Controlling Ethanol Use in Chain Elongation by CO2 Loading Rate

Chain elongation is an open-culture biotechnologicalprocess which converts volatile fatty acids (VFAs) intomedium chain fatty acids (MCFAs) using ethanol and otherreduced substrates. The objective of this study was toinvestigate the quantitative effect of CO2 loading rate onethanol usages in a chain elongation process. We supplieddifferent rates of CO2 to a continuously stirred anaerobicreactor, fed with ethanol and propionate. Ethanol was used toupgrade ethanol itself into caproate and to upgrade thesupplied VFA (propionate) into heptanoate. A high CO2loading rate (2.5 LCO2·L−1·d−1) stimulated excessive ethanoloxidation (EEO; up to 29%) which resulted in a high caproate production (10.8 g·L−1·d−1). A low CO2 loading rate (0.5 LCO2·L−1·d−1) reduced EEO (16%) and caproate production (2.9 g·L−1·d−1). Heptanoate production by VFA upgrading remainedconstant (∼1.8 g·L−1·d−1) at CO2 loading rates higher than or equal to 1 LCO2·L−1·d−1. CO2 was likely essential for growth ofchain elongating microorganisms while it also stimulated syntrophic ethanol oxidation. A high CO2 loading rate must be selectedto upgrade ethanol (e.g., from lignocellulosic bioethanol) into MCFAs whereas lower CO2 loading rates must be selected toupgrade VFAs (e.g., from acidified organic residues) into MCFAs while minimizing use of costly ethanol

Environmental Impact Evaluation for Heterogeneously Catalysed Starch Oxidation

Oxidised starch is currently produced from native starch using sodium hypochlorite as an oxidising agent. The use of hypochlorite has undesired side reactions and produces stoichiometric amounts of waste (salt), thus alternative oxidation methods are desired. In this study, the potential of two catalysed starch oxidation methods to reduce the environmental impact (EI) of oxidised starch production are assessed. We compared the EI of oxidation with molecular oxygen (heterogeneously catalysed) and hydrogen peroxide (homogeneously catalysed) to hypochlorite oxidation through life cycle assessment (LCA). The results confirm that hypochlorite oxidation is the main environmental hotspot in the current process of oxidised starch production, and that both hydroperoxide oxidation and molecular oxygen oxidation can significantly lower the EI of the process. The impact reduction is most significant in the categories of freshwater eutrophication (∼67 %), ozone depletion (∼66 %), climate change (35–60 %) and resource use (40 %–78 %) for peroxide and molecular oxygen oxidation, respectively