Removal of cyanide from acrylonitrile wastewater using gas membrane

Acrylonitrile wastewater is one of the most refractory industrial wastewaters as it contains cyanide at a high concentration. This study introduced a safe, effective and economic strategy, that is, use of the gas membrane to acrylonitrile wastewater treatment. Due to the complicated constituents of acrylonitrile wastewater, cyanide removal rate by gas membrane is very low. In order to enhance HCN removal, the operational conditions were optimized; pre-treatment strategies for fouling mitigation were also proposed and tested for acrylonitrile wastewater. The optimal operational parameters were achieved at an acidified pH of 5.0, wastewater velocity of 0.14 m s(-1), NaOH concentration of 10% and a temperature of 40 °C. The major factor affecting HCN removal was the pH of the acidified wastewater. The reason for the low removal rate was further explored and found to be the decrease of HCN transfer coefficient, which was caused by membrane fouling. Furthermore, the predominant foulants have been identified as colloidal organic materials and inorganic salts. Alkalization, which is effective in reducing these materials, has been proven to be most effective in mitigating membrane fouling and improving HCN removal, which was also confirmed by a pilot-scale study. The overall removal rate was therefore significantly enhanced to 87.1%.     

涂铁砂过滤去除水中磷的研究

试验制备一种涂铁砂(IOCS)滤料用于对水中磷的去除,与石英砂相比IOCS表面粗糙,空隙多,比表面积大,且附有α-Fe_2O_3晶体,吸附能力增强。通过过滤试验研究了IOCS滤料在不同的试验条件下(pH、空床接触时间、进水磷浓度、滤床深度等)对水中磷的去除效果。结果表明:中性条件下磷的去除效果最佳,pH太高和太低都不利于磷的去除;中性条件下,当空床接触时间为13min,进水磷浓度为1.0 mg/L,滤床深度为50 cm时,去除效果较好,平均去除率可达82%;空床接触时间、进水磷浓度、滤床深度等是影响过滤运行周期的主要因素。     

Use of low-cost materials in the removal of arsenic from aqueous solution

The arsenic-removing capacity of some low-cost materials was tested by passing aqueous arsenic solutions (16 and 57 ppb) of pH 7 through materials packed in plastic buckets. It was found that the initial concentration of arsenic solutions and their retention time in adsorbents greatly affected the removal of arsenic from the aqueous solution. Maximum arsenic removal was observed when the packed materials were exposed to 16 ppb of arsenic solution. With 57 ppb of arsenic solution, arsenic removal was reduced on that of 16 ppb; however, the reduced arsenic concentration was close to the recommendations of the World Health Organization drinking water quality guidelines.     

Phosphonated cross-linked polyethylenimine for selective removal of uranium ions from aqueous solutions

Among many remediation techniques for metal ion removal, polymeric adsorbents are efficient and widely applied. This has made them comparable with other remediation techniques in terms of technical and economic efficiency, feasibility as well as green technology. This study was dedicated to the development of an insoluble modified chelating polymer for use as an adsorbent for abstraction of uranium from wastewaters. Cross-linked polyethylenimine (CPEI) was phosphonated by phosphorous acid for selective removal of uranium ions. The binding affinity of the phosphonated cross-linked polyethylenimine (PCPEI) to uranium ions was assessed as well as its ability to be regenerated for reuse. It exhibited high removal percentage for uranium ions up to 99% with high selectivity even in the presence of competing ions (Mn, Ni, As). The Freundlich isotherm was found to be the best fit describing the adsorption process of uranyl ions onto the PCPEI. The pseudo-second-order equation was found to better explain the adsorption kinetics, implying chemisorption. The thermodynamic study of the adsorption revealed high activation energies which confirmed the chemisorption as the mechanism of adsorption.     

Sorption behavior of florisil for the removal of antimony ions from aqueous solutions

Florisil was employed for the sorption of antimony ions from aqueous solutions. A detailed study of the process was performed by varying the sorption time, pH, and temperature. The sorption was found to be fast, equilibrium was reached within 15 min. Moreover, a maximum sorption has been achieved from solution when the pH ranges between 1-10. From kinetic experiments it follows that the process correlate with the second-order kinetic model. The overall rate process appears to be influenced by both boundary layer diffusion and intra-particle diffusion. The Langmuir and Dubinin-Radushkevich (D-R) type sorption isotherms can be applied to fit and interpret the sorption data. The mean energy of adsorption (9.73 kJ mol(-1)) was calculated from the Dubinin-Radushkevich (D-R) adsorption isotherm at room temperature. Furthermore, the thermodynamic parameters for the sorption were also determined, and the deltaH0 and deltaG0 values indicate a spontaneous endothermic behavior.     

Development of adsorbent for the simultaneous removal of organic and inorganic contaminants from aqueous solution

In this study, a modified adsorbent, alginate complex beads, was prepared and applied to the removal of mixed contaminants from wastewater. The alginate complex beads were generated by the immobilization of powdered activated carbon and synthetic zeolites onto alginate gel beads, which were then dried at 110 °C for 20 h until the diameter had been reduced to 1 mm. This dry technique increased the hardness of the adsorbent to assure its durability and application. The adsorption onto the alginate complex beads of organic and inorganic compounds, as target contaminants, was investigated by performing both equilibrium and kinetic batch experiments. From the adsorption isotherms, according to the Langmuir equation, the alginate complex bead was capable of effectively removing benzene, toluene, zinc and cadmium. From kinetic batch experiments, the removal efficiencies of benzene, toluene, zinc and cadmium were found to be 66.5, 92.4, 74.1 and 76.7%, respectively, for initial solution concentrations of 100 mg L(-1). The results indicated that the adsorbent developed in this study has the potential to be a promising material for the removal of mixed pollutants from industrial wastewater or contaminated groundwater.     

Characterization of fouled membranes from a membrane enhanced biological phosphorus removal system.

Characterization of fouled membranes is the first step towards a good understanding of membrane fouling nature and thus formulating effective engineering measures for fouling prevention and control. In this study, fouled membrane fibres collected from a pilot scale membrane enhanced biological phosphorus removal (MEBPR) process were systematically examined. Several analytical tools, including scanning electron microscopy (SEM), conventional optical microscopy (COM), energy dispersive X-ray (EDX) microanalysis, matrix assisted laser desorption/ionization--mass spectrometry (MALDI-MS) analysis, and conventional chemical analysis techniques were used. The results indicated that membrane fouling in the MEBPR process was mainly of an organic nature, and most extractable foulants were carbohydrates and humic or humic-like substances. Unlike in other wastewater treatment membrane bioreactors, microbial growth on fouled membranes was not substantial, probably due to the vigorous aeration applied and the strong hydrodynamic conditions within the membrane pore structure. After a period of sludge filtration, membrane surfaces became more hydrophobic and the resultant hydrophobic interactions between the fouled membranes and mixed liquor constituents might have accelerated the fouling process.     

Application of PTFE membrane for ammonia removal in a membrane contactor

The feasibility of a membrane contactor system for ammonia removal was studied. The mass transfer coefficient was used to quantitatively compare the effect of various operation conditions on ammonia removal efficiency. Effective removal of ammonia was possible with a Polytetrafluoroethylene (PTFE) membrane contactor system at all tested conditions. Among the various operation parameters, contact time and solution pH showed significant effect on the ammonia removal mechanism. The overall ammonia removal rate was not affected by influent suspended solution concentration unlike other pressure driven membrane filtration processes. Also the osmotic distillation phenomena which deteriorate the mass transfer efficiency can be minimized by preheating of influent wastewater. A membrane contactor system can be a possible alternative to treat high strength nitrogen wastewater by optimizing operation conditions such as stripping solution flow rate, influent wastewater temperature, and influent pH.     

