Integrated Treatment of Mining Dam Wastewater with Quaternized Chitosan and PAN/HPMC/AgNo3 Nanostructured Hydrophylic Membranes

This study was developed a novel nanostructured membrane by electrospinning process, from polyacrylonitrile (PAN) modify by hydroxypropyl methylcellulose (HPMC) polymers containing silver nitrite (AgNO3), to be used as a filter in an integrated wastewater dam treatment process to reuse it as drinking water. Different formulations (108 samples) were electrospun from PAN and (0, 5, 10 w%) HPMC and (0, 0.5, 1 w%) solutions to selected a more efficient formulation in water disinfection and higher hydrophilic character of the membrane to flow performance in the wastewater treatment. The PAN and HPMC phases in membranes were characterize by infrared spectroscopy and thermogravimetric analysis. The nanostructured membranes were characterized by Scanning electron microscopy and the fibers had a diameter between 251 ± 58 and 306 ± 49 nm. The presence of HPMC and AgNO3 in membrane formulation endows superhydrophilicity and permeability increase which up to 21,151 ± 445 L⋅m−2 Permeability h−1. After filtration process with PAN/HPMC/AgNO3, all the tested water potability indexes were achieved. The primary treatment, using quaternized chitosan reduced the turbidity parameter from 19,000 Nephelometric turbidity units (NTU) to 14 NTU, and after filtration with nanostructured membrane, to levels was below 1 NTU and pathogenic potential removed (Total Coliform and Escherichia coli). The results of this study indicated that the hydrophilic nanostructured membranes PAN/10% HPMC/1% AgNO3 have adequate properties to potential wastewater treatment mining for reuse. It’s give a sustainable strategy for managing wastewater which should be reduce the volume of water in the tailing’s dams and contributes to increasing the stability of dams and reducing risks with catastrophic environmental impact.


Introduction
Due to its high potential of environmental impacts and the repeated accidents of major proportions, the mining sector, in Brazil and worldwide, increasingly lives with socioenvironmental conflicts. Dam failure has always been treated as a low-probability event, even though it displays potentially catastrophic effects. However, in the last 20 years, the number of tailings dam failures has doubled worldwide [1]. Accidents like the gold tailings dam at Mount Polley, Canada, in 2014 produced a massive spill of contaminants. In Brazil, a Samarco accident in 2015 with 19 deaths and the release of 60 million m3 of tailings, and an accident at Mineradora Vale in the city of Brumadinho in 2019 with 275 deaths [2][3][4]. Among the main causes of tailings dam failures are infiltration, erosion, and excess water in the dam which causes overtopping [3]. Preventive actions such as controlling the volume of water which is stored in the reservoir of a dam shall contribute to reduce infiltration, erosion processes, pressure on the dam and the possibility of overtopping [3,5].
Therefore, wastewater treatment stored in reservoirs and their subsequent reuse have been increasingly recognized as sustainable strategies to decrease stored water volume, thus contributing with the dam risks proper management. Water reuse has direct and positive relationship with its local availability, and it can be considered one of the current and essential strategies to enable new water sources for the industry, consequently translating itself into an immense added value concerning the environment and sustainable development [5].
Mining wastewater treatment use processes such as decantation basins, flotation, coagulation/flocculation/ decantation to remove suspended solids and dissolved material. However, in order to reach potability standards for human consumption, filtration and disinfection technologies must be inserted in the process to retain bacteria, viruses and other suspended materials, thus ensuring this water is framed in specific drinking standards.
The wastewater filtration and disinfection using membrane technology exhibit several advantages, such as speed of wastewater treatment, use of small construction areas, with compact plants, it presents easy automation potential and it enables future expansions through modules [6][7][8][9]. Present high rejection rates, being able to filter particles between 0.0007 and 0.005 μm. And are also characterized by having high porosity, high specific surface area and spider web-like interconnected structure [10,11].
Electrospinning offers profuse benefits and presents itself as an innovative and practical method, due to its flexibility concerning nanostructured membrane formulation. Membranes can be easily functionalized by combining various modified polymers, as well as their morphology can be designed to achieve various desirable effects [12][13][14]. Is lowcost process, facile approach, able to synthesize materials in the form of fabrics with good tensile strength and welldefined porous structure. The dimensions of the fibers can be controlled by process parameters such as, applied voltage, feeding rate and collector distance [15][16][17][18].
Hydrophilicity, porosity and pore thickness are essential properties in the development of a nanostructured membrane for application in wastewater treatment [19,20]. The combination of polymeric materials is widely used to achieve hydrophilic properties in membranes. Polyacrylonitrile (PAN) is one of the commonly used polymers for electrospinning, it displays a good mechanical strength and chemical stability, having the characteristic to produce ultrafine and homogeneous fibers. However, membranes from PAN exhibit a hydrophobic nature and poor wettability, which reduce filtration performance [21]. The wettability of the membrane could be modify by blend with hydrophilic polymers, specifically to PAN membranes through the incorporation of Hydroxypropyl methylcellulose (HPMC), which increase the wettability and contributes to reduce the scale and improve the permeability of the membrane throughout the filtration [11,22].
This paper focuses on the use of nanostructured membranes for wastewater purification purposes. It describes the methodology to improve hydrophilicity and strength of PAN membranes by addition of hydroxypropyl methylcellulose (HPMC) and Ag to remove pathogenic microorganism, considering to pretended application. The morphologies and properties of the membranes electrospun were investigated by Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectrum (FTIR), while the heat behavior by Thermogravimetric measurements (TGA), water contact angle, mechanical properties of the nanofiber membranes, and permeability of membranes are evaluated too. According to the above test results was proposed the PAN/10% HPMC/1% AgNO 3 nanostructured membrane to the potential wastewater mining integrated treatment process which attend the guidelines of the World Health Organization (WHO) for drinking water [23].

