Hybrid electrocatalytic ozonation treatment of high-salinity organic wastewater using Ni-Ce/OMC particle electrodes

Enhancing microbial salt tolerance through low-voltage stimulation for improved p-chloronitrobenzene (p-CNB) removal in high-salinity wastewater

As an important raw material for the synthesis of chemical and pharmaceutical, hazardous carcinogen p-chloronitrobenzene (p-CNB) has been widely found in high-salinity wastewater which need to be treated carefully. Due to the high-salinity shock on microorganisms, conventional microbial treatment technologies usually show poor effluent quality. This study initially investigated the p-CNB removal performance of microorganisms stimulated by 1.2 V low-voltage in high-salinity wastewater under facultative anaerobic conditions and further revealed the enhanced mechanisms. The results showed that the p-CNB removal kinetic parameter kp-CNB in the electrostimulating microorganism reactor (EMR) increased by 104.37 % to 155.30 % compared to the microorganism reactor (MR) as the control group under the varying salinities (0-45 g/L NaCl). The secretion of extracellular polymeric substances (EPS) in halotolerant microorganisms mainly enhanced by 1.2 V voltage stimulation ranging from 0 g/L NaCl to 30 g/L NaCl. Protein concentration ratio of EMR to MR in loosely bound EPS achieved maximum value of 1.77 at the salinity of 15 g/L NaCl, and the same ratio in tightly bound EPS also peaked at 1.39 under the salinity of 30 g/L NaCl. At the salinity of 45 g/L NaCl, 1.2 V voltage stimulation mainly enhanced salt-in strategy of halotolerant microorganisms, and the intracellular Na+ and K+ concentration ratio of EMR to MR reached maximum and minimum values of 0.65 and 1.92, respectively. Furthermore, the results of microbial metagenomic and metatranscriptomic analysis showed the halotolerant microorganisms Pseudomonas_A and Nitratireductor with p-CNB removal ability were enriched significantly under 1.2 V voltage stimulation. And the gene expression of p-CNB removal, salt-in strategy and betaine transporter were enhanced under voltage stimulation at varying salinities. Our investigation provided a new solution which combined with 1.2 V voltage stimulation and halotolerant microorganisms for the treatment of high-salinity wastewater.

Cerium added corn-based biochar as particle electrode for electrochemical oxidation industrial wastewater

Three-dimensional (3D) electrochemical oxidation has become a popular advanced oxidation technology for wastewater treatment due to its various benefits. In this study, cerium (Ce) loaded biochar (Ce/BC) was used as a particle electrode to conduct the degradation of industrial wastewater released by the chemical industry. SEM, EDS, XRD, FTIR, XPS, and BET were used to characterize the properties of Ce/BC. The effects of some variables, including Ce loading (0-5%), pH (5-9), Ce/BC dosage (12.5-50.0 g/L), and working voltage (12-20 V), were evaluated with regard to COD elimination. The kinetics of COD oxidation and the energy consumption were carefully investigated. Tert-butanol significantly reduced the removal efficiency of COD, indicating that hydroxyl radicals generated during the process rather than direct electro-oxidation were the main mechanism for COD degradation. The treatment of industrial wastewater might benefit from the use of Ce/BC as particle electrode.

Decolorization of reactive azo dye using novel halotolerant yeast consortium HYC and proposed degradation pathway

The presence of high salinity levels in textile wastewater poses a significant obstacle to the process of decolorizing azo dyes. The present study involved the construction of a yeast consortium HYC, which is halotolerant and was recently isolated from wood-feeding termites. The consortium HYC was mainly comprised of Sterigmatomyces halophilus SSA-1575 and Meyerozyma guilliermondii SSA-1547. The developed consortium demonstrated a decolourization efficiency of 96.1% when exposed to a concentration of 50 mg/l of Reactive Black 5 (RB5). The HYC consortium significantly decolorized RB5 up to concentrations of 400 mg/l and in the presence of NaCl up to 50 g/l. The effects of physicochemical factors and the degradation pathway were systematically investigated. The optimal pH, salinity, temperature, and initial dye concentration were 7.0, 3%, 35 °C and 50 mg/l, respectively. The co-carbon source was found to be essential, and the addition of glucose resulted in a 93% decolorization of 50 mg/l RB5. The enzymatic activity of various oxido-reductases was assessed, revealing that NADH-DCIP reductase and azo reductase exhibited greater activity in comparison to other enzymes. UV-Visible (UV-vis) spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC-MS) were utilized to identify the metabolites generated during the degradation of RB5. Subsequently, a metabolic pathway was proposed. The confirmation of degradation was established through alterations in the functional groups and modifications in molecular weight. The findings indicate that this halotolerant yeast consortium exhibits promising potential of degrading dye compounds. The results of this study offer significant theoretical basis and crucial perspectives for the implementation of halotolerant yeast consortia in the bioremediation of textile and hypersaline wastewater. This approach is particularly noteworthy as it does not produce aromatic amines.