Layered double hydroxide (LDH)-coated attapulgite for phosphate removal from aqueous solution

In this study, a composite adsorbent, layered double hydroxide (LDH)-coated attapulgite (LDH-AP), was synthesized and characterized. Its potential application for LDH stabilizer and phosphate (P) removal from aqueous solution was evaluated using the batch mode and continuous mode in a packed bed column. The batch experiments revealed that the data of P adsorption onto LDH-AP could be well described by the Freundlich equation, and the maximum adsorption capacity was estimated to be 6.9 mg/g. The column experiments were conducted in the tap water and the results indicated that the competing anions could slightly decrease phosphate removal. The saturated column was regenerated by 0.2 mol/L of NaOH and the regenerated column was examined for its reuse in phosphate removal. The results of this study suggested that attapulgite could be used as an applicable stabilizer of LDH and LDH-AP could be potentially used as a promising filtration medium for phosphate removal.     

Simultaneous removal of nitrate and pesticides from groundwater using a methane-fed membrane biofilm reactor

Nitrate and pesticide contaminated ground- and surface-waters have been found around the world as a result of the use of these compounds in agricultural activities. In this study we investigated a biological treatment method to simultaneously remove nitrate and pesticides from contaminated water. Methane was supplied as the sole source of carbon to the microbial culture. A methane-fed membrane biofilm reactor (M-MBfR) was developed in which the methane was supplied through hollow-fiber membranes to a biofilm growing on the membrane surface. A methane-oxidizing culture enriched from activated sludge was used as inoculum for the experiments. Removal of nitrate and the four pesticides atrazine, aldicarb, alachlor, and malathion was examined both in suspended culture and in the M-MBfR. The maximum denitrification rate with suspended culture was 36.8 mg N gVSS(-1) d(-1). With the M-MBfR setup, a hydraulic retention time of approximately one hour was required to completely remove an incoming nitrate concentration of about 20 mg NO3-N l(-1). The microbial culture could remove three of the pesticides (aldicarb, alachlor, and malathion). However, no atrazine removal was observed. The removal rates of both nitrate and pesticides were similar in suspended culture and in membrane-attached biofilm.     

Simultaneous copper, cobalt and phenol removal from aqueous solutions by alternating biosorption and biodegradation

A strategy for removal of heavy metals and phenol from wastewaters is proposed. It involves consecutive cation biosorption by fungi, phenol biodegradation by the yeast association Candida sp. 2326 + Candida sp. 2327 and regeneration. Copper and cobalt removal from aqueous solutions containing 80-120 mg/L phenol by biosorption, using Rhizopus archizus cells immobilized onto poly (vinyl alcohol), was investigated by conducting a series of batch experiments. The removal efficiencies were 81% for Cu and 5% for Co. The residual concentrations of Cu (1.9 mg/L) and of Co (9.5 mg/L) did not change the biodegradation dynamics of phenol. A quantitative biodegradation of 120 mg/L phenol proceeded within 22 h. After biodegradation of phenol, the removal efficiencies achieved by biosorption after regeneration were 90% for Cu and 44% for Co. It was found that copper and cobalt form positively charged complexes with phenol. This complex formation hinders the retention of Cu and Co by the biosorbent and reduces the uptake of their cations.     

A membrane bioreactor for the removal of dimethyl sulphide and toluene from waste air.

In biotrickling filters, mass transfer of hydrophobic compounds is the limiting factor. Biofilters are static systems, and so control and regulation of operational parameters such as pH and nutrient supply can be a problem. In membrane bioreactors, these drawbacks can be avoided. The hydrophobic membrane separates the waste air from the aqueous phase, thus avoiding mass-transfer limitation, while pH and nutrient supply can be directly controlled. In this contribution, an overview will be given of results obtained during a four-year project. First, the physical chemical characteristics (solubility, permeability, diffusivity) and microbial adhesion of different membranes were tested. This led to the selection of a composite membrane consisting of a porous polyvinylidenefluoride (PVDF) support layer coated with a thin (1 or 2.5 microm) dense polydimethylsiloxane (PDMS) top layer. This membrane was mounted into a module provided with four parallel rectangular channels for gas flow (in contact with the porous layer) and nutrient solution (in contact with the dense layer) respectively. After inoculation, a biofilm developed on the dense layer. Experiments were performed with dimethyl sulphide and toluene as target VOCs. Operational characteristics such as elimination capacity as a function of the volumetric load and residence time, effect of nutrient supply, long-term performance) were determined. Mass transfer was studied by measuring concentration profiles along the channels of the module in different conditions.     

