Contribution of Thiosulfate to Chemical and Biochemical Oxygen Demand in Oil Shale Process Wastewater

Abstract

Thiosulfate accounted for a significant portion of the chemical oxygen demand (COD) (7 to 20 percent) and the biochemical oxygen demand (BOD) (14 to 41 percent) of the four oil shale process waters studied. Accurate measurement of the thiosulfate oxygen demand of retort water is critical in assessing its environmental impacts on receiving waters and in designing biological treatment systems to treat it. The contribution of thiosulfate to the COD of oil shale retort waters can be accurately measured in a standard COD test. The BOD of thiosulfate in retort water is more difficult to determine and may require the development of a special thiosulfate-acclimated seed. Thiosulfate recovery of a known thiosulfate spike ranged from 92 to 100 percent in the COD test and from 54 to 119 percent in the BOD test. Considerable variability in recovery was found between the process waters studied. When determining the BOD of oil shale process waters, care must be taken to insure that there is a viable population of thiosulfate-oxidizing bacteria.

Comparison of the microcolorimetric and macrotitrimetric methods for chemical oxygen demand of oil shale wastewaters

“…This sample matrix is particularly challenging because the process wastewaters presently available from pilot-scale facilities are highly contaminated with a complex spectrum of inorganic and organic solutes (6)(7)(8) and some are extremely turbid. Process waters can contain thiosulfate, chloride, and ammonia; up to 20% of the COD for one retort water was reportedly contributed by thiosulfate (9). Much of the characteristic organoleptic properties of these waters are contributed by nitrogen and oxygen heterocycles, compounds whose potential oxygen demands can only be partially accounted for by the COD test because of their resistance to acidic dichromate digestion (1, 2, [10][11][12].…”