Plasma-assisted pre-treatment of lignocellulosic biomass for anaerobic digestion

The conversion of industrial crops to energy has received significant attention recently as a means to reduce carbon emissions and meeting the renewable energy targets. Samples of whole crop maize (Zea mays L.) were pre-treated in tap water using a novel microbubble-enhanced dielectric barrier discharge (DBD) plasma reactor that generates highly reactive species in situ and distribute them using microbubbles. The pre-treated maize was then used as feedstock in batch and continuously-fed mesophilic continuously-stirred anaerobic digesters (AD). Half of the pre-treated samples were washed in deionized water prior to feeding to assess the effect of possible inhibitory by-products generated during pre-treatment. In batch AD experiments, DBD-plasma pre-treated and washed maize produced 18% greater biogas production in comparison to untreated raw samples, and unwashed samples produced 29% lower biogas than the untreated samples. These results suggest the production of inhibitors to the AD process, but biogas production can be enhanced by removing these inhibiting compounds. Continuously-fed AD reactors exhibited no noticeable change in biogas output between raw and plasma-treated maize. For AD reactors operating in batch, or with a relatively long residence time and fed with high lignocellulose feedstocks, plasma-microbubble pre-treatment could enhance biogas output and process efficiency.