Water/Wastewater
Biodegradability Test with Laboratory Wastewater Treatment Plants
Place: Somewhere Date: Any Occasion: Joyful!
A new symbol of technological progress and economic growth is complete. Many were invited to the opening ceremony; everyone came.
12:00. With the touch of a button and a flourish, the Minister of Economics opens the new production plant. In his official speech, he once again stresses the importance of the new product line for the safeguarding of the business location: Jobs, tax revenue, prosperity...
Then the guests of honour proceed to the enjoyable part.
13:14. The aroma of the festive meal is assaulted by a penetrating putrefactive note. The wastewater from the new plant has caused the city’s wastewater treatment plant to collapse. Citizens phone the town hall in alarm. Instead of higher tax revenues, there is the threat of fines for exceeding the discharge limits...
With biodegradability tests this would not have happened
Before wastewater can be led back to a body of water, it has to be cleaned - normally in a biological wastewater treatment plant. But is it even possible to clean it biologically? To determine this in advance, biodegradability tests are carried out in laboratory wastewater treatment plants.
Why biodegradability tests?
In a biological wastewater treatment plant, the bacteria of the sewage sludge ‘devour’ the organic wastewater components. They use part of this for their own energy needs; the organic compounds are degraded to carbon dioxide and water. They change part into their own body substance, to grow and reproduce; this creates excess sludge from which biogas is extracted in digestion tanks.
But not all organic compounds are biodegradable. Compounds that are not degraded by bacteria would end up in the water unchanged. Residuals of medicines, organic fluorine impregnating chemicals and other chemicals in rivers and even drinking water have made the headlines again and again.
Not only that: some compounds are toxic to the bacteria in the wastewater treatment plant. They prevent even compounds that are actually biodegradable from being removed from the wastewater.
Author Details: Gerhard Pauli
Behr Labor-Technik GmbH Spangerstraße 8 D-40599 Düsseldorf Tel: +49-211-7 48 47 53
Email:
g.pauli@
behr-labor.com
With biodegradability tests, one can make a prediction about this. Biodegradability tests can be required
• to test new chemicals or preparations before they go on the market (REACH process),
• to determine whether the wastewater of a company is leading to problems
• to determine whether the activated sludge of a wastewater treatment plant is breaking
www.envirotech-online.com IET November / December 2012
down certain wastewater components correctly - for example such medications as antibiotics, or hormones, cosmetics and household chemicals.
Biodegradability test: how does it work?
Tests on biodegradability are described, for example, in ISO 11733 (2004)1
.
For the testing of the biodegradability of a substance or preparation, one usually proceeds on the basis of an artificial wastewater that is comprised according to the specifications of the standard of biologically easily degradable substances and the nutrients necessary for the bacteria (for example, ammonia, phosphate and others). For the biodegradability test, this artificial wastewater is added to the substance to be tested.
The water from the collection tank is regularly - for example, daily - taken and analysed. It is studied in terms of TOC (total organic carbon) and/or COD (chemical oxygen demand), and depending on the situation
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