COD Removal Rate Research Articles

Complex inhibitions on anaerobic degradation of monosodium glutamate in wastewater under low COD/sulfate ratios

To investigate the complex inhibitions leading to the deterioration of reactor performance in anaerobic treatment of monosodium glutamate (MSG) wastewater under low COD/sulfate ratios, a comprehensive assessment of the overall reactor performance, sludge characteristics and microbial community characteristics was conducted in this study. The COD removal rate of the reactor was maintained above 90% throughout the experiment, but the gas yield decreased by 52% due to the complex competition between sulfate-reducing bacteria (SRB) and methane-producing archaea (MPA) resulting in a decreasing number of MPA. The sludge characteristics and microbial community features indicated that the complex competition between SRB and MPA included competition for hydrogen and survival space in the reactor. In addition, the competitive advantage of SRB for electrons led to the production of more sulfides in the reactor, further inhibiting the activity of MPA. Therefore, the complex inhibition within the reactor for anaerobic treatment of MSG wastewater with low COD/sulfate ratios, including sulfide toxicity inhibition, competition between SRB and MPA for substrate and space, not only led to a reduction in gas production, but also affected microbial activity and glutamate degradation.

Purification effects of recycled aggregates from construction waste as constructed wetland filler

Three groups of constructed wetlands based on gravel (#1), asphalt concrete + red brick (#2), and red brick (#3) were constructed to explore their purification effects and the characteristics of microbial community structure. The results show that the construction waste recycled aggregates have little leaching risk of heavy metals; the adsorption of nitrogen and phosphorus by the three fillers could be well fitted by pseudo-first-order and pseudo-second-order kinetic models (R2 > 0.96); the adsorption of NH4+-N by the three fillers could be well fitted by the Freundlich model (R2 > 0.656); the adsorption of phosphorus could be well fitted by the Langmuir and Freundlich models, except for gravel (R2 > 0.875). The average removal rate of COD, NH4+-N, TN, and TP was 60.85 %, 94.69 %, 73.42 %, 39.12 % (#1); 67.32 %, 20.31 %, 22.26 %, 27.81 % (#2); 67.35 %, 17.7 %, 25.8 % and 46.98 % (#3). There was no significant difference in the purification effect of the three fillers on COD. The adsorption effect on NH4+-N was: gravel > red brick/asphalt concrete, and the adsorption effect on TP was: asphalt concrete > red brick > gravel. The microbial population richness of the upper filler was #2 > #1 > #3, the uniformity was #1 > #2 > #3, and the diversity was #1/#2 > #3. The microbial communities were dominated by Proteobacteria, Actinobacteriota, Bacteroidota and Chloroflexi.

The electrochemical microbial tree: A new concept for wastewater treatment

Most wastewater treatment plants involve activated sludge units, in which the organic matter to be removed is oxidised by aerobic microorganisms. These units are highly energy intensive because of the power consumed to force oxygen transfer to the wastewater by aeration. An innovative device is presented here; it is called the “electrochemical microbial tree (EMT)” and is based on the opposite strategy: the organic matter is drawn up from the wastewater towards the air phase by capillary action along a porous structure, which hosts the microorganisms that oxidise the organic matter.The EMTs were made of carbon felt, with the bottom immersed in wastewater (14 cm), while the top emerged into the air at different heights (4, 8 or 12 cm). COD removal increased linearly with the height of the aerial section. The greatest height led to COD removal rates of 807 ± 62 mg O2/L/h, i.e. 2.6 times those of the control experiments. During COD removal, the pH decreased from 7.6 to 7.4 ± 0.2 with EMTs, while it increased to 7.9 ± 0.1 in the controls. The biofilm on the immersed section developed as the height of the aerial section increased. Many electroactive species were identified in the microbial populations, belonging to the Bacteroidia, Gammaproteobacteria and Clostridia classes. These observations revealed that electron transfer along the conductive felt contributed to organic matter oxidation, in parallel with mass transfer by capillarity. These pioneering results present the EMT as a promising new wastewater treatment disposal system that does not require any energy input.

