RESEARCH PAPER A Study on Techniques for Microalgae Separation and Lipid Extraction for Desmodesmus subspicatus A ´ ngeles Cancela 1 • Rocı ´o Maceiras 2 • Vı ´ctor Alfonsı ´n 2 • A ´ ngel Sa ´nchez 1 Received: 27 March 2017 / Revised: 20 June 2017 / Accepted: 23 June 2017 Ó University of Tehran 2017 Abstract An alternative for production of biodiesel is the use of lipids from microalgae. The process has different steps such as microalgae cultivation harvesting, lipids extraction, and transesterification. One of the most impor- tant steps is the microalgae separation from the culture before lipid extraction. Thus, the purpose of the present study is to compare different methods of microalgae har- vesting and total lipids extracting for freshwater Desmod- esmus subspicatus microalga. The methods used for harvesting were chemical coagulation and electrocoagula- tion. Both methods achieved high values of recovery effi- ciency (90%). However, electrocoagulation was considered more attractive because of its lower power consumption and the requirement of high dosages of coagulants for chemical coagulation. Two methods of extraction, Soxhlet and ultrasound irradiation, were tested using different solvents. The highest lipid extraction (36%) was obtained with ultrasound irradiation and ethanol. Thus, ultrasound- assisted extraction appears to be an efficient method for lipid extraction from D. subspicatus. Keywords Microalgae separation Á Chemical coagulation Á Electro-flocculation Á Lipid extraction Á Ultrasound Á Soxhlet Abbreviations U (V) Voltage I (A) Current t (h) Time of applying electric current V (m 3 ) Volume of the microalgal solution RE (%) Microalgae recovery efficiency c i (kg/m 3 ) Initial microalgae biomass concentration OD i (-) Optical density of the suspension to the start OD f (-) Optical density of the suspension at time t Introduction Citizens are facing a huge environmental responsibility, which it is the minimization of greenhouse gases emis- sions. For this reason, different technological processes for development of unconventional new reserves are being developed. Renewable energies play an important role in the coming global energy map (Chen et al. 2011). Microalgae lipids are considered a promising feedstock for producing biodiesel (Amaro et al. 2011; Francisco et al. 2009; Mata et al. 2010). The lipid content of microalgae cells can vary from 2 to 77% depending on the species and environmental conditions/growth (Florentino de Souza et al. 2014). The lipid content can be classified into neutral lipids, free fatty acids, and polar lipids (Balasubramanian et al. 2013). In recent works about productivity, different authors studied the fatty acid content and oil type of Sce- nedesmus species, for its use as a candidate alga to produce biodiesel (Arias-Pen ˜aranda et al. 2013; Damiani et al. 2014). The production of biodiesel from microalgae is associ- ated with the following key processes: cultivation, har- vesting, extraction of lipids, and transesterification. Although these steps are important, harvesting and extraction are the major limitations in the process. Advances in these areas are necessary to third-generation & Rocı ´o Maceiras rmaceiras@uvigo.es 1 Chemical Engineering Department, EEI, University of Vigo, 36310 Vigo, Spain 2 Defense University Center, Escuela Naval Militar, Plaza de Espan ˜a 2, 36920 Marı ´n, Spain 123 Int J Environ Res DOI 10.1007/s41742-017-0035-1