Biochar from the co-pyrolysis of Saccharina japonica and goethite as an adsorbent for basic blue 41 removal from aqueous solution.

The effects of utilizing goethite (5%, 10%, and 20%) in co-pyrolysis with low-lignin macroalgae, Saccharina japonica, on the carbon sequestration potential, magnetic, physicochemical, and dye (basic blue 41, BB41) removal properties of the resulting biochar were investigated. Biochars exhibited more aromaticity, better magnetic properties, and insignificant alterations to their point of zero charges (11.07 ± 0.03 to 10.59 ± 0.01) with goethite increment. Optimum conditions for high organic matter conversion and carbon preservation occurred using 5% goethite. Adsorption experiments showed that BB41 adsorption was highly pH-dependent, equilibrated later (from 12 h to 24 h) after goethite modification, and was best fitted to the pseudo-second-order model (higher R2 and lower SSE values). Langmuir monolayer adsorption capacity for BB41 was the highest amongst carbonaceous adsorbents in the literature [1494 mg/g (pristine); 1216 mg/g (5% goethite)]; initial BB41 concentration of 2000 mg/L at 30 °C and pH 8. The main governing mechanisms involved ion exchanges, hydrogen bonding, π-π interaction and pore-filling. Overall, low goethite amount (5%), co-pyrolyzed with macroalgae, offers an economically and environmentally effective way to produce magnetic biochar with enhanced carbon sequestration potential and superb cationic dye removal performance for environmental remediation applications.

Enhanced product selectivity in the microbial electrosynthesis of butyrate using a nickel ferrite-coated biocathode.

Microbial electrosynthesis (MES) is a potential sustainable biotechnology for the efficient conversion of carbon dioxide/bicarbonate into useful chemical commodities. To date, acetate has been the main MES product; selective electrosynthesis to produce other multi-carbon molecules, which have a higher commercial value, remains a major challenge. In this study, the conventional carbon felt (CF) was modified with inexpensive nickel ferrite (NiFe2O4@CF) to realize enhanced butyrate production owing to the advantages of improved electrical conductivity, charge transfer efficiency, and microbial-electrode interactions with the selective microbial enrichment. Experimental results show that the modified electrode yielded 1.2 times the butyrate production and 2.7 times the cathodic current production of the CF cathode; product selectivity was greatly improved (from 37% to 95%) in comparison with CF. Microbial community analyses suggest that selective microbial enrichment was promoted as Proteobacteria and Thermotogae (butyrate-producing phyla) were dominant in the NiFe2O4@CF biofilm (~78%). These results demonstrate that electrode modification with NiFe2O4 can help realize greater selective carboxylate production with improved MES performance. Hence, this technology is expected to be greatly useful in future reactor designs for scaled-up technologies.

Theoretical Modeling of the Impact of Salt Precipitation on CO2 Storage Potential in Fractured Saline Reservoirs.

Deep saline reservoirs have the capacity to hold large volumes of CO2. However, apart from the high brine salinity, which poses an injectivity challenge, a high percentage of saline reservoirs are also fractured. The mechanisms of drying and salt precipitation and the resulting impact on CO2 injection are unique in fractured reservoirs. Analytical models were developed to investigate the impact of salt precipitation on CO2 injectivity and storage capacity. Two types of fractured saline reservoirs were considered: type I fractured reservoirs, where storage capacity and injectivity are contributed by only fractures, and type II fractured reservoirs, where both fractures and the adjacent rock matrix blocks contribute to CO2 storage and injectivity. We found that, depending on the initial brine salinity, salt precipitation could severely impair CO2 injectivity and reduce storage capacity. Salt precipitation had a fourfold impact on CO2 injectivity compared to storage capacity. Type I reservoirs with high irreducible brine saturation were less susceptible to salt clogging in the fractures. The results also suggest that fractures with rectangular aperture were less likely to be plugged by salt compared to elliptical fractures. Contrary to previous reports, some fractured deep saline reservoirs may not be suitable for CO2 storage. Generally, type II fractured reservoirs were found to be more suitable for CO2 storage in terms of susceptibility to salt clogging. The findings provide valuable understanding of the mechanisms and effect of drying and salt precipitation on CO2 storage potential, making a strong case for CO2 storage in naturally fractured deep saline reservoirs.

