Chemical Oxygen Demand Removal Rate Research Articles

Labile oxygen-driven catalytic ozonation via surface peroxide pathway for efficient wastewater treatment

The aluminosilicate-based heterogeneous catalysts hold great promise for industrial catalytic ozonation; however, the lack of exploration into novel active sites and mechanism studies has impeded their development. In this work, we demonstrate that labile oxygen (Olab) can be generated in mullite (mullite-Olab) by the introduction of extra Al-O4 tetrahedral units. In our experiments, mullite-Olab exhibits excellent performance in terms of catalytic ozone activation, with a degradation rate of 87.4 % within 15 min for nonbiodegradable atrazine, corresponding to a high quasi-first-order rate constant (k, 0.112 min−1), while the degradation constant is close to 0 for mullite without Olab. Operando Raman and density functional theory (DFT) simulations further reveal that Olab activates ozone via a novel surface peroxide pathway to generate surface Olab-O* species with a high oxidizing ability. The mullite-Olab is stable with an average Al3+ leaching of 0.339 ppm during cycling, meeting the effluent discharge standard of the total Al. Moreover, we achieve the kilogram synthesis of mullite-Olab, which shows promising activity in the catalytic ozonation of acrylic fiber wastewater, with the chemical oxygen demand (COD) and total organic carbon (TOC) removal rates of 46.0 %±4.8 % and 24.9 %±2.8 % for 5 cycles. This work is the first to demonstrate the role of Olab in ozone activation and provides an advanced mullite-Olab catalyst for future nonbiodegradable wastewater treatment.

Syntrophy between bacteria and archaea enhances methane production in an EGSB bioreactor fed by cheese whey wastewater

The cheese-making process generates large amounts of cheese whey wastewater (CWW), which is abundant in nutrients but difficult to dispose of, contributing to the eutrophication of natural environments due to inadequate waste management. Here we show the anaerobic digestion of CCW by syntrophy between bacteria and archaea in an expanded granular sludge bed (EGSB) bioreactor as a low-cost alternative for bioremediation and biofuel production. The performance of the EGSB bioreactor and the composition of the natural microbial community were evaluated. During the operation of the EGSB bioreactor, physicochemical parameters such as alkalinity ratio (0.25), pH (7.5), and temperature (26°C) were attained and maintained, as well as light- and oxygen-free conditions, which favored the metabolism of oxygen-sensitive bacteria and methane-producing archaea (methanogens). Under these conditions, the chemical oxygen demand (COD) removal rate was highly efficient (> 89%). Methane (CH4) was produced from organic matter degradation by a few methanogens, mainly from Methanosaeta spp., and was enhanced by the metabolic interaction between bacteria and archaea. The biochemical methane potential (BMP) was >335 mL CH4/gCOD, indicating that the syntrophic microbial community is very efficient in removing organic matter and CH4 produced from CWW. Our results suggest that CWW could be treated in EGSB bioreactors and used as a sustainable alternative to CH4 production and also provide insights for the design of synthetic microbial communities (SynComs) for bioremediation, biogas production, and other biotechnological processes.

Enhanced removal of phenol and chemical oxygen demand from coking wastewater using micro and nano bubbles: Microbial community and metabolic pathways

The treatment of coking wastewater with high phenol concentrations has been a challenge for conventional biological treatment technology. In this short communication, phenol-degrading bacteria domesticated by micro and nano bubbles (MNBs) water are used to treat the high- concentration phenol in an MNBs aeration reactor (MNB-AR). The results show that the MNB-AR can greatly improve the removal of phenol and chemical oxygen demand (COD). At a phenol concentration of 1000 mg L−1, the phenol and COD removal rates in the MNB-AR are 55 % and 39 % higher than in the conventional bubble aeration reactor respectively. MNB-AR performs more stably and reaches a higher phenol tolerance under fluctuating high-phenol-concentration loadings. Metagenomic analysis shows that MNBs promote the growth and metabolism of aerobic microorganisms related to phenol degradation, and enhance gene abundance related to carbon metabolism. MNBs aeration combined with microorganisms is an efficient solution for treating coking wastewater.

Impact of liquid velocity and stacking modes on the performance of anaerobic fluidized bed microbial fuel cell

A stacked anaerobic fluidized bed microbial fuel cell (AFB-MFC) consisting of 10 individual air-cathode MFCs was constructed to measure its power generation performance at different liquid velocities and stacking modes. Open-circuit voltages produced in parallel and series connection modes were observed to reach the peak value of 617.6 mV and 5.3 V, respectively, at the liquid velocity of 7.5 mm/s. In series mode, the stacked AFB-MFC had the highest power density of 3440.1 mW/m2. The chemical oxygen demand removal rate of the stacked AFB-MFC under series connection reached up to 96.87%, slightly higher than that under the parallel condition. The results illustrated that a proper liquid velocity can effectively improve the mass transfer efficiency of the stacked AFB-MFC, while mitigating the internal resistance. By putting the stacked MFCs in series connection mode, voltage losses are evident, indicating that high internal resistances lead to the generation of a parasitic cross current.

Study on the treatment of corn alcohol wastewater by the internal circulation anaerobic reactor.

To comprehensively assess the efficacy of employing the internal circulation (IC) anaerobic reactor for corn alcohol wastewater treatment and investigate its feasibility, this study focused on anaerobic digestion parameters, energy balance, and the composition of the prokaryotic microbial community. During the operation of the reactor, the hydraulic retention time was progressively reduced from 4.8 to 1.6 days while achieving an average organic loading rate of 12.46 kg chemical oxygen demand (COD)/(m3·d). Moreover, the removal rate of COD exceeded 98%, and the energy balance (ΔE) reached 10.29 kJ/g fed COD. The initial manifestation of organic acidosis in the reactor was a decline in gas production, which is primarily caused by propionic acid accumulation. The subsequent analysis revealed a high diversity of prokaryotes in granular sludge, with the predominant archaea primarily involved in methane production through the acetic acid pathway. The IC anaerobic reactor shows exceptional performance in treating corn alcohol wastewater by optimizing its operating conditions. Energy balance analysis confirmed the feasibility of the process. The findings of this study may offer valuable insights for optimizing control strategies and engineering applications.

Degradation of residual xanthate in flotation tailing wastewater by activated H2O2 with natural ilmenite: A heterogeneous fenton-like reaction catalyzed at natural pH

Efficient treatment of residual xanthate from tailing wastewater has attracted soaring interesting recently. Herein, effect of activated H2O2 by natural ilmenite (FeTiO3) as a catalyst on sodium butyl xanthate (SBX) degradation was systematically investigated. More than 98 % SBX degradation efficiency was achieved by the method under optimal conditions (a natural pH = 8.7, [FeTiO3]0 = 4.0 g/L, [H2O2]0 = 2.0 mM, and [SBX]0 = 40.0 mg/L), and chemical oxygen demand (COD) removal rate was 85.41 %. Kinetic studies indicated that SBX degradation efficiency in FeTiO3-H2O2 system conformed with a pseudo first order kinetic equation. Also, comparative experiments indicated that this system degraded SBX was superior to the H2O2 alone and FeTiO3 alone systems. Reactive oxygen species (ROS) were determined by quenching experiments and electron paramagnetic resonance (EPR) tests, suggesting that OH and O2− were the primary reactive radicals in FeTiO3-H2O2 system. Cycling experiments and leaching metal ion tests suggested that FeTiO3 still exhibited high catalytic activity and excellent stability after five times of recycling. Finally, possible degradation pathways and mechanism of SBX in this system were proposed. Consequently, this study promotes the application of natural iron-based minerals as a catalyst in wastewater treatment, and provides new insights into the effective treatment of organic pollutants in tailing wastewater.