Preparation of Nanostructured Membrane
The electrospinning of the solutions was performed using a device (Instor -Projects and Robotics, Brazil). The solutions were placed in a 5 mL disposable plastic syringe, equipped with a stainless-steel needle (N724-24G/2"/3, Hamilton) and horizontally connected to a flow control pump. The nanofibers were collected on a 100 × 100 mm metal covered with aluminum foil Electrospinning was carried out with a relative humidity of (55 ± 5) % at a temperature of (20 ± 1)°C [24,25].
By crosslinking the inserted factors (Table 1), a total number of 108 samples was defined. The influence of electrospinning parameters (Flow rate, Tip-to-collector distance, Electrical field) and the addition of HPMC and AgNO 3 on the morphology and mean fiber diameter of the was investigated [26]. The criterion used to establish the electrospinning parameters for each solution was the parameter that 1 3 produced fibers with smaller mean diameter. Thus, from the experimental planning, a sample was chosen for the analyzed concentration. The fibers diameters were determined using the software SizeMeter, four SEM micrographs were analyzed for each membrane sample, and the diameters of 60 fibers (15 for each image) were measured and calculated at their average values.

Fourier Infrared Transform Spectroscopy (FTIR)
The infrared spectra were recorded on a Shimadzu model IR Prestige-21 spectrophotometer. The spectra were obtained in the range between 400 and 4000 cm −1 accumulating 40 scans with resolution of 1 cm −1 .

Thermogravimetric Analysis (TGA/DTG) and Mechanical Properties
Thermogravimetric Analysis (TGA/DTG) were performed in a TGA Q5000 (Moldulated) TA Instruments. The samples (12 mg) were placed in Platinum-HT pan and heating rate 10.00 °C/min to 950.00 °C in dynamic atmosphere of nitrogen (50 mL/min).
The Dynamic mechanical analysis (DMA) measurements were carried on a DMA Q800 (TA Instruments). Rectangular specimens with dimensions of 17 × 5 mm and thickness between 0.04 and 0.07 mm were tested in tensile mode. The measurement was carried out at 25 °C in the Ramp force 1.0000 N/min to 18.0000 N. Three specimens were tested for each nanofiber membranes.

Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS)
The morphology of the electrospun membranes was investigated via scanning electron microscopy (SEM, JEOL-JSM-6390-LV, 18 kV). Membrane images obtained by SEM were used to: (1) measure the fiber diameter of 108 samples; (2) measure the thickness of the membranes through the image of the membranes cross section; and (3) analyze the membranes morphology before and after treatment wastewater.
X-ray photoelectron spectroscopy (XPS) analyzes were performed in an ultra-high vacuum environment (pressure: 10-9 mbar) (Scienta Omicron, Germany) using a non-monochromatic X-ray source, Al anode (Kα = 1486.7 eV), with 20 mA emission power and 15 kV voltage. The survey spectra were obtained with 160 eV analyzer step energy and 1 eV acquisition step. High-resolution spectra were collected in the Ag 3d, C 1 s and N 1 s regions with 20 eV analyzer step energy and − 0.05 eV acquisition step.

Porosity Calculation
The porosity of a fibrous membrane is characterized by the amount of empty spaces in its total volume [20]. The tests to assess the membranes porosity were carried out using samples of the membranes manufactured at nine different concentrations and their porosity was calculated using Eq. (1).
In order to assess the membrane volume, the samples were cut to the size of (2 × 2 cm) corresponding to an area of 4 cm 2 . To obtain the thickness, the membranes were frozen in liquid nitrogen and fractured. The cross-sectional images of each membrane were obtained by SEM and measured using the SizeMeter software [27]. The volume occupied by the fibers was determined through the product of the mass by the relative density of each membrane. The samples were weighed and the relative density was calculated from the proportion of relative mass of each component (PAN (1.184 g/cm 3 ), HPMC (1.26 g/cm 3 ) and AgNO 3 (4.35 g/ cm 3 ), considering the concentration of each sample. All procedures were performed three times for each sample, and then their average was reported.

Measurement of Water Contact Angle
Water contact angle and underwater oil contact angle measurements are performed using a contact angle.
The water contact angle analysis of PAN membranes modified with HPMC and AgNO 3 were performed using a contact angle instrument Sinterface, model PAT-1 M, operated at temperature of (24 ± 1) °C using 8.8 μL distilled water droplets in all measurements and limit time of experiment 60 s.

Permeability of Nanostructured Filtering Membranes
In the permeability study, the membranes were cut in circular shape with the aid of a template, their useful area was measured at 10.75 cm 2 , and inserted into the permeation cell on a porous support. Then, the cell was closed and connected to the system. The complete system consists of a feed tank of approximately 4 L, a pressure gauge at the outlet of the permeation cell, a pressure regulating valve and a pump to allow recirculation of the feed solution. The system operates continuously, with concentrate and permeate recycling. Ultrapure water was used, and the pressure curve vs. permeate flow was obtained for operating pressures of 0.3; 0.4; 0.5 bar for 1 h. Three measurements of the permeate flow were performed for each of the defined pressures, and the results were obtained following Eq. (2) [28].

Primary Wastewater Treatment
With regard to the primary treatment process for bauxite tailings wastewater, it is subdivided into 03 stages, coagulation, flocculation and decantation (Fig. 1A) The analyses related to these steps were performed in according to the methodology described by in (previous) work [29,30]. Mining wastewater samples were subjected to primary treatment in a Jar Test equipment (Mod. 218/6, Nova Ética Comp. Ltda, Brazil), using as a coagulant, the biodegradable polymer quaternized chitosan. The treatment parameters were defined with a dosage of 5 mg/L of quaternized chitosan, rotation speed in the coagulation (fast mixing) 150 rpm for 1 min, 40 rpm for 10 min in the flocculation (slow mixing) and 0 rpm for 20 min for decanting. After decanting the samples were collected 6 cm below the water surface in the jar.

Secondary Wastewater Treatment
In order to evaluate the performance of electrospun membranes in reaching the potability parameters for water after primary treatment, the tests were carried out for nine models of membranes previously which were selected according to their fibers with smaller mean diameter among the 108 membranes defined in the experimental design (Table SI1).
A filtration (Fig. 1B) system made of stainless steel was used to carry out the analysis. With aid of a template, the membranes were cut and superimposed on a porous steel mesh that was coupled inside the equipment, which was closed. The water was inserted through one of the holes in the equipment in order to pass through the membrane and be collected through the other hole in the system. The filtered material samples were collected in specific bottles and identified. Three collections of 1 L of filtered wastewater were performed for each membrane sample.

