The extensive work carried out by the DOE/NREL sponsored Aquatic Species Program to explore large-scale algae production for biodiesel provided a number of recommendations for further work. Key among these was to isolate native, local strains for mass cultivation to ensure adaptation to local seasonal conditions. Currently, there are widespread efforts in the field to screen large numbers of algal strains for lipid production from widely differing natural habitats. Most of these are unlikely to thrive in the specific conditions of algae production ponds (water quality, nutrient sources, mixing, large seasonal light and temperature changes, grazing zooplankton, etc.), as discovered during the Aquatic Species Program. It is well known from limnology studies (McCormick and Cairns 1994) and municipal ponding operations (Benemann et al. 1977; Murry and Benemann 1980) that certain algae strains dominate the population at different seasons and in response to nutrient and other environmental parameters. An ecologically sound approach is to identify seasonally dominant strains in outdoor ponds at a specific site and with regard to local environmental factors and the desired objectives (i. e., high-lipid strains for biodiesel, bioremediation, value-added co-products, etc.).

Algal strains that have been identified for their high oil content and suitability for mass production include the following: Botryococcus braunii, Dunaliella tertio — lecta, Euglena gracilis, Isochrysis albana, Nannochloris sp., Neochloris oleo — abundans, Phaeodactylum tricornutum, Chrysotila carterae, Prymnesium parvum, Scenedesmus dimorphus, Tetraselmis chui, and Tetraselmis suecica (Oilgae 2009 and Chap. 1 of this book). Unfortunately, many of these species are adapted to waters with far higher salinity and grow very slowly in freshwater, while others tolerate wide ranges in salinity. Genera commonly found in wastewater ponds include the following: Chlorella (Ponnuswamy et al. 2013), Chlorococcum, Mi­crocystis and Phormidium (Mahapatra and Ramachandra 2013) Chlorella, Euglena and Selenastrum (Ojala et al. 2013) and Scenedesmus, Ankistrodesmus, Micrac — tinium, Oocystis, Phytoconis, Chlamydomonas, Oscilitoria, and Synechocystis (De Pauw and Van Vaerenbergh 1981). In his work on dairy wastewater treatment, Woertz et al. (2009) worked with batch cultures that were dominated by Scene — desmus, Micractinium, Chlorella, and Actinastrum. Because these strains thrive in wastewater operations, they are prime candidates for bioremediation-biofuel production.

Three final points of consideration for selecting the ideal algal strains would be the ease of harvesting, the ease of cell lysis, and/or lipid extraction and the ability to grow under autotrophic and heterotrophic conditions. While the cyanobacterium Microcystis proliferates in wastewater ponds, its small size (2-5 microns) would make it difficult to harvest. Various strains of Chlorella have been studied for their production of oil, but one of the main impediments in dealing with this genus is its resistance to cell lysis (Gerken et al. 2013; Zheng et al. 2011). Given the consid­erations of algae’s ability to grow in wastewater, be relatively easy to harvest and lyse, and contain a significant amount of oil, the candidate genera would include Euglenia, Scenedesmus, Selenastrum, Chlamydomonas, and Actinastrum. Species of the genus Chlorella can be added to this list with the understanding that future technologies will overcome the challenge of breaking open the cell walls. A con­sortium of two to five of these types of algae along with epiphytic wastewater bacteria could be the essential components of an algae-based wastewater treatment system that yields a high-quality effluent and a significant amount of triglycerides that can be converted into biodiesel or chemicals of industrial significance.