Next Article in Journal
Unveiling the Motivational Factors behind Generation Z’s Conference Attendance for Sustaining Future Participation
Previous Article in Journal
Using the Life Cycle Approach for Multiobjective Optimization in the Context of the Green Supply Chain: A Case Study of Brazilian Coffee
Previous Article in Special Issue
Accelerating Electricity Generation and Cr (VI) Removal Using Anatase–Biochar-Modified Cathode Microbial Fuel Cells
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Sustainability
Volume 15
Issue 18
10.3390/su151813984
sustainability-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Efficient Organic Pollutant Removal by Bio/MNs Collaborating with Pseudomonas aeruginosa PAO1

by
Chengbin Zhang
1,2,
Qijun Wang
1,2,
Wenqing Xie
1,2,
Ye Wang
1,2,
Zitong Li
1,2 and
Guiping Ren
1,2,*
1
The Key Laboratory of Mineral Resources in Western China (Gansu Province), School of Earth Sciences, Lanzhou University, Lanzhou 730000, China
2
The Key Laboratory of Strategic Mineral Resources of the Upper Yellow River, Ministry of Natural Resources, Lanzhou 730000, China
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(18), 13984; https://doi.org/10.3390/su151813984
Submission received: 29 July 2023 / Revised: 2 September 2023 / Accepted: 18 September 2023 / Published: 20 September 2023
(This article belongs to the Special Issue Mineral and Microorganism Interactions for Sustainability)
Browse Figures
Review Reports Versions Notes

Abstract

:
Organic pollution is one of the main sources of environmental pollution, which poses a serious threat to the ecological environment and human health. In this study, we synthesized a composite material consisting of biochar-supported magnetite nanoparticles (Bio/MNs) and collaborated with Pseudomonas aeruginosa PAO1 (P. aeruginosa PAO1) to conduct a bio-chemical composite remediation approach for organic pollution. The results of the scanning electron microscope (SEM) and X-ray diffractometer (XRD) show that Bio/MNs composites have been prepared successfully. Under light conditions, the highest removal rate of organic pollution by Bio/MNs synergistic P. aeruginosa PAO1 reached 81.5%. Gradient experiments revealed a direct correlation between the removal rate of organic pollution and the dosage of P. aeruginosa PAO1, as well as the input of Bio/MNs, within a specific range. Moreover, due to the positively charged nature of organic pollution, its maximum removal rate reaches 98.6% at pH = 11, exhibiting a 1.76-fold increase compared to that at pH = 3. The experimental results show that the collaboration between Bio/MNs and P. aeruginosa PAO1 expedited the electron transfer rate and increased the generation of ·OH and O2−, consequently facilitating the efficient degradation of organic pollutants. These findings inspire Bio/MNs collaborative microorganisms for providing new methods for the green and sustainable removal of organic pollutants.

1. Introduction

Organic pollution constitutes a primary source of environmental contamination and a significant challenge for humanity [1,2]. Furthermore, organic pollution significantly contributes to water contamination, presenting a substantial menace to both the ecological environment and human health [3]. Taking methylene blue (MB) as an example, the exposure of individuals to MB can lead to symptoms such as nausea, vomiting, and respiratory distress. Prolonged exposure has the potential to induce carcinogenesis and genetic alterations [4,5]. Therefore, the effective removal of organic pollutants, such as MB, stands as an urgent necessity.
Universally, adsorption and degradation emerge as the predominant techniques for the removal of organic pollution [6]. Notable degradation approaches encompass photodegradation, ozone treatment, chemical oxidation, and others [7,8,9]. These methods have demonstrated significant advancements in the field of MB degradation. Nevertheless, problems endure concerning the efficiency of adsorption, production costs, and dye affinity [7]. In recent years, nanomaterials have shown great application prospects in the removal of dyes from wastewater due to their extensive surface area, high adsorption properties, low resistance to diffusion, and faster equilibrium rate [10,11]. The researchers successfully prepared new nano silver particles and poly (styryl-n-isopropylacrylamide-methacrylic acid) composite material, leading to the proficient adsorption and catalytic reduction of methylene blue [12]. Similarly, the photocatalytic performance of organic pollutants can be effectively improved by utilizing nano-scale zinc oxide (nZnO) due to its exceptional sensitivity to ultraviolet light [13]. Furthermore, the study indicates that iron oxides hold noteworthy promise in the decomposition of organic substances [14,15]. The heterogeneous semiconductor structure between the magnetite nanoparticles (MNPs) and ore particles increases the surface reactivity, resulting in a degradation rate of MB of up to 96% [16]. Notably, the semiconductor properties of MNPs also allow the photocatalyst to aggregate and oxidize the solution, increasing the durability of the catalyst and making it more efficient at degrading MB [17]. In addition, a BiFeO3/Fe3O4 catalyst was mechanically synthesized, which promoted the formation of electrons and holes due to the change in the band gap under light conditions and achieved the complete degradation of MB in 40 min [3]. However, single nanoparticles face the challenges of easy agglomeration, poor uniformity, and poor electrical conductivity, which will limit the degradation of MB [18]. Therefore, enhancing the dispersion of nanoparticles can facilitate the separation of electron–hole pairs, thus augmenting their photocatalytic efficiency in dealing with organic pollutants [2]. Based on this, it is imperative to identify an effective and cost-efficient dispersant capable of enhancing the degradation of organic pollutants by magnetite nanoparticles.
The biochar, being a highly porous material with abundant sources and a low cost, serves as an exceptional solid support substrate [19]. Furthermore, as a carbonaceous material, biochar possesses the ability to effectively sequester organic pollutants [20]. It is noteworthy that the exceptional electron supply capacity, electron mediating capacity, and electron acceptance capacity of biochar also contribute to its auxiliary degradation of organic pollutants [21,22]. Thus, the combination of biochar and degradable materials can achieve the efficient removal of organic pollutants [23,24]. For instance, studies have shown that carboxymethyl cellulose stabilized zinc oxide/biochar nanocomposites with a saturation adsorption capacity of 17.01 g/kg for MB [25]. Under ultraviolet irradiation, the removal rate of MB reached 83.1%. In addition, researchers synthesized biochar supported by nano-metallic silver particles through carbothermal synthesis. Because pine biochar promotes the separation of electron–hole pairs and enhances electron transfer, the maximum net degradation of MB reached 15.88 g/kg [26]. Moreover, Fe3O4/lignin nanoparticles loaded with biochar were employed for the degradation of MB, achieving a maximum removal efficiency of 621.52 mg/g [27]. These composites exhibit significant potential for the degradation of organic pollutants. However, the single composite material limits the continuous production of electrons [28,29]. Fortunately, it has been discovered that microorganisms with extracellular electron transport capabilities can generate and transfer electrons to external receptors through the surrounding medium. This novel finding presents a promising avenue for tackling environmental pollutants [30,31]. It was found that P. aeruginosa PAO1 is a typical extracellular respiratory bacterium, which interacts with anatase and has a maximum photocurrent density of 37.72 mA/cm2 [32]. In addition, studies have shown that mineral-microbial interactions have some potential in the treatment of organic pollution. The degradation of organic pollutants may be closely related to the microbial reduction of Fe(III) minerals [33,34]. Additionally, with the participation of electrogenic microorganisms, structural iron can undergo multiple redox reaction cycles to achieve sustainable reactive oxygen species (ROS) generation and organic degradation [34].
Organic pollution is an important pollutant that affects the ecological environment and human health. In this study, magnetic nanoparticles loaded with corncob biochar are synthesized by chemical methods, and the electroactive microorganism P. aeruginosa PAO1 is introduced as the exogenous electron donor for the first time to explore the degradation of organic pollutants by microbial cooperative composite materials under light conditions. Through microstructure characterization and material composition analysis of the composite, successful loading was further confirmed. Subsequently, by discussing the effect of MB removal under different conditions, a possible mechanism for the P. aeruginosa PAO1 co-degradation of organic pollutants is proposed. The results demonstrate that this method can efficiently remove MB, providing a new approach for the green and sustainable removal of organic pollutants.