Characterization of Wastewater Samples Before and After Treatments Steps
The wastewater samples were collected in three stages of the treatment process, at the Brazilian Aluminum Company (CBA)/Votoratim tailings dam (Mirai Mining Unit, Brazil), after the primary treatment process and after the secondary treatment (filtration). The parameters considered as performance indicators for treatment and control systems were analyzed. For samples collected in the three step phases of the process, analysis was carried out on 13 parameters and compared according to their limits established by the WHO Guidelines.

Analyses of Aluminum, Total Coliforms, Escherichia coli, Conductivity, Iron, Manganese, Dissolved oxygen, pH, Suspended Solids, Dissolved Solids and Turbidity of Wastewater Samples Before and After Treatments Steps
The determination of Metals (Aluminum, iron, manganese) was performed: Digestion of 100 mL of sample with concentrated nitric acid and hydrochloric acid 1: 1 in a heating plate with a temperature not exceeding 90 °C. Bulk sample for 100 mL flask and taken to the measuring equipment. Equipment used: Optima 7300 DV ICP Spectrometer (ICP with Plasma flame). Equipment with validation and performance testing through Perkin Elmer. The determination of conductivity, dissolved oxygen and pH was performed from direct reading in the sample on electrodes for conductivity, dissolved oxygen and pH respectively. The equipment used was Digimed DM-32 Conductivometer with RBC calibration by Visomes, Digimed Oximeter with RBC calibration by Evagon and pH Meter Digimed DM-22 with RBC calibration by Visomes. The solids were determined according to the Standard Methods for the Examination of Water and Wastewater 23rd Edition-Method 2540 B, C and F. For total solids, an empty porcelain capsule is placed in a muffle furnace for 1 h at 550-600 °C and 1 more hour in the desiccator, then weighed in Analytical Balance (P 0 ). The homogenized sample is introduced into the capsule that is kept in an oven for 3 days at 103-105 °C, placed again in a desiccator for 1 h and then weighed (P 1 ). Total solids are numerically calculated by the equation TS = P 1 -P 0 /V, where V is the sample volume. The fractions of suspended solids were determined using a glass fiber membrane with 1.2 µ pores as a filter and placed in a muffle furnace for 15 min at 550-600 °C and another 1 h in the desiccator, then weighed on a scale. Analytical (P 0 ). The sewage samples are vacuum filtered and the filter containing the suspended residue is then taken to an oven for 1 h at 103-105 °C, then stored in a desiccator for 1 h and weighed on an analytical balance (P 1 ). The value of suspended solids is calculated by the equation SS = P 1 -P 0 /V, where V is the sample volume. Dissolved solids are calculated by difference, using the equation DS = TS-SS. For the determination of microbiological parameters, Total Coliforms and Escherichia coli, the Quanti-Tray/2000 technique was used (IDEXX Laboratories Inc., Westbrook, ME, USA). This technique has 95% confidence and is performed according to the following steps: First the Colilert reagent is added in 100 mL of water sample and stirred. Then the sample is poured into a specific tray and sealed in a Quanti-Tray Sealer model 2×. The tray is placed in an incubator at 35 °C for 24 h. After 24 h the tray is removed and the yellow wells are counted, which is positive for total coliforms. For the detection of E. coli, the tray is transferred to a cabinet with UV light in a dark environment and counting the positive wells. The determination of the turbidity of the samples was made through direct reading in glass cuvettes of the Digimed DM-TU Turbidimeter equipment with calibration Traceable through Visomes.
The influence of the parameters (flow rate, tip-collector distance, electric field) of the electrospinning process on the diameters and morphology of the resulting fibers was studied. In all the concentrations there was a slight increase in the average of the diameters of the fibers with the increase of the flow and a decreasing trend with the increase of the applied electric field. The average fiber diameter of PAN/10% HPMC/1% AgNO 3 increased from 320 ± 24 to 402 ± 43 nm with an increase in the flow rate and decreased from 376 ± 70 to 346 ± 32 nm with an increase in the electric field. The same occurs with PAN/1% AgNO 3 fibers, which went from 289 ± 19 to 383 ± 29 nm and from 341 ± 48 to 331 ± 65 nm, with an increase in flow rate and electric field, respectively. Similar results have been reported for the electrospinning of polycaprolactone [31] and polyimides [26]. In relation to the flow, the increase generally results in thicker fibers due to the greater mass in the formation of the fibers. The impact of the electric field is explained by the result of the greater stretching of the jet that produces finer fibers. For the parameter tip-collector distance, the average diameter of the fibers did not present a trend and varied with the increase of the tip-collector distance. In the electrospinning process, greater distances favor the electrospinning jet solvent to vaporize before the solidified fiber strand reaches the metallic collector, thus producing finer fibers. However, if this distance exceeds an ideal limit, the electric field may be reduced and the fiber will elongate less, resulting in a larger diameter. Figure 2 shows the SEM micrographs of the selected membranes. One can see that the surface of the nanofibers is relatively smooth and few defects are found. The fibers of the membranes presented not significant variation concerning average diameter, that are between 251 ± 58 nm and 306 ± 49 nm. Fig. SI1 shows the SEM micrographs of the . With a flow rate of 1 mL⋅h −1 and an electric field of 20 kV, the membranes showed defects in the formation of fibers, such as the appearance of beads. Reducing the electric field to 17 kV, the membranes stopped showing defects, however the average diameters were between 380 ± 63 and 464 ± 57 nm. Fibers without defects and with the smallest diameters (347 ± 52 and 281 ± 65 nm), were obtained by reducing the flow rate to 0.5 mL⋅h −1 . These results show an improvement in the spinning capacity of the fibers due to the change in the process parameters. In this case, the reduction in the flow rate and the electric field resulted in membranes without defects and a significant reduction in diameter. Through the experimental planning it was possible to optimize the electrospinning process, thus allowing the development and selection of membranes with intended morphology for application in wastewater treatment.

