Many coal-fired and nuclear power plants in the U.S. are supported by steam electric power. This generation involves processes that require the discharge of water with constituents such as arsenic, lead, mercury, selenium, chromium and cadmium. Once these constituents are discharged, they may impact the environment. Because of this, utilities are working to reduce these constituents through improved wastewater treatment before their release.
In 2015, the EPA finalized a rule revising the regulations for the steam electric power generating category. It also set the first federal limits on the levels of heavy metals in wastewater that can be discharged from power plants.
Although the EPA has postponed certain compliance deadlines for Effluent Limitation Guidelines, tighter regulations are still on the horizon for steam electric power stations. These anticipated regulations have prompted various studies and led to the implementation of new technologies to help reduce metals in process wastewaters.
As the requirements in the power industry are becoming more stringent, original equipment manufacturers are being motivated to develop new wastewater treatment technologies that are also more cost-competitive.
Biological wastewater treatment systems have risen to the top as more and more utilities seek treatment of flue gas desulfurization (FGD) wastewater. These systems have been proven to help reduce heavy metals in the FGD wastewater before discharge.
As the power industry continues to make advancements in biological wastewater treatment, it has uncovered advantages and disadvantages transferrable to the mining industry — an industry that has not seen an update to its own effluent guidelines since the late 1970s.
At its core, a biological treatment system is a system that uses bacteria or microbes to break down and remove organic matter. These microbes can effectively reduce certain constituents in water or wastewater that should not be discharged to surface water. When used in the power and mining industries, biological treatment systems can vary depending on the type of water being treated and the available power and infrastructure near the treatment system.
It is critical to know the water balance for these systems, so the treatment equipment can be right-sized. It’s also essential for system operators to understand how plant operations will impact the way the wastewater treatment system operates and performs.
Biological systems, while useful and effective in reducing metals, also come with unique challenges. These systems typically thrive when receiving consistent quality wastewater. Any upset or change to normal operation that impacts the quality of the water being treated can have adverse impacts on the biological system.
It is important that the system incorporate some type of equalization measures upstream of the biological system. This could be as simple as a tank or pond where the water is stored so that impacts due to influent quality changes are minimized before entering the treatment process. It is essential that the engineering design around a biological system accounts for these types of upsets.
Overall, the mining industry has potential to leverage lessons learned on biological wastewater treatment from the power industry to reduce the presence of metals in wastewater.
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