2. Materials and Methods

2.1. Preparation of Biochar and Composites

To prepare corncob biochar, the corncob is washed and air-dried before being pulverized. Subsequently, the corncob was put into a carbonization furnace at 500 °C under oxygen-limited conditions for 2 h. The resulting unaltered corncob biochar is then cooled to the surrounding temperature using a cooler, ground, and subsequently sieved through a 200-mesh steel sieve. It is then subjected to washing with deionized water and 0.1 mol/L HCI, followed by drying at a temperature of 90 °C. The prepared biochar (marked as Bio) was stored in plastic containers for further application.
The preparation method of a corn biochar-loaded magnetite nanoparticles composite is as follows: the utilized reagents are composed of FeSO4·7H2O, FeCI3·6H2O, and KOH solutions. The salts purchased and used in the experiment were of analytical grade, and all chemicals were used without further purification. A 10% solution of FeCl3·6H2O and FeSO4·7H2O was prepared, followed by strict sonication mixing of 8 mL of the FeCl3·6H2O solution and 16 mL of the FeSO4·7H2O solution with 1 g of the corncob biochar for a duration of 10 min [35]. The mixture was titrated by 100 mL of 0.15 mol/L KOH solution to prepare a corncob biochar supported by the magnetite nanoparticles (marked as Bio/MNs). Then, the Bio/MNs were filtered by a filter and dried at 100 °C for 36 h. Finally, the prepared Bio/MNs were put in the ultra-clean table (SW-CJ-1FD, Suzhou, China) for ultraviolet sterilization and stored in plastic containers for further application.

2.2. Characterization of the Composites

The prepared Bio/MNs were passed through a 400-mesh steel sieve for characterization analysis. The Bio/MNs were identified with an X-ray diffractometer (XRD, Ultima IV, Tokyo, Japan) under Cu kα radiation operating at 40 kV and 40 mA, the morphological features were measured by a scanning electron microscope (SEM, JSM-6510, Tokyo, Japan) that operated at 10 kV, and the working distance was 10 mm.

2.3. Cultivation of Microorganisms

P. aeruginosa PAO1 was used in the experiment. A single colony of P. aeruginosa PAO1 was picked up and aerobically cultured in 100 mL of Luria–Bertani no-sodium chloride medium (LBNS: 10 g/L tryptone, 5 g/L yeast extract). Subsequently, it was continuous-shock-cultured in an oscillating incubator (ZQPL-200, Tianjin, China) at 35 °C and 150 rpm for 15 h to obtain a P. aeruginosa PAO1-containing suspension. The suspension was then subjected to low-speed intelligent centrifugation (LSC-50H, Wuxi, China) at 4000× g rpm for 10 min. The resulting concentrated solution was washed twice with a phosphate-buffered medium (containing 5 g/L tryptone, 0.25 g/L yeast extract, 19.2 g/L Na2HPO4·12H2O, and 7.8 g/L NaH2PO4·2H2O) at pH 7.0. Finally, the cells were diluted in the phosphate buffer medium to obtain a bacterial concentrate on an ultra-clean table.
In order to complete batch experiments, bacteria were cultured in the phosphate-buffered medium. Tryptone and yeast extract were used as the carbon source for P. aeruginosa PAO1. Notably, these mediums were sterilized using the autoclave (SN510C, Shanghai, China) at 121 °C for 20 min, and all these works were carried out on the ultra-clean table. The pH value was measured using a pH meter (PH610, Beijing, China).

2.4. Measurement of the Adsorption and Removal of MB

A 50 mg/L MB reserve solution was prepared using a methylene blue reagent for the MB removal experiment, which was conducted in a 100 mL conical bottle, and the conical bottle mouth was sealed with tissue culture sealing film during the experiment. In order to avoid accidental phenomena and reduce experimental errors, the degradation experiment was repeated three times for each group. An external light-emitting diode (LED) with a cooling system served as the light source, with an operating wavelength ranging from 400 to 700 nm and a light intensity of 60 mW/cm2 (FGH-1, Photoelectric Instrument Factory, Beijing Normal University, Beijing, China). During the experiment, the LED was placed on the side of the conical bottle, about 5 cm away, for irradiation. Before the experiment began, various experimental materials were first put into a conical bottle with MB, and the magnetic stirrer (MS5, Beijing, China) was started to achieve a certain adsorption saturation state. Then, the LED was started to analyze the effects of light exposure, the P. aeruginosa PAO1 injection volume (1–4 mL), the biochar dosage (1–4 g/L), and the pH values of the solutions (2, 4, 6, 8) on MB removal. The concentration of MB was determined using an ultraviolet-visible spectrophotometer (SP-756P, Shanghai, China) at a wavelength of 664 nm. First, standard solutions of MB with concentrations ranging from 2 to 40 μg/mL were prepared, and the standard curve for the MB concentration was established using UV-VIS spectrophotometry. Finally, the absorbance of the solution was measured at different time intervals to determine the concentration of MB. Finally, the data statistics and the drawing of the graph were completed by the drawing software (Origin 2021).