Innovative spherical biochar for pharmaceutical removal from water: Insight into adsorption mechanism.

In this study, we developed an innovative spherical biochar with high porosity and excellent paracetamol (PRC) adsorption capacity. The optimal pyrolysis temperatures for the preparation of spherical biochar (derived from pure glucose) and non-spherical biochar (from pomelo peel wastes) were obtained at 900 °C and 700 °C, respectively. Various advanced techniques were applied to characterize the prepared biochars. Spherical and non-spherical biochars exhibited large specific surface area (1292 and 1033 m2/g) and high total pore volume (0.704 and 1.074 cm3/g), respectively. The adsorption behavior of PRC onto two biochars was conducted utilizing batch experiments. Results demonstrated that the adsorption process was slightly affected by the change of solution pH (2-11) and addition of NaCl (0.05-1.0 M) and was able to achieve fast equilibrium (∼120 min). The maximum adsorption capacity of spherical biochar (286 mg/g) for PRC was approximately double that of non-spherical biochar (147 mg/g). The signal of thermodynamic parameters was negative ΔG° and ΔH° values, but positive ΔS° value. The adsorption mechanism consisted of pore-filling, hydrogen bonding formations, n-π and π-π interactions, and van der Waals force. The adsorption capacities of two biochars were insignificantly dependent on different real water samples containing PRC. Consequently, the biochars can serve as a green and promising material for efficiently removing PRC from water.

Facile magnetic biochar production route with new goethite nanoparticle precursor.

This study developed a green and novel magnetic biochar via the co-pyrolysis of firwood biomass pre-treated with 10% (w/w) of either solid-phase (admixing; G10BCA) or liquid-phase (impregnation; G10BCI) goethite mineral (α-FeOOH). Newly fabricated magnetic biochars were characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES), Brunauer-Emmett-Teller (BET) equipment, X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), proximate and elemental analyzer, and vibrating sample magnetometry. The effects of magnetic precursor, iron loading, and aqua-treatments on recoverability, magnetic property, and stability (resistance to α-FeOOH reconstructive crystallization/dissolution reactions) were explored and compared to those of magnetic biochar derived from conventional ferric chloride precursor (F10BCI). Results confirmed a direct correlation between biochar yields and ash contents with iron loading, irrespective of the used types of magnetic precursors (α-FeOOH or FeCl3). Although FeCl3 can generate magnetic biochar (F10BCI) with higher total carbon content (83.6%) and surface area (299 m2/g), α-FeOOH proved to be more effective at yielding magnetic biochars with nanostructured surfaces, lower water extractable components (thus green; G10BCA = 0.21 mg/mL and G10BCI = 0.16 mg/mL), higher magnetic saturation (G10BCA = 10.0 emu/g and G10BCI = 20.8 emu/g), higher ferromagnetic susceptibility, and excellent recoverability. α-FeOOH was undetected on the surface of G10BCA, post-aqua-treatments (over 30 days), and this demonstrated its stability in the face of demagnetization via α-FeOOH reformation reactions. Consequently, this study demonstrated that the admixing solid-phase α-FeOOH (10%) with firwood biomass offered a green, facile, and efficient way to thermochemically produce magnetic biochar. The produced biochar exhibited a superb stability to α-FeOOH reconstructive crystallization/dissolution reactions in aquatic (aqua) media, green attributes, good magnetic properties, and great potential applications in many areas of the economy.

Enzyme immobilization on porous chitosan hydrogel capsules formed by anionic surfactant gelation.