Membranes Porosities
The porosity of the membranes was measured to investigate the process optimization effect by modifying the electrospinning parameters determined in the experimental design. Figure 3 shows the variation in the porosity of electrospun membranes in relation to the diameters of their fibers and the results show high porosity and little variation, between 89.17 ± 1.20 and 91.60 ± 1.22%. The factor with the greatest influence on membrane porosity is the fiber diameters resulting from the electrospinning process [27]. In this case, as expected, the increase in porosity is consistent with the reduction in fiber diameter. Among the studied membranes, PAN/1% AgNO 3 membrane, presented the highest porosity (91.60 ± 1.22%) and the smallest fiber diameter (251 ± 58 nm), while the PAN/10% HPMC membrane obtained the lowest porosity (89.17 ± 1.20%) and the largest fiber diameter (306 ± 49 nm). As observed in the morphological analysis of the membranes, the electrospinning parameters (flow, tip-collector distance, electric field) strongly influenced the diameters of the membrane fibers, which are responsible for the differences in porosity presented. The high porosity presented by membranes formulated with PAN, modified with HPMC and AgNO 3 are an important property for wastewater treatment applications, together with the fiber diameter largely determine the penetration of water into the membrane and effectively control the retention rates of solids in the process filtration. High porosity, small pore size and large cumulative pore volumes provide several microporous channels that can significantly increase the flow of water and at the same time ensure the retention of fine particles, which is beneficial and favorable to increase performance and energy savings, fundamental properties in the wastewater treatment [32].