3. Results and Discussion

3.1. Characterization of Composites

SEM analyses were conducted to investigate the microstructure of the original biochar and Bio/MNs. The morphology and microstructure of both the original corn biochar and the Bio/MNs are depicted in Figure 1. The surface of the raw corn biochar has a smooth texture and contains a small amount of debris while exhibiting an intricate network of channels and pore structures (Figure 1a,b). In contrast, the microstructure of Bio/MNs exhibits irregularity, with scattered magnetite nanoparticles forming clusters and filling in the pores and channels of the biochar (Figure 1c,d). Therefore, drawing from the SEM findings, it can be inferred that the integration of magnetite nanoparticles and biochar was successful.
The SEM elemental mapping of the Bio/MNs and biochar is presented in Figure 2a,b, revealing clear observations of C (carbon) and O (oxygen) in both samples, with a uniform distribution indicated by the brightness of the map. Notably, Fe is exclusively found uniformly on the surface of Bio/MNs, reaching a high content of 45%. Furthermore, EDS elemental mapping analysis demonstrated that biochar contains 62.38% C and 37.62% O (Figure 2d). Compared with biochar, the surface carbon content of Bio/MNs is reduced to 41.96% due to the coverage of Fe3O4, while the oxygen and iron contents are increased to 46.14% and 11.9% (Figure 2c), respectively. The experimental results demonstrate the effective loading of Fe3O4 on biochar and the successful preparation of the Bio/MNs complex.
Figure 3 displays the XRD patterns of raw corn biochar and magnetic biochar derived from corn biochar with magnetite nanoparticles (Bio/MNs). The original biochar shows two diffraction peaks at 21.9° and 36.2°, and the corresponding material composition is organic matter. Notably, the overall peak intensity of Bio/MNs is relatively low, consisting of small diffraction peaks. And Bio/MNs show characteristic peaks at 2θ angles of 21.3°, 36.8°, 41.7°, and 53.6°, corresponding to the (111), (311), (400), and (422) crystal faces of magnetite nanoparticles. In addition, the Bio/MNs also contain the diffraction peaks of organic matter and an Fe2O3 characteristic. Fe2O3 may be caused by the oxidation of part of Fe3O4 during the preparation of Bio/MNs. Evidently, the successful preparation of Bio/MNs composites is demonstrated, with magnetite nanoparticles displaying a favorable crystallization effect within the biochar matrix.
The X-ray photoelectron spectroscopy (XPS) analysis of biochar and Bio/MNs (Figure 4) provides new evidence supporting the above conclusion. Figure 4a displays the full spectrum scan of biochar and Bio/MNs, revealing characteristic binding energy peaks of O1s and C1s in both samples at binding energies of 529 eV and 280 eV, respectively. However, only Bio/MNs exhibit characteristic binding energy peaks of Fe2p, with a binding energy around 708 eV (Figure 4a). Notably, the strength of the C1s diffraction peak decreases significantly, while that of the O1s diffraction peak slightly increases after combining biochar with Fe3O4. In addition, the XPS spectrum of Fe2p in Bio/MNs is presented in Figure 4b, illustrating the presence of two distinct forms of iron: Fe (III) and Fe (II). The relative abundances of Fe (III) and Fe (II) were determined to be 67.14% and 32.86%, respectively. Furthermore, the high-resolution Fe2p spectrum of Bio/MNs exhibits prominent peaks corresponding to Fe2p1/2 and Fe2p3/2, with binding energies measured at 725.5 eV and 712.3 eV, respectively. This further confirmed that Fe3O4 was successfully loaded with biochar and changed the elemental composition and content of the original biochar.

3.2. Results of MB Degradation by Different Repair Materials

Figure 5 illustrates the impact of various repair materials on MB degradation under light (L) and dark (D) conditions, revealing a significant disparity between single and compound repair agents in terms of their effectiveness. The dosage of P. aeruginosa PAO1 and Bio/MNs in this process is 3 mL and 0.2 g, respectively, while maintaining a pH value of 7. The degradation rate of MB by a single remediation material reached 36.4% at the 8th hour. It is noteworthy that, under identical conditions, the composite (Bio/MNs) with P. aeruginosa PAO1 exhibited an impressive degradation rate of up to 81.5% (Figure 5a). The results demonstrated that the combination of Bio/MNs and P. aeruginosa PAO1 exhibited superior efficacy in the degradation of MB, surpassing the performance of individual remediation materials. The predominant factor lies in the porous structure of biochar, which effectively encapsulates microorganisms, providing them with an optimal living environment while preventing direct contact with organic pollution within a short timeframe [36]. Consequently, this mechanism sustains the activity of microorganisms. Additionally, it is evident that light plays a crucial role in facilitating the degradation of MB. Under dark conditions, the degradation rate of MB by Bio/MNs and P. aeruginosa PAO1 was 45.2%. However, upon exposure to light, the degradation rate increased significantly to 81.5%, representing a 1.8-fold increase compared to that observed under dark conditions. Compared to the results of the previous study, the degradation rate of MB was increased by 73.5% [37]. This is due to the semiconducting nature of magnetite, which becomes excited under light conditions and generates photoelectrons and holes [38]. As an electroactive microorganism, P. aeruginosa PAO1 interacts with magnetite to enhance its extracellular electron transfer process [39,40], consequently accelerating the pace of MB degradation.
In order to further study the degradation process of MB in various repair materials, the kinetic curves of MB degradation were fitted (Figure 5b). The degradation process of MB of various restorative materials follows the pseudo-first-order kinetic equation. Among these, the removal rate constant of Bio/MNs synergistic P. aeruginosa PAO1 is 0.239 ± 0.025 d−1, which is the largest in the degradation of MB under illumination (Table 1). The fitting index value indicates a satisfactory level of fit (R2 = 0.945). Therefore, the fitting results showed that light promoted P. aeruginosa PAO1 and Bio/MNs in effectively removing MB. In addition, the results of multiple experiments showed that Bio/MNs and P. aeruginosa PAO1 had good cycling stability under light conditions.

3.3. Effect of the Microbial Dose on the Degradation of MB

To further investigate the degradation process of Bio/MNs by P. aeruginosa PAO1, various doses of P. aeruginosa PAO1 were examined in conjunction with Bio/MNs (0.2 g) to degrade MB under light. As shown in Figure 6a, when the Bio/MNs and pH were 0.2 g and 7, respectively, the degradation rate of MB increased with the increase in the P. aeruginosa PAO1 dose. The degradation rate of MB significantly increased when the dose of P. aeruginosa PAO1 was escalated from 1 mL to 4 mL. Notably, at a dosage of 4 mL, the degradation rate of MB reached its peak (77.1%), exhibiting a 2.3-fold enhancement compared to the P. aeruginosa PAO1-free group (32.7%). This degradation rate is 2.1 times that of previous studies [41]. The application of P. aeruginosa PAO1 combined with Bio/MNs resulted in a significant enhancement of MB removal by 46.3 mg/g [42]. It is worth noting that an increase in the number of microorganisms can directly release more electrons [40]. Furthermore, the increase in the number of bacteria further promotes the redox reactions interaction between microorganisms and magnetite, releasing more Fe (II) and thereby reducing MB [43].
In order to reveal the degradation kinetics of MB by the P. aeruginosa PAO1 dose, the fitted MB degradation time curve is shown in Figure 6b. The results show that the degradation process of MB follows the first-order kinetic equation. The ln (C/C0) value of MB showed a good linear relationship with the reaction time, and the fitting index value indicated a good fit (R2 > 0.85) (Table 2). When adding 0 mL, 1 mL, 2 mL, 3 mL, and 4 mL P. aeruginosa PAO1 to the system, the removal rate constants of MB were 0.071 ± 0.011, 0.129 ± 0.026, 0.180 ± 0.031, 0.233 ± 0.035, and 0.281 ± 0.048 d−1, respectively (Table 2). The fitting results further revealed that the degradation rate of MB exhibited a positive correlation with the P. aeruginosa PAO1 concentration.

3.4. Effect of the Bio/MNs Dosage on the Degradation of MB

The impact of the Bio/MNs dosage on MB degradation was further investigated while maintaining a fixed amount of P. aeruginosa PAO1 (3 mL), pH = 7, and light exposure. The degradation of MB increases with the increase in Bio/MNs, as depicted in Figure 7a. In the absence of Bio/MNs, the removal rate of MB at the fifth hour is merely 32.2%. By contrast, an escalation in Bio/MNs usage from 0.1 g to 0.4 g leads to a corresponding enhancement in the removal rate of MB from 67.9% to 98.8%, respectively. Compared to the results of the previous study, the removal rate of MB increased by 83.4% [44]. A possible reason for this result is that the attachment of Fe/Mn minerals with redox reaction activity to biochar will change the properties of biochar [45] and participate in the electron transfer process of the contaminant fixed biochar [46]. Moreover, biochar acts as an electron mediator in the reduction in Fe (III) minerals by reducing bacteria [47]. As the Bio/MNs dosage is heightened, certain soluble groups within the biochar matrix will disperse into the solution and engage in the redox reaction process within the solution [43]. This also revealed that, with the increase in the Bio/MNs dose, the electron mediators also increased, and more Fe (III) was reduced, thereby increasing the removal rate of MB.
In order to reveal the degradation kinetics of MB by the addition of Bio/Mns, the fitted MB degradation time curve is shown in Figure 7b. The results show that the degradation process of MB conforms to the first-order kinetic equation. The ln (C/C0) values of MB showed a good linear relationship with the reaction time, and the fitting index values were well fitted (R2 > 0.95) (Table 3). In addition, when 0.4 g of Bio/MNs is added, the degradation rate constant of MB is 1.059 ± 0.138 d−1. Consequently, the fitting results also demonstrated a positive correlation between the dosage of Bio/MNs and the removal rate of MB.

3.5. Effect of pH on the Degradation of MB

The impact of pH on the removal rate of MB by P. aeruginosa PAO1 with Bio/MNs under light conditions was investigated across a range of initial values (3–11). As depicted in Figure 8a, when the Bio/MNs and P. aeruginosa PAO1 were 0.2 g and 3 mL, respectively, an increase in the pH value corresponded to an increase in the MB removal rate. When the initial pH value is 3, the removal rate of MB is 56.0% at the fifth hour. In contrast, when the initial pH was increased to 11, the removal rate increased to 98.6%, which is 1.76 times greater than that observed at pH = 3. It is worth noting that the removal rate of MB is 93.4% higher than that of previous studies, and the removal effect is very significant [23]. These results indicate that the initial pH of the solution has a significant effect on the removal of MB by P. aeruginosa PAO1 in collaboration with Bio/MNs. This is because there are functional groups and surface charges in Bio/MNs, so the initial pH value has a very important influence on the degradation of MB in the composite [5]. Furthermore, the capacity of H+ binding sites on biochar is limited under acidic conditions. Notably, the researchers found that the biochar and Fe3O4 complex had a zero potential pH of 1.74. As the pH value increases from 4 to 11, the surface of the complex becomes negatively charged [48]. However, MB is a positively charged cationic dye [49]. Therefore, under the condition of a low pH value, there is electrostatic repulsion between MB and Bio/MNs, resulting in a lower removal rate of MB. As the pH value increases, there is an electrostatic attraction between MB and Bio/MNs, leading to the enhanced degradation of MB.
To delve deeper into the influence of the initial pH value on MB removal, the kinetics curve of MB degradation was subjected to fitting. The degradation process of MB under various pH conditions follows the first-order kinetic equation (Figure 8b). In particular, when the pH value is 11, the removal rate constant of Bio/MNs synergistic P. aeruginosa PAO1 is 1.048 ± 0.083 d−1 (Table 4). Moreover, the fitting index revealed a high degree of fit (R2 = 0.98). Therefore, the fitting results show that the removal rate of MB increases with the increase in the initial pH value.

3.6. Mechanistic Analysis

The mechanism by which Bio/MNs collaborate with P. aeruginosa PAO1 to degrade MB organic pollution is illustrated in Figure 9. Initially, the porous structure of biochar rapidly adsorbs MB, thereby impeding its further diffusion [5]. Additionally, the abundant pores within biochar provide favorable sites for microbial attachment, thereby affording a protective niche for microorganisms [36]. Notably, P. aeruginosa PAO1 acts as the main electron donor throughout the system. Magnetite and biochar act as electron mediators in the system. In particular, part of the extracellular electrons produced by P. aeruginosa PAO1 will enter the magnetite valence band and then transfer to the conduction band and transfer electrons under light excitation. The primary factor lies in the photoexcited electron transfer pathway within the Bio/MNs—P. aeruginosa PAO1-MB system [50]. Upon light excitation, Bio/MNs generate photogenerated electrons and holes. P. aeruginosa PAO1 utilizes bioelectrons generated through metabolism to effectively scavenge light-induced holes, thereby facilitating the separation of photogenerated electron–hole pairs and enhancing the current output [51], thus speeding up the extracellular electron transfer process of P. aeruginosa PAO1. In addition, biochar can increase the release of O2− and ·OH [52]. Therefore, Bio/MNs collaborate with P. aeruginosa PAO1 to significantly remove MB organic pollutants under light conditions.
Not only that, magnetite, as a typical semiconductor mineral, interacts with P. aeruginosa PAO1 to produce photoelectrons (e−) and light holes (h+) under light conditions (Equation (1)) [53]. Photoelectrons and light holes react with oxygen or water to generate free radicals (·OH) and singlet oxygen (O2−), which can efficiently decompose the organic pollutant MB (Equations (2)–(5)) [54]. Interestingly, O2− can be converted to 1O2 and H2O2 in the presence of water (Equation (6)). And 1O2 can effectively remove MB organic pollutants (Equation (7)) [55]. Moreover, in the presence of H2O2, it reacts with iron on the surface of Fe3O4 nanoparticles by the heterogeneous Fenton method, resulting in more ·OH and HO2· free radicals [3]. The main mechanism is shown in Equations (8)–(10) [56]. Therefore, Fe2+ and Fe3+ in magnetite nanoparticles effectively improve the removal rate of MB.
Fe3O4 + hγ → Fe3O4 + h+ + e−
h+ + H2O → H+ + ·OH
e− + O2 → O2−
MB + ·OH → CO2 + H2O + byproducts
MB + O2− → CO2 + H2O + byproducts
2O2− + 2H2O → 1O2 + H2O2 + 2OH−
MB + 1O2 → CO2 + H2O + byproducts
Fe3+ + H2O2 → Fe2+ + H+ + HO2·
Fe2+ + H2O2 → Fe3+ + HO− + ·OH
Fe3+ + HO2· → Fe2+ + H+ + O2

