Improvement strategy of citrate and biochar assisted nano-palladium/iron composite for effective dechlorination of 2,4-dichlorophenol.

Rapid passivation and aggregation of nanoscale zero-valent iron (nZVI) seriously limit its performance in the remediation of different contaminants from wastewater. To overcome such issues, in the present study, nano-palladium/iron (nPd/Fe) was simultaneously improved by biochar (BC) prepared from discarded peanut shells and green complexing agent sodium citrate (SC). For this purpose, a composite (SC-nPd/Fe@BC) was successfully synthesized to remove 2,4-dichlorophenol (2,4-DCP) from wastewater. In the SC-nPd/Fe@BC, BC acts as a carrier with dispersed nPd/Fe particles to effectively prevent its agglomeration, and increased the specific surface area of the composite, thereby improving the reactivity and stability of nPd/Fe. Characterization results demonstrated that the SC-nPd/Fe@BC composites were well dispersed, and the agglomeration was weakened. The formation of the passivation layer on the surface of the particles was inhibited, and the mechanism of SC and BC improving the reactivity of nPd/Fe was clarified. Different factors were found to influence the reductive dichlorination of 2,4-DCP, including Pd loading, Fe:C, SC addition, temperature, initial pH, and initial pollutant concentration. The dechlorination results revealed that the synergistic effect of the BC and SC made the removal efficiency and dechlorination rate of 2,4-DCP by SC-nPd/Fe@BC reached to 96.0 and 95.6%, respectively, which was better than that of nPd/Fe (removal: 46.2%, dechlorination: 45.3%). Kinetic studies explained that the dechlorination reaction of 2,4-DCP and the data were better represented by the pseudo-first-order kinetic model. The reaction rate constants followed the order of SC-nPd/Fe@BC (0.0264 min-1) > nPd/Fe@BC (0.0089 min-1) > SC-nPd/Fe (0.0081 min-1) > nPd/Fe (0.0043 min-1). Thus, SC-nPd/Fe@BC was capable of efficiently reducing 2,4-DCP and the dechlorination efficiency of BC and SC synergistically assisted composite on 2,4-DCP was much better than that of SC-nPd/Fe, nPd/Fe@BC and nPd/Fe. Findings suggested that SC-nPd/Fe@BC can be promising for efficient treatment of chlorinated pollutants.

Efficacy and mechanism of enhanced Sb(V) removal from textile wastewater using ferric flocs in aerobic biological treatment.

Antimony contamination from textile industries has been a global environmental concern and the existing treatment technologies could not reduce Sb(V) to meet the discharge standards. To overcome this shortcoming, ferric flocs were introduced to expedite the biological process for enhanced Sb(V) removal in wastewater treatment plant (WWTP). For this purpose, a series of laboratorial-scale sequential batch reactor activated sludge processes (SBRs) were applied for Sb(V) removal with varied reactor conditions and the transformation of Fe and Sb in SBR system was investigated. Results showed a significant improvement in Sb(V) removal and the 20 mg L-1 d-1 iron ions dosage and iron loss rate was found to be only 15.2%. The influent Sb(V) concentration ranging 153-612 µg L-1 was reduced to below 50 µg L-1, and the maximum Sb(V) removal rate of the enhanced system reached about 94.3%. Furthermore, it exhibited high stability of Sb(V) removal in the face of antimonate load, Fe strike and matrix change of wastewater. Sludge total Sb determination and capacity calculation revealed decreasing in Sb adsorption capacity and desorption without fresh Fe dosage. While sludge morphology analysis demonstrated the aging and crystallization of iron hydroxides. These results verify the distinct effects of fresh iron addition and iron aging on Sb(V) removal. High-throughput gene pyrosequencing results showed that the iron addition changed microbial mechanisms and effect Fe oxidized bacterial quantity, indicating Sb(V) immobilization achieved by microbial synergistic iron oxidation. The present study successfully established a simple and efficient method for Sb(V) removal during biological treatment, and the modification of biological process by iron supplement could provide insights for real textile wastewater treatment.

Occurrence of selected antibiotics in urban rivers in northwest Pakistan and assessment of ecotoxicological and antimicrobial resistance risks.