OBJECTIVES: Sodium dodecyl sulfate (SDS)-chitosan hydrogels have been employed for adsorption of anionic dyes and metallic substances. Two mutant forms of Thermoanaerobacter ethanolicus alcohol dehydrogenase (TeSADH) were used as model enzymes to develop a novel enzyme immobilization technique employing newly formulated porous chitosan hydrogels. RESULTS: The enzyme immobilized on chitosan hydrogel capsules formed by 5 g/l SDS gelation and subsequent treatment with 0.05 M NaOH was 28-35% higher in NADPH production than that formed by 20 g/l SDS gelation only under the same conditions. A 48-h asymmetric biphasic reduction of acetophenone with immobilized TeSADH enzyme at 50 °C showed 68% increase in (R)-1-phenylethanol production than the free enzyme. Compared to the free enzyme which denatured and lost its activity at 80 °C, the immobilized enzyme retained about 25% of its initial activity after 2-h incubation. CONCLUSION: In contrast to the conventional chitosan hydrogel which suffers thermal and operational stability, the newly formulated porous chitosan hydrogel capsules have excellent enzyme loading efficiency and stable at harsh temperatures. Especially, this newly developed enzyme immobilization method would be applicable for food processing.

Magnetic Ti3C2Tx (Mxene) for diclofenac degradation via the ultraviolet/chlorine advanced oxidation process.

In this study, a magnetic titanium carbide (Ti3C2Tx) MXene was synthesized through a one-step chemical co-precipitation method using ammonium bifluoride as a mild etchant and was investigated for photocatalytic degradation of diclofenac (DCF) via the ultraviolet (UV)/chlorine process. The DCF degradation was enhanced by the generation of active radicals such as the hydroxyl radical and reactive chlorine species compared with that resulting from UV and chlorination treatment alone as well as UV/H2O2 processes at pH 7. The first-order rate constant of the UV/chlorine process was 0.1025 min-1, which is 12.7 and 6.8 times higher than those of the only UV and UV/H2O2 processes, respectively. Magnetic nanoparticles on the surfaces of Ti3C2Tx sheets not only enhanced the adsorption capacity of the synthesized composite but also increased the rate of electron transfer in solution. In addition, the effects of different operating conditions such as magnetic Ti3C2Tx dose, pH, and initial chlorine concentration on DCF degradation were investigated. Magnetic Ti3C2Tx showed high stability and photodegradation efficiency during seven consecutive degradation reaction cycles. The derivatives of DCF during the photocatalytic degradation process were also investigated based on the observed intermediate products and a degradation pathway was proposed. Thus the synthesized magnetic Ti3C2Tx is a simple and affordable photocatalyst, which can significantly enhance DCF degradation in the UV/chlorine advanced oxidation process.

Multi-membrane formation in chitosan hydrogel shell by the addition of goethite nanoparticles.

In this study, chitosan (an abundant natural biopolymer) was used as a polysaccharide source to synthesize multi-membrane hydrogel capsules (MHC) using a novel approach. The MHC material was formed in a single step self-assembly approach by an in-situ immobilization of goethite nanoparticles (GNP) during the chitosan-anionic surfactant complex formation reaction. The pivotal role of GNP in the formation of multi-membrane was thoroughly discussed herein. Some important factors effecting the formation and property of MHC were explored. The results of adsorption study (Co ≈ 1000 mg/L, 30 °C, and pH ≈ 7.0) demonstrated that MHC (1321 ±â€¯35.6 mg/g) exhibited excellent adsorptive capacity for Congo red dye compared to HC (244 ±â€¯35.6 mg/g) and GNP (91.1 ±â€¯19.6 mg/g). Therefore, the unique characteristics of multi-membranes structures breeds an exciting prospect of application in diverse fields, especially wastewater treatment because of its excellent adsorption capacity for dye contaminants.

Preparation and characterization of alginate-kelp biochar composite hydrogel bead for dye removal.

