title: Optimization of the integrated citric acid-methane fermentation process by air stripping and glucoamylase addition.
abstract: To solve the problem of extraction wastewater in citric acid industry, an integrated citric acid-methane fermentation process was proposed. In the integrated process, extraction wastewater was treated by mesophilic anaerobic digestion and then reused to make mash for the next batch of citric acid fermentation. In this study, an Aspergillus niger mutant strain exhibiting resistance to high metal ions concentration was used to eliminate the inhibition of 200 mg/L Na(+) and 300 mg/L K(+) in anaerobic digestion effluent (ADE) and citric acid production increased by 25.0 %. Air stripping was used to remove ammonium, alkalinity, and part of metal ions in ADE before making mash. In consequence, citric acid production was significantly improved but still lower by 6.1 % than the control. Results indicated that metal ions in ADE synergistically inhibited the activity of glucoamylase, thus reducing citric acid production. When 130 U/g glucoamylase was added before fermentation, citric acid production was 141.5 g/L, which was even higher than the control (140.4 g/L). This process could completely eliminate extraction wastewater discharge and reduce water resource consumption.
authors.affiliation: The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Xu
authors.forename: Yang-Qiu
authors.initials: YQ
authors.lastname: Chen
authors.forename: Hong-Jian
authors.initials: HJ
authors.lastname: Zhang
authors.forename: Ke
authors.initials: K
authors.lastname: Wang
authors.forename: Lei
authors.initials: L
authors.lastname: Tang
authors.forename: Jian-Hua
authors.initials: JH
authors.lastname: Zhang
authors.forename: Xu-Sheng
authors.initials: XS
authors.lastname: Chen
authors.forename: Zhong-Gui
authors.initials: ZG
authors.lastname: Mao
mesh_terms: D000388:Air; D001234:Aspergillus niger / Q000254:growth & development*; D019343:Citric Acid / Q000378:metabolism*; D005087:Glucan 1,4-alpha-Glucosidase / Q000737:chemistry*
chemical_list: D019343:Citric Acid; D005087:Glucan 1,4-alpha-Glucosidase