Development of 1000 L Pilot Scale Biodigester for Assessment of Biogas Production and Quality in Biodigestion of Organic Substrates

Abstract

Anaerobic digestion or biodigestion shows potential to become a cost-effective waste management strategy whereby industrial solid or semi-solid waste is upcycled into an alternative source of energy in the form of biogas. Biogas is a mixture of organic and inorganic gases composed primarily of methane (CH4), carbon dioxide (CO2), hydrogen sulfide (H2S) and trace gases. The general aim of this study was to test organic substrates with differing nitrogen contents for biogas production through biodigestion, which initially included the use of spent-mushroom-substrate (SMS), that is, the leftover straw/cotton seed substrate (70%/30%, respectively) following specialty mushroom production at the University of Arizona. The specific aim of this study was to investigate how three ratios of the substrate combination of oak wood pellets and soybean hull pellets, namely 1:3, 1:1, and 3:1 (oak:soy), using a 1000-L batch and stand-alone biodigester with horse manure providing the needed bacterial inocula, impacted biogas production and biogas composition. The results showed that the 1:3 treatment’s mean biogas yield of 2,854 L significantly exceeded that of the 1:1 treatment of 2,003 L (P<0.05), which in turn significantly exceeded that of the 3:1 treatment of 393 L (P<0.05). The biogas methane contents of the three treatments were statistically indistinguishable from one another (P<0.05); namely, 51% for the 1:3 treatment, 44% for the 1:1 ratio, and 48% for the 3:1 treatment. Similarly, the biogas CO2 contents of the three treatments were statistically indistinguishable (P<0.05); namely, 39% for the 1:3 treatment, 33% for the 1:1 ratio, and 36% for the 3:1 treatment. Thus, the 1:3 oak:soy treatment constituted the optimal treatment among the three treatments tested. This study is arguably the first or one of the first to investigate the use of oak wood and soybean hull as organic substrates for biogas production using biodigesters in the scale of 1000 L.