The alginate-kelp biochar composite hydrogel bead (Alg-KBC) was successfully developed via physical crosslinking with Ca2+. The composite material was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma optical emission spectrometry (ICP-OES), and elemental analyzer. The Alg-KBC showed high removal capacity for crystal violet (CV), from aqueous solution (33.8% more than that of the pristine alginate bead). The adsorption isotherm data were fitted to the nonlinear forms of the Langmuir, Freundlich, and Redlich-Peterson isotherm models. Also, the adsorption kinetics data were analyzed with the nonlinear forms of the pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. Both chemisorption and physisorption with an indispensable role of external mass transfer and stagewise pore diffusion were essential in the adsorption process. Thus, by impregnating biochar powder in alginate, a bio-platform, a composite hydrogel bead which has higher affinity for cationic dye in aqueous medium and also eliminates the onerous task of separating biochar powder from the adsorbate solution, was obtained. Hence, the Alg-KBC can be considered for efficient dye removal in the wastewater treatment process.

Characterization and adsorption performance evaluation of waste char by-product from industrial gasification of solid refuse fuel from municipal solid waste.

This study investigated the effect of steam and air flowrate combinations on the syngas efflux, physicochemical properties and adsorption performances (on congo red, CR and crystal violet, CV removal) of waste char by-product from the industrial gasification of solid refuse fuel from municipal solid waste. The BET surface area (11.4 m2/g), porosity (74.7%), fixed carbon content (25.8 wt%) and hydrophilicity (0.09) were enhanced with lower steam rate and higher air supply rate combination (MSWC-L) than for the higher steam rate and lower air supply rate combination (MSWC-H). Adsorption performances were higher for MSWC-L than MSWC-H on both CR (35.7-49.7 mg/g) and CV (235 to 356 mg/g) removal, suggesting that, higher air supply rate (214 Nm3/h; at 0.36 equivalence ratio) with lower steam rate (37 kg/h) were more effective gasification process conditions. Results showed that, syngas efflux was more sensitive to air supply rate than steam supply rate. Reactions in the combustion zone were not only limited to the pyrolysis gas vapours but to the char also. In conclusion, the waste chars from municipal solid waste gasification showed good potential as adsorbents in wastewater treatment.

Adsorption mechanism of hexavalent chromium onto layered double hydroxides-based adsorbents: A systematic in-depth review.

An attempt has been made in this review to provide some insights into the possible adsorption mechanisms of hexavalent chromium onto layered double hydroxides-based adsorbents by critically examining the past and present literature. Layered double hydroxides (LDH) nanomaterials are typical dual-electronic adsorbents because they exhibit positively charged external surfaces and abundant interlayer anions. A high positive zeta potential value indicates that LDH has a high affinity to Cr(VI) anions in solution through electrostatic attraction. The host interlayer anions (i.e., Cl-, NO3-, SO42-, and CO32-) provide a high anion exchange capacity (53-520 meq/100 g) which is expected to have an excellent exchangeable capacity to Cr(VI) oxyanions in water. Regarding the adsorption-coupled reduction mechanism, when Cr(VI) anions make contact with the electron-donor groups in the LDH, they are partly reduced to Cr(III) cations. The reduced Cr(III) cations are then adsorbed by LDH via numerous interactions, such as isomorphic substitution and complexation. Nonetheless, the adsorption-coupled reduction mechanism is greatly dependent on: (1) the nature of divalent and trivalent salts utilized in LDH preparation, and the types of interlayer anions (i.e., guest intercalated organic anions), and (3) the adsorption experiment conditions. The low Brunauer-Emmett-Teller specific surface area of LDH (1.80-179 m2/g) suggests that pore filling played an insignificant role in Cr(VI) adsorption. The Langmuir maximum adsorption capacity of LDH (Qomax) toward Cr(VI) was significantly affected by the natures of used inorganic salts and synthetic methods of LDH. The Qomax values range from 16.3 mg/g to 726 mg/g. Almost all adsorption processes of Cr(VI) by LDH-based adsorbent occur spontaneously (ΔG° <0) and endothermically (ΔH° >0) and increase the randomness (ΔS° >0) in the system. Thus, LDH has much potential as a promising material that can effectively remove anion pollutants, especially Cr(VI) anions in industrial wastewater.

