Anaerobic columnar denitrification of high nitrate wastewater

Anaerobic columns were used to test the effectiveness of biological denitrification of nitrate solutions ranging in concentration from 1 to 10 kg NO3/m3. Several sources of nitrate (Ca(CNO3)2, NaNO3, NH4NO3, and actual nitrate wastes from a UO2 fuel fabrication plant) were evaluated as well as two packing media. The packing media were anthracite coal particles, whose effective diameter size ranged between 2 and 3 mm, and polypropylene Raschig rings 1.6 x 1.6 diameter. The anthracite coal proved to be the better packing media as excessive hydraulic short circuiting occurred in a 120 x 15 cm diameter glass column packed with the polypropylene rings after 40 days operation. With anthracite coal, floatation of the bed occurred at flow rates greater than 0.80 cm3/s. Tapered columns packed with anthracite coal eliminated the floatation problem, even at flow rates as high as 5 cm3/s. Under optimum operating conditions the anthracite coal behaved as a fluidized bed. Maximum denitrification rates were 1.0--1.4 g NO3/m3/s based on initial bed volume. Denitrification kinetics indicated that rates of denitrification became substrate inhibited at nitrate concentrations greater than 6.5 kg NO3/m3 Anaerobic columns packed with anthracite coal appear to be an effective method of nitrate disposal for nitrate rich wastewater generated at UO2 fuel fabrication plants and fuel reprocessing facilities. (U.S.)