Effects of a novel Mg-C micro-electrolysis system for phenolic wastewater degradation: material characterization, influencing factors, and model optimization

ABSTRACT This study investigated a novel magnesium carbon micro-electrolysis (Mg-C ME) system for strengthening the removal of phenolic compounds in wastewater. The effects of the Mg/C mass ratio, aeration intensity, initial pH and reaction time on the degradation of three phenolic compounds and the COD removal efficiency in the simulated wastewater were evaluated using one-factor-at-a-time (OFAT) method. The optimum values obtained for the Mg/C mass ratio, aeration intensity, initial pH and reaction time were 3:1, 4.0 L/(L·min), 5.0 and 2.5 h, respectively. The experimental removal rates of catechol, resorcinol, and phenol, under the mentioned conditions, were obtained to be 95.6%, 71.5%, and 48.8%, respectively. Meanwhile, the COD removal rates were 63.8%,44.7%,34.0%, respectively. Moreover, experiments were designed and analyzed based on the box-based designing response surface (BBD-RSM) method. According to the results, the Mg/C mass ratio was the most significant variable showing incremental effect on the removal efficiency of catechol in a way that maximum removal efficiency of catechol was achieved in Mg/C mass ratio of 3.23:1. The validation experiments showed that the maximum removal efficiency of catechol was 96.24% under optimization conditions. Resorcinol degradation characteristics analysis indicated that the Mg-C ME system performed a key function in phenolic compounds elimination. Results showed that the Mg-C ME has a considerable capability in removing the phenolic compounds and COD. Thus, it could be considered as an efficient pretreatment choice for treating phenolic wastewater in the future.

Bi5+ doping improves the electrochemical properties of Ti/SnO2–Sb/PbO2 electrode and its electrocatalytic performance for phenol

Ti/SnO2–Sb/PbO2 is an anode with a good catalytic performance which can be further improved by using metal doping. One of the most potential metals is bismuth (Bi). In this study, Ti/SnO2–Sb/PbO2 and Bi3+ or Bi5+ doped electrodes (Ti/SnO2–Sb/Bi3+-PbO2 and Ti/SnO2–Sb/Bi5+-PbO2) were prepared, and the microscopic morphology and surface chemical compositions of three electrodes were compared. X-ray diffraction results showed that although Bi3+ and Bi5+ doping both inhibited the formation of PbO2 films to a certain extent, Bi5+ doping not only reduced the grain size of PbO2 but also increased more active sites on the electrode surface. The X-ray photoelectron spectroscopy and cyclic voltammetry results found the copresence of Pb2+ and Pb4+ on the surface of the Ti/SnO2–Sb/Bi5+-PbO2 electrode, which could induce superconductivity with better electron transfer ability than the other two electrodes. The electrochemical activities of the three electrodes were analyzed by conducting cyclic voltammetry and linear sweep voltammetry tests, and Ti/SnO2–Sb/Bi5+-PbO2 exhibited the highest catalytic reaction activity with the highest oxygen evolution potential (1.98 V). In the electrocatalytic oxidation experiment of 1100 mg/L phenol by adopting Ti/SnO2–Sb/Bi5+-PbO2, the removal rate within 3 h and the COD removal rate within 30 h could reach 99.65% and up to 95.92%, respectively, with the highest apparent kinetic coefficient of phenol of 0.03040 min−1. Radical scavenging experiments determined that 89% of phenol was removed by electrocatalytically generated •OH oxidation. The energy consumption evaluation of three electrodes revealed that Bi5+-doped electrodes possessed the highest average current efficiency and the lowest energy consumption. This study proposed a new doping option for Ti/SnO2–Sb/PbO2, which provided a reference and theoretical basis for the better application of this electrode in electrocatalysis practice.

A novel constructed wetland based on iron carbon substrates: performance optimization and mechanisms of simultaneous removal of nitrogen and phosphorus.

