Organic Wastewater Treatment Research Articles

Preparation of needle coke composite cathode and its treatment of RhB wastewater

A novel Fe-loaded needle coke composite electro-Fenton electrode was prepared, characterized, and investigated as the heterogeneous catalytic cathode for oxygen reduction and OH generation for the first time. The novel electro-Fenton system constructed with the cathode and DSA anode was employed to degrade rhodamine B (RhB) in an aqueous solution. Optimal conditions for electrode preparation for the treatment of RhB were obtained by single-factor experiments. The occurrence of the Fenton reaction was verified by hydroxyl radical quenching experiments, and the RhB degradation pathway was inferred by spectroscopic analysis. The decolorization rate of RhB of nearly 100% and the COD removal efficiency of 81.6% were achieved. RhB was degraded by N-de-ethylation, chromophore cleavage, opening-ring, and mineralization in the presence of reactive oxygen species, mainly OH. The cost of RhB simulated wastewater treatment was estimated at RMB 13 yuan per cubic meter of wastewater. As a cheap carbon cathode material, needle coke can catalyze the two-electron transfer of O2 to produce H2O2, reducing the material cost of the electrode, and also increasing the conductivity of the electrode, reducing the cost of water treatment. The needle coke composite electrode can serve as a cost-effective electro-Fenton cathode in the field of refractory organic wastewater treatment represented by dye wastewater.

Efficient peroxymonosulfate activation of immobilized Fe–N–C catalyst on ceramsite for the continuous flow removal of phenol

Nowadays, developing environmentally friendly catalysts with both low cost and high efficiency was still a challenge in actual organic wastewater purification. Herein, the Fe–N–C catalyst was successfully immobilized on solid waste derived ceramsite for efficient degradation of phenol under continuous flow conditions by activating peroxymonosulfate (PMS). After the introduction of ceramsite, the microstructure of Fe–N–C catalyst was changed from granular structure to worm-like structure, promoting the dispersion of the nanoscale catalyst and providing more reactive sites. Therefore, the phenol removal rate and mineralization rate of the obtained 0.5FNNC within 30 min were up to 96.79% and 71.79%, respectively. In addition, the degradation rate of the optimal composite (0.5FNNC)/PMS system was about 4.06 times higher than that of bare Fe–N–C/PMS system. Intriguingly, the Fe ion leaching from 0.5FNNC during the degradation reaction was significantly lower than bare Fe–N–C owing to the strong catalyst-support chemical bonding. Based on electron paramagnetic resonance, quenching experiments, X-ray photoelectron spectroscopy analysis and electrochemical analysis, it was indicated that the non-radical processes (1O2 and high valent iron-oxo species) should be responsible for the phenol degradation. Meanwhile, the possible phenol degradation pathways were proposed, and the intermediates were evaluated for ecotoxicity by ECOSAR. Finally, a preliminary economic analysis of this process was carried out. Overall, this work would provide a new strategy for the construction of ceramsite based multi-pore composite catalysts and the large-scale application of persulfate oxidation technology in organic wastewater treatment.

Catalytic ozonation performance of calcium-loaded catalyst (Ca-C/Al2O3) for effective treatment of high salt organic wastewater

A novel Calcium-loaded catalyst (Ca-C/Al2O3) was prepared with a facile impregnation method, using polyethyleneimine (PEI)-polydopamine (PDA) as a coating agent and Al2O3 as supporter. The prepared Ca-C/Al2O3 catalyst showed a higher treatment performance for high salt organic wastewater, and removal rate of chemical oxygen demand (COD) was enhanced from 32.5% to 64.4% comparing with single ozonation. Besides, it also showed a good catalytic performance comparing with other catalysts reported in different literature. Catechol groups and reactive amine groups in the PEI-PDA coating worked as anchoring points for metal ions, facilitating the formation of dispersed calcium sites (Ca-O and Ca-N). Calcium sites and different types of nitrogen (graphite nitrogen, pyrrolic nitrogen, and pyridinic nitrogen) were identified as the active sites for the catalytic reaction. The analysis of electron paramagnetic resonance (EPR) and radical quenching tests revealed that hydroxyl radical (•OH) and singlet oxygen (1O2) were the reactive oxygen species (ROS) for treatment of high salt organic wastewater. According to the above results, the prepared Ca-C/Al2O3 catalysts showed a good catalytic permanence and used for advanced treatment of high salt organic wastewater.