4. Conclusions

In summary, Bio/MNs nanocomposites were successfully prepared by the chemical method and used to degrade MB in collaboration with P. aeruginosa PAO1. Comprehensive experimental analysis showed that Bio/MNs synergistic P. aeruginosa PAO1 could remove 81.5% of MB at 8 h under light conditions. Gradient experiments unveiled a proportional relationship between MB removal and the dosage of P. aeruginosa PAO1, as well as the incorporation of Bio/MNs within a specified range. Furthermore, MB functions as a cationic dye, and in acidic settings, due to the constraints on H+ binding sites on biochar, the pinnacle MB removal rate reaches 98.6% at pH = 11. This is because biochar not only alleviates the agglomeration problem of magnetite nanoparticles but also mediates the electron transfer between P. aeruginosa PAO1 and magnetite, thus promoting the production of photohole–electron pairs. In addition, the semiconductor properties of magnetite itself and the electric generation properties of P. aeruginosa PAO1 interact to further enhance the electron generation rate, thus speeding up the generation of ·OH and O2− and realizing the efficient removal of MB. Remarkably, the outcomes unveiled in this study wield substantial significance in enriching our existing comprehension of the collaborative degradation mechanisms of organic pollutants via nano-organic materials. This, in turn, furnishes innovative perspectives for the sustainable mitigation of such pollutants.

