Structuring your company around safe environmental practices is becoming a necessity
The waste you release into your sewer system can have an impact on local water quality as well as your operating costs. By looking into alternate chemistries for screenmaking and screen reclaiming, adopting sound procedures, and employing quality equipment, you’ll bring sustainability to the screen room and achieve higher quality with less regulatory scrutiny.
COD and BOD Testing
Chemical oxygen demand (COD):
The organic (carbon-based) material going down the drain is all going to be rendered harmless by using oxygen. This is either by direct chemical oxidation to carbon dioxide, water and byproducts, or by bacteria eating the chemicals. The bacteria are aerobic, meaning they need oxygen to do their work. The amount of oxygen needed relates to the amount of material in the effluent they must consume. COD measures how much carbon is in the water, which is a measure of the maximum amount of solvent that could, in principle, be eaten by the bacteria. Testing for COD takes approximately two hours.
Principle of COD testing: Use a chemical that reacts strongly with organic chemicals in water and changes color on reaction.
Practice: React your water sample at 148ºC for two hours with a known amount of the strong oxidizing agent potassium dichromate in sulphuric acid with silver sulphate as the catalyst. Measure the color of the resulting solution at 585 nm—the higher the value, the more potassium dichromate has been consumed by the COD. This is all done using a standardized reagent kit and a spectrometer.
Biological Oxygen Demand (BOD):
This indirectly measures how much oxygen gets consumed by a representative sample of bacteria.
Principle of BOD testing: Allow the bacteria to eat the organic chemicals in your waste water, consuming oxygen and producing carbon dioxide. Measure the amount of carbon dioxide produced.
Practice: Put a known cocktail of bacteria into your waste water sample at 20ºC, and seal the vessel along with a pellet of sodium hydroxide. Over five days the carbon dioxide produced by the bugs is absorbed by the pellet, creating a vacuum. Measure the vacuum with a manometer to calculate BOD.
Examples taken from King County (Seattle), WA and Clearwater, FL publicly owned treatment works.
Neil Bolding is MacDermid Autotype’s business-support manager. He is a 25-year veteran of the printing industry with experience in quality control and technical customer support. He has written articles for a variety of trade publications, spoken at numerous industry events, and regularly contributes to SGIA training programs. He currently sits on the SGIA’s Environmental Committee and the Membrane Switch Council. In 1994 he was the industry co-chair (product testing subcommittee) for the US EPA’s Design for the Environment Program. Bolding also is a member of the Academy of Screen Printing Technology.
Professor Steve Abbott is technical and research director at MacDermid Autotype, Wantage, England. After receiving a PhD in chemistry at Oxford for work he carried out at Harvard and serving in a post-doctoral position in Strasbourg, he went to work at ICI on new product development. In his role as research & technical director of MacDermid Autotype, Ab-bott has been responsible for ensuring a constant stream of new products and also for providing the science behind the coating and printing techniques used. He frequently collaborates with researchers at the University of Leeds, where he serves as a visiting professor, and is a frequent speaker at international conferences related to coating and printing. Abbott is a recipient of the Swormstedt award for technical writing from the Specialty Graphic Imaging Association.
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