How can adding peroxide upstream increase my influent BOD5? Why BOD5 vs BOD20 is key to understanding the phenomenon.
Wastewater contains a blend of many organic and inorganics compounds. In operating a treatment facility, we look at the oxygen demand from the pollutants. Wastewater oxygen demand can be estimated by tests such as BOD5, BOD20, COD, and TOC. The oldest tests are the microbial based BOD5 and BOD20. In these tests, a diluted sample of the influent is allowed to react with a microbial seed @ 20 Deg C for either 5 or 20 days. During this time, the microbes consume oxygen while digesting organics in the influent. Compounds that are not readily biodegradable or soluble are not fully consumed in the 5 day test. While the 20 day test will pick up more of the long run oxygen demand from insoluble compounds such as cellulose, long chain fatty acids, and grease. Always remember, COD > BOD20 > BOD5.
Now back to the case of hydrogen peroxide being used in a process upstream from the plant. While peroxide can be used to decrease BOD/COD by directly oxidizing the organics, in lower doses it can also increase the proportion of soluble vs insoluble organics. The peroxide reacts indiscriminately with the organics in solution. As a result, some of the recalcitrant and insoluble compounds become more bioavailable (or soluble). If there is not enough peroxide to actually fully oxidize the organics - you end up with higher levels of soluble organics that will show up in a BOD5 test. To see if this phenomenon is occurring in your system, you can check the waste stream with and without peroxide addition. You an also look at COD, filtered COD, and BOD20 - if these are relatively unchanged, it means BOD5 was impacted by increased organic bioavailability.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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