Phenol is one of major pollutants in industrial wastewater with high remediation priority. In the following a summary of some studies concerning phenol degradation in membrane reactors is reported. Wastewater from coal gasification has poor biodegradability and high toxicity. A laboratory-scale anaerobic-anoxic-oxic membrane reactor (AAO-MBR) system was developed to investigate the treatment ability of coal gasification wastewater by Wang et al (2012). The removal capacity of each pollutants used in this system was determined at different hydraulic residence times (HRT) and mixed liquor recycle ratios (R). The experimental results showed that this system could effectively deal with COD and phenol removal and remained in a stable level when the operational parameters were altered, while the nitrification was sensitive to operational conditions. The best performance was obtained at HRT of 48 h and R of 3. The maximum removal efficiencies of COD, NH4+-N and phenols were 97.4%, 92.8% and 99.7%, with final concentrations in the effluent of 71 mg/L, 9.6 mg/L and 3 mg/L, respectively. Organics degradation and transformation were analyzed by GC/MS (Gas Chromatography/Mass Spectrometry) and it was found that anaerobic process played an important role in degradation of refractory compounds. The effect of salt concentration on the performance of a membrane bioreactor (MBR) for treating an olefin plant wastewater was investigated by Sadeghi et al (2012). For this purpose, a lab-scale submerged MBR with a flat-sheet ultrafiltration membrane was used for treatment of synthetic wastewater according to oxidation and neutralization unit of olefin plant. The synthetic wastewater was adjusted to have 500 mg/L chemical oxygen demand (COD). Trials on different concentrations of sodium sulfate (Na2SO4) (020 - 000 ppm) in the feed were carried out under aerobic conditions in the MBR. The results showed that increasing the salt concentrations causes an increase in the effluent COD, phenol, and oil concentrations. These results are due to reduction of the membrane filtration efficiency and also decline in the microbial activity. But in all the trials, the effluent COD and oil concentration was well within the local discharge limit of 100 and 10 mg/L, respectively. These results indicate that the MBR system is highly efficient for treating the olefin plant wastewater, and although high salt concentrations decreased organic contaminant removal rates in the MBR, the effluent still met the discharge limits for treating the olefin plant wastewater. In municipal wastewater treatment plant (WWTP) effluents, the problem due to the presence of micropollutants in wastewater which may be able to disrupt the endocrine system of some organisms, has been faced by Abargues et al (2012). The fate of the alkylphenols-APs (4-(tert-octyl)) phenol, t-nonylphenol and 4-p-nonylphenol) and the hormones (estrone, 17 beta-estradiol and 17 alpha-ethinylestradiol) in a submerged anaerobic membrane bioreactor (SAMBR) pilot plant and in a conventional activated sludge wastewater treatment plant (CTP) has been compared. The obtained results were also compared with those obtained in a previous study carried out in an aerobic MBR pilot plant. The results showed that the APs soluble concentrations in the SAMBR effluent were always significantly higher than those in the CTP. Moreover, the analyses of the suspended fraction revealed that the AP concentrations in the SAMBR reactor were usually higher than in the CTP reactor, indicating that under anaerobic conditions the APs were accumulated in the digested sludge. The aerobic conditions maintained both in the CTP system and in the aerobic MBR favoured the APs and hormones degradation, and gave rise to lower concentrations in the effluent and in the reactor of these systems. Furthermore, the results also indicated that the degradation of APs under aerobic conditions was enhanced working at high solid retention time (SRT) and hydraulic retention time (HRT) values. Direct coupling of separation and photocatalytic degradation by using photocatalytic membrane is an attractive way to solve problems like membrane fouling by adsorbed organic macromolecules or elimination of small organic molecules which cannot be efficiently stopped by a membrane. A simple and robust synthesis route to a photo-catalytically active titania membrane was developed from a commercial TiO2 hydrosol and commercial alumina supports by Djafer et al (2010). Reproducible defect-free layers with a thickness of about 3 µm were prepared. The membrane performance in term of separation and photocatalytic activity were