Organobentonite for Sorption and Degradation of Phenol in the Presence of Heavy Metals

An experimental study was performed to determine the feasibility of usingorganobentonite modified with quarternary ammonium cations (QACs) as a reactive medium in immobilization and biodegradation barriers for mixed contaminants in the subsurface soil. Various factors, including interactions between heavy metals, organic contaminants, and soil microorganisms, were investigated when they coexisted with untreated bentonite and organobentonite. Batch sorption tests for cadmium and lead were conducted to quantify sorption selectivity of these metals on untreated bentonite and organobentonite. Metal concentrations of 50 × 10^-6 M slightly reduced the growth of soil microbes and partially interfered with the biodegradation of phenol. Soil microorganisms tested with untreated bentonite grew after approximately 25 hr of lag period and degraded phenol completely within 350 hr. The results from this study demonstrate that organobentonite could be used as a reactive medium for immobilization and biodegradation of organic contaminants in the presence of heavy metals in the subsurface soil.     

Development of an Environmentally Friendly Adsorbent for the Removal of Toxic Heavy Metals from Aqueous Solution

An effective adsorbent for the removal of heavy metals was manufactured by immobilization of jujube powder. The adsorptions of Cd, Zn and Cu from aqueous solutions by jujube complex beads (Type 1 and Type 2) were studied in a batch adsorption system. The adsorption data were fitted well with the Langmuir isotherm models. The adsorption capacities (β) for Cd, Zn and Cu were 4.23, 2.93 and 3.64 mg/g in Type 1 and 1.24, 0.70 and 1.35 mg/g in Type 2 beads. The removal efficiencies of the Type 2 beads, with a larger unit surface area, were lower than those of the Type 1 due to part of the casein or cyclic AMP being destroyed during the drying process of the Type 1. These values for Type 1 beads were higher than those of all other adsorbents for each heavy metal. A comparison of the kinetic models on the overall adsorption rate showed that the adsorption system was best described by pseudo-first-order kinetics. The removal efficiencies of Cd, Zn and Cu exhibited similar tendencies to those observed in the equilibrium tests. This indicates that the jujube complex beads developed in this study can be used as promising adsorbents for the removal of heavy metals from wastewater.     

Simultaneous Removal of Phosphate and Nitrate in Wastewater Using High-Capacity Anion-Exchange Resin

The removal of nutrients in wastewater is a critical issue in water treatment because released nutrients can cause serious adverse effects in water systems or the aquatic environment. In this study, a high-performing polymeric anion-exchange resin was developed for the removal of nutrients from wastewater. The resins were prepared by chloromethylation followed by amination under preferred conditions. The resins were investigated for the removal of nutrients such as phosphate, nitrate, and fluoride from water. The density of functional groups on the synthesized resin was approximately 33?% higher than on commercialized resins, and the specific surface area of synthesized resin was increased by approximately tenfold compared with commercialized resins. The adsorption capacity of synthesized resins (AMP16-FeCl₃) for anions was 285.8?mg/g, which was approximately three times higher than the capacity of commercialized resin (AMP16-OH). A study of the effects of the types of counterions and functional groups found that resins having hydroxide ion as a counterion showed higher capacity and selectivity for phosphate ion and that dimethylethanolamine as a resin functional group of resin was more efficient than trimethylamine.     

Removal of Phosphate from Aqueous Solution by Functionalized Mesoporous Materials

In the present study, the applications of mesoporous materials based on silica, namely post-synthesized, one-pot synthesized, and pure MCM-41, were investigated for the removal of phosphate from aqueous solution. The mesostructures were confirmed by X-ray diffraction, Brunauer?CEmmett?CTeller, Fourier transform spectroscopy, and transmission electron microscopy. The absorptions of phosphate by the mesoporous adsorbents were examined, with different adsorption models used to describe the equilibrium and kinetic data. The maximum adsorption capacities of the mesostructure adsorbents were found to be 45.162, 40.806, and 31.123 mg g^?C1 for the post-synthesized, one-pot synthesized, and pure MCM-41, respectively. The kinetic data showed that the adsorptions of phosphate onto the post-synthesized and pure MCM-41 followed the pseudo-first-order kinetic model, whereas the one-pot synthesized adsorbent was described by the pseudo-second-order model.     

A Laboratory Column Study on the Biodegradation of Toluene and Methyl tert–Butyl Ether: The Effect of Substrate Interactions

Soil vapor extraction (SVE) is one of the most effective remediation technologies for soil and groundwater contamination. Soil particles can be mobilized by air perturbation during SVE, resulting in the differentiation of porous media, which has not been well addressed. This paper developed a numerical method to study the flow pattern and quantify the change of porous media for the first time. Based on the mass equilibrium and Darcy’s law, a two-phase water–air flow model was constructed with integration of saturation, relative permeability, and capillary pressure during SVE. Relationship between porosity and saturation was deduced and coupled with the two-phase flow model for quantifying change of porous media in real time. Results reveal that both porosity and permeability increase sharply in the early stage of SVE then gradually to a quasi-steady state. These increases in vadose zone tapered off with distance from the SVE screen and the steady period occurred later as well. The influence radius of a single SVE well and the change degree in porosity and permeability of media were proportional to the extraction vacuum and the driving coefficient C, which is more sensitive than extraction vacuum according to the simulation results. Knowledge from this modeling exercise provides a useful tool to estimate the change of remediated zone and assess the environmental risk of remedial activities at real-world contamination sites.     

