AnSBBR WITH CIRCULATION APPLIED TO BIOHYDROGEN PRODUCTION TREATING SUCROSE BASED WASTEWATER: EFFECTS OF ORGANIC LOADING, INFLUENT CONCENTRATION AND CYCLE LENGTH

An anaerobic sequencing batch biofilm reactor (AnSBBR) containing immobilized biomass and operating with recirculation of the liquid phase (total liquid volume 4.5 L; treated volume per cycle 1.9 L) was used to treat sucrose-based wastewater at 30 oC and produce biohydrogen. The influence of applied volumetric organic load was studied by varying the influent concentration at 3600 and 5400 mgCOD.L and using cycle lengths of 4, 3 and 2 hours, obtaining in this manner volumetric organic loads of 9, 12, 13.5, 18 and 27 gCOD.L.d. Different performance indicators were used: productivity and yield of biohydrogen per applied and removed load, reactor stability and efficiency based on the applied and removed organic loads, both in terms of organic matter (measured as COD) and carbohydrate (sucrose). The results revealed system stability (32-37% of H2 in biogas) during biohydrogen production, as well as substrate consumption (12-19% COD; 97-99% sucrose). Conversion efficiencies decreased when the influent concentration was increased (at constant cycle length) and when cycle lengths were reduced (at constant influent concentrations). The best yield was 4.16 molH2.kg-SUC (sucrose load) at 9 gCOD.L.d (3600 mgCOD.L and 4 h) with H2 content in the biogas of 36% (64% CO2 and 0% CH4). However, the best specific molar productivity of hydrogen was 8.5 molH2.kgTVS.d (32% H2; 68% CO2; 0% CH4), at 18 gCOD.L.d (5400 mgCOD.L and 3 h), indicating that the best productivity tends to occur at higher organic loads, as this parameter involves the “biochemical generation" of biogas, whereas the best yield tends to occur at lower and/or intermediate organic loads, as this parameter involves "biochemical consumption" of the substrate. The most significant metabolites were ethanol, acetic acid and butyric acid. Microbiological analyses revealed that the biomass contained bacilli and endospore filaments and showed no significant variations in morphology between different experimental conditions.