ANAEROBIC DEGRADATION OF COMPLEX SUBSTRATES IN

M. FUENTES; C. THOMPSON; M. MUSSATI; P.A. AGUIRRE; N.J. SCENNA

RIo de Janeiro

Congreso; 2nd Mercosur Congress on Chemical Engineering. 4th Mercosur Congress on Process Systems Engineering; 2005

UFRJ

A study of the anaerobic digestion of synthetic complex substrates, containing carbohydrates and proteins, was carried out in two lab-scale, mesophilic fluidized-bed reactors, using sand as inert support for biofilm attachment. After start-up using a soluble substrate based on glucose and acetate, particulate substrates were fed to bioreactors. One reactor was fed with a mixture of sucrose and albumin (RAS), and a second reactor with sucrose and gelatin (RGS). Ninety-six percent of the chemical oxygen demand (COD) was removed up to 4 g COD L-1 d-1 of organic loading rate (OLR) for both reactors. A methane yield coefficient of 0.31 L CH4 per gram of COD removed was obtained, regardless the OLR applied. Experimental data indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. of 0.31 L CH4 per gram of COD removed was obtained, regardless the OLR applied. Experimental data indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. of 0.31 L CH4 per gram of COD removed was obtained, regardless the OLR applied. Experimental data indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. removed up to 4 g COD L-1 d-1 of organic loading rate (OLR) for both reactors. A methane yield coefficient of 0.31 L CH4 per gram of COD removed was obtained, regardless the OLR applied. Experimental data indicated that a concentration of 2.43 g L-1 as NaHCO3 in the feed stream was sufficient to prevent a pH decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. decrease below 6.6 for OLRs up to 6.24 and 4.16 g COD L-1 d-1 for RAS and RGS, respectively. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. fatty acid (VFA) levels and the VFA/alkalinity ratios were lower than the suggested limits for digester failure. At the operating conditions experienced, hydraulic retention times (HRTs) higher than 1 day are suggested to ensure a good system efficiency. The high performance may be attributable to the adequate bioreactor start-up procedure to minimize the undesirable wash-out of slow-growing methanogenic microorganisms. indicated that a concentration of 2.43 g L-1 as NaHCO3