Chemical Oxygen Demand Removal Rate Research Articles

Enhanced performance of microbial fuel cells with a bacteria/shape-controllable aligned carbon nanofibers hybrid biofilm

Improving the bacterial loading contents and extracellular electron transfer (EET) efficiency are promising strategies to enhance the overall performance of microbial fuel cells (MFCs). Herein, an aligned carbon nanofiber-bacteria (ACNF-bacteria) hybrid is prepared and used as an efficient anode employing the electrospinning and co-filtration method. The ACNF matrix reveals rich porous structure, large specific surface area, and obviously improved electrocatalytic performance compared to the pristine carbon cloth (CC) anode. Specifically, MFC with the ACNF-bacteria anode achieves a maximum power density of 704 mW m−2, which is 1.7, 2.1 times higher than that of ACNF, CNF and CC anode. Impressively, the coulombic efficiency and chemical oxygen demand (COD) removal rate for ACNF-bacteria anode reach 47.4% and 87.9%, respectively, far exceeding the CC anode (29.3% and 47.6%). Considering all the factors of low cost, facial fabrication, and high-power output, this novel ACNF-bacteria anode provides great potential for high-performance and cost-effective MFCs in a large scale.

Enhanced anaerobic digestion for degradation of swine wastewater through a Fe/Ni-MOF modified microbial electrolysis cell

Stainless steel mesh, as the common cathode of microbial electrolytic cell-assisted anaerobic digestion (MEC-AD), has the disadvantages of low specific surface area, poor biocompatibility and low catalytic activity, which limits the production of methane. Metal-organic frameworks (MOFs) have attracted much attention due to their adjustable pores and specific catalytic properties. However, little attention was paid to the combination of MOF and stainless-steel mesh to improve the performance of MEC-AD cathode. In this study, we combined stainless steel mesh with bimetallic MOF catalyst (Fe/Ni–NH2BDC) to prepare a composite cathode, and verified its promoting effect on AD of swine wastewater. The experimental results showed that the reactor with the carbonized MOF composite cathode (FeNi2-PAN2) achieved the highest soluble chemical oxygen demand removal rate of 82.92% and a maximum cumulative methane yield of 213.47 mL CH4/g COD under an applied voltage of 0.8 V, which were 33.14% and 57.56% higher than those of an anaerobic digestion (AD) control reactor, respectively, and higher than those of a carbon paper (CP) cathode reactor. The enrichment of Methanobacterium and Methanoculleus on the surface of FeNi2-PAN2 cathode surface indicated that FeNi2-PAN2 cathode enhanced hydrogenotrophic methanogenesis and improved the stability of AD.

Sustainable reuse of nickel converter slag as a heterogeneous electro-fenton catalyst for treating textile dyeing wastewater: Activity, mechanism and stability assessment

The high production and improper disposal of nickel converter slag (NCS) are raising serious concerns about its environmental impact, owing to the waste of resources and the foregone contribution to air, soil and groundwater pollution. This work uncovered that NCS could be reused as a superior catalyst for the treatment of textile dyeing wastewater by the heterogeneous electro-Fenton (hetero-EF) process. The NCS-laterite porous ceramsite (NLPC) catalyst showed the highest activity when the ratio of NCS to laterite was 3:2 and calcined at 900 °C. The methylene blue (MB) removal rate and chemical oxygen demand (COD) removal rate were 98.64% and 87.84%, respectively, after 30 min reaction under optimal operating parameters (100 g L−1 NLPC, 4 V of cell voltage and initial pH 3.0). Compared with the electro-Fenton (EF) system without NLPC catalyst, the degradation rate constant was increased by 223.9% (0.0452–1.464 min−1) and the energy consumption was reduced by 65.84% (2.02–0.69 kWh m−3). After six cycles, the MB removal rate only decreased by 5.35%, and the NLPC mass loss rate was 2.04%. Synergies between Co, Ni, Fe and Cu species to promote reactive oxygen species (ROS) generation were the predominant catalytic mechanism. Two possible pathways of MB degradation were deduced. In addition, the NLPC catalyst also showed excellent effects in different wastewater treatments. This work demonstrated an upgrade strategy for cleaner production of non-ferrous metallurgical by-products.

A revolving algae biofilm based photosynthetic microbial fuel cell for simultaneous energy recovery, pollutants removal, and algae production.