A newly-designed free-standing NiCo2O4 nanosheet array as effective mediator to activate peroxymonosulfate for rapid degradation of emerging organic pollutant with high concentration

Nowadays effective treatment of high concentration organic wastewater is still a formidable task facing human beings. Herein, for the first time, a well-defined ZIF-67-derived NiCo2O4 nanosheet array was successfully prepared by a feasible method. In comparison with ordinary NiCo2O4 nanosphere, the formation of nanosheet structure could offer more opportunities to exposure internal active sites of NiCo2O4, thereby resulting in smaller interface resistance and higher charge transfer efficiency. As expected, ZIF-67-derived NiCo2O4 nanosheet array displayed great performance in peroxymonosulfate (PMS) activation. More importantly, recyclable redox couples of Co3+/Co2+ and Ni3+/Ni2+ endowed the stable catalytic activity of NiCo2O4 nanosheet. Interestingly, developed NiCo2O4-1/PMS oxidation system could achieve the effective degradation of antibiotics with high concentration in a short time. Both radical and nonradical pathways were involved into PMS activation, wherein SO4−, OH, O2− and 1O2 were major reactive oxygen species. The formation paths of reactive oxygen species and effects of inorganic anions were also investigated. Electrochemical analyses revealed that NiCo2O4-1 with nanosheet structure mediated the electron transfer between PMS and tetracycline (TC), which played a vital role in TC degradation. Furthermore, developed NiCo2O4-1/PMS oxidation system displayed great removal ability towards TC in actual water samples, and degradation products were low toxicity or no toxicity. In short, current work not only developed an effective oxidation system for completing the rapid degradation of antibiotic with high concentration, but also shared some novel insights into the activation mechanism of SR-AOPs.

Enhanced anaerobic reduction of nitrobenzene at high salinity by betaine acting as osmoprotectant and regulator of metabolism

Anaerobic technology is extensively applied in the treatment of industrial organic wastewater, but high salinity always triggers microbial cell dehydration, causing the failure of the anaerobic process. In this work, betaine, one kind of compatible solutes which could balance the osmotic pressure of anaerobic biomass, was exogenously added for enhancing the anaerobic reduction of nitrobenzene (NB) at high salinity. Only 100 mg L−1 betaine dosing could significantly promote the removal efficiency of NB within 35 h at 9% salinity (36.92 ± 4.02% without betaine and 72.94 ± 6.57% with betaine). The relieving effects on salt stress could be observed in the promotion of more extracellular polymeric substances (EPS) secretion with betaine addition. Additionally, the oxidation-reduction potential (ORP), as well as the electron transfer system (ETS) value, was increased with betaine addition, which was reflected in the improvement of system removal efficiency and enzyme activity. Microbial community analysis demonstrated that Bacillus and Clostridiisalibacter which were positively correlated with the stability of the anaerobic process were enriched with betaine addition at high salinity. Metagenomic analysis speculated that the encoding genes for salt tolerance (kdpB/oadA/betA/opuD/epsP/epsH) and NB degradation (nfsA/wrbA/ccdA/menC) obtained higher relative abundance with betaine addition under high salt environment, which might be the key to improving salt tolerance of anaerobic biomass. The long-term assessment demonstrated that exogenous addition betaine played an important role in maintaining the stability of the anaerobic system, which would be a potential strategy to achieve a high-efficiency anaerobic process under high salinity conditions.

Activated persulfate by iron-carbon micro electrolysis used for refractory organics degradation in wastewater: a review.

