Miranda Maesen

Enzymatic electrosynthesis of formate through CO2 sequestration/reduction in a bioelectrochemical system (BES)

Bioelectrochemical system (BES) was operated using the enzyme formate dehydrogenase as catalyst at cathode in its free form for the reduction of CO2 into formic acid. Electrosynthesis of formic acid was higher at an operational voltage of -1V vs. Ag/AgCl (9.37mgL(-1) CO2) compared to operation at -0.8V (4.73mgL(-1) CO2) which was strongly supported by the reduction catalytic current. Voltammograms also depicted a reversible redox peak throughout operation at -1V, indicating NAD(+) recycling for proton transfer from the source to CO2. Saturation of the product was observed after 45min of enzyme addition and then reversibility commenced, depicting a lower and stable formic acid concentration throughout the subsequent time of operation. Stability of the enzyme activity after immobilization on the electrode and product yield will be studied further.

Temporal variations in natural attenuation of chlorinated aliphatic hydrocarbons in eutrophic river sediments impacted by a contaminated groundwater plume

Chlorinated aliphatic hydrocarbons (CAHs) often discharge into rivers as contaminated groundwater baseflow. Biotransformation, sorption and dilution of CAHs in the impacted river sediments have been reported to reduce discharge, but the effect of temporal variations in environmental conditions on the occurrence and extent of those processes in river sediments is largely unknown. We monitored the reduction of CAH discharge into the Zenne River during a 21-month period. Despite a relatively stable influx of CAHs from the groundwater, the total reduction in CAH discharge from 120 to 20 cm depth in the river sediments, on average 74 ± 21%, showed moderate to large temporal variations, depending on the riverbed location. High organic carbon and anaerobic conditions in the river sediments allowed microbial reductive dechlorination of both chlorinated ethenes and chlorinated ethanes. δ(13)C values of the CAHs showed that this biotransformation was remarkably stable over time, despite fluctuating pore water temperatures. Daughter products of the CAHs, however, were not detected in stoichiometric amounts and suggested the co-occurrence of a physical process reducing the concentrations of CAHs in the riverbed. This process was the main process causing temporal variations in natural attenuation of the CAHs and was most likely dilution by surface water-mixing. However, higher spatial resolution monitoring of flow transients in the riverbed is required to prove dilution contributions due to dynamic surface water-groundwater flow exchanges. δ(13)C values and a site-specific isotope enrichment factor for reductive dechlorination of the main groundwater pollutant vinyl chloride (VC) allowed assessment of changes over time in the extent of both biotransformation and dilution of VC for different scenarios in which those processes either occurred consecutively or simultaneously between 120 and 20 cm depth in the riverbed. The extent of reductive dechlorination of VC ranged from 27 to 89% and differed spatially but was remarkably stable over time, whereas the extent of VC reduction by dilution ranged from 6 to 94%, showed large temporal variations, and was often the main process contributing to the reduction of VC discharge into the river.

Kinetics of dechlorination by Dehalococcoides mccartyi using different carbon sources

Stimulated anaerobic dechlorination is generally considered a valuable step for the remediation of aquifers polluted with chlorinated ethenes (CEs). Correct simulation and prediction of this process in situ, however, require good knowledge of the associated biological reactions. The aim of this study was to evaluate the dechlorination reaction in an aquifer contaminated with trichloroethene (TCE) and its daughter products, discharging into the Zenne River. Different carbon sources were used in batch cultures and these were related to the dechlorination reaction, together with the monitored biomarkers. Appropriate kinetic formulations were assessed. Reductive dechlorination of TCE took place only when external carbon sources were added to microcosms, and occurred concomitant with a pronounced increase in the Dehalococcoides mccartyi cell count as determined by 16S rRNA gene-targeted qPCR. This indicates that native dechlorinating bacteria are present in the aquifer of the Zenne site and that the oligotrophic nature of the aquifer prevents a complete degradation to ethene. The type of carbon source, the cell number of D. mccartyi or the reductive dehalogenase genes, however, did not unequivocally explain the observed differences in degradation rates or the extent of dechlorination. Neither first-order, Michaelis-Menten nor Monod kinetics could perfectly simulate the dechlorination reactions in TCE spiked microcosms. A sensitivity analysis indicated that the inclusion of donor limitation would not significantly enhance the simulations without a clear process understanding. Results point to the role of the supporting microbial community but it remains to be verified how the complexity of the microbial (inter)actions should be represented in a model framework.

