Analytical Products for Water & Wastewater Analysis

Water/Wastewater

Rapid COD tests predict treatment plant upsets

Jun 08 2009

A fast chemical oxygen demand (COD) test can predict potential municipal wastewater treatment plant upsets before they occur, according to researchers at Bioscience (USA). The rapid, mercury-free method is intended for testing influent streams when reporting is not required. The Bioscience test measures organic and inorganic compounds that can be easily oxidized.

High COD found in the influent can signal an abnormal event such as slug loading of BOD or industrial discharge. High COD in the effluent may indicate that a toxic chemical is inhibiting or killing the biomass, or that a non-biodegradable compound is passing through the plant. As a rough prediction for domestic wastewater, COD is generally about 2.5 times the five-day BOD. A standard Bioscience COD test takes two hours for a sample to digest. The quick variation for upset prediction shortens the digestion time to as little as 15 minutes. Substituting a mercury-free reagent allows for simpler and cheaper disposal but should not be used when chloride concentrations may exceed the COD. Shortened digestion time typically results in COD readings 5 to 15 percent lower than those using standard methods. Tests with varying digestion times should be used to confirm that the results are within acceptable accuracy for a particular wastewater. Instead of the standard spectrophotometer, the rapid test utilizes a microprocessor-based colorimeter which allows appropriate built-in light filter to match one of the 70 pre-programmed test parameters or up to 20 user-programmed methods. The rapid reading system uses the same twist-tubes as Biosciences’ EPA-approved accu-TEST COD method. The colorimeter can also be used with a wide variety or pre-measured reagents to identify quantities of nutrients (nitrogen and phosphorous salts) or specific toxic or inhibitory compounds in a waste stream.