Program
All Presentations (pdf)

Monday
8:15 Brent Means
10:10 James J. Gusek
12:40 Jonathan M. Dietz
2:15 Kimberly R. Weaver
4:00 Brent Means

Tuesday
8:45 Robert Kleinmann
9:15 Brent Means
9:30 James J. Gusek
10:00 Glenn C. Miller
10:30 Linda Ann Figueroa
12:40 Art Rose
1:10 Charles A. Cravotta III
1:40 Danielle M C Huminicki
2:50 Bernard Aube
3:20 Timothy K. Tsukamoto
3:50 Bradley R. Shultz
4:20 Kimberly R. Weaver

Wednesday
8:00 Linda Ann Figueroa
8:30 John Senko
9:00 Song Jin
10:10 Jonathan M. Dietz
10:40 Daryle H. Fish
12:40 John Chermak
1:10 Griff Wyatt
1:40 Dan Mueller
2:50 Sean C. Muller
3:20 Jack Adams
3:50 Roger Bason
3:50 Mark B. Carew

Thursday
8:00 Rep. John E. Peterson
8:30 Scott Sibley
9:00 Charles A. Cravotta III
9:30 Michael R. Silsbee
10:30 Lykourgos Iordanidis
11:00 Mark Conedera
11:30 Barry Scheetz
1:25 William Benusa
1:55 Mike Sawayda
2:25 Susan J. Tewalt
3:25 Robert S. Hedin
3:55 Chad J. Penn
4:25 Ron Neufeld

Biological Selenium and Arsenic Reduction: An Overview

Author(s)

Jack Adams, Ph.D.
Director, Modified and Activated Carbon Technology Center
University of Utah
Metallurgical Engineering, 412 WBB
Salt Lake City, UT 84112
801-712-2760
jadams@mines.utah.edu

Terrence D. Chatwin
University of Utah

Ximena Diaz
University of Utah

Jan D. Miller
University of Utah

Abstract

Selenium and arsenic are common contaminants worldwide. Selenium is periodically related to sulfur and like sulfur, positively charged selenium forms soluble oxyanions. The chemical characteristics of selenium and arsenic are dominated by the fact that they readily change oxidation states or chemical form through chemical or biological reactions that are common in the environment. Selenium most commonly occurs in four oxidation states: SeO4 2-, SeO3 2-, Se 0, & Se 2-. Well aerated, alkaline surface waters contain the majority of selenium as selenate. Negative and zero valences are associated organic and elemental selenium while positive valences are associated with mineralogy and aqueous systems, with selenate being more mobile than selenite. The EPA maximum contaminant level (MCL) for selenium in drinking water is 50 parts of selenium per billion parts of water (50 ppb) and a maximum contaminant level goal (MCLG) of 20 ppb. Recommended levels for aquatic wildlife is 2 ppb. Arsenic may occur as a semi metallic element (As 0), arsenate (As4 3-), arsenite (As3 3-), or arsine (H3As).

Arsenate is the oxygenated pentavalent form of arsenic and is the most abundant species in oxygenated waters. The Environmental Protection Agency (EPA) has established a Maximum Contaminant Level (MCL) of 50 µg/L for arsenic in drinking water; this value will change to a 10 ppb national standard in 2006. Both selenium and arsenic are difficult to remove to levels that meet current drinking water and discharge criteria. They are used as electron acceptors by microorganisms transforming them to reduced states, thus removing or stabilizing them. Many of these metal transformations are coupled with the cytochrome system and are an energy source under anaerobic conditions.

Microbial selenium transformations have been investigated for decades and have been found to be a common occurrence; microbial reduction of arsenic has not been studied as extensively. Microbes responsible for selenium and arsenic reduction have been isolated from contaminated mining process and waste waters, mining waste rock materials, agricultural soils and drainages, petroleum refining and coalfired power generation wastewaters, and domestic wastewater treatment facilities. Selenium and arsenic reducing microbes can be found in numerous genera including Alcaligenes, Escherichia, Pseudomonas, Bacillus, Desulfovibrio, Shewanella, Enterobacter, Thauera, and numerous genera within Cyanobacteria and the sulfate reducing bacteria. Metal and metalloid reducing microbes are quite biquitous and can be cultured from environmental samples using common techniques. Some microbes are capable of direct selenium reduction under aerobic conditions by metal-active enzymes, possibly a detoxification mechanism. Similar reductions are thought to occur among some of the arsenic reducing microorganisms.

Fundamental considerations are important for successful application of selenium and arsenic biological treatments and involve several steps starting with site characterization, bioassessment and biotreatability testing, and biotreatment monitoring. While many microbes are capable of selenium and arsenic reduction, specific site environmental characteristics need to be taken into consideration for optimal metalloid reduction at any specific site. In general, biotreatments typically produce 1,000’s of times less sludge than conventional precipitation technologies and can be employed in several basic ways:

• Biostimulation through addition of nutrients that stimulate most or many of the site indigenous microbes
• Biostimulation through isolation of key site microbes, production of these microbes followed by reintroduction of this population back into the treatment system
• Bioaugmentation or the introduction of new microbes, possibly microbes already present at the site, but known to have the biochemical systems needed to transform the contaminant form present and have high transformation efficiencies
• Bioaugmentation/Biostimulation or a combination of both techniques that leads to a population of both new and indigenous microbes.

Selenium and arsenic reduction/sorption has been demonstrated in various waters with live microbial cells, microbial biomaterials, enzymes, and proteins that have a high affinity for these metalloids. These biomaterials can be immobilized and have been shown to rapidly reduce or sorb selenium and arsenic and various other metals and inorganic contaminants from various environmental waters.

Presentation

Biography

Dr. Adams’ background is in molecular and applied environmental microbiology and
environmental engineering. He has worked in environmental biotechnology for about 30
years for state & federal government agencies and industry. Dr. Adams’ headed U.S. Army
and U.S. Bureau of Mines Biotechnology Programs, directed the Bioremediation Center at
Weber State University and is the current director of the Modified & Activated Carbon
Technology Center at the University of Utah.