Antibiotics in aquatic systems of developing countries are a growing concern, particularly with the potential ecological risks and emergence of antimicrobial resistance. In Pakistan, antibiotics are widely consumed and released untreated into rivers, however, there is little information on their occurrence and potential risks. In this study, the concentrations and risk assessment of three commonly consumed antibiotics, ciprofloxacin (CIP), amoxicillin (AMX), and cefixime (CFM) belonging to different classes of fluoroquinolone, penicillin, and cephalosporin respectively were investigated in the Kabul River and its two tributaries, Bara River and Shah Alam River in the northwest region of the country. Composite samples were collected in different sampling campaigns and analyzed using the LC-ESI-MS/MS technique. All three antibiotics were found in higher concentrations ranging from 410 to 1810 ng/L, 180-850 ng/L, and 120-600 ng/L for CIP, AMX, and CFM respectively. The Friedman and Wilcoxon signed-ranked tests revealed insignificant differences in average concentrations of each antibiotic in the three rivers and the Pearson Correlation showed a significant positive correlation of CIP with both AMX and CFM indicating their similar pollution sources. Ecotoxicological risk assessment showed a higher risk to algae and bacteria (P. putida) in the rivers with CIP posing a greater risk. The potential risk of antimicrobial resistance development (ARD) was higher in all the three rivers, particularly in Kabul River where maximum risk quotients (RQARD) of 28.3, 9.4 and 3.4 were noted for CIP, CFM and AMX respectively. The human health (HH) risk was insignificant, though the RQHH was higher for the lower age groups (0-3 months). In addition, the combined flux of the antibiotics in the Kabul River was estimated as 59 tons/year with CIP having a significant flux relative to the other antibiotics.

Comparative Sb(V) removal efficacy of different iron oxides from textile wastewater: effects of co-existing anions and dye compounds.

Elevated Sb(V) concentration in textile wastewater is a growing environmental concern worldwide and has received wider attention in recent years. Iron oxides possess appealing characteristics as efficient and cost-effective adsorbents in large-scale applications. In the present study, Sb(V) adsorption capacity of α-Fe2O3, γ-Fe2O3, and Fe3O4 was compared under experimental conditions close to the practical textile wastewater treatment. Results demonstrated that α-Fe2O3 performed better under different pH values, reaction times, dye compounds, and co-existing ions as compared to γ-Fe2O3 and Fe3O4, and the adsorption equilibrium was achieved within 8 h. Sb(V) adsorption is found to be highly pH dependent, and higher removal was achieved in lower pH, indicating the involvement of electrostatic interactions. The pHpzc value of α-Fe2O3 was 7.15, which favored Sb(V) adsorption in practical wastewater having neutral pH value (pH ~ 7). Pseudo-first- and pseudo-second-order described the data and the simulated values of qe fitted well with the experimental values, indicating that pseudo-second-order model described the adsorption kinetics better with R2 (> 0.95) higher than of pseudo-first-order plots. The Langmuir and Freundlich models both described well the sorption data of all the adsorbents, where the R2 values were > 0.90 with a better fit in the Freundlich model for α-Fe2O3, suggesting that the adsorbent has heterogeneous surface characteristics. Similarly, characterizations revealed that the specific surface area, pore volume, and hydroxyl group content in α-Fe2O3 were higher than others, making it easier for contaminants to bind on to the active sites. Furthermore, the effect of dyes and co-existing anions on Sb(V) adsorption was negligible, except for SO42-, CO32-, and PO43- by the formation of inner-sphere complexes with iron oxides through competitive adsorption with [Sb(OH)6]-. Findings from the present study suggested that α-Fe2O3 effectively reduced Sb(V) in textile wastewater and could be a promising alternative for practical textile wastewater treatment.

Contamination level, source identification and health risk assessment of potentially toxic elements in drinking water sources of mining and non-mining areas of Khyber Pakhtunkhwa, Pakistan.