With the rapid economic development, the discharge of industrial wastewater and municipal wastewater containing many refractory organic pollutants is increasing, so there is an urgent need for processes that can treat refractory organics in wastewater. Iron-carbon micro electrolysis and advanced oxidation based on persulfate radicals (SO4-·) have received much attention in the field of organic wastewater treatment. Iron-carbon micro electrolysis activated persulfate (Fe-C/PS) treatment of wastewater is characterized by high oxidation efficiency and no secondary pollution. This paper reviews the mechanism and process of Fe-C/PS, degradation of organics in different wastewater, and the influencing factors. In addition, the degradation efficiency and optimal reaction conditions (oxidant concentration, catalyst concentration, iron-carbon material, and pH) of Fe-C/PS in the treatment of refractory organics in wastewater are summarized. Moreover, the important factors affecting the degradation of organics by Fe-C/PS are presented. Finally, we analyzed the challenges and the prospects for the future of Fe-C/PS in application, and concluded that the main future directions are to improve the degradation efficiency and cost by synthesizing stable and efficient catalysts, optimizing process parameters, and expanding the application scope.

Design of bentonite/polyurethane composite membrane with a high flux in treatment of organic wastewater by using the pigment volume concentration theory

The flux and rejection rate of the membrane in wastewater treatment are main factors to evaluate the efficiency of membrane separation. In this study, bentonite was added into polyurethane (PU) as a pigment to prepare a type of composite membrane. The properties of composite membrane were designed and regulated by the pigment volume concentration (PVC) theory to optimize the flux and rejection rate in organic wastewater treatment. FT-IR spectra showed the interaction between bentonite and PU matrix that the swelling degree depended on this synergistic effect. The hydrophilic surface of membrane was contributed by bentonite particles in PU matrix. The PVC of the 3# composite membrane (11.81%) was closest to the critical pigment volume concentration (CPVC). The rejection rate of methylene blue was 97.28%, and at the same time, the water flux was 48.52 L·m−2·h−1. In addition, the rejection rates of typical organic pollutants such as Rhodamine B, phenol and industrial wastewater reached 95.32%, 96.84% and 97.16%, and the fluxes were 36.36 L·m−2·h−1, 41.58 L·m−2·h−1 and 38.84 L·m−2·h−1, respectively. This kind of inorganic-organic composite membrane has the potential to be applied to organic wastewater treatment. This study provides a new method for designing composite membranes by using the PVC theory.

In-situ oxidation selective deposition of tetrahedral Ag3PO4{111} on monoclinic BiVO4{040} with highly efficient visible light-driven photocatalysis and long recycling

Photocatalytic technology utilizing solar energy to eliminate organic pollutants is considered to be a promising and sustainable method. Adopting light-driven and in-situ oxidation methods, tetrahedral Ag3PO4{111} (t-Ag3PO4) was selectively grown on monoclinic BiVO4{040} (m-BiVO4), and then m-BiVO4@t-Ag3PO4 with excellent visible light-driven photocatalytic properties and long recycling was obtained. When the catalyst dosage is 0.50 g/L, the m-BiVO4@t-Ag3PO4 heterojunction photocatalyst could remove 99.9 % of rhodamine B within 30 min under visible light irradiation, and the degradation efficiency after 11 cycles remains 97.2 %. The morphology details and photocatalytic properties were confirmed by SEM, TEM, DSR, PL, PC and EIS. Active species capturing experiments and electron spin resonce measurements show that the superoxide radical (·O2-) and hydroxyl radical (·OH) are the main active species during the photocatalysis process. This work provides a promising method for constructing heterojunction photocatalysts with controllable morphology and visible light persistent catalysis. m-BiVO4@t-Ag3PO4 heterojunction photocatalyst has the advantage of price in the market and good features for application in organic wastewater treatment.

