A combined treatment system of O3/UV oxidation and activated carbon adsorption: emerging contaminants in hospital wastewater.

Researchers have recently focused their attention on emerging contaminants (ECs) in wastewater because they pose serious health and environmental risks. Because ECs are persistent in the environment and have the ability to disrupt the physiology of target receptors, they have been labeled as contaminants of recent environmental concern. For removing various ECs, a variety of treatment technologies have been developed, including biological, chemical, and physical methods. However, no single technology can currently effectively remove ECs, whereas hybrid systems have consistently proven to be more effective. Furthermore, the majority of existing technologies are energy and resource intensive, as well as expensive to maintain and operate. Furthermore, the majority of advanced treatment technologies that have been proposed have yet to be evaluated for large-scale feasibility. Some ECs, particularly pharmaceuticals and pesticides, were found to be significantly removed using a hybrid technique that included ozone/UV and granular activated carbon (GAC). Besides, the removal of effluent parameters (TDS, COD, TOC) was enhanced through the GAC surface oxidization as a catalyst with NaOH before the process and by ozone within the procedure as well.

Comparison of different extracting agents for the recovery of Pb and Zn through electrokinetic remediation of mine tailings.

This study was conducted to investigate the feasibility of Electrokinetic Remediation to remove lead and zinc from real mine tailings, collected from the Lacan's lead and zinc Mineralized Flotation Processing Plant (Markazi province, Iran). High buffering capacity, high organic matter, and heavy metal contamination were the unique characteristics of this mine tailing. Electrokinetic remediation of the mine tailings was carried out in 11 separate experiments under constant voltage gradient of 2 V/cm for 9 days. Various enhancement techniques were tested, such as 1) electrolyte conditioning using chelating agents including ethylenediaminetetraacetic acid, citric acid, acetic acid, and hydrochloric acid; 2) increasing the concentration of the catholyte solution, and 3) adding chelating agents to the soil as a pre-treatment of the tailings and the electrolyte condoning simultaneously. The concentration of each electrolyte solution was selected based on the different extraction tests that resulted in the optimal or highest extraction percentage of lead and zinc. Electrolyte conditioning, in the case of using citric acid 1 M enhanced the removal of Pb and Zn dramatically. Catholyte conditioning, using citric acid 1 M, was the most effective enhancement technique for removing Zn (38.34%); also, the best removal efficiency of Pb (51.31%) was achieved using the same electrolyte solution in both electrode chambers. Increasing the acetic acid concentration was favorable for removal of both heavy metals. Compared to catholyte conditioning, pre-treatment coupled with catholyte conditioning could not improve the removal efficiency considerably.

Effect of biogenic jarosite on the bio-immobilization of toxic elements from sulfide tailings.

The discharge of toxic elements from tailings soils in the aquatic environments occurs chiefly in the presence of indigenous bacteria. The biotic components may interact in the opposite direction, leading to the formation of a passivation layer, which can inhibit the solubility of the elements. In this work, the influence of jarosite on the bio-immobilization of toxic elements was studied by native bacteria. In batch experiments, the bio-immobilization of heavy metals by an inhibitory layer was examined in the different aquatic media using pure cultures of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. A variety of analyses also investigated the mechanisms of metals bio-immobilization. Among different tests, the highest metal solubility yielded 99% Mn, 91% Cr, 95% Fe, and 78% Cu using A. ferrooxidans in 9KFe medium after ten days. After 22 days, these percentages decreased down to 30% Mn and about 20% Cr, Fe, and Cu, likely due to metal immobilization by biogenic jarosite. The formation of jarosite was confirmed by an electron probe micro-analyzer (EPMA), X-ray diffraction (XRD), and scanning electron microscope (SEM). The mechanisms of metal bio-immobilization by biogenic jarosite from tailings soil confirmed three main steps: 1) the dissolution of metal sulfides in the presence of Acidithiobacillus bacteria; 2) the nucleation of jarosite on the surface of sulfide minerals; 3) the co-precipitation of dissolved elements with jarosite during the bio-immobilization process, demonstrated by a structural study for jarosite. Covering the surface of soils by the jarosite provided a stable compound in the acidic environment of mine-waste.

Application of enhanced electrokinetic approach to remediate Cr-contaminated soil: Effect of chelating agents and permeable reactive barrier.

Enhanced electrokinetic (EK) technique was employed to remediate Cr-contaminated soil using a permeable reactive barrier (PRB) and chelating agents. Synthesized nanomagnetic Fe3O4 was used as a reactive material in PRB. Moreover, EDTA and citric acid (CA) were used as chelating agents. Sequential extraction method (SEM) was employed to determine Cr-elimination mechanism during the EK process. The results revealed that EDTA (78% Cr removal) was more effective than CA (54% Cr removal) in eliminating Cr from the contaminated soil during the EK process. The application of PRB in combination with EDTA was able to reduce the Cr removal rate to 70 and 66% by locating PRB in the middle section and near the anode/cathode reservoir, respectively. The use of PRB coupled with EDTA near the anode and cathode led to a more uniform Cr removal from the soil during the EK process. The highest energy consumption was 0.12 KWh during the EK remediation using PRB. Traditional EK remediation could only remove exchangeable and carbonate fractions of Cr. The use of chelating agents led to a significant (more than 90%) increase in Cr removal from the following fractions: exchangeable phase, carbonate phase, and bond to Fe-Mn oxides. In addition to electromigration (EM) mechanism, electroosmotic flow (EOF) played an important role in Cr removal during the EK process, especially when coupled with PRB.