Photosynthetic microbial fuel cell (PMFC) based on algal cathode can integrate of wastewater treatment with microalgal biomass production. However, both the traditional suspended algae and the immobilized algae cathode systems have the problems of high cost caused by Pt catalyst and ion-exchange membrane. In this work, a new equipment for membrane-free PMFC is reported based on the optimization of the most expensive MFC components: the separator and the cathode. Using a revolving algae-bacteria biofilm cathode in a photosynthetic membrane-free microbial fuel cell (RAB-MFC) can obtain pollutants removal and algal biomass production as well as electrons generation. The highest chemical oxygen demand (COD) removal rates of the anode and cathode chambers reached 93.5 ± 2.6% and 95.8% ± 0.8%, respectively. The ammonia removal efficiency in anode and cathode chambers was 91.1 ± 1.3% and 98.0 ± 0.6%, respectively, corresponding to an ammonia removal rate of 0.92 ± 0.02 mg/L/h. The maximum current density and power density were 136.1 mA/m2 and 33.1 mW/m2. The average biomass production of algae biofilm was higher than 30 g/m2. The 18S rDNA sequencing analysis the eukaryotic community and revealed high operational taxonomic units (OTUs) of Chlorophyta (44.43%) was dominant phyla with low COD level, while Ciliophora (54.36%) replaced Chlorophyta as the dominant phyla when COD increased. 16S rDNA high-throughput sequencing revealed that biofilms on the cathode contained a variety of prokaryote taxa, including Proteobacteria, Bacteroidota, Firmicutes, while there was only 0.23–0.26% photosynthesizing prokaryote found in the cathode biofilm. Collectively, this work demonstrated that RAB can be used as a bio-cathode in PMFC for pollutants removal from wastewater as well as electricity generation.

Emulsified oil removal from steel rolling oily wastewater by using magnetic chitosan-based flocculants: Flocculation performance, mechanism, and the effect of hydrophobic monomer ratio

Large amounts of wastewater that contained emulsified oil were generated in the steel rolling process of the steel industry. The weak interaction between flocculants and emulsified oil and the slow floc separation are the main bottleneck in oily wastewater treatment. To solve this problem, this study successfully prepared three magnetic chitosan-based flocculants (MCS) with different hydrophobic monomer contents to treat steel rolling oily wastewater (SROW). The oil content, turbidity, chemical oxygen demand (COD), and UV254 removal rates were investigated by using MCS and compared with commercial flocculants. Results showed that as the dosage was 6 mL/L, MCS-2 had an optimal effect on oil and turbidity removal with 95.79 % and 87.85 %, respectively. The best COD removal rate of 66.67 % was achieved at a dosage of 4 mL/L with MCS-3. GC–MS analysis showed that the removal efficiency of MCS on alkanes was significantly better than that of aromatic hydrocarbons. Density functional theory calculations demonstrated that the hydrophobic groups of MCS can combine alkanes and aromatic hydrocarbons through hydrophobic association. Furthermore, charge neutralization, hydrophobic association, and adsorption bridging contributed to emulsified oil removal synthetically. The increased content of hydrophobic monomers enhances the interaction between flocculants and emulsified oil, which was significant for SROW treatment.

Development, performance evaluation, and kinetic studies of microbial fuel cell based auto dripping bioelectrochemical reactor (AutoDriBER) for urine treatment

ABSTRACT A bioelectrochemical reactor is an assembly, which facilitates energy generation and resource recovery using electrochemically active microorganisms. To maximise energy production from wastewater in this bioreactor system special design is required. Therefore, in the present study, continuous flow auto dripping bioelectrochemical reactors (AutoDriBERs) were developed as a single and multi-electrode assembly for urine treatment. Further, their performance was assessed by connecting reactors in series and parallel arrangements. AutoDriBER configured in series connection showed the highest 93.64 ± 1.57% chemical oxygen demand removal rate with the 1.38 ± 0.64 V voltage and 2.54 W m−3 polarisation power density. The optimum flow rate for maximum voltage production was tested with various models i.e. the linear, exponential, Sweibull-1, and Sweibull-2 models to confirm voltage prediction and its validity. The Linear and exponential models were found best fitted for voltage production with R 2 value of 0.999. These findings infer a novel approach toward optimisation of the complex, inexpensive and self-sufficient design for electricity generation from energy-rich urine wastewater in rural areas.