Accelerated mining activities have increased water contamination with potentially toxic elements (PTEs) and their associated human health risk in developing countries. The current study investigated the distribution of PTEs, their potential sources and health risk assessment in both ground and surface water sources in mining and non-mining areas of Khyber Pakhtunkhwa, Pakistan. Water samples (n = 150) were taken from selected sites and were analyzed for six PTEs (Ni, Cr, Zn, Cu, Pb and Mn). Among PTEs, Cr showed a high mean concentration (497) µg L-1, followed by Zn (414) µg L-1 in the mining area, while Zn showed the lowest mean value (4.44) µg L-1 in non-mining areas. Elevated concentrations of Ni, Cr and a moderate level of Pb in ground and surface water of Mohmand District exceeded the permissible limits set by WHO. Multivariate statistical analyses showed that the pollution sources of PTEs were mainly from mafic-ultramafic rocks, acid mine drainage, open dumping of mine wastes and mine tailings. The hazard quotient (HQ) was the highest for children relative to that for adults, but not higher than the USEPA limits. The hazard index (HI) for ingestions of all selected PTEs was lower than the threshold value (HIing < 1), except for Mohmand District, which showed a value of HI >1 in mining areas through ingestion. Moreover, the carcinogenic risk (CR) values exceeded the threshold limits for Ni and Cr set by the USEPA (1.0E-04-1.0E-06). In order to protect the drinking water sources of the study areas from further contamination, management techniques and policy for mining operations need to be implemented.

Integrated green complexing agent and biochar modified nano zero-valent iron for hexavalent chromium removal: A characterisation and performance study.

In this study, nano zero-valent iron (nZVI) was loaded on biochar (BC) prepared from recycled waste peanut shells. The loaded BC in the nZVI@BC composite was assumed to weaken the agglomeration of nZVI and the environmentally-friendly complexing agents sodium citrate (Cit) and sodium carboxymethyl cellulose (CMC) were used to establish Cit-nZVI@BC and CMC-nZVI@BC for the effective removal of Cr(VI) from aqueous environments. The characterisation results suggested that Cit and CMC not only inhibited the oxidation of nZVI, but also effectively improved its reactivity. The experimental results demonstrated that the Cr(VI) removal efficiency by nZVI was less than 20%, while CMC-nZVI@BC enhanced the Cr(VI) removal efficiency to 80.73%, because CMC was coated on the nZVI surface for anti-passivation and improved the surface activity of nanoparticles. In addition, the Cr(VI) removal efficiency reached almost 100% with Cit-nZVI@BC, and the citrate dissociated the passivation layer on the surface of the zero-valent iron particles to ensure the reactivity of the zero-valent iron. The reaction mechanism of Cit-nZVI@BC includes adsorption, reduction, and co-precipitation, whereas CMC-nZVI@BC also involves surface complexation reactions. The kinetic studies revealed that the removal of Cr(VI) by Cit-nZVI@BC and CMC-nZVI@BC followed the second-order reaction kinetic model, and the reaction rates of Cit-nZVI@BC and CMC-nZVI@BC were both higher than that of nZVI. The results indicate that the prepared systems are promising for Cr(VI) remediation in contaminated environments.

Sodium citrate and biochar synergistic improvement of nanoscale zero-valent iron composite for the removal of chromium (â ¥) in aqueous solutions.

Sodium citrate (SC) is a widely-used food and industrial additive with the properties of complexation and microbial degradation. In the present study, nano-zero-valent iron reaction system (SC-nZVI@BC) was successfully established by modifying nanoscale zero-valent iron (nZVI) with SC and biochar (BC), and was employed to remove Cr(Ⅵ) from aqueous solutions. The nZVI, SC-nZVI and SC-nZVI@BC were characterized and compared using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyses (TGA), vibrating sample magnetometer (VSM), scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that nZVI was successfully loaded on the biochar, and both the agglomeration and surface passivation problems of nanoparticles were well resolved. The dosage of SC, C:Fe, initial pH and Cr(Ⅵ) concentration demonstrated direct effects on the removal efficiency. The maximum Cr(Ⅵ) removal rate and the removal capacity within 60 min were 99.7% and 199.46 mg/g, respectively (C:Fe was 1:1, SC dosage was 1.12 mol.%, temperature was 25°C, pH = 7, and the original concentration of Cr(Ⅵ) was 20 mg/L). The reaction confirmed to follow the pseudo-second-order reaction kinetics, and the order of the reaction rate constant k was as follows: SC-nZVI@BC > nZVI@BC > SC-nZVI > nZVI. In addition, the mechanism of Cr(Ⅵ) removal by SC-nZVI@BC mainly involved adsorption, reduction and co-precipitation, and the reduction of Cr(Ⅵ) to Cr(Ⅲ) by nano Fe0 played a vital role. Findings from the present study demonstrated that the SC-nZVI@BC exhibited excellent removal efficiency toward Cr(Ⅵ) with an improved synergistic characteristic by SC and BC.

