Contactor System Research Articles

Comparison of separation performance of absorption column and membrane contactor system for biohydrogen upgraded from palm oil mill effluent fermentation

AbstractTreatment of palm oil mill effluent (POME) via fermentation under controlled conditions can produce a high‐value biohydrogen (H2) mixture containing carbon dioxide (CO2). This H2 can be enriched before it can be used for renewable energy, that is, in fuel cell. In this work, H2 was upgraded via two techniques, namely absorption column and membrane contactor system. Ammonium hydroxide (NH4OH), potassium hydroxide (KOH), and mixed solution of NH4OH and KOH were used as the chemical absorbents for both techniques. In the absorption column, it was found that the mixed solution provided the highest H2 purity (99%) at 1 M concentration with a gas flow rate of 0.2 L/min. Meanwhile, the mixed solution and KOH solution showed similar separation performance with H2 purity of up to 75% in the gas–liquid membrane contactor. On investigating the separation performance for each of the compared techniques, it was found that the absorption column has a superior ability to purify H2 than the membrane contactor system. However, the membrane contactor is more sustainable as it has the least drop in H2 purity at a longer separation time during the separation process. Both techniques have their own advantages in purifying H2, and thus they can be fairly considered for gas upgrading.

Numerical Investigation on the Effect of Flow Parameters in CO2 Capturing Using Aqueous MEA Absorbent in HFMC Systems

Nowadays, CO2 as the product of fossil fuel combustions, is polluting the air and the human environment, and it causes global warming. To reduce the negative effect of CO2 presence, it should be removed from the air by capturing methods. Hollow fiber membrane contactor (HFMC) system is one of the most efficient method for CO2 capturing than the other feasible capturing methods. In the present paper an HFMC absorbing system has been simulated using COMSOL Multiphysics software and the effect of flow rates of gas and liquid on the amount of CO2 removal has been studied. Aqueous solution of Mono-ethanolamine (MEA) is entered as the absorbent liquid in the tubes, and CO2 is removed from the shell side by the diffusion phenomena by participating in the chemical reaction with MEA. The results show that the higher liquid flow rate the higher %CO2 removal from the inserted gas. Against this result, the percentage of CO2 removal decreases with increasing the gas flow rate as expected. Higher gas flow rate leads the gas velocity to higher values and less possibility of absorbing by the diffusion method. The rate of the CO2 removal variation with liquid flow rate is higher than the CO2 removal variation whit the gas flow rate.

Performance comparison of ultrasonic-assisted and magnetic stirred absorption methods for CO2 separation

Chemical absorption is the most matured and preferred separation process which is extensively used for CO2 removal from natural gas. The current contactor systems used in the absorption process suffer from several drawbacks including excessive footprint, operating, and maintenance issues. Ultrasonic irradiation is a new alternative technique to assist the CO2 absorption process without the aforementioned limitations. Thus, the aim of this paper is elucidating the potential of the ultrasonic-assisted CO2 absorption system. To achieve this, the performance of the ultrasonic-assisted system was compared to that of the conventional stirring method. Two different solvents with dissimilar reaction mechanisms were chosen. The first part of the experiments was conducted in the ultrasonic-assisted batch vessel, while the second part was accomplished in the stirred batch cell. The parameters including ultrasonic power, ultrasonic frequency, stirring speed, and initial feed pressure were 18 W, 1.7 MHz, 500 rpm, and 11 bar, respectively. Besides, the operating temperature and the concentration were chosen based on the standard operating condition for each solvent. The mass transfer coefficient was calculated using the dynamic pressure-step method. The results revealed that in comparison with the stirring method, the ultrasonic-assisted absorption system significantly enhanced the CO2 absorption process at similar operating conditions. By using ultrasonic irradiation, the volumetric absorption coefficient increased almost three times for MDEA and nearly six times for MEA. In the latter, this improvement can be related to the physical effect of the ultrasound. However, for the slow kinetic solvents, this improvement might be attributed to the chemical effect of the ultrasound.

High rate biological contactor system using waste activated sludge from trickling filter/solids contact process

A high-rate biological contactor process (HRBC) can be used as primary treatment instead of a clarifier to remove particulate, colloidal and soluble fractions of organic matter via biosorption plus flotation and divert it to anaerobic digestion for methane production, simultaneously reducing secondary aeration energy demand. Pilot and bench tests were conducted at a range of contact times (15-60 min) and contactor dissolved oxygen (DO) (0.2-2.0 mg/L) using waste activated sludge (WAS) from a trickling filter/solids contact (TF/SC) process in the HRBC. Biosorption performance was lowest when contact times were <30 min and unstable at DO < 0.5 mg/L. The overall average of 20% sCOD capture was similar to previous findings by others using WAS from conventional AS. The biomethane potential (BMP) of the HRBC float material can be as high as that of primary sludge (340-400 mL CH4/g VS), which is much greater than WAS. Operating the HRBC with a long contact time (>30 min) or with high DO (>1 mg/L) increases the amount of biosorption but reduces the BMP of the float. It was also found that biosorption only effectively occurs when a WAS is paired with the wastewater from the same facility.

Spatial and temporal differences in the composition and structure of bacterial assemblages in biofilms of a rotating algal-bacterial contactor system treating high-strength anaerobic digester filtrate

The microbial assemblages in biofilms growing on rotating algal-bacterial contactors (RACs) used to treat high-strength anaerobic digester filtrate were characterized during a 4-month study. Typical RAC-based systems supplied with feedstocks containing high total ammonia and comparatively low dissolved inorganic carbon ratios are nitrite-accumulating. The RACs have biofilms on their sunlit exterior surfaces (2 m2) colonized by a mixture of phototrophs, chemoautotrophs, and heterotrophs, while the dark, internal media surface area (5 m2) is colonized by chemoautotrophic and heterotrophic bacteria. We assayed the relative abundance of bacterial V4 16S segments in the RAC biofilms from November through February detecting the most significant differences in composition between interior and exterior biofilm surfaces and over time. Ten operational taxonomic units accounted for over 69% of the total individuals counted. Nitrosomonas, the common ammonia-oxidizing bacterial genus, was the 10th most abundant OTU and although ubiquitous it was more abundant on the dark, inside surfaces of the RACs.

Experimental investigation of heat and moisture transfer performance of CaCl2/H2O-SiO2 nanofluid in a gas–liquid microporous hollow fiber membrane contactor

In this study, aqueous solution of CaCl2/SiO2 nanoparticles has been used as a desiccant in a gas–liquid hollow fiber membrane (HFM) air dehumidifier contactor system. The heat and mass (H/M) transfer properties HFM energy exchanger with CaCl2/H2O-SiO2 as desiccant solution studied experimentally for first time. Effects of different parameters on H/M transfer characteristics of system, including the nanoparticle concentration, liquid flow rate and liquid temperature were examined experimentally. The experiments arranged for desiccant temperatures of 20 °C and 26 °C, desiccant solutions of 0, 1%wt and 2%wt concentration and flow rates of 1.1, 1.25, 1.4 and 1.7 ml/s. The results indicated that the influence of particles on moisture removal rate is the greatest for the conditions of highest solution temperature and the highest particle. By introducing nanofluid solution as liquid desiccant in system the enhancing effect of reducing desiccant temperature on moisture removal lessens and declined to zero by increasing the solution flow rate with a high descending rate. For 2%wt nanoparticle concentration by 53% increase of absorbent flow rate, the value of temperature effectiveness reduced by 30%. This justifies adiabatic application of hollow fiber membrane systems with nanofluid desiccant.

Ammonium recovery from process water of digested sludge dewatering by membrane contactors

Abstract Membrane contactors are a promising alternative for nitrogen removal and recovery from process water compared to other physicochemical and biological sidestream treatment processes. Münster wastewater treatment plant (WWTP) is the first municipal WWTP in Germany operating a full-scale membrane contactor system to improve the nitrogen elimination and recovery efficiency. Factors influencing the operation and membrane performance are investigated in an accompanying research project. Additional operational aspects of the applied membrane modules are investigated in detail using a bench-scale membrane contactor. First results of the full-scale application demonstrate a high nitrogen removal efficiency of &amp;gt;95%.