In recent years, the combination of iron carbon micro-electrolysis (ICME) with constructed wetlands (CWs) for removal of nitrogen and phosphorus has attracted more and more attention. However, the removal mechanisms by CWs with iron carbon (Fe-C) substrates are still unclear. In this study, the Fe-C based CW (CW-A) was established to improve the removal efficiencies of nitrogen and phosphorus by optimizing the operating conditions. And the removal mechanisms of nitrogen and phosphorus were explored. The results shown that the removal rates of COD, NH4+-N, NO3--N, TN, and TP in CW-A could reach up to 84.4%, 94.0%, 81.1%, 86.6%, and 84.3%, respectively. Wetland plants and intermittent aeration have dominant effects on the removal of NH4+-N, while the removal efficiencies of NO3--N, TN, and TP were mainly affected by Fe-C substrates, wetland plants, and HRT. XPS analysis revealed that Fe(0)/Fe2+ and their valence transformation played important roles on the pollutants removal. High-throughput sequencing results showed that Fe-C substrates and wetland plants had considerable impacts on the microbial community structures, such as richness and diversity of microorganism. The relative abundance of autotrophic denitrification bacteria (e.g., Denitatsoma, Thauera, and Sulfuritalea) increased in CW-A than CW-C. The electrons and H2/[H] produced from Fe-C substrates were utilized by autotrophic denitrification bacteria for NO3--N reduction. Microbial degradation was the main removal mechanism of nitrogen in CW-A. Removal efficiency of phosphorus was enhanced resulted from the reaction of phosphate with iron ion. The application of CWs with Fe-C substrates and plants presented great potential for simultaneous removal of nitrogen and phosphorus.

Promotion of methane production and degradation of pyrolysis oil during its co-anaerobic digestion process via addition of N-doping hydro-chars

Pyrolysis of wastes usually produces toxic pyrolysis oil (PO), which has complex ingredients, including benzene series and long-chain macromolecule organic pollutants. Co-anaerobic digestion (co-AD) can be an economic and high-efficiency method for PO degradation and recovery of methane simultaneously, but complete degradation of PO has not been achieved yet. Addition of a hydro-char in the process is beneficial to PO degradation and methane production. In this study, to further enhance the effectiveness of the hydro-char, nitrogen (N) was doped into the hydro-char by plasma modification in a NH3 atmosphere; and the effectiveness of the N-doped hydro-chars for promoting PO degradation and methane production during the co-AD process were evaluated. The experimental results indicated that all the hydro-chars can reduce the biotoxicity of the PO, improve its degradation during the co-AD process, and increase the methane yield. Compared with the plain hydro-char (HC), the hydro-chars modified at ambient temperature (HC–NH3–P-25) and at 500 °C (HC–NH3–P-500) can help achieving complete PO degradation and increasing the methane yield more effectively. The anaerobic digestor containing the HC-NH3-P-500 had the highest apparent methane yield (169.03 mLCH4/mLPO) and highest COD removal rate (79.5%). The nitrogen content, specific surface area, and electron transfer capability are found to be the key factors affecting PO degradation and methane yield; and the HC-NH3-P-500 had the highest N-doping, most specific surface area and electron transfer capability, explaining its best performance. The microbial communities of the digestate with the addition of the hydro-chars were founded to be richer with Clostridia and Methanosarcina, which could enhance the electron transfer between different microorganisms and contribute to the PO degradation.

Continuously feeding fenton sludge into anaerobic digesters: Iron species change and operating stability

Fenton sludge generated from the Fenton process contains a large number of ferric species and organic pollutants, which need to be properly treated before discharge. In this study, Fenton sludge as an Fe(III) source for dissimilatory iron reduction (DIR) was continuously added with increasing dosage into an anaerobic digester to enhance the treatment. Results showed continuously feeding Fenton sludge to the anaerobic digester did not deteriorate the performance and increased methane production and COD removal rate by 2.2 folds and 14.0%, respectively. The Fe content of sludge in the digester increased from 40.25 mg/g (dry weight) to 131.53 mg/g after continuously feeding for 77days, and then declined to 109.17 mg/g when the feeding was stopped. Mass balance analysis showed that 20.5 to 48.4% of Fe in the Fenton sludge was released to the effluent. After experiment, the ratio of reducible Fe species to the total Fe was 75.1%, which maintained the high activity in DIR. Microbial community analysis showed that iron-reducing bacteria were enriched with the addition of Fenton sludge and the sludge in the digester had a higher conductivity and capacitance to strengthen the electron transfer of DIR. All results suggested that feeding Fenton sludge into anaerobic digesters was a feasible method to dispose of Fenton sludge as well as to enhance the performance of anaerobic digestion.

Effect of corn stover hydrochar on anaerobic digestion performance of its associated wastewater

Hydrothermal carbonation (HTC) is an effective method to enhance the fuel quality of biomass in a subcritical water environment, but generates large amounts of wastewater (HTCWW), which was converted through anaerobic digestion (AD) into methane in this study. However, the toxic and refractory substances contained in HTCWW tended to cause operation instability of the AD system. The solid product in HTC of corn stover (CS), named CS hydrochar, was modified with KOH immersion and then added to the AD reactor to improve the methanogenic performance. The results showed that the optimum dosage of modified hydrochar (MCH) was 15 g/L, and the COD removal rate was increased by 19.3% and methane yield was increased by 42.3%–301 mL/g-COD, as the pore and the oxygen-containing functional groups of MCH provided colonization points for microorganisms, and also enhanced the electron transfer efficiency among methanogenic archaea. In addition, the increased alkalinity of MCH due to alkaline modification increased the pH buffering capability, and accelerated the consumption of acetic acid and butyric acid in the early AD stage (0–8 days) and propionic acid in the late AD stage (12–18 days), which then alleviated the organic acid accumulation and reduced the lag period by 2 days. The adverse effects of toxic and refractory substances of HTCWW on the AD performance were also decreased due to the adsorption of MCH at the beginning of the AD process, and latterly the adsorbed substances could be degraded by the microorganisms colonized on the MCH surface. The finding of this study showed AD is a feasible method to recover organic energy contained in HTCWW, and the associated hydrochar can be used as an effective promoter for the AD of HTCWW.

The pretreatment effects of various target pollutant in real coal gasification gray water by coupling pulse electrocoagulation with chemical precipitation methods

To prevent the scale formation in the equipments and pipelines after pre-treated coal gasification gray water (CGGW) entering the reuse system and reduce the influence of various pollutants in the effluent on subsequent biochemical treatment, this study presented a coupled use of pulse electrocoagulation (PEC) and chemical precipitation (CP) coupling method for the pretreatment of coal gasification gray water (CGGW). In addition, the operation parameters of PEC and the reaction conditions of PEC–CP were optimized based on iron plate as electrode and total hardness, turbidity and sludge yield as assessment indicators. Due to the formation of multi-hydroxyl iron by several minutes of pulse current, and the addition of pH regulator and coagulant aid, the efficient removal of various ions, hardness and turbidity was significantly reduced via various mechanism such as redox, precipitation, adsorption and coagulation reaction. The result indicated that under the optimal operation conditions, the total hardness, turbidity, and Fen+ of PEC–CP effluents were 275.0 mg/L, 3.0 NTU and 5.6 mg/L, respectively and sludge amount was 0.88 kg/m3. The removal rates of Si, B, Mn, Ba, COD, NPOC and NH4+–N by PEC–CP reached 80.0%, 75.4%, 97.0%, 99.8%, 35.0%, 33.6% and 23.8%, respectively. The present results suggested that the CGGW pretreatment effluents could be not only reused directly, but also greatly alleviate the scaling problem of water pipeline and coal gasification production facilities.

Separation of oil-water emulsions by a novel packed bed electrocoagulation (EC) process using anode from recycled aluminum beverage cans

Electrocoagulation (EC) is an emerging technology for the elimination of oil and COD content from oily wastewaters. However, higher operating costs and electrode passivation are pressing challenges for its wide speared application. To overcome this setback, the present work has attempted to develop a new and inexpensive electrode using recycled aluminum (Al) beverage cans for the treatment of oily wastewater by electrocoagulation (EC) technology. It could be an alternative to conventional plate or tube electrodes in the EC process, it is the first contribution into the literature. In current work, recycled Al beverage cans filled with steel wool was used as anode, and commercial stainless-steel mesh (304) with cylindrical shape was used as cathode. The main EC performance measure was COD removal efficiency, impacts of significant process parameters in the EC process (such as operating voltage, electrocoagulation time, stirring rate, and NaCl concentration) on the effectiveness of EC process were investigated by using response surface methodology (RSM) based Box-Behnken Design (BBD) model. The RSM analysis results demonstrated that the highest COD removal rate of 93.53% was achieved under optimal conditions of operating voltage (15 V), electrocoagulation time (10 min), stirring rate (250 rpm), and NaCl concentration (1 g/L). In addition, energy consumption analysis was performed, an electrical energy efficiency of 0.160 kWh/kg COD was achieved. Afterward, ATR-FTIR spectroscopy, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and XRD analysis were performed under optimal conditions to characterize anode, and generated sludge during the EC process. Collectively, the findings in this study paves the way toward the development of sustainable EC technology for separation of emulsified oil-water mixtures, which gives the importance of the circular economy and sustainable management of industrial wastewaters.