Implication and evaluations of indoor soot particles from domestic fuel energy sources using characterization techniques in northern Pakistan.

Soot particles emitted from the burning of solid fuel sources in the households carry important environmental and public health implications. In this study, the indoor soot particles released from firewood, cow dung, and bagasse burning at households of selected rural areas of Khyber Pakhtunkhwa province of Pakistan were investigated by characterization analyses to study its morphological and elemental compositions. Results demonstrated diverse compositions of soot particles from each fuel source. The surface areas of soot particles emitted by the firewood, cow dung, and bagasse were about 0.3, 0.4, and 8.64 m2  g-1 , respectively. For the soot particles emitted by the firewood burning, the major functional groups for aromatic compounds were C═C at the 1,431-1,599 at 1,000-2,000 cm-1 . The absorbance rate of alkanes was about 1,599-1,431 at 1,000-2,000 cm-1 . However, silicon band vibration was more prominent in bagasse soot particles as compared to other samples. The emission of soot particles with high surface area in the atmosphere could provide an elevated adsorption sites for atmospheric pollution and trap more energy resulting in increased atmospheric temperature. Findings from the present study suggest that current households' fuel combustion practices significantly contribute to increase the particulate matter in the atmosphere and possible enhance climate change phenomenon and related disasters in northern Pakistan.

Regression analysis of hydro-meteorological variables for climate change prediction: A case study of Chitral Basin, Hindukush region.

In the present study, hydro-meteorological variables of Chitral Basin in Hindukush region of Pakistan were studied to predict the changes in climatic components such as temperature, precipitation, humidity and river flow based on observed data from 1990 to 2019. Uncertainties in climate change projection were studied using various statistical methods, such as trend variability analysis via stationarity test and validation of regression assumptions prior to fitting of regression estimates. Also, multiple regression models were estimated for each hydro-meteorological variables for the given 30 years of observed data. Results demonstrated that temperature and, precipitation were inversely related with one another. It was observed from the regression model that temperature is decreases by 0.309 °C on the average increases in precipitation by one unit. Temperature also decreases for the increase in humidity by average 0.086 °C. Since, precipitation is negatively related with temperature, thus for increases in temperature the annual precipitation decreases by 0.278 mm annually. Humidity on the other hand, increases by 0.207% by increasing in precipitation and the temperature that causes humidity to decrease by 0.99%. Thus, it demonstrated that the flow in Chitral river increases due to precipitation by 0.306 m3/s for the change in precipitation by one unit. Findings from the present study negated the general perceptions that flow in the Chitral river has increased due to recession of glaciers with increase in the intensity of temperature.

Appraisal of groundwater recharge in Neelum watershed (Upper Indus Basin) using geospatial water balance technique.

Water availability is important for survival of millions of people living in the Himalayan region of Upper Indus Basin and adequate monitoring system is for better water resources management. In the present study, groundwater recharge appraisals in the Neelum watershed (Upper Indus Basin) were investigated by using water balance and geospatial modeling techniques on monthly time-scale climate data from 1989 to 2015. Results demonstrated that on an average out of total annual rainfall (i.e., 2028 mm), about 46% of the rainfall convert to surface runoff and 35% loss to atmosphere via evapo-transpiration (ET), while the remaining 18% contribute to infiltrate the groundwater recharge. Groundwater recharge enhanced during snow-melt from December to March and the rainfall infiltration increased during July and August months. Similarly, the infiltration ranges 106-177 mm from January to March and 45-51 mm from December to July. The groundwater discharge in the form of oozing from the spring occurred during the remaining six months, which ultimately contributed to the baseflow of the stream. Findings from the study revealed variations in groundwater recharge during the years and hence recommended more hydrological studies to predict future changes in climate and land use for sustainable development of freshwater resources in the Upper Indus Basin.

Adsorption behavior and mechanism of arsenic on mesoporous silica modified by iron-manganese binary oxide (FeMnOx/SBA-15) from aqueous systems.

