Screening of bioflocculant-producing strains and optimization of its nutritional conditions by using potato starch wastewater

Abstract: In recent years, researchers have paid more and more attention to bioflocculants in waste disposal study. Because the bioflocculants were usually biodegradable and their degradation products were harmless to environment, so the bioflocculants have a good application prospects. However, it was not widely used to practical application till now, because of its low flocculation ability of producing strain and high cost. One measure to decrease the cost associated with the production on industrial scale was to employ low-cost substrates. To develop a novel bioflocculant, a novel technology of producing bioflocculant was studied through screening biofloccuant-producing microorganism which could utilize potato starch wastewater as substrate, then its nutritional conditions was optimized. Moreover, the study would provide a new way for potato starch wastewater reutilization.In the study, 100 strains were isolated from activated sludge. Each strain was cultured separately in either nutrient agar or potato dextrose agar as primarily screening flocculant-producing strain medium. The flocculation rate of fermentation broth against Kaolin clay suspension was used as the evaluation index, 13 bioflocculant-producing strains were screened. According to the ability of strains fermenting potato starch wastewater and producing flocculants, one high yield strain was obtained, named as F5, which was identified as Candida anglica by 26SrDNA analysis. The nutritional contditons that C. anglica fermented potato starch wastewater to produce bioflocculant were optimized through single factor test and the orthogonal test. The results showed that under the conditions of pH value 5.6, inoculum size 10%( volume fraction), 150 r/min and 28℃ for 48 h, the best nutritional compositions were: 1 mL/100 mL glycerin as adding carbon sources, 0.05 g/100 mL (NH4)2SO4 as nitrogen source, 0.1 g/100 mL MgCl2 and 0.1 g/100 mL KH2PO4. The test showed that C. anglica could grow well in non-sterilization potato starch wastewater as basic substrate, and could accumulate flocculation active substance effectively. At that time, the flocculation rate of fermentation broth against Kaolin clay suspension was 94.6%, the CODCr removal rate of potato starch wastewater was 93.7%, and the yield of bioflocculant was 1.36 g/L. It indicated that C. anglica would be a new strain for producing bioflocculants. The results could provide a reference for potato starch wastewater treatment and biological reuse.