Electric power plants must meet EPA and local wastewater requirements for effluent, including those under the Clean Water Act. Under the Clean Water Act, the EPA has identified 65 pollutants and classes of pollutants as “toxic pollutants”, of which 126 specific substances have been designated “priority” toxic pollutants. Failing to do so can result in severe fines that quickly escalate.
Typically, fossil-fuel burning power stations, especially coal-fired plants, are a large source of industrial wastewater. Many plants discharge wastewater with significant levels of metals such as mercury, lead, chromium, and cadmium from sources such as flue gas mercury control, flue-gas desulfurization, and fly ash/bottom ash. Wastewater can also include arsenic and selenium as well as nitrogen compounds. Plants with air pollution controls such as wet scrubbers also usually transfer any captured pollutants to the wastewater stream.
For the power generation industry, this means installing a wastewater treatment system that effectively separate the contaminants from the water so it can be legally discharged into sewer systems or even re-used.
However, traditional wastewater treatment systems can be complex, often requiring multiple steps, a variety of chemicals and a considerable amount of labor. Even when the process is supposedly automated, too often technicians must still monitor the equipment in person. This usually requires oversight of mixing and separation, adding of chemicals, and other tasks required to keep the process moving. Even then, the water produced can still fall below mandated requirements.
Although paying to have power plant wastewater hauled away is also an option, it is extraordinarily expensive. In contrast, it is much more cost effective to treat the industrial wastewater at its source, so treated effluent can go into a sewer and treated sludge passes a Toxicity Characteristics Leaching Procedure (TCLP) test and can be disposed of as non-hazardous waste in a local landfill.
Fortunately, complying with EPA and local wastewater regulation has become much easier with more fully automated, wastewater treatment systems. Such systems not only reliably meet regulatory wastewater requirements, but also significantly reduce the cost of treatment, labor and disposal when the proper separating agents are also used.
Cost-Effective, Automated Wastewater Treatment
In contrast to labor-intensive multiple step processes, automated wastewater treatment can help to streamline production, usually with a one-step process, while lowering costs at industrial facilities.
An automated wastewater treatment system can eliminate the need to monitor equipment in person while complying with EPA and locally mandated requirements. Such automated systems separate suspended solids, emulsified oil and heavy metals, and encapsulate the contaminants, producing an easily de-waterable sludge in minutes,
The water is typically then separated using a de-watering table or bag filters before it is discharged into sewer systems or further filtered for re-use as process water. Other options for de-watering include using a filter press or rotary drum vacuum. The resulting solids are non-leachable and are considered non-hazardous, so will pass all required testing.
These systems are available as manual batch processors, semi-automatic, automatic and can be designed as a closed loop system for water reuse or provide a legally dischargeable effluent suitable for the sewer system. A new, fully customized system is not always required. In many cases, it can be faster and more cost effective to add to or modify a power plant’s current wastewater treatment systems when this is feasible.
However, because every wastewater stream is unique to its industry and application, each wastewater treatment solution must be suited to or specifically tailored to the application.
The first step in evaluating the potential cost savings and effectiveness of a new system is to sample the wastewater to determine its chemical make-up followed by a full review of local water authority requirements.
The volume of wastewater that will be treated is also analyzed, to determine if a batch unit or flow-through system is required. Other considerations include the size restrictions, so the system fits within the facility’s available footprint.
Despite all the advances in automating wastewater treatment equipment, any such system requires effective separating agents which agglomerate with the solids in the wastewater so the solids can be safely and effectively separated out.
Because of the importance of separating agents for wastewater treatment, a special type of bentonite clay is used in certain wastewater chemical treatments. The treatment chemicals are formulated to break oil and water emulsion, provide heavy metals removal, and promote flocculation, agglomeration and suspended solids removal.
Bentonite has a large specific surface area with a net negative charge that makes it a particularly effective adsorbent and ion exchange for wastewater treatment applications to remove heavy metals, organic pollutants, nutrients, etc. As such, bentonite is essential to effectively encapsulate the materials. This can usually be achieved in one-step treatment, which lowers process and disposal costs.
In contrast, polymer-based products do not encapsulate the toxins, so systems that use that type of separating agent are more prone to having waste products leach back out over time or upon further agitation.
Today’s automated systems along with the most effective separating agents can provide power industry operators with an easy, cost-effective alternative so they remain compliant with local ordinances and the EPA. Although there is a cost to these systems, they do not require much attention and can easily be more economical than paying fines or hauling.
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