Iron-manganese binary oxides (FeMnOx) can remove contaminants from aqueous solutions with high efficiency, and mesoporous silica (SBA-15) is widely used as a supporting material due to its large specific surface area and good stability. In this study, SBA-15 was used to support FeMnOx in the synthesis of a novel arsenic (As) adsorbent (FeMnOx/SBA-15), and its characteristics under different reaction conditions, such as pH, temperature, presence of competing ions, and humic acid, were tested. The results showed that the contaminant adsorption efficiency of the novel adsorbent was better than that of bare FeMnOx, as the addition of SBA-15 decreased the agglomeration effect of FeMnOx. Additionally, FeMnOx/SBA-15 underwent calcination to further enhance its performance. The state of iron and manganese in FeMnOx/SBA-15 and the corresponding arsenic removal efficiency were improved by calcination at 350 °C with an FeMnOx/SBA-15 mass fraction of approximately 45%. Almost 90% of As (50 mL, 5.0 mg L-1) could be removed by 0.2 g L-1 of FeMnOx/SBA-15 (mass ratio of 45% and calcination temperature of 350 °C). The FeMnOx/SBA-15 could regenerate and still be used after four consecutive cycles. The high As sorption capacity, ability to regenerate, and reusability of FeMnOx/SBA-15 confirmed that this adsorbent is promising for treating As-contaminated drinking water.

Applications and characteristics of Fe-Mn binary oxides for Sb(V) removal in textile wastewater: Selective adsorption and the fixed-bed column study.

In this study, the selective adsorption performance of different Fe-Mn binary oxides (FMBOs) towards Sb(V) in the textile wastewater under different concentrations of coexisting anions, surfactants and dyes were investigated. Results showed that the influences of different anions on the Sb(V) removal followed an order of phosphate > carbonate > sulfate > nitrate > chloride. The frequently-used organic acid of acetate was found to have insignificant effect. The coexisting surfactant with sulfonic groups could have adverse effect on the removal due to sulfonic groups could compete the adsorptive sites on Fe oxides with Sb(V). While the quaternary ammonium surfactant might have minor effect. The influences of the three widely used dyes on the Sb(V) adsorption decreased in the following order: reactive black-5 >acid orange-7> disperse blue-60, which confirmed that the dyes with sulfonic groups would have relatively higher effect. The selective adsorption capacities of Sb(V) by FMBOs followed an order of FMBO3> FMBO5 >FMBO10> FMBO20>PFO. Fixed-bed column adsorption supplied useful parameters and evidently indicated that the cyclic utilization of FMBO3 was cost-efficient for practical dynamic Sb(V) removal. The Sb(V) removal by FMBO3 from real textile wastewater can simultaneously improve the removal efficiency, stabilize pH and prevent the increase of iron concentration as compared to the traditional coagulation, further demonstrating the high practical applicability of FMBO3.

TiC doped palladium/nickel foam cathode for electrocatalytic hydrodechlorination of 2,4-DCBA: Enhanced electrical conductivity and reactive activity.

Titanium carbide (TiC) with excellent electrical conductivity, chemical and thermal stabilities has been recognized as one of the most promising electrocatalysts. A novel cathode, titanium carbide doped palladium/nickel foam (TiC-Pd/Ni foam), was synthesized via electroless deposition to improve the performance of Pd/Ni foam in electrocatlytic hydrodechlorination (ECH). TiC can be co-precipitated onto the surface of cathode during galvanic replacement reaction between Pd(II) solution and Ni foam. Both constant potential and constant current tests proved that TiC-Pd/Ni foam cathode performed remarkably higher activity for 2,4-dichlorobenzoic acid (2,4-DCBA) than Pd/Ni foam cathode, owing to the excellent conductivity of TiC and enhanced water dissociation over TiC-Pd/Ni foam cathode. Under the optimized reaction conditions of -0.85 V (vs Ag/AgCl), electrolyte of 10 mM and initial pH of 4, 99.8% of aqueous 2,4-DCBA (0.2 mM) was removed within 90 min. The removal process of the aqueous 2,4-DCBA obeyed first-order decay kinetic model. Over 86.3% of 2,4-DCBA can still be removed by TiC-Pd/Ni foam cathode in the fifth consecutive run within 120 min, which was much higher than that of Pd/Ni foam cathode (37.5%). Consequently, TiC-Pd/Ni foam cathode was a promising design for enhanced ECH activity and reduced operation cost.

Prevalence of selected pharmaceuticals in surface water receiving untreated sewage in northwest Pakistan.

