Study On Single Cell Protein Production From Potato Starch Processing Wastewater By Yeast Fermentation

Potato starch processing wastewater(PSPW)is a kind of valuable biomass resource with high rates of chemical oxygen demand,in which has a lot of organic nutrients such as starch,soluble fiber,protein and carbohydrates.Until now,crafts often used in China to treat this wastewater was anaerobic-aerobic biological combination process.However,this process not only deals with high cost,but also does not realize the recovery of wastewater resources.To collect single cell protein(SCP)and remove chemical oxygen demand(COD)from PSPW,in this paper,the basic research on the screening of yeasts,the combination of strains and the optimization of fermentation conditions were carried out.First of all,in allusion to the features of PSPW,and with combination of the investigation of industrial yeast characteristics,five industrial yeasts,i.e.Geotrichum candidum link,Candida utilis,Saccharomycopsis fibuligera,Candida tropicalis and Saccharomyces cerevisiae were selected out for the fermentation of the wastewater.The growth rule and SCP yield of five kinds of yeasts fermented PSPW were compared.The results showed that the quality of the produced SCP could be guaranteed when the fermentation time was controlled to 12 h,and C.utilis and S.fibuligera were proved to be the best yeasts for the production of SCP from PSPW.After fermenting PSPW for 12 h at an initial pH 6 and 28? with an initial COD of 13215 mg/L,a shaking speed of 180 r/min and an inoculated amount of 10%(v/v),the SCP yield,water-soluble protein(WSP)yield and COD removal of C.utilis reached 1.73 g/L,0.273 g/L and 38.77%,respectively.The co-culturing of the yeasts that were significant difference in nutrition and metabolic property could maximize the conversion and utilization of various organic substances in the wastewater,resulting in a better COD removal and SCP production.For the improvement of COD removal and SCP yield,C.utilis and S.fibuligera were used as the basic fermentative bacteria respectively to carry out the research on the production of SCP by the combined flora from PSPW.The results showed that the mixture of C.utilis,G.candidum link and C.tropicalis was the best combination for the fermentation of potato starch processing wastewater.Fermented under the condition of an initial pH 6,28?,an initial COD of 12594 mg/L,an inoculum ratio of 1:1:1(v/v)and an inoculated amount of 10%(v/v),the COD removal rate of the three-strain mixture averaged 46.97%,and a SCP yield of 2.48 g/L and a WSP yield of 0.398 g/L were obtained,which were 1.17,1.33 and 1.45 times of C.utilis respectively.For further improvement of the efficiency of SCP production from PSPW by mixed microflora,the mixing ratio of C.utilis,G.candidum link and C.tropicalis,as well as the fermentation conditions were optimized.The results showed that the optimum ratio of C.utilis,G.candidum link and C.tropicalis was 5:9:1,the optimal fermentation conditions were 12% of the total inoculation amount,24? in temperature,pH vaule of 4.13 and shaking speed of 200 r/min.Fermented under the optimal conditions,the COD removal rate of the three-strain mixture with a inoculum ratio of 5:9:1 averaged 56.9%,and a SCP yield of 3.06 g/L and a WSP yield of 0.53 g/L were obtained,which increased by 16.6%,21.9% and 21.8%,respectively,compared with that of the three-strain mixture fermented under the pre-optimized conditions.