Ozone direct oxidation pretreatment and catalytic oxidation post-treatment coupled with ABMBR for landfill leachate treatment

Ozone oxidation of actual waste leachate coupled with culture of microalgae for efficient lipid production under different temperatures

The production of waste leachate (WL) has been increasing annually with the growth of population and the improvement of living standards, but it has become a difficult task to treat and resource it. Furthermore, the shortage of energy is becoming more serious, so the development of renewable energy instead of expensive fossil fuels is especially essential for productive life. This study constructed a system to oxidize WL by ozone at different temperatures and used it as a culture substrate for microalgae to produce biodiesel. It was shown that the biomass and lipid content of microalgae reached 420 ± 43.59 mg/L and 41 ± 2.2 % at a low temperature of 15 °C, respectively. Compared with the reaction system at 5 °C, the oxidation of WL by ozone at 25-45 °C was more effective in removing ammonia nitrogen, total phosphorus, and chromaticity. Three-dimension excitation emission matrix (3D-EEM) fluorescence spectroscopy results showed that the fluorescence intensity of dissolved organic matter in WL was reduced by 59.4 %-67.7 % after the ozone oxidation, which improved the bioavailability of WL and laid a nutrient foundation for the growth of microalgae. At 45 °C, 72.7 % of the chromaticity of WL was removed by ozone oxidation alone, and the ozone-coupled microalgae treatment system reduced ammonia nitrogen from 416.25 ± 1.05 to 214.6 ± 7.99 mg/L in WL. In addition, microalgae regulated the antioxidant system to mitigate oxidative damage induced by high concentrations of reactive oxygen species (ROS) caused by extreme temperatures by adjusting the levels of superoxide dismutase (SOD), catalase (CAT) and reduced glutathione (GSH). The lipids of microalgae cultured in WL were dominated by saturated and unsaturated fatty acids, and the saturated fatty acids content of lipids reached 60.8 % at 15 °C, which was favorable for the production of biodiesel with better lubricating and combustion properties. This study provides a valuable theoretical basis for the resource utilization of WL and the practical production of microalgae biodiesel in cold regions.

Heterogeneous Activation of NaClO by Nano-CoMn2O4 Spinel for Methylene Blue Decolorization

In this study, the nano-spinel CoMn2O4 was synthesized by coprecipitation pyrolysis and employed to heterogeneously activate hypochlorite (NaClO) for the oxidative decolorization of methylene blue (MB). The crystal structure, elemental composition, surface morphology, and microstructure of the prepared CoMn2O4 nano-spinel were analyzed using a series of characterization techniques. The pyrolysis temperature was screened on the basis of MB decolorization efficiency and the leaching of metal ions during the reaction. The MB decolorization efficiency was compared using different catalysts and process. The impacts of CoMn2O4 dosage, effective chlorine dose, MB concentration, and initial pH on MB decolorization were explored. The catalytic mechanism of MB oxidation was elucidated through quenching experiments combined with radical identification. The degradation pathway of MB was preliminarily proposed based on the detection of the intermediates. The reusability of recycled CoMn2O4 was finally investigated. The results revealed that maximal MB oxidation efficiency and minimal leaching of Co and Mn ions were achieved at the calcination temperature of 600 °C. Complete oxidative decolorization of MB within 40 min was obtained at an initial MB concentration of 50 mg/L, a CoMn2O4 dosage of 1 g/L, an effective chlorine dose of 0.1%, and an initial pH of 4.3. Superoxide radical (O2•-) was found to be dominantly responsible for MB decolorization according to the results of radical scavenging experiments and electron paramagnetic resonance. The CoMn2O4 spinel can be recycled for five cycles with the MB removal in the range of 90.6~98.7%.

Preparation and performance of catalyst for organic peroxide wastewater treatment

To improve the oxidation pretreatment efficiency of wastewater from organic peroxides, a catalyst (CeO2-C catalyst) was developed using the calcination method with ceramic particles as the support. The crystalline structure and elemental composition of the CeO2-C catalyst were characterized by Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), and X-ray diffraction (XRD). This study explored the effects of CeO2 mass ratio, calcination temperature, and calcination time on the performance of the catalyst. The optimal preparation conditions were established through orthogonal experiments. Additionally, the synergistic effect of the catalyst on the ozone oxidation treatment of peroxide wastewater was investigated. The results indicated that the optimal preparation parameters were a CeO2 mass ratio of 4 %, a calcination temperature of 500 °C, and a duration of 5 h, respectively. After five cycles of reuse, the catalytic activity slightly decreased but remained relatively stable. With an ozone flow rate of 6 L/min, the CeO2-C/ozone catalytic oxidation process achieved a Chemical Oxygen Demand (COD) removal rate of 28.11 % in wastewater, and the B/C (the ratio of BOD concentration to COD concentration) of wastewater improved from 0.093 to 0.152. The calcination method proved effective for preparing the CeO2-C catalyst, which demonstrated significant catalytic performance and held promising application prospects in the oxidation pretreatment of organic peroxide wastewater.

