On-line gradient monitoring during plug-flow hydrolysis: a tool to support flexible operation?

Abstract

Abstract Hydrolysis at changing hydraulic retention time (HRT), recirculation, bedding straw content in the feed, bioaugmentation and the impact of those changes on gradient formation in the liquid phase in plug-flow reactors (PFRs) was examined. The pH, conductivity and oxidation-reduction-potential (ORP) were monitored at three spots along the PFRs to study potential correlations of gradient formation to process performance during a total process time of 123 weeks. Local on-line monitoring showed good correlations to acidogenesis: namely the pH and ORP to the acidification, to butyric (and lactic) acid concentration and to the acid yield. The ORP (inlet) showed the most stable correlation to acidogenesis under dynamic operation, while the conductivity (outlet) correlated to the acid concentration in dependance on the feedstock. Multiple measurement spots as used in this study allow to gain more information about acidogenic fermentation than a single measurement spot, simplifying process control and automation attempts with recalcitrant feedstock.