A Novel Method for Biological Perchlorate Reduction Using Elemental Sulfur as an Electron Donor

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

CBET-0755670 Ergas Intellectual Merit. This project describes a novel process to entirely break down perchlorate in contaminated ground and surface waters to innocuous products. We have enriched a microbial consortium capable of coupling elemental sulfur (S0) oxidation with perchlorate reduction. This stable consortium not only successfully degrades perchlorate using S0 as the sole electron donor, but also does this at NaCl concentrations typical of ion exchange (IX) brines, currently a common removal technique. In addition, we have recently isolated a bacterial strain capable of perchlorate reduction in this system. Preliminary upflow packed bed bioreactor experiments show degradation of perchlorate from 100 to < 4 ppb at empty bed contact times of eight hours; however, profiles of perchlorate concentration vs. depth in the reactors indicate higher loading rates are feasible. The use of S0 as an electron donor is an elegant and cost-effective method of biological perchlorate removal. Elemental sulfur, a by-product of the petroleum refining industry, is relatively inexpensive and available. Use of S0 reduces the risk of bioinstability due to carry over of organic substrates to water distribution or groundwater recharge systems. Sulfur-oxidizing bacteria are slow growing autotrophs that, although metabolically very active, produce very little excess sludge, reducing the need for backwashing. Sulfur granules can be used as media in simple packed bed bioreactors, or can be integrated into IX brine treatment and reuse systems or in situ permeable reactive barrier (PRB) systems. Specific objectives of the proposed interdisciplinary research project are (1) to investigate conditions for sulfur-oxidizing, perchlorate-reduction (including concentration, salinity, pH, temperature, and cocontaminants NO3 -, RDX, and HMX), (2) to determine dominant and active community members involved in perchlorate reduction, (3) to investigate operating conditions and performance of packed bed sulfur-oxidizing bioreactors for direct treatment of perchlorate contaminated water in bioreactors or perchlorate contaminated IX brines. Experiments will be carried out at flask, column and pilot scale. In a closely knit and well established interaction between environmental engineering and microbiology research groups, we will identify additional members of the microbial consortium (e.g. sulfate-reducers and sulfur-oxidizers) using both traditional and culture independent techniques, and compare bioreactor degradation rates to the genetic potential of the perchlorate-metabolizing culture. This knowledge will allow us to follow community robustness during reactor operation under varying conditions, and to develop a seed community and protocols that can be used in new systems. Bench-scale bioreactor experiments will be used to investigate conditions for treatment of spent IX regenerant brines and to examine the effect of co-contaminants on perchlorate degradation. Pilot-scale bioreactor experiments, at a contaminated site in Massachusetts, will be used to examine perchlorate loading rates, operational stability, scale-up, and costs for typical water utility applications along with co-contaminant effects. This research will expand the understanding of perchlorate reduction supported by autotrophic bacteria in contaminated aquifer systems and lead to novel and cost-effective bioremediation solutions. The broader impacts of this research are varied and far-reaching. The project will provide information on the feasibility of removing perchlorate from water supplies while minimizing disposal of process wastes. This study will also define an unusual microbial community relevant to human activities. Anticipated benefits include data for design of reliable and cost-effective biological treatment systems, in situ PRBs, and IX systems that can remove perchlorate and recycle contaminated brine streams. With upcoming new standards for perchlorate this project will serve as a model for drinking water utilities and military sites. In addition, the PIs join a core group of researchers at the University of Massachusetts who are studying the occurrence, toxicology, and treatment of perchlorate. This group will share equipment and expertise, develop interdisciplinary educational programs, such as seminars and journal clubs, and organize conferences on this topic in New England. The PIs have an excellent track record in engaging undergraduates, middle and high school science teachers, and high school students in research. We will work with the UMass College of Engineering REU program and our established connections with faculty to recruit undergraduates from the University of Puerto Rico Mayaguez to work on this project. We will develop modules on perchlorate.