Preparation of Fe-loaded needle coke particle electrodes and utilisation in three-dimensional electro-Fenton oxidation of coking wastewater

Novel iron-loaded needle coke spherical electrodes were fabricated for the first time using the sintering method. With DSA as the anode, nickel foam as the cathode and the spherical electrodes as the particle electrodes, a three-dimensional (3D) electro-Fenton system was constructed to treat coking wastewater. Using the chemical oxygen demand (COD) removal efficiency of coking wastewater as an indicator of electrode performance, the optimal conditions for particle electrode preparation were determined by single-factor experiments as consisting of a 4:1 catalyst-to-binder ratio, Fe2+ loading for the preparation of the particle electrodes of 2.5%, a particle size of 5.5 ± 0.5 mm, and a sintering temperature of 400 °C. Response surface methodology was applied to model and optimise the 3D electro-Fenton process for treating coking wastewater. Under the optimal conditions of an electrode spacing of 5 cm, applied voltage of 11.15 V, initial pH of 2.62, and particle electrode dosing of 12.23 g L−1, the removal rates of COD, NH3–N, NO3−–N, total nitrogen, colour, and UV254 were 87.5%, 100%, 72.2%, 84.8%, 95%, and 72.4%, respectively. Spectral analysis revealed that the 3D electro-Fenton system strongly degraded coking wastewater, causing decomposition of large molecules of organic compounds and residuals primarily consisting of olefins and alkanes. Because the prepared particle electrodes exhibited stable physical and chemical structure, they have great potential for engineering applications due to their resistance to water flow erosion, stable catalytic reaction activity, and reusability.

Pretreatment Hydrolysis Acidification/Two-Stage AO Combination Process to Treat High-Concentration Resin Production Wastewater

The rapid development of the resin industry has led to a large amount of high-concentration resin production wastewater, which has created serious water pollution problems while limiting the development of related enterprises. In this study, a combined pretreatment hydrolysis acidification/two-stage anaerobic oxic (AO) process for high-concentration resin production wastewater was constructed, and the effect of operation time on the treatment efficiency of the hydrolysis acidification and the two-stage AO unit was investigated using chemical oxygen demand (COD), total nitrogen (TN), and NH3-H (ammonia nitrogen) as indicators. The effect of operation time on the treatment efficiency of the hydrolysis acidification and the two-stage AO unit was investigated. Results showed that the pretreatment of “alkaline digestion + ozone oxidation” could effectively remove volatile phenols and phenolic organic pollutants from the wastewater. The average removal rates of COD, TN, and NH3-H (ammonia nitrogen) of resin production were 91.96%, 85.35%, and 85.67%, respectively. The average concentrations of final biochemical effluent were 404.7, 21.4, and 11.4 mg/L, respectively.

Fenton Process for Treating Acrylic Manufacturing Wastewater: Parameter Optimization, Performance Evaluation, Degradation Mechanism

Acrylic manufacturing wastewater is characterized by high toxicity, poor biodegradability, high chemical oxygen demand (COD) and ammonia nitrogen. Herein, we exploited traditional Fenton technology to treat acrylic fiber manufacturing wastewater. The impacts of key operating variables including the initial concentration of H2O2 (CH2O2), the initial concentration of Fe2+ (DFe2+), and solution pH (pH) on the COD removal rate (RCOD) were explored and the treatment process was optimized by Response Surface Methodology (RSM). The results indicated that the optimum parameters are determined as pH 3.0, 7.44 mmol/L of Fe2+ and 60.90 mmol/L of H2O2 during Fenton process. For the actual acrylic manufacturing wastewater treatment shows that the removal rates for COD, TOC, NH4+-N and TN are 61.45%~66.51%, 67.82%~70.99%, 55.67%~60.97% and 56.45%~61.03%, respectively. It can meet the textile dyeing and finishing industry water pollutant discharge standard (GB4287-2012). During the Fenton reaction, the effective degradation and removal of organic matter is mainly achieved by HO• oxidation, supplemented by flocculation and sedimentation of Fe3+ complexes. This study will provide useful implications in the process parameters for the practical application of Fenton method in acrylic acid production wastewater.

Application of Aspergillus niger in Practical Biotechnology of Industrial Recovery of Potato Starch By-Products and Its Flocculation Characteristics

This study developed a practical recovery for potato starch by-products by A. niger and applied it on a plant scale to completely solve the pollution problems. Soughing to evaluate the effect of A. niger applied towards the production of by-products recycling and analyze the composition and characteristics of flocculating substances (FS) by A. niger and advance a possible flocculation mechanism for by-product conversion. After fermentation, the chemical oxygen demand (COD) removal rate, and the conversion rates of cellulose, hemicellulose, pectin, and proteins were 58.85%, 40.19%, 53.29%, 50.14%, and 37.09%, respectively. FS was predominantly composed of proteins (45.55%, w/w) and polysaccharides (28.07%, w/w), with two molecular weight distributions of 7.3792 × 106 Da and 1.7741 × 106 Da and temperature sensitivity. Flocculation was mainly through bridging and ionic bonding, furthermore, sweeping effects may occur during sediment. Flocculation was related to by-products conversion. However, due to severe pollution problems and resource waste, and deficiencies of existing recovery technologies, converting potato starch by-products via A. niger liquid fermentation merits significant consideration.

Nitrogen-doped graphene oxide with enhanced bioelectricity generation from microbial fuel cells for marine sewage treatment

With the increasing demand for clean water and energy, microbial fuel cell (MFC) as a promising technology for obtaining energy from wastewater has attracted great research interest in the last two decades. The performance of the anode electrode is the most critical factor limiting the large-scale application of MFC. Graphene materials as a suitable candidate have been successfully used as the anode due to their excellent biocompatibility and efficient extracellular electron transfer (EET) ability. Here, nitrogen-doped graphene oxide (NGO) was prepared by a simple one-step hydrothermal method. X-ray photoelectron spectroscopy (XPS) was used to analyse the valence states of the surface chemical elements and their associated molecular species. Fourier transform infrared spectroscopy (FTIR) was used to identify the surface functional groups, and Raman spectroscopy was used to analyse the information about surface defects. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) revealed the increased electrochemical activity and rapid EET ability from the NGO electrodes. Scanning electron microscopy demonstrated the two-dimensional layered structure of the NGO with some wrinkled texture. MFCs equipped with the modified NGO anode achieved the highest power density of 708.3 mW/m2 with an output voltage of 498.6 mV in comparison with the other graphene-based electrodes, i.e., graphene and graphene oxide. Moreover, the chemical oxygen demand (COD) removal rate increased significantly from 18.1% to 45.6%. The analysis of the bacterial community using a high-throughput sequencing indicated that the relative abundance of the electricigens increased on the NGO electrode biofilim, and the relative expression of ccoN gene coding cytochrome-c oxidase (Cco) was markedly up-regulated. These results demonstrated that NGO modification effectively enhanced the bio-electrocatalytic activity of MFC with improved wastewater treatment capacity.

Construction of microbial electrodialysis cells equipped with internal proton migration pathways: Enhancement of wastewater treatment, desalination, and hydrogen production

Microbial electrodialysis cells (MEDCs) offer simultaneous wastewater treatment, water desalination, and hydrogen production. In a conventional design of MEDCs, the overall performance is retarded by the accumulation of protons on the anode due to the integration of an anion exchange membrane (AEM). The accumulation of protons reduces the anolyte pH to become acidic, affecting the microbial viability and thus limiting the charge carrier needed for the cathodic reaction. This study has modified the conventional MEDC with an internal proton migration pathway, known as the internal proton migration pathway-MEDC (IP-MEDC). Simulation tests under abiotic conditions demonstrated that the pH changes in the anolyte and catholyte of IP-MEDC were smaller than the pH changes in the anolyte and catholyte without the proton pathways. Under biotic conditions, the performance of the IP-MEDC agreed well with the simulation test, showing a significantly higher chemical oxygen demand (COD) removal rate, desalination rate, and hydrogen production than without the migration pathway. This result is supported by the lowest charge transfer resistance shown by EIS analysis and the abundance of microbes on the bioanode through field emission scanning electron microscopy (FESEM) observation. However, hydrogen production was diminished in the second-fed batch cycle, presumably due to the active diffusion of high Cl¯ concentrations from desalination to the anode chamber, which was detrimental to microbial growth. Enlarging the anode volume by threefold improved the COD removal rate and hydrogen production rate by 1.7- and 3.4-fold, respectively, owing to the dilution effect of Cl¯ in the anode. This implied that the dilution effect satisfies both the microbial viability and conductivity. This study also suggests that the anolyte and catholyte replacement frequencies can be reduced, typically at a prolonged hydraulic retention time, thus minimizing the operating cost (e.g., solution pumping). The use of a high concentration of NaCl (35 g L−1) in the desalination chamber and catholyte provides a condition that is close to practicality.