Supported ionic liquid membranes (SILMs) as a contactor for selective absorption of CO2/O2 by aqueous monoethanolamine (MEA)

Application of membrane contactors in a combination of monoethanolamine as a solvent system for post-combustion CO2 capture has been extensively studied in the last decades. Due to the better performance to capture CO2 at low concentration, the potentialities of novel technology of supported ionic liquids membranes (SILMs) for absorption process in gas-liquid membrane contactor system are currently being explored to improve and compliment previous technology. In this study, a modified hydrophobic gas-liquid membrane contactor system was prepared using Liqui-Cel® parallel flow module as a membrane support and 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [emim] [NTf2] ionic liquid as a supporting phase. Under moderate operating conditions, parallel flow mode and use of monoethanolamine (MEA) as an absorbent, the effects of absorbent temperature and gas velocity on the CO2 absorption efficiency and CO2/O2 selectivity were determined using this modified module. Further investigation to compare the performances of blank and modified membrane module was implemented at different temperatures (303–348 K) and gas velocities (4.63 × 10−6 to 3.70 × 10−5 m s−1). Results revealed that efficiency of the CO2 absorption process of the modified module is almost doubled with an average selectivity factor of CO2/O2 around 5 times compared to blank contactor system. Thus, this modified membrane contactor system had shown a great potential for further used in the real industrial CO2 capture and beneficial to bottleneck the issue of MEA oxidation that usually occurred in previous gas-liquid membrane contactor system.

Novel continuous ultrasonic contactor system for CO2 absorption: Parametric and optimization study

High frequency ultrasonic-assisted absorption in a batch system has shown significant enhancement for CO2 removal. Nevertheless, its performance in continuous mode has yet to be studied. A novel continuous high frequency ultrasonic contactor system for CO2 capture has been developed to study the effect of gas flow rate (15–25SLPM), liquid flow rate (0.1–0.5SLPM), pressure (10–50bar) and voltage (0–30V) on the absorption performance. A validated quadratic model was developed, and the optimum condition was identified using central composite design coupled with response surface methodology. Based on the results, current system demonstrated better absorption performance as compared to other contactors.

Feasibility of Biohydrogen Purification from Carbon Dioxide Mixture via Integrated Microalgae-Membrane Contactor Towards Zero Carbon Emission

Biohydrogen (H2) mixed with carbon dioxide (CO2) produced from the fermentation of Palm Oil Mill Effluent (POME) could be a potential renewable energy source. However, an effective technique to treat both gases towards zero carbon emission has become a major concern. In this study, a new approach was introduced to treat H2/CO2 mixture from POME fermentation by an integrated microalgae-membrane contactor system. Polyvinylidine fluoride (PVDF) hollow fibre membrane used in the integrated membrane contactor system abled to give the highest purified H2% from mixed H2/CO2 in the microalgae liquid absorbent (Chlorella Vulgaris) (69.4%) followed by Bold Basal Medium (BBM) (59.1%) and distilled water (55.9%). This initial result showed that the microalgae possessed better ability to absorb CO2 into the liquid stream via the PVDF membrane contactor. Next, investigation on optimizing the system’s operational parameters using BBM as liquid absorbent showed the highest CO2 absorption flux and efficiency were obtained at initial solution pH of 10. Further investigation showed that the absorption efficiency was enhanced as the liquid flow rate increased up to 0.4 L/min and the gas flow rate was at 0.1 L/min. Upon utilizing 0.6 g/L microalgae, the purified H2% found to remarkably increase up to 83.2%. In conclusion, the use of the developed integrated microalgae-membrane contactor system to purify the bio-H2 from CO2 mixture is a promising alternative method for zero carbon emission especially in palm oil industry.

Membrane gas-solvent contactors undergoing oscillating solvent flow for enhanced carbon dioxide capture

Membrane gas-solvent contactors are a hybrid approach that combine membrane gas separation with solvent absorption to undertake highly efficient CO2 removal. However, solvent boundary layer in many gas-solvent membrane contactors has a high mass transfer resistance to CO2 capture. Here, for the first time, an oscillating solvent flow was applied to a polydimethylsiloxane (PDMS) membrane contactor system to enhance the absorption of CO2. The oscillating solvent flow enhanced the overall mass transfer coefficient of CO2 (Kov) compared to the non-oscillating solvent flow. The effect of the oscillating solvent frequency and amplitude on Kov was investigated. Increasing the oscillating frequency from 0.83 Hz to 2.03 Hz resulted in 53% enhancement in Kov. Doubling the value of the oscillating amplitude increased Kov by 30%. An oscillating Reynolds number (Reos) was introduced to the oscillating solvent flow described by the root mean square oscillating solvent velocity (uos,rms). Using this Reynolds number, a Sherwood number correlation (Shos) was proposed for the hollow fibre membrane contactor, which accounted for the enhancement effects of solvent oscillation on the performance of gas-solvent membrane contactor.

An experimental study on synthesis of glycolic acid via carbonylation of formaldehyde using PTFE membrane contactor

The batch and continuous synthesis of glycolic acid via carbonylation of formaldehyde using high-temperature and high-pressure poly(tetrafluoroethylene) (PTFE) membrane contactor was demonstrated in this paper. The experiments in conventional stirred tank reactor were also conducted for comparison. The results showed that the yield of glycolic acid was significantly improved in membrane contactor system compared to the stirred tank reactor. At reaction temperature of 120 °C and reaction pressure of 5.0 MPa, the yield of glycolic acid was higher than 90% when the reaction time was 1 h, while it was only about 45% in the conventional stirred tank reactor. The enhancement of yield was due to the improvement of mass transfer or dispersion of CO in membrane contactor system, which could provide larger gas-liquid contact area and shorter mass transfer distance. The stability of PTFE hollow fibre membranes was also investigated by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), liquid entry pressure (LEP), bubble point (BP) and contact angle (CA) measurements. The characterizations indicated that PTFE membranes exhibited good chemical and thermal stability in this reaction system. This study provided new idea and reference for the carbonylation of formaldehyde and similar gas-liquid reactions.

Extraction of 137Cs from Acidic Feed by Centrifugal Contactors Using a Solution of Calix[4]arene-bis-1,2-benzo-crown-6 in Phenyltrifluoromethyl Sulphone

Extraction of 137Cs from 1.6 L of diluted aqueous simulated high-level waste (SHLW) (at 1 M HNO3) was carried out using a two-stage centrifugal contactor system (bowl volume 200 mL) into 2 × 10−3 M solution of calix[4]arene-bis-1,2-benzo-crown-6 in phenyltrifluoromethyl sulphone. Batch extraction studies were done to optimize the conditions for the centrifugal contactor runs. Extraction and stripping experiments were carried out at 2000 rotations per minute, keeping the organic and aqueous flow rate at 15 mL/min. Alamine 336 was used at a very low concentration (0.4 vol %) to effect efficient stripping of the extracted radiocesium. The studies were carried out using SHLW as well and the results indicated quantitative extraction and stripping in the first stage of operations while the repeat runs suggested lower extraction as well as stripping efficiencies.

A Single Tube Contactor for Testing Membrane Ozonation

A membrane ozonation contactor was built to investigate ozonation using tubular membranes and inform computational fluid dynamics (CFD) studies. Non-porous tubular polydimethylsiloxane (PDMS) membranes of 1.0–3.2 mm inner diameter were tested at ozone gas concentrations of 110–200 g/m3 and liquid side velocities of 0.002–0.226 m/s. The dissolved ozone concentration could be adjusted to up to 14 mg O3/L and increased with decreasing membrane diameter and liquid side velocity. Experimental mass transfer coefficients and molar fluxes of ozone were 2.4 × 10−6 m/s and 1.1 × 10−5 mol/(m2 s), respectively, for the smallest membrane. CFD modelling could predict the final ozone concentrations but slightly overestimated mass transfer coefficients and molar fluxes of ozone. Model contaminant degradation experiments and UV light absorption measurements of ozonated water samples in both ozone (O3) and peroxone (H2O2/O3) reaction systems in pure water, river water, wastewater effluent, and solutions containing humic acid show that the contactor system can be used to generate information on the reactivity of ozone with different water matrices. Combining simple membrane contactors with CFD allows for prediction of ozonation performance under a variety of conditions, leading to improved bubble-less ozone systems for water treatment.

Membrane contactor aided catalyst recycle and organic acid recovery from aqueous solutions using porous hydrophobic polyvinylidene fluoride barriers

The present study investigates the performance of indigenous hydrophobic polyvinylidene fluoride (PVDF) based porous membranes for separation of valuable organics such as acetamide catalyst and tartaric acid from aqueous media. Dehydration of acetamide was carried using ultraporous hydrophobic PVDF membrane by vacuum membrane distillation (VMD) technique. Effect of feed concentration on membrane performance was studied. Membrane exhibited a high total flux of 0.32 kg/m2h with <1.2% acetamide losses in permeate during concentration of acetamide catalyst from 30% to 70% (w/v). The separation of tartaric acid from synthetic mixture was carried out using indigenous ultraporous PVDF/Polyurethane (PU) blend membrane by liquid-liquid membrane contactor (LLMC) system. Influence of various additives such as LiCl2, ZnCl2, glycerol and polyvinylpyrrolidone (PVP) on membrane performance was studied. PVDF/PU/glycerol membrane exhibited extraction efficiency of nearly 12% for initial acid and extractant concentration of 100 mol/m3 and 30%, respectively, within a processing time of 2 h. All the indigenously synthesized membranes were characterized using analytical tools to study the physico-chemical properties of polymer films. A mathematical model for VMD system has also been developed to validate the experimental results. The study inferred that the processes employed could be considered as alternative techniques over conventional methods for recovery of both solid catalyst and organic acids which are widely used in industry.

17α-Ethinylestradiol and 17β-estradiol removal from a secondary urban wastewater using an RBC treatment system.

The presence of micropollutants that include endocrine-disrupting compounds (EDC) in aquatic environments is currently one of the most relevant aspects of water quality due to their adverse effects on aquatic organisms and human health. From the several categories of EDC, 17β-estradiol (E2) is a natural hormone, which is prevalent in vertebrates, associated with the female reproductive system and maintenance of the sexual characters. 17α-Ethinylestradiol (EE2) is a synthetic hormone produced from the natural hormone E2 and is an essential component of oral contraceptives. These compounds are susceptible to bioconcentration and have high potential to bioaccumulation. Wastewater treatment plants are the main point source of E2 and EE2 into aquatic environments, but conventional wastewater treatment systems are not specifically designed for steroid removal. To overcome this problem, biological tertiary treatment may be a solution for the removal of emergent pollutants such as E2 and EE2. The main purpose of the present study is to provide a solution based on the optimization of a rotating biological contactor system to remove estrogens, specifically E2 and EE2, and to quantify their removal efficiency on different matrices, namely real wastewater and different synthetic wastewaters. All assays presented viable removal efficiencies for compound E2 with values always above 50%; real wastewater yielded the highest removal efficiencies. EE2 removal had better removal efficiencies with synthetic wastewater as feed solution, with removals above 15%, whereas the removal efficiency with real wastewater was inexistent.

Synthesis of mechanically robust epoxy cross-linked silica aerogel membranes for CO 2 capture

Abstract Mesoporous SiO2 aerogels are multi-functional porous materials with diverse applications. However, the fragile characteristics and low mechanical strength of mesoporous SiO2 aerogels limits their development for use in industrial applications. The mechanical strength of SiO2 aerogels can be greatly enhanced by the addition of tri-epoxy cross-linkers. Tri-epoxy cross-linked SiO2 aerogels with tri-epoxy concentrations of 7.5%, 15%, 30% and 45% were coated on macroporous Al2O3 membrane supports. The surface of the tri-epoxy cross-linked SiO2 aerogel membranes became superhydrophobic after fluoroalkylsilane (FAS) modification. Compared to native SiO2 aerogel membranes in the absence of tri-epoxy cross-linker, the pore size of the tri-epoxy cross-linked SiO2 aerogel membranes with tri-epoxy concentrations of 15% and 30% increased to approximately 6 nm, resulting in an increase in the CO2 absorption flux. The highest CO2 absorption flux of 1.4 mmol/m2s was reached for the tri-epoxy cross-linked SiO2 aerogel membrane with a tri-epoxy concentration of 15%. The durability of the as-prepared SiO2 aerogel membranes for CO2 absorption is also demonstrated in this work. Consequently, the mechanically robust tri-epoxy cross-linked SiO2 aerogel membranes have potential applications in membrane contactor systems for CO2 capture.

