Enhanced reduction of sulfate by iron-carbon microelectrolysis: interaction mechanism between microelectrolysis and microorganisms.

Sulfate wastewater has a wide range of sources and greatly harms water, soil, and plants. Iron-carbon microelectrolysis (IC-ME) is a potentially sustainable strategy to improve the treatment of sulfate (SO42-) wastewater by sulfate-reducing bacteria (SRB). In this study, an iron-carbon mixed micro-electrolysis bioreactor (R1), iron-carbon layered bioreactor (R2), activated carbon bioreactor (R3), and scrap iron filing bioreactor (R4) were constructed by up-flow column experimental device. The performance and mechanism of removing high-concentration sulfate wastewater under different sulfate concentrations, hydraulic retention times (HRT), and chemical oxygen demand (COD)/SO42- were discussed. The results show that the iron-carbon microelectrolysis-enhanced SRB technology can remove high-concentration sulfate wastewater, and the system can still operate normally at low pH. In the high hydraulic loading stage (HRT = 12 h, COD/SO42- = 1.4), the SO42- removal rate of the R1 reactor reached 98.08%, and the ORP value was stable between - 350 and - 450 mV, providing a good ORP environment for SRB. When HRT = 12 h and influent COD/SO42- = 1.4, the R1 reactor sulfate removal rate reached 96.7%. When the influent COD/SO42- = 0.7, the sulfate removal rate was 52.9%, higher than the control group. Biological community analysis showed that the abundance of SRB in the R1 reactor was higher than that in the other three groups, indicating that the IC-ME bioreactor could promote the enrichment of SRB and improve its population competitive advantage. It can be seen that the synergistic effect between IC-ME and biology plays a vital role in the treatment of high-concentration sulfate wastewater and improves the biodegradability of sulfate. It is a promising process for treating high-concentration sulfate wastewater.

Reparation of nano-FeS by ultrasonic precipitation for treatment of acidic chromium-containing wastewater.

Nano-FeS is prone to agglomeration in the treatment of chromium-containing wastewater, and ultrasonic precipitation was used to synthesize nano-FeS to increase its dispersion. The optimization of the preparation method was carried out by single factor method (reaction temperature, Fe/S molar ratio and FeSO4 dropping flow rate) and response surface methodology. Dynamic experiments were constructed to investigate the long-term remediation effect and water column changes of nano-FeS and its solid particles. The changes of the remediation materials before and after the reaction were observed by SEM, and the mechanism of the remediation of chromium-containing wastewater by nano-FeS prepared by ultrasonication was revealed by XRD. The results showed that the reaction temperature of 12 °C, Fe/S molar ratio of 3.5 and FeSO4 dropping flow rate of 0.5 mL/s were the best parameters for the preparation of nano-FeS. The nano-FeS has efficient dispersion and well-defined mesoporous structure in the form of needles and whiskers of 40-80 nm. The dynamic experiments showed that the average removal of Cr(VI) and total chromium by nano-FeS and its immobilized particles were 94.97% and 63.51%, 94.93% and 45.76%, respectively. Fe2+ and S2- ionized by the FeS nanoparticles rapidly reduced Cr(VI) to Cr(III). Part of S2- may reduce Fe3+ to Fe2+, forming a small iron cycle that gradually decreases with the ion concentration. Cr(III) and Fe2+ form Cr(OH)3 and FeOOH, respectively, with the change of aqueous environment. Another part of S2- reacts with Cr(III) to form Cr2S3 precipitate or is oxidized to singlet sulfur. The FeS nanoparticles change from short rod-shaped to spherical shape. Compared with the conventional chemical precipitation method, the method used in this study is simple, low cost, small particle size and high removal rate per unit.

Improved GWO and its application in parameter optimization of Elman neural network.

