| With the development of industry and the increase of population,the issue of the treatment,disposal,and recycle of high-concentration organic wastewater has received more attention.High-concentration organic wastewater contains a large amount of carbohydrates.These organic matters are easily degraded by microorganisms,producing short-chain organic acids.Which with high added value,can realizing the recycle of organic wastewater.Electrodialysis technology is clean production technology,the key is ion exchange membrane,and the main function is to concentrate and separate the electrolyte solution.The subject of this paper is how to realize and improve the recycle of organic wastewater,and has conducted research in two aspects: on the one hand,simulated high-concentration organic wastewater was used as substrate for anaerobic fermentation of microorganisms to produce organic acids.Then the electrodialysis technology was coupled with anaerobic fermentation technology to remove and concentrate organic acids in the fermentation broth.At the same time added inorganic carbon source and OH-into fermentation broth to adjust p H.On the other hand,the problem of membrane fouling during the desalination process of high-salt and high-concentration dyeing wastewater by electrodialysis was studied,and a pretreatment method was developed to avoid membrane fouling.The following conclusions were got through this paper study:(1)In batch experiments,the accumulation of organic acids in fermentation broth resulted the p H continuous decrease(<3)and severe product inhibition in control(C)groups.The main products were lactic acid(35%)and ethanol(20%).So the main metabolic pathways of microorganisms were lactic acid fermentation pathway.And the total organic acids production in the C groups only 3.5 g.In experimental(E)groups,the organic acids in the fermentation broth were separated by electrodialysis every day,and the separation efficiency was above 90%.While separated the organic acids,electrodialysis also added OH-ions and inorganic carbon to the fermentation broth to adjust p H and supplement carbon source.Each electrodialysis experiment can supplemented TIC 200 ppm.Therefore,after the end of the experiment,the carbon balance in the E groups was as high as 130%,while the carbon balance in the C groups was only 90%.The main products in the experimental group were lactic acid(80%)and butyric acid(20%),and a small amount of propionic acid,valeric acid and caproic acid were also produced.The main metabolic pathways of the microorganisms were homoacetogenic fermentation and mixed acid fermentation.The final organic acids production reached 13 g,which was 4 times that of the C group.Experiments show that the coupling of electrodialysis and anaerobic fermentation technology can achieved p H control and remove product inhibition,improve microbial activity,and promote microbial anaerobic fermentation of acid production.(2)The continue experiment was started on the basis of product inhibition.The main product in the fermentation broth was caproic acid(70%).Electrodialysis was used to separate the organic acids each day,while can changed the fermentation pathway.And ultimately main produce was lactic acid,which accounts for 80% of the total production.The yield of organic acid was as high as 1.5 g L-1 d-1,the total output of the final organic acids reached 170 g,and 75% of the carbon in the substrate was converted into organic acids.Electrodialysis can adjusted the p H of the fermentation broth while separating the organic acids.In addition,the p H can be controlled by adjusting the number of electrodialysis.This results provide a theoretical basis for the industrial application of the recycle of organic wastewater.Furthermore,organic fouling of ion exchange membrane was observed during organic acids recovery and chemical cleaning was demonstrated as a favorable method for membrane fouling control.(3)Anion exchange membranes were polluted by Remazol Brilliant Blue R(RBBR)in electrodialysis process as well as in static adsorption experiment,aiming to study the mechanism.The RBBR molecules was then oxidized using advanced oxidation as pretreatment further to verify feasibilities of this method by electrodialysis.The reversible gel layer formed by PBBR molecules on the surface of membrane was observed,which prevented ions through the membranes and was the primary reason caused the organic fouling.The effect of ozone oxidation on RBBR is better than that of H2O2+UV in acidic conditions.The color removal rate reached 100% within 90 minutes since oxidized RBBR by ozone.After RBBR was ozonized,the Anthraquinone structure was broken and the ultraviolet peak of the aromatic substances weakened.While the membrane fouling cannot occur in the electrodialysis process since the solution was oxidized,and the desalination efficiency can reach 90%.The optimal dosage(O3/foulant ratio of 35:1)was confirmed in this paper.A theoretical method for the remove membrane organic fouling was proposed.In this research found that,advanced oxidation technology can used as a pre-treatment measure for the membrane organic fouling,to avoid the formation of membrane fouling and provide conditions for the industrial application of ion exchange membranes. |
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