PAN-HPMC Phase Characterization in Membranes by Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and Thermogravimetric Analysis (TGA)
The FTIR spectra of the nanostructured membranes of PAN and PAN/10% HPMC/1% AgNO 3 are shown in Fig. 4. The PAN membrane presents the characteristic signals at 2870-2930 cm −1 signals could be associated to the stretching (γ) of the group's CH and CH 2 and to 2243 cm −1 to vibrations of the γC≡N groups.
The signal at 1454 cm −1 is attributed to methylene (CH 2 ) bending and at 1253 cm −1 could be identify the C-N stretching [15,33]. The spectrum of the PAN/10% HPMC/1% AgNO 3 membrane (Fig. 4), show a characteristic absorption at 3468 cm −1 due to -OH of HPMC and at 2926 cm −1 overlaps absorptions of γCH 2 and δCH 2 characteristic of the both phases (PAN and HPMC) present in the nanofibers.
The existence of dipole-dipole interactions between the -OH and C≡N polymer groups in the PAN and PAN/10% HPMC/1% AgNO 3 membranes affected the intensity ratio of the C≡N 2243 /CH 2293 signals. The intensity ratio in the PAN, 0.82, change to 1.11 when the intensity ratio in the PAN, 0.82, went to 1.1 after the membranes were added with 10% HPMC and 1% AgNO 3 . Additionally, 1078 signal due to the CO present in the HPMC structure shows a slight displacement up to 1070 cm −1 and the CO 1070 /CH 1454 intensity ratio varies from 1.05 in the PAN to 1.17 in the PAN/10% HPMC/1% AgNO 3 membrane. The FTIR analysis of the PAN/1% AgNO 3 membrane, no changes in the spectrum were observed with the presence of silver in the PAN nanofibers [34,35]. This suggests an intramolecular homogeneity of the electrospun membranes, where the properties of the fibers are enhanced after being modified with HPMC and added with AgNO 3 .
In Fig. 5A, XPS survey spectra of PAN/10% HPMC/1% AgNO 3 membrane identified the presence of C, O, N and Ag elements on the surface of the fibers as expected.
The XPS spectra of silver atoms does not yield a single photoemission peak, but a small spaced doublet caused by the spin-orbit splitting of the d-orbitals The Ag 3d spin orbits (Fig. 5B) are Ag(3d5/2) 368.60 eV and Ag(3d3/2) 374.62 eV, characteristic of metallic silver presences in membrane nanofibers [36].
The thermogravimetric behavior of PAN membrane formulations could be observed in (Fig. 6). The PAN/10% HPMC membrane from these polymer blend presented a degradation onset temperature (T onset ) at 282 °C and maximum degradation rate temperature (T max ) in 284.6 °C. These degradation temperatures were lower than PAN membrane (T onset 291 °C, T max 297 °C), behavior that could be associated to interaction between HPMC and PAN polymer phases. The membranes PAN/1% AgNO 3 and PAN/10% HPMC/1% AgNO 3 show similar thermal behavior in presence of 1% AgNO 3 . Their second thermal degradation in both membranes show a weight loss at 378 °C t lower temperatures of PAN and PAN/10%HPMC, which was consequence to AgNO 3 presence [37,38]. The thermogravimetric behavior and Infrared spectroscopies characterization support the compatibility of PAN/10% HPMC/1% AgNO 3 formulation which introduce a positive impact on the membrane properties as wettability and permeability.

Mechanical Behavior of Membranes
The tensile stress and the deformation of the membranes are analyzed to assess the mechanical behavior that these could have due to the transmembrane pressure during filtration process [39].
The stress-strain curves of PAN and PAN/10% HPMC/1% AgNO 3 electrospun membranes (Fig. 7) obtained employed static collector with randomly oriented nanofibers. The addition of HPMC (10%) improved tensile strength of PAN membrane probability due to the stiffness provided to the

