# An Innovative Low-Cost Equipment for Electro-Concentration of Microalgal Biomass
## 1 Introduction  
The R&D (research and development) on microalgal usage has expanded tremendously over the last two decades. From biofuels to mutraceutical, this microorganism has led an industrial expansion of novel products for different markets worldwide. Microalgae cells are tiny, usually ranging from one to ten micrometers with a low specific gravity (1-1.1 g/L) [1], and when produced in large-scale reactors (such as open ponds or Photobioreactors), they tend to be highly diluted (on the order of 1 to 2 g/L) [2; 3].  
Given its nature, the most troublesome step of microalgae research and production is the concentration and dewatering of produced biomass. This process is a labor-intensive and time-intensivestep, which separates the microalgal biomass from water for effective downstream processing [4]. Algae concentration and separation from the exhausted media demands large amounts of energy [5]; therefore, extended operation times are required to concentrate significant amounts of biomass.  
In a broad view, in the last ten years, over 1100 research papers focused on algal production and metabolite extraction have been published. To the author's knowledge, the vast majority of these papers used centrifuges for algae concentration. Other technologies for algal concentration, such as flocculation (auto-, bio- or microbial flocculation), flotation, filtration, etc., exist; however, flocs collected may contain a certain amount of flocculant (organic or inorganic), which in turn may contaminate the final biomass, thus reducing the suitability of produced biomass for some purposes [6].  
In 2018, the National Alliance for Advanced Biofuels and Bioproducts (NAABB) in its final report [7] recommended that electroflotation was the most efficient and sustainable method for algae concentration and dewatering. There are three established electrolytic methods: electrocoagulation, electroflotation and electrofloculation. This physical/chemical process is founded on the principle of the movement of electrically charged particles in an electric field [4] and the in situ generation of flocculants during metal electrolysis [8].  
Briefly, an electric current is applied to the solution between two electrodes; then, metal ions are released from the sacrificial anode through electrolytic oxidation. At the same time, oxygen and hydrogen microbubbles generated at the anode and cathode flow through the suspension [9]. Metal ions react with the pollutants, forming flocs, which in turn can be lifted to the surface by the microbubbles or sediment in the lower part of the reactor [6; 10; 11] and can be easily removed from the system's surface [12].  
In 2018 [13], we proposed an Arduino-based magnetic stirrer for the harvesting of biomass through electroflotation. In this study, we found that a short distance between electrodes, medium mixing rates (200 rpm (round per minute)) and 50 W could remove up to 100% of algal biomass from 500 mL of culture media. Other authors have studied potential variables such as voltage, pH, time, current intensity, electrode material, temperature and submerged area of electrodes. Each one of those experiments employed inexpensive materials and equipment found in most laboratories around the world (glass beakers, magnetic stirrer, power supply and lab stands) [1; 3; 4; 5; 6; 8; 13]. Despite its simplicity, there is no available equipment for the concentration and harvesting of algal biomass through electroflotation. This may occur because there is no consensus on which are the most critical variables for biomass concentration, which makes it challenging to build equipment that can be used for different species of both microalgae and cyanobacteria.  
The aim of this project is to design and build efficient, low-cost (\(<\)300 USD (United States dollar)) electroflotation equipment for the concentration and dewatering of algal biomass. To achieve the above, the interaction of three key factors (number of electrodes, mixing rate and time) was employed.