Aerobic degradation kinetic of the effluent derived from the anaerobic digestion of two-phase olive mill solid residue

Sánchez, E., Rincón, B., Borja, R, Travieso, L., Raposo, F. and Colmenarejo, M.F. (2007) Aerobic degradation kinetic of the effluent derived from the anaerobic digestion of two-phase olive mill solid residue. International Biodeterioration & Biodegradation, 60 (1), 60-67. (doi:10.1016/j.ibiod.2006.10.002).

Abstract

Aerobic biodegradability of the effluent derived from the anaerobic digestion of two-phase olive mill solid residue was assessed in laboratory-scale batch reactors of 1.5–l volume. Five experimental runs at influent substrate concentrations in the range of 660–13100 mg COD l?1 were carried out at a ratio of substrate-to-microorganisms concentration S0/X0 equal to unity. Chemical oxygen demand (COD), soluble chemical oxygen demand (SCOD), volatile suspended solids of the mixed liquor (MLVSS), pH, dissolved oxygen, saturation percentage (% sat.) and temperature were determined during the experiments. An increase in the influent substrate concentration caused a decrease in COD and SCOD removals at similar times of aeration ?. The non-biodegradable fractions of COD and SCOD were determined to be 43.1% and 53.1% of their initial values, respectively. It was found that a first-order kinetics adequately described the variation of biodegradable SCOD with ?. The values of the first-order reaction constants were found to be 0.074, 0.044, 0.040, 0.033, and 0.013 h?1 (1.776, 1.056, 0.960, 0.792, and 0.312 d?1) for Runs 1–5, respectively, with variance coefficients lower than 10% in all cases. During the experiments the growth of microorganisms appeared to be in the exponential phase. Hence, first-order reactions were assumed to describe the increase in MLVSS concentration with ?. The values of the specific growth rate ? were determined to be: 0.0064, 0.0075, 0.0084, 0.0091, and 0.0038 h?1 (0.154, 0.180, 0.202, 0.218, and 0.091 d?1) for initial substrate concentrations of 660 (Run 1), 1400 (Run 2), 2600 (Run 3), 6600 (Run 4), and 13100 (Run 5) mg COD l?1, respectively. Finally, the values of the maximum specific growth rate ?M and the saturation constant KS of the Monod equation with their standard deviations (p<0.05) were determined to be 0.23±0.01 d?1 and 160±8 mg SCOD l?1, respectively.

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