Highly efficient removal of organic contaminant with wide concentration range by a novel self-cleaning hydrogel: Mechanism, degradation pathway and DFT calculation

A novel carbon nitride based self-cleaning hydrogel photocatalyst (KI-PCN gel, potassium and iodine co-doped carbon nitride confined in alginate) has been successfully constructed by a facile method. Fabricated photocatalyst showed enhanced synergistic adsorption-photocatalytic degradation property on a high concentration of methylene blue (HMB) because of enhanced carrier separation efficiency and improved light adsorption capacity of KI-PCN. As expected, the KI-PCN gel showed the highest apparent rate constant value (Kapp =0.0310 min−1), which was about 38.8 and 5.8 times as that of blank hydrogel (Kapp=0.0008 min−1) and PCN gel (Kapp=0.0053 min−1), respectively. Meanwhile, KI-PCN gel can continuously adsorb low concentration of MB (LMB), and the MB-adsorbed KI-PCN gel can self-clean under light irradiation. The bench-scale experiments simulating real river showed that KI-PCN gel can effectively and continuously remove LMB (0.1–20 ppm), indicating the possibility for the removal of contaminants in natural rivers. Furthermore, the possible degradation pathways were proposed by combining the density functional calculations (DFT) and intermediates identified by liquid chromatography-mass spectrometry (LC-MS). This work proposed a new perspective to acquire a novel self-cleaning and easily recyclable photocatalyst for treatment of wide concentration range organic wastewater as well as remediation of natural waterbody.

Hydrothermal oxygen uncoupling of high-concentration biogas slurry over Cu-α-Fe2O3·α-MoO3 catalyst

A hydrothermal oxygen uncoupling (HTOU) method which combines aqueous phase reforming (APR) and oxygen uncoupling was proposed to treat biogas slurry (BS). Based on Le Chatelier's principle, this novel approach was constructed and realized by Cu–α-Fe2O3·α-MoO3 catalyst with van der Waals heterojunction-redox property. Additionally, the catalyst was synthesized by integrating a simple one-pot sol-gel method and thermal hydrogenating. Results indicated that the optimal removal efficiencies of non-purgeable organic carbon (NPOC) (76.29%), total nitrogen (TN) (45.56%), and ammonia nitrogen (AN) (29.03%) were achieved on the Cu–α-Fe2O3·α-MoO3 catalyst at 225.00 °C for 30.00 min, respectively. The significant performance of Cu–α-Fe2O3·α-MoO3 could be attributed to three aspects. (1) The α-MoO3 nanosheets with van der Waals heterostructures obtained at the calcination temperature of 600.00 °C, which can provide the superior performance of APR for hydrogen generation. (2) The adsorbed oxygen species were eliminated by thermal hydrogenating which had a surface passivation effect. (3) The effect of oxygen uncoupling in the lattice oxygen and gaseous oxygen release reaction was beneficial to the degradation of organic matter. Moreover, the reuse of catalysts studies further revealed that the deactivation of catalysts originated from carbon deposition of aromatic polymers and heavy metals oxides pollution. Overall, these findings disclosed that the HTOU could be a promising alternative to the treatment of high-concentration organic wastewater.

Efficient activation of peroxydisulfate by a novel magnetic nanocomposite lignin hydrogel for contaminant degradation: Radical and nonradical pathways

A novel magnetic nanocomposite lignin hydrogel (MNLH) was synthesized and applied for peroxydisulfate (PDS) activation in this study. Detailed characterization data indicated that the unique 3-dimensional (3D) structure of the lignin hydrogel is beneficial in dispersing magnetic nanoparticles (nZVI/Ni particles), which enhances the maximum exposure of nZVI/Ni particles. The 3D structure of the lignin hydrogel provides more attachment sites for nZVI/Ni, PDS and contaminants, accelerating the electron transfer between nZVI/Ni and PDS and promoting the degradation of contaminant. Notably, the optimized MNLH0.8 catalyst (where the number 0.8 indicates the mass ratio of [Lignin hydrogel]/[nZVI/Ni] = 0.8) exhibits excellent performance for PDS activation. Under the MNLH0.8/PDS system, 5 mg/L bisphenol A (BPA, 40 mL) can be completely degraded within 15 min with 0.05 g/L catalyst and 0.66 mM PDS. Quenching experiments and electron spin resonance (ESR) spectra reveal that both radicals (O2•−) and nonradicals (1O2) are generated in the MNLH0.8/PDS system as the dominant active species for BPA degradation. In addition, the MNLH0.8 catalyst still shows effectiveness for BPA degradation in the presence of inorganic anions and natural organic matter (NOM). UPLC-Q-TOF-MS system was used to identify the BPA degradation products and four possible pathways for BPA degradation were proposed. According to the results of toxicity prediction, BPA can eventually be transformed into nontoxic products. Additionally, the MNLH/PDS system can effectively degrade different contaminants in water, which highlights promising applications for organic wastewater treatment.

