FIG 4.

Effect of nitrate (0, 2, 4, 6, 8, or 13 mM) on souring in an up-flow, packed-bed bioreactor injected with CSBA medium with 2 mM sulfate and electron donors as follows: stages I to V, 3 mM (each) acetate, propionate, and butyrate; stages VI to IX, 3 mM acetate and 3 mM propionate; stages X to XIII, 3 mM propionate. The concentrations of sulfate, sulfide, nitrate, nitrite, acetate, propionate, and butyrate in the effluent are shown as a function of time. The numbered arrows indicate sampling for DNA isolation. (Top) S-species. (Bottom) VFA.