Anaerobic biohydrogen production from dairy wastewater treatment in sequencing batch reactor (AnSBR): Effect of organic loading rate

Abstract

Dairy wastewater was evaluated for biological hydrogen (H 2) production in conjugation with wastewater treatment in a suspended growth sequencing batch reactor (AnSBR) employing sequentially pretreated [heat-shock (100 °C, 2 h) and acid (pH 3.0, 24 h)] mixed consortia. The bioreactor was operated at mesophilic (room) temperature (28 ± 2 °C) under acidophilic conditions (pH 6.0) with a total cycle period of 24 h consisting of FILL (15 min), REACT (23 h), SETTLE (30 min), and DECANT (15 min) phases at three different organic loading rates (OLR) of 2.4, 3.5, and 4.7 Kg COD/m 3-day, respectively. H 2 evolution rate differed significantly with the substrate/OLR of wastewater used as substrate [OLR 2.4 Kg COD/m 3-day - volumetric H 2 production rate: 0.3683 mmol H 2/m 3-min; specific H 2 production rate: 0.0184 mmol H 2/min-g COD L; OLR 3.5 Kg COD/m 3-day - volumetric H 2 production rate: 1.105 mmol H 2/m 3-min; specific H 2 production rate: 0.0245 mmol H 2/min-g COD L and OLR 4.7 Kg COD/m 3-day - volumetric H 2 production rate: 0.7367 mmol H 2/m 3-min; specific H 2 production rate: 0.0107 mmol H 2/min-g COD L]. Substrate (COD) removal efficiency of 64.7 (substrate degradation rate (SDR): 1.577 Kg COD/m 3-day), 60 (SDR: 3.168 Kg COD/m 3-day), and 50% (SDR-3.2 Kg COD/m 3-day), respectively, was observed at operating OLR of 2.4, 3.5, and 4.7 Kg COD/m 3-day, respectively. The system showed rapid stabilization tendency (2.4 Kg COD/m 3-day: 39 days; 3.5 Kg COD/m 3-day: 14 days; 4.7 Kg COD/m 3-day: 24 days) with respect to H 2 generation and COD reduction. A surge in pH values from 5.8 to 4.5 (2.4 Kg COD/m 3-day), 5.82 to 4.62 (3.5 Kg COD/m 3-day), and 6.28 to 4.56 (4.7 Kg COD/m 3-day) was observed during stabilized phase of operation.