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Servo Controlled Optimization of Nitrification—Denitrification of Waste Water in Soil¹

ABSTRACT

Based on potentials of platinum electrodes in conjunction with a Calomel reference electrode, a servo controller was used to meter trickling filter secondary waste water application to soil columns. The controller "optimized" denitrification by adjusting both the frequency of application as a function of the potential voltage observed 6 cm below the soil surface, and the duration of each application as a function of the potential 30 cm below the surface, of four Chigley gravelly loam soil columns. Digested municipal waste water sludge was added to three of the four columns at a rate of 7.5 metric tons(carbon)/ha in an upper 30-cm layer of the profile. The servo controller applying waste water to the column with no sludge requested waste water continuously. This column converted essentially all TKN-N to NO₃-N. The conversion of TKN to NO₃ took place in the upper 3 cm of the profile. Under the experimental conditions, the disappearance of solution N in the column without sludge was about 45%. Addition of sludge to the profile increased the apparent denitrification, such that the total N removal was > 90%.

Key Words: redox potential • sludge-amended soils • rapid infiltration • soil columns • platinum black electrodes

¹ Contribution of the Off. of Res. and Devel., U. S. Environ. Prot. Agency.

² Soil Scientist, Wastewater Manage. Branch, Robert S. Kerr Environ. Res. Lab., Ada, OK 74820.

Received for publication March 14, 1977.