Anaerobic Sequencing Batch Reactors Co-digesting Whey and Glycerin as a Possible Solution for Small and Mid-size Dairy Industries: Environmental Compliance and Methane Production.

A significant part of whey generated in Brazil is from small and mid-size dairy companies. Cheese whey has great potential for methane production through anaerobic biological processes but presents instabilities due to its high biodegradability. To study an alternative for the destination of this residue, the aim of this work was to investigate methane from the co-digestion of whey with glycerin and its environmental compliance at 55 °C in an anaerobic sequencing batch biofilm reactor. The best performance indicators were obtained with an influent composed of 88% cheese whey and 12% glycerin (by volume), fed-batch mode and organic loading rate of 19.3 kgCOD m-3 day-1 at 55 °C. This operational condition allowed us to achieve a methane productivity of 203 molCH4 m-3 day-1, a methane yield close to theoretical value, and to remove 68% of all organic matter in the influent. A kinetic metabolic model was fitted to the experimental data, which indicated methanogenesis with preference for the acetoclastic route. Finally, the energy production (approximately 197 MWh month-1) from an industrial scale reactor and its volume (three reactors of 152 m3) were assessed for a mid-size dairy industry, which could save up to US$ 22,000.00 per month in oil demand.