Efficient Removal of Antimony(V) from Antimony Mine Wastewater by Micrometer Zero-Valent Iron.

This paper investigates the effectiveness of two commercial micron zero-valent irons (mZVIs) in removing Sb(V) from antimony mine wastewater. The wastewater contains a range of complex components and heavy metal ions, including As(V), which can impact the removal efficiency of mZVI. The study aims to provide insights into actual working conditions and focuses on influencing factors and standard conditions. The results demonstrate that mZVI can reduce Sb(V) concentration in the mine wastewater from 3875.7 µg/L to below the drinking water standard of 5 µg/L within 2 h. Adding a small amount of mZVI every 30 min helps to maintain a high removal rate. The study confirms the existence of a reduction reaction by changing the atmospheric conditions of the reaction, and the addition of 1,10-phenanthroline highlights the important role of active Fe(II) in the adsorption and removal of Sb(V) by mZVI. Additionally, the paper presents an innovative experimental method of acid treatment followed by alkali treatment, which proves the interfacial reaction between mZVI and Sb(V). Overall, the study demonstrates that the removal of Sb(V) by mZVI entails a dual function of reduction and adsorption, highlighting the potential of mZVI in repairing Sb(V) in antimony mine wastewater.

Using a promising biomass-based biochar in photocatalytic degradation: highly impressive performance of RHB/SnO2/Fe3O4 for elimination of AO7.

The release of industrial dyes into the environment has recently increased, resulting in harmful effects on people and ecosystems. In recent years, the use of adsorbents in photocatalytic nanocomposites has attracted significant interest due to their low cost, efficiency, and eco-friendly physical and chemical characteristics. Herein, Acid Orange 7 (AO7) removal was investigated by photocatalytic degradation using Rice Rusk Biochar (RHB), Tin (IV) Oxide (SnO2), and Iron Oxide (Fe3O4) as heterogeneous nanocomposite. After the preparation of RHB, the nanocomposite was synthesized and characterized using Field Emission Scanning Electron Microscope (FESEM), X-ray Powder Diffraction (XRD), Brunauer-Emmett-Teller (BET), and Fourier-Transform Infrared Spectroscopy (FT-IR). To optimize the elimination of AO7 by the One-Factor-At-a-Time (OFAT) method, effective parameters including mixing ratio (RHB:SnO2:Fe3O4), dye concentration, solution pH, and nanocomposite dose were studied. The results showed that the removal efficiency of AO7 after 120 min under the optimal mixing ratio of 1:1.5:0.6, dye concentration of 75 mg/l, solution pH of 4, and nanocomposite dose of 0.7 g/l was 92.37%. Moreover, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removal rates were obtained at 82.22 and 72.22%, respectively. The Average Oxidation State (AOS) and Carbon Oxidation State (COS) of the AO7 solution were increased after the process, indicating biodegradability improvement. Various scavenger effects were studied under optimal conditions, and the results revealed that O2- and H+ reactive species play a crucial role in the photocatalytic degradation of AO7. The reusability and stability of nanocomposite were tested in several consecutive experiments, and the degradation efficiency was reduced from 92 to 79% after five consecutive cycles. It is expected that this research contributes significantly to the utilization of agricultural waste in photocatalytic nanocomposites for the degradation of environmental pollutants.

Microplastics in urban waters and its effects on microbial communities: a critical review.

Microplastic (MP) pollution is one of the emerging threats to the water and terrestrial environment, forcing a new environmental challenge due to the growing trend of plastic released into the environment. Synthetic and non-synthetic plastic components can be found in rivers, lakes/reservoirs, oceans, mountains, and even remote areas, such as the Arctic and Antarctic ice sheets. MPs' main challenge is identifying, measuring, and evaluating their impacts on environmental behaviors, such as carbon and nutrient cycles, water and wastewater microbiome, and the associated side effects. However, until now, no standardized methodical protocols have been proposed for comparing the results of studies in different environments, especially in urban water and wastewater. This review briefly discusses MPs' sources, fate, and transport in urban waters and explains methodological uncertainty. The effects of MPs on urban water microbiomes, including urban runoff, sewage wastewater, stagnant water in plumbing networks, etc., are also examined in depth. Furthermore, this study highlights the pathway of MPs and their transport vectors to different parts of ecosystems and human life, particularly through mediating microbial communities, antibiotic-resistant genes, and biogeochemical cycles. Overall, we have briefly highlighted the present research gaps, the lack of appropriate policy for evaluating microplastics and their interactions with urban water microbiomes, and possible future initiatives.

Investigating the effect of hydrogen peroxide as an electron acceptor in increasing the capability of slurry photocatalytic process in dye removal.

