Anaerobic digested dairy manure as a nutrient supplement for cultivation of oil-rich green microalgae Chlorella sp. Liang Wang, Yecong Li, Paul Chen, Min Min, Yifeng Chen, Jun Zhu, Roger R. Ruan * Department of Bioproducts and Biosystems Engineering, University of Minnesota, 1390 Eckles Avenue, St. Paul, MN 55108, USA article info Article history: Received 13 July 2009 Received in revised form 19 October 2009 Accepted 21 October 2009 Available online 24 November 2009 Keywords: Anaerobic digested dairy manure Algae Nutrients removal Lipid content Chlorella abstract The present study was to investigate the effectiveness of using digested dairy manure as a nutrient supplement for cultivation of oil-rich green microalgae Chlorella sp. Different dilution multiples of 10, 15, 20, and 25 were applied to the digested manure and algal growth was compared in regard to growth rate, nutrient removal efficiency, and final algal fatty acids content and composition. Slower growth rates were observed with less diluted manure samples with higher turbidities in the initial cul- tivation days. A reverse linear relationship (R 2 = 0.982) was found between the average specific growth rate of the beginning 7 days and the initial turbidities. Algae removed ammonia, total nitrogen, total phosphorus, and COD by 100%, 75.7–82.5%, 62.5–74.7%, and 27.4–38.4%, respectively, in differently diluted dairy manure. COD in digested dairy manure, beside CO 2 , proved to be another carbon source for mixotrophic Chlorella. Fatty acid profiles derived from triacylglyceride (TAG), phospholipid and free fatty acids showed that octadecadienoic acid (C18:2) and hexadecanoic acid (C16:0) were the two most abundant fatty acids in the algae. The total fatty acid content of the dry weight increased from 9.00% to 13.7% along with the increasing dilution multiples. Based on the results from this study, a process combining anaerobic digestion and algae cultivation can be proposed as an effective way to convert high strength dairy manure into profitable byproducts as well as to reduce contaminations to environment. Published by Elsevier Ltd. 1. Introduction Land disposal methods have traditionally been used to manage animal manures (de Godos et al., 2009). However, the potential of exporting tremendous nitrogen and phosphorus into water bodies makes it not sustainable. Conventional biological treatments such as activated sludge sequential-batch processes (Zhang et al., 2006; Wang et al., 2009) provide potential approaches for a cor- rect waste management, but the associated high energy inputs re- tard their widespread implementation in rural areas (de Godos et al., 2009). Algae based wastewater treatment processes have been gaining tremendous attentions since 1960s (Golueke and Oswald, 1962; Lau et al., 1995; Tam and Wong, 2000) because they could potentially offer many advantages over the common activated sludge process that requires high energy input for aer- ation and high cost for subsequent sludge processing. The success of an algae based system relies on the ability of the algal cells to assimilate organic carbon (heterotrophic growth) (Burrell et al., 1984) as well as inorganic nutrients such as nitrogen and phos- phorus (Lau et al., 1995) from the wastewater for their growth without an aerobic environment being created and maintained. The obtained algal biomass contain high ratios of hydrocarbons in the form of extractable lipids such as free fatty acids, triacyl- glyceride (TAG), phospholipid and glycolipid, and are ideal feed- stocks for biodiesel production. Manure grown algae can also be used as soil conditioner (Wilkie and Mulbry, 2002), animal feed supplement (Barlow et al., 1975) and fermentation substrate (Ue- noa et al., 1998). With all the above-mentioned merits, co-locat- ing algae production with animal waste treatment could be made environmentally effective as well as economically viable in a not distant future. Recovery of nutrients from swine manure wastewaters by mic- roalgae has been extensively investigated by a number of research- ers and a lot of experience has been gained in pilot-scale operations (Barlow et al., 1975; Fallowfield and Garrett, 1985; de Godos et al., 2009) with algal productivities varying from 7 to 33 g/m 2 /day and simultaneous reductions of COD, nitrogen and phosphorus. The experience gained for dairy manure is not as much as that for swine manure but still can be found in several lit- eratures (Lincoln et al., 1996; Woertz, 2007; Mulbry et al., 2008). From an outdoor algal turf scrubber (ATS) raceway system, Mulbry et al. (2008) concluded that projected annual operation costs were 0960-8524/$ - see front matter Published by Elsevier Ltd. doi:10.1016/j.biortech.2009.10.062 * Corresponding author. Tel.: +1 612 625 1710; fax: +1 612 624 3005. E-mail addresses: wangx739@umn.edu (L. Wang), ruanx001@umn.edu (R.R. Ruan). Bioresource Technology 101 (2010) 2623–2628 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech