Highly effective permeability and antifouling performances of polypropylene non-woven fabric membranes modified with graphene oxide by inkjet printing and immersion coating methods.

In the current study, graphene oxide (GO)-modified polypropylene non-woven fabric (PP-NWF) membranes were prepared via inkjet printing and immersion coating methods. Scanning electron microscopy, Fourier transform infrared spectroscopy, contact angle measurements, pure water permeation (JPWP) and protein adsorption were tested to evaluate the impact of the GO nanosheet on the characteristics and performance of modified PP-NWF membranes. The results showed that the exfoliated GO nanosheets uniformly deposited on the membrane surface and firmly embedded into the interlaced fibers, resulting in the improvement of membrane hydrophilicity, permeability and antifouling properties comparing with original PP-NWF membranes. The GO-printed and GO-coated membranes had 113 and 188% higher fluxes, and 70.95 and 75.74% lower protein adsorptions than the original PP-NWF membranes, respectively. After cross-linked treatment, ultrasound processing was conducted to evaluate the stability of the modified PP-NWF membranes. The results demonstrated that there was almost no decrease in permeation after ultrasonic treatment indicating that the cross-linking treatment could enhance the immobilization of the GO nanosheets on and into the modified membranes.

Management of occupational exposure to engineered nanoparticles through a chance-constrained nonlinear programming approach.

Critical environmental and human health concerns are associated with the rapidly growing fields of nanotechnology and manufactured nanomaterials (MNMs). The main risk arises from occupational exposure via chronic inhalation of nanoparticles. This research presents a chance-constrained nonlinear programming (CCNLP) optimization approach, which is developed to maximize the nanaomaterial production and minimize the risks of workplace exposure to MNMs. The CCNLP method integrates nonlinear programming (NLP) and chance-constrained programming (CCP), and handles uncertainties associated with both the nanomaterial production and workplace exposure control. The CCNLP method was examined through a single-walled carbon nanotube (SWNT) manufacturing process. The study results provide optimal production strategies and alternatives. It reveal that a high control measure guarantees that environmental health and safety (EHS) standards regulations are met, while a lower control level leads to increased risk of violating EHS regulations. The CCNLP optimization approach is a decision support tool for the optimization of the increasing MNMS manufacturing with workplace safety constraints under uncertainties.

[Modeling formation of aerobic granule and influence of hydrodynamic shear forces on granule diameter].

A one-dimension aerobic granule mathematical model was established, basing on mathematical biofilm model and activated sludge model. The model was used to simulate simple aerobic granule process such as nutrients removal, granule diameter evolution, cycle performance as well as depth profiles of DO and biomass. The effluent NH4(+) -N concentration decreased as the modeling processed. The simulation effluent NO3(-)-N concentration decreased to 3 mg x L(-1) as the granules grew. While the granule diameter increased from 1.1 mm on day 30 to 2.5 mm on day 100, the TN removal efficiency increased from less than 10% to 91%. The denitrification capacity was believed to enhance because the anoxic zone would be enlarged with the increasing granule diameter. The simultaneous nitrification and denitrification occurred inside the big aerobic granules. The oxygen permeating depth increased with the consumption of substrate. It was about 100-200 microm at the beginning of the aeration phase, and it turned to near 800 microm at the end of reaction. The autotrophs (AOB and NOB) were mostly located at the out layer where the DO concentration was high. The heterotrophic bacteria were distributed through the whole granule. As hydrodynamic shear coefficient k(de) increased from 0.25 (m x d)(-1) to 5 (m x d)(-1), the granule diameter under steady state decreased form 3.5 mm to 1.8 mm. The granule size under the dynamic steady-state decreased with the increasing hydrodynamic shear force. The granule size could be controlled by adjusting aeration intensity.

PB/PANI-modified electrode used as a novel oxygen reduction cathode in microbial fuel cell.

This study focuses on the preparation of a new type of Prussian Blue/polyaniline (PB/PANI)-modified electrode as oxygen reduction cathode, and its availability in microbial fuel cell (MFC) for biological power generation. The PB/PANI-modified electrode was prepared by electrochemical and chemical methods, both of which exhibited good electrocatalytical reactivity for oxygen reduction in acidic electrolyte. The MFC with PB/PANI-modified cathode aerated by either oxygen or air was shown to yield a maximum power density being the same with that of the MFC with liquid-state ferricyanide cathode, and have an excellent duration as indicated by stable cathode potential for more than eight operating circles. This study suggests a promising potential to utilize this novel electrode as an effective alternative to platinum for oxygen reduction in MFC system without losing sustainability.

[Effect of aeration intensity on the nitrogen and phosphorus removal performance of AOA membrane bioreactors].

The ability of simultaneous phosphorus and nitrogen removal of sequencing batch membrane bioreactor run in anaerobic/oxic/ anoxic mode (AOA MBR) was examined under three aeration intensities [2.5, 3.75 and 5.0 m3 x (m2 x h)(-10]. The results showed that the averaged removals of COD were over 90% at different aeration intensities. And the higher aeration intensity was, the more ammonia nitrogen removal rate achieved. The removal rates of NH4(+) under the three aeration intensities were 84.7%, 90.6% and 93.8%, respectively. Total nitrogen removal rate increased with the increasing aeration intensity. But excessive aeration intensity reduced TN removal. The removal rates of TN under the three aeration intensities were 83.4%, 87.4% and 80.6%, respectively. Aeration intensity affected the denitrifying phosphorus ability of the AOA MBR. The ratio of denitrification phosphorus removal under the three aeration intensities were 20%, 30.2% and 26.7%, respectively.

[Coupling anaerobic baffled reactor and membrane-aerated biofilm reactor].

Based on the consistent anaerobic status of outer layer of membrane-aerated biofilm reactor (MABR) and internal anaerobic baffled reactor (ABR), MABR and ABR were started up separately. The aerating membrane module was installed into a compartment of anaerobic baffled bioreactor to form the Hybrid MAB-ABR (HMABR). After the installation of membrane module, total COD and VFA concentrations in the HMABR effluent were deceased by 59.5% and 68.1% respectively, with increased nitrogenous pollutant remove efficiency by 83.5%, at influent COD concentration of 1600 mg/L and NH4+ -N concentration of 80 mg/L. When organic loading rate was increased by 50%, the effluent COD concentration was still below the level of 60 mg/L, indicating its good capability of counteracting influent organic loading fluctuation. Due to the decreased COD concentration and increased nitrate concentration in the third compartment after installing the membrane module, the biogas volume and methane contents in the third compartment were decreased, resulting in the steady and excellent effluent quality. In this hybrid process, the improved simultaneous removal of carbon and nitrogen for high-strength nitrogenous organic pollutants was realized in a single reactor.

[Influence of controlling factors on partial nitrification performance in membrane bioreactor].

A membrane bioreactor (MBR) was developed successfully to carry out partial nitrification process. Temperature, and dissolved oxygen (DO) were investigated as the factors which may affect the results. It has been proved that the optimal operational parameters were at 35 degrees C, ammonia loading 0.45 kg x (m3 x d)(-1) and < 0.5 mg/L, respectively, with the effluent NO3(-) -N concentration below 20 mg x L(-1) and rho(NO2(-) -N)/rho(NH4(+) -N) ratio being close to 1.0. It is not observed severe membrane fouling during all the experiment. Fluorescence in situ hybridization analysis indicated that aerobic ammonium oxidizers were the dominant population, and nitrite-oxidizing bacteria were inhibited. The microbiological community analysis further provided the necessary biological information for the realization of partial nitrification.

[Preparation and characterization of polyvinyl alcohol microsphere pre-coated dynamic membranes].