Efficient biodegradation of acetoacetanilide in hypersaline wastewater with a synthetic halotolerant bacterial consortium

The high concentrations of salt and refractory toxic organics in industrial wastewater seriously restrict biological treatment efficiency and functional stability. However, how to construct a salt-tolerant biocatalytic community and realize the decarbonization coupled with detoxification toward green bio-enhanced treatment, has yet to be well elucidated. Here, acetoacetanilide (AAA), an important intermediate for many dyes and medicine synthesis, was used as the model amide pollutant to elucidate the directional enrichment of halotolerant degradative communities and the corresponding bacterial interaction mechanism. Combining microbial community composition and molecular ecological network analyses as well as the biodegradation efficiencies of AAA and its hydrolysis product aniline (AN) of pure strains, the core degradative bacteria were identified during the hypersaline AAA degradation process. A synthetic bacterial consortium composed of Paenarthrobacter, Rhizobium, Rhodococcus, Delftia and Nitratireductor was constructed based on the top-down strategy to treat AAA wastewater with different water quality characteristics. The synthetic halotolerant consortium showed promising treatment ability toward the simulated AAA wastewater (AAA 100-500 mg/L, 1-5% salinity) and actual AAA mother liquor. Additionally, the comprehensive toxicity of AAA mother liquor significantly reduced after biological treatment. This study provides a green biological approach for the treatment of hypersaline and high concentration of organics wastewater.

Advanced treatment of high-salinity wastewater by catalytic ozonation with pilot- and full-scale systems and the effects of Cu2+ in original wastewater on catalyst activity

In this work, heterogeneous catalytic ozonation for the treatment of bio-treated saccharin sodium production wastewater (BSSW) was comprehensively investigated with pilot- and full-scale systems, with special emphasis on the effects of Cu²⁺ in the original wastewater on catalyst activity. The results of semi-batch and continuous experiments show that heterogeneous catalytic ozonation was effective in removing organic compounds from high-salinity wastewater and that Cu²⁺ in the original wastewater had a substantial effect on the performance of the process. The retention of 0.15 mM Cu²⁺ in BSSW increased the chemical oxygen demand (COD) removal by 31% in semi-batch reactor with heterogeneous catalytic ozonation. The stable COD removal efficiencies ranged from 74% to 66.4% for a 9-month operation, indicating that Cu²⁺ with an appropriate concentration in the original BSSW not only improved the COD removal efficiencies but also inhibited catalyst deactivation; catalyst deactivation was mainly caused by the deposition of inorganic salts on the catalyst surface. Cu²⁺ combined with some anions to inhibit the formation and deposition of inorganic salts that could easily cause deactivation. The deposited copper salts were readily eliminated, especially during backflushing operations. Moreover, in a full-scale study, heterogeneous catalytic ozonation with 0.15 mM Cu²⁺ in BSSW exhibited stable COD removal efficiencies (51%-83%) after over 3 years of operation. This study offers a new idea for using the inherent properties of wastewater to perform advanced treatments on high-salinity industrial wastewater through heterogeneous catalytic ozonation.

Efficient and recyclable Ni-Ce-Mn-N modified ordered mesoporous carbon electrode during electrocatalytic ozonation process for the degradation of simulated high-salt phenol wastewater

In this study, an efficient and stable NiO/CeO₂/MnO₂-modified nitrogen-doped ordered mesoporous carbon (NOMC) particle electrode was developed, in which the metal oxides were mosaicked within the pore channels by one-pot skeleton hybridization, and the comodification of NiO/CeO₂/MnO₂/N was found to improve the electrocatalytic activity and stability of the particle electrode. The improved stability of the ordered mesoporous carbon towards pore collapse was applied to the degradation of simulated high-salt phenol wastewater by an electrocatalytic ozonation process using simple binder pelletization. The modified ordered mesoporous carbon shows a specific surface area of 269.7 m² g^-1 and a pore size of 3.17 nm, and SEM and TEM were used to show that the mesoporous structure is well maintained and the metal nanoparticles are well dispersed. The electrochemically active area of the Ni_2%/Ce_0.5%/Mn_2.5%-NOMC particle electrode reaches 224.65 mF cm^-2, which indicates that NiO improves the capacitance of the ordered mesoporous carbon and accelerates the electron transfer efficiency. Encouragingly, the phenol removal efficiency is found to reach up to 93.0% for 60 min over a wide range of pH values, with an initial phenol concentration of 150 mg L^-1, low current (0.03 A) and fast reaction rate (0.0895 min^-1), and the presence of CeO₂ ameliorates the low activity of the particle electrode under acidic conditions. These results indicate that the presence of pyridine-N and β-MnO₂ effectively mitigates carbon corrosion and improves electrode stability, as the accumulation of large amounts of ·OH at 20 min and the maintenance of a degradation efficiency of more than 90% after eight cycles provides a viable solution for the widespread practical application of ordered mesoporous carbon particle electrodes.