Gas-liquid membrane contactors: Modeling study of non-uniform membrane wetting

Current available models for simulation of the separation process in gas-liquid membrane contactor (MC) systems consider a uniform partial membrane wetting along the membrane length (Lmem). However, transmembrane pressure changes along the Lmem. Additionally, the available models usually consider a simplified uniform pore size to represent the micro-porous MC. Additionally, not all pores in a MC have the same size. In this study, a pore-scale network model is developed to simulate the physical separation of H2S using MCs by taking to account for (i) transmembrane pressure variation and (ii) pore size distribution of MC. The model results are compared with the experimental results of H2S separation. Modeling results indicate that membrane wetting is non-uniformly distributed along Lmem. The membrane wetting ratio is maximum at the inlet of the liquid phase, and it decreases toward the liquid outlet. Also, increasing the inlet gas pressure reduces the membrane wetting ratio, and leads to higher H2S separation. Moreover, the model results indicate that shifting of the pore size distribution of MC towards smaller pore size declines the membrane wetting ratio and increases the H2S separation efficiency.

PENGOLAHAN AIR LIMBAH DENGAN SISTEM REAKTOR BIOLOGIS PUTAR (ROTATING BIOLOGICAL CONTACTOR) DAN PARAMETER DISAIN

A rotating biological contactor (or RBC) is a type of fixed media filter which removes both organic matter and ammonia from water. It can be added to a packaged plant for more efficient ammonia removal, replacing the aerator in both location and function.The RBC consists of a series of rotating discs. These discs are coated with a biological slime like the slime on rocks in a healthy stream. This slime is rotated through the air and and then through the wastewater so that it picks up oxygen in the air and breaks down B.O.D. in the wastewater. Since the discs rotate through the air, there is no need to pump air into the wastewater. And since the slime stays on the discs, there is no need to recycle sludge. The present study describes basic consideration of rotating biological contactor (RBC) system for wastewater treatment. The design of an RBC system must include the following consideration sach as organics and surface loading criteria, staging of RBC units, peripheral velocity, temperature, effluent characteritics and secondary clarifier. The RBC system have some advantages : smaller basin, less upset, high loading rate, nitrification/de-nitrification, high tolerance, low OM Cost, durable constructions, odorless, no noise, and stable sludge characteristics. Kata Kunci : Reaktor bioloigis putar, air limbah, parameter disain.

Prediction of CO2/O2 absorption selectivity using supported ionic liquid membranes (SILMs) for gas–liquid membrane contactor

ABSTRACTGiven their unique and tunable properties as solvents, ionic liquids (ILs) have become a favorable solvent option in separation processes, particularly for capturing carbon dioxide (CO2). In this work, a simple method that can be used to screen the suitable IL candidates was implemented in our modified gas–liquid membrane contactor system. Solubilities, selectivities of CO2, nitrogen (N2), and oxygen (O2) gases in imidazolium-based ILs and its activity coefficients in water and monoethanolamine (MEA) were predicted using conductor-like screening model for real solvent (COSMO-RS) method over a wide range of temperature (298.15–348.15 K). Results from the analysis revealed that [emim] [NTf2] IL is a good candidate for further absorption process attributed to its good hydrophobicity and CO2/O2 selectivity characteristics. While their miscibility with pure MEA was somehow higher, utilizing the aqueous phase of MEA would be beneficial in this stage. Data on absorption performances and selectivity of CO2/O2 are scarce especially in gas–liquid membrane contactor system. Therefore, considering [emim] [NTf2] IL as a supporting material in supported ionic liquid membranes (SILMs), using aqueous phase of MEA as an absorbent would result in a great membrane-solvent combination system in furthering our gas–liquid membrane contactor process. In conclusion, COSMO-RS is a potentially great predictive utility to screen ILs for specified separation applications. In addition, this work provides useful results for the [emim] [NTf2]-SILMs to be extensively applied in the field of CO2 capture and selective O2 removal.