Sandra Van Roy

From industrial sites to environmental applications with Cupriavidus metallidurans

Cupriavidus metallidurans CH34 and related strains are adapted to metal contaminated environments. A strong resistance to environmental stressors and adaptation make it ideal strains for survival in decreasing biodiversity conditions and for bioaugmentation purposes in environmental applications. The soil bacterium C. metallidurans is able to grow chemolithoautotrophically on hydrogen and carbon dioxide allowing a strong resilience under conditions lacking organic matter. The biofilm growth on soil particles allows coping with starvation or bad conditions of pH, temperature and pollutants. Its genomic capacity of two megaplasmids encoding several heavy metal resistance operons allowed growth in heavy metal contaminated habitats. In addition its specific siderophores seem to play a role in heavy metal sequestration besides their role in the management of bioavailable iron. Efflux ATPases and RND systems pump the metal cations to the membrane surface where polysaccharides serve as heavy metal binding and nucleation sites for crystallisation of metal carbonates. These polysaccharides contribute also to flotation under specific conditions in a soil-heavy metals–bacteria suspension mixture. An inoculated moving bed sand filter was constructed to treat heavy metal contaminated water and to remove the metals in the form of biomass mixed with metal carbonates. A membrane based contactor allowed to use the bacteria as well in a versatile wastewater treatment system and to grow homogeneously formed heavy metal carbonates. Its behaviour toward heavy metal binding and flotation was combined in a biometal sludge reactor to extract and separate heavy metals from metal contaminated soils. Finally its metal-induced heavy metal resistance allowed constructing whole cell heavy metal biosensors which, after contact with contaminated soil, waste, solids, minerals and ashes, were induced in function of the bioavailable concentration (Cd, Zn, Cu, Cr, Co, Ni, Tl, Pb and Hg) in the solids and allowed to investigate the speciation of immobilization of those metals.

Characterization and optimization of β-galactosidase immobilization process on a mixed-matrix membrane.

β-Galactosidase is an important enzyme catalyzing not only the hydrolysis of lactose to the monosaccharides glucose and galactose but also the transgalactosylation reaction to produce galacto-oligosaccharides (GOS). In this study, β-galactosidase was immobilized by adsorption on a mixed-matrix membrane containing zirconium dioxide. The maximum β-galactosidase adsorbed on these membranes was 1.6 g/m², however, maximal activity was achieved at an enzyme concentration of around 0.5 g/m². The tests conducted to investigate the optimal immobilization parameters suggested that higher immobilization can be achieved under extreme parameters (pH and temperature) but the activity was not retained at such extreme operational parameters. The investigations on immobilized enzymes indicated that no real shift occurred in its optimal temperature after immobilization though the activity in case of immobilized enzyme was better retained at lower temperature (5 °C). A shift of 0.5 unit was observed in optimal pH after immobilization (pH 6.5 to 7). Perhaps the most striking results are the kinetic parameters of the immobilized enzyme; while the Michaelis constant (K(m)) value increased almost eight times compared to the free enzyme, the maximum enzyme velocity (V(max)) remained almost constant.

Stability investigations of zinc and cobalt precipitates immobilized by in situ bioprecipitation (ISBP) process

In situ bioprecipitation (ISBP), which involves immobilizing the metals as precipitates (mainly sulphides) in the solid phase, is an effective method of metal removal from contaminated groundwater. This study investigated the stability of metal precipitates formed after ISBP in two different solid-liquid matrices (artificial and natural). The artificial matrix consisted of sand, Zn (200 mg L(-1)), artificial groundwater and a carbon source (electron donor). Here the stability of the Zn precipitates was evaluated by manipulation of redox and pH. The natural system matrices included aquifer material and groundwater samples collected from three different metal (Zn and Co) contaminated sites and different carbon sources were provided as electron donors. In the natural matrices, metal precipitates stability was assessed by changing aquifer redox conditions, sequential extraction, and BIOMET assay. The results indicated that, in the artificial matrix, redox manipulation did not impact the Zn precipitates. However the sequential pH change proved detrimental, releasing 58% of the precipitated Zn back into liquid phase. In natural matrices, the applied carbon source largely affected the stability of metal precipitates. Elemental analysis performed on the precipitates formed in natural matrix showed that the main elements of the precipitates were sulphur with Zn and Co.

