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Effect of dissolved oxygen concentration on the aerobic stabilization of swine waste Husdon, John Thomas Ross

Abstract

A series of batch tests were conducted to evaluate the effect of dissolved oxygen concentration on the aerobic stabilization of swine waste. The batch tests were conducted over a 14 day period and the effect of oxygen concentration was measured by changes in Chemical Oxygen Demand (COD) of the waste. Three, five litre capacity, digesters were used and were held at the following dissolved oxygen concentrations; high O₂ level (15-20 mg/1), medium O₂ level (5-8 mg/1) and low O₂ level (.5- 2 mg/1). The reduction in COD of the waste at the end of one week of oxidation was 48.7% for the high O₂ level, 35.3% for the medium O₂ level and 15.6% for the low O₂ level. The reduction in COD at the end of 14 days of oxidation was 57.8%, 50.7% and 38.9% respectively for the three levels of oxygen. The addition of one litre of aerated swine waste to four litres of the raw swine waste did not appreciably alter the reduction in COD noted in the above tests. The reduction in COD for this batch test was 60.9 for the high O₂ level, 34.6 for the medium O₂ level, and 31.1 for the low O₂ level. In this test all three levels of dissolved oxygen removed approximately the same percentage of filtered COD during the first two days of oxidation. In the high and medium O₂ level digesters this was accompanied by a reduction in total COD. A similar reduction in total COD did not occur at the low O₂ level. Correlations were made with the COD determination and determinations for Total Organic Carbon. These correlations were very high (regression coefficient = .93) when the sample was prepared using a mechanized tissue grinder. Grinding the sample resulted in a higher value for total organic carbon as well as an increase in precision.

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