Removal of ammonium from aqueous solutions using alkali-modified biochars

Biochars converted from agricultural residuals can effectively remove ammonium from water. This work further improved the sorption ability of biochars to aqueous ammonium through alkali modification. Three modified biochars were prepared from agricultural residuals pre-treated with NaOH solution through low-temperature (300 °C) slow pyrolysis. The modified biochars effectively removed ammonium ions from water under various conditions with relatively fast adsorption kinetics (reached equilibrium within 10 h) and extremely high adsorption capacity (>200 mg/g). The Langmuir maximum capacity of the three modified biochars were between 313.9 and 518.9 mg/g, higher than many other ammonium adsorbents. Although the sorption of ammonium onto the modified biochar was affected by pH and temperature, it was high under all of the tested conditions. Findings from this work indicated that alkali-modified biochars can be used as an alternative adsorbent for the removal of ammonium from wastewater.     

γ-Ray-induced degradation of lignocellulosic materials

Lignocellulosic plant materials were treated with various swelling agents and exposed to γ radiation from ⁶⁰Co or ¹³⁷Cs. At dosages of 50 Mrad or above, lignocellulosic materials were extensively degraded and solubilized in water. Addition of water, NaOH, or H₂SO₄ to the substrate increased the degree of solubilization. Complete solubilization was achieved for samples of sugarcane bagasse, newspaper, cotton linters, cotton cloth, sawdust, and α-cellulose powder. About 35% total sugar and 5% reducing sugar per dry weight of sugarcane bagasse could be obtained by this method. Most of the soluble carbohydrates seemed to be disaccharides or larger molecules and glucose degradation products. Solubilization of cellulose was dosage dependent and although the rate of solubilization was increased by adding alkali, released sugar was further decomposed by the alkali and by high dosage of radiation.     

Aquaporin-1 Tunes Pain Perception by Interaction with Nav1.8 Na+ Channels in Dorsal Root Ganglion Neurons

Aquaporin-1 (AQP1) water channels are expressed in the plasma membrane of dorsal root ganglion (DRG) neurons. We found reduced osmotic water permeability in freshly isolated DRG neurons from AQP1^−/− versus AQP1^+/+ mice. Behavioral studies showed greatly reduced thermal inflammatory pain perception in AQP1^−/− mice evoked by bradykinin, prostaglandin E₂, and capsaicin as well as reduced cold pain perception. Patch clamp of freshly isolated DRG neurons showed reduced action potential firing in response to current injections. Single action potentials after pulse current injections showed reduced maximum inward current, suggesting impaired Na_v1.8 Na⁺ function. Whole-cell Na_v1.8 Na⁺ currents in Na_v1.8-expressing ND7-23 cells showed slowed frequency-dependent inactivation after AQP1 transfection. Immunoprecipitation studies showed AQP1- Na_v1.8 Na⁺ interaction, which was verified in live cells by single-particle tracking of quantum dot-labeled AQP1. Our results implicate the involvement of AQP1 in DRG neurons for the perception of inflammatory thermal pain and cold pain, whose molecular basis is accounted for, in part, by reduced Na_v1.8-dependent membrane Na⁺ current. AQP1 is, thus, a novel target for pain management.     

Influence of NH3/CO2 Modification on the Characteristic of Biochar and the CO2 Capture

This paper was aimed to study the influence of modification of biochar on the performance of CO₂ adsorption. Biochar, obtained from cotton stalk pyrolysis in a fixed bed reactor, was modified with ammonia and CO₂. The physicochemical properties of biochars were characterized by the Fourier transform infrared spectroscopy and automatic adsorption equipment (Micromeritics, ASAP 2020, USA). CO₂ adsorption of biochar was performed in thermogravimetric analyzer. The results showed that the surface area of char was increased significantly by CO₂ modification, while N-contained compound on char surface was enriched obviously by NH₃ modification. CO₂ adsorption of biochar increased greatly with CO₂ and NH₃ modification. CO₂ adsorption was mainly attributed to physical adsorption at 20 °C, and the adsorption quantity (maximum = 99 mg/g) was proportional to the micropore volume of the char. However, at 120 °C, molecular thermal motion increase, chemical adsorption start to play a dominated role, and the adsorption was directly proportional to the N content of this char.     

Simplified method for alkali treatment of low-quality roughages for use by small-holders in developing countries

The method described is a modification of the soaking procedure of Beckmann and of Torgrimsby. As the effluent NaOH solution is successively replenished and re-used many times before being discarded, pollution is minimised. Furthermore, the amounts of water and alkali consumed are smaller than with the Beckmann method, and the same container is used for all treatments and washing. The method is adaptable to small-scale farming.In Experiment 1, Cynodon hay was treated with 0, 50 or 100 kg NaOH/tonne dry matter (DM), by a modification of the Beckmann method. Significant (P < 0.01) improvements in digestibility of dry matter (DM), organic matter (OM), and cell wall constituents (CWC) were obtained, and voluntary feed intake was raised significantly (P < 0.01).In Experiment 2, both NaOH and Ca(OH)₂ treatments at 0, 50, 100 and 150 kg alkali/tonne DM of maize stover, significantly (P < 0.01) increased DM and OM digestibility, but the response was greater with NaOH. A combination of NaOH and Ca(OH)₂ treatments had no consistent effect on digestibility, but the trend was a decline in digestibility when Ca(OH)₂ was applied at high rates of 100 and 150 kg Ca(OH)₂/tonne DM. The recovery of DM increased with Ca(OH)₂ treatment, but decreased with NaOH.In Experiment 3, the treatment of maize stover with 0, 25 or 50 kg Ca(OH)₂/tonne DM, in combination with 0, 100 or 150 kg NaOH/tonne DM, significantly (P < 0.01) decreased DM, OM, and CWC digestibility below that achieved by NaOH alone.It is concluded that with the modified method an initial allowance of 100–150 kg NaOH/tonne DM of stover and replenishment of 40–60 kg NaOH/tonne DM is optimal.     

Chemical Modification Causes Similar Change in Dependence on Water Activity of Chymotrypsin Hydration and Catalysis in Hexane

Amino groups in alpha-chymotrypsin were reacted with pyromellitic anhydride, introducing 17 to 32 additional carboxyl groups. This modification causes a major change in the water adsorption isotherm of the lyophilized protein powder. Little water is bound by the modified enzyme at water activity (a_w) below 0.35, but it shows increased water binding at a_w over 0.5. This correlates with a similar change in the a_w dependence of the catalytic activity of the enzyme powder suspended in hexane, with a much steeper increase in activity of the modified chymotrypsin.     

Kinetics and competitive modeling of cesium biosorption onto iron(III) hexacyanoferrate modified pine cone powder

This study looked at incorporation of iron(III) hexacyanoferrate onto chemically treated pine cone via iron(III) surface loading and its application for cesium (Cs) adsorption in the presence of alkali/alkali earth metals. The optimum iron(III) loading concentration was 2.50 mol l⁻¹ at pH 7, while optimum hexacyanoferrate (HCF) loading was achieved at a hexacyanoferrate concentration of 0.26 mol l⁻¹. The best-fitting kinetic model was confirmed using the closeness of the predicted equilibrium capacities to the experimentally determined capacity, three error determination methods, and the comparative plots of predictive and experimental uptake of Cs with time. The adsorption rate constants were reduced by alkali/alkali metal addition and the reduction was higher in the HCF-modified pine. The mechanism of Cs adsorption onto raw pine followed the pseudo-second-order model and involved stripping of the hydration water from the metal ion. The presence of Na⁺ did not alter the adsorption mechanism but Ca²⁺ addition changed the best-fitting model to pseudo-first-order. The diffusion-chemisorption model best fitted Cs adsorption onto HCF-modified pine and involved adsorption of Cs in its hydrated form, which migrated easily through the zeolite-like lattice of hexacyanoferrate. Addition of Na⁺ and Ca²⁺ changed the best-fitting model to a pseudo-first-order model.     

Carrier Interfacial Engineering by Bismuth Modification for Efficient and Thermoresistant Perovskite Solar Cells

Organic–inorganic halide perovskite solar cells (PSCs) have emerged as attractive alternatives to conventional solar cells. It is still a challenge to obtain PSCs with good thermal stability and high permanence, especially at extreme outdoor temperatures. This work systematically studies the effects of Bi³⁺ modification on structural, electrical, and optical properties of perovskite films (FA_0.83MA_0.17Pb(I_0.83Br_0.17)₃) and the performance of corresponding PSCs. The results indicate that Bi³⁺ modified PSCs can achieve better thermal stability, photovoltaic response, and reproducibility compared with control cells due to the decreased grain boundaries, enhanced crystallization, and improved electron extraction from perovskite film. As a result, the modified PSC exhibits an optimized power conversion efficiency (PCE) of 19.4% compared with 18.3% for the optimized control device, accompanied by better thermoresistant ability under 100–180 °C and enhanced long‐term stability. The degradation rate of the modified device is reduced by an order of magnitude due to effective structural defect modification in perovskite photoactive layer. It could maintain more than two months at 60 °C. These results shed light on the origin of crystallization and thermal stability of perovskite films, and provide an approach to solve thermal stability issue of PSCs.     