To alleviate membrane fouling and reduce the price of membrane module, polyvinyl alcohol microsphere pre-coated dynamic membranes (PVA-MS/PCDMs) were investigated detailedly. It was prepared when the polyvinyl alcohol microsphere of the pre-coated reagent deposited on the surface and entered the pores of porous substrate common filter cloth which was low-cost by means of circulatory filtration. The morphology and structure of PVA-MS/PCDMs were examined using scanning electron microscope (SEM), and approximate maximal separated aperture, water contact angle, pure water permeation resistance and relative Zeta potential of the membrance surface were also determined. The results showed that pure water permeation resistance of PVA-MS/PCDMs was between 0.64 x 10(10) m(-1) and 3.84 x 10(10) m(-1) and the approximate maximal separated aperture reached microfiltration level. The hydrophilicity of PVA-MS/PCDMs increased with increasing PVA-MS pre-coated mass. The relative Zeta potential of the PVA-MS/PCDMs, which were measured using 0.01 mol x L(-1) KCl solution, pH 8.0 +/- 0.2 and at 20 degrees C, reached a peak value of -36.4 mV with pre-coated mass of 15.7 g x m(-2) PVA-MS on the membrance surface. In addition, evolutions of PVA-MS/PCDMs flux versus time were investigated using a 4 hours short-term filtration experiment at 9.5 kPa in an SMBR and the permeability coefficient of PVA-MS/PCDMs were measured by the extracellular polymeric substances (EPS) diffusion experiments. Results indicated that the PVA-MS/PCDMs presented dramatically high anti-fouling characteristics when the pre-coated mass of PVA-MS was 23.9-61.9 g x m(-2).

[Denitrifying phosphorus removal in MUCT-MBR].

The self-designed MUCT-MBR simplifies the MUCT process with reducing reactors from 5 to 2, which greatly reduces land occupied by equipment. Instead of secondary sedimentation tank, the membrane effluent quality is quite safe, and the operation is simple. In the investigation about simultaneous phosphorus and nitrogen removal of MUCT-MBR, the results showed that: when the proportions of C, N and P in the influent were 33.3/5/1-25/5.5/1, the average removal rate of COD, TN and TP in the whole experimental process were 89.3%, 75.4% and 79.2%, respectively. And the sludge settling capacity had no influence on the membrane effluent quality. The key factor of N and P removal rates is denitrifying phosphorus removal in anoxic condition. The proportion of denitrifying phosphate accumulating organisms (DPAOs) and the rate of denitrifying phosphorous removal were 84.2% and 67.07% on the 58th day, respectively.

[Combined MBR-RO process treating high strength wastewater].

The performances of A/O-MBR/RO system for the removal of nitrogen and COD were investigated. Result indicated that most organic was removed in the A/O-MBR and the average removal efficiency was 95.6%. The water quality of RO effluent which in terms of TOC < 0.9 mg x L(-1), TN < 12.65 mg x L(-1), total rigidity < 0.038 mol x L(-1), total alkalinity < 14.6 mg x L(-1) could meet the water quality requirements for the town wastewater reuse. The average removal efficiency of organic was almost unaffected by COD/N, but the process of TN removal was affected by COD/N. TN removal was primarily based on simultaneous nitrification and denitrification (SND) process occurred in the aerobic zone and the average removal efficiency of TN was 89.4% with average COD/N of 10.2. Both aerobic SND and conventional biological nitrification/denitrification contributed to nitrogen removal, the average removal efficiency of TN was 72%, 74% with average COD/N of 7.1 and 5.6. The fouling cake layer formed on the RO membrane surface was observed by scanning electric microscopy. The membrane fouling was characterized by Fourier transform infrared spectroscopy technique which showed that the major components of the foulants were soluble microbe products.

Improving phosphate buffer-free cathode performance of microbial fuel cell based on biological nitrification.