Decolorization of cationic and anionic dye-laden wastewater by steam-activated biochar produced at an industrial-scale from spent mushroom substrate.

The feasibility of producing biochar and its steam-activated counterpart in a large scale (1000 kg) from spent mushroom substrate (SMS) and their usage as effective environmental remediation tools to augment current SMS management strategies were explored. Steam-activated SMS biochar exhibited enhanced surface area (332 m2/g), pore volume (0.29 cm3/g), and porosity (77.1%). The effectiveness of activation was higher on the cationic dye, crystal violet (CV) by 4.1 times increase from 255 mg/g to 1057 mg/g. The biochar and its steam-activated counterpart, respectively exhibited high COD and color removal efficiencies of 49.6% and 40.1%, and 67.7 and 99.6% for CV-spiked real wastewater. Reusability studies confirmed the dominant role of chemisorption in the adsorption process. The lower production cost coupled with the superior physicochemical properties and adsorption performances rendered the biochar with/without steam activation, as a promising alternative adsorbent to serve as a green, viable and effective environmental remediation tool.

Effect of water washing pretreatment on property and adsorption capacity of macroalgae-derived biochar.

The effects of water washing pretreatment process on the property and adsorption capacity of biochar were investigated at different biochar/water ratios from 1:5 to 1:100 (w/v). Saccharina japonica macroalgae-derived biochars (B300, B450, and B600) were prepared at 300 °C, 450 °C, and 600 °C, respectively. The optimal biochar/water ratio was obtained at 1:10. The results indicated that the washing pretreatment can contribute to dramatically increasing the specific surface area of biochars, but slightly increasing their porosity. The washed biochars were carbonaceous microporous materials (67-80% micropore volume), with their specific surface area and porosity being B600 (543 m2/g and 86%), B450 (521 m2/g and 75%), and B300 (188 m2/g and 80%), respectively. The unwashed biochars exhibited a significantly higher ash content (59%-65%) than washed biochars (26%-35%). Equilibrium adsorption study demonstrated that the Langmuir maximum adsorption capacity (Qomax) of crystal violet cationic dye decreased in the following order: unwashed-B450 (1719 mg/g) > washed-B450 (1277 mg/g) > commercial activated carbon (492 mg/g). The washing pretreatment can remove solute-inorganic minerals to prevent their release from biochar during the dye adsorption. The washed biochar with its excellent adsorption capacity can serve as a highly sustainable and industrially viable adsorbent for the removal of cationic dyes from waste bodies.

Rice straw-based biochar beads for the removal of radioactive strontium from aqueous solution.

Biochars from agricultural residues have recently attracted significant attention as adsorbents for purifying contaminated water and wastewater. In this study, the removal of strontium from aqueous solutions was investigated using rice straw-based biochar (RSBC) beads in both batch and continuous fixed-bed column systems. The RSBC beads had negatively charged surfaces and exhibited a large surface area (71.53m2/g) with high micro-porosity. The synthesized beads showed a maximum adsorption capacity of 175.95mg/g at an initial strontium concentration of 10g/L at 35°C and pH7. Furthermore, they showed a good selectivity toward strontium ions in the presence of competing ions such as Al3+, Mg2+, and K+. The effects of different operating conditions like flow rate and initial strontium concentration were investigated in the fixed-bed column reactor. The Thomas, Adams-Bohart, and Yoon-Nelson models were applied to the experimental data to predict the breakthrough curves using non-linear regression. Both the Thomas and the Yoon-Nelson models were appropriate for describing entire breakthrough curves under different operating conditions. Overall, RSBC beads demonstrate great potential as efficient adsorbents for the treatment of wastewater polluted with strontium in a continuous operation mode.

