| Sweet potato starch wastewater contains a large amount of organic substances,such as starch,protein,sugars,fats,etc.,belonging to a type of organic wastewater with random concentration.Generally,sweet potato starch wastewater has no toxicity,containing however a high level of chemical oxygen demand(COD).The sweet potato starch processing wastewater containing starch,fat,amino acids and other nutrients is treated as a medium for microorganisms to cultivate target microorganisms.On one hand,this procedure can reduce the COD of waste liquid.One the other hand,it can also reduce the consumption of drugs during microorganisms cultivation.It not only saves the cost of efficient target microbial production but also achieves the dual role of pollutant removal and microbial preparation.According to characteristics of sweet potato starch wastewater,this study mainly adopted the conventional detection methods in water pollution treatment to detect the basic components of sweet potato starch wastewater.COD and BOD of sweet potato starch wastewater are 18000-27000mg/L and 4000-7000mg/L respectively.B/C of sweet potato starch wastewater 0.18-0.25.It is not conducive to the growth of microorganisms due to its low biodegradability.In addition,it is also difficult to use aerobic biochemical treatment directly.Therefore,white rot fungi were chosen to pretreat the sweet potato starch wastewater.Firstly,in this paper,twenty strains with higher resistance to chromium were obtained through domestication,selection and separation technology from soils contaminated seriously soil around the electroplating factory.Among them ZJ-2,ZJ-3,ZJ-7,ZJ-8,ZJ-12,ZJ-13,ZJ-17,and ZJ-18 were selected because of their resistence to Cr(?)(150mg/L and 200mg/L).The growth curve and pH variation during strains cultivation were measured.ZJ-8 was chosen as a subsequent experimental straindue,then,the sweet potato starch wastewater was fermented and cultivated.The effect of the reduction of chromium on the components of the cells was studied.The mechanism of chromium reduction by the chromium reducing bacteria was explored.After sweet potato starch wastewater was treated with white rot fungi,biodegrade ability was significantly improved.The optimum conditions for the treatment of sweet potato starch wastewater by white rot fungi were are:OD600(2.5-3),30?,reaction time(60h),initial pH(6),shaking speed(150r/min).COD removal rate of wastewater was 64%and the biodegrade ability was 0.51 at this condition.Among them,ZJ-8 was chosen as a subsequent experimental straindue to its strong Cr(?)resistance and high removal rate(67%),after morphological,physiological and biochemical characteristics and 16S rDNA sequence analysis,ZJ-8 was identified as Ochrobactrum sp..The Cr(?)removal efficiency was investigated by measuing the Cr(VI)concentration in the solution under different culture conditions.The experimental results showed that the optimum pH range for Cr(VI)removal was 7-9,the inoculum size was 6%(volume fraction),the initial Cr(VI)concentration was 50 mg/L,and the temperature was 30?.After 72 hours,the strain could reduce 89.4%of Cr(VI).The results showed that reduction of Cr(VI)between the components of cells cultured in LB liquid medium and sweet potato starch wastewater medium were almost the same.The metabolites and reductases in intracellular secretions had reduction capacity for Cr(VI).The cell membrane debris barely had any ability to reduce Cr(VI).Instead of some common metabolites,reductases of extracellular secretions canindeed reduce Cr(VI).This study presents the feasibility of using sweet potato starch wastewater as a microbial culture medium through a large number of experiments.In addition,Ochrobactrum sp.ZJ-8 is expected to be used for chromium-contaminated water and soil restoration. |
PDF Full Text Request