The hydrogen peroxide role in photocatalytic degradation of an anionic azo dye, Acid Orange 7 (AO7), was investigated in a slurry reactor. Commercial ZnO nanoparticles with an average size between 10 to 30 nm were used as catalysts. Optimum conditions for different parameters, including dye concentration (10-100 mg/L), catalyst concentration (0.1-0.5 g/L), and pH (5-10), were determined first in the absence of H2O2. Changes in the COD were measured for the optimum condition. The impact of adding hydrogen peroxide at different concentrations to the system operating at optimum conditions was investigated. It was observed that 0.416 mM hydrogen peroxide increased the system's efficiency and decreased reaction time by 40 min. The reaction followed first-order kinetic. Hydrogen peroxide alone did not contribute to oxidizing the contaminant, and its positive impact was attributed to decreasing electron-hole recombination in the photocatalytic process. Not only can the hydrogen peroxide-assisted photocatalytic process decrease retention time in treatment units, but it can also result in more contaminant degradation. Therefore, it can reduce the treatment cost.

Enhancement of the electro-activated persulfate process in dye removal using graphene oxide nanoparticle.

This study aimed to improve the speed of the electrochemical process by graphene oxide nanoparticle as a current accelerator in Acid Blue 25 removal from aqueous solutions. To do so, the effect of different parameters including pH, dye concentration, sodium persulfate concentration, the ratio of sodium persulfate to iron (II) sulfate concentration, current density, and the distance between electrodes was investigated on dye removal. Under optimal conditions of pH = 5, dye concentration = 200 mg/L, sodium persulfate concentration = 500 mg/L, iron (II) sulfate concentration = 100 mg/L, current density = 16.67 mA/cm2, and electrode distance = 2 cm, 95% of dye was removed after 60 min in the electro-activated persulfate process; while the modified electro-activated persulfate process achieved 95% dye removal after only 40 min under the same conditions. This system was able to remove 90% of dye after 60 min at a higher concentration (300 mg/L). Also, the modified electro-activated persulfate process obtained the removal of 80% of COD, and 54% of TOC after 180 min in the mentioned conditions, for the dye concentration of 300 mg/L.

Improving Fe-based heterogeneous Electro-Fenton nano catalyst using transition metals in a novel orbiting electrodes reactor.

In recent decades the electro-Fenton process has widely been utilized for removing recalcitrant compounds. However, this process is accompanied by several problems such as limited working pH range, production of significant amount of iron sludge, and incapability in reusing used iron ions. Hence, the heterogeneous electro-Fenton process is a convenient way to address these problems. One of the shortcomings of this method, in comparison with the homogeneous electro-Fenton process, is its lower reaction rate. In the first phase of this study, a heterogeneous Fe-based nanocatalyst was prepared. After optimizing the affecting parameters, three transition metals (M: Cu, Co and, Cr) were used in the second phase of the study to improve the performance of this nanocatalyst in removing the indicator pollutant (acid blue 25). The characteristics of nanocatalysts were determined via FESEM, XRD, FTIR, and N2 adsorption-desorption techniques. The results indicated an enhancement in dye removal efficiency (nearly 8 percent), and the reaction rate (nearly 64 percent) due to the nanocatalysts improved by the presence of transition metals. The reactions with Fe-based nanocatalyst containing copper ions in pH = 3, initial dye concentration = 200 mg L-1, I = 3.57 mA cm-2, nanocatalyst concentration = 100 mg L-1, electrodes angular velocity = 50 rpm, Na2SO4 concentration = 0.01 M were capable of removing 97% of dye, 79% of COD and, 65% of TOC. The nanocatalysts were used in 5 cycles, and the dye removal efficiency did not drop considerably, a feature that adds to their importance from an economic point of view. The concentration of leached transition metals into the solution was measured using the ICP-AES technique, which was less than the allowable Iranian standard concentration of discharge into the surface water bodies, thus no need for secondary treatment of wastewater.

Acid Orange 7 treatment and fate by electro-peroxone process using novel electrode arrangement.