Author Contributions

Conceptualization, G.R. and C.Z.; methodology, Q.W. and W.X.; validation, W.X. and Y.W.; formal analysis, Y.W. and Z.L.; investigation, Q.W., W.X. and Z.L.; writing—original draft preparation, G.R., C.Z., Q.W. and Y.W.; writing—review and editing, G.R. and C.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Natural Science Foundation of Gansu Province, China (Grant No. 23JRRA1083), the Gansu Nonferrous Geological Bureau Research Project (Grant No. YSJD2022-11 and No. YSJG2023-13), the Fundamental Research Funds for the Central Universities (Grant No. lzujbky-2022-it38 and No. lzujbky-2023-05), the Key Laboratory of Strategic Mineral Resources of the Upper Yellow River, Ministry of Natural Resources (Grant No. YSMRKF202214), and the Technical Innovation Center of Mine Geological Environment Restoration Engineering in Alpine Arid Area (Grant No. HHGCKK2201).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Novais, R.M.; Ascensao, G.; Tobaldi, D.M.; Seabra, M.P.; Labrincha, J.A. Biomass fly ash geopolymer monoliths for effective methylene blue removal from wastewaters. J. Clean. Prod. 2018, 171, 783–794. [Google Scholar] [CrossRef]
  2. Marimuthu, S.; Antonisamy, A.J.; Malayandi, S.; Rajendran, K.; Tsai, P.C.; Pugazhendhi, A.; Ponnusamy, V.K. Silver nanoparticles in dye effluent treatment: A review on synthesis, treatment methods, mechanisms, photocatalytic degradation, toxic effects and mitigation of toxicity. J. Photochem. Photobiol. B Biol. 2020, 205, 111823. [Google Scholar] [CrossRef]
  3. Volnistem, E.A.; Bini, R.D.; Silva, D.M.; Rosso, J.M.; Dias, G.S.; Cotica, L.F.; Santos, I.A. Intensifying the photocatalytic degradation of methylene blue by the formation of BiFeO3/Fe3O4 nanointerfaces. Ceram. Int. 2020, 46, 18768–18777. [Google Scholar] [CrossRef]
  4. Bedin, K.C.; Souza, I.P.; Cazetta, A.L.; Spessato, L.; Ronix, A.; Almeida, V.C. CO2-spherical activated carbon as a new adsorbent for Methylene Blue removal: Kinetic, equilibrium and thermodynamic studies. J. Mol. Liq. 2018, 269, 132–139. [Google Scholar] [CrossRef]
  5. Liu, X.J.; Li, M.F.; Singh, S.K. Manganese-modified lignin biochar as adsorbent for removal of methylene blue. J. Mater. Res. Technol. 2021, 12, 1434–1445. [Google Scholar] [CrossRef]
  6. Zhang, W.; Yan, H.; Li, H.; Jiang, Z.; Dong, L.; Kan, X.; Cheng, R. Removal of dyes from aqueous solutions by straw based adsorbents: Batch and column studies. Chem. Eng. J. 2011, 168, 1120–1127. [Google Scholar] [CrossRef]
  7. Liu, Y.; Yang, Z.H.; Song, P.P.; Xu, R.; Wang, H. Facile synthesis of Bi2MoO6/ZnSnO3 heterojunction with enhanced visible light photocatalytic degradation of methylene blue. Appl. Surf. Sci. 2018, 430, 561–570. [Google Scholar] [CrossRef]
  8. Aziz, K.H.H.; Mahyar, A.; Miessner, H.; Mueller, S.; Kalass, D.; Moeller, D.; Rashid, M.A.M. Application of a planar falling film reactor for decomposition and mineralization of methylene blue in the aqueous media via ozonation, Fenton, photocatalysis and non-thermal plasma: A comparative study. Process Saf. Environ. 2018, 113, 319–329. [Google Scholar] [CrossRef]
  9. Zhang, Y.; Wang, Y.; Guo, C.; Wang, Y. Molybdenum carbide-based photocatalysts: Synthesis, functionalization, and applications. Langmuir 2022, 38, 12739–12756. [Google Scholar] [CrossRef] [PubMed]
  10. Ahmad, A.; Mohd-Setapar, S.H.; Chuong, C.S.; Khatoon, A.; Wani, W.A.; Kumar, R.; Rafatullah, M. Recent advances in new generation dye removal technologies: Novel search for approaches to reprocess wastewater. RSC Adv. 2015, 5, 30801–30818. [Google Scholar] [CrossRef]
  11. Wang, Z.; Dai, L.; Yao, J.; Guo, T.; Hrynsphan, D.; Tatsiana, S.; Chen, J. Enhanced adsorption and reduction performance of nitrate by Fe–Pd–Fe3O4 embedded multi-walled carbon nanotubes. Chemosphere 2021, 281, 130718. [Google Scholar] [CrossRef] [PubMed]
  12. Liao, G.; Li, Q.; Zhao, W.; Pang, Q.; Gao, H.; Xu, Z. In-situ construction of novel silver nanoparticle decorated polymeric spheres as highly active and stable catalysts for reduction of methylene blue dye. Appl. Catal. A Gen. 2018, 549, 102–111. [Google Scholar] [CrossRef]
  13. Ercan, D.; Cossu, A.; Nitin, N.; Tikekar, R.V. Synergistic interaction of ultraviolet light and zinc oxide photosensitizer for enhanced microbial inactivation in simulated wash-water. Innov. Food Sci. Emerg. 2016, 33, 240–250. [Google Scholar] [CrossRef]
  14. Stan, M.; Lung, I.; Soran, M.L.; Leostean, C.; Popa, A.; Stefan, M.; Porav, A.S. Removal of antibiotics from aqueous solutions by green synthesized magnetite nanoparticles with selected agro-waste extracts. Process Saf. Environ. 2017, 107, 357–372. [Google Scholar] [CrossRef]
  15. Marsooli, M.A.; Fasihi-Ramandi, M.; Adib, K.; Pourmasoud, S.; Ahmadi, F.; Ganjali, M.R.; Plonska-Brzezinska, M.E. Preparation and characterization of magnetic Fe3O4/CdWO4 and Fe3O4/CdWO4/PrVO4 nanoparticles and investigation of their photocatalytic and anticancer properties on PANC1 cells. Materials 2019, 12, 3274. [Google Scholar] [CrossRef]
  16. Istiqomah, N.I.; Muzakki, A.T.; Nofrianti, A.; Suharyadi, E.; Kato, T.; Iwata, S. The effect of silica on photocatalytic degradation of methylene blue using silica-coated nizn ferrite nanoparticles. Key Eng. Mater. 2020, 855, 268–273. [Google Scholar] [CrossRef]
  17. Atrak, K.; Ramazani, A.; Fardood, S.T. Eco-friendly synthesis of Mg0.5Ni0.5AlxFe2−xO4 magnetic nanoparticles and study of their photocatalytic activity for degradation of direct blue 129 dye. J. Photochem. Photobiol. A Chem. 2019, 382, 111942. [Google Scholar] [CrossRef]
  18. Zhang, Y.; Xiangshi, P.; Tian, J.; Li, F.; Fan, X.; Ma, L.; Zhang, R. Synthesis of peroxymonosulfate composite catalyst (Fe0/Fe3O4/biochar) using waterworks sludge and walnut shell for degrading methylene blue. J. Environ. Chem. Eng. 2021, 9, 106856. [Google Scholar] [CrossRef]
  19. Wang, S.; Zhao, M.; Zhou, M. Biochar-supported nZVI (nZVI/BC) for contaminant removal from soil and water: A critical review. J. Hazard. Mater. 2019, 373, 820–834. [Google Scholar] [CrossRef]
  20. Inyang, M.; Dickenson, E. The potential role of biochar in the removal of organic and microbial contaminants from potable and reuse water: A review. Chemosphere 2015, 134, 232–240. [Google Scholar] [CrossRef]
  21. Qiu, Y.; Xu, X.; Xu, Z.; Liang, J.; Yu, Y.; Cao, X. Contribution of different iron species in the iron-biochar composites to sorption and degradation of two dyes with varying properties. Chem. Eng. J. 2020, 389, 124471. [Google Scholar] [CrossRef]
