Study On Removal Of Ammonia From Wastewater And Organic Acid From Straw Acid Hydrolysate By Novel Membrane Contactors

Membrane contactor is a general term of several membrane modules which have same characteristics.Membrane contactor separates two different types of fluids by porous membrane,the pores on the membrane provide mass transfer channel for the fluids and larger contact area,non-dispersive contact occur between two immiscibility phase.Membrane contactor is a novel and efficient contact mass transfer technology.Supported-gas membrane is an important kind of application process of membrane contactor,which is being paid more and more attention in dealing with ammonia-containing wastewater because of its advantage,such as larger specific surface area,simplicity of operation,free from secondary pollution and possibility of recovering pure by-products.However,the industrial application of traditional supported gas membrane module has been limited by its disadvantage,such as non-uniform flow in the shell side,low concentration of ammonium salt as by-product and leakage between feed solution and stripping solution which is caused by the damage of membrane.A modified dual-hollow fiber membrane contactor,which contains two sets of hydrophobic porous hollow fibers,was used to remove ammonia from its aqueous solution.In this study,it was studied that the influence of velocity of feed solution,feed-in ammonia concentration,concentration of absorbent in the stripping solution and temperature on the mass transfer performance of the dual-fiber contactor and the performance was compared indicated by that the dual-fiber module and conventional single-fiber module by using overall mass transfer coefficient and the concentration of by-product ammonium salt in the stripping solution.The experimental results showed that temperature of feed solution had more remarkable influence on the mass transfer performance than feed-in flow rate and feed-in ammonia concentration.The overall mass transfer coefficient increased as the temperature of feed solution increased.The overall mass transfer coefficient of dual-fiber module was much higher than that of single-fiber module at low stripping-solution flow rate and concentration of absorbent in the stripping solution.Under these identical experiment conditions,the osmotic distillation which caused the dilution of byproduct,namely aqueous solution of ammonium sulfate,was weakened because of the special configuration of dual-fiber module and the final concentration of ammonium sulfate was 9% higher than that obtained by using single-fiber module.The long-term operational stability of dual-fiber module was up to 20 times higher than that of single-fiber module when was the pretreated landfill leachate used as a feed.Membrane distillation is an another kind of important application of membrane contactor.This process has widely used in the fields of seawater desalination,removal or recovery of volatile compounds from aqueous solutions,concentration of the aqueous solution of non-volatile compounds and waste water treatment owing to its easiness to use low-grade heat source and high purity of products.A multiple-effect membrane distillation(MEMD)process,which base on the air-gap membrane distillation(AGMD)principle,was used to remove the volatile organic acids in the acid hydrolysate of lignocellulose.The effects of different operating variables were tested on the performance of MEMD process indicated by permeation flux J,gained-output-ratio GOR,rejection rate of glucose Rg and removal percentage of volatile organic acids ?.The experiment results showed that as the cold feed-in temperature T1 increased,permeation flux declined and GOR increased,the removal percentage of acetic acid had no obvious change and the removal percentage of levulinic acid increased;as the hot feed-in temperature T3 increased,permeation flux and GOR increased,the removal percentage of acetic acid increased and the removal percentage of levulinic acid had no obvious change;as the feed-in flow rate increased,permeation flux increased and GOR declined,the removal percentage of acetic acid and levulinic acid both declined.When the batch concentrating experiment was performed,the permeation flux and GOR both declined as the operation time elapsed.The rejection rate of glucose Rg was hardly affected by these operational factors and kept above 99.99% during the whole experimental process.The maximum value of J and GOR obtained were 5.5 L·m-2·h-1 and 12.4,respectively;the removal rate of acetic acid and levulic acid were 91.28% and 4.32%,respectively.MEMD process can concentrate the aqueous glucose solution with an initial glucose concentration of 20 g·L-1 to the final glucose concentration up to 280 g·L-1 in the concentrate,which is conducive to increase the concentration of ethanol in the final fermentation broth.