Synergistic dye adsorption by biochar from co-pyrolysis of spent mushroom substrate and Saccharina japonica.

The potential of activating terrestrial biomass (spent mushroom substrate, SMS) with ash-laden marine biomass [kelp seaweed, KE] via co-pyrolysis in the field of adsorption was first investigated. KE biochar (KBC), SMS biochar (SMSBC), biochar (SK10BC) from 10%-KE added SMS, and biochar (ESBC) from KE-extract added SMS were used for the adsorption of cationic dye crystal violet (CV). ESBC had highest fixed carbon content (70.60%) and biochar yield (31.6%). SK10BC exhibited high ash content, abundant functional groups, coarser surface morphology and Langmuir maximum adsorptive capacity (610.1mg/g), which is 2.2 times higher than that of SMSBC (282.9mg/g). Biochar activated by a small amount of high ash-containing biomass such as seaweed via co-pyrolysis can serve as viable alternative adsorbent for cationic dye removal.

Sequential treatment of PTA wastewater in a two-stage UASB process: focusing on p-toluate degradation and microbial distribution.

Two-stage upflow anaerobic sludge blanket (UASB) process was investigated as an efficient process configuration option for the treatment of purified terephthalic acid (PTA) wastewater. To study its feasibility in a defined condition, synthetic wastewater containing only the major pollutants (i.e., acetate, benzoate, terephthalate and p-toluate) was used. By focusing the role of the second stage on the p-toluate degradation, improved overall COD and p-toluate removal capacities of 4.18 and 1.35 g-thCOD/L·day could be achieved together with a complete COD removal efficiency. In this situation, all the pollutants except p-toluate were completely degraded in the first stage while 38 and 62% of p-toluate originally present in the wastewater were consecutively degraded in the individual stages. The concomitant methane production rate in each stage was 0.91 and 0.35 L/L·day respectively, and the methane yield on p-toluate was determined to be 0.12 L/g-thCOD. Batch tests using the granules obtained from each stage revealed that the acidogenic microorganisms enriched in both stages had a universal ability to degrade all aromatic pollutants present in the PTA wastewater. Moreover, image analysis using scanning electron microscope and confocal laser scanning microscopy combined with fluorescence in situ hybridization technique elucidated that the distribution of acidogens and methanogens within the granule was varied in each stage, which influenced the mass transfer regime resulting in the different pollutant degradation rates during the batch tests.

Surface solubilization of phenanthrene by surfactant sorbed on soils with different organic matter contents.

The effect of sorbed surfactant on the distribution of hydrophobic organic compounds (HOCs) during soil washing was investigated using a mathematical model. Phenanthrene (PHE) as an HOC and Triton X-100 (TX100) as a nonionic surfactant were used with two soils with low (SS) and high (BS) organic matter contents. The available carbon fraction (f(A,soil)(*)) after surfactant sorption was determined from surfactant coverage by measuring soil surface area using a methylene blue method. The sorbed surfactant was greatly effective as a sorbent for PHE, with an effectiveness factor (epsilon(soil)) in the range of 10.9-117.2 for SS and 39.7-121.3 for BS. Surface molar solubilization ratio (MSR(s)) and epsilon(soil) decreased with increasing TX100 dose. The MSR(s) decrement was lower for BS than for SS probably due to stronger affinity of PHE on organic matter in BS than in SS, which cause lower efficiency of soil washing than estimated by intrinsic sorption of PHE. These results suggest that soil washing in the field using surfactant for soils with high organic matter contents may give much lower efficiency than expected due to additional adsorption of HOC onto sorbed surfactant.

Synergic degradation of phenanthrene by consortia of newly isolated bacterial strains.

