Influence of Organic Load on Biohydrogen Production in an AnSBBR Treating Glucose-Based Wastewater.

An anaerobic sequencing batch reactor with immobilized biomass (AnSBBR) was applied to the production of biohydrogen treating a glucose-based wastewater. The influence of the applied volumetric organic load was studied by varying the concentration of influent at 3600 and 5250 mg chemical oxygen demand (COD) L(-1) and cycle lengths of 4, 3, and 2 h resulting in volumetric organic loads of 10.5 to 31.1 g COD L(-1). The results revealed system stability in the production of biohydrogen and substrate consumption. The best performance was an organic removal (COD) of 24 % and carbohydrate removal (glucose) of 99 %. Volumetric and specific molar productivity were 60.9 mol H2 m(-3) day(-1) and 5.8 mol H2 kg SVT(-1) day(-1) (biogas containing 40 % H2 and no CH4) at 20.0 g COD L(-1) day(-1) (5250 mg COD L(-1) and 3 h). The yield between produced hydrogen and removed organic matter in terms of carbohydrates was 0.94 mol H2 Mol GLU(-1) (biogas containing 52 % H2 and no CH4) at 10.5 g COD L(-1) day(-1) (3600 mg COD L(-1) and 4 h), corresponding to 23 and 47 % of the theoretical values of the acetic and butyric acid metabolic routes, respectively. Metabolites present at significant amounts were ethanol, acetic acid, and butyric acid. The conditions with higher influent concentration and intermediate cycle length, and the condition with lower influent concentration and longer cycle showed the best results in terms of productivity and yield, respectively. This indicates that the best productivity tends to occur at higher organic loads, as this parameter involves the biogas production, and the best yield tends to occur at lower and/or intermediate organic loads, as this parameter also involves substrate consumption.

Biomethane production in an AnSBBR treating wastewater from biohydrogen process.

An anaerobic sequencing batch reactor containing immobilized biomass (AnSBBR) was used to produce biomethane by treating the effluent from another AnSBBR used to produce biohydrogen from glucose- (AR-EPHG) and sucrose-based (AR-EPHS) wastewater. In addition, biomethane was also produced from sucrose-based synthetic wastewater (AR-S) in a single AnSBBR to compare the performance of biomethane production in two steps (acidogenic and methanogenic) in relation to a one-step operation. The system was operated at 30 °C and at a fixed stirring rate of 300 rpm. For AR-EPHS treatment, concentrations were 1,000, 2,000, 3,000, and 4,000 mg chemical oxygen demand (COD) L(-1) and cycle lengths were 6 and 8 h. The applied volumetric organic loads were 2.15, 4.74, 5.44, and 8.22 g COD L(-1) day(-1). For AR-EPHG treatment, concentration of 4,000 mg COD L(-1) and 4-h cycle length (7.21 g COD L(-1) day(-1)) were used. For AR-S treatment, concentration was 4,000 mg COD L(-1) day(-1) and cycle lengths were 8 (7.04 g COD L(-1) day(-1)) and 12 h (4.76 g COD L(-1) day(-1)). The condition of 8.22 g COD L(-1) day(-1) (AR-EPHS) showed the best performance with respect to the following parameters: applied volumetric organic load of 7.56 g COD L(-1) day(-1), yield between produced methane and removed organic material of 0.016 mol CH4 g COD(-1), CH4 content in the produced biogas of 85 %, and molar methane productivity of 127.9 mol CH4 m(-3) day(-1). In addition, a kinetic study of the process confirmed the trend that, depending on the biodegradability characteristics of the wastewaters used, the two-step treatment (acidogenic for biohydrogen production and methanogenic for biomethane production) has potential advantages over the single-step process.