Simultaneous Emerging Contaminant Removal and H2O2 Generation Through Electron Transfer Carrier Effect of Bi─O─Ce Bond Bridge Without External Energy Consumption

Conventional advanced oxidation processes (AOPs) require significant external energy consumption to eliminate emerging contaminants (ECs) with stable structures. Herein, a catalyst consisting of nanocube BiCeO particles (BCO-NCs) prepared by an impregnation-hydrothermal process is reported for the first time, which is used for removing ECs without light/electricity or any other external energy input in water and simultaneous in situ generation of H2O2. A series of characterizations and experiments reveal that dual reaction centers (DRC) which are similar to the valence band/conducting band structure are formed on the surface of BCO-NCs. Under natural conditions without any external energy consumption, the BCO-NCs self-purification system can remove more than 80% of ECs within 30 min, and complete removal of ECs within 30 min in the presence of abundant electron acceptors, the corresponding second-order kinetic constant is increased to 3.62 times. It is found that O2 can capture electrons from ECs through the Bi─O─Ce bond bridge during the reaction process, leading to the in situ production of H2O2. This work will be a key advance in reducing energy consumption for deep wastewater treatment and generating important chemical raw materials.

Recent progress and perspectives of typical renewable bio-based flocculants: characteristics and application in wastewater treatment

The research on bio-based flocculants for waste resource utilization and environmental protection has garnered significant attention. Bio-based flocculants encompass plant-based, animal-based, and microbial variants that are prepared and modified through biological, chemical, and physical methods. These flocculants possess abundant functional groups, unique structures, and distinctive characteristics. This review comprehensively discussed the removal rates of conventional pollutants and emerging pollutants by bio-based flocculants, the interaction between these flocculants and pollutants, their impact on flocculation performance in wastewater treatment, as well as their application cost. Furthermore, it described the common challenges faced by bio-based flocculants in practical applications along with various improvement strategies to address them. With their safety profile, environmental friendliness, efficiency, renewability, and wide availability from diverse sources, bio-based flocculants hold great potential for widespread use in wastewater treatment.

The efficiency and mechanism of excess sludge-based biochar catalyst in catalytic ozonation of landfill leachate

In this study, biochar was produced based on dehydrated excess sludge from the municipal wastewater treatment plant, which was used for catalytic ozonation of pollutants derived from landfill leachate. The necessary catalytic sites in the structure of biochar were originated from the inorganic metals and organic matters in the sludge, which included a large number of functional groups (e.g., C-C, CO, etc.), adsorbed oxygen (Oads accounted for 44.82%) and electron defects (ID/IG=1.01). These active sites could promote the generation of reactive oxygen species (ROS) (e.g., ·OH,·O2-, etc.). The synergistic interaction between the microorganisms in the activated sludge also facilitated the removal rates of pollutants. Proteobacteria, Bacteroidetes, and Deinococcu-Thermus were crucial in the bioreactor. In 16 days of reaction, the removal ratios of NH+4-N and COD were 98.95 ± 0.11% and 90.89 ± 0.47%, respectively. This study not only explains the mechanism of catalytic ozonation of biochar, but also provides a new way of the practical treatment of landfill leachate.

Construction of triphase interface for catalytic ozonation of polluted water

The utilization efficiency of ozone determines the cost of catalytic ozonation in water treatment. Herein, a triphase catalytic system was constructed by aerating ozone through a CeO2 loaded Al2O3 ceramic membrane (CeO2-CM) for disinfection and antibiotic degradation. Ozone aeration and a packed catalyst system (CeO2-Packing) were set as the controls. Results showed that CeO2-CM reduced the ozone escape by 34.6%-56.2%. The ozone utilization capacity of CeO2-CM for E. coli inactivation was 33.1% and 33.8% higher than those of CeO2-Packing and ozone aeration, respectively. The ozone utilization capacity of CeO2-CM for sulfamethoxazole degradation was 88.5% and 183.1% higher than those of CeO2-Packing and ozone aeration, respectively. CeO2-CM, with the lowest ozone escape and highest ozone utilization efficiency, significantly enhanced the performance of catalytic ozonation in disinfection and antibiotic degradation. This work proposes a feasible strategy for minimizing ozone consumption in water treatment.

Simultaneous removal of organics and ammonia using a novel composite magnetic anode in the electro-hybrid ozonation-coagulation (E-HOC) process toward leachate treatment

To achieve simultaneous organics and ammonia (NH₄⁺-N) removal toward leachate treatment, this study designed a composite anode (CA⁺), in which iron powders were attracted to RuO₂-IrO₂/Ti tube surface by an inserted magnet and utilized in electro-hybrid ozonation-coagulation (E-HOC). The E-HOC (CA⁺) resulted in higher chemical oxygen demand (COD) and NH₄⁺-N removal with most content of CO₂/H₂O and gaseous N in product compared with E-HOC (Fe⁺), electrolysis ozonation and single ozonation. Reactive chlorine species (RCS) and coagulants were co-produced by compositing RuO₂-IrO₂/Ti and Fe powders, resulting in multiple reactions including electrocoagulation, ozone oxidation, synergistic between ozone and coagulants (SOC), electrolytic chloride and synergistic oxidation between active chlorine and ozone (SCO) occurred. Hydroxyl radical (•OH) generated through SOC reaction was promoted due the RCS generation in E-HOC. The interaction between •OH and Cl^-/ClO^- also contributed to enhanced Cl•/ClO• production. Consequently, synergy of chlorine, coagulants and ozone enhanced reactive species generation which contributed to favorable organics and NH₄⁺-N removal. Enhanced •OH and RCS are also attributed to conversion of bio-refractory organics like polyphenol, polycyclic aromatics and S-containing to biodegradable ones, e.g., aliphatic compounds and CHO. This study provides an easily operating strategy for leachate treatment with high content organics and NH₄⁺-N.

Electro-dissolved ozone flotation (E-DOF) integrated anoxic/oxic membrane reactor for leachate treatment from a waste transfer station

With high organics and ammonia, leachate from waste transfer stations (WTSs) is among the most complex wastewater that cannot be easily disposed by signal biological processes. In this study, an electro-dissolved ozone flotation (E-DOF) was established, in which dissolved ozone flotation (DOF) and electro-coagulation (EC) occurred concurrently in one unit and integrated with anoxic/oxic membrane bioreactor (A/O-MBR) to dispose leachate from a WTS. In the integrated reactor, E-DOF acted as pretreatment and advanced treatment unit. A/O-MBR acted as secondary treatment unit. The E-DOF pretreatment achieved 34.48% COD and 16.96% NH3-N removal efficiency through synergistic effect between EC and DOF. BOD5/COD of leachate was increased from 0.32 to 0.51 after E-DOF pretreatment, indicating the enhancement of biodegradability. Molecular weight distribution (MWD) and three-dimensional excitation-emission matrix (3D-EEM) analysis demonstrate that the reduction of molecular weight and elimination of refractory organics through EC, ozone, and their interacted product (•OH) are attributed to biodegradability enhancement in lechate. Microbial community analysis proved that chemoheterotrophy and oxic chemoheterotrophy functions, mainly provided by Truepera, Aquamicrobium, Saprospiraceae, and Lentimicrobiaceae, ensured the efficient degradation of organic in the secondary processes. E-DOF advanced treatment effectively disposed residual contaminant in MBR effluent. The E-DOF advanced treatment mainly disposed residual contaminant in MBR effluent. High removal efficiency of COD (98.59 ± 0.27%), NH3-N (95.59 ± 0.50%), TN (95.37 ± 0.73%), and TP (96.75 ± 1.66%) were observed in the integrated reactor, and final effluent met the discharge standards for inclusion in the sewage pipe network in China.

Advanced treatment of landfill leachate through combined Anammox-based biotreatment, O3/H2O2 oxidation, and activated carbon adsorption: technical performance, surrogate-based control strategy, and operational cost analysis

The complexity of landfill leachate makes it difficult to treat it with a single biological/ physical/chemical process. Moreover, the dynamic leachate characteristics pose a challenge for effective process control. Therefore, a combined treatment, consisting of a one-stage partial nitrification-Anammox process, an O₃/H₂O₂ process, and a granular activated carbon filtration (GAC) process, was investigated. Meanwhile, a novel surrogate-based ozone dose control strategy for O₃/H₂O₂ process was evaluated. Results show that this three-stage process offers high removal of total nitrogen (> 90%), COD (chemical oxygen demand, 60-82%), and micropollutants (atrazine, alachlor, carbamazepine, and bisphenol A, > 96%), satisfying discharge requirements. In the combined post-treatment, ozone dosing for COD removal can be real-time controlled by UVA₂₅₄ reduction monitoring, based on a specific correlation between COD and UVA₂₅₄ changes. On the other hand, O₃/H₂O₂ pre-treatment controlled at a 50% UVA₂₅₄ reduction shows to be the optimal point, when adsorption is designed as the main step for COD removal. Cost analysis shows that post-treatment with low (high) organic load i.e., COD ≤ (≥)540 mg/L, a combination with O₃/H₂O₂ (GAC) as the main step appears to be more cost-effective. Therefore, a dynamic operation strategy in response to the leachate change is recommended.

Combined oxidization and liquid ammonia pretreatment of bamboo of various ages and species for maximizing fermentable sugar release

To determine the potential for improving biomass enzymolysis, a combined oxidization and liquid ammonia pretreatment (OD-LAT) was employed for bamboo. The effects of oxidant, bamboo ages, and species on the pretreatment effectiveness and subsequent enzymolysis were studied. Under the optimal OD-LAT pretreatment and enzymolysis of the B-NA bamboo Neosinocalamus affinis, the glucan and xylan conversion reached 83.85% and 78.66%, respectively, and approximately 59.7-68.5 g of fermentable sugars can be produced per 100 g of dry bamboo, which was an approximately 5-8 fold increase compared with untreated sample. The H₂O₂ loading of 1.0 was the optimal oxidant dosage for the OD-LAT process. The OD-LAT pretreatment was only suitable for bamboo under three-year-old, and it significantly improved the enzymolysis of B-NA and B-BM, while it was limited to B-DO and B-PP. The pretreatment effects of bamboo were not only related to composition but also to the bamboo age, species, macro-structures and micro-structures.