Growing wastewater-born microalga Auxenochlorella protothecoides UMN280 on concentrated municipal wastewater for simultaneous nutrient removal and energy feedstock production Wenguang Zhou, Yecong Li, Min Min, Bing Hu, Hong Zhang, Xiaochen Ma, Liang Li, Yanling Cheng Paul Chen, Roger Ruan ⇑ Center for Biorefining, Bioproducts and Biosystems Engineering Department, University of Minnesota, 1390 Eckles Ave., Saint Paul, MN 55108, United States article info Article history: Received 22 February 2012 Received in revised form 2 April 2012 Accepted 4 April 2012 Available online xxxx Keywords: Auxenochlorella protothecoides UMN280 Biofuel feedstock production Municipal wastewater Nutrient removal Semi-continuous cultivation abstract Using wastewater to grow algae is probably the most promising route to reduce production costs asso- ciated with nutrients and water. In this study, a newly isolated facultative heterotrophic freshwater microalgae strain, Auxenochlorella protothecoides UMN280, was examined for algal growth, wastewater nutrient removal efficiency, and lipid accumulation in batch and semi-continuous cultivation with vari- ous hydraulic retention time using concentrated municipal wastewater (CMW) as cultivation media. The results of the 6 day batch cultivation showed that the maximal removal efficiencies for total nitrogen, total phosphorus, chemical oxygen demand (COD) and total organic carbon (TOC) were over 59%, 81%, 88% and 96%, respectively, with high growth rate (0.490 d 1 ), high biomass productivity (269 mg L 1 d 1 ) and high lipid productivity (78 mg L 1 d 1 ). Further fatty acid methyl ester (FAME) analysis showed that the microalgal lipids were mainly composed of C16/C18 fatty acids (accounting for over 94% of total fatty acid), which are suitable for high-quality biodiesel production. The system could be scaled up from 100 mL flasks to 25 L BIOCOIL reactors, and semi-continuously operated at hydraulic retention time of 3 days with a net biomass productivity of 1.51 g L 1 d 1 of dried algae. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Combining wastewater remediation with algal biomass produc- tion is likely one of the most economically and environmentally sustainable ways to produce bio-energy and bio-products since wastewaters provide not only water source but also most of the necessary nutrients for algae growth, and thus significant reduc- tions in production costs associated with credits for wastewater treatment, as well as mitigation of the greenhouse gas emissions can be achieved [1–4]. In the municipal wastewater treatment process, there is a stream, called concentrated municipal wastewater (CMW), which is a recycle stream collected from local municipal wastewater treatment plant after dewatering activated sludge [4], was proved to be a viable medium for algae cultivation because: (1) CMW is abundant with macronutrients such as nitrogen (N), phosphorus (P), and micronutrients such as Mg, Na, K, Fe, Ca, Cu and Zn all of which are necessary nutrients promoting algae growth [5]. And the concentrations of these nutrients are much higher than those from any other stages in municipal wastewater treatment process [6]. (2) High concentration (around 1000 mg/L) of total organic car- bons (e.g. acetate acid) in CMW was favorable to those mixotrophic algae species (e.g. Chlorella sp.) for high cell density cultivation and lipids accumulation [4,7]. (3) At St. Paul Municipal Wastewater Treatment Plant, one million gallons per day of CMW could be generated as a sustainable wastewater supply for algal growth. (4) Microalgae grown on CMW tend to aggregate and form self-sedimentation without addition of any flocculants [8], which could extensively reduce harvesting cost. Thus, in this study, CMW was used to cultivate microalgae and some key parameters such as daily biomass yield, lipid productivity as well as nutrient removal efficiency were evaluated throughout the experiment. Growing algae on municipal wastewater for wastewater treat- ment purpose was investigated as early as in the 1950s [9]. How- ever, the concept of using wastewater as a medium for algae-based biofuel production was mentioned in the close-out report for the Aquatic Species Program (ASP) conducted from 1978 to 1996 [1]. One of the key challenges for wastewater-based algae-biofuel pro- ject is to select robust microalgal strains which could adapt well in such wastewater environment with effective nutrient removal and high biomass and lipid productivity. It is hypothesized that some algae species and/or strains which naturally thrive in wastewater environment should perform better 0306-2619/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2012.04.005 ⇑ Corresponding author. Tel.: +1 612 625 1710; fax: +1 612 624 3005. E-mail address: ruanx001@umn.edu (R. Ruan). Applied Energy xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Please cite this article in press as: Zhou W et al. Growing wastewater-born microalga Auxenochlorella protothecoides UMN280 on concentrated municipal wastewater for simultaneous nutrient removal and energy feedstock production. Appl Energy (2012), http://dx.doi.org/10.1016/j.apenergy.2012.04.005