Traditional neural networks used gradient descent methods to train the network structure, which cannot handle complex optimization problems. We proposed an improved grey wolf optimizer (SGWO) to explore a better network structure. GWO was improved by using circle population initialization, information interaction mechanism and adaptive position update to enhance the search performance of the algorithm. SGWO was applied to optimize Elman network structure, and a new prediction method (SGWO-Elman) was proposed. The convergence of SGWO was analyzed by mathematical theory, and the optimization ability of SGWO and the prediction performance of SGWO-Elman were examined using comparative experiments. The results show: (1) the global convergence probability of SGWO was 1, and its process was a finite homogeneous Markov chain with an absorption state; (2) SGWO not only has better optimization performance when solving complex functions of different dimensions, but also when applied to Elman for parameter optimization, SGWO can significantly optimize the network structure and SGWO-Elman has accurate prediction performance.

Exploring the migration and transformation behaviors of heavy metals and ammonia nitrogen from electrolytic manganese residue to agricultural soils through column leaching test.

Heavy metals (HMs) and ammonia nitrogen (AN) leaching from electrolytic manganese residue (EMR) result in the contamination of agricultural soils and water bodies. Batch and column leaching tests were conducted to simulate the release of HMs and AN in EMR during precipitation, as well as their migration and transformation in agricultural soils. The results show that Mn, AN, Cd, Ni, and Zn present in the EMR had high acid soluble fraction (un-fixed AN) content, and the leachability of Mn and AN was significantly higher than that of other hazardous elements. The cumulative release of hazardous elements in the EMR stockpile was well-fitted (R2 > 0.95) by the HILL model. Significant HMs and AN accumulated in the agricultural soils after contamination from the EMR leachate. The pollution degree of HMs in agricultural soils was ranked as Mn > Ni > Pb ≈ Zn ≈ Cr > Cd. The acid soluble fraction (un-fixed AN) content of Mn, Ni, Zn, and AN in agricultural soils increased significantly. The risk assessment code shows that the risk level of Mn in agricultural soils changed from medium to high; Ni and Zn in surface soils changed from low to medium. These results indicated that the leaching from EMR would significantly increase the ecological risk of HMs in surrounding agricultural soils, and the large release of AN would pose a great threat to aquatic systems if not properly addressed.

Adsorption mechanism of phosphorus on biomass ash modified with lanthanum immobilized by chitosan.

The immobilized lanthanum-modified biomass ash gel ball (CS-La-BA) was prepared with lanthanum chloride, biomass ash, and chitosan to remove phosphorus from water. CS-La-BA was characterized by several analytical techniques. SEM-EDS results showed that CS-La-BA has a well-developed pore structure and abundant adsorption sites. The surface area of BET is 75.46 m2/g and the pore size is mostly at 1.84 nm, indicating that it is a composite porous material with abundant microporous structure. The presence of La on biomass ash and the charge property of CS-La-BA were determined by XRD and zeta potential, and the adsorption mechanism of CS-La-BA on phosphate, including precipitation, electrostatic adsorption, ligand exchange, and complexation mechanism, was revealed by FTIR and XPS. The effects of pH, temperature, adsorbent dosage, initial phosphorus concentration, adsorption time, and coexisting ions on the phosphorus uptake performance of CS-La-BA were discussed. The adsorption experiment results show that the phosphorus removal rate of CS-La-BA can reach 95.6%. Even after six desorption and regeneration experiments, the phosphorus removal rate still reaches 68.13%, which indicates that CS-La-BA has good phosphorus adsorption performance and desorption and regeneration capacity. The phosphorus adsorption process of CS-La-BA conforms to the Freundlich isotherm adsorption equation and general-order kinetic model. The internal diffusion of the adsorption process is dominant, and the maximum adsorption capacity is 31.73 mg/g (25 ℃). Thermodynamic experiments show that the adsorption process of phosphorus by CS-La-BA is a spontaneous entropy increase process.

Preparation of lignite-loaded nano-FeS and its performance for treating acid Cr(VI)-containing wastewater.

In this study, lignite-loaded nano-FeS (nFeS@Lignite) was successfully prepared by ultrasonic precipitation, and its potential for treating acid Cr(VI)-containing wastewater was explored. The results showed that the 40--80-nm rod-shaped nFeS was successfully loaded onto lignite particles, and the maximum adsorption capacity of Cr(VI) by nFeS@Lignite reached 33.08 mg∙g-1 (reaction time = 120 min, pH = 4, temperature = 298.15 K). The adsorption process of Cr(VI) by nFeS@Lignite fitted the pseudo-second-order model and the Langmuir isotherm model, and thermodynamic results showed that the adsorption process was an endothermic process with an adsorption enthalpy of 28.0958 kJ·mol-1. The inhibition intensity of coexisting anions on Cr(VI) removal was in the order of PO43- > NO3- > SO42- > Cl-, and the increase of ionic strength resulted in more pronounced inhibition. Electrostatic adsorption, reduction, and precipitation were synergistically engaged in the adsorption of Cr(VI) by nFeS@Lignite, among which reduction played a major role. The characterization results showed that Fe2+, S2-, and Cr(VI) were converted to FeOOH, S8, SO42-, Fe2O3, Cr2O3, and Fe(III)-Cr(III) complexes. This research demonstrates that nFeS@Lignite is a good adsorbent with promising potential for application in the remediation of heavy metal-contaminated wastewater.

Study on the Preparation of Nano-FeS Loaded on Fly Ash and Its Cr Removal Performance.

Chromium has been considered as one of the most hazardous heavy metals because of its strong and persistent toxicity to the ecosystem and human beings. In this study, fly ash-loaded nano-FeS (nFeS-F) composites were constructed with fly ash as the carrier, and the performance and mechanism of the composites for the removal of Cr(VI) and total chromium from water were investigated. The composite was characterized by X-ray diffraction and transmission electron microscopy. The effects of fly ash size, molarity of FeSO4, and flow rate of FeSO4 solution on the removal of Cr(VI) and total chromium were investigated by a single factor experiment. The interaction of various factors was studied by the Box-Behnken response surface methodology. The optimum conditions of removal of Cr(VI)and total chromium by nFeS-F were determined. The results show that ① the optimal preparation conditions for nFeS-F were an FeSO4 concentration of 0.45 mol/L, a fly ash particle size of 120-150 mesh, and a flow rate of 0.43 mL/s.② The response surface model provides reliable predictions for the removal efficiencies of Cr(VI) and total chromium.③ The removal efficiencies of Cr(VI) and total chromium were 92.87 and 83.53%, respectively, under the optimal preparation conditions by the experimental test. This study provides an effective method for the removal of Cr(VI) and total chromium.

Dynamic experiments of acid mine drainage with Rhodopseudomonas spheroides activated lignite immobilized sulfate-reducing bacteria particles treatment.

Aiming at the problem that the treatment of acid mine drainage (AMD) by sulfate-reducing bacteria (SRB) biological method is susceptible to pH, metal ions, sulfate and carbon source. Lignite immobilized SRB particles (SRB-LP) and Rhodopseudomonas spheroides (R. spheroides) activated lignite immobilized SRB particles (R-SRB-LP) were prepared using microbial immobilization technology with SRB, R. spheroides and lignite as the main substrates. The dynamic experimental columns 1# and 2# were constructed with SRB-LP and R-SRB-LP as fillers, respectively, to investigate the dynamic repair effect of SRB-LP and R-SRB-LP on AMD. The mechanism of AMD treated with R-L-SRB particles was analyzed by scanning electron microscopy (SEM), fourier transform infrared (FTIR) spectrometer and low-temperature nitrogen adsorption. The result showed that the combination of R. spheroides and lignite could continuously provide carbon source for SRB, so that the highest removal rates of SO42-, Cu2+ and Zn2+ in AMD by R-SRB-LP were 93.97%, 98.52% and 94.42%, respectively, and the highest pH value was 7.60. The dynamic repair effect of R-SRB-LP on AMD was significantly better than that of SRB-LP. The characterization results indicated that after R-SRB-LP reaction, the functional groups of -OH and large benzene ring structure in lignite were broken, the lignite structure was destroyed, and the specific surface area was 1.58 times larger than before reaction. It illustrated that R. spheroides provided carbon source for SRB by degrading lignite. The strong SRB activity in R-SRB-LP, SRB can co-treat AMD with lignite, so that the dynamic treatment effect of R-SRB-LP on AMD is significantly better than that of SRB-LP.

