Technical Bulletin No. 0099: The Oxygen Demand of Strawboard Sludge Deposits
The attached Technical Bulletin is the ninth report on the Council's strawboard research directed by Professor D. E. Bloodgood at Purdue University. While dealing with the oxygen demand of benthal deposits caused by the settleable solids present in strawboard waste, the results are of more general interest in that similar deposits of cellulosic residues can act in a parallel manner. From the experimental work, it was obvious that the demand of such deposits is not uniformly exerted and that their oxygen demand is exerted over a considerably longer period than the five day interval measured by the BOD test. On the basis of this test only 10% of the oxygen demand is removed from raw strawboard waste by removal of settleable solids. However, for the reasons indicated above, this percentage may amount to as much as 50% when deposited in a stream bed on the basis of actual demand exerted. Hence, in instances where benthal deposits exist below mill outfalls, their removal together with settling of the mill effluent before discharge, can lead to a much greater improvement in stream oxygen levels than that reflected by settling performance test data. This observation indicates more strongly than ever how detrimental settleable material can be to surface waters and how frequently a larger degree of stream improvement can be affected by its removal from the effluent prior to discharge.