Wettability of PAN Membranes Modified with HPMC and AgNO 3
The adding HPMC to PAN was to increase hydrophilicity (wettability) in order to enhance permeability and decrease the tendency of fouling on the membrane during the filtration process. The wettability results of the membranes were appreciated from the contact angle measured in samples (A) PAN, (B) PAN/0.5% AgNO 3 and (C) PAN/1% AgNO 3 , which showed a reduction in the contact angle due to the insertion and increased concentration of AgNO 3 (Fig. 8). In samples PAN/5% HPMC; PAN/5% HPMC/0.5% AgNO 3 ; PAN/5% HPMC/1% AgNO 3 ; PAN/10% HPMC; PAN/10% HPMC/0.5% AgNO 3 ; PAN/10% HPMC/1% AgNO 3 , the spreading speed of the applied water drop did not allow the measurement of the contact angle, and this is characteristic of superhydrophilic surface.
By adding 0.5% of AgNO 3 , it was possible to decrease the membrane contact angle from 116.18° (A) to 93.01° (B), and after the addition of 1.0% of AgNO 3 (C), there was an even more intense reduction of the contact angle to 37.01°. This fact may be related to the difference in porosity between membranes (A) 90.52 ± 1.25%; (B) 91.53 ± 1.26% and (C) 91.60 ± 1.22%, which can alter the surface contact between the fiber and the applied water drop. When comparing the diameter of the membrane fibers (A) 293 ± 57 nm; (B) 277 ± 63 nm and (C) 251 ± 58 nm, a reduction in the diameter of the fibers can be observed, which may have led to an increase in the contact surface and porosity. This fact can be observed in the studies by [38], in which the addition of silver particles to electrophilic membranes caused an increase in hydrophilicity in the membranes, as it reduced the thickness of the fibers that make up the membrane and consequently increased its porosity.
In membrane samples PAN/5% HPMC; PAN/5% HPMC/0.5% AgNO 3 ; PAN/5% HPMC/1% AgNO 3 ; PAN/10% HPMC; PAN/10% HPMC/0.5% AgNO 3 ; PAN/10% HPMC/1% AgNO 3 , the incorporation of HPMC was expected to make the membranes hydrophilic. However, this effect proved to be very intense and the measurements of the contact angle for all samples containing HPMC were not possible, because the propagation of the drop of water on the membrane surface was instantaneous, not providing enough time to measure the contact angle. The addition of HPMC, due to its hydrophilic nature, caused a significant reduction in the contact angle that started to tend to 0 (zero), characterizing the superhydrophilic membrane. The increase in hydrophilicity in the membranes is one of the objectives of this study, because through this property, membranes with high permeability and low incidence of encrustations can be obtained, which are fundamental characteristics for membranes used in filtration to wastewater treatment.

Permeability of Nanostructured Filtering Membranes
In a hydrophilic membrane, water molecules can be spontaneously absorbed on the membrane surface in the separation process, which favors increased flow and water permeability. The performance of the membranes in terms of permeability was obtained at 3 different pressures (0.3, 0.4 and 0.5 bar) and are shown in Fig. 9.
As all membranes have the same thickness and porosity range, the membrane permeability results show that the Recent research of electrospinning modified PAN membranes to use in water filtration applications were resumed in Table 2. The permeability analyzes were carried out through direct filtration, with distilled water and pressure of 0.5 bar.
The PNIPAM/PAN/TiO 2 and PAN/10% HPMC/1% AgNO 3 membranes presented similar morphologies and could be associated the membrane permeability performance to the structural characteristics and composition of the blends which have directly impact on the wettability of the membranes.

Wastewater Sample
The sample of mine wastewater collected (A-Gross) in the CBA/Votorantim tailings dam analyzed (Table 3) was characterized by suspended solids (4,693.50 mg/mL) and turbidity (19,000 NTU). These high rates did not allow the analysis of total coliforms and Escherichia coli, which were carried out after the primary and secondary stages of treatments.

Primary Wastewater Step Treatment
The primary wastewater step treatment with quaternized chitosan [29] reduce the turbidity index from 19,000 NTU to 14.73 NTU (Table 3), with an efficiency rate of 99.92%. After being modified through quaternization, chitosan starts to have a greater cationic character and due to its broader branched molecular architecture, it is possible to aggregate a greater number of colloidal particles. This has increased its efficiency in reducing turbidity, making this water suitable for filtering.

