Two-stage thermophilic anaerobic digestion of cheese whey: Process optimization, comparison with single-stage, and full-scale estimation

The purpose of this study was to determine whether a single-stage or two-stage system of an anaerobic sequencing batch and fed-batch biofilm reactor (AnSBBR) would be more efficient for thermophilic whey treatment and bioenergy production. The best results were achieved at 55 degrees C and 15 kg-COD.m- 3.d-1 with organic matter removal of 96%, methane productivity of 142.9 mol-CH4.m- 3.d-1, and yield of 10.3 mol-CH4.kg-COD-1. In addition, temperature strongly impacted the microbial community diversity and had an inverse relation with the genus Methanosarcina. To treat all of the whey produced by a dairy industry, which generates 3.4 x 103 m3-whey.year- 1, a single-stage anaerobic digestion system of 80.0 m3 would be required, generating a power of 75.1 kW and an energy yield of 9.89 MJ.kg-COD-1. A two-stage system designed for the same industry would have a total working volume of 134.9 m3, combining thermophilic acidogenic reactors and mesophilic methanogenic reactors, with a power of 39.1 kW and energy yield of 5.14 MJ.kg-COD-1. The single-stage system would need an investment cost of U$$ 271,681.00, which is 42% cheaper compared to the two-stage system and would be able to supply 23.5% of the energy demand required by the dairy industry.