Development of an effective acidogenically digested swine manure-based algal system for improved wastewater treatment and biofuel and feed production Bing Hu a , Wenguang Zhou a , Min Min a , Zhenyi Du a , Paul Chen a , Xiaochen Ma a , Yuhuan Liu b , Hanwu Lei a , Jian Shi c , Roger Ruan a,b,⇑ a Center for Biorefining and Department of Bioproducts and Biosystems Engineering, University of Minnesota, 1390 Eckles Ave., St. Paul, MN 55108, United States b MOE Biomass Energy Research Center and State Key Laboratory of Food Science, Nanchang University, Nanchang, Jiang Xi Province 330047, China c Nantong University, Jiangsu Province 226007, China highlights " Coupling low cost and eco-friendly algae-based biofuel with animal feed production. " Developing an effective algal system on acidogenically digested manure by a 2 2 CCD way. " High algal growth rate and nutrient removal rates are obtained from the algal system. " Having high algal lipid productivity (3.63 g m 2 d 1 ) for low-cost biofuel production. article info Article history: Received 5 December 2012 Received in revised form 26 January 2013 Accepted 9 February 2013 Available online 16 March 2013 Keywords: Chlorella sp. Acidogenically digested swine manure Central composite design Biofuel feedstock production Nutrient removal abstract An effective semi-continuous process was developed to grow a locally isolated green microalga Chlorella sp. on acidogenically digested swine wastewater in bench scale for improved algal biomass production and waste nutrient removal using central composite design (CCD). The influences of two key parameters, namely wastewater dilution rate (DR) and hydraulic retention time (HRT), on algal biomass productivity and nutrient removal rates were investigated. The optimal parameters estimated from the significant sec- ond-order quadratic models (p < 0.05) were 8-fold DR and 2.26-d HRT. The cultivating experiment in a bench-scale multi-layer photobioreactor with the optimized conditions achieved stable algal productivity and nutrient removal rates, which fitted the predictive models well. Moreover, relatively high and stable protein and lipid contents (58.78% and 26.09% of the dry weight, respectively) were observed for the col- lected algae sample, indicating the suitability of the algal biomass as ideal feedstock for both biofuel and feed production. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Biomass energy made from traditional crops (oil seeds, sugar crops, wheat, etc.) is considered as a viable alternative to fossil fuels. However, advances in first generation biofuel technologies have encountered economic, ecological, and policy concerns, including competition for arable land with food and feed produc- tion, consequential significant food price hike, etc. Microalgae have great potential to replace current feedstock crops, because their productivity is much higher than terrestrial energy crops, and is not constrained by season and land availability and qual- ity. Algal cells provide lipids for biodiesel or crude oil produc- tion, carbohydrates for bioethanol and biobutanol production, and/or nutritional compounds for animal feed production [1]. Cultivation of algae on swine manure is considered to be a potentially practical and economical strategy for algal feedstock production and wastewater treatment. The combination could help relieve the livestock producers from the significant financial burden associated with the treatment of the unmanageable growing manure prior to discharge. However, the process has not been commercialized yet, since the strategy is still faced with the lack of suitable algae strains and the dearth of carbon in the wastewater [2,3]. Our previous report showed that locally isolated facultative het- erotrophic microalga strain Chlorella sp. (UMN271) was capable of 0306-2619/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2013.02.033 ⇑ Corresponding author at: Center for Biorefining and Department of Bioproducts and Biosystems Engineering, University of Minnesota, 1390 Eckles Ave., St. Paul, MN 55108, United States. Tel.: +1 612 625 1710; fax: +1 612 624 3005. E-mail address: ruanx001@umn.edu (R. Ruan). Applied Energy 107 (2013) 255–263 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy