Chemical Oxygen Demand Removal Rate Research Articles

Preparation and characterization of BiOBr/CuFe2O4 composite catalyst and constitute photo-Fenton system for degradation of polyacrylamide under visible light

A simple hydrothermal synthesis method was employed to fabricate a BiOBr/CuFe2O4 composite photo-Fenton catalyst with visible light response in this study. The effects of the CuFe2O4 dosage, the concentration of polyacrylamide (PAM), the reaction time, the pH of the initial solution and the light source on the reaction results were investigated. Under the visible light, ultraviolet light and sunlight irradiation, the chemical oxygen demand (COD) removal rate of PAM (250 mg/L) reached 62.43%, 69.21%, 65.17%, respectively. Simultaneously, the structure, morphology and optical properties were characterized. The improved activity of BiOBr/CuFe2O4 can be attributed to formation of Z-type heterojunction, synergistic effect of photocatalysis and Fenton catalysis. The free radical capture experiments show that •O2−, h+ and •OH are all active species of BiOBr/CuFe2O4 for decomposing PAM in photo-Fenton reactions. Finally, a possible electron transfer mechanism was proposed through the fitting of Mott-Schottky curve and Taut-plot curves.

Investigating the challenges of biogas provision in water limited environments through laboratory scale biodigesters

ABSTRACT The potential for biogas provision through household-scale anaerobic digestion in rural sub-Saharan Africa is limited due to perceived water shortages. The most common substrate is animal dung diluted 1:1 with water. Two experimental methods tested the potential of reducing water demand. The first experiment compared the chemical oxygen demand (COD) and volatile solid removal of four cow dung dilutions ranging from 3.5-10.6% total solids. In the second experiment, bioslurry filtrate was recirculated back into the fresh substrate at different concentrations. The highest COD removal rate of 28.3% was obtained from mixing equal volumes of dung with filtrate (mean total solids 7.4%) while the highest methane production rate of 0.40 g/L/day, calculated from COD balance, was obtained from undiluted cow dung (total solids 10.6%). Results suggest the potential for a 75-100% reduction in water demand.

Alkaline Prehydrolysis Prolongs Resin Life and Enhances the Adsorption of Phenolic Compounds

Phenolic compounds in oil wastewater are highly toxic and refractory. Hydrolysis at pH 12 for 12 h makes these compounds more vulnerable to attack and destruction. Under the binding and precipitation of polyaluminum chloride (PAC) at pH 8, the chemical oxygen demand (COD) was significantly reduced by 38%. The simulation found that hydrolysis + flocculation was a complex multistep process. The COD removal rate was mainly controlled by the prehydrolysis process. The metabolic pathway suggested that the m-cresol produced in the factory was oxidized to low water-soluble aldehyde. Alkaline hydrolysis converted the aldehyde into m-toluene-methanol, which was conducive to being captured by the PAC. Fourier transform infrared spectroscopy (FTIR) showed that the alkaline dehydrogenation of two m-methylphenyl carbinols produced a molecule that was removed by the resin. Generally, the particle size of the residue after alkaline hydrolysis was 6.4–8.3 nm, which was included in the pore size range of the resin. Therefore, the resin adsorption capacity for the hydrolyzed substances increased to 47,000 mg L−1, with 93% renewability. In short, hybrid technology reduces the concentration burden of the resin inflow and controls the molecular size of adsorbed substances for repurification. It strengthens the treatment effect of high COD wastewater and provides innovative ideas for extending the service life of resin.

Enhanced Wet Oxidation of Excess Sludge from Pharmaceutical Wastewater Treatment by NaOH

In the present study, enhanced wet oxidation of excess sludge from pharmaceutical wastewater by NaOH as an alkaline homogeneous catalyst was investigated. The experiments were carried out in a stainless-steel batch autoclave reactor. The highest volatile suspended solids (VSS) removal rate, 95.2%, was achieved at 260 °C within 60 min with an initial oxygen pressure of 1.0 MPa and NaOH 0.5 g·L−1. Simultaneously, the chemical oxygen demand (COD) removal rate of 57.3% was reached. The increase in volatile fatty acids (VFAs) demonstrated that the degradation of sludge was greatly accelerated by NaOH. Interestingly, the production of acetic acid, an intermediate by-product generated from the oxidation of organic compounds, increased significantly. These results illustrated that NaOH is a promising catalyst for the utilization of wet oxidation liquid of excess sludge as a carbon source for the treatment of wastewater.

Comparative analysis in the performances of four in‐ground lagoon anaerobic digesters treating palm oil mill effluent (POME)

AbstractWhile palm oil mill effluent (POME) from different sources will have varying characteristics due to the different process flows in mills, efficient monitoring and performance evaluation of anaerobic digesters in POME treatment are crucial to ensure stable biogas production with minimal operational problems. Therefore, this study aims to evaluate and compare the performances of in‐ground lagoon anaerobic digesters under mesophilic conditions in four different biogas plants (BGPs A, B, C and D) located in Malaysia with respect to total chemical oxygen demand (COD) removal and total biogas produced. Results show that all BGPs are still functioning well with satisfactory methane yields (.135–.364 Nm3 CH4/kgCOD removed) and COD removal efficiencies (67%–85%). ANOVA analysis shows that organic loading rate (OLR), temperature (T) and recirculation ratio (RR) have significant effects on the COD removal and biogas production of all four plants. BGP B has the highest amount of biogas produced (4.12 × 105 Nm3/month) and COD removal rate amongst other BGPs due to its most stable and lowest T (<40°C), high RR, and consistent and high COD load. Conversely, BGP D has the lowest COD removal and biogas production, which are mainly contributed by a high COD inlet (92 000 mg/L) and a high T in the anaerobic digester (48.7°C). Despite having a similar design of an anaerobic digester, this comparative study reveals that different BGPs will have different optimum operating conditions and limitations, depending not only on the operating conditions of the BGP (OLR, T and RR) but also on the raw POME quality stemming from the palm oil milling process. A future study would be focused on the optimisation of four BGPs for maximum biogas removal.

Iron/carbon conductive materials for enhancing anaerobic treatment of synthetic acrylamide wastewater

AbstractBACKGROUNDMost studies have focused on the degradation of acrylamide (AM) by a single strain. There are relatively few studies on the treatment of AM by anaerobic activated sludge. Previous studies have shown that conductive particles can change the mode of electron transport between anaerobic microorganisms. Therefore, this study compared the enhancement effect of three different particles (Fe3O4, granular activated carbon (GAC), graphite) on the treatment of synthetic AM wastewater by anaerobic activated sludge under different temperature conditions (30, 25, 20 °C) and particle dose (2, 6 g L−1).RESULTSThe results showed that 6 g L−1 GAC improved the removal rate of chemical oxygen demand (COD) and AM by 22.95% and 19% compared with the control group at 30 °C, respectively, indicating that the addition of GAC contributes to the degradation of AM and improves COD removal rate. Results of high‐performance liquid chromatography (HPLC) showed that the activated sludge with GAC obviously promoted the degradation of AM. Besides, a large amount of propionic acid was detected in all experimental groups during the reaction, and the activated sludge with GAC promoted degradation of propionic acid.CONCLUSIONAnaerobic activated sludge supplemented with sufficient GAC can not only absorb and degrade AM synchronously but also accelerate the conversion of intermediates, such as acrylic and propionic acids. Based on the results of HPLC and liquid chromatography–mass spectrometry, a possible method of degradation of AM by anaerobic activated sludge was proposed. © 2023 Society of Chemical Industry (SCI).

Photocatalytic Degradation of Sulfamethoxazole from a Synthetic Pharmaceutical Wastewater Using Titanium Dioxide (TiO2) Powder as a Suspended Heterogeneous Catalyst

Some medications in aquatic media pose a serious environmental risk. Sulfamethoxazole (SMX) is a member of the sulfonamide group. Photocatalysis offers a promising technique to degrade organic pollutants into environmentally friendly substances. This study examined the effect of operating conditions (pH, time, and temperature) of the ultraviolet (UV)/TiO2 photocatalytic process on the degradation of SMX in an aqueous solution. Decreasing the pH value positively affects SMX degradation, and better removal values were obtained at a pH equal to 4. The optimum operating conditions for complete degradation in a solution containing 500 mg/L of SMX, TiO2 0.5 mg/L irradiation time of 420 min, and pH 4. Under these conditions, Chemical Oxygen Demand (COD) removal was 62.6% at a temperature of 25 ℃. The effect of temperature was studied at three temperatures (25, 40, and 60 ℃) with pH 4. The elevation of temperature increased the COD removal rate to 99.62% at 60 ℃. Finally, the results of the reaction kinetics study showed that a first-order kinetics model described organic contamination removal data over time, and the obtained activation energy was 42.195 kJ/mol.

Treatment of coking wastewater using a needle coke electro-Fenton cathode: optimizing of COD, NH4+-N, and TOC removal and characterization of pollutants.

Coking wastewater is a typical organic refractory wastewater characterized by high chemical oxygen demand (COD), NH4+-N, and total organic carbon (TOC). Herein, coking wastewater was treated using a heterogeneous electro-Fenton (EF) system comprising a novel iron-loaded needle coke composite cathode (Fe-NCCC) and a dimensionally stable anode. The response surface methodology was used to optimize the reaction conditions. The predicted and actual COD removal rates were 92.13 and 89.96% under optimum conditions of an applied voltage of 4.92 V, an electrode spacing of 2.29 cm, and an initial pH of 3.01. The optimized removal rate of NH4+-N and TOC was 84.12 and 73.44%, respectively. The color of coking wastewater decreased from 250-fold to colorless, and the BOD5/COD increased from 0.126 to 0.34. Gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy show that macromolecular heterocyclic organic compounds decomposed into straight-chain small molecules and even completely mineralized. The energy consumption of the EF process was 23.5 RMB Yuan per cubic meter of coking wastewater. The EF system comprising the Fe-NCCC can effectively remove pollutants from coking wastewater, has low electricity consumption, and can simultaneously reduce various pollution indicators with potential applications in the treatment of high-concentration and difficult-to-degrade organic wastewater.

Catalytic Ozonation of Pesticide Wastewater by Using MCM-41 and ZSM-5/MCM-41 as Catalysts

In the present study, two catalysts, MCM-41 and ZSM-5/MCM-41, were prepared by the hydrothermal synthesis method and their catalytic ozonation performances on pesticide wastewater were investigated. MCM-41 and ZSM-5/MCM-41 were proved to be a mesoporous structure and a micro-mesoporous structure, respectively, by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption measurements. The experimental results indicated that the chemical oxygen demand (COD) removal rate increased from 57.46% without catalysts to 79.35% and 87.56%, respectively, in the presence of MCM-41 and ZSM-5/MCM-41 after 100 min of catalytic ozonation. The catalytic activity of ZSM-5/MCM-41 was found to be greater than that of MCM-41. OH· played an important role in the catalytic ozonation, which was verified by the tert-butanol test. The catalysts had highest activity at pH of 7, and both higher and lower pH values reduced the catalytic ozonation. The optimal ozone dosage was found to be 22.0 mg L−1 min−1 for the COD removal of the pesticide wastewater. The catalysts could be reused five times without significant loss of the catalytic activity, suggesting that the catalysts could be promising catalysts for the catalytic ozonation of the pesticide wastewater.

Enhanced degradation of quinoline in three-dimensional electro-Fenton system through NiCo2S4/g-C3N4 particles

The stability and toxicity of quinolines are difficult to degrade by conventional physicochemical and biological methods, posing a threat to human health and the environment. In this study, we prepared NiCo2S4/g-C3N4 particles and applied them in an electrochemical reactor to form a three-dimensional catalytic particle electro-Fenton system (3D-EF), which can efficiently remove quinoline from wastewater. The NiCo2S4/g-C3N4 catalytic particles were characterized by XRD, SEM, TEM, XPS. The optimum conditions for 3D-EF were 30 min reaction time, 60 g/L NiCo2S4/g-C3N4 particles dosage, pH value of 3, 67.6 mmol/L H2O2 concentration, 12.1 ms/cm conductivity and 5 A current. Under the optimum conditions, a chemical oxygen demand (COD) removal rate of 95.6% was achieved. NiCo2S4/g-C3N4 catalytic particles can be easily recovered by filtration and can be reused. Kinetic analysis showed that the COD degradation of quinoline solutions by the 3D-EF followed a first-order kinetic model. To determine the important role of hydroxyl radicals in the electrochemical process, electron paramagnetic reaction (EPR) and radical scavenging experiments were performed. Finally, in order to elucidate the degradation mechanism, the intermediates were identified by high performance liquid chromatography-mass spectrometry (HPLC-MS) and two possible degradation pathways were proposed. Meanwhile, the biochemical analysis of quinoline wastewater was also performed.

Treatment and prevention of pollutants in the wastewater from a scheelite and fluorite processing plant

Mineral processing wastewater contains high levels of chemical oxygen demand (COD), suspended solids (SS) and heavy metal ions, and its substandard discharge will pose a threat to the ecological environment and human health. In this study, a combined method of coagulation and Fenton oxidation was used to remove pollutants from scheelite and fluorite processing wastewater. The experimental results showed that the overall removal rates of COD, SS, Pb2+ and Zn2+ from the wastewater samples reached 88.41 %, 99.73 %, 99.09 % and 99.31 %, respectively, after stepwise treatment with poly ferric sulfate (PFS) coagulation and Fenton oxidation. The main contributors of COD in the wastewater samples were sodium oleate (NaOL) and benzohydroxamic acid (BHA). The maximum COD removal by PFS coagulation was >90 % for NaOL solution, but <45 % for BHA solution. The COD removal effect of Fenton process on NaOL solution was also better than that of BHA. This indicated that the removal effect of COD was not only related to the experimental conditions but also to the structure of organic compounds. Based on the above research, a monitoring and management system of pollutants was established, and the effective removal of pollutants was confirmed by industrial tests in a plant. This study provides a certain theoretical basis and technical support for the efficient treatment of mineral processing wastewater and is of great significance for the protection of the ecological environment around the mine.

Pilot-scale study and biochemical verification of salt-tolerant catalyst Fe-Bi@γ-Al2O3 for catalytic ozonation of high-salinity wastewater

In this study, Fe-Bi@ γ-Al2O3 was used as a catalyst to construct a heterogeneous catalytic ozonation system for the treatment of high-salinity organic wastewater and its biochemical verification was studied. The optimum operating conditions and degradation mechanism of Fe-Bi@ γ-Al2O3 catalytic ozonation of high salinity wastewater were systematically investigated. The biodegradability of wastewater before and after treatment was also studied. Under the optimum operating conditions of ozone dosage of 160 mg/L, catalyst filling rate of 15%, ratio of height to diameter of 15, hydraulic retention time of 210 min and recycle ratio of 500%, the removal rate of COD is 45.13%. The mechanical strength of Fe-Bi@ γ-Al2O3 catalyst is almost unchanged after being reused for 20 times. The results of Ultraviolet and visible spectrophotometry (UV-Vis), 3D (Three-Dimensional)-fluorescence and Gas Chromatography-Mass Spectrometer (GC-MS)showed that humus, fulvic acid and undissolved microbial organic matter were degraded. In the biochemical verification experiment, after the high salinity wastewater was used to impact the bio-reactor, the mixed liquor suspended solids (MLSS) was basically stable at 9597 mg/L, 8856 mg/L, 9414 mg/L and 8741 mg/L, and the mixed liquor volatile suspended solids (MLVSS) was basically stable at 7042 mg/L, 6940 mg/L, 6949 mg/L and 6519 mg/L. The dissolved oxygen (DO) in the four reactors were 2.9 mg/L, 3.48 mg/L, 3.6 mg/L and 2.92 mg/L respectively, and the sludge Volume Index (SVI30) were 93 mL/g, 98 mL/g, 93 mL/g and 91 mL/g respectively. After two cycles (20d) of 30% high salinity wastewater, the chemical oxygen demand (COD) removal rates of the four reactors were 78%, 84%, 86% and 91%, respectively. When the reaction time is 40 min, the BOD5/COD (B/C) value of the high-salinity wastewater reaches 0.91, and the biodegradability of the wastewater is improved significantly. Scanning electron microscope (SEM) showed that the granular sludge in the reactor had compact structure and smooth surface, and there were a lot of fungi and filamentous microorganisms on the sludge surface.in that condition of salinity stress, the microbial community in the activate sludge changed to a great extent, and Proteobacteria and Bacteroidetes became the main phylum. The Fe-Bi@ γγ-Al2O3 catalyst has good catalytic performance and can be used for deep treatment of high-salt organic wastewater.

Enhanced degradation of azo dye using mixed cultures of white-rot fungi in a modified rotating packed disc bioreactor and reuse of treated water

Reactive azo dyes are toxic and carcinogenic. In this study, mixed cultures of white-rot fungi (WRF) are used to treat synthetic reactive black 5 (RB-5) wastewater in a modified rotating packed disc bioreactor (RPDB). The continuous degradation studies were carried out for 25 days under the influence of the recycle stream in which 3665 L of synthetic effluent was treated. The dye wastewater was completely decolorized with more than 93 % chemical oxygen demand (COD) reduction using the mixed fungal culture. During the continuous operation, the COD of influent reduced more than 85 % for successive 25 days of continuous operation at hydraulic retention time of 10.8 h. The dry biomass loading was about 0.14 g/g GAC at the end of the continuous process. The rate of COD removal followed first order kinetics with a rate constant of 0.026 per hour. The treated water was reused to produce melanin from microbial culture.

Evaluation of the Efficiency of Ti/IrO2/RuO2 Anode in COD Removal from Paper Industry Wastewaters by Electrooxidation Method

In the research, the electrooxidation method of the electrochemical treatment methods in thebatch system was explored a variety of experimental conditions for the treatment of wastewater from thepaper sector. 4 anodes and 4 cathodes sieve type plates with dimensions of 7 cm x 10 cm were positionedat 0,5 cm intervals in the 2000 mL volume jacketed glass reactor used for the treatment of wastewater fromthe paper industry, and 1200 mL wastewater was used in the testing. 4 coated Ti/IrO2/RuO2 electrodes ofthe sieve type were used as the anode material and 4 uncoated Ti electrodes of the sieve type were utilizedas the cathode material in the electrooxidation of effluent from the paper industry. In the experiments, theremoval rate of the COD (Chemical Oxygen Demand) pollutant parameter; The effects of supportingelectrolyte types and concentrations such as KCl, NaCl, NaNO3, and Na2SO4, and parameters such as initialpH value and current density of wastewater without supporting electrolyte were investigated. According tothe results obtained; In the experiments conducted at the natural pH value of wastewater, 18.55 mA/cm2was the most effective current density, 0.50 M NaCl was the most effective supporting electrolyte type andconcentration. The COD removal rate at the best conditions (37.11 mA/cm2current density) was 90.62%.In optimum conditions; 73.20% COD removal efficiency has been achieved.

Treatment of compressed leachate from refuse transfer stations by freeze-melt method

A small amount of leachate with complex composition will be produced during the compressing of municipal solid waste in refuse transfer stations. In this study, the freeze-melt method, a green and efficient wastewater treatment technology, was used to treat the compressed leachate. The effects of freezing temperature, freezing duration, and ice melting method on the removal rates of contaminants were investigated. The results showed that the freeze-melt method was not selective for the removal of chemical oxygen demand (COD), total organic carbon (TOC), ammonia-nitrogen (NH3-N) and total phosphorus (TP). The removal rate of contaminants was positively correlated with freezing temperature and negatively correlated with freezing duration, and the slower the growth rate of ice, the higher the purity of ice. When the compressed leachate was frozen at −15 °C for 42 h, the removal rates of COD, TOC, NH3-N and TP were 60.00%, 58.40%, 56.89% and 55.34%, respectively. Contaminants trapped in ice were removed during the melting process, especially in the early stages of melting. The divided melting method was more beneficial than the natural melting method in removing contaminants during the initial stage of melting, which contributes to the reduction of produced water losses. This study provides a new idea for the treatment of small amounts of highly concentrated leachate generated by compression facilities distributed in various corners of the city.

