Standard analytical methods for the determination of trace metals in flue gas desulfurization (FGD) and municipal wastewater, such as ICP-MS by EPA Method 200.8 or EPA Method 6020, are often prone to mass spectral interferences brought on by the presence and concentrations of common constituents such as chloride, carbon, sulfur, bromine, and alkali earth metals (sodium, calcium, potassium, magnesium). Such interferences can lead to results that may be biased high by as much as an order of magnitude for metals such as arsenic (As), chromium (Cr), copper (Cu), nickel (Ni), selenium (Se), cadmium, (Cd), vanadium (V), and zinc (Zn). Unfortunately, these interferences associated with most analytical methods applied to the regulatory monitoring can result in biased data artificially representing systematic problems.
In order to meet individual state regulations and air quality standards set by the US EPA, coal fired power plants are required to remove sulfur dioxide emissions from the flue gas they generate. This is more often accomplished through a limestone slurry injection into the stack which may contain additional treatment chemicals like dibasic acid or metal chelators. The resultant wastewater from the majority of FGD systems is unique even among industrial wastewater streams due to the varying approaches to stack emission control and coal sources. The unusual and constantly shifting composition of FGD wastewater presents circumstances that would otherwise rarely be encountered in analyzing wastewater samples and presents issues that many laboratories are not capable of recognizing or resolving.
Municipal wastewater systems do not typically contain the concentration of interfering compounds as coal fired power plants but they can still pose difficulties for standard ICP-MS analytical platforms. Input into municipal wastewater has a direct impact on the presence and concentration of interferences. Carbon can be introduced from fruit processing plants, zinc from road and roof runoff, and halogens (nitrogen, phosphorous, and sulfur) from the ubiquitous application of pesticides, herbicides, and fertilizers. The introduction of these analytes culminates into a greater possibility of spectral interferences with standard ICP-MS and non-compliance with NPDES permits.
Without an analytical technique to eliminate the interferences that lead to elevated results, decision makers might be acting on inaccurate data. Inaccurate data can also lead to confusion about the actual concentration of trace metals in wastewater and the effectiveness of various treatment techniques, investigation or implementation of unnecessary treatment technologies, fines for permit violations, and costly delays. Of particular concern are arsenic and selenium since the discharge allowances have been reduced due to regulations and standard ICP-MS instruments cannot support the new regulations.
Brooks Applied Labs has some of the lowest detection limits commercially available to our clients. Contact Us to get a customized list of our current MDL/MRL’s for your project.
Alternative to HR-ICP-MS (ICP-QQQ-MS)
One method that can accurately quantify these metals in such a challenging matrix is high-resolution ICP-MS (HR-ICP-MS); however this is an expensive analysis and not very realistic for limited budgets. Brooks Applied Labs, in close cooperation with representatives of the electric utilities, university research groups, and environmental engineering firms, has conducted extensive research and investigation to develop specialized and reliable analytical methods/techniques using inductively coupled plasma triple quadrupole mass spectrometry (ICP-QQQ-MS). Our approach overcomes the matrix-associated interferences for the determination of most of the periodic table without incurring the prohibitive costs of HR-ICP-MS.
Specialized Mercury Testing
As one of the preeminent commercial laboratories in mercury analysis and research, Brooks Applied Labs also provides electrical utilities with comprehensive services for the accurate determination of mercury in industrial wastewater samples. Nearly 35% of the mercury that currently goes into US coal-fired power plants is captured by air pollution control systems, whose key functions are typically to trap particulates or sulfur emitted with flue gasses. However, the mercury that is captured by FGD systems tends to persist in a highly volatile form due to the composition of the wastewater and can prove difficult to properly collect and analyze without the unrivaled experience found at Brooks Applied Labs.
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Brooks Applied Labs has some of the lowest detection limits commercially available to our clients. Contact Us to get a customized list of our current MDL/MRL’s for your project.
Wastewater Treatment Plant Optimization
Chemical modeling of treatment processes is often performed in a controlled laboratory setting to minimize variables which may interfere with mechanism identification and optimization. Once the mechanisms are understood for ideal conditions, application to real world samples can be initiated.
When pursuing chemical modeling associated with variable waste streams, all active variables must be taken into consideration. Interfering compounds, such as soluble salts, organic molecules, and other metals, may preferentially interact with the projected treatment process or the target metal. An excellent example is the competitive binding between arsenate and phosphate on iron packing materials (both having triangular pyramidal structures). At specific pH ranges, phosphate can dramatically decrease the binding efficiency for arsenate onto sorbent materials; thus, decreasing coprecipitation and column treatment processes. Interferences may include competitive binding, induced solubility of flocculent and precipitates, increased buffering capacity, and encapsulation of active sites. By no means is the presented list exhaustive; therefore, the importance of an encompassing vision with regards to remediation cannot be over stressed.
In addition, stratification of contaminants through substrate columns can also result in varying treatment efficiencies. Substrate stratification is not limited to solid materials; rather, redox conditions within water columns can affect metals speciation which in turn, would affect coprecipitation efficiencies as associated with waste water treatment plants. Other factors which may induce stratification of water columns is thermal variability as well as UV penetration (temporal variability throughout the year).
Concurrent application of speciation analysis with accurate total elemental testing can provide unparalleled information to identify the chemistry of the wastewater and to make correlations for varying waste streams. While chemical modeling has a utility in static treatment systems the probability of model failure for variable waste streams is high. Many times non-target compounds in the waste stream, such as persulfate, can play a key role in treatability and without monitoring the molecular form of the target element can be a costly endeavor.
Collaborations with Brooks Applied Labs benefit from our small business status. By reducing our costs and streamlining operational processes, we can offer analytical services with unparalleled quality along with faster turn around times and competitive pricing.
Feel free to contact a Brooks Applied Labs representative to identify how we can work with you to solve your monitoring and treatment needs.