The U.S. Environmental Protection Agency (EPA) sets stringent Effluent Limitation Guidelines (ELG) with regard to the discharge of wastewater by coal-fired power plants. To meet these standards, power plants have been primarily looking to install the best available technology. Controlling the proportion of trace metals in wastewater not only requires effective removal solutions but also technology to monitor and manage these processes. And that is precisely the unique value proposition of P S Analytical (PSA), which specializes in the manufacture and support of instrumentation used to detect and measure trace metal levels. Founded in 1983, PSA develops and produces online wastewater analyzers for mercury, arsenic, selenium, and other trace metals. The company initially focused on supplying accessories for automating and improving the detection limits of numerous instruments in the industry before developing its own analysis system for ultra-low-level mercury determination in 1988.

“If we look at mercury, not only are the samples difficult to analyze, but the ELG limits also mean that parts per trillion levels are needed to be measured. Building on our extensive experience and working directly with industrial partners, we have developed an analysis system that overcomes these issues. It offers sub-precipitation (sub-ppt) detection limits, handling even the toughest flue-gas desulfurization (FGD) wastewater sample using less than 5 milliliters of reagent per measurement cycle,” says Paul Stockwell, sales manager at PSA. This makes the system ideal for long-term end-to-end monitoring of the removal process, providing information to engineers and scientists to help ensure the effective functioning of their removal technology.

PSA has been manufacturing and supplying instrumentation for the determination of mercury and various hydride forming elements for over 30 years. The company’s detector technology is based on atomic fluorescence spectrometry, which offers an extremely sensitive, element-specific detector with linearity spanning over 7 orders of magnitude.
These detector systems first convert the analyte—a substance whose chemical constituents are being measured—into its gaseous form, unlike most competitors that rely on liquid samples, thereby eliminating potential matrix interferences and improving efficiency. “We also have the capability of introducing 100 percent of the analyte into the detector, which improves the detection limit significantly,” remarks Dr. Warren Corns, R&D Manager at PSA. Furthermore, to offer accurate results for concentrations below one part per trillion, PSA provides an online analyzer that digests samples using UV photolysis. The final measurement is based on cold vapor generation with gold amalgamation atomic fluorescence spectrometry. The online analyzer offers a measurement cycle time between 10-20 minutes with sub-ppt. detection limits and relative accuracy limits typically below 20 percent when compared to the US EPA methods such as EPA 1631 and 245.7.

An attractive feature of PSA’s online analyzer is that it uses minimal quantities of reagent volumes and carrier gas, and field trials to date have indicated that more than 95 percent uptime is achievable. The instrument has the capacity to analyze sequentially up to 12 sample streams that can be used to test different wastewater streams and also to monitor the effectiveness of mercury control technologies by running inlet and outlet streams.

PSA also has an element-specific online instrument for selenium and arsenic that are listed in the EGL priority pollutants. “The technology used is very similar, but in this case, we use UV photolysis with hydride generation AFS. Since selenium and arsenic exist in different chemical forms and valence states, the analyzer has to convert all species to Se(IV) and As(III) prior to the hydride generation step,” mentions Stockwell. The system has been successfully trialed at several power plants on various waste streams applying different control technologies. Continuing to enhance its capabilities to incorporate unique customer demands, PSA has moved to a new factory in the UK and plans to partner with removal technology suppliers to help meet ELG standards more effectively.