Synergistic advancements in sewage-driven microbial fuel cells: novel carbon nanotube cathodes and biomass-derived anodes for efficient renewable energy generation and wastewater treatment

Microbial fuel cells (MFCs) offer a dual solution of generating electrical energy from organic pollutants-laden wastewater while treating it. This study focuses on enhancing MFC performance through innovative electrode design. Three-dimensional (3D) anodes, created from corncobs and mango seeds via controlled graphitization, achieved remarkable power densities. The newly developed electrode configurations were evaluated within sewage wastewater-driven MFCs without the introduction of external microorganisms or prior treatment of the wastewater. At 1,000°C and 1,100°C graphitization temperatures, corncob and mango seed anodes produced 1,963 and 2,171 mW/m2, respectively, nearly 20 times higher than conventional carbon cloth and paper anodes. An advanced cathode composed of an activated carbon-carbon nanotube composite was introduced, rivaling expensive platinum-based cathodes. By optimizing the thermal treatment temperature and carbon nanotube content of the proposed cathode, comparable or superior performance to standard Pt/C commercial cathodes was achieved. Specifically, MFCs assembled with corncob anode with the proposed and standard Pt/C cathodes reached power densities of 1,963.1 and 2,178.6 mW/m2, respectively. Similarly, when utilizing graphitized mango seeds at 1,100°C, power densities of 2,171 and 2,151 mW/m2 were achieved for the new and standard cathodes, respectively. Furthermore, in continuous operation with a flow rate of 2 L/h, impressive chemical oxygen demand (COD) removal rates of 77% and 85% were achieved with corncob and mango seed anodes, respectively. This work highlights the significance of electrode design for enhancing MFC efficiency in electricity generation and wastewater treatment.

Co-Fe-N@biochar anode for improvment the electricity generation performance of microbial fuel cell

ABSTRACT Microbial fuel cells (MFCs) can generate energy while processing organic pollutants, which has a great impact on environmental wastewater treatment applications. In this study, a gel polymer was formed by Co-Fe-N co-doping biochar (Co-Fe-N@BC), which was used as the anode material to improve the electricity generation performance of MFC. The Co-Fe-N@BC material prepared at 900℃ carbonised biomass into more graphitic carbon, and its total resistance (3.56 Ω) was significantly reduced. In the corresponding dual-chamber MFC, the current density was 2.81 A/m2, and the power density reached 1181 mW/m2 at maximum. Among the materials tested, the Co-Fe-N@BC anode MFC had the highest chemical oxygen demand removal rate and coulombic efficiency, reaching 91% and 13%, respectively. It is proved that MFC with Co-Fe-N@BC anode has the best electrochemical performance.

The impact of multi-walled carbon nanotubes on the mechanical and environmental properties of porous concrete in removing pollutants for use in surface runoffs

Surface water is commonly acknowledged as the most polluted among the several water sources available. The principal pollutants consist of various industrial toxins, organic dyes, and heavy metals, specifically found in surface runoffs. The potential for enhancing water quality through the extraction of pollutants from runoff appears promising with the implementation of porous concrete, in conjunction with other additives. This study investigates the impact of varying quantities of coarse and fine aggregates, with variable water-to-cement ratios, on the mechanical properties of concrete. Furthermore, the effectiveness of MWCNT in the removal of chemical oxygen demand (COD) and the dye pollutant methylene blue via surface absorption and production cost are examined in this research. The results reveal that the MWCNT had significant effectiveness in removing COD and dye pollutants from surface runoff water. The greatest rate of COD removal observed was 71.34 %, while the maximum percentage of dye removal was 91.89 %. In addition, the integration of MWCNTs into the porous concrete matrix yielded improved mechanical characteristics, indicating a positive influence of this addition. Concerning the cost of samples, the inclusion of MWCNT resulted in an increase in the overall cost. However, the utilization of porous concrete pavements offers a promising prospect for cost savings, and with advancements in water purification and mechanical qualities, this method has considerable benefits.

