Thermoplastic starch wastes are converted and stored into acetone through butanol in a depressurised digester

Abstract

A biofilm containing both hydrolytic fermentative bacteria and acidogenic bacteria (including acetogenic and acetoclastic bacteria) was developed for the treatment of plastic wastes in a twophase, batch digester. The biotransformation and further degradation were electrochemically observed. It was found that the organic wastes were initially fermented in a single-phase (i.e. liquid phase) digester, where it entirely obeyed microbial growth kinetics in accumulating acetate. As the carbonates produced were vaporised, the single-phase became a two-phase fermentation (gas and liquid) accumulating volatile fatty acids (VFAs), where it obeyed a proton driving force based on Le Chatelier's principle. Interestingly, as the digester was depressurised to the saturated vapour pressure of water, the accumulated VFAs were rapidly transformed into acetone via butanol, so that the VFAs forms were not observable. It was found that in extreme conditions, the organic feeds were converted and stored into acetone, via butanol.

Electrochemical communication in anaerobic digestion

“…In particular, the hydrolytic fermentative bacteria associate with syntrophic bacteria (acetogenic bacteria) to produce shorter volatile fatty acids and dissociate with acidogenic bacteria. The microbial association ( Figure 5A) was electrochemically studied in disaccharides-fermentation [101]. The electron and proton (produced in the fermentation) are assumed to conduct through the ψ network between the interspecies.…”

“…Residual shorter-chain VFAs (valerate  butyrate << acetate) show the largest proportion of the digested liquor (except for water). It was known as an 'acetoclastic inhibition' in conventional fermentation processes, but Oh group [101] represented it as a microbial association excreting 'acetate' to store a maximum amount of residual energy and building a peculiar structure of bioflocculation. Figure 5A shows a mole-production of acetate in the initial mole of palm oil waste [104], lactose [105], and cassava [106].…”

“…. As the vapour phase hypothetically increases, the feeding sugars are converted and accumulated into 'acetone' around the saturated vapour pressure of water in the isochoric condition [101].…”