How Low-Temperature Evaporation Treats FGD Wastewater

Veolia Water Technologies’ low-temperature CoLD crystallizer technology can help coal power plants clean and recover water for reuse from the wastewater produced in wet scrubber systems. The innovative solution provides effective wastewater treatment at lower capital and operational expenses than those of conventional thermal zero liquid discharge options.

Despite rising competition from natural gas and renewables, coal still is the single largest source of electricity worldwide. To generate electricity as clean and as efficiently as possible, coal-fired power plants require intensive water management operations, particularly in the treatment of two of their largest sources of wastewater: bottom ash transport water and flue gas desulfurization wastewater.

Steam-electric utilities can reap substantial regulatory and economic benefits by deploying a safe, robust, and cost-effective approach based on low-temperature zero liquid discharge (ZLD) solutions that promote water conservation and safe disposal of stable, non-hazardous solids in a responsible way, while removing the broad spectrum of pollutants and reducing the volume of wastewater discharged.

Processing Wastewater to Meet Regulations

Because coal combustion produces gases that react easily with other substances to form compounds that can be a risk to human health, coal-fired power plants “scrub” these pollutants, particularly sulfur dioxide, from their exhaust emissions through a process called flue gas desulfurization (FGD). The technique, which sprays the gas with water and a sorbent reagent, is essential to control the build-up of corrosive salts and suspended solids absorbed from the gas stream. The process, however, produces a blowdown byproduct that needs to be cleaned before discharge because it contains toxins collected from the gas. In particular, boron, organics, and small amounts of heavy metals, such as mercury and selenium, are damaging for both aquatic ecosystems and terrestrial plants.

As part of a transition to cheaper forms of electricity generation in North America, the number of retired coal-fired power plants in the U.S. has been growing. It is estimated that more than 400 ponds cover 30 square miles at more than 200 coal-fired plants in 35 states, according to AECOM, an engineering firm that consults with coal utilities on regulatory compliance issues. This prompted the federal government to issue coal plant wastewater management rules in 2015 mandating the treatment of, among others, FGD wastewater, targeting the removal of suspended solids and dissolved solids, particularly dissolved salts also found in the source coal.

Under the current administration, the federal regulatory landscape has evolved as the U.S. Environmental Protection Agency (EPA) proposed last year to revise the 2015 standard and roll back effluent guidelines to relax FGD pollution limits. But because of rising public concern about the effects of exposure to heavy metals, even at trace levels, some states still plan to enforce the implementation of state rules following the initial federal guidelines.

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Article written for Power Magazine's May 2020 issue by Veolia Water Technologies' Rob Lawson, business development manager, and Matias Navarro, manager of Marketing and Strategic Market Development.