Catalytic membrane electrode with Co3O4 nanoarrays for simultaneous recovery of water and generation of hydrogen from wastewater

Tremendous research efforts have been devoted to new methods of water decontamination and water splitting at low cost and less energy consumption. Herein, we developed a robust electrochemical strategy with an efficient membrane electrode to remove refractory organic pollutants and simultaneously produce pure hydrogen in wastewater. Firstly, the membrane anode was constructed with a three-dimensional (3D) nanoneedle array of Co3O4 and Ti membrane, exhibiting superior degradation of phenol and dye with Na2SO4 as the electrolyte in a conventional electrocatalytic membrane reactor (ECMR). For the phenol degradation, ≥99% removal efficiency of phenol, 99.5% chemical oxygen demand (COD) removal rate, 92.5% total organic carbon (TOC) removal rate, 88.7% current efficiency and 0.061 kW h (g COD)−1 energy consumption can be obtained. For the dye degradation, ≥99% decolor efficiency and 95.2% COD removal rate, 87.6% TOC removal rate, 82.1% current efficiency and 0.12 kW h (g COD)−1 energy consumption can be achieved. The obtained membrane electrode can provide more active CoOOH sites, dramatically increase the electric fields and overcome mass transfer limitation in a flow-through configuration, thereby significantly enhance the catalytic performance. Finally, we designed a H-type ECMR with the proton exchange membrane (PEM) as the separator for pure H2 production, i.e., PEM-ECMR, demonstrating superior degradation performance of phenol and dye, stable production of high-purity hydrogen (11–15 mL h−1), and excellent long-term stability (100 days) and low voltage input (below 3.0 V). This work demonstrates a promising pathway towards reducing cost and energy consumption for water decontamination and simultaneous hydrogen production.

Effect of asparagine, corncob biochar and Fe(II) on anaerobic biological treatment under low temperature: Enhanced performance and microbial community dynamic.

To ensure the efficiency of anaerobic biological treatment technology at lower temperature will expand the application of anaerobic reactor in practical industrial wastewater treatment. Through a batch experiment, asparagine, corncob biochar and Fe2+ were selected as strengthening measures to analyze the effects on the anaerobic sludge characteristics, microbial community and functional genes in the low temperature (15°C). Results showed that after 21 days, asparagine began to promote chemical oxygen demand (COD) removal by the anaerobic treatment, with highest COD removal rate (81.65%) observed when the asparagine concentration was 1mmol/L. When adding 3g biochar, 25mg/L Fe2+, and the combination of biochar and Fe2+, the COD removal rates reached to 82%, 92% and 97%, respectively. In the presence of asparagine, both biochar and Fe2+ alone or in combination increased the activity of protease (16.35%-120.71%) and coenzyme F420 (5.63%-130.2%). The relative abundance of Proteobacteria and Methanobacterium increased in the presence of biochar and Fe2+. In addition, the KEGG results showed that the combined addition of biochar and Fe2+ enhanced bacterial replication and repair and promoted amino acid metabolism of archaea.

Application of hybrid electrocoagulation and electrooxidation process for treatment of wastewater from the cotton textile industry.

The hybrid electrocoagulation-electrooxidation (EC-EO) process was evaluated for its capability to remove color, total organic carbon (TOC), and chemical oxygen demand (COD). Aluminum (Al/Al) and iridium dioxide-coated onto titanium (IrO2/Ti) electrodes were selected as anode/cathode for EC and EC-EO experiments, respectively. The box-Behnken statistical experimental design was used to optimize different operating conditions of the processes. The selected EC operating parameters are the concentrated dye concentration, applied current density, electrolysis time, and pH. The three chosen operating conditions for hybrid EC- EO processes are applied current density, pH, and electrolysis time. The results were evaluated based on the interaction effects of operating parameters of the treatment methods on the percentage of COD, TOC, and color removal. The EC process achieved 89% color and 76% COD removal rate at the optimum operating conditions. Likewise, the hybrid EC-EO process obtained 97% COD and color removal efficiency. FT-IR and 1H and 13C NMR spectroscopy combined approach was employed to analyze the dye degradation extent. Both analysis results confirm the complete degradation of the organic contaminants into carbon dioxide and water. Thus, this study discloses that the treatment method using mesh IrO2/Ti electrodes is a promising technology that could reach the discharge limit for industrial effluents. In addition, the optimum operating conditions are tested for real industrial wastewater effluents and show excellent performance in removing pollutants. Furthermore, the treatment method's mineralization study and economic analysis were performed and compared to other studies.

Prediction and optimization of the performance in an osmotic microbial fuel cell for water purification and bioelectricity production using a developed process model

To better understand and mathematically express the process of osmotic microbial fuel cells (OsMFCs), a model describing the integration of electrogen growth kinetics and osmotic mass transfer was developed and validated in this study. Low root mean square error (RMSE) and mean relative error (MRE) were obtained for simulated water flux, voltage generation, and chemical oxygen demand (COD) removal, which revealed a reasonable accuracy of the developed model. The local sensitivity analysis indicated that operating parameters such as draw solution concentration, anode hydraulic retention time (HRT) and influent COD concentration played important roles in influencing the key performance of OsMFCs. At the benchmark settings of anode HRT (4 h), influent COD (880 mg L−1), and external resistance (3000 Ω), a voltage increment of approximately 9.4% was predicted with an increased draw solution concentration from ∼0 to 3.0 mol L−1 (sodium chloride, NaCl), revealing the merit brought by the combined effects of water flux-facilitated proton advection and the high conductivities of electrolytes in OsMFCs. Shortening the anode HRT from 14 to 0.5 h at a fixed draw solution concentration of 0.5 mol L−1 was able to achieve approximately 9.3% increment in voltage output, whereas, the COD removal compromised from 99.2% to less than 20%. High COD removal rate of over 95% was obtained when the examined influent COD was as low as approximately 300 mg L−1. The optimization of combined parameters indicated that the optimized operation was at a draw solution concentration of ∼1.0 mol L−1 (NaCl), anode HRT ranging between 4 and 8 h, and a low influent COD of ∼300 mg L−1 at the model settings.

Anaerobic co-digestion of molasses vinasse and three kinds of manure: A comparative study of performance at different mixture ratio and organic loading rate

Studies have shown that animal manures have a promoting effect in improving anaerobic digestion (AD). In this study, swine manure, chicken manure, and cattle manure (named in order SM, CM, and BM groups) were selected as co-digestion substrates of molasses vinasse (MV). The AD performance of three combinations was compared at the same organic loading rate (OLR) of different ratios (manure SCOD: MV SCOD of 1:1, 1:3, 1:5, 1:7, 1:9, stage I), and at the same ratio with increased OLR (ratio of 1:7, stage II) conditions. In stage I, all groups worked well for the 1:7 ratio, with CM performing better than the other groups. As the ratio increased to 1:9, the AD performances of all groups obviously decreased, while the BM group was more stable, with a soluble chemical oxygen demand (SCOD) removal rate 11.7% higher than for the SM group and 12.2% for CM group. In stage II, the SCOD removal efficiency of the CM group was the best and reached 70.9 ± 0.4%. The microbial community analyses indicated that the hydrogenotrophic methanogen Methanobacteriaceae were dominant in the CM group. Synergistaceae with the function of acetogenesis, and Anaerolineaceae with the function of hydrolyzing polysaccharides, were enriched in stages I and II, respectively. In stage I with the ratio of 1:9, the Anaerolineaceae and acetotrophic methanogens Methanosarcinaceae played an important role in the BM group. This study utilized waste as a mixed raw material without increasing the cost of raw materials, the optimal mixed co-digestion ratio and the tolerance to high OLR impact of the stable and efficient MV anaerobic system reactor were determined. The results provide a reference for the treatment of animal manure as a substrate for anaerobic co-digestion of MV and also provide promising potential for the engineering application of anaerobic co-digestion of MV in biogas plants.

