Biomethane yield of novel source segregated dairy excreta under different anaerobic digestion systems

Source Segregation (SS) is a novel strategy in dairy housing that can reduce emissions and separate organic matter and nutrients more efficiently than traditional slurry solid-liquid separation. The anaerobic digestion (AD) methane yield of the SS fractions, however, is unknown. We aimed at unveiling the biomethane yield of these fractions by conducting AD experiments under different configurations: batch, continuous feeding, and fed-batch. In the batch test, the solid (SF) and liquid fraction (LF) from the SS system, a slurry collected from the pit (CS), and a self-made slurry (MF) were used as substrates. The results showed that the specific CH4 yields of the SF and MF were in same range and both higher than the CS. We concluded that SS can increase the CH4 yield of dairy excreta mainly by reducing losses in the animal house. The SF and MF were then compared in a continuously-fed thermophilic test, where SF had a higher specific (174 compared to 105 NL kg-1 VS) and volumetric (12.2 compared to 9.9 NL CH4 kg-1 excreta) yields. We concluded that the SF can effectively substitute slurry in AD without compromising the yield, possibly increasing economic viability by reducing transport costs and reactor size. Further, SF produced 356 NL CH4 kg-1 VS and a digestate with 1.8% lower dry matter in the fed-batch as compared to continuous feeding. Continuously stirred fed-batch can thus increase the CH4 yield of the SF and reduce the DM of its digestate potentially contributing to lower emissions in storage and field application.