Treatment Of Garlic Processing Wastewater With Membrane Separation Process

Garlic processing wastewater is a very special kind of refractory wastewater in the food processing industry.The chemical oxygen demand?COD?of garlic processing wastewater tend to over than 5000 mg O₂/L,and the allicin can hinder the growth of bacteria.Therefor,the treatment methods for general wastewater can not meet the demand of garlic wasterwater.But to consider from the perspective of food science,the contents of garlic processing wastewater caused the increase of COD,such as carbohydrates and protein contaminants,are not only contaminants but also valuable resources.In this paper,a method of ultrafiltration membrane for processing the garlic wastewater was studied,and the molecular weight distribution?MWD?of neutral polysaccharides,acidic polysaccharide and protein substances in garlic wastewater were measured.Finally,the nutrient substances were extracted from garlic processing wastewater by filtration with ultrafiltration membrane.1.Firstly,to explore the contents of garlic processing wastewater caused the increase of COD:determinate the MWD of carbohydrate and protein.The results showed that,the MWD of polysaccharide in garlic wastewater was mainly between Mw 3k-5k Dalton,and this part of polysaccharides is 60.21%of the total polysaccharides.In addition,the results were also confirmed by the measurements of exclusion chromatography.The MWD of proteins in garlic wastewater was over Mw 4.5k Dalton,and the MWD of acidic polysaccharides was mainly between Mw 10k-50k Dalton.Then,according to the MWD of substances in garlic wastewater,we determined the type of ultrafiltration membrane used for filtration.2.A sewage treatment system?S2?for the ultrafiltration and purification of garlic processing wastewater was developed.This system uses 5 kinds of ultrafiltration membranes?30k,10k,1k,300,150 Dalton?in series,and it is able to achieve the extraction of resources from garlic wastewater and the satisfaction of national sewage comprehensive emission standard.The garlic wastewater of total sugar concentration of 6 mg/m L was purified by this sewage treatment system?S2?,then its sugar concentration can be reduced 99.6%,to achieve25?g/m L;COD was reduced 99.7%,to achieve 16 mg O₂/L;BOD was dropped 99.8%,to achieve 8 mg O₂/L;the turbidity decreased of 100%.This indicator reached the primary standard of the integrated wastewater discharge standard of the“South North Water Transfer Project”.At the same time,the garlic polysaccharide,allicin,protein can be extracted from the garlic wastewater for turning waste into treasure.3.In this paper,we discussed the influences of initial concentration of garlic wastewater,operating pressure and quality of water sample on the work efficiency of this system?S2?.The experiments show that this system can be applied to the garlic wastewater which the initial concentration is less than 21 mg/mL,and this concentration is much higher than the real industrial samples?2⁶ mg/mL?.The level of work stress can change the flow rate of system,but it has little effect on the quality of outlet water.Under certain operating pressure,quality of water sample has little effect on this system?S2?.We also studied the dynamic stability of the quality of outlet water for this system.Then we developed the fast method for monitoring the quality of outlet water and determined the carbohydrate is the main influence factor of the quality of outlet water.At the same time,we conducted a study of membrane efficiency and the timing of collecting concentrated solution and cleaning the membranous can provide the reference for the industrial production.In addition,we proposed several methods for further purification in order to dispose the different concentrations of wastewater in the most energy-efficient way.