Digestate quality and biogas enhancement with laterite mineral and biochar: Performance and mechanism in anaerobic digestion

Low biodegradation poses significant challenges to widespread adaptation of anaerobic digestion (AD) technology mainly attributed to low biogas yield. The biodegradation of organic substrate can be increased by enhancing direct interspecies electron transfer (DIET) by adding laterite mineral and biochar to the AD system. This study evaluates the efficiency of Laterite-mineral (LM), biochar (BC) and combination of LM and BC (LM-BC) to enhance biogas yield. Varying concentrations of LM (0.1–0.3%), BC (0.2–0.6 g/L), and LM-BC (0.05% + 0.1 g/L- 0.15% + 0.3 g/L) were introduced in AD systems of cow-manure (CM) at mesophilic conditions (37 °C). Results showed that BC0.6 g/L and LM0.3% produced the highest biogas (417 mLg−1 VS and 409 mLg−1 VS, respectively), followed by LM0.05% - BC0.1 g/L (367 mLg−1 VS). The BC0.6 g/L and LM0.3% also showed a higher chemical oxygen demand (COD) removal rate (41% and 40.2%, respectively) than the control group (30.1%) and LM0.05% - BC0.1 g/L (37.1%). Moreover, digestate with BC0.6 g/L and LM0.3% (5.73 and 5.65%, respectively) had higher fertility than LM0.05 % -BC0.1 g/L (5.39%) and control check CK (4.56%). Hence, BC0.6 g/L and LM0.3% are comparable to enhance the efficiency of AD system via DIET and are recommended for integration into large-scale AD systems.

A novel lateral epitaxial Bi2O3@BiOCl heterostructure for photocatalytic antibiotic degradation in an internal circulation fluidized bed reactor

Designing highly active and stable photocatalysts and promising photocatalytic devices can promote the practical application of photocatalysis, which remains in its early stage. Herein, we design an internal circulation fluidised bed photocatalytic reactor packed with epitaxial Bi2O3@BiOCl (BO@BOC) lateral heterostructures for high-efficiency antibiotic degradation. BO@BOC with defect-free lateral connection forces can initially drive the directional migration of electrons, resulting in efficient charge utilisation, and can subsequently generate abundant hydroxyl and superoxide radicals for superior ciprofloxacin (CIP) degradation (0.0524 min−1). The corresponding pseudo-first-order rate coefficient k of BO@BOC is 0.0524 min−1, which is approximately 57.1 and 10.1 times greater than that of pure BO and BOC, respectively. An 800 mL photocatalytic circulating fluidised bed reactor incorporated with BO@BOC/sponge operated under an LED panel exhibits long-term (10 days) stable CIP degradation (over 90 %) and a satisfactory chemical oxygen demand removal rate in river water, demonstrating its potential as a commercially viable photocatalytic system.

Treatment of mixed wastewater by vertical rotating microalgae-bacteria symbiotic biofilm reactor

A novel vertical rotating microalgae-bacteria symbiotic biofilm reactor was built to treat the mixed wastewater containing municipal and soybean soaking wastewater. The reactor was operated in both sequential batch and semi-continuous modes. Under the sequential batch operation mode, the maximum removal rates for Chemical Oxygen Demand (COD), Total Nitrogen (TN), Total Phosphorus (TP), and Ammonia Nitrogen (NH4+-N) of the mixed wastewater were 95.6 %, 96.1 %, 97.6 %, and 100 %, respectively. During the semi-continuous operation, the water discharge indices decreased gradually and eventually stabilized. At stabilization, the removal rates of COD, TN, and NH4+-N achieved 98 %, 95 %, and 99.9 %, respectively. The maximum biomass productivity of the biofilm was 2.69 g·m−2·d-1. Additionally, the carbohydrate, protein and lipid comprised approximately 22 %, 51 % and 10 % of the dry weight of Chlorella. This study demonstrates the great potential of the microalgae-bacteria symbiotic biofilm system to treat food and domestic wastewater while harvesting microalgal biomass.

