April 22, 2010
Kurita Develops a New Wastewater Treatment Technology to Help Power Plants Reduce Their Environmental Impact
Kurita Water Industries Ltd. (Head Office: Shinjuku-ku Tokyo, President: Hiroshi Saito) has developed a wastewater treatment technology to help coal-fired power plants reduce their environmental impact to a large extent by removing selenium, a regulated substance, from wastewater. Kurita will deliver the first system based on this technology to an electric power company in Japan.
Selenium* is a substance contained in coal and other materials, and selenium in wastewater has been regulated by law since 1994. It is generally difficult to remove selenium from wastewater by conventional methods, and coal-fired power plants have been in need of a technology to effectively remove selenium from wastewater to ensure efficient wastewater treatment.
Kurita began developing a new technology to remove selenium from wastewater from power plants in response to the enforcement of new wastewater regulations and to the needs of customers who own and operate power plants. Through joint research with an electric power company in Japan, Kurita has successfully developed a new system to treat selenium-containing wastewater through the use of a composite metal reductant.
With this new system, power plants can remove selenium from wastewater to below a concentration of 0.1 mg/L, which is the regulation standard set for this pollutant in wastewater in Japan, and the plants can also decrease the amount of sludge produced in comparison with the use of conventional technologies.
Kurita will promote the use of this system, which can greatly contribute to the reduction of the environmental impact caused by electric power companies and coal-fired power plants, both in and outside Japan.
- *Metal selenium is a red or gray solid substance. Selenium is a chemical element with the atomic number 34. In nature, it exists on its own but more usually combines with a range of metals to form selenium compounds. Coal contains a trace of selenium.
Wastewater from the gas treatment process of coal-fired / coal gasification power plants contains selenium, which has been regulated under the Japanese Water Pollution Control Act since 1994. To comply with this law, companies in Japan are required to reduce the amount of selenium in wastewater to below the regulation standard (0.1 mg/L).
2. Kurita's approach
Kurita has been delivering a range of selenium treatment systems to coal-fired power plants, and based on this experience it began developing a new selenium removal technology to meet its customers' need to reduce their environmental impact and to comply with stricter wastewater regulations. Subsequently, Kurita has successfully developed a treatment system for selenium-containing wastewater, which can remove a greater amount of selenium than conventional technologies while generating a smaller amount of sludge as a byproduct.
3. New treatment system for selenium-containing wastewater
Selenium is gasified into selenium dioxide through the combustion of coal and then solidifies as the gas temperature drops. Selenium that was not removed by the electrostatic precipitator (ESP) flows into the flue-gas desulfurization equipment and dissolves into water. Depending upon conditions, a part of the dissolved selenium is converted into selenate ion (hexavalent), which is difficult to remove with ordinary wastewater treatment methods.
Previously, selenate in wastewater was usually reduced through contact with a metal reductant under acidic conditions and then removed by the coagulation-sedimentation method. With this conventional approach, however, selenate at high concentration could not be effectively removed and the approach also has the following disadvantages: the cost of the chemicals used for the reduction of selenate is high and the amount of sludge generated as a byproduct increased.
Kurita's new treatment system for selenium-containing wastewater consists of a newly developed composite metal reductant, which can efficiently remove selenium by strongly reducing selenate to solid selenium (zero-valent), thereby enabling efficient treatment of wastewater.
The newly developed technology has the following advantages over conventional technologies:
- (1)It stably lowers selenium concentration to below 0.1 mg/L, which is the regulation standard defined by the Japanese Water Pollution Control Act.
- (2)It decreases the amount of sludge generated as a byproduct by 30%, thereby reducing the sludge disposal cost as well.
- (3)It requires 20% less use of chemicals in the reduction process, which in turn will decrease the running costs.
4. Future deployment
Coal-fired power plants in Japan are in need of leading-edge wastewater treatment technologies to comply with enhanced wastewater regulations. Also in recent years, the need for the development of technologies that contribute to reduce environmental impact has been rapidly increasing among customers. Kurita therefore expects that demand for its newly developed wastewater treatment system will grow strongly in the future.
In Japan, Kurita will promote the installation of this system for electric power companies and other clients who own coal-fired power plants in our proposals for updating the existing facilities, and we will also proactively promote the sales of this system in other countries where the need for coal-fired power generation is growing.