In Situ Coupling Carbon Defective C3N5 Nanosheet with Ag2CO3 for Effective Degradation of Methylene Blue and Tetracycline Hydrochloride.

The development of novel catalysts for degrading organic contaminants in water is a current hot topic in photocatalysis research for environmental protection. In this study, C3N5 nanosheet/Ag2CO3 nanocomposites (CNAC-X) were used as efficient photocatalysts for the visible-light-driven degradation of methylene blue (MB), and tetracycline hydrochloride (TC-HCl) was synthesized for the first time using a simple thermal oxidative exfoliation and in situ deposition method. Due to the synergistic effect of nanosheet structures, carbon defects, and Z-scheme heterojunctions, CNAC-10 exhibited the highest photocatalytic activity, with photodegradation efficiencies of 96.5% and 97.6% for MB (60 mg/L) and TC-HCl (50 mg/L) within 90 and 100 min, respectively. The radical trapping experiments showed that ·O2− and h+ played major roles in the photocatalytic effect of the CNAC-10 system. Furthermore, intermediates in the photodegradation of MB and TC-HCl were investigated to determine possible mineralization pathways. The results indicated that C3N5 nanosheet/Ag2CO3 photocatalysts prepared in this work could provide an effective reference for the treatment of organic wastewater.

Integrating adsorption and in situ advanced oxidation for the treatment of organic wastewater by 3D carbon aerogel embedded with Fe-doped carbonitrides.

Wastewater containing organic pollutants with high toxicity and poor biodegradability poses a considerable threat to human health and the ecosystem. Although adsorption and advanced oxidation processes (AOPs) are currently the most widely used technologies for wastewater treatment, limitations of these two independent processes make the treatment effect unsatisfactory. Herein, a system of integrating adsorption and subsequent in situ AOPs is established by a 3D carbon aerogel embedded with Fe-doped carbonitrides (Fe-NC/CAG). The SEM and BET analysis demonstrate that Fe-NC/CAG possesses porous structures with a specific surface area of 518.7 m2/g. The XRD result indicates the formation of Fe0 and Fe3O4 in Fe-NC/CAG. The impacts of operational parameters such as Fe-NC/CAG dosage, pollutants concentration, temperature, initial pH, and inorganic ions on the adsorption efficiency are investigated. The adsorption kinetics is predominantly based on the pseudo-second-order model. After adsorbing organic pollutants, the Fe-NC/CAG is immersed in peroxymonosulfate (PMS) solution. The adsorbed pollutants are in situ degraded by PMS-based AOPs, leading to the regeneration of Fe-NC/CAG. At optimum conditions, the integrating process established by Fe-NC/CAG achieves over 90% removal of antibiotics, phenolics, and dyes as well as keeps stable performance even after 6 cycles. This integrating adsorption and AOPs system is expected to open up a rich field for wastewater treatment.

Erratum for “Integrated Approach to Treatment of High-Strength Organic Wastewater by Using Anaerobic Rotating Biological Contactor” by Milad Ebrahimi, Hamidreza Kazemi, S. A. Mirbagheri, and Thomas D. Rockaway

Erratum for “Integrated Approach to Treatment of High-Strength Organic Wastewater by Using Anaerobic Rotating Biological Contactor” by Milad Ebrahimi, Hamidreza Kazemi, S. A. Mirbagheri, and Thomas D. Rockaway

Siphon-driven interfacial photocatalytic reactors enhanced by capillary flow for continuous wastewater treatment

