-rich substrates were added to sustain the SRB and promote continuous sulfate reduction. Five trials were conducted testing four carbon treatments at three different ratios of chemical oxygen demand (COD) and three controls; each carbon treatment and control group were run in triplicate (n=45). Trials 1 and 2 were conducted over the course of one week, while Trials 3 and 4 lasted for four weeks. Trial 5 was extended for eight weeks and included an additional carbon treatment administered at the halfway point. At the conclusion of each trial, water samples from the flask wetland microcosms were mixed with 0.10 M barium chloride (BaCl2) solution to induce turbidity. Ultraviolet Visible (UV Vis) Spectroscopy was used to measure final sulfate concentrations using the Mettler Toledo Method. Results show the acid substrates were successful in promoting SRB to utilize sulfate in the system, with up to 98% sulfate reduction after a 4-week experimental period. The mushroom compost and cow manure were less efficient, with sulfate reduction of 30-50% at all concentrations. Trial 5 demonstrated that overall, an additional carbon treatment at four weeks is helpful for maintaining reduction rates, with the exception of higher ratios of lactic acid. The 4:1 and 6:1 treatments of lactic acid demonstrated continued sulfate reduction throughout the eight weeks without an additional treatment. Time was a critical component in the success of SRB reduction of sulfate. The 1-week trials demonstrated negligible sulfate reduction, while the 4-week trials exhibited substantial reduction of sulfate in all treatments, especially the acid treatments. Overall, this research provided insights into long-term strategies for sulfate reduction and water quality improvement in coal ash disposal areas. By leveraging natural processes of biological sulfate reduction, this study proposes sustainable solutions for environmental remediation and regulatory compliance.

Repository Citation

Shea, Ryka, "Bioremediation of Effluent Water in a Coal Ash Disposal Area: Optimizing Microbial Sulfate Reduction" (2024). Electronic Theses and Dissertations. 590.
https://scholarworks.sfasu.edu/etds/590

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.