Fig. 2

Effects of HRT and pH on oxidation–reduction potential (ORP) (a, d), total organic carbon (TOC)/sulfate concentrations (b, e), and low-molecular-weight organic substrate concentrations (c, f) at each depth of the bioreactor under the neutral (a–c) and acid (d–f) conditions. Symbols ORP, saltires; TOC, gray circles; sulfate, open circles; acetate, gray squares; propionate, open squares; butyrate, closed squares; glucose, open triangles; ethanol, gray triangles