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ABSTRACT: A study of the anaerobic digestion of wastewater derived from the production of protein isolates from chickpea flour was carried out in a laboratory-scale, mesophilic (35 °C) fluidised-bed reactor with saponite as bacterial support. Soluble chemical oxygen demand (SCOD) removal efficiencies in the range of 96.8–85.2% were achieved in the reactor at organic loading rates (OLR) of between 0.58 and 2.10 g chemical oxygen demand (COD)/l per day, hydraulic retention times (HRT) of between 14.9 and 4.5 days and average feed COD concentration of 9.1 g/l. Eighty-five percent of feed COD could be removed up to OLR of 2.1 g COD/l per day. The yield coefficient of methane production was 0.34 l of methane (at STP) per gram COD removed and was virtually independent of the OLR applied. Because the buffering capacity of the experimental system was maintained at favourable levels with excess total alkalinity present at all loadings, the rate of methanogenesis was not affected by loading. Experimental data indicated that a total alkalinity in the range of 1090–2130 mg/l as CaCO3 was sufficient to prevent the pH from decreasing to below 7.2 for OLR of up to 2.7 g COD/l per day. The volatile fatty acid (VFA) levels and the VFA/alkalinity ratio were lower than the suggested limits for digester failure (0.3–0.4) for OLR and HRT up to 2.7 g COD/l per day and 3.5 days, respectively. For a HRT of 2.8 days (OLR of 3.00 g COD/l per day) the start of acidification was observed in the reactor.
Process Biochemistry.
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ABSTRACT: A comparative kinetic study of the anaerobic digestion of vinasse and vinasse following a 2 h treatment with ozone, ozone plus UV light or ozone plus UV light in the presence of titanium dioxide was carried out. All pretreatments decreased both chemical oxygen demand (COD) and total organic content (TOC). Those using no catalyst failed to improve the specific rate of methane production during anaerobic digestion but succeeded in increasing the yield coefficient (YP/S, in ml CH4/mg TOC). Finally, the pretreatment using ozone, UV light and titanium dioxide decreased COD and TOC, and increased the yield coefficient and also the mean specific rate of anaerobic digestion (by 25%) relative to untreated vinasse.
Process Biochemistry. 37(7):699-706.
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ABSTRACT: A study of the kinetics of the anaerobic digestion process of wastewater derived from the production of protein isolates from extracted sunflower flour was carried out in a laboratory-scale fluidised bed reactor with saponite as support for the mediating bacteria at mesophilic temperature (35°C). The reactor operated satisfactorily between hydraulic retention times (HRT) of 1.1 to 20.0 days, removing between 98.3 and 80.0% of the initial chemical oxygen demand (COD). Macroenergetic parameters, calculated using Guiot's kinetic model, gave a yield coefficient for the biomass (Y) of 0.075 g VSS/g COD and a specific rate of substrate uptake for cell maintenance (m) of 0.021 g COD/g VSS day. The experimental results also showed the rate of substrate uptake, Rs (g COD/g VSS day) correlated with the concentration of biodegradable substrate, S (g COD/l), through an equation of the Michaelis-Menten type. This proposed model predicted the behaviour of the reactor very accurately showing deviations lower than 10% between the experimental and theoretical values of substrate uptake rates.
Process Biochemistry.
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ABSTRACT: A study of the effect of substrate concentration and temperature variation on batch anaerobic digestion of piggery waste was carried out in laboratory-scale completely mixed reactors. The variation of chemical oxygen demand (COD), total volatile fatty acids (TVFA), alkalinity, pH and methane production with digestion time followed the same pattern at mesophilic (35 °C) and ambient temperatures (16.8–29.5 °C). The process was more stable at mesophilic than at ambient temperatures. The rate of COD removal correlated with the digestion time through an equation of the Grau kinetic model type. An increase in the initial concentration of organic matter caused a reduction of COD removal rate. In addition, COD removal rates at ambient temperatures were significantly lower than those obtained at mesophilic temperature.
Process Biochemistry.
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ABSTRACT: A kinetic study of the anaerobic biodegradation of two-phase olive pomace (TPOP) was carried out using a laboratory-scale stirred tank reactor. The reactor was operated at 35°C. The influent contained between 20% and 100% TPOP, representing in terms of total chemical oxygen demand (TCOD) 34.5–. The hydraulic retention times (HRTs) were set between 40.0 and . It was found that the increase of influent substrate concentration favoured the process failure reducing the pH and increasing the ratio of the total volatile fatty acid (TVFA) to alkalinity. This ratio was found to be proportional to the substrate concentration (S), as follows: TVFA/alkalinity=0.04(S). The kinetic model of Andrews was used to describe the relation between anaerobic biodegradation of TCOD and Volatile Solids (VS) and the formation of methane. The values of the kinetic constants for TCOD removal were determined to be , and , respectively, for maximum substrate utilization rates (RSmax), saturation constant (KS) and inhibition constant (Ki). Process inhibition started at substrate concentrations of around . For VS biodegradation the kinetic constant values, RSmax, KS and Ki, were , 37 and , respectively. Inhibition started at VS concentration of around . The rates of TCOD removal were lower than those observed for VS removal and inhibition of VS removal occurred at a lower concentration compared to that for TCOD. The QM(max), KS and Ki constants for methane production were approximately , and , respectively. Inhibition of methane formation started at a substrate concentration of around . TCOD and VS removal rates were higher than the rate of methane formation and these differences increased when the substrate concentration increased. This fact was underlined by the decrease of pH, the increase of TVFA/alkalinity ratio and the reduction of methane production rate.
