This study aimed to screen high-performance flocculant-producing bacteria for flocculating suspended matter in wheat distillery wastewater. After the preliminary and secondary screening, a high-performance flocculant-producing bacteria strain was screened from the activated sludge of wheat distillery wastewater. Single factor and orthogonal experiments were used to optimize the culture and flocculent conditions for the flocculant-producing bacteria. A superior strain of Klebsiella M1 was

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... d and identified by 16S rDNA. The initial flocculating degree was up to 72%. Based on single-factor tests, the optimum flocculent conditions were a resting time of 30 min, 8%(v/v) culture medium dosage, and 3%(v/v) CaCl2. The optimum culture conditions were an incubation temperature of 30 °C for 48 h at pH 4.5 and rotation speed of 150 rpm. Under the optimum conditions, the flocculating degree was up to 82%. The best fermentation medium components were 15 g/L glucose, 2 g/L peptone, 1 g/L KH2PO4, and 2.5 g/L K2HPO4. A high flocculating degree was also achieved with the low-cost medium. The Klebsiella M1 bacteria strain can be used as a good bioflocculant produced bacteria for wheat distillery wastewater. Wheat distillery wastewater," BioResources 13(4), 7738-7757. 7739 symptoms of weakness and ataxia (Yokoi et al. 1997; Rudén 2004) . Therefore, it is necessary to develop a safe and efficient green flocculant that does not produce the secondary pollution. Because of the innocuity, high efficiency, and green environmentalfriendly nature of microbial flocculants (bioflocculant), they have been attracting major interest from the scientific research community (Liu et al. 2013) . Bioflocculants, which are obtained through fermentation with bacteria or fungi under unique culture conditions, extraction, and refinement, is a metabolic product produced by microorganisms or their secretions. A bioflocculant consists of polymers possessing flocculating activity that can combine with pollutants in wastewater and then generate sediment to be filtered (Vijayalakshmi and Raichur 2003). Most studies have shown that the primarily components of bioflocculant are polysaccharides and proteins (Liu et al. 2009). Most of them are polysaccharides (Luo et al. 2014). Bioflocculants have been used to treat many types of wastewater, such as food, printing and dyeing, minerals, and milk (Wang et al. 2007; Okaiyeto et al. 2015). However, the study of microbial flocculating bacteria on flocculating wheat distillery wastewater has not been conducted. Because the flocculating ability of bacteria can show strong specificity for different types of sewage, it is necessary to consider various flocculant-producing bacteria. (Agunbiade et al. 2017; Li et al. 2017). High-performance flocculant-producing bacterial strains were screened to produce bioflocculant from wheat distillery wastewater, which was selected as the raw material, and the conditions of flocculation and culturing were optimized to develop a highly efficient green purification process for wheat distillery wastewater. Many factors influence the production and flocculant activity of bioflocculants, such as the composition of the culture medium, bacteria culture conditions, and flocculating conditions (Luo et al. 2014) . The optimization of the above conditions is beneficial to the flocculating effect of the bioflocculant. Kurane et al. (1986) reported that when the optimum culture temperature was 30 ℃, the amount of bioflocculants and cell growth were two times higher than at 25 ℃ and 37 ℃. When the initial pH value was 9.5, the cell growth rate was higher than at a pH of 7. Zhao and Liu (2008) showed that under optimum culture conditions (pH = 12, culture temperature = 30 ℃, rotation speed = 150 rpm, and incubation time = 74 h), the amount of bioflocculant was the highest, up to 95.0%, which was higher than that of the control group). Yang et al. (2009) showed that the added bioflocculant amount, pH, coagulant aid (CaCl2), and mixing speed have a substantial influence on the flocculating degree. Carbon, nitrogen, and inorganic salts are key factors to determine the cost of the culture medium. Obtaining the optimum carbon and nitrogen sources and the best phosphate ratio in a flocculating bacteria culture affects the cell growth, bioflocculant production, and leads to a lower cost of the culture medium Murthy and Praveen 2013; Zhao et al. 2013b) . This study optimized the conventional culture conditions, carbon source, nitrogen source, and phosphate ratio. The optimum carbon source was determined using glucose, sucrose, lactose, maltose, and starch. The optimum nitrogen source was determined using single or multiple nitrogen combinations of beef extract, sodium nitrate, urea, ammonium sulphate, and peptone. The optimum inorganic phosphate dosage was obtained by determining the best ratio of potassium dihydrogen phosphate (KH2PO4) and potassium hydrogen phosphate (K2HPO4).