A metabolic model for targeted volatile fatty acids production by cofermentation of carbohydrates and proteins.

Anaerobic mixed-culture fermentations are interesting processes to valorise organic wastes by converting them to volatile fatty acids. One of the main issues is that certain operational conditions (e.g. pH or different substrate concentrations) can vary significantly the product spectrum. So far, there are no tools that take into the account the characteristic features of cofermentation processes, which hinders the possibility of designing processes that use real wastes as substrates. In this work a mathematical model was developed for the production of volatile fatty acids from organic wastes with a high concentration of carbohydrates and proteins. The model reproduces satisfactorily experimental results and is also able of giving mechanistic insight into the interactions between carbohydrates and proteins that explain the observed changes in the product spectrum. We envision this model as the core of an early-stage design tool for anaerobic cofermentation processes, as shown in this work with different examples.

Assessment of morphological changes of Clostridium acetobutylicum by flow cytometry during acetone/butanol/ethanol extractive fermentation.

Acetone/butanol/ethanol (ABE) fermentation by Clostridium acetobutylicum was investigated in extractive fed-batch experiments. In conventional fermentations, metabolic activity ceases when a critical threshold products concentration is reached (~21.6 g solvents l(-1)). Solvents production was increased up to 36.6 and 37.2 g l(-1), respectively, using 2-butyl-1-octanol (aqueous to organic ratio: 1:0.25 v/v) and pomace olive oil (1:1 v/v) as extraction solvents. The morphological changes of different cell types were monitored and quantified using flow cytometry. Butanol production in extractive fermentations with pomace olive oil was achieved mainly by vegetative cells, whereas the percentage of sporulating cells was lower than 10%.

Fermentation of biologically pretreated wheat straw for ethanol production: comparison of fermentative microorganisms and process configurations.

The pretreatment of lignocellulosic biomass with white-rot fungi to produce bioethanol is an environmentally friendly alternative to the commonly used physico-chemical processes. After biological pretreatment, a solid substrate composed of cellulose, hemicellulose and lignin, the two latter with a composition lower than that of the initial substrate, is obtained. In this study, six microorganisms and four process configurations were utilised to ferment a hydrolysate obtained from wheat straw pretreated with the white-rot fungus Irpex lacteus. To enhance total sugars utilisation, five of these microorganisms are able to metabolise, in addition to glucose, most of the pentoses obtained after the hydrolysis of wheat straw by the application of a mixture of hemicellulolytic and cellulolytic enzymes. The highest overall ethanol yield was obtained with the yeast Pachysolen tannophilus. Its application in combination with the best process configuration yielded 163 mg ethanol per gram of raw wheat straw, which was between 23 and 35 % greater than the yields typically obtained with a conventional bioethanol process, in which wheat straw is pretreated using steam explosion and fermented with the yeast Saccharomyces cerevisiae.

Biocatalytic generation of Mn(III)-chelate as a chemical oxidant of different environmental contaminants.

The objective of this study was to investigate the enzymatic generation of the Mn(3+) -malonate complex and its application to the process of oxidizing several organic compounds. The experimental set-up consisted of an enzymatic reactor coupled to an ultrafiltration membrane, providing continuous generation of Mn(3+) -malonate from a reaction medium containing versatile peroxidase (an enzyme produced by Bjerkandera adusta strain BOS55), H(2) O(2) , MnSO(4,) and malonate. The effluent of the enzymatic reactor was introduced into a batch-stirred reactor to oxidize three different classes of compounds: an azo dye (Orange II), three natural and synthetic estrogens, and a polycyclic aromatic hydrocarbon (anthracene). The enzymatic reactor provided the Mn(3+) complex under steady-state conditions, and this oxidative species was able to transform the three classes of xenobiotics considerably (90-99%) with negligible loss of activity.