Electro-peroxone is a novel advanced oxidation process that surpasses ozonation or peroxone because of its advantages. In this technology, combining ozone and hydrogen peroxide generated electrochemically leads to the production of hydroxyl radicals, which are the strongest oxidizing agents. In this study, a cylindrical reactor with a continuous circular flow using novel arrangements of electrodes was used to examine the effects of variant parameters on dye removal efficiency. Acid Orange 7 (C16H11N2NaO4S) served as an indicator pollutant. Based on overall energy consumption and energy consumption per dye removed weight, electro-peroxone not only has proper efficiency at high dye concentrations, it also has the least energy consumption per dye removed weight; 53 KWh kg-1 is achieved for 500 mg L-1 initial dye concentration at 99% removal efficiency after 40 min. The results show that at the optimum condition of [Dye] = 500 mg L-1, pH = 7.7, applied current = 0.5 A, O3 rate = 1 L min-1, and [Na2SO4] = 0.1 M, dye is removed completely after 90 min and COD and TOC removal is 99% and 90%, respectively. LC-MS results also showed that AO7 initially was converted to more toxic compounds than AO7 like benzoic acid but finally linear acidic intermediate with less toxicity such as fumaric acid was formed.

Ecological role of Acinetobacter calcoaceticus GSN3 in natural biofilm formation and its advantages in bioremediation.

This study assessed the role of a new Acinetobacter calcoaceticus strain, GSN3, with biofilm-forming and phenol-degrading abilities. Three biofilm reactors were spiked with activated sludge (R1), green fluorescent plasmid (GFP) tagged GSN3 (R2), and their combination (R3). More than 99% phenol removal was achieved during four weeks in R3 while this efficiency was reached after two and four further operational weeks in R2 and R1, respectively. Confocal scanning electron microscopy revealed that GSN3-gfp strains appeared mostly in the deeper layers of the biofilm in R3. After four weeks, almost 7.07 × 107 more attached sludge cells were counted per carrier in R3 in comparison to R1. Additionally, the higher numbers of GSN3-gfp in R2 were unable to increase the efficiency as much as measured in R3. The presence of GSN3-gfp in R3 conveyed advantages, including enhancement of cell immobilization, population diversity, metabolic cooperation and ultimately treatment efficiency.

Kinetic study on photocatalytic degradation of Acid Orange 52 in a baffled reactor using TiO2 nanoparticles.

In this study, a baffled photocatalytic reactor was used for the treatment of colored wastewater containing the azo dye of Acid Orange 52 (AO52). A study on the active species of the photocatalytic process using TiO2 nanoparticles indicated that hydroxyl radical and superoxide have the greatest contribution to the dye degradation process respectively. Given that a level of biological oxygen demand/chemical oxygen demand (BOD5/COD) equal to 0.4 was achieved after about 5 hr from the beginning of the experiment, the reactor seems to be capable of purifying the wastewater containing AO52 dye after this time in order to discharge into a biological treatment system to continue the treatment process. The results of the liquid chromatography-mass spectrometry (LC-MS) test showed that during the first 4 hr of the experiment, with the breakdown of the azo bond, the contaminant was decomposed into the benzene annular compounds with less toxicity indicating a reduction in the toxicity of wastewater after removing the dye agent. The study on the kinetics of these reactions followed the pseudo-first-order kinetic model in all conditions and corresponded well to Langmuir-Hinshelwood model. According to the kinetic model for the simultaneous occurrence of possible pathways, the kinetic constant of production and degradation of intermediate products in optimal conditions was estimated to be between 0.0029 and 0.0391 min-1.

Highly efficient phenol degradation in a batch moving bed biofilm reactor: benefiting from biofilm-enhancing bacteria.

In this study, the efficiency improvement of three moving bed biofilm reactors (MBBRs) was investigated by inoculation of activated sludge cells (R1), mixed culture of eight strong phenol-degrading bacteria consisted of Pseudomonas spp. and Acinetobacter spp. (R2) and the combination of both (R3). Biofilm formation ability of eight bacteria was assessed initially using different methods and media. Maximum degradation of phenol, COD, biomass growth and also changes in organic loading shock were used as parameters to measure the performance of reactors. According to the results, all eight strains were determined as enhanced biofilm forming bacteria (EBFB). Under optimum operating conditions, more than 90% of initial COD load of 2795 mg L-1 was reduced at 24 HRT in R3 while this reduction efficiency was observed in concentrations of 1290 mg L-1 and 1935 mg L-1, in R1 and R2, respectively. When encountering phenol loading shock-twice greater than optimum amount-R1, R2 and R3 managed to return to the steady-state condition within 32, 24 and 18 days, respectively. SEM microscopy and biomass growth measurements confirmed the contribution of more cells to biofilm formation in R3 followed by R2. Additionally, established biofilm in R3 was more resistant to phenol loading shock which can be attributed to the enhancer role of EBFB strains in this reactor. It has been demonstrated that the bacteria with both biofilm-forming and contaminant-degrading abilities are not only able to promote the immobilization of other favorable activated sludge cells in biofilm structure, but also cooperate in contaminant degradation which all consequently lead to improvement of treatment efficiency.