Biosorption and Desorption of Lead(II) by Hydrilla verticillata

The potential of nonliving biomass of Hydrilla verticillata to adsorb Pb(II) from an aqueous solution containing very low concentrations of Pb(II) was determined in this study. Effects of shaking time, contact time, biosorbent dosage, pH of the medium, and initial Pb(II) concentration on metal-biosorbent interactions were studied through batch adsorption experiments. Maximum Pb(II) removal was obtained after 2 h of shaking. Adsorption capacity at the equilibrium increased with increasing initial Pb(II) concentration, whereas it decreased with increasing biosorbent dosage. The optimum pH of the biosorption was 4.0. Surface titrations showed that the surface of the biosorbent was positively charged at low pH and negatively charged at pH higher than 3.6. Fourier transform infrared (FT-IR) spectra of the biosorbent confirmed the involvement of hydroxyl and C?O of acylamide functional groups on the biosorbent surface in the Pb(II) binding process. Kinetic and equilibrium data showed that the adsorption process followed the pseudo-second-order kinetic model and both Langmuir and Freundlich isothermal models. The mean adsorption energy showed that the adsorption of Pb(II) was physical in nature. The monolayer adsorption capacity of Pb(II) was 125 mg g^?1. The desorption of Pb(II) from the biosorbent by selected desorbing solutions were HNO₃ > Na₂CO₃ > NaOH > NaNO₃.     

Enhancement of cyanobacterial salt tolerance by combined nitrogen

Presence of certain nitrogenous compounds in the growth medium significantly enhanced the salt tolerance of the fresh-water cyanobacterium Anabaena sp. strain L-31 as well as the brackish water cyanobacterium Anabaena torulosa. Among these, nitrate, ammonium, and glutamine were most effective followed by glutamate and aspartate. These nitrogenous compounds also inhibited Na⁺ influx in both Anabaena spp. with the same order of effectiveness as that observed for protection against salt stress. The inhibition of Na⁺ influx on addition of the nitrogenous substances was rapid; nitrate and ammonium inhibited Na⁺ influx competitively. Proline and glycine did not affect Na⁺ influx and also had no influence on the salt tolerance of either Anabaena sp. The observed protection was not consequent to a stimulatory effect of combined nitrogen on growth per se. Uptake of NO₃⁻ and NH₄⁺ increased during salt stress but was not correlated with growth. Intracellular levels of NO₃⁻ and NH₄⁺ were found to be inadequate to constitute a major component of the internal osmoticum. The results suggest that inhibition of Na⁺ influx by combined nitrogen is a major mechanism for protection of cyanobacteria against salt stress.     

Study on the Adsorption of Cr3+ by Peanut Shell: Adsorption Kinetics,Thermodynamics, and Isotherm Properties

The pollution of heavy metals in soil to the environment is becoming more and more serious, resulting in the reduction of crop production and the occurrence of medical accidents. In order to remove heavy metal ions from soil and reduce the harm of heavy metals to the environment, modified peanut shell was used to adsorb Cr³⁺ in this article. The effects of different adsorption conditions on the adsorption rate and adsorption capacity of Cr³⁺ on ZnCl₂ modified peanut shell were studied, the best adsorption conditions were explored, and the relationship of kinetics, thermodynamics and adsorption isotherm properties of adsorption process were explored. The results showed that the optimum adsorption pH value, dosage, initial concentration, adsorption temperature and contact time of ZnCl₂ modified peanut shell were 2.5, 2.5 g/L, 75 μg/mL, 25 °C and 40 min, respectively. The prepared materials were characterized and analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD) analyzer. It was concluded that the modified peanut shell had a good adsorption capacity to Cr³⁺. The kinetic study showed that the adsorption process of Cr³⁺ on peanut shell modified by zinc chloride was in accordance with the quasi-second-order kinetic model. The adsorption process belonged to exothermic reaction and belonged to spontaneous reaction process. In summary, it is proved that zinc chloride modified peanut shell can efficiently adsorb Cr³⁺, which can be used for the treatment of heavy metal wastes in industry, which is beneficial to environmental protection and avoid heavy metal pollution.     