Eisenia fetida growth inhibition by amended activated carbon causes less bioaccumulation of heavy metals

Purpose

Activated carbons (ACs) were applied to evaluate the effects of surface oxidation on bioavailability and bioaccumulation of cadmium (Cd) and copper (Cu) in freshwater sediment along with Eisenia fetida biomass change.

Materials and methods

A modified sequential extraction procedure was conducted to measure the changes in bioavailable fractions of heavy metals 6 weeks after the addition of nitric acid-oxidized AC. Bioaccumulation of heavy metals in E. fetida was analyzed after 2 weeks of exposure to AC-amended contaminated sediments. Changes in biomass of earthworms caused by AC amendments were observed over 2 weeks of exposure to clean sand.

Results and discussion

Surface oxidation of AC caused little impact on AC surface properties except for oxygen contents leading to enhanced sorption capacity for heavy metals. Bioavailable fractions of the heavy metals increased after 6 weeks, and less was bioavailable with various ACs than without AC. The earthworms were exposed to the sediments mixed with ACs for 6 weeks. After 2 weeks of exposure, bioaccumulation of Cd and Cu decreased drastically. More than 76 % of Cd and 80 % of Cu reductions were observed with each type and dose of AC. Weight loss of E. fetida incubated in clean sand for 13 days after AC amendments was observed, but was not affected by surface oxidation.

Conclusions

Inhibited growth of E. fetida due to AC could be responsible for the reduced bioaccumulation of Cd and Cu in the earthworms as AC inhibited the movement of earthworms, leading to less bioturbation and decreased consumption of nutrients.     

Photocatalytic Degradation of Chlorophenol Compounds using Poly Aromatic Star Copolymer

This study investigated the encapsulation and photocatalysis of chlorophenol compounds in water using porphyrin-(polystyrene-b-2-dimethylaminoethyl acrylate) star polymer. The chloride ions generated during photocatalytic process were identified and quantified. 2,4,6-Trichlorophenol, pentachlorophenol, and 2,4-dichlorophenol were satisfactorily decomposed in the photoreactor using porphyrin-(polystyrene-b-2-dimethylaminoethyl acrylate) star polymer, with removal efficiencies of 2,454, 498, and 760 mg/g of porphyrin-(polystyrene-b-2-dimethylaminoethyl acrylate) star polymer. The half-life times reached around 30 min, with the exception of that for 2,4-dichlorophenol. The star polymer-impregnated porphyrin is a promising photocatalyst for the removal of chlorophenols.     

Removal of Benzene Using the Characteristics of Block Copolymers for Encapsulation

This study assessed the aqueous benzene removal capacity of a polymeric adsorbent, based on an amphiphilic material, in a batch experiment. Two types of polystyrene-block-poly(N-isopropylacrylamide) have structures containing a hydrophobic core and hydrophilic shell. The encapsulation mechanism of benzene by a polymeric adsorbent was investigated, and found to be attributable to the Van der Waals interactions between the benzene aromatic ring and the hydrophobic core of the adsorbent. The equilibrium data were analyzed using the Langmuir and Freundlich adsorption isotherms, and found to be a good fit to both. The maximum adsorption capacity for benzene by the polymeric adsorbent was found to be 194.53 mg/g. The kinetic data followed a pseudo-first-order kinetic model. Polystyrene-block-poly(N-isopropylacrylamide) showed the potential to be an effective adsorbent for application to wastewater treatment.     

Comparison of Surface-Modified Adsorbents for Phosphate Removal in Water

Three novel composite adsorbents, sulfate-coated zeolite (SCZ), hydrotalcite (SCH), and activated alumina (SCAA), were characterized and employed for the removal of phosphate from aqueous solution using equilibrium and kinetic batch experiments. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction spectrum were used to study the surface characteristics of the coated layer. Equilibrium tests showed that the adsorption of phosphate followed both Langmuir and Freundlich isotherms. The powder-type SCZ was better for phosphate removal (maximum binding energy, ???=?111.49?mg?g^?1) compared to hydrotalcite and activated alumina. The adsorption of phosphate was considered to take place mainly by ion exchange. The kinetic data followed a pseudo-second-order kinetic model. The initial adsorption of phosphate onto the sulfate-coated adsorbents was fast, indicating that the sulfate-coated materials developed in this study can be used as promising adsorbents for the removal of phosphate from wastewater or sewage.     

Degradation of Organic Compounds in Actual Wastewater by Electro-Fenton Process and Evaluation of Energy Consumption

We investigated the Fe-regeneration-based cathodic electro-Fenton process using commercial electrodes, to achieve reducing the initial Fe dose and consequent sludge accumulation. The obtained results provided insights into the cathodic electro-Fenton process using two-electrode electrochemical system. The grade 2 Ti mesh electrode could effectively regenerate Fe(II) at 1.2 V, whose potential was lower than those of the two other electrode systems reported in the literatures. In the actual wastewater treatment, compared with general-Fenton process, the reduction in the initial Fe injection was 33% and the sludge reduction was 38%. Furthermore, the removal efficiency using electro-Fenton was at least 5% higher than that of the general-Fenton process at the same initial dose. The low cell voltage (1.2 V) led to lower energy consumption (3.5 J mg^?1) relative to those of other electro-Fenton systems, i.e., anodic electro-Fenton and peroxide generation. With its competitive degradation performances, low energy consumption, and reduced initial Fe injection, the present cathodic electro-Fenton process was shown to be a promising route of waste treatment.