Integrated ozonation and mineralization of alkyl xanthate: Influence of operation parameters and structure-activity relationship

Xanthate is widely used in the flotation process of sulfide ores, and large amount of flotation wastewater with xanthate is produced and caused serious wastewater pollution due to its excessive usage. This study intensively studied ozonation and various ozone based advanced oxidation processes (AOPs) for alkyl xanthates (AXs) degradation and mineralization, including catalytic ozonation, peroxone and photocatalytic ozonation. The key operation parameters, such as ozone dosage, ratio of different oxidants and solution were studied. All integrated ozonation processes improved the mineralization efficiency of AXs, among which TiO2 photocatalytic ozonation is the most efficient, and the chemical oxygen demand (COD) removal rate can reach 84.9% in 60 min. A quantitative structure-activity relationship (QSAR) model was also established for ozonation of xanthates for the first time, based on quantum chemical calculation of series of xanthate structures and their degradation rate constants in ozonation. It reveals that the main factor affecting the ozonation rate constant is the molecular volume, which is negatively linearly correlated with the length of carbon chain of alkyl substituent group. The degradation intermediates of potassium amyl xanthate were measured by ultraviolet-visible spectroscopy (UV-Vis) and gas chromatography-mass spectroscopy (GC-MS), based on which a degradation path of xanthate was proposed. This work provides deeper understanding of advanced oxidation and mineralization of AXs, and may guide the development of treating technology for flotation wastewater.

Shale gas hydraulic fracturing flowback fluid treatment using a modified vortex flocculation reactor: Effects of the axial and tangential inlet angles

Flocculation technology has been widely applied in treating shale gas hydraulic fracturing flowback fluid. To improve flocculation efficiency, we designed a series of vortex flocculation reactors with variable axial and tangential inlet angles. It was found that a flow field beneficial to flocculation would be formed when the axial and tangential inlet angles were 45° and 30°, respectively. Under this condition, the turbulent dissipation rate of the flow field was high near the inlet and decreased step by step from the bottom to the top of the reactor. The flocs were denser and more resistant to shearing and oscillations. Moreover, this reactor exhibited superior chemical oxygen demand and turbidity removal rates of 78.21% and 88.10%, respectively, which increased by 28.08% and 23.69%, when compared with the traditional reactor (both axial and tangential inlet angles were 0°). This study is a reference for developing and optimizing high-performance vortex flocculation reactors.

Potential application of a newly isolated microalga Desmodesmus sp. GXU-A4 for recycling Molasses vinasse

The development of cost-effective and energy-efficient technologies for the stabilization of organic wastewater by microalgae has been essential and sought after. In the current study, GXU-A4 was isolated from an aerobic tank treating molasses vinasse (MV) and identified as Desmodesmus sp. based on its morphology, rbcL, and ITS sequences. It exhibited good growth with a high lipid content and chemical oxygen demand (COD) when grown using MV and the anaerobic digestate of MV (ADMV) as the growth medium. Three distinct COD concentrations for wastewater were established. Accordingly, GXU-A4 removed more than 90% of the COD from molasses vinasse (MV1, MV2, and MV3) with initial COD concentrations of 1193 mgL−1, 2100 mgL−1, and 3180 mgL−1, respectively. MV1 attained the highest COD and color removal rates of 92.48% and 64.63%, respectively, and accumulated 47.32% DW (dry weight) of lipids and 32.62% DW of carbohydrates, respectively. Moreover, GXU-A4 grew rapidly in anaerobic digestate of MV (ADMV1, ADMV2, and ADMV3) with initial COD concentrations of 1433 mgL−1, 2567 mgL−1, and 3293 mgL−1, respectively. Under ADMV3 conditions, the highest biomass reached 13.81 g L-1 and accumulated 27.43% DW of lipids and 38.70% DW of carbohydrates, respectively. Meanwhile, the removal rates of NH4–N and chroma in ADMV3 reached 91.10% and 47.89%, respectively, significantly reducing the concentration of ammonia nitrogen and color in ADMV. Thus, the results demonstrate that GXU-A4 has a high fouling tolerance, a rapid growth rate in MV and ADMV, the ability to achieve biomass accumulation and nutrient removal from wastewater, and a high potential for MV recycling.