investigated. The pure water permeance was 150 L h-1 m-2 bar-1 and the measured molecular weight cut-off was around 50 kDa corresponding to an ultrafiltration membrane. The photocatalytic efficiency was tested by photo-oxidation under UV irradiation of a reference organic dye (methylene blue) for comparison with reference TiO2 photocatalysts, and also with phenol as typical organic pollutant in water. The measured values of quantity of destroyed organic molecules per units of time and of membrane surface area are in the range 0.8-3.8 x10-8 mol s-1 m-2. Phenol decomposition was carried out under UV irradiation in a recycle batch photocatalytic membrane reactor (PMR) by Yang et al (2011). To overcome the problem of post-recovery of the catalyst particles after water treatment, surface modification of polypropylene macroporous membrane was performed with the technique of photoinduced reversible addition-fragmentation chain transfer grafting polymerization of acrylic acid. TiO2 photocatalysts were introduced into the acrylic acid grafted membrane surface. In the tests on the PMR the normalized membrane flux reached 1.7 times that of the unmodified membrane for the poly(acrylic acid) (PAAc) modified membrane. Introducing TiO2 photocatalysts into the membrane surface reduced slightly the normalized membrane flux. For the PMR with a grafting degree of 12.9% (wt) of PAAc on the membrane surface, the corresponding decomposition percentage was 32.5% after 6 h UV light irradiation. The role of membrane in phenol degradation in high-phenol-fed MBR (membrane bioreactor) was explored by Ahn et al (2011). Phenol elimination in high-phenol-fed MBRs resulted in complete mineralization and the high-phenol-fed MBR exhibited greater biomass-specific phenol removal rates (0.4-1.5 mg phenol/(mg VSS.d) than the low-phenol-fed MBR. In the high-phenol-fed MBR, filamentous non-settling microbes were more abundant than in the low-phenol-fed MBR. Batch experiment, high-acclimated and non-settling microbes were separately collected from the high-phenol-acclimated bioreactor, and their specific phenol degradation was determined at 5.1 mg phenol/(mg VSS.d). The greater specific phenol degradation rate of the non-settling microbes than the observed phenol elimination rate in the high-phenol-fed MBR indicated that the high-phenol-acclimated and non-settling microbes had greater degradation activity than the rest of sludge microbes in the bioreactor. According to these findings, the role of membrane in the high-phenol-fed MBR was identified as the containment of non-settling and biodegradative microbes in bioreactor, and in turn, the membrane-driven increase of non-settling phenol degrading microbes enhanced phenol elimination in the high-phenol-fed MBR. A novel process to biodegrade phenol present in an acidic (1 M HCl) and salty (5% w/w NaCl) synthetically concocted wastewater was studied by Livingston (1993). The process utilized a membrane bioreactor, in which the phenol present in the wastewater was separated from the inorganic components by means of a silicone rubber membrane. Transfer of the phenol from the wastewater into a biological growth medium allowed biodegradation to proceed under controlled conditions which were unaffected by the presence of inorganic species in the synthetic wastewater. At a wastewater flow rate of 18 mL h-1 (contact time 6 h), 98.5% of phenol present in the wastewater at an inlet concentration of 1000 mg L-1 was degraded; at a contact time of 1.9 h, 65% of the phenol was degraded. Phenol degradation was accompanied by growth of a biofilm on the membrane tubes and by conversion of approximately 80% of the carbon entering the system to CO2 carbon. Analysis of the transport of phenol across the membrane revealed that the major resistance to mass transfer derived from the diffusion of phenol across the silicone rubber membrane. A mathematical model was used to describe the transfer of phenol across the membrane and the subsequent diffusion and reaction of phenol in the biofilm attached to the membrane tube. This analysis showed that (a) the attached biofilm significantly lowers the mass transfer driving force for phenol across the membrane, and (b) oxygen concentration limits the phenol degradation rate in the biofilm. These conclusions from the model are consistent with the experimental results. The effect of adaptation of mixed culture in the phenol biodegradation was studied by Marrot et al (2006). The degradation experiments were carried out at different phenol concentrations from 0.5 to 3 g L-1. Biological treatment showed to be economical and practical leading to a complete