Dynamic experiment on the treatment of acidic chromium-containing wastewater by lignite loaded nano FeS.

In terms of the problem of severe pollution to the ecological environment caused by the acidic chrome-containing wastewater produced in the tanning, electroplating, metallurgy, printing and dyeing and other industries, based on the good adsorbability, reducibility and other properties of heavy metals such as Cr(vi) by lignite and nano FeS, the lignite-loaded nano FeS adsorbing material (nFeS-lignite) was prepared by ultrasonic precipitation method. NFeS-lignite and lignite were used as fillers to construct 1# and 2# dynamic columns to carry out the dynamic treatment experiment of acidic chrome-containing wastewater. And nFeS-lignite and lignite were characterized by XRD, SEM and EDS to explore the regularity, long-acting properties and removal mechanism of acidic chrome-containing wastewater treated by NFeS-lignite and lignite. The results indicate that: ① during 25 days of operation, the average removal percentages of Cr(vi) in the 1# and 2# dynamic columns are 71.6% and 53.1%. The average removal percentages of total chromium in 1# and 2# dynamic columns are 54.4% and 28.8%, and the average effluent pH of 1# and 2# dynamic columns is 5.3 and 7.3. ② According to XRD, SEM, EDS and FTIR analysis, the reducing groups in the structure of nFeS-lignite, such as -CH3, -CH2, C-O and Ar-OH, participate in the reaction and are oxidized to C[double bond, length as m-dash]C, C[double bond, length as m-dash]O and other groups. A large number of sediment crystals appeared on the particle surface, and new diffraction peaks such as FeOOH, Cr(OH)3 and Cr2S3 appeared at the same time, indicating that after Cr(vi) was reduced to Cr(iii), it would be fixed on the surface of nFeS-lignite in the form of precipitation such as hydroxide and sulfide.

Study of the preparation of Maifan stone and SRB immobilized particles and their effect on treatment of acid mine drainage.

The problems of acid mine drainage (AMD) in coal mine acidic wastewaters arise from a range of sources, including severe pollution with heavy metals and SO4 2- and difficulties during treatment. Based on the ability of Maifan stone to adsorb heavy metals and the dissimilatory reduction of SO4 2- by sulfate-reducing bacteria (SRB), Maifan stone-sulfate-reducing bacterium-immobilized particles were prepared via immobilization techniques using Shandong Maifan stone as the experimental material. A single factor experiment was used to investigate the influences of the dosage of Maifan stone, the particle size of Maifan stone and the dosage of SRB on the pH improvement effect and the removal rates of SO4 2-, Fe2+ and Mn2+. The Box-Behnken response surface method was used to determine the optimal preparation conditions for the Maifan stone and SRB immobilized particles in accordance with the ion removal rate and pH improvement effect when dealing with AMD. The results show that: (1) the optimal preparation conditions for Maifan stone synergistic SRB immobilized particles are determined by single factor experiment: the dosage of Maifan stone is 5 g, the particle size of Maifan stone is 0.075-0.106 mm, and the dosage of SRB is 25 mL per 100 mL; the removal rates of SO4 2-, Fe2+ and Mn2+ from AMD by the Maifan stone and SRB immobilized particles prepared under these conditions were 92.22%, 95.41% and 86.05%, and the pH was increased from 4.08 to 7.45. (2) From the variance analysis of the response surface model, it can be seen that the model effectively predicts the SO4 2- removal rate, Fe2+ removal rate, Mn2+ removal rate and pH change. (3) After further optimization using the response surface method, the optimal preparation conditions of Maifan stone and SRB immobilized particles are determined as follows: Maifan stone dosage is 5 g, Maifan stone particle size is 0.075-0.106 mm, and SRB dosage is 25 mL per 100 mL. Through experiments, the removal rates of SO4 2-, Fe2+ and Mn2+ from AMD by the Maifan stone and SRB immobilized particles prepared under these conditions were 92.12%, 95.93% and 87.14%, respectively, and the pH was increased from 4.08 to 7.49.

