The Art of Contaminant Removal: Advanced Wastewater Treatment Technology to Eliminate Selenium Pollution



selenium-factory

Editor’s Note:
As we move closer to September 30, 2015, the date scheduled for the EPA to issue the Effluent Limitations Guideline (ELG) Final Rule, options and challenges of removing selenium and other contaminants related to coal-ash are a hot topic, especially among coal-fired power plants. First proposed in 2013, the rule is included in the Steam Electric Power Generating category (40 CFR 423) and focuses on regulating wastewater discharges from these power plants.

Lisa Farmen, a chemical engineer and founder of Crystal Clear Technologies, is an expert in the subject of water technologies in regard to removal of heavy metal contaminants such as Se. She offered to educate our readers on this hot topic in the environmental services industries.

selenium
Selenium is a mineral naturally found in soil. Most sedimentary rock formations contain Se. (Photo credit: Periodictable)

Selenium (Se) is a naturally occurring, semi-metallic trace element (Se; atomic number 34) that, in very small amounts, is an essential nutrient in the diets of all animals; in excess, however, it is quite dangerous. At concentrations of only twice the beneficial levels, the toxicity of it can yield devastating short- and long-term health effects, including damage to the nervous system and a decline in reproduction. As Se moves from water and into wildlife, it can bio-accumulate in organisms and become more concentrated in species as it travels up the food chain, eventually reaching lethal levels.

Sources of Selenium Pollution

Cooling Tower
Cooling Tower

Environmental impacts of selenium contamination came to the public’s attention with a high-profile incident in the 1980s. Belews Lake, North Carolina, suffered a severe fish die-off and the loss of 16 of 20 species of fish, as the result of high levels of Se leaching from ash piles. Since then, the EPA’s hardline approach on electric steam plants have proposed limiting waste water levels of Se at levels that only novel technology can approach.

The primary source of selenium pollution in the power plant sector is the fuel source, i.e. coal and oil. Here’s the breakdown of the process. Coal is used to heat water and convert it to steam, which in turn powers the turbine and produces electricity. It also generates waste heat energy, a bi-product of the useful electricity that is often cooled using selenium-laden groundwater. When cycled up in cooling towers, it generates levels higher than allowable discharge.

Sneaky in Nature

With the duplicity and dexterity of a supernatural comic book villain, Se proves difficult to sequester, adsorb or remediate. A masterful shape shifter, it abides as different species dependent upon its environment. It essentially possesses the ability to insert itself into the DNA of a species by replacing sulfur, the key bonding element within DNA chains, which in turn can damage future generations to the point of death. Kesterson National Wildlife Refuge in northern California is a tragic example of the devastating nature of this particular contaminant.

In the latter half of the 20th century, high levels of selenium at Kesterson National Wildlife Refuge caused a rapid die off of migratory waterfowl, fish, insects, plants and algae. (Bruce Waddell/USFWS)
In the latter half of the 20th century, high levels of it at Kesterson National Wildlife Refuge caused a rapid die off of migratory waterfowl, fish, insects, plants and algae. (Bruce Waddell/USFWS)

There are several species of selenium found in the environment, including selenide (Se-2), selenite (Se+4), selenate (Se+6) and selenium (Se0). Both selenide (Se -2) and Se0 are insoluble. Selenate (Se+6, SeO42-) and selenite (Se+4, SeO32-) are the primary oxidation states found ionized in water. Any removal or remediation approach has to consider all the speciations that may be included. The aquatic discharge level for Se is 1 µg/L and, given the large volumes of water that power plants use, surface water discharge to receiving waters will require extremely low levels of Se removal.

Removal Strategies and Challenges

The ideal adsorbent should be able to remove selenium from a complex soup of total dissolved solids containing sulfates, alkali metals and inorganic complexes. Coefficient (Kd) defines the affinity for the engineered adsorbent to remove low levels of metals from a complex water matrix, such as FGD wastewater, which has Total Dissolved Solids (TDS) levels ranging from 4,000 – 68,000 mg/L with sulfate being at least 50% of the TDS value to very low single digit ppb levels.

Existing strategies for selenium removal typically involve reduction of selenate, which is not easily adsorbed onto particulates, to selenite, which can be easily immobilized. Biological reduction of Se with anaerobic bacteria or algae has proven very effective, but requires a huge footprint. Other Se removal technologies include reverse osmosis, ion exchange and electrocoagulation. However, one common issue with FGD wastewater is that it is generally high in TDS and sulfates, which means there are many ionized species competing for the active sites on solid phase extraction (SPE) material. Such a crowded field of contaminants causes many of these technologies to be ineffective, much less capable of, reaching low removal levels.

Nano Needle in a Haystack

nanotech-wastewater
Crystal Clear Technologies uses nano-materials in their patented NMX™ to reach single digit ppb to low ng/L metal removal in high TDS wastewater.

Fortunately, there is another option when it comes to tackling the challenge of selenium removal. It may seem small on the surface, but its effect on the environment will be gigantic! Crystal Clear Technologies (CCT) has developed and patented functionalized nano-materials, which act like antibodies to sequester or chelate specific contaminant metals found in high TDS process waters, such as Se. The other metals in the TDS population are invisible to the active sites, resulting in a high capacity, target-specific engineered media that can reach single digit part per billion to part per trillion metal removal in high TDS wastewater. The SPE material, branded NMX™, can surgically remove both selenite and selenate from high TDS high sulfate FGD wastewater to single digit ppb levels. NMX™ passes the TCLP test, which allows the exhausted media to be landfilled as non-hazardous solid waste, thus terminating liability.

NMX simply removes the Se from the haystack of TDS, uses a small amount of product as its target represents a fraction of a percent of TDS total make up, and requires a small footprint.

Lisa Farmen, President of Crystal Clear Technologies, Inc., and Brent Hepner of C.I.Agent Stormwater Solutions, both contributed to this post.

About Lisa Farmen:

Ms. Farmen is the Founder and CEO/President of Crystal Clear Technologies, Inc., which developed nano-enhanced materials capable of removing metals and chemical contaminants from water at an affordable cost. As a chemical engineer, she built an OEM engineering and manufacturing company specializing in water, wastewater and chemical recovery systems for the electronics industry. She built revenue to $8M then sold the company to a group of investors.

Ms. Farmen received her B.S. from Colorado State University and Executive M.B.A. in International Business from Golden Gate University in San Francisco.

About Crystal Clear Technologies, Inc.

CCT

Founded in 2000 by Lisa Farmen, Crystal Clear Technologies, Inc. (CCT) operates with the mission to innovate and incorporate nano-materials to enable clean, safe water anywhere in the world. Researchers at CCT have developed and patented novel water and waste water treatment technologies capable of removing heavy metals from high TDS process waste water. For more information, visit http://www.Crystalclearcleanwater.com.

 

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