Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Cultivation of Chlorella vulgaris in manure-free piggery wastewater with high-strength ammonium for nutrients removal and biomass production: Effect of ammonium concentration, carbon/nitrogen ratio and pH Hongli Zheng a, ⁎ , Xiaodan Wu a , Guyue Zou a , Ting Zhou a , Yuhuan Liu a , Roger Ruan a,b a MOE Biomass Energy Research Center and College of Food Science and Technology and State Key Laboratory of Food Science and Technology, Nanchang University, 235 East Nanjing Road, Nanchang, Jiangxi 330047, People’s Republic of China b Center for Biorefining and Department of Bioproducts and Biosystems Engineering, University of Minnesota, 1390 Eckles Avenue, St. Paul, MN 55108, United States ARTICLE INFO Keywords: Microalga Manure-free piggery wastewater Ammonia toxicity Nutrients removal ABSTRACT Ammonia toxicity is a major disadvantage of microalgal growth when high-strength ammonium wastewaters like manure-free piggery wastewater (MFPW) were used as microalgal growth medium. In the present study, the effect of ammonium concentration, carbon/nitrogen ratio, and pH on ammonia toxicity of Chlorella vulgaris cultivated in the MFPW and nutrients removal was investigated. The three important parameters affected am- monia toxicity of C. vulgaris and nutrients removal of the MFPW significantly. The ammonium concentration of the MFPW could be decreased by air stripping. Microalga grew best at a carbon/nitrogen ratio of 25:1 with the maximum biomass concentration of 3.83 g L -1 , the highest cell viability of 97%, and the removal of 100% ammonia, 95% of total phosphorus, and 99% of chemical oxygen demand. Ammonia toxicity was alleviated by pH control. The application of the established strategies can enhance nutrients removal of the MFPW while mitigating ammonia toxicity of C. vulgaris. 1. Introduction Environmental pollution caused by piggery wastewater has become highly serious and attracted widespread concern worldwide. More than 11 millions tons of piggery wastewaters in 2014 were discharged to the environment directly in China (Che et al., 2017). On one hand, amounts of nitrogen, plenty of phosphorus, and a lot of heavy metals in piggery wastewater are the main contaminants; on the other hand, the above nitrogen, phosphorus, and heavy metals have the potential to be used as resources via the availability of technologies (Cantrell et al., 2008). At present, physical and chemical methods as well as biological methods are the common technologies for resource recovery from piggery was- tewater (Christenson and Sims, 2011). Algal biotechnology has been considered as a promising method to recover nutrients from piggery wastewater (Wang et al., 2016; Lu et al., 2016). Treatment of high-strength ammonium wastewater is still a chal- lenge. A common feature of piggery wastewater is the high-strength ammonium (Zheng et al., 2018), which is toxic for microalgae (Yuan et al., 2011). Therefore, ammonium toxicity is an obstacle to microalgal cultivation in piggery wastewaters. To enhance microalgal growth in piggery wastewaters and promote nutrients removal, ammonium toxicity should be mitigated during the process for piggery wastewater treatment by microalgae. Our research group develops a strategy to alleviate ammonia toxicity in microalgal cultivation by the addition of glucose to adjust carbon/nitrogen of the wastewater (Lu et al., 2018). However, due to the high cost of glucose, this strategy may not be widely applied. Ammonia toxicity to microalgae could also be con- trolled by blending the high-strength ammonium wastewaters with nitrate-rich wastewater (Yuan et al., 2011). However, in a real-world application, the plants generating high-strength ammonium waste- waters might be far away from the plants, which produced nitrate-rich wastewaters. There is still little information on the factors affecting ammonia toxicity to microalgae grown on high-strength ammonium wastewaters. To enhance the efficiency of the wastewater-based mi- croalgal cultivation system, the factors which affect ammonia toxicity to microalgae should be investigated. In addition, the practical and cost-saving strategies to alleviate ammonia toxicity should be devel- oped. This study aims at investigating the effect of three prime factors, ammonium concentration, carbon/nitrogen ratio, and pH, on ammonia toxicity to microalga grown on the manure-free piggery wastewater (MFPW) and nutrients removal performance. Furthermore, we https://doi.org/10.1016/j.biortech.2018.11.019 Received 10 September 2018; Received in revised form 31 October 2018; Accepted 5 November 2018 ⁎ Corresponding author at: Nanchang University, 235 East Nanjing Road, Nanchang, Jiangxi 330047, People’s Republic of China. E-mail address: honglizheng@ncu.edu.cn (H. Zheng). Bioresource Technology 273 (2019) 203–211 Available online 07 November 2018 0960-8524/ © 2018 Elsevier Ltd. All rights reserved. T