The effect of solvents polarity and extraction conditions on the microalgal lipids yield, fatty acids profile, and biodiesel properties.

This study reports the effects of polar (acetone/methanol) and non-polar (chloroform/hexane) solvents on lipid yield, fatty acids methyl esters (FAMEs) composition, and biodiesel properties of microalgae. The lipids yield extracted by hexane and chloroform (100.01 and 94.33 mg/g) were higher than by methanol and acetone (40.12 and 86.91 mg/g). The polarity of solvents also affected FAMEs composition of microalgal lipids. Total saturated fatty acids and unsaturated fatty acids of extracted lipids were 61.53% and 38.47% by chloroform and 38.85% and 61.15% by methanol. Moreover, polar and non-polar solvents affected the biodiesel properties such as cetane number and oxidative stability. In addition, higher ratio of chloroform to methanol and higher temperature increased the lipid yield and saturation degree of lipids, through ultrasound-assisted lipid extraction method. Overall, the results revealed that the lipids yield, FAMEs composition, and biodiesel quality of microalgal biomass can be significantly affected by solvents polarity and extraction conditions.

Sequential cultivation of microalgae in raw and recycled dairy wastewater: Microalgal growth, wastewater treatment and biochemical composition.

In this study, two cycles of mixotrophic and one cycle of heterotrophic cultivation of Scenedesmus quadricauda (freshwater) and Tetraselmis suecica (marine water) microalgae in dairy wastewater (DWW) were investigated. Dry weights of S. quadricauda and T. suecica were found to be 0.43 and 0.58 g/L after the first cycle and 0.36, and 0.65 g/L after the second cycle of mixotrophic cultivation, respectively. Chlorophyll a content of both microalgae in the first cycle was significantly higher than the second cycle. S. quadricauda removed 92.15% of total nitrogen, 100% of phosphate, 100% of sulfate and 76.77% of total organic carbon, after two cycles of cultivation. The dominant fatty acids during the first and second cycle of S. quadricauda and T. suecica cultivation were C18:1 and C18:3n-3, respectively. The results suggest that by reusing DWW in two consecutive cycles of microalgal cultivation, higher pollutants removal efficiency and microalgal biomass production can be achieved.

Hexavalent chromium removal from water by microalgal-based materials: Adsorption, desorption and recovery studies.

The current study presents a comprehensive comparison towards the potential of different microalgal-based materials for the removal of hexavalent chromium (Cr(VI)) from water. Among the tested materials, microalgal biochar showed the highest removal efficiency (100%) of Cr(VI). The highest monolayer estimated adsorption capacities were 23.98, 25.19 and 24.27 mg/g at 5, 22 and 35 °C, respectively. Experimental data showed good compliance with pseudo-second-order kinetic model. The results of continuous column studies showed that the column removal efficiency increased from 52.33 to 57.58% by increasing the adsorbent dose from 0.125 to 0.200 g. Desorption efficiency of Cr(VI) by 0.1 M NaOH was increased from 51.16 to 59.41% by sonication bath as compared to roller shaker. More than 97% of desorbed Cr(VI) was recovered in less than 10 min by BaCl2. This study shows that non-living microalga materials are more effective than living cells in the removal and recovery of Cr(VI) from water.

Versatile applications of freshwater and marine water microalgae in dairy wastewater treatment, lipid extraction and tetracycline biosorption.

In this study, freshwater (Scenedesmus quadricauda, Sq) and marine water (Tetraselmis suecica, Ts) microalgae were used for the treatment of dairy wastewater (DWW). Sq and Ts showed the highest biomass productivity as 0.47 and 0.61 g/L, respectively. Removal efficiencies of total nitrogen (TN), phosphate (PO43-), and total organic carbon (TOC) were observed as 86.21, 89.83 and 64.47% by Sq and 44.92, 42.18 and 40.16% by Ts, respectively. After wastewater treatment, lipids were extracted from microalgal biomasses. Fatty acid methyl esters (FAMEs) analysis revealed that saturated fatty acids (SFAs) are dominant in Sq and polyunsaturated fatty acids (PUFAs) in Ts. After lipid extraction, removal of tetracycline (TC) from water by microalgal biomasses was also investigated. Maximum adsorption capacities of Sq and Ts were found to be 295.34 and 56.25 mg/g, respectively. Results of this study revealed the versatile applications of microalgae for wastewater treatment, lipid production and TC removal from water.