Catalytic membrane reactors based on photo-Fenton reactions have been widely applied in organic wastewater treatment. Conventional porous membrane reactors require a multi-cycle operation to achieve a high degradation efficiency. To realize the continuous treatment of wastewater with high efficiency, we propose a novel siphon-driven interfacial photocatalytic reactor based on the β-FeOOH-coated fabrics in the current work, in which the feed transport is within the fabric rather than across the fabric. The liquid flow is driven by gravity without additional energy input and can be adjusted by the structural parameters to match the reaction rate. Moreover, the confined capillary flow ensures sufficient contact between the feed and catalysts, as well as sufficient sunlight utilization, leading to the high degradation efficiency (>99 %) for a variety of organic contaminants such as tetracycline and dyes. The relationship between the fabric structural parameters and degradation performance was also investigated to achieve an optimal design.

Facile synthesis of Ag/AgCl/3D-rGO with rapid catalytic degradation toward Methyl Orange and Rhodamine B

Ag/AgCl/3D-rGO is facilely synthesized by a mild method, and the resulting composite catalyst is systematically characterized by means of Scanning Electron Microscope, Energy Dispersive Spectrometer, Raman Spectra, X-Ray Photoelectron Spectroscopy and X-Ray Diffraction. The characterization result shows that Ag/AgCl nanoparticles are homogeneously dispersed throughout the sheet surface of the block graphene oxide. The catalytic activity of the resulting composite is assessed by the degradation of Methyl Orange (MO) and Rhodamine B (RhB) in the presence of sodium borohydride. The pseudo-first order kinetic study shows that Ag/AgCl/3D-rGO possesses outstanding catalytic degradation activity toward both MO and RhB. The degradation rates of MO and RhB can reach 92 % and 98 % in 15 min, respectively, indicating the rapid catalytic performance of the resulting Ag/AgCl/3D-rGO in the presence of sodium borohydride. In addition, the possible formation and dyes degradation mechanism of Ag/AgCl/3D-rGO are also proposed. The excellent catalytic activity reveals that Ag/AgCl/3D-rGO may have a promising potential application in organic dye wastewater treatment.

Insights into the mechanism of electrostatic field promoting ozone mass transfer in water: A molecular dynamics perspective

Ozone is the main role of ozone-based advanced oxidation process for organic wastewater treatment, which is usually added in water by aeration. However, the low solubility of ozone in water seriously affects the degradation efficiency. In this article, the external electrostatic field (EF) was proposed to improve the ozone solubility in water. The mass transfer characteristics of ozone in a gas-liquid two-phase system under EF were studied by molecular dynamics (MD) simulation. The microscopic mechanism of ozone mass transfer in water promoted by external EF was revealed by analyzing Gibbs dividing surface (GDS) interface structure, interfacial water molecular orientation, surface tension, liquid phase viscosity, hydrogen bond network and ozone self-diffusion coefficient. Our findings reveal that EF can enhance the thickness of GDS region (from 0.4648 nm to 0.4996 nm when EF is 0.2 V/nm) as well as its ozone content. The dipole moment orientation of water molecules also tends to point in the EF direction due to the influence of EF, making the difference in dipole moment orientation of water molecules in the first and second layers of GDS region gradually disappear. In addition, compared with the absence of EF, the existence of external EF can decrease the surface tension (from 77.6162 mN/m to 73.3480 mN/m when EF is 0.2 V/nm) at the gas-liquid interface and the viscosity of liquid phase (from 0.293 mPa·s to 0.162 mPa·s when EF is 0.2 V/nm), break the network of hydrogen bond in liquid phase, and increase the mobility of ozone (self-diffusion coefficient of ozone changes from 1.3232 × 10−6 cm2·s−1 to 1.8812 × 10−6 cm2·s−1 when EF is 0.2 V/nm). All these properties changes indicate that the presence of external EF enhances the ability of ozone to penetrate the interface of the two-phase system, and then improves the ozone mass transfer efficiency in water.

