Construction And Application Of Adsorption-Membrane Separation Coupling System Based On Nitrogen-doped Porous Carbon

Coking wastewater was produced in the processes of high-temperature coal carbonization,chemical by-products refinement as well as gas purification,with complex components.After traditional biochemical treatment,coking wastewater still contains many organic pollutants that are difficult to be biodegraded,such as phenols,benzene,quinoline and polycyclic aromatic hydrocarbons,which have high acute biological toxicity and teratogenic carcinogenicity.Their discharge without further treatment will cause serious adverse effects on the ecosystem of the receiving water body,and even endanger human health.Therefore,there is an urgent need to develop advanced treatment technologies for refractory pollutants to achieve wastewater discharge or recycling.Considering the highly toxic by-products generation and environmental friendliness,the adsorption process is a suitable solution as the end of pipe treatment for refractory organics in coking wastewater.Nitrogen-doped micro-mesoporous carbon prepared by carbonization and KOH activation of urea-formaldehyde resin（UFCAs）realized effective adsorption of quinoline,phenol and pyridine in coking wastewater.The effects of carbonization and activation temperature on the physical and chemical properties of UFCAs were studied.The results showed that with the increase of carbonization temperature,the adsorption rate of nitrogen-doped porous carbon for quinoline increased at first and then decreased,and with the increase of activation temperature,the adsorption efficiency of quinoline by UFCAs gradually increased.Among them,UFCA-900 whose carbonization and activation temperature were both 900°C had large specific surface area(S_BET=1469.94 m²/g)and excellent adsorption properties:the adsorption removal rate of quinoline reached 98.40%about 16 min,and the maximum adsorption capacity of quinoline was 721.90 mg/g at 318 K,the adsorption capacity of phenol and pyridine at 298 K were 341.59 mg/g and 225.08 mg/g,respectively.The adsorption kinetics of UFCA-900 obeyed the pseudo-second-order model,and the adsorption process was endothermic.The regeneration experiment proved that after six adsorption-desorption cycles of UFCA-900 that chemical regeneration with ethanol,the removal rate of quinoline could still reach the level of the initial adsorbent（removal rate≥97.79%）.The adsorption mechanism included electrostatic interactions,π-πinteractions and hydrogen bonds.To achieve well separation of adsorbents,this study used UFCA-900 to construct an Adsorption-Membrane Separation coupling system（AMS）to study the effect of adsorbent dosage and hydraulic retention time（HRT）on the removal rate of quinoline in the dynamic adsorption process.The results showed that when the dosage of UFCA-900 was 1.0 g/L and 1.5g/L,the removal rate of quinoline by AMS remained above 90%in 120 min and 180 min,respectively.Under the condition of 1.0 g/L UFCA-900,an additional 1.0 g UFCA-900 was added every hour,the removal rate of quinoline has been maintained above 90%,and stable operation of 360 min can be realized.When the HRT=1～6 h,there was little effect on the dynamic adsorption and removal of quinoline.The study found that the trans-membrane pressure（TMP）increased less than 0.3 k Pa during the AMS operation,and about 92%of membrane fouling was reversible.AMS was used to treat the actual coking wastewater,when the condition of 1 g/L UFCA-900 and HRT=4 h,the removal rate of UV₂₅₄ can be kept at 62.15%for 240 min.TMP increased by 17.59 k Pa,and the reversible membrane fouling accounted for92.38%of the total membrane fouling.A catalytic ozonation/membrane separation-adsorption/membrane separation coupling system（COMS-AMS）was constructed,and the AMS was used as the subsequent treatment process of COMS to further remove refractory pollutants and the intermediate products of catalytic ozone oxidation.The effects of Mg O dosage and HRT on quinoline removal during dynamic operation in COMS were studied.It was found that HRT=4 h,0.2 g/L Mg O and 4mg/L O₃,the removal rate of quinoline by the reactor stabilized at 92.17%,the contribution of ozone oxidation,catalysis,and membrane filtration was 51.15%,22.33%and 16.16%,respectively.In COMS-AMS,when the HRT=4 h,0.2 g/L Mg O and 4 mg/L O₃ were added to COMS,the adsorbent in AMS was 1.0 g/L,and the removal efficiency of quinoline by COMS-AMS remained above 98%after 540 min operation.The removal rate of organics in actual coking wastewater(in terms of UV₂₅₄)was maintained at more than 71%.Taken together,a simple strategy for in-situ nitrogen-doped porous carbon has been developed in this study and the resultant composite UFCA-900 has a large adsorption capacity for refractory pollutants in coking wastewater.Based on this,an adsorption-membrane separation coupling system was constructed,which realized the continuous and efficient treatment of biochemical effluent and advanced oxidation effluent of coking wastewater.This study can provide a new idea for the safe and efficient advanced treatment of refractory pollutants.