Resourceful Regeneration Of Wastewater From Potato Starch Processing And Deep Purification Of The Tail Water With Visible-Light-Driven Photocatalytic Degradation Technology

The potato,a kind of most important food and economic crop in high-altitude arid and semi-arid regions in northwestern china,can be manufactured into Potato starch.The potato starch processing industry is the largest pillar industry in Gansu and Ningxia provinces and the important way for farmers to get rid of poverty.It has made great contributions to the development of the local rural economy.However,the waste water of rich foam,high turbidity and high concentration is being discharged from potato starch processing,which is the main source of black and odor bodies in rivers and villages in the area and cause serious pollution of the water environment and severely affecting the normal life of nearby residents.Therefore,the measure of dealing with potato starch waste water has become a bottleneck restricting the development of the potato processing industry.This paper try to solve this problem by extracting and recycling the useful components,B-starch,fine fiber,potato protein and so on,contained in the waste water according to the characteristics of these components and then treat the water by anaerobic and aerobic collection methods for pollution control.The treated tail water was deeply purificated by photocatalytical technology to meet the quality requirements of reuse of recycled water for the last.With the prospective development of the potato processing industry,a complete set of resources,high-efficiency,low-cost processing technology to achieve the resource utilization of various components in waste water is in a crying need.?1?Based on the physical and chemical properties of the potato starch processing waste water,which has the B-starch,proteins,amino acids,organic acids,and oligosaccharides,the comprehensive recovery of B-starch,fine fiber,potato protein powder,and methane gas were carried out in sequenc.The comprehensive treatment technologies such as centrifugal separation,acid-flocculation sedimentation,UASB,and efficient immobilized microorganism aerobic were adopted for dealing with potato starch processing wastewater.As a result,the extraction rate of potato protein is higher than 85%,and the purity of the extracted protein powder is higher than 80%.Which means the purpose of resource treatment of potato starch processing waste water was achieved.The deproteinated waste water is treated with anaerobic and aerobic combined technologies for pollution control.The removal rates of COD_cr,NTU,TN,TP and BOD₅ from the discharged tail water are up to 99%,96%,90%,86%,and 99.7%,respectively,compared to the original waste water.?2?CuFe₂O₄ and MgFe₂O₄ cocatalysts were synthesized by self-propagating combustion method,and Ag₃PO₄@CuFe₂O₄ and Ag₃PO₄@MgFe₂O₄ catalysts were synthesized by ion exchange precipitation method.The composite catalysts were characterized by XRD,XPS,BET,PL,UV-vis DRS,SEM,VSM and TEM.As a result,the CuFe₂O₄ and MgFe₂O₄particles were uniformly dispersed on the surfaces of Ag₃PO₄ of the cubic structure.The degradation rate constants of RhB for Ag₃PO₄@CuFe₂O₄?10%?and Ag₃PO₄@MgFe₂O₄?10%?were 0.1423 min^-1 and 0.1370 min^-1,respectively.The photocatalytic activity of the composite catalyst was more than 2 times than that of Ag₃PO₄,which indicated that the photocatalytic stability and recovery performance of the catalyst are improved by introduction of CuFe₂O₄ and MgFe₂O₄.In addtionthe photocatalytic mechanism of the composite catalysts were discussed.?3?NiFe₂O₄ promoter was synthesized by hydrothermal method.Two-dimensional graphene oxide?GO?and three-dimensional MIL-101?MOF?mediators were used to synthesize a series of Ag₃PO₄/GO/NiFe₂O₄ and Ag₃PO₄/MIL-101/NiFe₂O₄ ternary composites by ion exchange precipitation and an in-situ precipitation methods,respectively.Thecompositecatalystswerecharacterizedbythesamemeasurelike Ag₃PO₄@CuFe₂O₄?10%?and Ag₃PO₄@MgFe₂O₄?10%?.The experimental results demonstrated that the charge transfer rate and photogenerated hole-electron separation efficiency of the composite were promoted by introduction of GO and MOF.In addition,the fluorescence lifetime and the photocatalytic activity of the composite catalysts were respectively enhanced as well.The degradation rate constants of RhB for Ag₃PO₄/GO/NiFe₂O₄?8%?and Ag₃PO₄/MIL-101/NiFe₂O₄?20%?composite catalysts were0.1956 min^-1 and 0.1018 min^-1,respectively.The photocatalytic activity of Ag₃PO₄/GO/NiFe₂O₄?8%?and Ag₃PO₄/MIL-101/NiFe₂O₄?20%?were 2.3 times and 1.78times than that of the pure Ag₃PO₄,respectively.Besides,recycling experiments show that the composite catalyst has excellent photocatalytic stability and recoverability.The degradation mechanism study shows that the charge transfer mechanism of the synthesized composite catalyst is Z-scheme type.It means that photocatalytic activity mainly depends on the separation effect of photogenerated electron-hole pairs.?4?The photocatalytically active semiconductor-semiconductor binary composite catalysts Ag₃PO₄@CuFe₂O₄?10%?and Ag₃PO₄@MgFe₂O₄?10%?and semiconductor-mediator-semiconductor ternary complex catalysts Ag₃PO₄/GO/NiFe₂O₄?8%?and Ag₃PO₄/MIL-101/NiFe₂O₄?20%?were used in visible light photocatalytic deep purification to treat waste water from potato starch processing and resourceful utilization to discharge tail water.The purification results showed that the prepared four silver phosphate-based composite catalysts have the effect of deep purification,Ag₃PO₄/GO/NiFe₂O₄?8%?composite catalyst has the best purification effect.The removal rates of COD_cr,TOC,and TN in the tail water reached 60.7%,35.1%,and 10.0%,respectively.The deep purification trend was consistent with the degradation trend of the RhB evaluation system,but the degradation rate and the purification efficiency needed to be increased,and the purification mechanism needed to be explored in the follow-on work.