To reduce the amount of phosphate buffer currently used in Microbial Fuel Cell's (MFC's), we investigated the role of biological nitrification at the cathode in the absence of phosphate buffer. The addition of a nitrifying mixed consortia (NMC) to the cathode compartment and increasing ammonium concentration in the catholyte resulted in an increase of cell voltage from 0.3 V to 0.567 V (external resistance of 100 Omega) and a decrease of catholyte pH from 8.8 to 7.05. A large fraction of ammonium was oxidized to nitrite, as indicated by an increase of nitrate-nitrogen (NO(3)(-)-N). An MFC inoculated with an NMC and supplied with 94.2 mgN/l ammonium to the catholyte could generate a maximum power of 2.1+/-0.14 mW (10.94+/-0.73 W/m(3)). This compared favorably to an MFC supplied with either buffered or non-buffered solution. The buffer-free NMC inoculated cathodic chamber showed the smallest polarization resistance, suggesting that nitrification resulted in improved cathode performance. The improved performances of the phosphate buffer-free cathode and cell are positively related to biological nitrification, in which we suggest additional protons produced from ammonium oxidation facilitated electrochemical reduction of oxygen at cathode.

[Performance of constructed wetland for municipal wastewater tertiary treatment: winter and summer comparison].

An improved three-stage vertical flow constructed wetland (CW) was used for tertiary treatment of effluent from two typical Dalian municipal wastewater treatment plants. The experiments were carried out under ambient condition in Dalian for the whole year. Performances of the CW for COD, TN, NH4(+) -N and TP removal in summer (Jun.-Aug.), winter (Nov.-Jan. the second year) and spring (Feb.-Apr.) were compared. In summer, the removal rates of COD, TN, NH4(+) -N and TP reached 88.5%, 76%, 100% and 98%, respectively. While in winter they reached 88%, 85.3%, 86.4% and 97%, respectively. In spring, the removal rates reached 87.7%, 76.7%, 70.3% and 95.5%, respectively. The effluent water quality for summer, winter and spring were: COD 2.8, 3.8 and 3.9 mg x L(-1), respectively; TP 0.02, 0.05, and 0.07 mg x L(-1), respectively; TN 6.8, 2.9, and 9.2 mg x L(-1), respectively; NH4(+)-N 0.01, 0.3, and 8.1 mg x L(-1), respectively. Results showed good performance of CW for Dalian municipal wastewater tertiary treatment, especially for COD and TP removal. The effluent COD and TP meet the needs of Environmental Quality Standard for Surface Water (GB 3838-2002) III, whereas the effluent TN and NH4(+)- N meet the needs of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) class I A and B, separately. The pollutant removal loads in summer, winter and spring were as flow: COD 4.9, 5.1, and 5.0 g x (m2 x d)(-1); TN 3.4, 3.0, and 5.5 g x (m2 x d)(-1); NH4(+) -N 0.2, 0.6, and 3.7 g x (m2 x d)(-1); TP 0.15, 0.30, and 0.28 g(m2 x d)(-1). It is indicated that no significant influence of seasons on pollutant removal is found by comparing the removal rates as well as pollutant removal loads in different seasons, however, the removal of NH4(+) -N and TN in CW is mainly influenced by influent pollutant loads.

[Characteristics of simultaneous nitrification and denitrification in moving bed membrane bioreactor].

To investigate the removal efficiency of synthetic wastewater and characteristics of simultaneous nitrification and denitrification (SND) performances, a new type of moving bed membrane bioreactor (MBMBR) had been developed by using carriers instead of activated sludge in membrane bioreactor (MBR). Results showed that good organics removal and SND performances was achieved during the 67 d experimental period. COD, ammonium and total nitrogen removal efficiencies of MBMBR remained 88.3%-99.2%, 72.1%-99.8% and 62.0%-96.3% respectively as influent COD were 573.5-997.7 mg/L and ammonium nitrogen were 45.5-99.2 mg/L. Moreover, batch experiments results showed the optimum DO for nitrogen removal was 1 mg/L, ammonium and total nitrogen removal efficiencies were 100% and 60.0%, respectively. Aerobic denitrification may occur in biofilm system. When DO concentration was 3 mg/L and the organic carbon source was abundant, 99.0% total nitrogen removal efficiency and 99.8% SND efficiency was achieved in batch experiment. The microstructure of biofilm was examined using SEM. Results showed that some cavities were present, which would be favorable to enhance substrate and oxygen to transfer from the bulk to the interior of biofilm.