Biosorption of phosphate from synthetic wastewater by biosolids

The aim of this study was to determine the potential of phosphate (P) removal from wastewater by biosolids prepared by the immobilization of P-accumulating bacteria onto organic bentonite. Organic bentonite was prepared by treating bentonite clay with quaternary ammonium salt — cetyltrimetylammonium (CTA) bromide. Cation exchange capacity (CEC) of the bentonite was found to be 179.0 meq/100 g of the dry bentonite. The CTA occupied ca. 175% of the CEC. Modification of bentonite with CTA in amounts higher than 55% of the CEC resulted in the change of zeta potential of particles from negative to positive. Only in reactors containing organic bentonite samples occupied with 3.5 and 28% of the CEC was P efficiently removed from wastewater by combined adsorption and bacterial uptake in the biomass. Organic bentonite samples with higher CTA loadings (from 55 to 175% of the CEC) showed bactericidal effects. To enhance P removal from wastewater in the aerated biological system, biosolids consisting of P-accumulating bacteria and organic bentonite can be used, but special attention should be given to the configuration of sorbed CTA molecules and its potential desorption.     

Speciation of inorganic arsenic and selenium in leachates from landfills in relation to water quality assessment

Speciation of arsenic and selenium was carried out on water samples taken from rivers used as water intake points in the vicinity of landfill areas used for land-based waste disposal system. Leachates from these landfill areas may contaminate the river water through underground seepage or overflowing, especially after a heavy downpour. Preconcentration of the chemical species was done using a mixture of ammonium pyrrolidinethiocarbamate-chloroform (APDTC-CHCl₃). Because only the reduced forms of both arsenic and selenium species could be extracted by the preconcentrating mixture, suitable reducing agents such as 25% sodium thiosulfate for As(III) and 6M HCl for Se(IV) were used throughout the studies. Care was taken to exclude the interfering elements such as the alkali and alkali earth metals from the inorganic arsenic and selenium species by introducing 12% EDTA solution as the masking agent. The extracted mixture was irradiated in a thermal neutron flux of 4 × 10¹²/cm/s from a TRIGA Mk.II reactor at the Malaysia Institute of Nuclear Technology Research (MINT). Gamma rays of 559 keV and 297 keV from⁷⁶As and⁷⁵Se, respectively, were used in the quantitative determination of the inorganic species. Mixed standards of As(III) and Se(IV) used in the percentage efficiency procedure were prepared from salts of Analar grade. The water quality evaluation was viewed from the ratio of the inorganic species present.     

Effect of Ionic Composition of Suspending Solution on Virus Adsorption by a Soil Column

The effect of various electrolytes on the adsorption of poliovirus was measured in 250-cm-long soil columns with ceramic samplers at different depths. Viruses suspended in deionized water moved much farther through the soil than those suspended in tap water, whereas movement in sewage water was intermediate. The salt content of the tap water and sewage water promoted virus adsorption, but evidently the organic compounds in sewage retarded adsorption. When viruses were suspended in chloride solutions of K⁺, Na⁺, Ca⁺, and Mg²⁺, virus adsorption increased as the cation concentration and valence increased. The depth of virus penetration was related to the ionic strength of the solutions. Virus penetration data for NO₃⁻, SO₄²⁻, and H₂PO₄⁻ salts of K⁺, Na⁺, and Ca²⁺ indicated that other anions were more effective than Cl⁻ in promoting virus adsorption. Also, NH₄⁺ was more effective than other cations in limiting the penetration depth of viruses. It seems that ions composed of radicals are more effective than ions composed of single atoms in promoting virus adsorption. Al³⁺ was the most effective ion in limiting virus penetration, probably owing to flocculation of the viruses. Adding AlCl₃ concentrations to secondary sewage effluent to provide an Al³⁺ concentration of 0.1 mM reduced the virus penetration depth to 40 cm. These studies show that the ionic composition of the suspending solutions must be considered in predicting virus penetration depths, and it may be practical to add low concentrations of a flocculating agent such as AlCl₃ to sewage water to limit virus movement through very porous soils.     

