Search

Spent printed circuit boards comminuted to 750 microns were bioleached in a double-stage continuous bioreactor to study the recovery of Fe, Cu, Ni, Zn, Pb, and Co. The first stage of the bioreactor was a bubble column in which an acidophilic consortium of Leptospirillum ferriphilum and Sulphobacillus benefaciens was used to oxidise iron(II) into iron(III) to produce an acidic ferric solution at 1 g/l Fe3+. This solution was then used to leach the metals contained in PCBs under mechanical stirring in the second stage of the bioreactor. It was found that in the first 400 h the average value of the redox potential in the second stage was much lower than that in the outlet from the first stage and Cu dissolution yield was below 1%, whereas yields of the other metals were relatively high (Fe 75%, Zn 33%, Ni 55% and Co 73%); after 400 h a significant increase in dissolution yield was observed (79%, 76%, 78% and 82%, respectively) while Pb dissolution yield remained constant at 7%. It is concluded that that solid/liquid ratio strongly influences bacterial activity, due to the expected toxicity of PCBs on micro-organisms., Spent printed circuit boards comminuted to 750 microns were bioleached in a double-stage continuous bioreactor to study the recovery of Fe, Cu, Ni, Zn, Pb, and Co. The first stage of the bioreactor was a bubble column in which an acidophilic consortium of Leptospirillum ferriphilum and Sulphobacillus benefaciens was used to oxidise iron(II) into iron(III) to produce an acidic ferric solution at 1 g/l Fe3+. This solution was then used to leach the metals contained in PCBs under mechanical stirring in the second stage of the bioreactor. It was found that in the first 400 h the average value of the redox potential in the second stage was much lower than that in the outlet from the first stage and Cu dissolution yield was below 1%, whereas yields of the other metals were relatively high (Fe 75%, Zn 33%, Ni 55% and Co 73%); after 400 h a significant increase in dissolution yield was observed (79%, 76%, 78% and 82%, respectively) while Pb dissolution yield remained constant at 7%. It is concluded that that solid/liquid ratio strongly influences bacterial activity, due to the expected toxicity of PCBs on micro-organisms.

All surfaces that are immersed in seawater rapidly become covered by nitrogenous compounds, proteins, carbohydrates, salts, silica and bacteria in a few hours, and by a grown biofilm in a few days. These biodeterioration, physical and chemical damages involve important cleaning costs. Organostanic paintings used up to now to protect the surfaces against this spoiling will be prohibited in 2008 because of their toxicity. That's why the stake today is to find alternatives to these paintings. The solution which is here suggested consists in acting on the first stages of the formation of the biofilm i.e. the proteins and bacterial adsorption on the surface. For this, the surface is chemically modified then functionalized by enzymes. Enzymes will act locally on the bacteria and thus prevent their adsorption on the surface. The different stages of the grafting are controlled by Infra Red and X-Ray Photoelectron Spectroscopy. In addition, a new enzymatic test making it possible to test the activity of the grafted enzyme was set up and validated. It enables to check the effectiveness of the grafted enzyme towards a model bacterial suspension., Tout matériau immergé en milieu marin se recouvre de composés azotés, protéines, carbohydrates, sels, silice, puis de bactérie en quelques heures, et d'un biofilm mature en quelques jours. Cela altère ses propriétés physico-chimiques, entraîne un risque accru de corrosion localisée et de biodétérioration, avec pour conséquences des coûts d'entretien et de nettoyage importants. Les peintures contenant des sels de tributylétain (TBT) utilisées jusqu'à présent pour protéger ces surfaces se sont avérées toxiques pour le milieu marin [C. Alzieu, Ocean Coast.Manage. 40 (1998) 23-36]. Elles sont désormais soumises à des normes internationales, avec une interdiction d'application des sels TBT effective depuis 2003, et une interdiction totale en 2008. Il est donc aujourd'hui nécessaire de rechercher des alternatives à ces peintures. La solution ici proposée consiste à agir sur les premières étapes de formation du biofilm, à savoir la fixation de protéines et des premières bactéries sur la surface. Pour cela, la surface est modifiée chimiquement et fonctionnalisée par des enzymes, lesquelles vont agir localement sur la bactérie par hydrolyse de certains constituants de sa paroi, empêchant ainsi son adhésion à la surface. Les différentes étapes du greffage ont été contrôlées par Infra Rouge et par Spectroscopie de Photoélectrons X. Ces analyses ont permis de valider chaque étape du greffage. En parallèle, un nouveau test enzymatique pour tester l'activité de l'enzyme greffée a été mis en place et validé. Il a permis de vérifier l'efficacité de l'enzyme greffée vis-à-vis d'une suspension bactérienne modèle.