Feasibility study for reclamation of a secondary treated sewage effluent mainly from industrial sources using a dual membrane process

A feasibility study for reclamation of a secondary treated sewage effluent mainly from industrial sources (60%) in Singapore has been conducted using a dual membrane UF-RO process. The pilot system had a treatment capacity of 2 m³/h. The UF unit and RO unit were operated at 70–80% and 40% water recovery, respectively. Six-month run for the pilot was carried out to study the stability and fouling tendency of membranes.

The characteristics of the raw feed indicated that ammonia-N was consistently high at 30–50 mg/L. Very high fluctuations in iron (0.3–3.7 mg/L), turbidity (1–27.1 NTU) and TOC (3.2–56.7 mg/L) were observed. Nitrate was low at <0.2 mg/L. The results of the study showed that dosage of alum in the UF process significantly reduced organic foulants and phosphate scalants. The polymeric RO membrane could tolerate organics from industrial wastewater and performed >96% salt rejection at the end of the study after 6 months. The study concluded the dual membrane process was capable of reclaiming the sewage effluent mainly from industrial sources for industrial use.     

Application of microfiltration and ultrafiltration processes to cork processing wastewaters and assessment of the membrane fouling

The filtration of wastewaters generated in the cork industrial process is investigated by using three membranes in tangential filtration laboratory equipment. The three membranes used were two microfiltration membranes with pores sizes of 0.65 and 0.1 μm (DUR-0.65 and DUR-0.1 membranes), and a ultrafiltration membrane with a molecular weight cut-off of 300 kDa (BIO-300K membrane). The water hydraulic permeability was determined for each membrane (values of 860, 248 and 769 L h⁻¹ m⁻² bar⁻¹ were found), and the influence on the permeate flux of the main operating variables, such as transmembrane pressure, feed flow rate, temperature and nature of the membranes, was established. The effectiveness of the different membranes and operating conditions was evaluated by determining the removal obtained for several parameters which measure the global pollutant content of the effluent: COD, absorbance at 254 nm, tannic content, color and ellagic acid, which is selected as a major model pollutant among the different organic compounds present in this wastewater. The values of the corresponding retention coefficients depended on the operating conditions, but in all cases were in the sequence: ellagic acid and color > absorbance at 254 nm > tannic content > COD. Globally, the higher removals were obtained for the BIO-300K membrane at 20 °C, with Q_F = 5.3 L h⁻¹ and TMP = 1.8 bar. Finally, the fouling of the membranes was assessed, and the corresponding mechanism for each membrane was established by fitting the experimental data to various filtration fouling models reported in the literature.     

Role of membrane pore size in tertiary flocculation/adsorption/ultrafiltration treatment of municipal wastewater

Flocculation, adsorption onto powered activated carbon (PAC), and ultrafiltration (UF), alone and in combination, were tested for tertiary treatment of the secondary effluent from municipal wastewater treatment at the Ashkelon plant (in southern Israel). Encouraging and reliable results of total organic carbon (TOC) of <3 mg/l were achieved with a combination of 130 mg/l FeCl₃, 0.6 g/l PAC and UF. The relative contribution of the UF membrane to the reduction of TOC changed with the molecular weight cut-off (MWCO) of the membrane, from a negligible 2.9% for a 100-kDa-MWCO membrane to 17% for 10- and 2-kDa membranes. The latter membranes, however, developed significant fouling, with a 35% drop in flux during first 30 min of the filtration cycle. The flux drop for the 50- and 100-kDa membranes was in the low range of 3%. The optimal MWCO interval of 20- to 50-kDa in combination with flocculation/PAC pretreatment gave a significant reduction in organic content with minimal membrane fouling. Detailed GC–MS analysis showed that the combined treatment gave very efficient retention of organic compounds with molecular weights below 800 Da, with the consequent absence of harmful compounds in the tertiary effluent. It was therefore concluded that the recommended flocculation/adsorption protocol constitutes an effective pretreatment for UF and that the obtained tertiary effluent can be used for unrestricted irrigation.     

Membranverfahren in der industriellen Abwasserbehandlung

This report presents the possibilities of utilising membrane methods for the treatment of industrial wastewater, covering following different systems: substance separation with porous membranes; substance separation with non‐porous membranes, and membrane activation methods. The last is an aerobic biological wastewater treatment method where the unit for secondary treatment is replaced by a membrane filtration unit. This latter method is the focus of the article. The positive effects of these methods are described, such as high influent concentrations, small plant volumes, high demands on effluent quality, re‐use of purified wastewater, evenly distributed hydraulic load, and low area availability. The report presents examples of how these methods have been successfully used in both pilot plants and on an industrial scale. It can be concluded that membrane methods can successfully be utilised in industrial wastewater treatment, with new applications being found on an almost daily basis.     

