| Coking wastewater is a typical organic wastewater with characteristic of high toxic,nonbiodegradation and high concentrated,showing feature of complicated components,inbalanced nutrition,non-biodegradation,et al.As one of the core unit in the whole treatment process,biological treatment faces limitations including toxicity inhibition,high organic load,making the biological effluent was difficult to meet the emission standard.Therefore,pretreatment of coking wastewater is of great importance to mitigate the impact of biological system load and change solution properties of biochemical system.Based on all these concerns,adsorption is selected as the pretreatment method of coking wastewater,among which adsorbents is the most critical technical issue.Herein,the widely used and functional carbonaceous adsorbents were used in the adsorption experiment.In order to achieve targeted adsorption and provide basis for the development of practical adsorbents,the surface properties and pore structure of the adsorbents were examined and different organic components in the coking wastewater were separated,and correlation of organic matter molecular weight,molecular structure and adsorbent properties?specific surface area,pore size distribution,surface functional groups,et al.?were evaluated..Based on the composition and characteristic of coking wastewater,the solution properties changes of coking wastewater before and after adsorption process were investigate changes which will be a key factor in determining the subsequent wastewater treatment process.Four kinds of carbonaceous sorbents with different pore structures made by wood?A1?,coconut shell?A2?,coal?A3?and coke?H?,respectively,were selsected as model adsorbent to static remove total organic carbon?TOC?in coking wastewater.For the purpose of fully understand the correlation between surface chemical porperties and pore size distribution of carbonaceous sorbents and its adsorption performance toward coking wastewater,the adsorbents were characterized by fourier transform infrared spectrometer?FT-IR?,Brunauer-Emmett-Teller?BET?,scanning electron microscope?SEM?,energy dispersive spectrometer?EDS?and X-ray photoelectron spectroscopy?XPS?,respectively.Besides,the factors that influenced the adsorption behavior of coking wastewater by carbonaceous sorbents including adsorption time,pH values,initial concentrations,adsorption temperature et al were investigated.After adsorption process,the molecular weight?MW?distribution,UV254,SUVA,EMMs and BOD5/COD were analyzed to evaluate the solution properties of coking wastewater.The key conclusions of this work are summarized as follows:?1?The four kinds of carbonaceous sorbents used in this study are mesoporous materials with BET surface areas:A1?1723.59 m2/g?>H?1716.19 m2/g?>A2?911.55 m2/g?>A3?505.23m2/g?,average pore diameter:A1?5.14 nm?>H?5.02 nm?>A3?3.81 nm?>A2?3.45 nm?.When the temperature was 25 oC and the adsorbent concentration was 6 g·L-1,the TOC removal efficiencies of carbonaceous sorbents toward coking wastewater were A2>A1>H>A3.The carbonaceous adsorbent could quickly and efficiently removes the organics substance in coking wastewater,but the adsorption of organic substance was not conducive under alkaline conditions.The adsorption process of four kinds of carbonaceous sorbents with respect to organic substance could be well described by pseudo-second order kinetic.The adsorption process was not only controlled by internal diffusion but also film diffusion.The adsorption performance could be well described by Redlich-Peterson adsorption isotherm equation.The adsorption process was spontaneous process because of the?G vaule was less than 0.The adsorption process was an exothermic reaction which was mainly physical adsorption.The adsorption process was an exothermic reaction,and low temperatures was beneficial to the adsorption reaction.High temperature was not conducive to adsorption reaction,but it could shorten the adsorption time.?2?The proportion of low molecular weight TOC?<1K Da?in coking wastewater was more than 79.75%and it was the main component of the wastewater.The study about the molecular weight distribution,UV254,SUVA,and EEMs indicated that A1 and A2 with large micropore area preferentially adsorbed low molecular weight organics?<1 K Da?,while A3and H could refractory high molecular weight organics and reduced the aromatic structure degree of coking wastewater.Carbonaceous sorbent with micropores?<2 nm?and small mesopores?2 nm10 nm?was more suitable for the treatment of coking wastewater.The GC/MS data showed that coking wastewater had a large variety of organic compounds,mainly composed of phenolic organic compounds.The BOD5/COD value of raw coking water was 0.32,and its biodegradability was relatively poor.The removal efficiency of A3 and H towards the refractory organics was better than A1 and A2.The biodegradability of coking wastewater could be enhanced by the treatment of A3 and H. |
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