Introduction Biofuel production from renewable resource has been extensively paid attention as a sustainable alternative for fossil fuel. As the feed of third-generation biofuels, Microalgae can produce variety of lipids, proteins, and carbohydrates in large quantities and in a relatively short time. Regarding the compatibility of these microorganisms with culture diffrent conditions and independence from the seasons of the year, the rapid growth rate, absorbing carbon dioxide and improving air quality, renewablity, non-competing with food supplies, the existence of large quantities of lipid and carbohydrate inside their cells, and abillity of biofuels production, Microalgae are known as one of the most suitable options for the biofuels production. Biofuel production from Microalgae consists of several stages, including cultivation, harvesting, drying, cell disruption, extraction (lipids or carbohydrates), and the production of biofuels. Conclusion In the present study, by reviewing each stage of the biofuels production from Microalgae, its importance and application for bioenergy production is discussed. Algal biofuel is not yet competitive with fossil fuels due to its high costs. Researchers are trying to produce economic algal biofuel by improving the growth of Microalgae and enriching their reserves of oil and carbohydrates, creating genetic changes, improving the design of photobioreactros, developing harvesting and drying methods, improving methods of extracting lipid and carbohydrate, and producing valuable products.

Dye is the first known pollutant in industrial wastewater, and its small amount is very undesirable in water. Most of the dyes contain complex organic molecules and are harmful to aquatic life and humans due to the presence of metals, aromatics and other compounds in their structure. Removing or reducing the amount of this pollutant entering the environment is essential, and biological absorption is one of these methods. The main purpose of this research is to investigate the removal of blue reactive textile dye by spirulina Microalgae. In the process of conducting the research, the effect of variables such as contact time, injected algae dose and wastewater concentration was investigated on the dye removal process and the amount of absorption of the samples was measured by a spectrophotometer and the number of experiments was determined by the design expert software via response surface method (RSM) and the analysis of variance (ANOVA) statistical tool was used to analyze the obtained results. Based on the obtained results, in the optimal conditions of the experiment, the best percentage of dye removal by spirulina Microalgae was 100% in contact time of 30 minutes with a dose of 10 ml of injected algae into wastewater with a color concentration of 50 mg/L. Therefore, the use of Microalgae, in addition to being an inexpensive and easy-to-operate method for color removal from colored wastewater such as textile wastewater, it will be of interest to researchers as an environmentally friendly method to remove hard degradable pollutants.

Preparation of Microalgae to produce biofuel involves three stages: cultivation, dewatering and oil extraction. Efficient dewatering of Microalgae is the main challenge in industrial scale. The high cost of Microalgae production is due to the lack of suitable method for harvesting. This paper aims to describe and compare the different Microalgae harvesting methods. As a matter of fact, these methods are divided into three categories which are described as chemical, mechanical and electrical methods. The chemical method consists of coagulation and flocculation steps but none of these steps are economical. Centrifuging is a common method for mechanical harvesting. Relatively this method has high efficiency but it is not cost beneficial because of high energy consumption. Among the electrical methods, electrocoagulation is a new method for Microalgae harvesting which offers higher efficiency and demands lower energy than other methods.

One of the important bottle-necks in production of Microalgae based biodiesel is the lack of an efficient method for harvesting of Microalgae from the culture medium. In this study, the electroflocculation method was developed for harvesting of Microalgae Dunaliella cells from culture medium. The effect of several parameters such as the current density, electrical conductivity of culture medium, time, electrode gap, and electrode type on harvesting efficiency and energy consumption were also determined. The maximum harvesting efficiency of this method was 97.44% at EC=1.35 S m-1 and current density of 90 A m-2 during 3 minutes electroflocculation process in a 300 ml beaker. The maximum efficiency was achieved by aluminum electrodes with 1 cm distance between electrodes and the maximum energy consumption for this practice was 0.621 kW h m-3. It was concluded that electroflocculation is an efficient and cost effective method for Microalgae harvesting.