Recovery of uranium by immobilized microorganisms

Summary Some attempts were made to recover uranium from sea and fresh water using immobilized Streptomyces viridochromogenes and Chlorella regularis cells. The cells immobilized in polyacrylamide gel have the most favorable features for uranium recovery; high adsorption ability, good mechanical properties, and applicability in a column system. The adsorption of uranium by the immobilized cells is not affected by the pH values between 4 and 9. These results show that uranium adsorption becomes independent of pH after immobilization. The amounts of uranium adsorbed by the immobilized cells increased linearly with temperature, suggesting that the adsorption of uranium by the immobilized cells is an endothermic reaction. The immobilized cells can recover uranium almost quantitatively from both fresh and sea water containing uranium, and almost all uranium adsorbed is desorbed with a solution of Na₂CO₃. Thus the immobilized cells of Streptomyces and Chlorella can be used repeatedly in adsorption-desorption process.Studies on the Accumulation of Heavy Metal Elements in Biological Systems. XXI     

Growth, water use efficiency, and proline content of hydroponically grown tomato plants as affected by nitrogen source and nutrient concentration

Tomato plants (Lycopersicon esculentum Mill. cv. Counter) were grown in 12-L polyethylene containers in aerated and CaCO₃-buffered nutrient solutions containing different concentrations of complete stock solutions with either nitrate (stock solution N) or ammonium (stock solution A) as the only nitrogen source (X1 = standard concentration with 5 mM NO₃ ^–-N or NH₄ ⁺-N, and X3, X5.5, X8 and X11 = 3, 5.5, 8, 11 times the standard concentration), or a mixture of both stock solutions (N:A ratio = 100:0, 75:25, 50:50, 25:75, 0:100) at moderate nutrient concentration (X3). Total dry matter production and fruit dry weight were only slightly affected by increasing nutrient concentration if nitrate was supplied as the sole nitrogen source. Compared to nitrate, ammonium nitrogen caused a decrease in total dry weight (32–86% between X1 and X11), but led to an increase in both total dry weight and fruit dry weight (11% and 30%) at low concentration if supplied in addition to nitrate nitrogen (N:A ratio = 75:25). Dry matter partitioning in plants was affected by the strength of the nutrient solution, but even more by ammonium nitrogen. Fruits accumulated relatively less dry matter than did the vegetative parts of tomato plants when supplied with nutrient solutions containing ammonium as the only nitrogen source (fruit dry weight to total dry weight ratio 0.37 and 0.15 at low and high nutrient concentration), while nitrate nitrogen rather supported an increase in dry matter accumulation in the reproductive organs (fruit dry weight to total dry weight ratio 0.39–0.46). The water use efficiency (WUE) was only slightly affected by the strength of the nutrient solutions containing nitrate nitrogen (2.9–3.4 g DW (kg H₂O)^–1), while ammonium nitrogen led to a decrease in WUE from 2.4 to 1.3 g DW (kg H₂O)^–1at low (X1) and high (X11) nutrient concentration, respectively. The proline content of leaves fluctuated (0.1–5.0 mol (g fresh weight)^–1) according to nutrient concentration and global radiation, and reflected enhanced sensitivity of plants to these potential stress factors if ammonium was the predominant N source supplied. It was concluded, that proline is a reliable indicator of the environmental stress imposed on hydroponically grown tomato plants.     

Helix VIII of NhaA Na(+)/H(+) antiporter participates in the periplasmic cation passage and pH regulation of the antiporter

The crystal structure of Escherichia coli NhaA determined at pH 4 has provided insights into the mechanism of activity of a pH-regulated Na⁺/H⁺ antiporter. However, because NhaA is active at physiological pH (pH 6.5-8.5), many questions related to the active state of NhaA have remained unanswered. Our Cys scanning of the highly conserved transmembrane VIII at physiological pH reveals that (1) the Cys replacement G230C significantly increases the apparent K_m of the antiporter to both Na⁺ (10-fold) and Li⁺ (6-fold). (2) Variants G223C and G230C cause a drastic alkaline shift of the pH profile of NhaA by 1 pH unit. (3) Residues Gly223-Ala226 line a periplasmic funnel at physiological pH as they do at pH 4. Both were modified by membrane-impermeant negatively charged 2-sulfonatoethyl methanethiosulfonate and positively charged 2-(trimethyl ammonium)-ethylmethanethiosulfonate sulfhydryl reagents that could reach Cys replacements from the periplasm via water-filled funnels only, whereas other Cys replacements on helix VIII were not accessible/reactive to the reagents. (4) Remarkably, the modification of variant V224C by 2-sulfonatoethyl methanethiosulfonate or 2-(trimethyl ammonium)-ethylmethanethiosulfonate totally inhibited antiporter activity, while N-ethyl maleimide modification had a very small effect on NhaA activity. Hence, the size—rather than the chemical modification or the charge—of the larger reagents interferes with the passage of ions through the periplasmic funnel. Taken together, our results at physiological pH reveal that amino acid residues in transmembrane VIII contribute to the cation passage of NhaA and its pH regulation.     

