Date of Award
Bachelor of Science
BOD and COD are two very important and highly regulated aspects of the paper industry. The first is the biochemical oxygen demand, BOD, and it is simply the amount of oxygen that bacteria need to digest the nutrients in a wastestream. The second is the chemical oxygen demand, COD, and is the amount of oxygen required to fully oxidize all the material present in an effluent sample using hot concentrated chemicals.
One aspect of recycling that has not been discerned is the effect of repeatedly recycling paper fibers on the BOD and COD of the effluent. This is important because the government, and the general public, are forcing higher and higher levels of recycle in a furnish. If a fiber exerts a higher BOD or COD as it is recycled than a virgin fiber, the resulting effluent will be naturally higher in BOD and COD. This in itself would not be very important of the EPA were not lowering the BOD and COD effluent limits as the years go by. Therefore, an effluent that may be naturally higher in BOD and COD will be regulated down to an even lower limit. This costs a significant amount of money to reach these new goals.
Virgin Kraft Softwood was repeatedly recycled in a loop consisting of slurrying the pulp to a target freeness, draining the pulp on a screen and catching the effluent, testing the effluent for BOD and COD, pressing the fiber web, and drying the web. The dried fibers were· then run through the same loop. This process was completed six times. From this BOD and COD data was collected.
Many problems occurred with the BOD and many of the data points were faulty. The COD fared better, and a discernible trend was observed. The BOD and COD went down as the number of recycles increased. This could be due to residual chemicals and the easy to break off fiber chunks getting washed away in the first few recycles. Many of the problems related to the DO meters. The first DO meter broke and was not able to be repaired. The second gave varied readings and was very difficult to calibrate. The last problem was contamination of starch from felt pressing pad. This caused a possible increase in the BOD and COD loading from that contaminant.
Closing of the recycle loop would give a baseline reading for the BOD and COD due to keeping the chemicals and the fines in the loop. A good dependable DO meter would solve the dissolved oxygen problem.
Stager, Ken, "BOD and COD Loading Effects of Repeatedly Recycled Paper Fibers" (1996). Paper Engineering Senior Theses. 512.