MBR的脱氮除磷工艺研究

采用厌氧/缺氧池/好氧MBR工艺处理模拟的城市生活污水,就系统主要的运行参数对氮磷去除的影响进行了研究.结果表明:TN、TP、NH3-N去除率分别达到80%、90%、95%以上,出水各项指标完全满足城市杂用水水质标准的要求.     

Potential application of manganese coated sand in the removal of Mn(II) from aqueous solutions.

The aim of this study was to explore the applicability of manganese coated sand (MCS) in the presence and absence of sodium hypochlorite for the removal of Mn(II) (2 mg/L) from aqueous solutions. Sand itself is widely used as a filter media for the treatment of wastewaters and it was reported that during the treatment, Mn(II), which is present in the wastewater, is to be deposited on the surface of sand in the form of manganese dioxide. The present investigation dealt with various MCS samples, prepared in the laboratory by various doses of Mn(II) (i.e. from 0.05 to 0.2 mol/L) and the samples were obtained from the pilot plant and naturally coated in the water treatment plant for the removal of Mn(II) in the batch and column studies. Moreover, it was realised that the role of hypochlorite is multifunctional as it not only enhances the uptake of Mn(II) on the surface of MCS through oxidation of Mn(II) into Mn(IV) and hence the formation of manganese dioxide, but it was also supposed to disinfect the bacteria or harmful pathogens from the waste/surface waters. The results obtained clearly inferred that various MCS samples used for the removal of Mn(II) from aqueous solutions showed comparable removal efficiency. However, the presence of sodium hypochlorite greatly enhanced the removal of Mn(II) as more than 80% Mn(II) was removed in the presence of sodium hypochlorite at around pH 6.5. Similarly, while comparing the column data it was again noted that the breakthrough points occurred after the 4,100 and 6,500 bed volumes, respectively, in the absence and in the presence of sodium hypochlorite (2 mg/L).     

Exploring the potential of membrane bioreactors to enhance metals removal from wastewater: pilot experiences.

The potential of membrane bioreactors to enhance the removal of selected metals from low loaded sewages has been explored. A 1400 litre pilot plant, equipped with an industrial submerged module of hollow fibre membranes, has been used in three different configurations: membrane bioreactor, operating in sequencing batch modality, for the treatment of real mixed municipal/industrial wastewater; membrane-assisted biosorption reactor, for the treatment of real leachate from municipal landfills; continuously fed membrane bioreactor, for the treatment of water charged with cadmium and nickel ions. The results show that: (a) in treating wastewaters with low levels of heavy metals (< one milligram per litre concentration), operating high sludge ages is not an effective strategy to significantly enhance the metals removal; (b) Hg and Cd are effectively removed already in conventional systems with gravitational final clarifiers, while Cu, Cr, Ni can rely on a additional performance in membrane bioreactors; (c) the further membrane effect is remarkable for Cu and Cr, while it is less significant for Ni. Basically, similar membrane effects recur in three different experimental applications that let us estimate the potential of membrane system to retain selected metal complexes. The future development of the research will investigate the relations between the membrane effect and the manipulable filtration parameters (i.e., permeate flux, solids content, filtration cycle).     