[Simultaneous nitrification and denitrification of membrane-aerated biofilm reactor].

A carbon membrane-aerated biofilm reactor was developed to treat municipal wastewater, in which the carbon and nitrogen were removed simultaneously. The results showed that COD removal, NH4+-N removal and TN removal efficiency could reach 82.5%, 95.1% and 84.2%, respectively, under the conditions of intra-membrane pressure of 13.6 kPa, HRT of 14 h, influent COD and NH4+-N concentrations of 338 mg/L and 75 mg/L. However, in the last period during the operation of the reactor, the TN removal efficiency dramatically decreased because of the excessive growth of biomass on the nonwoven fiber, which also had serious negative effect on nitrification course. The microbiological community and spatial profiles were observed by fluorescence in situ hybridization and scanning electron microscopy. The anaerobic and anoxic bacteria were mainly located in the outer anaerobic region of the biofilm, while the aerobic ammonium oxidizing bacteria were mainly located in the inner aerobic region of the biofilm. The co-existing and coupling effect of aerobic nitrifying bacteria and anaerobic denitrifying bacteria provided the large biological potential for the simultaneous nitrification and denitrification in the carbon membrane-aerated biofilm reactor.

[Photocatalytic reduction of nitrate using metal-doped titania].

Metal Fe or Cu doped P25 titania was prepared using the photodeposition method and characterized by TEM, ICP, XRD and UV-Vis, further tested for photocatalytic nitrate reduction and TN removal, under 20 W UV lamp irradiation. The influencing factors such as the pH values of solution, stirring gas, metal loadings, hole scavenger formic acid amount and co-doped Ag-Cu/TiO2 are investigated and discussed in detail. The experimental results after 2 h reaction indicated that with the increase of Cu loadings, nitrate conversion increases too, while a loading of 0.5% is optimal for highest N2 selectivity and TN (total nitrogen) removal. Using N2 as stirring gas and under acidic conditions, the N2 selectivity is lower (62%), but the highest conversion of nitrate and removal of TN can reach 36.9% and 23.2% respectively. Using CO2 as stirring gas, the highest selectivity for nitrogen 88.4% is obtained with 0.5% Cu/TiO2, 0.06 mol/L formic acid. Under the same conditions, using the prepared bimetallic titania (1%, 1:1 Ag/Cu), the conversion of nitrate and removal of TN are 48.1%, 34.2%, and N2 selectivity is 72.2%.

[Promoting high-temperature hydrolysis under alkaline condition].

The effect of alkaline thermal hydrolysis method on excess sludge and its characteristic parameters(such as soluble chemical oxygen demand, volatile fatty acids, ammonia-nitrogen, pH value, sludge concentration, etc.) were investigated. The results show that the addition of alkali can reduce the resistance of the sludge cells to high temperature and enhance the release and the hydrolysis of organic materials from the sludge cells with the increase of temperature, pH value and reaction time. The concentration of SCOD reached 17,950 mg/L and SCOD/TCOD was 0.65 on the conditions of pH 13, 170 degrees C and 75 min. The maximal dissolving rate of suspended solids (SS) was 67% and 72% for volatile suspended solids (VSS) at pH 13 with 60 min. The concentration of SCOD after alkaline thermal hydrolysis treatment increased with the increase of sludge concentration, in which the nice linear relation was reached and the correlation coefficient (R2) was above 0.97. The increasing rate of the SCOD was improving with the increase of the pH value and the SCOD of unit sludge reached 672 mg/g at pH 13. The effect of three factors on the SCOD was investigated through orthogonal experiment at the temperature of 170 degrees C, the importance was sludge concentration,pH value and reaction time in turn.