This study investigated the occurrence of four non-steroidal anti-inflammatory drugs (NSAIDs) and four benzodiazepines/anti-depressants (ADs) in municipal wastewater in Mardan city, Pakistan, and in River Kabul and River Indus receiving untreated sewage. Liquid chromatography with a triple quadrupole tandem mass spectrometry (LC-MS/MS) was used for the analysis of paracetamol, diclofenac, ibuprofen, and codeine (NSAIDs) and diazepam, bromazepam, lorazepam, and temazepam (ADs). Except codeine and lorazepam, all the target compounds were observed in sewage and surface water in various concentrations. In sewage, paracetamol was found at the higher end (32.4 µg/L) of the reported ranges in literature for other countries. Results of river samples showed that the target compounds were usually lower in concentration than the respective EC50 values for aquatic organisms. However, the levels for paracetamol and ibuprofen were critical depicting the consequence of untreated disposal. Environmental risk assessment by estimating the risk quotient (RQ) as the ratio of measured environmental concentration and predicted no-effect concentration showed medium to high (RQ > 1 and 0.1 < RQ < 1) risk from paracetamol and ibuprofen to aquatic organisms in River Kabul and Kalpani stream, Pakistan.

Adsorption of mercury (II) from aqueous solutions using FeS and pyrite: A comparative study.

In this study, a comparative evaluation of synthetic FeS and natural pyrite was performed to investigate their adsorptive potentials toward Hg(II) in aqueous system. Characterization analyses such as BET, SEM and TEM suggested that FeS had porous structures with abundant active sites, while pyrite with a hard and smooth surface relied mainly on surface adsorption to immobilize Hg(II). Results of batch tests revealed that FeS offered much greater Hg(II) maximum adsorption capacity (769.2 mg/g) as compared to pyrite (9.9 mg/g). Both iron sulfides showed high removal efficiency (>96%) with the initial Hg(II) concentration (1 mg/L) at pH = 7.0 ± 0.1, and the effluent could meet the permissible effluent concentration (<50 µg/L). Condition experiments (such as pH, co-ions) proved that the adaptive capacity of FeS was significantly higher than that of pyrite. A pseudo-second-order kinetic model was better able to illustrate the sorption kinetics on both FeS and pyrite (R2 ≥ 0.9992). XRD and XPS analyses supported that precipitation, ion exchange and surface complexation were main reaction mechanisms involved in the adsorption process. In addition, it was also revealed that the structural changes of FeS before and after adsorption was much larger than pyrite. Findings from this study suggest FeS is a promising candidate for treatment of high-concentration Hg(II)-containing wastewater (<20 mg/L), while pyrite can be applied as a long-term adsorbing material in the immobilization of wastewater containing low Hg(II) concentration (<1 mg/L) due to its cost-effective property and local availability.

Assessment of tap water quality and corrosion scales from the selected distribution systems in northern Pakistan.

Corrosion deposits formed within drinking water distribution systems deteriorate drinking water quality and resultantly cause public health consequences. In the present study, an attempt was made to investigate the concurrent conditions of corrosion scales and the drinking water quality in selected water supply schemes (WSS) in districts Chitral, Peshawar, and Abbottabad, northern Pakistan. Characterization analyses of the corrosion by-products revealed the presence of α-FeOOH, γ-FeOOH, Fe3O4, and SiO2 as major constituents with different proportions. The constituents of all the representative XRD peaks of Peshawar WSS were found insignificant as compared to other WSS, and the reason could be the variation of source water quality. Well-crystallized particles in SEM images indicated the formation of dense oxide layer on corrosion by-products. A wider asymmetric vibration peak of SiO2 appeared only in Chitral and Abbottabad WSS, which demonstrated higher siltation in the water source. One-way ANOVA analysis showed significant variations in pH, turbidity, TDS, K, Mg, PO4, Cl, and SO4 values, which revealed that these parameters differently contributed to the source water quality. Findings from this study suggested the implementation of proper corrosion prevention measures and the establishment of international collaboration for best corrosion practices, expertise, and developing standards.

Occurrence and removal of antibiotics and the corresponding resistance genes in wastewater treatment plants: effluents' influence to downstream water environment.

