Loading...
Impacts of rare earth elements on biological wastewater treatment processes
Salmon, Olivia
Salmon, Olivia
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2019
Date Submitted
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
Rare earth elements (REEs) underpin a host of technologies that are central to modern society, including portable electronics, renewable and clean energy components, medical devices, and military equipment. Obtaining purified REE end products involves numerous physical and chemical processes, many of which generate large volumes of waste that, if not handled appropriately, can cause significant environmental, economic, and social impacts. In some cases, industrial operators involved in the processing or recycling of REEs may seek to discharge REE-impacted wastewater to municipal water resources recovery facilities (WRRFs). However, little is currently understood about the potential for REE-containing wastewater to affect the performance of conventional wastewater treatment processes, particularly biological treatment processes. The study described in this thesis was developed to investigate impacts of REEs on the mixed microbial communities that treat wastewater. To this end, a series of experiments were developed to evaluate multiple biological wastewater treatment components and REEs. To evaluate and visualize potential inhibition thresholds of REEs, culture plates containing varying concentrations of REEs were prepared and inoculated with activated sludge collected from a local WRRF. Concurrently, bench-scale bioreactors were developed to mimic aerobic activated sludge and anaerobic sludge digester conditions in full-scale WWRFs. Aerobic and anaerobic test reactors were treated with high-priority REEs as salts and chelated compounds, and wastewater treatment performance parameters were tracked to evaluate potential impacts from REEs. Additionally, DNA was extracted from sludge samples collected from the aerobic bioreactor system for high-throughput sequencing to evaluate microbial composition shifts as a function of REE treatment. Aerobic culture plate experiments indicated toxicity of europium, gadolinium, lanthanum, neodymium, and yttrium to activated sludge inocula when present at concentrations of 270-400 mg/L. Additionally, clear inhibition to nitrification processes from gadolinium and yttrium salts were identified in the aerobic reactor experiments. Impacts to nitrification performance measures were supported by microbial community analysis, which indicated distinct changes to community composition as a function of REE treatment. In contrast to findings identified in the aerobic reactor system, anaerobic bioreactor experiments did not reveal meaningful impacts to digestion performance measures from the REE treatments that were investigated. However, >97% of unchelated REE treatments were bound up in bioreactor solids. Taken together, our experimental results do not support the viability of allowing concentrations > 10 mg/L of REE to enter WRRFs, which has important implications as public and private entities weigh the benefits and costs of varying REE processing and disposal technologies.
Associated Publications
Rights
Copyright of the original work is retained by the author.