Study On The Degradatiobn Of COD_cr In Citrus Can Wastewater By Low Temperature Plasma Technology

A large number of wastewater will be produced in the process of citrus can processing,which contains a lot of carbohydrate and pectin.The composition is complex and the chemical oxygen demand(COD_cr)value is high.If this kind of wastewater is discharged directly without treatment,it will pollute the water body,cause the damage of water resources,and have a serious impact on the environment.Low temperature plasma technology is a new technology for wastewater treatment,which combines high energy electron radiation,ozone oxidation and photochemical catalytic oxidation.It has the advantages of simple operation,fast degradation rate,wide treatment range,no secondary pollution,and can be carried out under normal temperature and pressure.It is a promising water treatment technology.In this study,low temperature plasma was used to treat the wastewater from the processing of citrus can.The sugar,pectin,?-carotene and water quality in the wastewater were studied.The specific research and content are as follows:The low temperature plasma technology was used to treat the sugars in the orange can processing wastewater.The changes of the sugar content and the degradation of CODCr were compared after the different treatment time of the low temperature plasma.The relationship between the COD_cr value of the sugars and the number of C,h,O atoms was analyzed.There is a good linear relationship between the COD_cr value and the concentration of carbohydrate solution.The COD_cr value of 1 mmol?CH2O?is 2.49 ± 0.25 mg / L.The sugar content and COD_cr value of 12 kinds of sugars treated by low temperature plasma decreased with the increase of treatment time.After treatment for 10-40 min,the COD_cr value decreased significantly,and after treatment for 40 min,it tended to be flat.After 60 minutes of low temperature plasma treatment,the COD_cr value and sugar content decreased by 42%-49% and 49%-56% respectively.The results show that the low temperature plasma can reduce the COD_cr value by degrading the sugar content in the wastewater.The pectin in orange can processing wastewater was treated by low-temperature plasma technology.The COD_cr value,pH,pectin content,viscosity,esterification degree,sugar content and particle size of pectin in the wastewater were measured after treatment by low-temperature plasma technology.The effect of low-temperature plasma technology on the internal groups of pectin was analyzed by Fourier Infrared spectroscopy.There is a linear relationship between pectin concentration and COD_cr in the solution.The COD_cr value of pectin solution with different concentrations is reduced by 45%-50%;pH value is decreased;galacturonic acid content is increased by 0%-22%;viscosity is decreased by 20%±2%;degree of esterification is decreased by 17%-21%;total sugar content is decreased by 1%-15%;pectin particle size is significantly reduced;low temperature plasma shortens the long chain molecules of pectin in wastewater to form small molecules Sugars and aldehydes can not only effectively reduce the COD_cr value in water,but also facilitate the further biochemical treatment of wastewater.The carotenoids in orange can wastewater were treated by low temperature plasma,and the mechanism of color change was explored.The content of ?-carotene solution decreased by 89%-92% after being treated by low temperature plasma for 180 minutes,and the color of the solution changed from orange to almost colorless.Low temperature plasma can degrade the pigment in the wastewater of Citrus canning and improve the transparency of water.The acid waste water,alkali waste water after acid-base decapsulation and the return water after rinsing orange slices in the production process of citrus can processing enterprises were collected and treated by low temperature plasma.The changes of chroma,turbidity,soluble solids,pH,COD_cr and total sugar of wastewater under different treatment conditions were studied.With the increase of treatment time,treatment power and treatment temperature,the amount of CODCr degradation of wastewater increases,the COD_cr of acid wastewater can be reduced by 45%-60%,the COD_cr of alkaline wastewater can be reduced by 37%-57%,and the COD_cr of recycled wastewater can be reduced by 70%-79%;the chroma,turbidity,soluble solids,total sugar content of wastewater are decreased,and the water quality is significantly improved.Low temperature plasma was used to optimize the treatment conditions of the wastewater produced in the processing of Citrus cans.The factors affecting the amount of CODCr degradation and the amount of CODCr degradation per unit energy consumption were as follows: power > time > pH value.The optimal conditions for the treatment of acid wastewater and recycled wastewater were pH value 7,88 W power and treatment 90 Under the optimal conditions,the degradation amount of CODCr was 684.75 ± 11.34 mg / L and 711.88 ± 10.77 mg / L,respectively.The optimal conditions for alkaline wastewater treatment were pH 9,88 W power,90 min treatment,and the degradation amount of CODCr was 519.83 ± 9.03 mg / L after treatment under the optimal conditions.According to the degradation amount of CODCr per unit energy consumption,the degradation amount of CODCr per unit energy consumption of acid waste water,alkali waste water and recycled waste water is the largest at the pH value of 9 and 18 W.Under this condition,the degradation amount of CODCr per unit energy consumption of acid waste water is 44.88 ± 0.81 mg / W,the degradation amount of CODCr per unit energy consumption of recycled waste water is 54.33 ± 0.51 mg / W,and the degradation amount of CODCr per unit energy consumption of alkaline waste water is 38.21 ± 0.56 mg / W.The results show that the low temperature plasma treatment can significantly reduce the COD_cr value and improve the quality of the wastewater.The technology is feasible for the treatment of the wastewater.