Ultimate Oxygen Demand-An Alternative Method for Testing Oxygen Demand
in a Sewage Treatment Facility


Mary Beth Bishop
Environmental Studies
University of Montana


    In 1986 the Missoula Wastewater Treatment Facility requested a permit change from the biological oxygen demand (BOD) test to the carbonaceous biological oxygen demand (CBOD) test. The permit change request is based on an EP A evaluation which stated that BOD may not be a suitable test because the nitrogenous oxygen demand is expressed in the effluent but not in the influent testing. However, nitrogenous oxygen demand is ignored in the CBOD test and nitrogen loading could be allowed to increase if no limits are placed on nitrogen loading. The Clark Fork already has a problem with algae and an increase in ammonia may increase the secondary oxygen demand reducing the water quality in this section of the Clark Fork River.

    The ultimate oxygen demand (UOD) is proposed as a better means of assessing the percent removal of both the carbonaceous and nitrogenous oxygen dem3lld in the effluent. The UOD can be easily calculated for both the influent and effluent waters using the amount of org3ltic carbon and nitrogen in the wastewater.