N-doped carbon intercalated Fe-doped MoS2 nanosheets with widened interlayer spacing: An efficient peroxymonosulfate activator for high-salinity organic wastewater treatment

Peroxymonosulfate (PMS) heterogeneous catalysis dominated by nonradical pathway showed excellent adaptability for pollutant removal in complex water matrixes. Herein, ultra-small Fe-doped MoS2 nanosheets with N-doped carbon intercalation (CF-MoS2) were synthesized via a one-step hydrothermal method to treat high salinity organic wastewater. CF-MoS2 exhibited an expanded interlayer spacing by 1.63 times and the specific surface area by 9 times compared with Fe-doped MoS2 (F-MoS2), substantially increasing the active sites. Homogeneous Fe2+ catalytic experiments confirmed that the promotion of carbon intercalated MoS2 (C-MoS2) on Fe3+/Fe2+ redox cycle was much higher than pure MoS2. Besides, the considerable removal of tetracycline (TC) under high salinity conditions (0–7.1%) was attributed to the dominant role of PMS nonradical oxidation pathways, including 1O2 and surface-bound radicals. The catalytic sites included Fe3+/Fe2+, Mo4+/Mo5+/Mo6+, C=O, pyridine N, pyrrolic N and hydroxyl groups. Finally, density functional theory (DFT) was employed to get the radical electrophilic attack sites and nucleophile attack sites of TC, and the results were consistent with the TC degradation products determined by HPLC-MS. This work would broaden the application of MoS2-based catalysts, especially for PMS catalytic removal of organic pollutants from high salinity wastewater.

Using carbon dioxide-added microalgal-bacterial granular sludge for carbon-neutral municipal wastewater treatment under outdoor conditions: Performance, granule characteristics and environmental sustainability

Microalgal-bacterial granular sludge (MBGS) process has a gorgeous prospect for municipal wastewater treatment, but the research on the treatment of complex organic wastewater by MBGS process with CO2 addition under outdoor conditions is not enough. Therefore, this paper evaluated the feasibility of CO2-added MBGS process for complex organic wastewater disposal under natural day-night cycles. The results showed that the addition of CO2 overall improved the removal efficiency of pollutants. Typically, the removal efficiency of total phosphorus increased averagely from 88.5 % to 95.0 % in 12-h day cycle and from 26.2 % to 45.3 % in 12-h night cycle. The addition of CO2 increased the size of MBGS from 1.0 mm to 16.5 mm within 30 days due to extracellular polymeric substances secretion and the dominant filamentous microalgae on granules. The decrease of catalase activity and malondialdehyde content indicated that CO2 reduced oxidative damage and maintained the normal growth of MBGS. Further estimates of the collected gas showed that CO2-added MBGS process could reduce global CO2 emissions by one hundred million tons per year. This study is expected to contribute to the goal of carbon neutrality in the area of wastewater treatment by MBGS process.

Synthesis of silica nanofibers-supported BiOCl/TiO2 heterojunction composites with enhanced visible-light photocatalytic performance

Heterogeneous photocatalysts with high catalytic performance and recyclability have attracted widespread attention in organic wastewater treatment. In the study, we designed and synthesized a novel ternary BiOCl/TiO2/silica nanofibers (BTS) composite with enhanced photocatalytic performance via a modified sol-gel method and precipitation/calcination method. In the composite, BiOCl nanosheets and TiO2 nanoparticles are uniformly dispersed on the surface of silica nanofibers in turn, where they are closely combined to form BiOCl/TiO2 heterojunction structure. The composite displays superior degradation performance for rhodamine B (RhB) than bare BiOCl or TiO2 as well as TiO2/silica nanofibers (TS). The excellent photocatalytic performance of BTS is mainly attributed to the enhanced dispersibility of BiOCl and TiO2 given by SNF and the effective construction of BiOCl/TiO2 heterojunction. The radical scavenger and EPR tests found that superoxide radical anions (O2•−) are the dominant active species in the reaction system. It is proposed that the BTS composite shows great potential for wide application in the field of sewage treatment driven by solar energy.