International Biodeterioration & Biodegradation.
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ABSTRACT: A study of the effect of hydraulic retention time (HRT) on the anaerobic acidogenic fermentation of two-phase olive pomace (TPOP) was carried out at laboratory-scale and mesophilic temperature (35 °C). The experimental results obtained demonstrated that the optimum value of HRT for the acidogenic fermentation process was 12 days, for which a maximum production of total volatile fatty acids (TVFA) and, specifically, of acetic and butyric acids were obtained. It was found that a multicomponent substrate removal kinetics model adjusted very well to the experimental data obtained. A second-order kinetic model was used for the degradation of non-soluble COD whilst a first-order model was appropriate for studying both the total and soluble COD reduction. The values of the kinetic constants obtained were: 0.29, 0.29 and 0.12 g COD/g VSS per day for non-soluble, total and soluble COD degradation, respectively. A similar model was used to determine the kinetic constants for product formation, obtaining values of: 0.0007, 0.0024, 0.0022, 0.0031 and 0.0022 g COD per litre per day for acetic, propionic, butyric, valeric+caproic and TVFA, respectively. The order of the reaction of volatile fatty acids production was determined in each case, the values being in the range of 1.7–2.4, values very close to second-order. The value of the apparent kinetic constant was minimum for acetic acid formation (0.0009 g COD per litre per day) and maximum for valeric+caproic acids (0.0031 g COD per litre per day) because in the hydrolysis process of complex organic matter, long chain fatty acids appear first and faster than acetic acid. The kinetic model used was validated by comparing the theoretical and experimental values of the product formation rate (RP). The small deviations obtained (in the range between 1.0 and 20.8%) suggest that the proposed model predicts the kinetics of volatile acids production accurately.
Process Biochemistry.
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ABSTRACT: The effect of influent substrate concentration on the performance of down-flow anaerobic fixed bed reactors (AFBR) treating piggery wastewater was studied at hydraulic retention times (HRTs) in the range of 1–6 days at tropical temperatures (24.2–30.5 °C). Six down-flow anaerobic fixed bed reactors of 6-l total volume and 5-l effective volume operated in parallel at influent strengths of 2, 4, 6, 8, 10 and 12 g total COD (TCOD) l−1. The highest substrate removal efficiencies were obtained in reactors that operated at influent strengths in the range of 4–8 g TCOD l−1 at HRTs of 1 and 2 days. At higher influent strengths, the efficiency of the process deteriorated. The removal rates of TCOD, soluble chemical oxygen demand (SCOD), biological oxygen demand (BOD) and total suspended solids (TSS) were increased with the influent strength up to 8 g TCOD l−1, decreasing further for higher influent substrate concentrations. In addition, the concentration of microorganisms within the reactors increased with the influent strength. The results obtained demonstrated that the substrate removal rate was correlated with the effluent substrate concentration through a second-order kinetic model for multicomponent substrate degradation. The values of the kinetic constants obtained increased with the influent strength and were found to be 0.59, 0.83, 0.88, 1.09, 1.17 and 1.26 g TCOD g−1 volatile suspended solids (VSS) per day for influent strengths of 2, 4, 6, 8, 10 and 12 g TCOD l−1, respectively, for a probability level of 95% (P≤0.05).
Process Biochemistry.
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ABSTRACT: A study of the anaerobic digestibility of two-phases olive mill solid waste (OMSW) was carried out in a laboratory-scale completely stirred tank reactor at mesophilic temperature (35 °C). The reactor was operated at influent substrate concentrations of 34.5 g COD/l (OMSW 20%), 81.1 g COD/l (OMSW 40%), 113.1 g COD/l (OMSW 60%) and 150.3 g COD/l (OMSW 80%). The hydraulic retention time (HRT) varied between 40.0 and 8.3 days for the first feed used (OMSW 20%) and between 50 and 10 days for the other three influent substrate concentrations. Chemical oxygen demand (COD) and volatile solids (VS) removal efficiencies of 88.4 and 90.9%, respectively, were achieved at an organic loading rate (OLR) of 12.02 g COD/l day for the most concentrated substrate used (OMSW 80%). The maximum methane production rate was found to be 2.12 l CH4/l day for the above-mentioned OLR and a HRT of 12.5 days. The system can tolerate OLRs as high as 15.03 g COD/l day with COD and VS removal efficiencies of 82.9 and 86.6%, respectively, for this feed concentration. The methane yield coefficients were 0.30, 0.27, 0.23 and 0.20 l methane STP/g COD removed for the OMSW concentrations of 20, 40, 60 and 80%, respectively.
Process Biochemistry.
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ABSTRACT: A kinetic study of the anaerobic digestion of two-phase olive mill solid waste (OMSW) was carried out in a laboratory-scale completely stirred tank reactor at mesophilic temperature (35 °C). The reactor was operated at three different feed substrate concentrations: 34.5, 81.1 and 113.1 g COD/l. The hydraulic retention time (HRT) varied between 40.0 and 8.3 days for the first feed used and between 50 and 10 days for the other two feed substrate concentrations. The results were evaluated using the Chen–Hashimoto methane production model to determine the kinetic constants of the process. The kinetic constants (μmax and K) were affected by the feed substrate concentration and decreased by 63 and 65%, respectively, when the feed concentration increased from 34.5 to 113.1 g COD/l. This behaviour is believed to be due to the higher levels of phenolic compounds and biotoxicity present in the most concentrated substrate used. Methane production was reproducible within 10% deviations.
Biochemical Engineering Journal.