removal of phenol. High concentrations of phenol were inhibitory for growth; so it was for the rates of substrates utilization that were greater at low initial concentrations. Haldane kinetics model for single substrate was used to obtain maximum specific growth rates (μm = 0.438 h−1), half saturation (K = 29.54 mg L-1) and substrate inhibition constant (K-i = 72.45 mg L-1). These results were in agreement with those reported in the literature for phenol removal abilities in different systems, although the concentration in phenol was significant, and the Haldane model was acceptable. References Ahn S, Song I, Choung Y, Park J (2011) Improved phenol degradation in high-phenol-fed MBR by membrane-driven containment of non-settling biodegradation microbes. Desalination and Water Treatment 31:320-325 Abargues MR, Robles A, Bouzas A, Seco A (2012) Micropollutants removal in an anaerobic membrane bioreactor and in an aerobic conventional treatment plant. Water Science and Technology 65:2242–2250 Djafer L, Ayral A, Ouagued A (2010) Robust synthesis and performance of a titania-based ultrafiltration membrane with photocatalytic properties. Separation and Purification Technology 75:198-203 Livingston AG (1993) A novel membrane bioreactor for detoxifying industrial waste-water. 1. Biodegradation of phenol in a synthetically concocted waste-water. Biotechnology and Bioengineering 41:915-926 Marrot B, Barrios-Martinez A, Moulin P, Roche N (2006) Biodegradation of high phenol concentration by activated sludge in an immersed membrane bioreactor. Biochemical Engineering Journal 30:174-183 Sadeghi F, Mehrnia MR, Nabizadeh R, Sarrafzadeh MH (2012) Treatment of synthetic olefin plant wastewater at various salt concentrations in a membrane bioreactor. Clean-Soil Air Water 40:416-421 Yang S, Gu JS, Yu HY, Zhou J, Li SF, Wu XM, Wang L (2011) Polypropylene membrane surface modification by RAFT grafting polymerization and TiO2 photocatalysts immobilization for phenol decomposition in a photocatalytic membrane reactor. Separation and Purification Technology 83:157-165 Wang ZX, Xu XC, Gong Z, Yang FL (2012) Removal of COD, phenols and ammonium from Lurgi coal gasification wastewater using A(2)O-MBR system. Journal of Hazardous Materials 235:78-84
Phenol degradation using membrane reactor
MOLINARI, Raffaele
2013-01-01
Abstract
Phenol is one of major pollutants in industrial wastewater with high remediation priority. In the following a summary of some studies concerning phenol degradation in membrane reactors is reported. Wastewater from coal gasification has poor biodegradability and high toxicity. A laboratory-scale anaerobic-anoxic-oxic membrane reactor (AAO-MBR) system was developed to investigate the treatment ability of coal gasification wastewater by Wang et al (2012). The removal capacity of each pollutants used in this system was determined at different hydraulic residence times (HRT) and mixed liquor recycle ratios (R). The experimental results showed that this system could effectively deal with COD and phenol removal and remained in a stable level when the operational parameters were altered, while the nitrification was sensitive to operational conditions. The best performance was obtained at HRT of 48 h and R of 3. The maximum removal efficiencies of COD, NH4+-N and phenols were 97.4%, 92.8% and 99.7%, with final concentrations in the effluent of 71 mg/L, 9.6 mg/L and 3 mg/L, respectively. Organics degradation and transformation were analyzed by GC/MS (Gas Chromatography/Mass Spectrometry) and it was found that anaerobic process played an important role in degradation of refractory compounds. The effect of salt concentration on the performance of a membrane bioreactor (MBR) for treating an olefin plant wastewater was investigated by Sadeghi et al (2012). For this purpose, a lab-scale submerged MBR with a flat-sheet ultrafiltration membrane was used for treatment of synthetic wastewater according to oxidation and neutralization unit of olefin plant. The synthetic wastewater was adjusted to have 500 mg/L chemical oxygen demand (COD). Trials on different concentrations of sodium sulfate (Na2SO4) (020 - 000 ppm) in the feed were carried out under aerobic conditions in the MBR. The results showed that increasing the salt concentrations causes an increase in the effluent COD, phenol, and oil concentrations. These results are due to reduction of the membrane filtration efficiency and also decline in the microbial activity. But in all the trials, the effluent COD and oil concentration was well within the local discharge limit of 100 and 10 mg/L, respectively. These results indicate that the MBR