Minimization of metal sulphides bioleaching from mine wastes into the aquatic environment.

The continuous presence of toxic elements in the aquatic environments around mine tailings occurs due to bioleaching or chemical extraction promoted by the mining operations. Biogenic passivation treatment of tailings dams can be a new environment-friendly technique to inhibit the solubility of heavy metals. In spite of current bioleaching researches, we tried to minimize the mobility of the trace elements in the laboratory scale through the formation of a passivation layer in the presence of a mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The X-ray diffraction (XRD) and scanning electron microscope (SEM) represented the jarosite generation as an inhibitory layer on the mineral surfaces of the tested materials. More detailed observations on electron probe micro-analyzer (EPMA) showed the co-precipitation of metals with the passivation layer. Thereby, the passivation layer demonstrates potential in elements immobilization which, in turn, can be optimized in the natural systems. Our working hypothesis was to exploit and optimize the formation of the passivation layer to maximize the immobilization of heavy metals (e.g., Cu, Cr). The optimization process of bioleaching experiments using indigenous bacteria caused a reduced solubility for Cu (from around 20% to 4.5%) and Cr (from around 30% to 10.6%) and the formation of 6.5 gr passivation layer. The analyses finally represented the high efficiency of the passivation technique to minimize metals bioleaching in comparison to earlier studies.

Immobilization of hexavalent chromium in contaminated soil using nano-magnetic MnFe2O4.

Nano-magnetic MnFe2O4 was prepared and examined to immobilize Cr(VI) in the soil. According to the results of scanning electron microscopy (SEM) and X-ray diffraction (XRD) the formation of nano-magnetic MnFe2O4 with the particle size of less than 200 nm was demonstrated. Compared with the untreated soil, the leachability of Cr(VI) was reduced from 70.95% to 4.22% through toxicity characteristic leaching procedure (TCLP) at a dosage of 2 g/L of nanoparticles and 192 h remediation time. At the same condition, the physiologically based extraction test (PBET) human bioaccessibility of chromium was reduced from 86.76% to 4.42%. Moreover, the plant bioavailability of hexavalent chromium (using EDTA) was reduced from 83.72% to 5.53%. According to the sequential extraction procedure (SEP) the loosely bounds Cr (90.28%) was converted to the relatively strong bound (Fe-Mn oxides fraction, 92.09%) revealed the significant decrease in risk of release and availability of chromium after immobilization procedure. Further, results of column experiments of Cr(VI) elution revealed that almost all of the water-soluble chromium was converted to the associated synthesized nanoparticles phase. Overall, the present study proved that nano-magnetic MnFe2O4 significantly enhanced the hexavalent chromium immobilization through a decrease in leachability, plant bioavailability, human bioaccessibility, and risk of release.

Optimization of material and energy consumption for removal of Acid Red 14 by simultaneous electrocoagulation and electroflotation.

Decolorization of wastewater of industries which consume dye is an environmental priority. Electrocoagulation and electroflotation methods are appropriate for treatment of these wastewaters. This study investigates the effect of four parameters, electrical conductivity, current density, initial dye concentration, and initial pH, on the performance of a simultaneous electrocoagulation/electroflotation system for removal of Acid Red 14. The optimum values of these parameters were determined based on the amount of electrical energy and aluminum consumption and the best performance of coagulation and bubble generation. The optimum condition was revealed to be electrical conductivity=1,600 µS/cm, current density=60 mA/cm2, initial dye concentration=185 mg/L and initial pH=7. After less than 180 min of electrolysis, 90% dye removal was achieved with a specific energy consumption=102 kWh/kg dyeremoved, anode dissolution=2.09 kg Al/kg dyeremoved and sludge total suspended solids=15,050 mg/L. Liquid chromatography-UV-mass spectroscopy analyses were conducted on samples of raw and treated wastewater. Results showed that intermediate compounds formed from the breaking of the dye molecules. The advantages of this method are a low material and energy consumption. The amount of produced sludge was low; consequently sludge disposal and management costs would be reduced. This method should be used cautiously for treatment of textile wastewater due to the formation of intermediate compounds.

Synthesis of nano- alumina powder from impure kaolin and its application for arsenite removal from aqueous solutions.

Adsorption is considered a cost-effective procedure, safer to handle with high removal efficiency. Activated alumina is the most commonly used adsorbent for the removal of arsenic from aqueous solutions. However, activated alumina has a low adsorption capacity and acts kinetically in a slow manner. An ideal adsorbent should have a high surface area, physical and/or chemical stability and be inexpensive. To meet this requirement, nanomeso porous γ-alumina with a high surface area (201.53 m2/g) and small particle size (22-36 nm) was prepared from inexpensive kaolin as the raw material, by precipitation method. The research results showed that adsorbent has the high adsorption capacity (for initial arsenite concentration up to 10 mg/L, in which 97.65% recovery was achieved). Optimal experimental conditions including pH, initial arsenite concentration and contact time were determined. Langmuir, Freundlich and Dubinin- Radushkevich isotherm models were applied to analyze the experimental data. The best interpretation for the experimental data was given by Langmuir adsorption isotherm equation and the maximum arsenite adsorbed by synthesized nano γ-alumina (qe) was found to be 40 (mg/g).