Development of a production chain from vegetable biowaste to platform chemicals.

BACKGROUND: A future bioeconomy relies on the development of technologies to convert waste into valuable compounds. We present here an attempt to design a biotechnological cascade for the conversion of vegetable waste into acetoin and electrical energy. RESULTS: A vegetable waste dark fermentation effluent containing mainly acetate, butyrate and propionate was oxidized in a bioelectrochemical system. The achieved average current at a constant anode potential of 0 mV against standard hydrogen electrode was 177.5 ± 52.5 µA/cm2. During this step, acetate and butyrate were removed from the effluent while propionate was the major remaining component of the total organic carbon content comprising on average 75.6%. The key players with regard to carbon oxidation and electrode reduction were revealed using amplicon sequencing and metatranscriptomic analysis. Using nanofiltration, it was possible to concentrate the propionate in the effluent. The effluent was revealed to be a suitable medium for biotechnological production strains. As a proof of principle, the propionate in the effluent of the bioelectrochemical system was converted into the platform chemical acetoin with a carbon recovery of 86%. CONCLUSIONS: To the best of our knowledge this is the first report on a full biotechnological production chain leading from vegetable waste to the production of a single valuable platform chemical that integrates carbon elimination steps leading to the production of the valuable side product electrical energy.

Integration of membrane filtration in two-stage anaerobic digestion system: Specific methane yield potentials of hydrolysate and permeate.

Two-stage biogas systems consisting of a CSTR-acidification reactor (AR) and an anaerobic filter (AF) were frequently described for microbial conversion of food and agricultural wastes to biogas. The aim of this study is to investigate the integration of a membrane filtration step in two-stage systems to remove inert particles from hydrolysate produced in AR in order to increase the efficiency of the subsequent AF. Hydrolysates from vegetable waste (VW) and grass/maize silage (G/M) were treated in cross-flow ceramic membrane filtration system (pore size 0.2 µm). Organic acids were extracted efficiently through filtration of hydrolysate. For both the substrates, membrane permeability was stable and high (46.6-49.3 L m-2 h-1 bar-1). Filtration process effectively improved the specific methane yield of permeate by 40% (VW) and 24.5% (G/M) compared to hydrolysate. It could be shown that, the filtration-step increased hydrolysate's degradability, which lead to higher conversion efficiency in the following AF.

Effects of target pH-value on organic acids and methane production in two-stage anaerobic digestion of vegetable waste.

Vegetable waste is one of the major organic residues available for sustainable bioenergy production. The aim of this work is to study the influence of pH-value on process stability, hydrolysis, degradation degree and methane production in two-stage anaerobic system. A mixture of vegetable wastes with carrot mousse, carrots, celery, cabbage and potatoes was treated in two-stage system at target pH-values 5.5 and 6 in acidification reactor (AR). At pH 6, high concentrations of organic acids were recorded whereas high amount of hydrolysate was produced at pH 5.5. The chemical oxygen demand (COD) concentration in the hydrolysate produced in AR was 21.85% higher at pH 6 compared to pH 5.5, whereas the overall specific methane yield was slightly higher at pH 5.5 (354.35±31.95 and 326.79±41.42Lkg-1 oDMadded, respectively). It could be shown, that the described two-stage system is well suited for manure-free digestion of vegetable waste.