Pollutant Removal and Energy Recovery from Swine Wastewater Using Anaerobic Membrane Bioreactor: A Comparative Study with Up-Flow Anaerobic Sludge Blanket

Due to its high content of organics and nutrients, swine wastewater has become one of the main environment pollution sources. Exploring high-efficient technologies for swine wastewater treatment is urgent and becoming a hot topic in the recent years. The present study introduces anaerobic membrane bioreactor (AnMBR) for efficient treatment of swine wastewater, compared with up-flow anaerobic sludge blanket (UASB) as a traditional system. Pollutant removal performance, methanogenic properties, and microbial community structures were investigated in both reactors. Results showed that by intercepting particulate organics, AnMBR achieved stable and much higher chemical oxygen demand (COD) removal rate (approximately 90%) than UASB (around 60%). Due to higher methanogenic activity of anaerobic sludge, methane yield of AnMBR (0.23 L/g-COD) was higher than that of UASB. Microbial community structure analysis showed enrichment of functional bacteria that can remove refractory organic matter in the AnMBR, which promoted the organics conversion processes. In addition, obvious accumulation of acetotrophic and hydrotrophic methanogens in AnMBR system was recorded, which could broaden the organic matter degradation pathways and the methanogenesis processes, ensuring a higher methane yield. Through energy balance analysis, results concluded that the net energy recovery efficiency of AnMBR was higher than that of UASB system, indicating that applying AnMBR for livestock wastewater treatment could not only efficiently remove pollutants, but also significantly enhance the energy recovery.

Molecular insights into the catalytic oxidation of methanol-to-olefins wastewater with phosphoric acid modified sludge biochar

With the development of methanol-to-olefin (MTO) process, the effective disposal of wastewater was one key factor for the long-period and benign development of this technology. Herein, a sludge-based biochar catalyst (GSC-P) was synthesized and used in photo-Fenton reaction for the degradation of MTO wastewater from the outlet of a biological aerated filter. More iron was distributed on the surface of GSC-P catalyst, facilitating the photo-Fenton oxidation of MTO wastewater, with chemical oxygen demand (COD) removal rate of 75.4% and total organic carbon (TOC) removal rate of 62.5%. The 2223 unique molecular formulas assigned by a Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in the original MTO wastewater showed that CHO compounds shared the lowest peak numbers (20.2%) but the highest peak abundance (51.6%) among the four groups. Besides, lipids, unsaturated hydrocarbons, lignins and proteins were the main structural types. After photo-Fenton treatment of 60 min, there were 56.7%–74.0% of compounds removed by the analysis of van Krevelen diagram, indicating that the MTO wastewater was degraded efficiently. Three possible evolution processes of dissolved organic matters during the photo-Fenton reaction were disclosed at the molecular-level.

Preparation and immobilization of Bi2WO6/BiOI/g-C3N4 nanoparticles for the photocatalytic degradation of tetracycline and municipal waste transfer station leachate

Bi2WO6/BiOI nanoparticles were embedded into graphitic carbon nitride (g-C3N4) to fabricate a new visible-light-driven photocatalyst (Bi2WO6/BiOI/g-C3N4). Furthermore, the immobilization of Bi2WO6/BiOI/g-C3N4 was performed by a new method characterized by using polytetrafluoroethylene (PTFE) as an adhesive agent and boric acid (H3BO3) as a pore-forming agent. Bi2WO6/BiOI/g-C3N4 possesses the higher photocatalytic performance than Bi2WO6/BiOI and g-C3N4 for tetracycline degradation because of the enhancement of light absorption and electron/hole (e–/h+) pairs separation. After immobilization, Bi2WO6/BiOI/g-C3N4 still remained considerable activity and stability. For the degradation of tetracycline, the immobilized photocatalyst presented the degradation rate of over 90 % within 120 min, whereas the photocatalytic degradation of municipal waste transfer station (MWTS) leachate for 28 h presented the chemical oxygen demand (COD) removal rate of 56.1 % and the total organic carbon (TOC) removal rate of 50.4 %. Additionally, the biodegradability of the two test solutions was enhanced evidently after the photocatalytic degradation. This work mainly provides a new photocatalyst immobilization method to promote the large-scale application of photocatalytic degradation.