Second Wastewater Step Treatment
After filtering the A-Primary water, the membranes were dried, and prepared for SEM analyses. The micrograph (Fig. 10) shows suspended and colloidal particles adheres to the fibers and a layer is formed on the membrane surface.
In membranes PAN/0.5% AgNO 3 , PAN/5% HPMC/0.5% AgNO 3 , PAN/5% HPMC/1% AgNO 3 , and PAN/10% HPMC/0.5% AgNO 3 it is possible to observe empty spaces between the pores that were not completely filled by the retained solids, as well as polymeric fibers belonging to the membranes that were not covered. As shown in Fig. 10, the membranes after the wastewater treatment clearly shows a large amount of suspended particulate material that adheres to the surface of the membranes. The filtration of wastewater depends a lot on the quantity and size of the particles of contaminants present in Fig. 10 SEM images of nanostructured membranes after bauxite effluent filtration the water, which can contribute to the increase of fouling and reduce the life of the membrane. In this study, two factors contributed significantly to guarantee the performance of the wastewater treatment achieved by the membranes. The primary treatment, that significantly reduced the suspended solid particulate material of wastewater and the high hydrophilicity presented by the modified membranes that gave the membranes antifouling properties. Table 4 presents the results of the analysis of wastewater A-Primary before and after going through the second treatment step with PAN and PAN/HPMC/AgNO 3 membranes. To evaluate the results, the drinking water standards established by the WHO were considered. In general, the formulated membranes reduced virtually all tested parameters.
The microbiological parameters, Total Coliforms and Escherichia coli, which are used as indicators of treatment efficiency and fecal contamination, respectively, showed an absent result in all evaluated membranes. This result is in agreement with the researched literature [37], who report the high efficiency in bacterial removal presented by membranes in filtration processes.
Concerning aluminum, all results were below the established limit, with a maximum reduction of 0.324 to 0.0081 mg/L. Water conductivity was stable for all samples. In regard to iron, there was a non-uniform reduction similar to the other tested parameters. However, four results were above the maximum established limit. Although manganese is already below the limit after the primary treatment only, filtration efficiency of virtually all membranes was 50%.
Concerning the retention of suspended solids from the wastewater, all electrospun membranes obtained significant results, with a maximum reduction from 658.43 to 21.79 mg/L and removal efficiency of 95.78%. The retention of suspended solids is greatly due to the morphology of the membrane pores, which in this case are formed by a tangle of very thin overlapping fibers, granting the membrane a high contact surface, which favors the retention of most solid material present in the wastewater. This fact can be seen in the images of the membranes (Fig. 11) in which all membranes, after being used in filtration, had a large number of solids retained on the surface.
The relationship between these parameters, turbidity and suspended solids, can be seen in the results presented after the mining wastewater. When the results obtained are analyzed (Fig. 12) and the efficiency in filtration for the evaluated membranes is achieved, a trend in reducing these parameters can be seen.
The presence of particles of varying sizes suspended in water, such as clay, silt, finely divided organic matter, plankton and other microscopic organisms can make water look cloudy or muddy. These factors are considered to be the main causes of water turbidity. In the case of bauxite tailings, the main cause of high turbidity in are the clay particles present in the ore, which, when broken down in the beneficiation process, remain suspended in the water.
This integrated system, primary (quaternized chitosan) and secondary processes with PAN/10% HPMC/1% AgNO 3 nano-fiber hydrophilic membrane is effective in the process of filtering and framing water in the who drinking parameters.

Conclusions
Different PAN/HPMC/AgNO 3 composition were formulated and establish electrospinning parameters to obtain a nanostructured membrane. The PAN/10% HPMC/1% AgNO 3 membrane show higher hydrophilicity and high porosity. The morphologies were characterized by uniform fiber with average diameter between: 251 ± 58 and 306 ± 49 nm.

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These characteristics improved the permeability behavior (21,151 ± 445 L⋅m −2 ⋅h −1 ), reduced wastewater dam turbidity and eliminated the pathogenic microorganisms, Total Coliforms and Escherichia coli, obtaining a water with the characteristic parameters of drinking water. The efficiency of this membrane, added to the high flow rate, classifies it for potential use in integrated wastewater treatment processes, which can prevent the accumulation of large volumes of water in the dam and consequently its impact on stability, reducing the environmental risks of disasters.