Enzymatic production of pectic oligosaccharides from onion skins

Onion skins are evaluated as a new raw material for the enzymatic production of pectic oligosaccharides (POS) with a targeted degree of polymerization (DP). The process is based on a two-stage process consisting of a chelator-based crude pectin extraction followed by a controlled enzymatic hydrolysis. Treatment of the extracted crude onion skins pectin with various enzymes (EPG-M2, Viscozyme and Pectinase) shows that EPG-M2 is the most appropriate enzyme for tailored POS production. The experiments reveal that the highest amount of DP2 and DP3 is obtained at a time scale of 75-90min with an EPG-M2 concentration of 26IU/mL. At these conditions the production amounts 2.5-3.0% (w/w) d.m for DP2 and 5.5-5.6% (w/w) d.m for DP3 respectively. In contrast, maximum DP4 production of 5.2-5.5% (w/w) d.m. is obtained with 5.2IU/mL at a time scale of 15-30min. Detailed LC-MS analysis reveals the presence of more methylated oligomers compared to acetylated forms in the digests.

BIOLOGICAL ASSESSMENT AND REMEDIATION OF CONTAMINATED SEDIMENTS

Various approaches to clean contaminated aquatic environments have been proposed. In recent years, natural attenuation has received increasing attention and it is generally accepted that microorganisms are the principal mediators of the natural attenuation of many pollutants. However, the complexity of environmental systems such as sediments requires a multifaceted approach to understand microbial processes and their potential. This is even more so under in situ conditions, where the activity of pollutant degrading microorganisms is generally slow, partial and constrained spatially and/or temporally. Recent developments in molecular biology and genomics are offering tools to explore microbial processes at a level that encompasses the genetic characteristics of the local microbial players, culturable or not, as well as their organization into complex communities and their interactions both with each other and with the target chemicals. It is now possible to study microbes directly in their environments at the population level as well as at the single cell level and to link biology to geochemistry. Integrative knowledge from culture-independent studies based on functional characters and assessment of the diversity and quantity of catabolic genes in response to pollution, will allow a deeper understanding of and a rational intervention in environmental processes. Moreover, the use of genomic libraries to retrieve genes from natural bacterial communities without cultivation will allow a breakthrough in accessing new microbial capabilities. In this chapter, the main features, advantages and limitations of these innovative approaches to the biomonitoring and analysis of intrinsic bioremediation potential of polluted environments and sediments are critically reviewed. Then, the potential of the same strategies in the integrated chemical, physical and biological monitoring and characterization of polluted sediments subjected to natural decontamination is shown through the description of the main results of case studies performed on a) polychlorinated biphenyl (PCB)-contaminated marine sediments of the Porto Marghera area of Venice Lagoon (Italy) in which the occurrence of PCB-reductive dechlorination processes has been demonstrated for the first time in the literature, b) sediments contaminated by chlorinated aliphatic hydrocarbons (CAHs) collected from different positions of the eutrophic river Zenne (Vilvoorde, Belgium), where they have been found to act as a natural biobarrier for the CAHs occurring in the groundwater that is passing through the sediment zone, hereby reducing the risk of surface water contamination, and c) other environmental contaminated systems subjected to ex-situ and in situ active bioremediation, where these processes are described on the basis of the experience accumulated in pilot and real-life systems.

Continuous production of pectic oligosaccharides from onion skins with an enzyme membrane reactor

The aim of this research was to valorize onion skins, an under-utilized agricultural by-product, into pectic oligosaccharides (POS), compounds with potential health benefits. To achieve high hydrolysis performance with the multi-activity enzyme Viscozyme L, an innovative approach was investigated based on a cross-flow continuous membrane enzyme bioreactor (EMR). The influence of the various process conditions (residence time, enzyme concentration, substrate concentration) was investigated on productivity and yield. The composition of the POS mixtures in terms of mono- and oligosaccharides was assessed at the molecular level. At optimized conditions, a stable POS production with 22.0g/L/h volumetric productivity and 4.5g/g POS/monosaccharides was achieved. Compared to previous results obtained in batch for the enzyme Viscozyme L, EMR provided a 3-5× higher volumetric productivity for the smallest POS. Moreover, it gave competitive results even when compared to batch production with a pure endo-galacturonase enzyme, demonstrating its feasibility for efficient POS production.

Supercritical CO2 Extraction of Nannochloropsis sp.: A Lipidomic Study on the Influence of Pretreatment on Yield and Composition

Algal lipids have gained wide interest in various applications ranging from biofuels to nutraceuticals. Given their complex nature composed of different lipid classes, a deep knowledge between extraction conditions and lipid characteristics is essential. In this paper, we investigated the influence of different pretreatments on lipid extraction with supercritical CO2 by a lipidomic approach. Pretreatment was found to double the total extraction yield, thereby reaching 23.1 wt.% comparable to the 26.9 wt.% obtained with chloroform/methanol. An increase in acylglycerides was concurrently observed, together with a nearly doubling of free fatty acids indicative of partial hydrolysis. Moreover, an alteration in the distribution of glyco- and phospholipids was noted, especially promoting digalactosyldiglycerides and phosphatidylcholine as compared to monogalactosyldiglycerides and phosphatidylglycerol. At optimized conditions, supercritical CO2 extraction provided a lipid extract richer in neutral lipids and poorer in phospholipids as compared to chloroform/methanol, though with a very similar fatty acid distribution within each lipid class.