In-situ anaerobic treatment removes the passivation layer of sponge iron to restore the nitrogen and phosphorus removal performance of SBR

Sponge iron (s-Fe0) has a large specific surface area, is cheap and easy to obtain, and has a good reduction capacity. Therefore, its efficacy in enhanced wastewater denitrification and phosphorus removal has been extensively examined. Because of the strong magnetic properties and reactivity of s-Fe0, a passivation layer dominated by iron oxides is formed in liquid phase environments, and this layer inhibits the dissolution of Fe0. In this study, s-Fe0 was used as the carrier filler in an SBR reactor to remove the passivation layer on the surface of s-Fe0 by anaerobic means, and the performance of this reactor was investigated for the removal of chemical oxygen demand (COD), nitrogen, and phosphorus from actual domestic wastewater. The anaerobic treatment of the reactor for 4 days effectively removed the passivation layer on the s-Fe0 surface while the carbon source of the system was maintained with normal feed water. The average removal rates of COD, NH4+-N, and TP in the reactor were 85.67%, 99.8%, and 93.98%, respectively, and the efficient removal of phosphorus in the system was stable for 22–26 days. X-ray diffraction and microbial community analysis showed that, in addition to the formation of FePO4, Fe(PO3), and Fe2P4O12 precipitates were generated in the system to remove phosphorus, and that a synergistic effect aided biological phosphorus removal. Additionally, the presence of abundant microorganisms with corrosion functionality (such as Rhodobacter, Brevundimonas, and Thiobacillus) in the activated sludge system, on the s-Fe0 carrier surface, and inside the carrier, played an essential role in the corrosion and removal of the s-Fe0 passivation layer. These results demonstrated that s-Fe0 is a promising material for nitrogen and phosphorus removal, and anaerobic treatment can effectively alleviate the passivation of s-Fe0. Thus, the efficient removal of phosphorus from actual domestic wastewater can be sustainably achieved.

Experimental investigation on decomposition characteristics of doxycycline in wastewater using hydrothermal treatment: Exploring the way to complete decomposition

Doxycycline is widely found in medical and aquaculture wastewater, posing a great threat to the ecological environment. In this study, the doxycycline was decomposed by hydrothermal method, and its decomposition properties and paths were analyzed. By using univariate experimental method, the influence of hydrothermal temperature (100–340 °C), hydrothermal time (30–120 min) and mass concentration (1–4 wt%) on the decomposition rate of doxycycline, chemical oxygen demand and nitrogen distribution in the product were studied, and the Pearson correlation coefficient of chemical oxygen demand, Total nitrogen and doxycycline removal rate was obtained. The results showed that the removal rate of doxycycline increased with the hydrothermal temperature, decreased with the reactant concentration, and increased first and then decreased with the hydrothermal time. The quantitative relation between the removal rate of doxycycline and operation conditions (temperature, time, and concentration) was obtained by using the response surface method, and the optimization conditions of the hydrothermal decomposition of doxycycline were gotten. The averaged removal rate of doxycycline reached 99.5% at temperature of 260 °C, reaction time of 102.2 min, and mass concentration of 1.4 wt%. Finally, the liquid chromatography and mass spectrometry were used for quantitative and qualitative analysis of liquid products, and three potential hydrothermal decomposition routes of doxycycline were proposed. This study will lay the foundation for the hydrothermal treatment of medical and aquaculture wastewater containing antibiotics.