Three different bacteria capable of degrading phenanthrene were isolated from sludge of a pulp wastewater treatment plant and identified as Acinetobacter baumannii, Klebsiella oxytoca, and Stenotrophomonas maltophilia. Phenanthrene degradation efficiencies by different combinations (consortia) of these bacteria were investigated and their population dynamics during phenanthrene degradation were monitored using capillary electrophoresis-based single-strand conformation polymorphism (CE-SSCP). When a single microorganism was used, phenanthrene degradation efficiency was very low (48.0, 11.0, and 9.0% for A. baumannii, K. oxytoca, and S. maltophilia respectively, after 360 h cultivation). All consortia that included S. maltophilia degraded approximately 80.0% of phenanthrene and reduced lag time to 48 h compared to the 168 h of pure A. baumannii culture. CE-SSCP analysis showed that S. maltophilia was the predominant species during phenanthrene degradation in the mixed culture. The results indicate that mixed cultures of microorganisms may effectively degrade target chemicals, even if the microorganisms show low degradation activity in pure culture.

Coagulation of soil suspensions containing nonionic or anionic surfactants using chitosan, polyacrylamide, and polyaluminium chloride.

Effective coagulation and separation of particles in a soil-washed solution is required for a successful soil washing process. The effectiveness of chitosan (CS), a polycationic biodegradable polymer, as a coagulant was compared to polyacrylamide (PAA) and polyaluminium chloride (PAC) for the coagulation of a soil suspension (5 gL(-1)). The effect of surfactants in the coagulation process was investigated using Triton X-100 (TX-100), a nonionic surfactant, and sodium dodecyl sulfate (SDS), an anionic surfactant. CS (5 mgL(-1)) removed 86% and 63% of the suspended soil in the presence of TX-100 (5 gL(-1)) and SDS (5 gL(-1)), respectively, after 30 min at a pH of 6. The results prove that coagulation in the presence of TX-100 is more effective than with SDS. CS was found to be more efficient compared to PAA and PAC under all coagulation conditions. The optimum concentration of CS required for maximum coagulation of soil suspension was 5 mgL(-1). PAA and PAC could not achieve the same degree soil removal as CS even after increasing their concentrations up to 50 mgL(-1). Maximum levels of 50% and 60% soil removal were achieved using PAA (50 mgL(-1)) and PAC (50 mgL(-1)), respectively, after 30 min from a 5 gL(-1) suspension containing TX-100 (5 gL(-1)). The soil coagulation process was found to decrease with an increase in the pH of the suspension, and maximum coagulation was achieved with an acidic pH.

The removal of nitrate from aqueous solutions by chitosan hydrogel beads.

A physico-chemical investigation of the adsorption of nitrate by chitosan hydrobeads was conducted. The adsorption of nitrate by chitosan hydrobeads was increased with a decrease in the pH of the solution. The adsorption process was found to be temperature dependant with an optimum activity at 30 degrees C. Adsorption capacity was found to decrease with increases in temperature after 30 degrees C, indicating the exothermic nature of this process. Theoretical correlation of the experimental equilibrium adsorption data for the nitrate-chitosan hydrobeads system was properly explained by the Langmuir isotherm model. This was supported by the fact that homogeneity index was close to unity (0.98-1.08) from Langmuir-Freundlich isotherm model. The maximum adsorption capacity was 92.1mg/g at 30 degrees C. The kinetic results corresponded well with the pseudo-second-order rate equation. Intra-particle diffusion also played a significant role at the initial stage of the adsorption process. Thermodynamic parameters such as the Gibbs free energy (DeltaG(0)), enthalpy (DeltaH(0)), and entropy (DeltaS(0)) for the nitrate adsorption were estimated. Results suggest that the adsorption process is a spontaneous, exothermic process that has positive entropy. Desorption of nitrate from the loaded beads was accomplished by increasing the pH of the solution to the alkaline range, and a desorption ratio of 87% was achieved around pH 12.0.