Impact of ammonia concentration on Spirulina platensis growth in an airlift photobioreactor Xin Yuan a , Amit Kumar b , Ashish K. Sahu c , Sarina J. Ergas d,⇑ a Department of Civil & Environmental Engineering, University of Massachusetts, Amherst, MA, USA b Pollution Prevention & Control Core, UNESCO-IHE, Delft, The Netherlands c Aquateam – Norwegian Water Technology Center AS, Oslo, Norway d Department of Civil & Environmental Engineering, University of South Florida, 4202 E. Fowler Ave., ENB 118, Tampa, FL, USA article info Article history: Received 11 July 2010 Received in revised form 1 November 2010 Accepted 3 November 2010 Available online 12 November 2010 Keywords: Airlift bioreactor Algae Ammonia High strength wastewater treatment Spirulina platensis abstract Spirulina platensis was cultivated in a bench-scale airlift photobioreactor using synthetic wastewater (total nitrogen 412 mg L 1 , total phosphorous 90 mg L 1 , pH 9–10) with varying ammonia/total nitrogen ratios (50–100% ammonia with balance nitrate) and hydraulic residence times (15–25 d). High average biomass density (3500–3800 mg L 1 ) and productivity (5.1 g m 2 d 1 ) were achieved when ammonia was maintained at 50% of the total nitrogen. Both high ammonia concentrations and mutual self-shading, which resulted from the high biomass density in the airlift reactor, were found to partially inhibit the growth of S. platensis. The performance of the airlift bioreactor used in this study compared favorably with other published studies. The system has good potential for treatment of high strength wastewater combined with production of algae for biofuels or other products, such as human and animal food, food supplements or pharmaceuticals. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Microalgae cultivation has been practiced worldwide for production of biofuels and other products, such as human and ani- mal food, food supplements, pigments and pharmaceuticals (Chisti, 2007; Kumar et al., 2010a). In addition to light and CO 2 , the provi- sion of nitrogen (N), phosphorus (P) and micronutrients are essen- tial for the growth of algae. In common algae media, commercial fertilizers are typically used as the main nutrient sources. How- ever, greater economic sustainability can be achieved if commer- cial fertilizers are replaced by impaired water sources, such as municipal, agricultural or industrial wastewaters. This strategy yields additional environmental benefits, as algae remove N and P from the wastewater. The presence of N and P in wastewater dis- charges is a world-wide environmental problem, which results in eutrophication and hypoxia in wastewater receiving waters. In addition, the implementation of nutrient removal in conventional enhanced biological nutrient removal facilities carries high energy, chemical and sludge disposal costs (Metcalf and Eddy, 2003). Several types of wastewater that contain high concentrations of ammonia have been proposed for cultivation of algae, including livestock effluents and centrate from anaerobic digestion of sludges (Craggs et al., 2004; Kebede-Westhead et al., 2006; Mulbry et al., 2008; Wang et al., 2010; Kumar et al., 2010a). However, tox- icants present in these wastewaters can inhibit the growth of mic- roalgae (Munoz and Guieysse, 2006). Among these toxicants, free ammonia is a serious concern, as the ammonia concentrations in these wastewater sources range from a few hundred to greater than 1000 mg L 1 (Fux et al., 2006). Although ammonia is an excel- lent source of N for algal growth (Morris, 1974), free ammonia is toxic to most strains of microalgae due to the uncoupling effect of ammonia on photosynthetic processes in isolated chloroplasts (Crofts, 1966). The speciation of ammonia and ammonium is strongly dependent on pH, therefore algal strains may not be sig- nificantly inhibited by free ammonia at low pH while considerable inhibition may occur at pH values of 9.0 or higher (Azov and Goldman 1982). A potential solution to this problem in wastewater treatment facilities is to decrease the ammonia concentration in the algal growth reactor feedwater by diluting the high ammonia wastewaters with other wastewater sources, such as nitrified sec- ondary effluent. This research utilized cultures of Spirulina platensis, a species of obligate phototrophic cyanobacteria (blue-green algae). Due to its rich protein, vitamin and potassium content, S. platensis has been used as a human dietary supplement, as well as a food and supple- ment in aquaculture, aquarium, and poultry industries (Vonshak and Guy, 1991). In addition, due to its multicellular structure and ability to self-aggregate, gravity settling, a relatively inexpensive separation methods, work well for harvesting S. platensis (Olguin, 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.11.019 ⇑ Corresponding author. Tel.: +1 813 974 1119; fax: +1 813 974 2957. E-mail address: sergas@eng.usf.edu (S.J. Ergas). Bioresource Technology 102 (2011) 3234–3239 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech