ELECTROLYSIS OF WATER CONTAINING MICROALGAE FOR REMOVAL OF HARMFUL SPECIES AND PRE-TREATMENT OF MICROBIAL FUEL CELL FEED

In the present project, an experimental work is presented about the electrolysis of water containing harmful microalgae and pre-treatment of microbial fuel cell feed. The work has been carried out at the laboratory of Electrochemical Engineering under the supervision of Prof. Michele Mascia of the Department of Mechanical, Chemical Engineering and Materials, University of Cagliari, and under the supervision of Dr. Mirella Di Lorenzo at the laboratories of the Bioprocessing Research Unit of the Department of Chemical Engineering, University of Bath. Uncontrolled algal growth in water systems causes a number of serious issues that range from unpleasant odors and tastes to eutrophication. Microcystis aeruginosa, a blue-green alga, and Chlorella vulgaris, a green one, were adopted as the model microalgae. A fixed bed electrochemical reactor in flow was tested, which was equipped with three dimensional electrodes constituted by stacks of grids electrically connected in-series, with the electric field parallel to the fluid flow. Nb grids coated with conductive diamond and titanium grids coated with Ir/Ru mixed oxides were used as anode packing, while titanium grids coated with platinum as cathode one. The reactor was characterised for mass transfer, by the limiting current densities techniques, and flow behavior, by pulse-response curves with an inert tracer. Electrolysis experiments were carried out in continuous and in batch recirculated mode with flow rates corresponding to Re from 10 to 80, Cl- concentrations up to 600 mg dm-3, and current densities ranging from 10 to 60 A m-2. The absorbance of chlorophyll-a pigment and the concentration of products and by-products of electrolysis were measured. A simple plug flow mathematical model at steady state was implemented, combining the pseudo-first order kinetics, describing chemical and electrochemical reactions, with the axial dispersion, which accounts for the non-ideal flow behavior of the system. The model allowed obtaining the concentration profiles of chloride and chloride oxidation by-products, which were compared with experimental data, with good agreement in a wide range of flow rates. The model was also successfully used to simulate the performance of the reactor in the single-stack configuration used for the experiments and in multi-stack configurations. In this present study, first laboratory-scale preliminary results for a cost-effective and green solution to the treatment of algae contaminated water systems are also given since current methodologies to treat algae are costly and require harsh chemicals. In particular, an integrated closed-loop system that combines the electrolysis unit with a stack of miniature single chambered air-cathode microbial fuel cells (MFCs) for the treatment of algae contaminated wastewater and energy generation is reported. The effect that MFC design and number of MFC units in the stack have on performance was investigated. Guidelines on the system optimisation are therefore also provided. This work is believed to be a first step towards an effective removal of microalgae that is not only self-sustainable but can also generate extra useful energy.

Uncontrolled algal growth in water systems causes a number of serious issues that range from unpleasant odours and tastes to eutrophication. Microcystis aeruginosa and Chlorella vulgaris, were adopted as the model microalgae. A fixed bed electrochemical reactor in flow with three dimensional electrodes constituted by stacks of grids electrically connected in-series was tested, with the electric field parallel to the fluid flow. Electrolysis experiments were carried out in continuous and in batch recirculated mode with flow rates corresponding to Re from 10 to 80, Cl- concentrations up to 600 mg dm-3, and current densities ranging from 10 to 60 A m-2. The absorbance of chlorophyll-a pigment and the concentration of products and by-products of electrolysis were measured. Experimental data were quantitatively interpreted by a simple plug flow model, in which the axial dispersion accounts for the non-ideal flow behaviour of the system; the model was also successfully used to simulate the performance of the reactor in the single-stack configuration used for the experiments and in multi-stack configurations. In this present study, first laboratory-scale preliminary results for a cost-effective and green solution to the treatment of algae contaminated water systems are also given since current methodologies to treat algae are costly and require harsh chemicals. In particular, an integrated closed-loop system that combines the electrolysis unit with a stack of miniature single chambered air-cathode microbial fuel cells (MFCs) for the treatment of algae contaminated wastewater and energy generation is reported. The effect that MFC design and number of MFC units in the stack have on performance was investigated. Guidelines on the system optimisation are therefore also provided. This work is believed to be a first step towards an effective removal of microalgae that is not only self-sustainable but can also generate extra useful energy.