Biomethane production from whey treatment in an AnSBBR at thermophilic conditions

Abstract

An alternative to recover energy from waste treatment is through the anaerobic treatment of effluents using a discontinuous reactor configuration, such as ASBR and AnSBBR, to produce methane. This reactor configuration allows greater operation flexibility and stability, improved process control, as well as shorter start-up. The objective of this investigation was to study a mechanically stirred thermophilic anaerobic reactor (55 °C) containing immobilized biomass, operating in sequencing batch or fed batch (AnSBBR), to treat cheese whey for methane production under thermophilic conditions. The volume fed per cycle was 1.0 L with 1.5 L of residual volume. The reactor underwent an initial adaptation period of 29 days. After this period, the influence of the organic load by increasing the applied volumetric organic load, from 6.20 to 31.68 gCOD.L-1.d-1, was studied. The condition with volumetric organic load of 24.68 gCOD.L-1.d-1 presented the best overall results, attaining organic matter removal efficiency in the form of COD of 85.7% and 99.6% for carbohydrates. The yield of methane generated by the consumed organic matter was 13.13 mmolCH4.gCOD-1, with biogas production of 6506 NmL.cycle-1 and methane molar fraction equivalent to 73.68%. The molar productivity of methane achieved at this condition was 324.0 molCH4.m-3.d-1. The higher organic loads applied lead to loss of efficiency and instability of the reactor. The kinetic model of all conditions showed good fits, indicating that the preferred methane production route was hydrogenotrophic throughout the study period, but the acetoclastic pathway was also observed at all conditions. Changing feeding strategy from batch (2% cycle) to fed batch (50% cycle) did not improve efficiency, stability and methane production in the reactor. The energy recovery from whey production of small, medium and large cheese producers was also estimated, allowing a monthly energy recovery of 179 MWh, 536 MWh and 1090 MWh, respectively. Microbiological analysis indicated the presence of cocci, rod-shaped and filamentous microorganisms at all conditions, as well as endospores, allowing to conclude that the support material was effective in maintaining the biomass. © 2018 by Nova Science Publishers, Inc. All rights reserved.