  22. Zhang, S.; Wei, Y.; Metz, J.; He, S.; Alvarez, P.J.; Long, M. Persistent free radicals in biochar enhance superoxide-mediated Fe (III)/Fe (II) cycling and the efficacy of CaO2 Fenton-like treatment. J. Hazard. Mater. 2022, 421, 126805. [Google Scholar] [CrossRef] [PubMed]
  23. He, Y.; Wang, Y.; Hu, J.; Wang, K.; Zhai, Y.; Chen, Y.; Zhang, W. Photocatalytic property correlated with microstructural evolution of the biochar/ZnO composites. J. Mater. Res. Technol. 2021, 11, 1308–1321. [Google Scholar] [CrossRef]
  24. Zhang, G.; Zhao, Z.; Yin, X.A.; Zhu, Y. Impacts of biochars on bacterial community shifts and biodegradation of antibiotics in an agricultural soil during short-term incubation. Sci. Total Environ. 2021, 771, 144751. [Google Scholar] [PubMed]
  25. Wang, S.; Zhou, Y.; Han, S.; Wang, N.; Yin, W.; Yin, X.; Wang, J. Carboxymethyl cellulose stabilized ZnO/biochar nanocomposites: Enhanced adsorption and inhibited photocatalytic degradation of methylene blue. Chemosphere 2018, 197, 20–25. [Google Scholar] [CrossRef]
  26. Shi, J.; Wang, J.; Liang, L.; Xu, Z.; Chen, Y.; Chen, S.; Wang, S. Carbothermal synthesis of biochar-supported metallic silver for enhanced photocatalytic removal of methylene blue and antimicrobial efficacy. J. Hazard. Mater. 2021, 401, 123382. [Google Scholar] [CrossRef]
  27. Zhu, S.; Xu, J.; Kuang, Y.; Cheng, Z.; Wu, Q.; Xie, J.; Chen, K. Lignin-derived sulfonated porous carbon from cornstalk for efficient and selective removal of cationic dyes. Ind. Crops Prod. 2021, 159, 113071. [Google Scholar] [CrossRef]
  28. Shan, L.W.; Wang, G.L.; Liu, L.Z.; Wu, Z. Band alignment and enhanced photocatalytic activation for α-Bi2O3/BiOCl (001) core–shell heterojunction. J. Mol. Catal. A—Chem. 2015, 406, 145–151. [Google Scholar] [CrossRef]
  29. Shi, L.; Dong, H.; Reguera, G.; Beyenal, H.; Lu, A.; Liu, J.; Fredrickson, J.K. Extracellular electron transfer mechanisms between microorganisms and minerals. Nat. Rev. Microbiol. 2016, 14, 651–662. [Google Scholar] [CrossRef]
  30. Dong, H.; Huang, L.; Zhao, L.; Zeng, Q.; Liu, X.; Sheng, Y.; Chen, H. A critical review of mineral–microbe interaction and co-evolution: Mechanisms and applications. Natl. Sci. Rev. 2022, 9, nwac128. [Google Scholar] [PubMed]
  31. Wang, Z.; Chen, C.; Liu, H.; Hrynshpan, D.; Savitskaya, T.; Chen, J.; Chen, J. Enhanced denitrification performance of Alcaligenes sp. TB by Pd stimulating to produce membrane adaptation mechanism coupled with nanoscale zero-valent iron. Sci. Total Environ. 2020, 708, 135063. [Google Scholar] [CrossRef]
  32. Liu, J.; Liu, X.; Ding, H.; Ren, G.; Sun, Y.; Liu, Y.; Lu, A. Enhanced mechanism of extracellular electron transfer between semiconducting minerals anatase and Pseudomonas aeruginosa PAO1 in euphotic zone. Bioelectrochemistry 2021, 141, 107849. [Google Scholar] [CrossRef]
  33. Lovley, D.R.; Baedecker, M.J.; Lonergan, D.J.; Cozzarelli, I.M.; Phillips, E.J.; Siegel, D.I. Oxidation of aromatic contaminants coupled to microbial iron reduction. Nature 1989, 339, 297–300. [Google Scholar] [CrossRef]
  34. Zeng, Q.; Dong, H.; Wang, X.; Yu, T.; Cui, W. Degradation of 1,4-dioxane by hydroxyl radicals produced from clay minerals. J. Hazard. Mater. 2017, 331, 88–98. [Google Scholar] [CrossRef] [PubMed]
  35. Imran, M.; Khan, Z.U.H.; Iqbal, M.M.; Iqbal, J.; Shah, N.S.; Munawar, S.; Rizwan, M. Effect of biochar modified with magnetite nanoparticles and HNO3 for efficient removal of Cr (VI) from contaminated water: A batch and column scale study. Environ. Pollut. 2020, 261, 114231. [Google Scholar] [PubMed]
  36. Xu, Z.; Xu, X.; Yu, Y.; Yao, C.; Tsang, D.C.; Cao, X. Evolution of redox activity of biochar during interaction with soil minerals: Effect on the electron donating and mediating capacities for Cr (VI) reduction. J. Hazard. Mater. 2021, 414, 125483. [Google Scholar] [PubMed]
  37. Nkutha, C.S.; Shooto, N.D.; Naidoo, E.B. Adsorption studies of methylene blue and lead ions from aqueous solution by using mesoporous coral limestones. S. Afr. J. Chem. Eng. 2020, 34, 151–157. [Google Scholar] [CrossRef]
  38. Ren, G.; Sun, M.; Sun, Y.; Li, Y.; Wang, C.; Lu, A.; Ding, H. A cost-effective birnessite–silicon solar cell hybrid system with enhanced performance for dye decolorization. RSC Adv. 2017, 7, 47975–47982. [Google Scholar] [CrossRef]
  39. You, Y.; Zheng, S.; Zang, H. Stimulatory effect of magnetite on the syntrophic metabolism of Geobacter co-cultures: Influences of surface coating. Geochim. Cosmochim. Acta 2019, 256, 82–96. [Google Scholar] [CrossRef]
  40. Wang, Q.; Ren, G.; Zhao, X.; Zhang, C.; Wang, Y.; Xie, W.; Ke, Z. Sunlight-hematite promoted denitrification by Pseudomonas aeruginosa: A little-known form of nitrogen-cycling enhancement. Appl. Geochem. 2022, 146, 105464. [Google Scholar] [CrossRef]
  41. Abdelrahman, E.A.; Hegazey, R.M.; El-Azabawy, R.E. Efficient removal of methylene blue dye from aqueous media using Fe/Si, Cr/Si, Ni/Si, and Zn/Si amorphous novel adsorbents. J. Mater. Res. Technol. 2019, 8, 5301–5313. [Google Scholar] [CrossRef]
  42. Liu, S.; Li, J.; Xu, S.; Wang, M.; Zhang, Y.; Xue, X. A modified method for enhancing adsorption capability of banana pseudostem biochar towards methylene blue at low temperature. Bioresour. Technol. 2019, 282, 48–55. [Google Scholar] [CrossRef]
  43. Zou, D.; Tong, J.; Feng, C.; Wang, Y.; Li, X.; Zheng, X.; Liu, Y. Synthesis of biochar@ α-Fe2O3@ Shewanella loihica complex for remediation of soil contaminated by hexavalent chromium: Optimization of conditions and mechanism. Chemosphere 2022, 303, 134858. [Google Scholar] [CrossRef] [PubMed]
  44. Ding, Y.H.; Floren, M.; Tan, W. Mussel-inspired polydopamine for bio-surface functionalization. Biosurf. Biotribol. 2016, 2, 121–136. [Google Scholar] [CrossRef]
  45. Mumme, J.; Getz, J.; Prasad, M.; Lüder, U.; Kern, J.; Mašek, O.; Buss, W. Toxicity screening of biochar-mineral composites using germination tests. Chemosphere 2018, 207, 91–100. [Google Scholar] [CrossRef]
  46. Xu, Z.; Xu, X.; Tsang, D.C.; Yang, F.; Zhao, L.; Qiu, H.; Cao, X. Participation of soil active components in the reduction of Cr (VI) by biochar: Differing effects of iron mineral alone and its combination with organic acid. J. Hazard. Mater. 2020, 384, 121455. [Google Scholar] [CrossRef]
  47. Kappler, A.; Wuestner, M.L.; Ruecker, A.; Harter, J.; Halama, M.; Behrens, S. Biochar as an electron shuttle between bacteria and Fe (III) minerals. Environ. Sci. Technol. Lett. 2014, 1, 339–344. [Google Scholar] [CrossRef]
  48. Tie, J.; Sang, S.; Shang, Z.; Li, Y.; Xu, Z.; Lian, M.; Du, C. Preparation of Al-loaded magnetic Chinese medicine residue-derived biochar and application of it in fluoride removal. Ind. Crops Prod. 2022, 184, 115037. [Google Scholar] [CrossRef]