Fractionation and leaching of heavy metals in soils amended with a new biochar nanocomposite.

In this study, surface soils of the Bama Pb-Zn mine-impacted area were sampled for an area surrounding the mineral processing plant. After collecting 65 samples and analyzing them for initial Cu, Pb, Zn, and Cd metal contents, the area was zonated based on the concentration distribution using ordinary kriging in R. A single homogenous sample was prepared by mixing equal weights of each sample as being representative of the whole impacted area (ST). Next, a synthetic model soil (SM) was prepared according to the mean ST texture (SM), divided into two portions, where one portion was amended with a biochar composite (10% w/w) (SMA), both portions were artificially contaminated with Cu, Pb, Zn, and Cd (SMAC and SMC). The mixed soil ST, and the model soils SMC and SMAC, were subjected to soil sequential extraction procedure to determine the variations in fractionation of heavy metals. Results showed that the fractionation in the unamended model soil (SMC) was very close to the original real soil (ST). Moreover, in both amended and unamended soils, Cd and Pb had the highest and the lowest mobility, respectively. Zn and Cu showed intermediate mobilities. The performance of the amendment was evaluated using a 150-day column leaching test taking leachate samples at designated time intervals, and Cu, Pb, Zn, and Cd concentrations were analyzed. Results of column leaching were in good agreement with the soil fractionation as Cd and Pb showed the highest and the lowest mobilities, respectively. Leaching through the soil column was also simulated by HP1 model. Results of simulation found in acceptable proximity to the experimental data despite remarkable differences due to limitations in defining soil to the simulation system.

Simultaneous immobilization of heavy metals in soil environment by pulp and paper derived nanoporous biochars.

BACKGROUND: Biochars are the new generation of sustainable soil amendments which may be applied both to fertilize and remediate the impacted soils. The aim of current research has been synthesis and characterization of pulp and paper-derived biochars and determination of their mechanisms in simultaneous immobilization of heavy metals (Cu2+, Pb2+, and Zn2+) within contaminated soil. In a novel attempt, three different solid wastes of Mazandaran Wood and Paper Industries (barks and effluent sludge) were utilized to produce biochars. METHODS: The thermogravimetric behavior of the three selected biomasses were initially analyzed and the proper pyrolysis condition has been determined, accordingly. Alterations in surface active groups, before and after the pyrolysis process, have been detected by Fourier transform infrared (FTIR) spectroscopy. Elemental analysis and acid digestion procedure have been employed to measure C, H, N, S, O, and P contents of the biochars. Moreover, porosity and morphological characteristics have been monitored by Brauner-Emmet-Teller (BET) porosimetry and scanning electron microscopy (SEM). Batch adsorption tests have been designed and carried out. Finally, a set of soil sequential extraction experiments was performed over both amended/unamended soils which together with a post-sorption FTIR analysis, explained the possible competitive immobilization mechanism. RESULTS: Porosimetry study indicated the nanoporosity of the chars and the distribution pattern of adsorbed metals over the char samples. Batch sorption tests suggested remarkable uptake capacity for each char. The results of post sorption tests suggested that Cu is mainly involved in organic bonds of -NH2, -OH and -COOH groups, Pb forms insoluble hydroxide, phosphate or carbonate precipitates, and Zn is mostly engaged in the residual fraction. CONCLUSIONS: Accordingly, the bulky wastes are confirmed to have the potential to form sustainable biochar soil amendments.

MBBR system performance improvement for petroleum hydrocarbon removal using modified media with activated carbon.

Moving bed biofilm reactor (MBBR) system has a successful operation in the treatment of different types of wastewater. Since the media, i.e. the place of growth and formation of biofilm, play the main role in the treatment in this system, MBBR systems were operated in the present research with modified Bee-cell media. Activated carbon granules of almond or walnut shells were placed in media pores to improve the treatment of refinery oil wastewater and their operation with MBBR system was compared with the conventional Bee-cell media. In these experiments, the effects of organic loading rate, hydraulic retention time (HRT), media filling ratio (MFR), and activated carbon concentration (ACC) used in the media were investigated on the operation of MBBR systems. The analysis of results estimated the optimal values of HRT, MFR, and ACC used in the media between the studied levels, being equal to 22 h, 50%, and 7.5 g/L, respectively. Under these conditions, total petroleum hydrocarbons removal efficiencies for MBBR systems using Bee-cell media with carbon of almond, carbon of walnut shells, and a carbon-free system were 95 ± 1.17%, 91 ± 1.11%, and 57 ± 1.7%, respectively, which confirms the adsorption ability of systems with the media containing activated carbon in the removal of petroleum compounds from wastewater.

