Development of a new bioethanol feedstock – Anaerobically digested fiber from confined dairy operations using different digestion configurations

Abstract

Abstract Two types of digesters, continuous stirring-tank reactor (CSTR) and plug flow reactor (PFR), were integrated into a biorefining concept to generate a new cellulosic ethanol feedstock –anaerobically digested fiber (AD fiber) from dairy cow feces. Cellulose content in AD fibers was significantly increased during the anaerobic digestion. CSTR and PFR AD fibers had cellulose contents of 357 and 322 g kg −1 dried AD fiber. The AD fibers were enzymatically hydrolyzed after being pretreated by dilute sulfuric acid or dilute sodium hydroxide, and the hydrolysates were used to produce ethanol. Alkali pretreatment was concluded as a suitable pretreatment method for AD fibers. Under the optimal conditions the AD fibers processed by CSTR and PFR produced ethanol of 26 g kg −1 and 23 g kg −1 dry feces, respectively. Energy balance analysis further indicated that CSTR was a preferred digestion method to prepare AD fiber for ethanol production.