Effect of organic shock loading on anaerobic performance of pumice-reinforced up-flow anaerobic sludge bed for incineration leachate treatment

The research and application of leachate in the treatment of leachate in UASB reactors are increasing, but UASB also has problems such as poor resistance to organic load impact and unstable operation. In order to improve the anaerobic performance stability of an up-flow anaerobic sludge bed reactor (UASB) subjected to high organic loading shock, pumice was added to the leachate from the incineration. The reinforcement effect of pumice on the anaerobic efficiency of the reactor was studied by increasing the influent load. The results showed that with a gradual increase in the influent organic load [11.6‒66.6 kg COD/(m3∙d)] and without the addition of pumice, irreversible acidification took place in the reactor (R1) when the influent load reached 14.51 kg COD/(m3∙d). The average methane output and content were reduced to 39.7 L/d and 66.16%, respectively. In contrast, the reactor (R2) with pumice could still be operated stably when the influent organic load reached 40.04 kg COD/(m3∙d). The COD removal rate reached 91.80%, and the average methane output and content were increased by 42.30% and 15.20%, respectively. The results of analyzing the sludge microbial community structure in the reactor showed that the adding of pumice could selectively enrich the methanogenic bacterium methanosaeta, promote the decomposition of volatile fatty acid (VFA), effectively mitigate the acid inhibition effect of VFA on the anaerobic reactor, and enhance the balance between acidogenic bacteria (Chloroflexi and Proteobacteria) and methanogenic bacterium (Methanosaeta) to a great degree. These results prove that the addition of pumice filler can reinforce the resistance of UASB to organic loading.

Study on the mechanisms of enhanced biological nitrogen and phosphorus removal by denitrifying phosphorus removal in a Micro-pressure swirl reactor

To reveal the mechanisms of enhanced biological nitrogen and phosphorus removal by denitrifying phosphorus removal in a Micro-pressure swirl reactor (MPSR), this study used a MPSR to treat municipal wastewater and enriched denitrifying phosphate accumulating organisms (DPAOs) by using its alternating anaerobic-anoxic-aerobic environment. The coupling of denitrification phosphorus removal (DPR) and simultaneous nitrification endogenous denitrification phosphorus removal (SNEDPR) was achieved in MPSR, and the average removal rates of COD, NH4+-N, TN and TP were 91.57%, 98.51%, 85.88%, 96.08% respectively. The results of the batch experiments showed that DPAOs activity in the low dissolved oxygen (DO) and high DO zones were 70.5% and 74.3%. The results of intracellular carbon source conversion patterns, microbial assays and functional gene prediction indicated that Flavobacterium and Dechloromonas dominated the DPR process in the low DO zone. Based on these findings, nutrient removal pathways within the MPSR were integrated.

Green biohydrogen production in a Co-digestion process from mixture of high carbohydrate food waste and cattle/chicken manure digestate

This study was investigated biohydrogen production on the effects of different ratio of food waste to seed digestate and pH value from co-digestion process in anaerobic reactor. The seed digestate was mixture of cattle manure 45%, corn silage 25%, chicken manure 15%, and olive pomace 15% which was collected from the biogas plant in central Italy. It was found that the peaks of total biogas and the biohydrogen productions were 1355 ± 26 and 436 ± 10 mL whereas the biohydrogen yield was 50.4 mL/g-VS (45.8 mL/g-COD) with 43.33% COD removal rate, the bacteria to substrate volatile solids (VS) ratio was 2:1 where seed digestate to food waste was 6:4 under pH 6.5. As a consequence, food waste with a high COD concentration can be adapted C/N ratio by the cattle manure and chicken manure in the seed digestate which resulted in a high biohydrogen production. The food waste co-digestion system mixed with biogas plant digestate is one of approach to increase total biogas production.

