Ammonium level induces high purity propionate production in mixed culture glucose fermentation

Abstract

Propionate is an important chemical widely applied in industry and its production via fermentation is economic. Many literature studies have reported propionate was produced with pure culture fermentation. However, the following by-products production in pure culture fermentation limits its application. In this work, a high purity of propionate production from glucose in mixed culture fermentation (MCF) under the condition of high ammonium concentration was first investigated. The bottle tests showed that up to 1.4 g L⁻¹ of ammonium severely inhibited propionate degradation but had little effect on acetate degradation. In fed-batch experiments, propionate was produced with more than 16 g L⁻¹ concentration and the purity reached more than 90% of liquid metabolites. Under the sequential batch operation, the propionate yield was 0.37–0.47 g COD per g COD and propionate accounted for 98% of liquid metabolites. The microbial community analysis revealed that Betaproteobacteria and Deltaproteobacteria, the propionate-utilizing microbes, were decreased from 7.94% to 3.72% at high ammonium levels, while Methanosaeta that mainly appeared at high ammonium concentration in the literature was the dominating aceticlastic methanogen. Hence, this work demonstrates a great potential application of MCF to effectively produce high purity propionate.