Energetic feasibility of a two-stage anaerobic digestion system compared to a single-stage system treating whey and glycerin

•Tested viability of a two-stage system producing H2 and CH4 from whey and glycerin;•Highest methane productivity: 185.9 molCH4.m−3.d−1 at 11.8 kgCOD.m−3.d−1;•Energy yield of two-stage system: 7.0 MJ.kgCOD−1 with US$ 8170 of savings;•Energy yield of single-stage system: 12.0 MJ.kgCOD−1 with US$ 13,920 of savings;•Two-stage should be used when single-stage achieves less than 8.8 molCH4.kgCOD−1.