This study aimed to search for a proper system for electro-flotation harvesting of microalgae Dunaliella salina with a minimization of metal contamination. An applied electrical current caused cell aggregation and produced small bubbles which levitated cell clusters to the top surface. Since no electrolytic erosion for cathodes (negative electrodes), we tested the harvesting by using planar cathodes, lying in the bottom of the reactor, made from different materials and forms. For a given electrical current, all cathodes resulted in a similar harvesting efficiency as well as the energy consumption. Unlike the cathode, the anode (positive electrodes) usually erodes in the electrolytic process. To avoid contamination of released metal, we used only graphite plates as the anode. Different settings of graphite anode plates (located above the cathode) were studied. For a given electrical current, all cases of anode settings had a similar harvesting efficiency but the energy consumption increased with the distance between the anode and the cathode. For a given setup of electrodes, we showed that both the harvesting efficiency and the energy consumption increased with the applied electrical current. By considering the above results as well as the fact that the stainless steel plate is cheaper and easier to handle in comparison to the graphite plate, we suggest that a combination of graphite anode and stainless steel cathode is an appropriate set for microalgae harvesting with an avoidance of metal contamination. Furthermore, for a convenience of the collection of the levitated microalgae cells, the top surface should be leaved widely opened by setting the graphite anode plates near the wall of the reactor. Finally, a large scale harvesting of the microalgae cultured with outdoor conditions is demonstrated in Nakhon Ratchasima, Thailand.

Microalgae are currently interesting in industry because it can generate many useful products, such as supplementary food, cosmetic and biomass energy. During the cultivation, the growth of microalgae is traditionally followed by cell counting with an optical microscope and a calculation of the cell density. To obtain a precise value of the cell density, the measurement should be performed by ones with good laboratory skills and it takes a long time. We develop a photometer to determine the cell density of microalgae. The photometer consists of a light dependent resistor as the sensor, a light emitting diode as the light source, and a microcontroller which controls all components as well as the cell density calculation using a calibration equation. To test the performance of our device, we cultivate marine microalgae Dunaliella Salina with different aerations and measure the cell density during 18-day cultivation period by using the photometer and the cell counting with an optical microscope. The results show that the cell density values obtained from both measurement methods increase with day of cultivation in a similar manner. Thus, the photometer is a good alternative device to follow the growth of microalgae. Furthermore, it is relatively inexpensive, quick and easy for the operator to use.