A novel pico-hydro power (PHP)-Microbial electrolysis cell (MEC) coupled system for sustainable hydrogen production during palm oil mill effluent (POME) wastewater treatment

Due to accelerating global efforts toward decarbonization, a clean hydrogen (H2) producing technology, Microbial Electrolysis Cell (MEC), has garnered considerable attention. However, MEC's external energy requirement has raised concerns about its sustainability, scalability and application costs. The objective of this research was to build a renewable energy generating system for MECs' performance enhancement during the treatment of Palm oil mill effluent (POME). A novel integration of a pico-hydro-power generator (PHP) with single-chambered MECs exceptionally improved its performance. The performance boost was observed as 1.16 m3-H2/m3d H2 and 113 A/m3current production in concomitant with 73% organics removal from Palm Oil Mill Effluent (POME) wastewater, which is higher than the previous single-chambered MECs studies. 78% H2 recovery rcat (H2) along with 57% coulombic efficiency (CE) corroborated the removal of a high percentage of electrons from POME organic materials to generate >96% pure H2. The MEC nourished POME wastewater degrading communities while stimulating growth of electroactive Geobacter in the anodic biofilm which produced H2. The overall H2 recovery, COD removal rate and energy efficiency of PHP-MEC are superior than other MECs powered by other external renewable energy sources reported to date. The PHP-MEC prototype paves the path of scale up studies to build a renewable energy dependent future.

Highly efficient Ni–Mo–P composite rare earth elements electrode as electrocatalytic cathode for oil-based drill sludge treatment

It is considered an effective strategy to improve electrochemical performance that introducing rare elements into metal catalysts, which would provide abundant electrochemical active sites and be a benefit for redox reactions. A new Ni–Mo–P composite electrode material modified with rare earth elements (light rare earth Nd and heavy rare earth Yb) was prepared, evaluating the current density of direct current electrodeposition, the doping ratio of Yb and Nd, and the cyclic voltammetry deposition (CVD) cycle numbers on electrode structure and electrochemical performance. The results showed that the electrode has the most obvious amorphous state, the lowest hydrogen evolution overpotential (41.5 mV vs Ag/AgCl) and charge transfer resistance (15.74 Ω/cm2), and remarkable stability when the molar ratio of Yb and Nd was 8:2 and the 20 cycle numbers under the CVD condition. The electrochemical performance and characterization of the electrode showed that there was a good synergistic effect between rare earth elements (Yb, Nd) and Ni–Mo–P alloys. The oil-based drill sludge (OBDS) treatment indicated that the organic matter content is significantly reduced by using the above-modified electrode as the cathode, and the COD and petroleum removal rate can reach up to 85.4 ± 1.2% and 66.2 ± 5.9%. The effect of degradation for aliphatic hydrocarbon was better than aromatic hydrocarbons and no other intermediates are produced during the degradation, which may eventually mineralize the organic matter. This research provided technical support for the preparation of new Ni–Mo–P electrodes modified with rare earth elements and confirmed that electrocatalytic technology was a suitable method for OBDS treatment.

The changing C/N of aggressive aniline: Metagenomic analysis of pollutant removal, metabolic pathways and functional genes

In order to optimize the degradation of high-concentration aniline wastewater, the operation of sequencing batch bioaugmentation reactors with different aniline concentrations (200 mg/L, 600 mg/L, 1000 mg/L) was studied. The results showed that the removal rates of aniline and COD in the three reactors could reach 100%. When the aniline increased to 600 mg/L, the nitrogen removal efficiency reached the peak (51.85%). The increase of aniline inhibited the nitrification, while denitrification was enhanced due to the increase of C/N ratio. But this change was reversed by the toxicity of high concentrations of aniline. The metagenomic analysis showed that when the aniline concentration was 600 mg/L, the abundance distribution of microbial samples was more uniform. The improved of aniline concentration had led to the increase of aromatic compounds degradation metabolic pathways. In addition, the abundance of aniline degradation and nitrogen metabolism genes (dmpB, xylE, norB) was also promoted.

