Study On The Degradation Of Nitrophenol Pollutants By Activated Carbon-Supported Nano-Zero-valent Iron-Micro Aerobic Biological Combination Technology

Nitrophenol compounds are important chemical raw materials,which are widely used in the production of medicine,pesticide,organic chemical and other related industries.These compounds have"mutagenesis,carcinogenesis and teratoeenesis"and are stable in chemical properties,difficult to biodegrade,and easy to accumulate in the environment,thus endangering the safety of ecological environment and human health.It is of great significance to explore a safe and efficient method for the removal of nitrophenolic pollutants.The study on the degradation of nitrophenolic pollutants by activated carbon supported nZVI/GAC-micro-oxygen biological combined technology was carried out with ONP,PNP and 2,4-DNP as target pollutants.The main results are as follows.1)Nano-sized zero-valent iron supported on activated carbon was prepared by liquid-phase reduction method,and the preparation conditions were optimized.The optimum conditions were as follows:2.334 g of FeSO₄ solution 100 mL,0.462mol/L of NaBH₄ solution 50 mL,and the dosage of activated carbon 5.182 g.The surface morphology and structure characteristics of the material were characterized by FTIR,XRD and XPS.nZVI was successfully loaded on the activated carbon with good dispersion.nZVI particles loaded on the activated carbon were uniform in size and spherical in shape.The results of N₂ adsorption-desorption?BET?test showed that the specific surface area of nZVI/GAC was 807.58m²/g and the pore diameter was2.26nm,The specific surface area and pore diameter of the activated carbon are smaller than those of the unloaded materials.2)The removal efficiency of nitrophenol pollutants by nZVI/GAC was studied through static adsorption experiments.When nZVI/GAC dosage was 2 mg/L,the removal efficiency of ONP,PNP and 2,4-DNP could reach 95.2%,and then the dosage,pH,initial concentration of pollutants,reaction time and temperature and so on all had effects on the removal rate of nitrophenol pollutants.When the dosage of nZVI/GAC was more than 2g/L,the removal effect did not change significantly with the increase of dosage,only increased by about 3%.With the increase of pH,the removal rate of nZVI/GAC nitrophenol decreased gradually.Under the dynamic adsorption experiment,the higher the initial pollutant concentration,the higher the initial filtration rate,the worse the removal efficiency of pollutants,and the faster the mass transfer zone moves,the shorter the penetration time,and the removal rate is less than 90%after the filtration rate is greater than 0.72 m/h.3)The removal kinetics of three nitrophenols by nZVI/GAC accords with pseudo-second-order kinetic equation,with correlation coefficient R²>0.99;The adsorption process can be described by Freundich isothermal adsorption model.The removal of nitrophenols by nZVI/GAC is mainly accomplished by the synergistic effect of activated carbon adsorption and nZVI reduction.The degradation products of ONP,PNP and 2,4-DNP were analyzed by HPLC-MS.ONP was reduced to2-Aminophenol,PNP was mainly reduced to PAP and a small amount was oxidized to hydroquinone,and 2,4-DNP was reduced to 2-amino-4-nitrophenol.4)Study on the treatment of PNP wastewater was carried out in a micro-oxygen baffled reactor?mABR?.The results showed that the removal rate of PNP was95%,when the HRT was 24 hours and the concentration of PNP influent was less than100 mg/L,using glucose as a carbon source.The removal rate of COD is the highest when DO concentration in downflow chamber is 0.3-0.5 mg/L.Based on the Monod equation and considering the inhibitory effect of nitrophenols on microorganisms,a kinetic model of nitrophenols degradation in micro-oxygen baffled reactor was established.5)The products of microaerobic biodegradation of PNP and 2,4-DNP were determined by HPLC-MS.The results showed that the main intermediates of PNP were p-aminophenol,hydroquinone and hydroquinone.The products of 2,4-DNP include2-amino-4-nitrophenol?2A4NP?,4-nitro-2-aminophenol?4A2NP?,2,4-aminophenol and phenol;the degradation pathway is that anaerobic microorganisms in micro-aerobic granular sludge reduce nitrophenol pollutants into corresponding aminophenol forms,and aminophenol can be converted into CH₄ and CO₂ by anaerobic microorganisms;aerobic microorganisms convert PNP into pyrogallol and hydroquinone.They open to the tricarboxylic acid cycle under the action of monooxygenase or dioxygenase.Aerobic biodegradation of nitrophenols is mainly metabolized through the intermediate pathway of hydroxybenzenes.6)The effect of nZVI/GAC-microorganism combined technology treating PNP and 2,4-DNP is better than that of single reactor.The initial concentration is200-280mg/L,the filtration rate was 0.24m/h,HRT was 30h,DO was 0.3-0.5mg/L,and COD removal rate can be maintained at about 95%.The combined technology can remove nitrophenols pollutants by adsorbing nitrophenols at the adsorption sites provided by activated carbon in nZVI/GAC granules,and then reducing nitrophenols to amino phenols corresponding to various Nitrophenols by nano-iron loaded on the surface of activated carbon.Under the action of anaerobic microorganisms and aerobic microorganisms in micro-aerobic granular sludge,these substances are converted into CO₂ and H₂O through different ways.