system is highly efficient for treating the olefin plant wastewater, and although high salt concentrations decreased organic contaminant removal rates in the MBR, the effluent still met the discharge limits for treating the olefin plant wastewater. In municipal wastewater treatment plant (WWTP) effluents, the problem due to the presence of micropollutants in wastewater which may be able to disrupt the endocrine system of some organisms, has been faced by Abargues et al (2012). The fate of the alkylphenols-APs (4-(tert-octyl)) phenol, t-nonylphenol and 4-p-nonylphenol) and the hormones (estrone, 17 beta-estradiol and 17 alpha-ethinylestradiol) in a submerged anaerobic membrane bioreactor (SAMBR) pilot plant and in a conventional activated sludge wastewater treatment plant (CTP) has been compared. The obtained results were also compared with those obtained in a previous study carried out in an aerobic MBR pilot plant. The results showed that the APs soluble concentrations in the SAMBR effluent were always significantly higher than those in the CTP. Moreover, the analyses of the suspended fraction revealed that the AP concentrations in the SAMBR reactor were usually higher than in the CTP reactor, indicating that under anaerobic conditions the APs were accumulated in the digested sludge. The aerobic conditions maintained both in the CTP system and in the aerobic MBR favoured the APs and hormones degradation, and gave rise to lower concentrations in the effluent and in the reactor of these systems. Furthermore, the results also indicated that the degradation of APs under aerobic conditions was enhanced working at high solid retention time (SRT) and hydraulic retention time (HRT) values. Direct coupling of separation and photocatalytic degradation by using photocatalytic membrane is an attractive way to solve problems like membrane fouling by adsorbed organic macromolecules or elimination of small organic molecules which cannot be efficiently stopped by a membrane. A simple and robust synthesis route to a photo-catalytically active titania membrane was developed from a commercial TiO2 hydrosol and commercial alumina supports by Djafer et al (2010). Reproducible defect-free layers with a thickness of about 3 µm were prepared. The membrane performance in term of separation and photocatalytic activity were investigated. The pure water permeance was 150 L h-1 m-2 bar-1 and the measured molecular weight cut-off was around 50 kDa corresponding to an ultrafiltration membrane. The photocatalytic efficiency was tested by photo-oxidation under UV irradiation of a reference organic dye (methylene blue) for comparison with reference TiO2 photocatalysts, and also with phenol as typical organic pollutant in water. The measured values of quantity of destroyed organic molecules per units of time and of membrane surface area are in the range 0.8-3.8 x10-8 mol s-1 m-2. Phenol decomposition was carried out under UV irradiation in a recycle batch photocatalytic membrane reactor (PMR) by Yang et al (2011). To overcome the problem of post-recovery of the catalyst particles after water treatment, surface modification of polypropylene macroporous membrane was performed with the technique of photoinduced reversible addition-fragmentation chain transfer grafting polymerization of acrylic acid. TiO2 photocatalysts were introduced into the acrylic acid grafted membrane surface. In the tests on the PMR the normalized membrane flux reached 1.7 times that of the unmodified membrane for the poly(acrylic acid) (PAAc) modified membrane. Introducing TiO2 photocatalysts into the membrane surface reduced slightly the normalized membrane flux. For the PMR with a grafting degree of 12.9% (wt) of PAAc on the membrane surface, the corresponding decomposition percentage was 32.5% after 6 h UV light irradiation. The role of membrane in phenol degradation in high-phenol-fed MBR (membrane bioreactor) was explored by Ahn et al (2011). Phenol elimination in high-phenol-fed MBRs resulted in complete mineralization and the high-phenol-fed MBR exhibited greater biomass-specific phenol removal rates (0.4-1.5 mg phenol/(mg VSS.d) than the low-phenol-fed MBR. In the high-phenol-fed MBR, filamentous non-settling microbes were more abundant than in the low-phenol-fed MBR. Batch experiment, high-acclimated and non-settling microbes were separately collected from the high-phenol-acclimated bioreactor, and their specific phenol degradation was determined at 5.1 mg phenol/(mg VSS.d). The greater specific phenol degradation rate of the non-settling microbes than the observed phenol elimination rate in the high-phenol-fed MBR indicated