Supramolecular photocatalyst of perylene bisimide decorated with α-Fe2O3: Efficient photo-Fenton degradation of organic pollutants

The composite of α-Fe2O3/PTCDI based on supramolecular photocatalyst of perylene bisimide (PTCDI) decorated with α-Fe2O3 was prepared via calcination of ferric nitrate with self-assembly PTCDI. The composite displayed an enhanced performance for the degradation of phenol pollutants and coking wastewater via photo-Fenton reaction relative to the single component, which owing to efficient charge transfer on the heterojunction and effective Fe3+/Fe2+ conversion. The degradation ratio of phenol by the composite catalyst was increased by 73 % and 17 % under photo-Fenton reaction compared with the constituent monomer of α-Fe2O3 and PTCDI respectively. For coking wastewater, the COD and TOC removal rates of α-Fe2O3/PTCDI were up to 66.7 % and 44.5 %. The enhanced degradation activity with photo-Fenton condition was attributed to the formed type II heterojunction between the two semiconductors, effectively inhibiting the recombination of e- and h+ and the injected electrons from PTCDI to α-Fe2O3 beneficial to the Fe3+/Fe2+ cycle, further promoting the Fenton reaction. This effective photo-Fenton degradation system shows potential application value in treatment of complex industrial wastewater.

Catalytic ozonation of high-salinity wastewater using salt-resistant catalyst Fe-Bi@γ-Al2O3

In this study, a salt-tolerant Fe-Bi@γ-Al2O3 catalyst with stable structure and excellent catalytic performance was prepared with an impregnation method by using γ-Al2O3 as the carrier. The effects of calcination temperature and calcination time on the catalytic activity of the Fe-Bi@γ-Al2O3 catalyst were evaluated. The catalyst was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, BET, X-ray diffraction, and X-ray fluorescence spectrometry to analyze the relationship between the catalyst's apparent morphology, structural characteristics, and catalytic activity. The optimal working conditions and organic degradation mechanism of Fe-Bi@γ-Al2O3 catalytic ozonation of a high-salinity organic wastewater system were studied. The active components Fe and Bi were successfully loaded on the surface of γ-Al2O3 in the form of Fe2O3 and Bi2O3 crystals. Under the working conditions of ozone aeration rate of 0.2 L/min, catalyst filling rate of 10 %, and pH = 11, the removal rate of COD in high-salinity organic wastewater was 83.9 %. The degradation mechanism of organic matter in wastewater was analyzed using ultraviolet absorption peak and three-dimensional fluorescence spectrum. Kinetic analysis of the COD removal rate of high-salinity organic wastewater under optimal working conditions was carried out. A 3E evaluation model of Fe-Bi@γ-Al2O3 catalyst for ozonation treatment of high-salinity organic wastewater was established to realize overall evaluation of the process performance.

Removal of furfural using zero gap electrocoagulation by a scrap iron anode from aqueous solution

In the present study, furfural removal by a new electrochemical reactor with a zero-gap distance between the scrap iron anode and the cathode from aqueous solutions was investigated. The effects of the operational parameters, including initial furfural concentration (100–600 mg/L), current density (0.68–3.44 mA/cm2), solution pH (4–11), and hydraulic retention time (5–180 min), were evaluated.The experimental results indicated that a current density of 2.75 mA/cm2, an initial furfural concentration of 100 mg/L, and a pH of 7.0 were the most favorable conditions for the complete removal of furfural (>88 %) within 120 min of hydraulic time. Based on the LC-MS analysis, furan-2-carboxylic acid, furan-2-yl hydrogen carbonate, furan-2-ol, furan-2(5H)-one, maleic acid, acetic acid, oxalic acid, and formic acid were the main intermediates identified in furfural degradation. The TOC and COD removal rates were 64.75 and 75.62 % in the zero-gap electrocoagulation (ZG-EC) system under the optimized conditions, respectively. According to the kinetic results, the rate of furfural removal by the ZG-EC process followed the pseudo-first-order kinetics (R2 > 0.9). Finally, the degradation pathway of furfural using the ZG-EC process is proposed.