Effect of Extraction Conditions on the Saccharide (Neutral and Acidic) Composition of the Crude Pectic Extract from Various Agro-Industrial Residues

The influence of different extraction methodologies was assessed on the composition of both neutral (arabinose, rhamnose, galactose) and acidic (galacturonic acid) pectic polysaccharides obtained from four agro-industrial residues, namely, berry pomace (BP), onion hulls (OH), pressed pumpkin (PP), and sugar beet pulp (SBP). For acidic pectic polysaccharides, the extraction efficiency was obtained as BP (nitric acid-assisted extraction, 2 h, 62.9%), PP (enzymatic-assisted extraction, 12 h, 75.0%), SBP (enzymatic-assisted extraction, 48 h, 89.8%; and nitric acid-assisted extraction, 4 h, 76.5%), and OH (sodium hexametaphosphate-assisted extraction, 0.5 h, 100%; and ammonium oxalate-assisted extraction, 0.5 h, 100%). For neutral pectic polysaccharides, the following results were achieved: BP (enzymatic-assisted extraction, 24 h, 85.9%), PP (nitric acid-assisted extraction, 6 h, 82.2%), and SBP (enzymatic assisted extraction, 48 h, 97.5%; and nitric acid-assisted extraction, 4 h, 83.2%). On the basis of the high recovery of pectic sugars, SBP and OH are interesting candidates for the further purification of pectin and production of pectin-derived products.

The addition of organic carbon and nitrate affects reactive transport of heavy metals in sandy aquifers

Organic carbon introduction in the soil to initiate remedial measures, nitrate infiltration due to agricultural practices or sulphate intrusion owing to industrial usage can influence the redox conditions and pH, thus affecting the mobility of heavy metals in soil and groundwater. This study reports the fate of Zn and Cd in sandy aquifers under a variety of plausible in-situ redox conditions that were induced by introduction of carbon and various electron acceptors in column experiments. Up to 100% Zn and Cd removal (from the liquid phase) was observed in all the four columns, however the mechanisms were different. Metal removal in column K1 (containing sulphate), was attributed to biological sulphate reduction and subsequent metal precipitation (as sulphides). In the presence of both nitrate and sulphate (K2), the former dominated the process, precipitating the heavy metals as hydroxides and/or carbonates. In the presence of sulphate, nitrate and supplemental iron (Fe(OH)(3)) (K3), metal removal was also due to precipitation as hydroxides and/or carbonates. In abiotic column, K4, (with supplemental iron (Fe(OH)(3)), but no nitrate), cation exchange with soil led to metal removal. The results obtained were modeled using the reactive transport model PHREEQC-2 to elucidate governing processes and to evaluate scenarios of organic carbon, sulphate and nitrate inputs.

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.

Biorefinery of algae: Technical and economic considerations

cascading; fractionation; extraction; maximal valorization; multiple product recovery; proteins; lipids; carbohydrates; minor compounds

Sustainable Approach for the Immobilization of Metals in the Saturated Zone: In Situ Bioprecipitation

In order to remediate three sites in the vicinity of a non-ferrous industrial site, where groundwater was historically contaminated with metals, the best available technique should be selected. Because the groundwater contained high concentrations of metals and high sulphate concentrations (up to 2000 ppm), the feasibility of sulphate reduction and subsequent metal immobilization due to metal sulphide precipitation was examined in the lab before selecting an appropriate remediation technology. Because of the very high metal concentrations in the groundwater and their potential toxic effects on microbial life chemical reagents were also evaluated for immobilization of the metals in situ. The first site (site 1) was characterized by a contamination of Zn (500ppm-3ppm) up to a depth of 130 m-bg. A screening for inducibility of biological activity was performed at two depths – 30 m-bg (below ground) and 65 m-bg -- using microcosm experiments containing both aquifer solids and groundwater. Different electron-donors were selected including pure chemical agents such as lactate and waste products such as molasses and glycerol. Glycerol resulted in the most efficient metal and sulphate removal after about 106 days. Extremely high Zn concentrations were found in the groundwater of the second site (site 2), i.e., up to about 2000 ppm. Similar lab tests applied for site 1 were performed, but in addition chemical agents (NaS2 and CaSx) were used. Whereas the sulphide containing chemical agents immediately resulted in low Zn concentrations in the groundwater, it took >140 days before biological sulphate removal started. Glycerol, lactate and molasses resulted in efficient Zn removal. Site 3 was characterized by relative shallow contamination (<10 m-bg) of mainly Co (30-300 ppm), and containing typical sulphate concentrations in the range of 300-1200 ppm. Rapid microbial sulphate reduction (within 50 days) was induced in the tests containing nutrient-amended lactate, cheese whey and soy oil.

New Membrane Reactor Concept for the Biodegradation of Recalcitrant Organic Compounds

Waste water treatments are very often restricted to BOD and nutrient removal. However two problems still arise being heavy metals and toxic organic compounds, resposible for high COD concentrations. The BICMER (Bacteria Immobilized Composite MEmbrane Reactor) stands for the removal and recovery of heavy metals and the complete mineralization of recalcitrant organics. The BICMER functions via specific immolibized bacteria which are responsible for metal removal or biodegradation capacity.