Kinetic modeling and determination role of sono/photo nanocatalyst-generated radical species on degradation of hydroquinone in aqueous solution.

Experimental findings of sonophotocatalytic process were used in degradation of hydroquinone to assess kinetic modeling and determine the effect of various active radical species. First, the effects of three photocatalytic, sonocatalytic, and sonophotocatalytic processes were studied for hydroquinone removal to determine kinetic constants and calculate the activation energy of reactions, and then the selected process was evaluated to determine active radical species. The reactor was composed of two parts, one included ultrasonic probe (sonocatalytic part) with powers 22, 80, and 176 W and the second part was the location of UV lamp (photocatalytic part) with tubular flow and power 15 W. After three systems were examined and the efficient system was selected, the role of different active species such as hydroxyl radical (OH(·)), superoxide radical (O2 (·-)), hole (h(+)), electrons (e (-)), and single oxygen molecule ((1)O2) and contribution of each of them were determined in hydroquinone degradation. According to tests, the results of this study showed that sonophotocatalytic integrated method as selected system among three systems studied followed the first-order equation for hydroquinone degradation and active hydroxyl species with 45 % and electron and hole with 15 and 10 %, respectively, had the highest and lowest contributions to conversion of hydroquinone. The findings showed that dissolved oxygen increases the capability of active radical formation so that 28.2 % of hydroquinone removal was increased under aeration compared to without aeration. Also, removal efficiency decreased 62 % with N2 injection due to the withdrawal of oxygen from the sample. By adding 25 Mm of sodium azide (NaN3) to stock solution, 46.5 % reduction was developed because single oxygen ((1)O2) played the role of an active species. The advantages of integrated sonocatalytic and photocatalytic method are the generation of active radical species with more variety and ultimately the formation of higher amounts of powerful hydroxyl radical that increases degradation rates of refractory compounds and low-risk internal and final products. It has an appropriate performance in the degradation of refractory compounds by optimizing effective operational factors.

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.

Application of concrete surfaces as novel substrate for immobilization of TiO2 nano powder in photocatalytic treatment of phenolic water.

BACKGROUND: In this study, concrete application as a substrate for TiO2 nano powder immobilization in heterogeneous photocatalytic process was evaluated. TiO2 immobilization on the pervious concrete surface was done by different procedures containing slurry method (SM), cement mixed method (CMM) and different concrete sealer formulations. Irradiation of TiO2 was prepared by UV-A and UV-C lamps. Phenolic wastewater was selected as a pollutant and efficiency of the process was determined in various operation conditions including influent phenol concentration, pH, TiO2 concentration, immobilization method and UV lamp intensity. FINDINGS: The removal efficiency of photocatalytic process in 4 h irradiation time and phenol concentration ranges of 25-500 mg/L was more than 80 %. Intermediates were identified by GC/Mass and spectrophotometric analysis. CONCLUSIONS: According to the results, photocatalytic reactions followed the pseudo-first-order kinetics and can effectively treate phenol under optimal conditions.

Cultivation of aerobic granules in a novel configuration of sequencing batch airlift reactor.

Aerobic granules can be formed in sequencing batch airlift reactors (SBAR) and sequencing batch reactors (SBR). Comparing these two systems, the SBAR has excellent mixing condition, but due to a high height-to-diameter ratio (H/D), there is no performance capability at full scale at the present time. This research examined a novel configuration of SBAR at laboratory scale (with a box structure) for industrial wastewater treatment. To evaluate chemical oxygen demand (COD) removal efficiency and granule formation of the novel reactor (R1), in comparison a conventional SBAR (R2) was operated under similar conditions during the experimental period. R1 and R2 with working volumes of 3.6 L and 4.5 L, respectively, were used to cultivate aerobic granules. Both reactors were operated for 4 h per cycle. Experiments were done at different organic loading rates (OLRs) ranging from 0.6-4.5 kg COD/m3.d for R1 and from 0.72-5.4 kg COD/m3.d for R2. After 150 days of operation, large-sized black filamentous granules with diameters of 0.5-2 mm and 2-11 mm were formed in R1 and R2, respectively. In the second part of the experiment, the efficiency of removal of a toxic substance by aerobic granules was investigated using aniline as a carbon source with a concentration in the range 1.2-6.6 kg COD/m3.d and 1.44-7.92 kg COD/m3.d in R1 and R2, respectively. It was found that COD removal efficiency of the novel airlift reactor was over 97% and 94.5% using glucose and aniline as carbon sources, respectively. Sludge volume index (SVI) was also decreased to 30 mL/g by granulation in the novel airlift reactor.