The purpose of this investigation was to use the manometric method to determine the effect of the following variables on the B.O.D. values of a neutralized acid industrial waste: pH, type of seed, age of seed, adapted seed, dilution water, and dilution. In order to determine the effect of each variable on the B.O.D. of the waste, the temperature and agitation of the Warburg apparatus were kept at fixed values. While the optimum condition for one variable was being determined, the remaining factors were kept constant. As the optimum condition of each variable was found, it was used as a reaction constant, and this process was continued until the list of variable factors was completed.

Since only a limited number of tests were run for each variable, no definite conclusions can be drawn. However, the following trends were indicated from the data obtained: A pH of 4.1 depressed the B.O.D. values and they were exerted only after long lag periods; the waste exerted a higher B.O.D. with much shorter lag periods when the pH was raised to 7.1. River water seed caused the waste to exert higher B.O.D. values than did garden soil seed, fresh sewage seed, and settled sewage seed. This indicated that the river water contained a microbiological population adapted to the utilization of the waste under study. The age of seed made little difference in the B.O.D. values exerted for the seeds studied. The waste gave higher B.O.D. values when adapted seeds of river water, adapted soil seed, end activated sludge were used than when regular garden soil seed was used. It is believed that the bacterial organisms in the river water below the waste outfall had become adapted to the waste material. The presence of mineral nutrients as found in river water or the addition of mineral nutrients as recommended by Standard Methods for the Examination of Water and Sewage (1) are necessary for the waste to exert a normal B.O.D. The presence of a substance toxic to the B.0.D. test is indicated because the B.0.D. values increased with increasing dilution.

The bottle B.O.D. values, obtained from another investigator, were not given for all of the tests; therefore, no conclusions were drawn except that the bottle B.O.D. values vere in the same general range as the corresponding manometric B.O.D. values.