Experimental study of the remediation of acid mine drainage by Maifan stones combined with SRB.

The problems of acid mine drainage (AMD) in coal mine acidic wastewaters arise from a range of sources, including severe pollution with heavy metals and SO42- and difficulties during treatment. Based on the ability of Maifan stone to adsorb heavy metals and the dissimilatory reduction of SO42- by sulfate-reducing bacteria (SRB), Maifan stone-sulfate-reducing bacterium-immobilized particles were prepared via immobilization techniques using Shandong Maifan stone as the experimental material. The effects of Maifan stones containing SRB on mitigating AMD were investigated by constructing Dynamic Column 1 with Maifan stone-sulfate-reducing bacterium-immobilized particles and by constructing Dynamic Column 2 with SRB mixed with Maifan stones. By the use of adsorption isotherms, adsorption kinetics, a reduction kinetics model and X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies, the mechanism by which Maifan stone-sulfate-reducing bacterium-immobilized particles mitigate AMD was revealed. The results showed that the total effect of Maifan stone-sulfate-reducing bacterium-immobilized particles on AMD was better than that of biological Maifan stone carriers. The highest rates for the removal of Fe2+, Mn2+, and SO42- in AMD were 90.51%, 85.75% and 93.61%, respectively, and the pH value of the wastewater increased from 4.08 to 7.64. The isotherms for the adsorption of Fe2+ and Mn2+ on Maifan stone-sulfate-reducing bacterium-immobilized particles conformed to the output of the Langmuir model. The adsorption kinetics were in accordance with Lagergren first-order kinetics, and the kinetics for the reduction of SO42- conformed to those of a first-order reaction model.

Adsorption behaviors and mechanisms of Cu2+, Zn2+ and Pb2+ by magnetically modified lignite.

The study aims to solve the problems of limited capacity and difficult recovery of lignite to adsort Cu2+, Zn2+ and Pb2+ in acid mine wastewater (AMD). Magnetically modified lignite (MML) was prepared by the chemical co-precipitation method. Static beaker experiments and dynamic continuous column experiments were set up to explore the adsorption properties of Cu2+, Zn2+ and Pb2+ by lignite and MML. Lignite and MML before and after the adsorption of heavy metal ions were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectrometer (FTIR). Meanwhile, the adsorption mechanisms of Cu2+, Zn2+ and Pb2+ by lignite and MML were revealed by combining the adsorption isotherm model and the adsorption kinetics model. The results showed that the pH, adsorbent dosage, temperature, initial concentration of heavy metal ions, and contact time had an influence on the adsorption of Cu2+, Zn2+ and Pb2+ by lignite and MML, and the adsorption processes were more in line with the Langmuir model. The adsorption kinetics experiments showed that the adsorption processes were jointly controlled by multiple adsorption stages. The adsorption of heavy metal ions by lignite obeyed the Quasi first-order kinetic model, while the adsorption of MML was chemisorption that obeyed the Quasi second-order kinetic model. The negative ΔG and positive ΔH of Cu2+ and Zn2+ indicated the spontaneous and endothermic nature reaction, while the negative ΔH of Pb2+ indicated the exothermic nature reaction. The dynamic continuous column experiments showed that the average removal rates of Cu2+, Zn2+ and Pb2+ by lignite were 78.00, 76.97 and 78.65%, respectively, and those of heavy metal ions by MML were 82.83, 81.57 and 83.50%, respectively. Compared with lignite, the adsorption effect of MML was better. As shown by SEM, XRD and FTIR tests, Fe3O4 was successfully loaded on the surface of lignite during the magnetic modification, which made the surface morphology of lignite coarser. Lignite and MML removed Cu2+, Zn2+ and Pb2+ from AMD in different forms. In addition, the adsorption process of MML is related to the O-H stretching vibration of carboxylic acid ions and the Fe-O stretching vibration of Fe3O4 particles.