Modification of water flows and nitrogen fluxes by shelterbelts

The introduction of shelterbelts (mid-field trees linear structures) in a uniform agricultural landscape composed mainly of cultivated fields is one of the best tools for managing heat balance and water regime in the landscape. Evapotranspiration rates, surface runoff and percolation of water across a soil profile are controlled by shelterbelts. The heat transfers from cultivated fields to shelterbelts by advection processes enhance evapotranspiration rates from trees. Depth of groundwater table and thermal conditions have important bearing on the uptake of groundwater by trees. The studies showed that in the Turew agricultural landscape, located near Poznan, Poland, shelterbelts use for evapotranspiration 40 percent more water than cultivated fields. For air heating cultivated fields use 280 percent of solar energy more than shelterbelts. The shelterbelts limit N-NO₃⁻ spreading with groundwater very effectively. Concentrations of inflowing nitrates with groundwater dropped to 2.3–24.4 percent of the input from fields. In contrast to nitrate ions the ammonium behave entirely different. Often concentration of ammonium increased in groundwater under shelterbelts. Higher concentrations of N-NH₄⁺ under shelterbelts than under field indicated that ammonium ions were released during decomposition of organic matter. This supposition was directly proved by estimates of very high rates of urease activity which enzyme converts urea nitrogen into NH₃ in the final stages of protein decomposition. It was estimated that N₂O fluxes from soil of shelterbelts are much smaller than from cultivated fields. The balance of nitrogen inputs and outputs in a shelterbelt indicated that the internal recycling of this element is of crucial importance for the controlling efficiency of nitrogen compounds spreading in an environment.     

The influence of control parameters of extraction and concentration over oxidation and degradation of amino acids

The detailed thermal decomposition characteristics of several amino acids in different fase state — dry and moist crystals (Trp, Arg HCl, Lys HCl), water solutions (Trp) are determined. It is found that thermodecomposition of Trp in water solutions is inhibited by Na₂S₂O₃ and oxyethylidendiphosphonic acid. The method of finding optimal control parameters (temperatur of moist crystals, heating surfaces, drying agent) during amino acid drying on the bases of their thermodecomposition kinetics is given. The received results can be used for technolodical optimization of different stages of amino acid extraction and concentration processes.     

Biogas upgrading using single-walled carbon nanotubes by molecular simulation

Abstract

Biogas from anaerobic digestion of biological wastes is a renewable energy resource that mainly contains CH₄, CO₂, trace amounts of H₂S and a fraction of H₂O vapour. In order to transfer biogas into biomethane to meet the standards for use as vehicle fuel or for injection in the natural gas grid, removing H₂S from biogas in advance is necessary. In addition, biogas is usually saturated with water vapour. It is significant to study the effect of the presence of H₂O on the biogas separation performance. Adsorption of H₂S/CO₂/CH₄ and H₂O/CO₂/CH₄ ternary mixtures using single-walled carbon nanotubes (SWCNT) were investigated via the Grand Canonical Monte Carlo (GCMC) method. We studied the effects of carbon nanotube diameter, –COOH modification, temperature and pressure on H₂S adsorption. The results indicate that the presence of hydrophilic –COOH groups does affect the separation of H₂S/CO₂/CH₄ mixtures. Temperature swing adsorption is more suitable than pressure swing adsorption for the separation of H₂S/CO₂/CH₄ mixtures. The effect of water vapour on the separation of CO₂/CH₄ was also investigated. The result shows that the presence of H₂O has little effect on the selectivity of CO₂/CH₄ in pristine CNT, but the selectivity of CO₂/CH₄ with the presence of H₂O is markedly enhanced after modification in –COOH modified SWCNT with specific modification degree. It is expected that this work could provide some useful information for biogas upgrading.