Transient behaviour of dense catalytic membranes based on Cu- and Co-doped Bi4V2O11 (BIMEVOX) in the oxidation of propene and propane

ME-doped γ-Bi₄V₂O₁₁ (BIMEVOX) oxides are highly oxide ion conducting materials and this property may be profitably used in selective oxidation of hydrocarbons. The catalytic properties of BICUVOX and BICOVOX when shaped as dense membranes displayed in catalytic dense membrane reactor are examined in the oxidation of propene and of propane. Mirror-polished BICUVOX and BICOVOX membranes studied previously were poorly active for propene oxidation because of a small number of active sites but showed an excellent stability and reproducibility (lasting more than 1 month) during which products of mild oxidation (acrolein, hexadiene) and CO were formed. Membranes with depolished surfaces exhibit high conversions of propene (up to 60 mol%), and also of propane (up to 20 mol%) but – contrary to mirror-polished membranes – a complex transient behaviour is observed during which syngas production occurs. The membrane polarisation followed by in situ solid electrolyte potentiometry shows that the oxygen reservoir is far higher than expected on the reaction side which is separated (by the membrane) from the oxidising side where (diluted) oxygen is reduced to O²⁻ specie. The influence of oxygen partial pressure on the catalytic performance suggests that the electronic conductivity of the material is limiting the oxygen flux through the membrane, and thus is determining the catalytic properties and transient behaviours of depolished membranes.     

Hydrodechlorination of chloroorganic compounds in ground water by palladium catalysts: Part 1. Development of polymer-based catalysts and membrane reactor tests

A polymer-based catalytic membrane reactor was developed and applied for hydrodechlorination of chlorobenzene as a model compound of ground and waste water contaminants. The catalytically active membrane consists of a non-porous, thin film (about 3–7 μm) of poly(dimethylsiloxane) (PDMS) loaded with nano-sized Pd clusters. They were built-in either directly or as nano-sized, supported catalysts. A composite membrane, consisting of porous poly(acrylonitrile) (PAN) support and a Pd-loaded thin PDMS film, was fabricated on a coating machine. Defect-free membrane envelopes of 0.1 m² were produced and fitted into a membrane test cell. Gaseous hydrogen as reductant for hydrodechlorination is fed from the membrane’s back side directly to the catalyst, embedded in the PDMS layer. The chemical reactions at the Pd surface are accompanied by absorption of chlorobenzene from the water phase into the PDMS layer and desorption of benzene and HCl back to the water phase. The specific activity of supported catalysts decreased only slightly by PDMS incorporation, e.g., from 31 l/g(Pd) min for Pd/Fe on titania to 16 l/g(Pd) min for the same catalyst built-in a 7 μm thick supported PDMS membrane and measured in the membrane test cell. Directly built-in Pd clusters are less active and more difficult to prepare on a larger scale. Some catalyst deactivation was observed and may be balanced by development of more suited nano-sized supported catalysts.     

臭氧、臭氧/双氧水催化氧化深度处理化工废水

对比了臭氧、臭氧催化氧化、臭氧/双氧水和臭氧/双氧水催化氧化4种工艺深度处理化工废水的效果,结果表明,当进水COD和色度分别为95.7 mg/L和90倍时,4种工艺出水的COD去除率分别为23.66%、26.77%、29.24%、32.97%,色度去除率分别为64.44%、64.44%、82.22%、82.22%,催化剂和双氧水均能小幅强化臭氧氧化效果。连续臭氧氧化可使出水COD降至20 mg/L,同时当臭氧投加量为60 mg/L时,4种工艺出水均具有一定的可生化性,满足后序生化工艺的需求。     

Electrochemical treatment of pentachlorophenol in water and pulp bleaching effluent

Adsorbable organic halides (AOX) compounds produced during bleaching of pulp are recalcitrant and known to have eco-toxic effect. We have studied the removal of pentachlorophenol (PCP) as a model AOX compound in water as well as in pulp bleaching effluent of a bamboo based mill by electrochemical treatment in batch mode. It was found that 10 mg L⁻¹ of PCP in water was removed almost completely in <10 min at a current density of 6 mA cm⁻² in the presence of 1000 mg L⁻¹ NaCl serving as an electrolyte and source of chloride ions. The initial rate of PCP removal was found to decrease at alkaline pH (9.3) as compared to that at acidic pH (5.5). PCP removal in neutralized raw pulp bleach effluent (containing 1830 mg L⁻¹ of chloride) was very slow and incomplete even after 2 h of electrochemical treatment at a current density of 15 mA cm⁻². Various pretreatments of raw bleach effluent such as, alkaline sulfide using sodium sulfide, alkaline reduction using ferrous sulfate and coagulation using potash alum were evaluated. Electrochemical treatment of potash alum pretreated effluent (spiked with PCP) could achieve >90% removal of initial colour, COD and PCP in <1 h. The treatment scheme presented here may be a promising technology for removal of AOX, COD and colour from pulp bleaching effluent. The estimated cost of combined treatment (potash alum coagulation + electrochemical) is US$ 0.7–0.9 per cubic meter of the raw pulp bleach effluent.     

Performance of Reverse Osmosis and Nanofiltration in the Removal of Fluoride from Model Water and Metal Packaging Industrial Effluent

Fluoride forms a common aqueous effluent in many chemical industries. Excess of fluoride in the effluent can cause a health hazard. So, effluent containing fluoride needs treatment to reduce its concentration to a disposable value before discharging into public sewage. Removal of fluoride ion from model water solutions was investigated using polyamide thin film composite reverse osmosis and nanofiltration membranes. The effects of feed pressure, concentration, ionic strength, nature of cation associated to fluoride, and pH on the retention of fluoride ions were studied. Membranes were used to reduce fluoride ions and total salinity of a metal packaging industrial effluent. The retention of fluoride exceeds 90% for both membranes. This was found to depend on feed concentration, ionic strength, pH, and applied pressure. The Spiegler-Kedem model was applied to experimental results to determine phenomenological parameters σ and P_s, the reflection coefficient of the membrane and the solute permeability coefficient of ions. The convective and diffusive parts of the mass transfer were quantified with predominance of the diffusive contribution.     

印染工业园区综合废水处理试验研究

针对某印染工业园区综合废水成分复杂、可生化性差的特点,采用复合式ABR-铁碳内电解-接触氧化组合工艺对该废水进行处理.重点考察了反应器的启动,以及该工艺对CODCr及色度的去除效果.结果表明：复合式ABR-铁碳内电解组合工艺将进水m（BOD5）/m（CODCr）值从0.23提高至0.36左右,大大提升了废水的可生化性,经接触氧化工艺处理后,出水CODCr的质量浓度降至80 mg/L以下,脱色率达80％.     

Novel mesoporous aluminosilicate supported palladium-rhodium catalysts for diesel upgrading: II. Catalytic activity and improvement of industrial diesel feedstocks

Bimetallic PdRh catalysts (molar ratio Pd/Rh = 1 and 2) were prepared by impregnation of a mesoporous aluminosilicate (molar ratio Si/Al = 10 and 20). These materials are destined to be used in industrial processes aiming to improve diesel quality by hydrogenation and ring-opening of aromatic components. The four catalysts were examined for their activity in hydrogenation of naphthalene and tetralin model feedstocks, at 6 MPa, including in the presence of sulfur containing compounds. The capacity of one of these catalysts to improve the quality of hydrogenated industrial light cycle oil containing ≤50 wt ppm of sulfur was evaluated in a pilot plant. In these industrial conditions, the catalyst has a higher catalytic activity at lower temperature than a reference state of-the-art catalyst, giving a seven-point improvement of the cetane number at 280–300 °C and with formation of less than 10% of non-selective cracking products.     

Lanthanum ferrite membranes in ammonia oxidation: Opportunities for ‘pocket-sized’ nitric acid plants

This paper reports the application of mixed conducting perovskite membranes for simultaneous in situ O₂ separation and catalytic oxidation of ammonia to nitric oxide. Calcium and strontium-substituted lanthanum ferrite perovskites (La_1−xA_xFeO_3−δ, with A = Ca, Sr and x = 0.1–0.2) were prepared by a conventional wet complexation route with citric acid. Dense membrane disks were obtained by uniaxial pressing of the calcined powders followed by sintering. The oxidation of ammonia over these catalytic membranes in the temperature range of 1000–1333 K leads to NO selectivities up to 98% with no N₂O production, showing stable performance during several days on stream. This novel process demonstrates the great potential for intensification of nitric acid manufacture into miniaturized plants and is considered to be particularly attractive for on-site production of this important bulk chemical.     

Effect and mechanism of ultrafiltration membrane fouling removal by ozonation

This study is aimed using ozonation to remove the fouling that occurs on ultrafiltration membranes. Polyvinylidene fluoride (PVDF) was utilized for the membrane material. The tertiary effluent from industrial park wastewater plant was treated by an ultrafiltration membrane process. A bench-scale system was performed to evaluate the efficiency of fouling removed by an ozonation process. The results should be a valuable reference encouraging the recovery of tertiary effluent by the membrane process. The ozonation process was done via the direct continuous dosing of ozone into the influent. The ozone gas mass flow rate was 8.79 mg/min; the residual ozone concentration in the influent flow was maintained at about 4.02 mg/L throughout the test. It was demonstrated that without ozonation the permeate flux dropped to 60% after 1 h, but that with ozonation it could be maintained at 90% through the test. The SEM observations showed that much fouling that had clogged the membrane was effectively removed by ozonation. The mechanism of fouling removed was also illuminated by the IR analysis. It was observed that the ozone could oxidize and destroy the organic fouling, and the cross flow could flush away any loose fragments on the filtration cake.     

Comparison of different catalysts in the membrane-supported dehydrogenation of propane

Dehydrogenation of propane is studied in a high temperature packed bed catalytic membrane reactor with a hydrogen-selective silica membrane. The silica membrane is prepared by a two-step sol–gel process. The removal of hydrogen in the membrane reactor results in higher propane conversion and higher propene yields in comparison to an equivalent fixed-bed reactor. Unfortunately, as a result of the H₂ removal coking is favoured in the membrane reactor. Therefore, the higher propene yields are found only for the first 100–120 min time on stream. However, the lower selectivity of the membrane reactor due to coking is compensated to some extend by a reduced hydrogenolysis. Two commercial dehydrogenation catalysts of different activity were tested in the membrane reactor: Cr₂O₃/Al₂O₃ and Pt–Sn/Al₂O₃. The two catalysts show a different activity, coking, and regeneration behaviour in the membrane-supported propane dehydrogenation.     

Reactive distillation with KATAPAK

KATAPAK-SP and -S are structured catalytic packings for reactive distillation or gas–liquid reactors available from laboratory to industrial scale. Applying the KATAPAK-SP concept, the ratio of catalyst volume fraction to separation efficiency can be varied over a wide range, therefore the design of a reactive distillation column can be further optimized to fit each reaction system best.

Pressure drop, separation efficiency, dynamic liquid hold-up and residence time distribution have been investigated for KATAPAK-SP in a diameter of 250 mm. Results for different gas and liquid loads are presented. The findings are compared with results for the structured laboratory scale packing KATAPAK-S and the industrial scale packing KATAPAK-S 170.Y.

The dehydration of tert-butyl alcohol was selected as a sample reaction to illustrate the influence of different catalytic structures on the performance of the reactive distillation column. The setups are compared with respect to dimensions and economics.     

Processing of biscuit industrial effluent using thin film composite nanofiltration membranes

Nanofiltration (NF) is a membrane-based separation process having significant potential for the treatment of industrial effluents to enable water reuse. It has the ability to remove low molecular weight trace contaminants from water, which cannot be separated by conventional treatment methods. In the present investigation, a thin film composite polyamide membrane was synthesized by interfacial polymerization technique and evaluated for the treatment of biscuit industrial effluent. The synthesized membrane was characterized using Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy to elucidate structure and intermolecular interactions, crystallinity, thermal stability and cross-sectional morphology, respectively. The influence of operating parameters such as feed pressure 0–21 kg/cm² and total dissolved solids (TDS) of 3160 ppm on water flux and impurity rejection was determined. An average flux of 11.63 L/m² h was obtained at a constant pressure of 21 kg/cm². The TDS, chemical oxygen demand (COD), and biochemical oxygen demand (BOD) rejections were found to be 53.62, 80, and 74%, respectively, at a water recovery of 65%. A statistical mechanical model was used to validate the experimental data. Based on this study, a detailed economic estimation for processing biscuit effluent of 1 m³/h feed capacity using commercial NF system is presented. The study revealed that the synthesized NF membrane could be an effective alternative for the treatment of various industrial effluents as well as to reduce the load on reverse osmosis process for desalination of seawater and effluent treatment through high degree of COD and BOD separation.     

AgBiVMo oxide catalytic membrane for selective oxidation of propane to acrolein

A metal ions (Ag, Bi, V, Mo) modified sol–gel method was used to prepare a mesoporous Ag_0.01Bi_0.85V_0.54Mo_0.45O₄ catalytic membrane which was used in the selective oxidation of propane to acrolein. By optimizing the preparation parameters, a thin and perfect catalytically active membrane was successfully prepared. SEM results showed that the membrane thickness is 5 μm. XRD results revealed that Ag_0.01Bi_0.85V_0.54Mo_0.45O₄ with a Scheelite structure, which is catalytically active for the selective oxidation of propane to acrolein, was formed in the catalytic membrane only when AgBiVMoO concentrations were higher than 40%. Catalytic reaction results demonstrated that the selective oxidation of propane could be controlled to a certain degree, such as to acrolein, in the catalytic membrane reactor (CMR) compared to the fixed bed reactor (FBR). For example, a selectivity of 54.85% for acrolein in the liquid phase was obtained in the CMR, while only 8.31% was achieved in the FBR.     

H2S adsorption on polycrystalline UO2

We report results on the adsorption and desorption of H₂S on polycrystalline UO₂ at 100 and 300 K, using ultrahigh vacuum X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and temperature programmed desorption (TPD). Our work is motivated by the potential for using the large stockpiles of depleted uranium in industrial applications, e.g., in catalytic processes, such as hydrodesulfurization (HDS) of petroleum. H₂S is found to adsorb molecularly at 100 K on the polycrystalline surface, and desorption of molecular H₂S occurs at a peak temperature of 140 K in TPD. Adsorption rates of sulfur as a function of H₂S exposure are measured using XPS at 100 K; the S 2p intensity and lineshapes demonstrate that the saturation coverage of S-containing species is 1 monolayer (ML) at 100 K, and is 0.3–0.4 ML of dissociation fragments at 300 K. LEIS measurements of adsorption rates agree with XPS measurements. Atomic S is found to be stable to >500 K on the oxide surface, and desorbs at 580 K. Evidence for a recombination reaction of dissociative S species is also observed. We suggest that O-vacancies, defects, and surface termination atoms in the oxide surface are of importance in the adsorption and decomposition of S-containing molecules.     

Treatment of Leather Plant Effluent by Membrane Separation Processes

Abstract

A scheme is proposed for the treatment of the leather plant effluent using membrane based separation processes. The effluent coming out from the various upstream units of the leather plant (except chrome tanning) are combined and a two step pressure driven membrane processes involving nanofiltration (NF) and reverse osmosis (RO) are adopted after a pretreatment consisting of gravity settling, coagulation, and cloth filtration. The entire membrane separation scheme is validated by conducting experiments under a continuous cross flow mode. A detailed parametric study for cross flow experiments is investigated to observe the effects of the operating conditions, i.e., the transmembrane pressure drop and the cross flow velocity on the permeate flux and quality for both NF and RO. Using a combination of osmotic pressure and solution diffusion model for both NF and RO, the effective osmotic pressure coefficient, solute diffusivity, and the solute permeability through the membrane are obtained by optimizing the experimental permeate flux and concentration (in terms of total dissolved solids) values for this complex industrial effluent. The BOD and COD values of the finally treated effluent are well within the permissible limits (in India).     

Clean-up to Chirality—Liquid Membranes as a Facilitating Technology?

Liquid membranes have been suggested as a clean technology due to characteristics such as high specificity, intensity and productivity as well as low emissions and energy utilisation. However when applying liquid membrane systems to real problems, in this paper chiral extraction of phenylalanine and lactic acid extraction from an industrial effluent, problems have been encountered with the specificity of the liquid membrane system used. Relatively low enantioselectivities (maximum 2·4) were observed with the chiral emulsion liquid membrane system investigated (maximum 1·6), although this was in excess of an analogous solvent extraction system studied. In lactic acid extraction, although batch extraction from model solutions was in excess of 75% in 2 min, when a real lactic acid containing industrial effluent was used the extent of extraction was reduced to around 20%. This effect was found to result from the co-extraction of other anions present in the effluent. In the case of chloride ions, a co-transport mechanism was noted. Thermal and photometric back-extraction strategies have been suggested as a means of enhancing overall liquid membrane extraction selectivities. © 1997 SCI.