[Effects of aeration intensity on characteristics of aerobic granules in sequencing batch airlift reactor (SBAR)].

This study investigated the physical performances of mature aerobic granules in SBAR, including granular shape and structure, mean size and granular relative strength, and cell metabolic activities to excrete extracellular polymeric substances (EPS), and nitrification and microbial activity, which performed visible differences at superficial upflow velocity of 1.8 cm x s(-1) and 0.9 cm x s(-1) respectively. Results show that granular surface was more irregular at the low aeration intensity than that at the high aeration intensity and granular interstice performed increasing with it. In 55 days, comparing with high aeration intensity, the sludge productivity and the mean size of aerobic granules at the low aeration intensity were increased by 33% and 25%, respectively, while the granular relative strength and EPS were reduced by 6% and 12%, respectively. The sludge volume index in two reactors were about between 10 mL x g(-1) and 15 mL x g(-1), which implied that granules at both aerations behaved well settling ability. The two reactors still performed well nitrification characteristic and ability to remove COD. The activity of nitrifying bacteria in aerobic granules at the low aeration intensity was lower than that at the high aeration intensity, while heterotrophs performed higher activity at the low aeration intensity.

[Effect of extra-cellular polymeric substances on filtration of modified non-woven fabric in membrane bio-reactor].

The effect of extra-cellular polymeric substances (EPS) on filtration of polyvinyl alcohol modified polypropylene non-woven in submerged membrane bioreactor (SMBR) was investigated by statistical method. The results show that soluble extra-cellular polymeric substances (EPSs) of activated sludge on the non-woven modules surface, components (protein/carbohydrate, P/C) of EPSs and relative hydrophobicity (RH) have a significant influence on filtration performance of module B, the Pearson's correlation coefficient (r(p)) related to membrane fouling resistance are 0.868, 0.840, 0.890, respectively. Modified module can effectively restrict the adsorption of EPSs, can reduce the ratio of P/C in EPSs and can decrease the accumulation of activated sludge. After hydrophilic modification of non-woven, the filtration performance is improved obviously and the un-fouling performance is increased.

[Preparation and characterization of cross-linked polyvinyl alcohol microspheres as a novel precoating reagent in dynamic membrane].

In order to modify the membrane surface by adsorbing a precoated layer, cross-linked polyvinyl alcohol microspheres were prepared via an emulsion polymerization that PVA cross linked with glutaraldehyde which was extracted by anhydrous aether. Effects of concentration of PVA solution, the volume ratio of aqueous phase to oil phase, the selection of surface active agent (SAA) and its concentration on the stabilization of emulsion were studied. When the concentration of PVA solution was 2.7%, the volume ratio of PVA solution/n-heptane was 40:60 and the concentration of span-80 was 1.30 g/dL, the prepared microspheres contented our needs. The size of microspheres diminished with the stirring speed increasing under the condition of enough span-80. It became smaller with the accretion of an aimed cross-linking degree which has little affection on surface charge. The contact angle of PVA microspheres with distilled water showed that these microspheres were hydrophilic. Morphology of PVA microspheres were observed by SEM. The FTIR results suggested that functional groups varied with the change of aimed cross-linking degrees.

[Innovative application of carbon tube aerated membranes to enhance anaerobic baffled reactor for wastewater treatment].

New type hybrid biological reactor was developed by initiating the carbon membrane aeration in ABR which was augmented with carbon aerated membranes to improve wastewater treatment by removing COD, NH4(+) -N and TN. The results showed that on the conditions of intra-membrane pressure of 0.025 MPa, HRT 24 h, influent COD 2000 mg/L, NH4(+) -N 50 mg/L, simultaneous nitrification and denitrification was happened, and COD and NH4(+) -N decreased from 156 mg/L, 36 mg/L to 45 mg/L, 6 mg/L respectively after the membrane aeration with biofilm was initiated in the third compartment of ABR.TN removal reached 87.66%, and VFA and biogas was decreased by 77.12% and 30%, respectively.