Membrane Based Separation Process For Removal/Recovery Of Ammonia From Wastewater

Ammonia is a common pollutant in industrial wastewater with a wealth ofsources and great harm. So it is of great significance to remove and recover ammoniafrom wastewater. Nowadays, the most widely used method to treatammonia-containing wastewater is air stripping or steam stripping. But these methodshave a series of problems such as high energy consumption, high running cost,secondary pollution, equipment fouling and so on. Meanwhilesupported-gas-membrane technology shows great market potential in terms ofammonia-containing wastewater treatment because of its advantages of lowinvestment cost, low energy consumption, little space occupation, high ammoniarecovery rate, no secondary pollution and easy manipulation. Although adding limeinstead of sodium hydroxide for adjusting pH value can greatly reduce the cost ofpretreatment, it is not favored to use lime due to the fear of membrane pollution.Supported-gas-membrane process for removal/recovery of ammonia from wastewaterstreams, which were pretreated by the process of adding lime—microfiltration—ultrafiltration, was studied by using membrane contactors made from microporoushydrophobic polypropylene hollow fibers. The experimental feasibility was identifiedand the effects of operational factors on the mass transfer performance were studied.And on the basis of the study, this process was used to treat landfill leachate.When aqueous solution of ammonium chloride was used as a feed, the long-termoperational stability was good. The overall mass transfer coefficient decreased by7.2%after running for450hours. On the other hand, when aqueous solution of ammoniumsulfate was used as a feed, the membrane module was easy to be polluted whichfurther led to the sharp decrease of K value, as a result of calcium sulphate’soversaturation and crystallization on the membrane surface. However, the operationalstability of the membrane module was greatly extended after removing calciumsulphate crystal from the feed by adding seed crystal—extending static duration—filtrating. The overall mass transfer coefficient decreased by15.2%after running for450hours. Feed pH and temperature were important factors affecting the masstransfer. Whereas, the variation in feed ammonia concentration and feed flow rate hadnegligible effect on the membrane process, and the mass transfer performance wouldbe limited only when the stripping concentration or flow rate were very little.The experiments were carried out to investigate thesupported-gas-membrane-based separation process for removal/recovery of ammonia from landfill leachate by using industrial scale membrane modules made frommicroporous hydrophobic polypropylene hollow fibers. The effects of pretreatmenttechnologies such as foam separation and lime flocculation-coagulation on surfacetension and COD of the landfill leachate were examined. The effects of feedcharacteristics and operational factors on the overall mass transfer coefficient and thelong-term operational stability were also investigated. The experimental resultsshowed that the pretreatment steps could significantly increase the surface tension ofthe landfill leachate, and could greatly reduce its chroma and COD value. More than99%of ammonia in the landfill leachate could be removed effectively by this processwith configuration of two membrane modules in series under the followingexperimental conditions: feed flow rate of100L/h, feed-in ammonia concentration of1000~3000mg/L, acidic-stripping-solution flow rate of200L/h, sulfuric acidconcentration of6~10%and temperature of20~30℃. Meanwhile, an aqueous solutionof10~15%ammonium sulfate was obtained as a by-product. The pilot-scaledemonstration test had been operated for two months in which it showed greatoperational stability and reliability.