In this study, the occurrence of 8 antibiotics [3 tetracyclines (TCs), 4 sulfonamides, and 1 trimethoprim (TMP)], 12 antibiotic resistance genes (ARGs) (10 tet, 2 sul), 4 types of bacteria [no antibiotics, anti-TC, anti-sulfamethoxazole (SMX), and anti-double], and intI1 in two wastewater treatment plants (WWTPs) were assessed and their influences in downstream lake were investigated. Both WWTPs' effluent demonstrated some similarities, but the abundance and removal rate varied significantly. Results revealed that biological treatment mainly removed antibiotics and ARGs, whereas physical techniques were found to eliminate antibiotic resistance bacteria (ARBs) abundance (about 1 log for each one). UV disinfection did not significantly enhance the removal efficiency, and the release of the abundantly available target contaminants from the excess sludge may pose threats to human and the environment. Different antibiotics showed diverse influences on the downstream lake, and the concentrations of sulfamethazine (SM2) and SMX were observed to increase enormously. The total ARG abundance ascended about 0.1 log and some ARGs (e.g., tetC, intI1, tetA) increased due to the high input of the effluent. In addition, the abundance of ARB variation in the lake also changed, but the abundance of four types of bacteria remained stable in the downstream sampling sites.

Fe3O4 and MnO2 assembled on honeycomb briquette cinders (HBC) for arsenic removal from aqueous solutions.

In this study, a novel composite adsorbent (HBC-Fe3O4-MnO2) was synthesized by combining honeycomb briquette cinders (HBC) with Fe3O4 and MnO2 through a co-precipitation process. The purpose was to make the best use of the oxidative property of MnO2 and the adsorptive ability of magnetic Fe3O4 for enhanced As(III) and As(V) removal from aqueous solutions. Experimental results showed that the adsorption capacity of As(III) was observed to be much higher than As(V). The maximum adsorption capacity (2.16 mg/g) was achieved for As(III) by using HBC-Fe3O4-MnO2 (3:2) as compared to HBC-Fe3O4-MnO2 (2:1) and HBC-Fe3O4-MnO2 (1:1). The experimental data of As(V) adsorption fitted well with the Langmuir isotherm model, whereas As(III) data was described perfectly by Freundlich model. The pseudo-second-order kinetic model was fitted well for the entire adsorption process of As(III) and As(V) suggesting that the adsorption is a rate-controlling step. Aqueous solution pH was found to greatly affect the adsorption behavior. Furthermore, co-ions including HCO3(-) and PO4(3-) exhibited greater influence on arsenic removal efficiency, whereas Cl(-), NO3(-), SO4(2-) were found to have negligible effects on arsenic removal. Five consecutive adsorption-regeneration cycles confirmed that the adsorbent could be reusable for successive arsenic treatment and can be used in real treatment applications.

Arsenic removal from aqueous solutions using Fe3O4-HBC composite: effect of calcination on adsorbents performance.

The presence of elevated concentration of arsenic in water sources is considered to be health hazard globally. Calcination process is known to change the surface efficacy of the adsorbent. In current study, five adsorbent composites: uncalcined and calcined Fe3O4-HBC prepared at different temperatures (400°C and 1000°C) and environment (air and nitrogen) were investigated for the adsorptive removal of As(V) and As(III) from aqueous solutions determining the influence of solution's pH, contact time, temperature, arsenic concentration and phosphate anions. Characterizations from FTIR, XRD, HT-XRD, BET and SEM analyses revealed that the Fe3O4-HBC composite at higher calcination temperature under nitrogen formed a new product (fayalite, Fe2SiO4) via phase transformation. In aqueous medium, ligand exchange between arsenic and the effective sorbent site ( = FeOOH) was established from the release of hydroxyl group. Langmuir model suggested data of the five adsorbent composites follow the order: Fe3O4-HBC-1000°C(N2)>Fe3O4-HBC (uncalcined)>Fe3O4-HBC-400°C(N2)>Fe3O4-HBC-400°C(air)>Fe3O4-HBC-1000°C(air) and the maximum As(V) and As(III) adsorption capacities were found to be about 3.35 mg g(-1) and 3.07 mg g(-1), respectively. The adsorption of As(V) and As(III) remained stable in a wider pH range (4-10) using Fe3O4-HBC-1000°C(N2). Additionally, adsorption data fitted well in pseudo-second-order (R2>0.99) rather than pseudo-first-order kinetics model. The adsorption of As(V) and As(III) onto adsorbent composites increase with increase in temperatures indicating that it is an endothermic process. Phosphate concentration (0.0l mM or higher) strongly inhibited As(V) and As(III) removal through the mechanism of competitive adsorption. This study suggests that the selective calcination process could be useful to improve the adsorbent efficiency for enhanced arsenic removal from contaminated water.