Efficient removal of Cr(VI) by polydopamine-modified lignin from aqueous solution: Batch and XAFS studies

Lignocellulose has the potential to become a bio-based adsorbent due to its biodegradability and renewability. In this study, a novel polydopamine-functionalized-lignin (lignin@PDA), prepared via self-polymerization of dopamine (PDA) on lignin, was used as a bio-based adsorbent for rapid scavenging of hexavalent chromium (Cr(VI)). The morphology, functional groups, crystalline structure, and chemical composition of lignin@PDA were characterized with a scanning electron microscope–energy dispersive spectrometer, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The Cr(VI) adsorption process of lignin@PDA was studied using batch experiments as a function of pH, ionic strength, adsorbent dose, and contact time at room temperature. The adsorption rate of lignin@PDA was five times greater than that of the unmodified lignin, with a maximum adsorption capacity of 102.6 mg/g in an acidic medium. The adsorption of Cr(VI) on lignin@PDA fit the pseudo-second-order equation and the Freundlich model, indicating that the adsorption process was mainly dominated by chemisorption and surface complexation. The thermodynamic parameters showed that adsorption of Cr(VI) on lignin@PDA was an endothermic and spontaneous process. The X-ray absorption fine structure results showed that sorption and reduction of Cr(VI) into Cr(III) occurred simultaneously on lignin. Moreover, PDA coating not only improved the reactivity of lignin but also promoted the complete reduction of Cr(VI) by lignin. According to these results, polydopamine-functionalized-lignin is a promising bio-based adsorbent for immobilization of Cr(VI) from wastewater.

     

Efficiency of membrane processes for taste and odor removal.

The occurrence of tastes and odors (T&O) in drinking water is considered as one of the main problems by the drinking water companies. Thus, several treatment processes were developed over the years to control T&O including air stripping, activated carbon and oxidation using ozone. However, little information is available in the literature on the use of membranes for T&O removal. Therefore, the objectives of this paper are to present potential of membrane processes for removal of taste and odor causing compounds. Several membranes were tested including ultrafiltration (UF), UF combined with powdered activated carbon (PAC), nanofiltration (NF) and low pressure reverse osmosis (LP RO) membranes. The results of this study indicate that the combination of UF with PAC is effective for T&O control whereas the benefit of NF and LP RO remains unclear for T&O control.     

Effect of NaCl on nitrate removal from ion-exchange spent brine in the membrane biofilm reactor (MBfR)

The H(2)-based membrane biofilm reactor was used to remove nitrate from synthetic ion-exchange brine at NaCl concentrations from ～3 to 30 g/L. NaCl concentrations below 20 g/L did not affect the nitrate removal flux as long as potassium was available to generate osmotic tolerance for high sodium, the H(2) pressure was adequate, and membrane fouling was eliminated. Operating pHs of 7-8 and periodic citric acid washes controlled membrane fouling and enabled reactor operation for 650 days. At 30 psig H(2) and high nitrate loading rates of 15 to 80 g/m(2) d, nitrate removal fluxes ranged from 2.5 to ～6 g/m(2) d, which are the highest fluxes observed when treating 30 g/L IX brine. However, percent removals were low, and the H(2) pressure probably limited the removal flux.     

The removal and degradation of pharmaceutical compounds during membrane bioreactor treatment

Pharmaceutical compounds such as non-steroidal anti-inflammatory drugs (NSAIDs) and antibiotics have been detected in sewage treatment plant (STP) effluents, surface and ground water and even in drinking water all over the world, and therefore have developed as compounds of concern. Membrane bioreactor (MBR) treatment has gained significant popularity as an advanced wastewater treatment technology and might be effective for an advanced removal of these pollutants. This paper evaluates the treatment of wastewater containing three NSAIDs (acetaminophen, ketoprofen and naproxen) and three antibiotics (roxithromycin, sulfamethoxazole and trimethoprim) performed in two MBRs with sludge retention times (SRTs) of 15 (MBR-15) and 30 (MBR-30) days over a period of four weeks. It was observed that NSAIDs were removed with higher efficiencies than the antibiotics for both MBRs, and the MBR-30 presented higher removal efficiencies for all the compounds than obtained by MBR-15. Removal rates ranged from 55% (sulfamethoxazole) up to 100% (acetaminophen, ketoprofen). Besides mineralisation biological transformation products of ketoprofen and naproxen produced by wastewater biocoenosis were identified in both MBR permeates using liquid chromatography coupled with mass spectrometry (LC-MS). The results indicated the importance of investigating the environmental fate of pharmaceuticals and their transformation products reaching the environment.