pH-depended flushing in an automatized batch leach bed reactor system for volatile fatty acid production.

In a two-stage CSTR system, the anaerobic digestion effluent from the second stage (methane reactor) can be used for pH-control in the acidification reactor. But using batch leach bed reactors, controlling the pH-value is key affecting factor due to dynamic process conditions. The aim of this work was to study, an automatized technical-scale leach bed reactor system for VFA-production with pH-dependent flushing. It was developed and tested at mesophilic and thermophilic operating conditions and compared to a time-controlled flushing mode. The reactors were fed with grass silage and the experiments were run for 35 days. Total cumulative VFA yields up to 270 g kg-1VS were achieved and extracted from the reactor. The methane formation in the leach bed reactors was successfully suppressed with a pH-controlled flushing mode. As a result of the extraction of the VFA from the leach bed reactors, the methane potential decreased by up to 50 %.