that the high-phenol-acclimated and non-settling microbes had greater degradation activity than the rest of sludge microbes in the bioreactor. According to these findings, the role of membrane in the high-phenol-fed MBR was identified as the containment of non-settling and biodegradative microbes in bioreactor, and in turn, the membrane-driven increase of non-settling phenol degrading microbes enhanced phenol elimination in the high-phenol-fed MBR. A novel process to biodegrade phenol present in an acidic (1 M HCl) and salty (5% w/w NaCl) synthetically concocted wastewater was studied by Livingston (1993). The process utilized a membrane bioreactor, in which the phenol present in the wastewater was separated from the inorganic components by means of a silicone rubber membrane. Transfer of the phenol from the wastewater into a biological growth medium allowed biodegradation to proceed under controlled conditions which were unaffected by the presence of inorganic species in the synthetic wastewater. At a wastewater flow rate of 18 mL h-1 (contact time 6 h), 98.5% of phenol present in the wastewater at an inlet concentration of 1000 mg L-1 was degraded; at a contact time of 1.9 h, 65% of the phenol was degraded. Phenol degradation was accompanied by growth of a biofilm on the membrane tubes and by conversion of approximately 80% of the carbon entering the system to CO2 carbon. Analysis of the transport of phenol across the membrane revealed that the major resistance to mass transfer derived from the diffusion of phenol across the silicone rubber membrane. A mathematical model was used to describe the transfer of phenol across the membrane and the subsequent diffusion and reaction of phenol in the biofilm attached to the membrane tube. This analysis showed that (a) the attached biofilm significantly lowers the mass transfer driving force for phenol across the membrane, and (b) oxygen concentration limits the phenol degradation rate in the biofilm. These conclusions from the model are consistent with the experimental results. The effect of adaptation of mixed culture in the phenol biodegradation was studied by Marrot et al (2006). The degradation experiments were carried out at different phenol concentrations from 0.5 to 3 g L-1. Biological treatment showed to be economical and practical leading to a complete removal of phenol. High concentrations of phenol were inhibitory for growth; so it was for the rates of substrates utilization that were greater at low initial concentrations. Haldane kinetics model for single substrate was used to obtain maximum specific growth rates (μm = 0.438 h−1), half saturation (K = 29.54 mg L-1) and substrate inhibition constant (K-i = 72.45 mg L-1). These results were in agreement with those reported in the literature for phenol removal abilities in different systems, although the concentration in phenol was significant, and the Haldane model was acceptable. References Ahn S, Song I, Choung Y, Park J (2011) Improved phenol degradation in high-phenol-fed MBR by membrane-driven containment of non-settling biodegradation microbes. Desalination and Water Treatment 31:320-325 Abargues MR, Robles A, Bouzas A, Seco A (2012) Micropollutants removal in an anaerobic membrane bioreactor and in an aerobic conventional treatment plant. Water Science and Technology 65:2242–2250 Djafer L, Ayral A, Ouagued A (2010) Robust synthesis and performance of a titania-based ultrafiltration membrane with photocatalytic properties. Separation and Purification Technology 75:198-203 Livingston AG (1993) A novel membrane bioreactor for detoxifying industrial waste-water. 1. Biodegradation of phenol in a synthetically concocted waste-water. Biotechnology and Bioengineering 41:915-926 Marrot B, Barrios-Martinez A, Moulin P, Roche N (2006) Biodegradation of high phenol concentration by activated sludge in an immersed membrane bioreactor. Biochemical Engineering Journal 30:174-183 Sadeghi F, Mehrnia MR, Nabizadeh R, Sarrafzadeh MH (2012) Treatment of synthetic olefin plant wastewater at various salt concentrations in a membrane bioreactor. Clean-Soil Air Water 40:416-421 Yang S, Gu JS, Yu HY, Zhou J, Li SF, Wu XM, Wang L (2011) Polypropylene membrane surface modification by RAFT grafting polymerization and TiO2 photocatalysts immobilization for phenol decomposition in a photocatalytic membrane reactor. Separation and Purification Technology 83:157-165 Wang ZX, Xu XC, Gong Z, Yang FL (2012) Removal of COD, phenols and ammonium from Lurgi coal gasification wastewater using A(2)O-MBR system. Journal of Hazardous Materials 235:78-84I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