Performance and Energy Utilization Efficiency of an Expanded Granular Sludge Bed Reactor in the Treatment of Cassava Alcohol Wastewater

In recent years, expanded granular sludge blanket (EGSB) reactor has been widely used in the treatment of high-concentration organic wastewater, but its research mainly focused on treatment efficiency and microbial community composition. There were few studies on the relationship of operation conditions and energy utilization efficiency. Therefore, the methanogenic characteristics and energy utilization efficiency of EGSB reactor were studied by using cassava alcohol wastewater (CAW) as a raw material at (36 ± 1) °C. The results show that the degradation of volatile fatty acids (VFAs) is an important step affecting methane generation compared to the hydrolysis stage. When organic load rate (OLR) was 12.73 gCOD/L·d, the chemical oxygen demand (COD) removal rate was above 95%, the methane production efficiency of raw material was 202.73 mLCH4/ gCOD·d, the four-stage conversion efficiency was the highest, and the energy utilization efficiency was 62.26%, which was the optimal stage for EGSB reactor to treat CAW. These findings support high-efficiency bioenergy recovery from CAW in practice and highlight the potential wide application of high-performance anaerobic reactors for CAW.

Catalytic valorization of Kraft lignin into feedstock chemicals with methyltrioxorhenium (MTO) catalyst in microbial electrochemical cell

In this study, the authors investigate a novel approach to valorize Kraft lignin using the catalyst Methyltrioxorhenium (MTO) in tandem with in-situ produced H2O2 in a Microbial Electrochemical Cell (MEC). This study demonstrates the in-situ oxidation of Kraft lignin using different concentrations of MTO catalyst (2 mM to 8 mM) and H2O2 (5.24 ± 0.40 mM to 8.91 ± 0.70 mM) in three MECs. The depolymerized Kraft lignin samples were characterized using FTIR, CHNS/O, and 1H NMR analysis. The MTO/H2O2 combination showed high selectivity towards the oxidation of Kraft lignin, resulting in both aromatic ring and side chain cleavage reactions and the production of valuable feedstock chemicals. The oxidation also led to a reduction of 68.42 % to 78.18 % in Chemical Oxygen Demand (COD) of lignin. The selective oxidation favored the recovery of Guaiacyl (G) unit-derived feedstock chemicals, with Guaiacol being the most abundant compound (45.04 mg/mL) among the quantified products by HPLC. Additionally, the system demonstrated high efficiency in anodic wastewater treatment, achieving BOD and COD removal rates ranging from 67.68 % to 72.55 %. This method showcases the use of a sustainable system in combination with a selective catalyst to produce valuable products from usually discarded Kraft lignin while simultaneously treating wastewater.

Nutritional ingredients and fertilizer potential of the dewatering effluent after sludge wet air oxidation

Wet air oxidation (WAO) is an effective technology for sludge treatment, and the treated sludge was mechanically dewatered to generate sludge cake and filtrate effluent. The sludge cake can be used as a soil conditioner or sent to landfills, but the effluent is usually sent back to wastewater treatment plants with nutrient waste. In this study, we proposed to use the effluent to process water-soluble organic fertilizer and analyzed its characteristics systematically and its effect on seed germination. The results showed that humic acid, protein, and polysaccharide were decomposed in different degrees in WAO with a chemical oxygen demand (COD) removal rate of 60–70%. After a WAO treatment at 240 °C, phosphorus, potassium, and heavy metals remained in the solid phase. At the same time, the effluent contained ammonium of more than 2800 mg/L, amino acids of nearly 3000 mg/L, humic acid derivatives of 2400 mg/L, and acetic acid of 3900 mg/L. Acetic acid was helpful in seed germination, while the other components were critical to root growth. The diluted effluent significantly prompted the germination and development of three kinds of plant seeds, particularly Spring Onion, with a germination index exceeding 200%.

Application of Attached Growth System for Laundry Wastewater Treatment

Laundry wastewater can be treated in a small-scale aerobic wastewater treatment (WWT) system utilizing a microbubble generator (MBG). However, removing pollutants, precisely chemical oxygen demand (COD), is often low, especially under high wastewater load conditions. This study aims to improve the WWT system’s performance by incorporating an attached growth system. The research was conducted in a small-scale WWT system with a volume of 832 L in Cokrodiningratan, Code Riverbank, Yogyakarta, treating real wastewater from a nearby laundry shop. Experiments were performed batch-wise for one week with suspended and nylon-fabric-attached growth systems. Wastewater samples from the WWT system were taken and analyzed for COD concentrations. Results indicate that the attached growth system outperforms the suspended growth system. During operation, the suspended growth system achieved a COD removal rate of approximately 78% (temperature range of 26-28°C, a pH level of 6.3-7.1, and influent COD: 377.5 mg/L). In contrast, with the introduction of attachment media under similar batch operation conditions (temperature range: 26-28°C, pH level: 6.4-7.4, influent COD: 755.5 mg/L), the COD removal efficiency increased to 94%. The incorporation of attachment media led to a notably stable performance outcome.

Effects of salinity and betaine addition on anaerobic granular sludge properties and microbial community succession patterns in organic saline wastewater

In this study, the effects of different salinity gradients and addition of compatible solutes on anaerobic treated effluent water qualities, sludge characteristics and microbial communities were investigated. The increase in salinity resulted in a decrease in particle size of the granular sludge, which was concentrated in the range of 0.5-1.0 mm. The content of EPS (extracellular polymeric substances) in the granular sludge gradually increased with increasing salinity and the addition of betaine (a typical compatible solute). Meanwhile, the microbial community structure was significantly affected by salinity, with high salinity reducing the diversity of bacteria. At higher salinity, Patescibacteria and Proteobacteria gradually became the dominant phylum, with relative abundance increasing to 13.53% and 12.16% at 20 g/L salinity. Desulfobacterota and its subordinate Desulfovibrio, which secrete EPS in large quantities, dominated significantly after betaine addition.Their relative abundance reached 13.65% and 7.86% at phylum level and genus level. The effect of these changes on the treated effluent was shown as the average chemical oxygen demand (COD) removal rate decreased from 82.10% to 79.71%, 78.01%, 68.51% and 64.55% when the salinity gradually increased from 2 g/L to 6, 10, 16 and 20 g/L. At the salinity of 20 g/L, average COD removal increased to 71.65% by the addition of 2 mmol/L betaine. The gradient elevated salinity and the exogenous addition of betaine played an important role in achieving stability of the anaerobic system in a highly saline environment, which provided a feasible strategy for anaerobic treatment of organic saline wastewater.

Evaluation of combined efficiency of conventional coagulation-flocculation process with advanced oxidation process (sulfate-hydroxyl radical) in leachate treatment

This study evaluated a novel municipal solid waste leachate (MSWL) treatment system called the Batch flow leachate treatment system (BFLTS). This process uses a combination of coagulation/flocculation (C-F), advanced oxidation (sulfate-hydroxyl radical), and extended aeration of activated sludge (EAAS) to treat MSWL. The results indicated that the primary treatment phase using coagulation/flocculation with 0.8 g L<sup>-1</sup> FeCl<sub>3</sub> at pH 6 achieved 67% turbidity and 63% chemical oxygen demand (COD) reduction. The secondary treatment phase with the presence of both K<sub>2</sub>S<sub>2</sub>O<sub>8</sub> and H<sub>2</sub>O<sub>2</sub> peroxides was more efficient than single peroxide processes. While PS-based or H<sub>2</sub>O<sub>2</sub>-based single peroxide processes are less effective (UV-PS 65.7%, UV-H<sub>2</sub>O<sub>2</sub> 43.2%, Heat-PS 58.6%, Heat-H<sub>2</sub>O<sub>2</sub> 34.5%, and Heat-PS/H<sub>2</sub>O<sub>2</sub> 74.8%). The UV-PS/H<sub>2</sub>O<sub>2</sub> system achieved the highest COD removal rate of 89.4%. In the third treatment phase, the efficient removal of COD and Biochemical oxygen demand (BOD) under optimal operating conditions was 87.3% and 94.7% respectively. Overall, the BFLTS treatment system has demonstrated high efficiency in removing COD, BOD, TSS, Turbidity, TKN, and Heavy metals by 99%, 98%, 97%, 89%, 86%, and 98%, respectively. This hybrid process has potential for reducing organic load in MSWL and can be used for various leachates.

Preparation of PrFexCo1–xO3/Mt catalyst and study on degradation of 2-hydroxybenzoic acid wastewater by catalytic wet peroxide oxidation

In this study, the perovskite nanocomposite PrFexCo1–xO3(Pr(S)) was successfully synthesized by the sol–gel method; PrFexCo1–xO3/Al-pillared montmorillonite (Pr(S)/Mt) catalysts were prepared by impregnation (D) method and solid-melting (G) method, respectively, with Pr(S) as the active component and Al-pillared montmorillonite as the carrier. The catalysts were applied to treat the 2-hydroxybenzoic acid (2-HA)-simulated wastewater by catalytic wet peroxide oxidation (CWPO) technique, and the chemical oxygen demand (COD) removal rate and the 2-HA degradation rate were used as indicators to evaluate the catalytic performance. The results of the experiment indicated that the solid-melting method was more conducive to preparing the catalyst when the Co/Fe molar ratio of 7:3 and the optimal structural properties of the catalysts were achieved. The influence of operating parameters, including reaction temperature, catalyst dosage, H2O2 dosage, pH, and initial 2-HA concentration, were optimized for the degradation of 2-HA by CWPO. The results showed that 97.64% of 2-HA degradation and 75.23% of COD removal rate were achieved under more suitable experimental conditions. In addition, after the catalyst was used five times, the degradation rate of 2-HA could still reach 76.93%, which implied the high stability and reusability of the catalyst. The high catalytic activity of the catalyst was due to the doping of Co into PrFeO3, which could promote the generation of HO·, and the high stability could be attributed to the loading of Pr(S) onto Al–Mt, which reduced the leaching of reactive metals. The study of reaction mechanism and kinetics showed that the whole degradation process conformed to the pseudo-first-order kinetic equation, and the Langmuir–Hinshelwood method was applied to demonstrate that catalysis was dominant in the degradation process.

Impact of Natural Microorganisms on the Removal of COD and the Cells Activity of the Chlorella sp. in Wastewater

In the treatment of wastewater containing only chemical oxygen demand (COD) by Chlorella sp., the cell activity and proliferation ability of Chlorella sp. decreased with the culture time, which affected the removal of COD in wastewater. To solve these problems, the Chlorella sp.–natural microorganism symbiosis system was prepared. The system was used to explore how natural microorganisms affect the cell activity and the proliferation ability of Chlorella sp. in wastewater. In the treatment of COD by Chlorella sp., the removal rate of COD decreased from 45.47% to 28.88%, with a decrease in the cell activity and proliferation ability of Chlorella sp. In the Chlorella sp.–natural microorganism symbiotic system, the removal rate of COD reached 45.75%. With the introduction of natural microorganisms, the circulation of CO2 and O2 between Chlorella sp. and natural microorganisms promoted photosynthesis and respiration, which enhanced the cell activity of Chlorella sp. Under the condition that the dosage of natural microorganisms was between 1% and 6%, the concentration of Chlorella sp. was close to the logarithmic growth phase, which maintained the proliferation ability of Chlorella sp. At the same time, the natural microorganisms grew and proliferated in wastewater containing only COD through preying on Chlorella sp.