Methanogen colonization and ‘end-of-life’ use of spent lignocellulose from a solid-state reactor as an inoculum source

Abstract

Methanogen colonization on lignocellulosic feedstocks has been known, but few attempts have been made to characterize and quantify it. This study used total specific methanogenic assay (TSMA) to quantify the methanogenic activity build-up on ten lignocellulose and brought out distinct variations and patterns of conferred activity. TSMA of up to 53L CH4/d/kg residual TS was recorded. Based on the high methanation potential, the ‘end-of-life’ use of spent lignocellulose as a high-performance inoculum source was proposed for the solid-state reactors. The TSMA was devised to quantify the methanation potential of the spent lignocellulose-based solid-inoculum source. Further, “S/I analog” was proposed in solid-state reactor calculation- organic loading rate and inoculation volume. The study also used the two derivatives- TSMA and VS flux rates, to study the implication of the colonization on the reactor's waste stabilization potential. Here, a new concept of “equalization point” was presented. It referred to the stage of digestion where cumulative methanogen colonization build-up was adequate to convert cumulative VS generated from decomposing feedstock, i.e., the relative ratio of ≥1. This new direction would generate insights into the upper limits to which volumetric feed rates can be supported, enabling a higher reactor space economy.