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Whether you're an analyst-of-all-trades at a municipality or a water quality specialist at a commercial laboratory, we have the information you need to succeed. Water Environment Laboratory Solutions focuses on day-to-day laboratory concerns, as well as discussing certification issues, staff management approaches, and new & revised analytical methods. |
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Vol. 15, No. 5 October/November 2008
FEATURES
Get Better BOD Results
Three simple changes to the BOD test can virtually eliminate blank failures
Christopher Fair and Estelle Riche
Used to evaluate the performance of most U.S. wastewater treatment plants, the 5-day biochemical oxygen demand (BOD) test consists of diluting a sample to 300 mL with nutrient-laden water, measuring its dissolved-oxygen (DO) concentration, incubating it for 5 days, and then measuring its DO again to determine how much the concentration has changed. Samples typically are analyzed in sets, including one “blank” sample that contains only dilution water. |
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The blank sample serves as a quality control. For the test to be considered valid, the blank must lose less than 0.21 mg/L of oxygen. This has proven to be the most difficult objective to achieve in the BOD test. Three problems contribute to poor blank results (greater than 0.20 mg/L): poor DO measurements, insufficiently cleaned sample bottles, and poor-quality water.
Over the years, various analysts have offered numerous solutions that have provided some improvement, but none completely eliminated the problem. Researchers recently evaluated three approaches ― a luminescent DO probe designed for the BOD test, disposable polyethylene terephthalate (PET) bottles, and a water-purification system ― to see if they might have better success.
Do You See What I See?
Two modifications to colorimetry analysis can make phosphorus
measurements more reliable
Rebecca L. Gilmore, Sarah Goertzen, Sudhir Murthy, Imre Takács, and D. Scott Smith
To meet stringent phosphorus limits in their National Pollutant Discharge Elimination System permits, many treatment plants rely on chemical phosphorus removal. This typically involves adding iron or aluminum salts to wastewater to precipitate, coprecipitate, or adsorb soluble phosphates, which are removed when solids are wasted. Although this process is widely used, its removal mechanism is poorly understood, so plant personnel have difficulty determining the exact amount of metal salt needed for effective treatment. Therefore, to ensure that treatment plants are meeting phosphorus limits without wasting chemicals, the analytical methods for phosphorus must be optimized to measure trace levels of phosphate.
Researchers recently introduced a surface complexation model (SCM) to describe the phosphorus removal process using iron (Fe[III]; see Water Environment Research, 80[5], pp. 407–416 and 428–438). This chemical equilibrium-based model is supported with laboratory data where simple abiotic samples containing phosphorus and iron are mixed for different amounts of time, filtered, and then colorimetrically analyzed for residual phosphate. These data indicate that SCM methods could model chemical phosphorus removal but include a lot of “noise” — probably because the standard colorimetric method for phosphorus determination has not been optimized for low-level analysis. So, researchers set out to optimize it.
NEWS
U.S. EPA Works To Ally Labs Nationwide
For several years, the U.S. Environmental Protection Agency (EPA) has been working to create a nationwide network of water laboratories with analytical capabilities to detect, assess, and respond to the intentional or accidental contamination of the drinking water supply. The result of that work is the burgeoning Water Laboratory Alliance (WLA).
Negotiating Alternative Testing Procedures
On June 3, the U.S. Environmental Protection Agency (EPA) announced the first use of its expedited approval process for alternative testing methods for Safe Drinking Water Act reporting.
Following the 1996 amendments to the act, EPA has been able to expedite the approval of analytical methods by publishing them in the Federal Register instead of using a formal rulemaking process. The agency issued a notice of its intent to use this power in April 2007 (72 FR 17902) but did not exercise it until now.
On the Clean Water Act (CWA) side of things, no such expedited method-approval process exists. The agency must use a formal rulemaking process to add methods to the list of approved CWA methods at 40 CFR 136. However, EPA’s Alternative Test Procedures (ATPs) allow site-specific use of more updated methods.
DEPARTMENTS
Web Notes
Reprints questions, and answers from WEF’s laboratory discussion boards.
Briefs
U.S. EPA Continues Work To Understand Potential Impacts of Pharmaceuticals in Water; Groups Ask U.S. EPA To Ban Nonmedical Triclosan Use; Marine Scientists Report Record-Size Dead Zone in Gulf of Mexico; New, Interactive Training Courses Available Online; and more.
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Click here to download
a PDF of the color images from the article "Size Doesn’t Matter"from the April-May 2008 issue. |
©2008 Water Environment Federation. All rights reserved. |
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