Fouling Behavior Of Dissolved Organic Matter In Steel Wastewater On Reverse Osmosis Membrane

The steel industry is heavy water consumption and heavy pollution industry.The composition of pollutants in wastewater from coking,ironmaking,steelmaking and steel rolling processes is complex.After the treatment of the conventional coagulation and sedimentation process,the water still contains many refractory organic compounds.The dual membrane process is usually used for further treatment to realize reuse of wastewater.However,the refractory organics in industrial wastewater are easy to adsorb and deposit on the surface of ultrafiltration and reverse osmosis membrane,causing membrane fouling,which leads to the decrease of membrane flux,increase of operating cost,and decrease of membrane module life.Therefore,this work aimed to investigate the characteristics of organics in water after ultrafiltration treatment,and their fouling behavior on reverse osmosis membrane,which have practical significance for wastewater pretreatment process and membrane cleaning optimization,reducing membrane pollution and operation cost.In this work,the macroporous adsorption resin was used to separate the different types of organics in ultrafiltration-treated steel wastewater.The fouling behavior of different types of dissolved organics on reverse osmosis membrane surface was analyzed.The main results are listed as follows.（1）The ultrafiltration effluent of iron and steel wastewater was separated into four components:hydrophobic bases（HOB）,hydrophobic acids（HOA）,hydrophobic neutrals（HON）and hydrophilic substances（HIS）.Dissolved organic carbon（DOC）,UV-Vis spectroscopy,UV₂₅₄,three-dimensional fluorescence spectroscopy（3D-EEM）and gas chromatography-mass spectrometry（GC-MS）were used to analyze the four components.The results showed that the content of organic matter in HOB was the lowest;HOA had a high content of humic acids-organic matter;The fluorescence response of HON was the strongest,mainly aromatic protein II;HIS had the highest content of organic compounds and more aromatic compounds.The hydrophobic components were mainly composed of long-chain alkanes and esters,while the hydrophilic component was mainly composed of alcohols.（2）Among the four components,the flux attenuation of HON was the most obvious,followed by HIS,which were 24.81%and 20.96%respectively.Reverse osmosis had obvious effect on the removal of organic compounds in each component,but there were still trace aromatic organic compounds in HIS effluent.The order of UV₂₅₄ removal rate was HOA>HON>HOB>HIS.The content of UV₂₅₄ in HIS effluent was the highest,indicating that trace humic acids in hydrophilic components passed through the reverse osmosis membrane.The RO produced water of four components basically does not contain fluorescent organics,which indicates that RO effectively rejects the fluorescent organics.（3）Scanning electron microscopy,Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to analyze the membrane surface fouled by different components.The results showed that the degree of membrane fouling of various components was different due to the combined effect of organic pollution and inorganic pollution.The surface fouling of raw water and HON membrane was denser than other membranes.HIS membrane surface contains more inorganic elements than others.The C element in the films polluted by HOB,HOA and HIS mainly belongs to C=O bond,while the C element in the films polluted by HON mainly belongs to C-C,C-H,N-C=O and C=O bond.The pollutants in HON water samples were easy to adhere to the membrane and difficult to clean,while the pollutants in HIS were easy to adhere and easy to clean.