  49. Fan, S.; Wang, Y.; Wang, Z.; Tang, J.; Tang, J.; Li, X. Removal of methylene blue from aqueous solution by sewage sludge-derived biochar: Adsorption kinetics, equilibrium, thermodynamics and mechanism. J. Environ. Chem. Eng. 2017, 5, 601–611. [Google Scholar] [CrossRef]
  50. Cheng, H.; Jing, Z.; Yang, L.; Lu, A.; Ren, G.; Liu, J. Sunlight-triggered synergy of hematite and Shewanella oneidensis MR-1 in Cr (VI) removal. Geochim. Cosmochim. Acta 2021, 305, 19–32. [Google Scholar] [CrossRef]
  51. Lu, Y.; Wu, D.; Qin, Y.; Xie, Y.; Ling, Y.; Ye, H.; Zhang, Y. Facile construction of BiOBr/CoAl-LDH heterojunctions with suppressed Z-axis growth for efficient photoreduction of CO2. Sep. Purif. Technol. 2022, 302, 122090. [Google Scholar] [CrossRef]
  52. Wu, W.; Zhu, S.; Huang, X.; Wei, W.; Jin, C.; Ni, B.J. Determination of instinct components of biomass on the generation of persistent free radicals (PFRs) as critical redox sites in pyrogenic chars for persulfate activation. Environ. Sci. Technol. 2021, 55, 7690–7701. [Google Scholar] [CrossRef] [PubMed]
  53. Lu, A.; Li, Y.; Ding, H.; Xu, X.; Li, Y.; Ren, G.; Hochella Jr, M.F. Photoelectric conversion on Earth’s surface via widespread Fe-and Mn-mineral coatings. Proc. Natl. Acad. Sci. USA 2019, 116, 9741–9746. [Google Scholar] [CrossRef]
  54. Thomas, M.; Naikoo, G.A.; Sheikh, M.U.D.; Bano, M.; Khan, F. Effective photocatalytic degradation of Congo red dye using alginate/carboxymethyl cellulose/TiO2 nanocomposite hydrogel under direct sunlight irradiation. J. Photochem. Photobiol. A Chem. 2016, 327, 33–43. [Google Scholar] [CrossRef]
  55. Cheng, X.; Guo, H.; Zhang, Y.; Wu, X.; Liu, Y. Non-photochemical production of singlet oxygen via activation of persulfate by carbon nanotubes. Water Res. 2017, 113, 80–88. [Google Scholar] [CrossRef]
  56. Kwan, W.P.; Voelker, B.M. Rates of hydroxyl radical generation and organic compound oxidation in mineral-catalyzed Fenton-like systems. Environ. Sci. Technol. 2003, 37, 1150–1158. [Google Scholar] [CrossRef] [PubMed]
Sustainability 15 13984 g001
Figure 1. SEM images of biochar (a,b) and Bio/MNs (c,d).
Figure 1. SEM images of biochar (a,b) and Bio/MNs (c,d).
Sustainability 15 13984 g001
Sustainability 15 13984 g002
Figure 2. SEM elemental mapping image (a,b) and EDS elemental mapping images (c,d) of biochar and Bio/MNs.
Figure 2. SEM elemental mapping image (a,b) and EDS elemental mapping images (c,d) of biochar and Bio/MNs.
Sustainability 15 13984 g002
Sustainability 15 13984 g003
Figure 3. XRD pattern of biochar and Bio/MNs.
Figure 3. XRD pattern of biochar and Bio/MNs.
Sustainability 15 13984 g003
Sustainability 15 13984 g004
Figure 4. The full spectrum of XPS for biochar and Bio/MNs (a); the narrow scan XPS spectrum of Fe2p (b).
Figure 4. The full spectrum of XPS for biochar and Bio/MNs (a); the narrow scan XPS spectrum of Fe2p (b).
Sustainability 15 13984 g004
Sustainability 15 13984 g005
Figure 5. MB degradation of different repair materials (a) and kinetic curves (b).
Figure 5. MB degradation of different repair materials (a) and kinetic curves (b).
Sustainability 15 13984 g005
Sustainability 15 13984 g006
Figure 6. MB degradation curve (a) and kinetic fitting curve (b) of different microbial contents.
Figure 6. MB degradation curve (a) and kinetic fitting curve (b) of different microbial contents.
Sustainability 15 13984 g006
Sustainability 15 13984 g007
Figure 7. MB degradation (a) and kinetic fitting curve (b) of Bio/MNs at different doses.
Figure 7. MB degradation (a) and kinetic fitting curve (b) of Bio/MNs at different doses.
Sustainability 15 13984 g007
Sustainability 15 13984 g008
Figure 8. MB degradation curve (a) and kinetic fitting curve (b) of different pH values.
Figure 8. MB degradation curve (a) and kinetic fitting curve (b) of different pH values.
Sustainability 15 13984 g008
Sustainability 15 13984 g009
Figure 9. Bio/MNs synergistic P. aeruginosa PAO1 degradation mechanism of MB.
Figure 9. Bio/MNs synergistic P. aeruginosa PAO1 degradation mechanism of MB.
Sustainability 15 13984 g009
Table 1. Kinetic parameter fitting of various experimental materials.
Table 1. Kinetic parameter fitting of various experimental materials.
SampleFitting EquationReaction Rate Constant (K/d−1)R2
Bio/MNs+ P. aeruginosa PAO1 + Lighty = Intercept + Slope × x0.239 ± 0.0250.945
Bio/MNs+ P. aeruginosa PAO1 + Darky = Intercept + Slope × x0.083 ± 0.0110.908
Bio + Lighty = Intercept + Slope × x0.031 ± 0.0010.992
Bio + Darky = Intercept + Slope × x0.023 ± 0.0020.919
MNs + Lighty = Intercept + Slope × x0.008 ± 0.0020.756
MNs + Darky = Intercept + Slope × x0.003 ± 0.0010.647
P. aeruginosa PAO1 + Lighty = Intercept + Slope × x0.063 ± 0.0020.991
P. aeruginosa PAO1 + Darky = Intercept + Slope × x0.004 ± 0.0010.773
Table 2. Kinetic parameter fitting of the bacterial gradient reaction.
Table 2. Kinetic parameter fitting of the bacterial gradient reaction.
SampleReaction Rate Constant (K/d−1)R2
0 mL P. aeruginosa PAO10.071 ± 0.0110.899
1 mL P. aeruginosa PAO10.129 ± 0.0260.859
2 mL P. aeruginosa PAO10.180 ± 0.0310.892
3 mL P. aeruginosa PAO10.233 ± 0.0350.916
4 mL P. aeruginosa PAO10.281 ± 0.0480.891
Table 3. Kinetic parameter fitting of Bio/MNs gradient reaction.
Table 3. Kinetic parameter fitting of Bio/MNs gradient reaction.
SampleReaction Rate Constant (K/d−1)R2
0.0 g Bio/MNs0.099 ± 0.0040.993
0.1 g Bio/MNs0.299 ± 0.0280.978
0.2 g Bio/MNs0.423 ± 0.0310.983
0.3 g Bio/MNs0.583 ± 0.0130.998
0.4 g Bio/MNs1.059 ± 0.1380.951
Table 4. Kinetic parameter fitting of the pH gradient reaction.
Table 4. Kinetic parameter fitting of the pH gradient reaction.
SampleReaction Rate Constant (K/d−1)R2
pH = 30.207 ± 0.0130.987
pH = 50.517 ± 0.0210.995
pH = 70.581 ± 0.0370.987
pH = 90.689 ± 0.0850.956
pH = 111.048 ± 0.0830.981
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Zhang, C.; Wang, Q.; Xie, W.; Wang, Y.; Li, Z.; Ren, G. Efficient Organic Pollutant Removal by Bio/MNs Collaborating with Pseudomonas aeruginosa PAO1. Sustainability 2023, 15, 13984. https://doi.org/10.3390/su151813984

AMA Style

Zhang C, Wang Q, Xie W, Wang Y, Li Z, Ren G. Efficient Organic Pollutant Removal by Bio/MNs Collaborating with Pseudomonas aeruginosa PAO1. Sustainability. 2023; 15(18):13984. https://doi.org/10.3390/su151813984

Chicago/Turabian Style

Zhang, Chengbin, Qijun Wang, Wenqing Xie, Ye Wang, Zitong Li, and Guiping Ren. 2023. "Efficient Organic Pollutant Removal by Bio/MNs Collaborating with Pseudomonas aeruginosa PAO1" Sustainability 15, no. 18: 13984. https://doi.org/10.3390/su151813984

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop