Effects of organic loading, influent concentration, and feed time on biohydrogen production in a mechanically stirred...

An anaerobic sequencing batch biofilm reactor (AnSBBR-total volume 7.5 L; liquid volume 3.6 L; treated volume per cycle 1.5 L) treated sucrose-based wastewater to produce biohydrogen (at 30 °C). Different applied volumetric organic loads (AVOL of 9.0, 12.0, 13.5, 18.0, and 27.0 kg COD m(-3) day(-1)), which were varied according to the influent concentration (3,600 and 5,400 mg COD L(-1)) and cycle length (4, 3, and 2 h), have been used to assess the following parameters: productivity and yield of biohydrogen per applied and removed load, reactor stability, and efficiency. The removed organic matter (COD) remained stable and close to 18 % and carbohydrates (sucrose) uptake rate remained between 83 and 97 % during operation. The decrease in removal performance of the reactor with increasing AVOL, by increasing the influent concentration (at constant cycle length) and decreasing the cycle lengths (at constant influent concentrations), resulted in lower conversion efficiencies. Under all conditions, when organic load increased there was a predominance of acetic, propionic, and butyric acid as well as ethanol. The highest concentration of biohydrogen in the biogas (24-25 %) was achieved at conditions with AVOL of 12.0 and 13.5 kg COD m(-3) day(-1), the highest daily production rate (0.139 mol H2 day(-1)) was achieved at AVOL of 18.0 kg COD m(-3) day(-1), and the highest production yields per removed and applied load were 2.83 and 3.04 mol H2 kg SUC(-1), respectively, at AVOL of 13.5 kg COD m(-3) day(-1). The results indicated that the best productivity tends to occur at higher organic loads, as this parameter involves the "biochemical generation" of biogas, and the best yield tends to occur at lower and/or intermediate organic loads, as this parameter involves "biochemical consumption" of the substrate.