Distribution modes of residual carbon and ash in coal gasification fine slag and its feasibility analysis as particle electrodes

From the perspective of environmental protection and resource utilization, the feasibility of treating m-cresol wastewater with coal gasification fine slag (GFS) as particle electrodes in an electrocatalytic system was evaluated to achieve the purpose of treating waste with waste. Characterization by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), Raman, and fourier transform infrared spectroscopy (FTIR) confirmed that the GFS featured a diverse inorganic framework, large specific surface area (as large as above 155 m² g^-1), hierarchical porous structure, and plenty of catalytic sites. The Venn diagram method was used to systematically propose the following distribution modes of residual carbon (RC) and ash in GFS: discrete distribution, embedded distribution, crosslinked distribution, and association and bonding. Only 8 g L^-1 of GFS particle electrodes prevented the formation of a yellow sticky passivation film on the anode. Compared to the two-dimensional electrocatalytic system (47.89%), the wastewater treatment efficiency was increased by 108.81%. Zero-order kinetic results showed that the reaction rate constant was the highest (2.1106 mg L^-1·min^-1) when the secondary flotation RC was adopted as particle electrodes. It was indicated that GFS in discrete mode played either no role or at most a minor role. Last but not least, the synergy of RC and ash was revealed from a molecular perspective. The RC exhibited hierarchical microporous/mesoporous/macroporous structure, which facilitated the entry of H₂O₂ into the catalytic sites of ash. Abundant catalytic sites in ash accelerated adsorption and oxidation processes on RC surfaces.

Application of a Spiral Symmetric Stream Anaerobic Bioreactor for treating saline heparin sodium pharmaceutical wastewater: Reactor operating characteristics, organics degradation pathway and salt tolerance mechanism

In this study, a Spiral Symmetry Stream Anaerobic Bioreactor (SSSAB) was adopted for treating actual saline heparin sodium pharmaceutical wastewater (HSPW). After adaptation, under the influent COD of 8731 mg/L, OLR of 6.98 kg COD/(m³•d) and salinity of 3.57 wt%, the COD removal reached up to 82%. This value is much higher than the reported for the other reactors at similar salinity. Benzenes are the major organic compounds in HSPW. The main rate-limiting steps are the degradations of phenol and p-cresol. In addition, the degradation pathways of typical benzenes in HSPW were analyzed. After adaptation, the soluble salt content in the granular sludge increased, and the bacterial extracellular polymers (EPS), especially tightly-bound EPS also significantly increased. 16S rRNA analysis revealed that the microbial community in the anaerobic granular sludge (AGS) had become adapted to the HSPW treatment since Mesotoga (12.4%), Anaerophaga (9.0%), Oceanotoga (6.1%) and Aminobacterium (4.1%) increased from previously below 1.0% values. The relative abundance of Methanosarcina in the upper layer of the reactor (68.7%) is significantly higher than that at the bottom (3.8%). This proves the superiority of the SSSAB structure. Finally, a model for salt-tolerant microorganisms is given, which proposes a mechanism for this study and provides reference for other anaerobic biological treatments of high-salt containing wastewater.

N-Doped Biochar as a New Metal-Free Activator of Peroxymonosulfate for Singlet Oxygen-Dominated Catalytic Degradation of Acid Orange 7

In this paper, using rice straw as a raw material and urea as a nitrogen precursor, a composite catalyst (a nitrogen-doped rice straw biochar at the pyrolysis temperature of 800 °C, recorded as NRSBC800) was synthesized by one-step pyrolysis. NRSBC800 was then characterized using XPS, BET, TEM and other technologies, and its catalytic performance as an activator for permonosulfate (PMS) to degrade acid orange 7 (AO7) was studied. The results show that the introduction of N-doping significantly improved the catalytic performance of NRSBC800. The NRSBC800/PMS oxidation system could fully degrade AO7 within 30 min, with the reaction rate constant (2.1 × 10 ^-1 min^-1) being 38 times that of RSBC800 (5.5 × 10^-3 min^-1). Moreover, NRSBC800 not only had better catalytic performance than traditional metal oxides (Co₃O₄ and Fe₃O₄) and carbon nanomaterial (CNT) but also received less impact from environmental water factors (such as anions and humic acids) during the catalytic degradation process. In addition, a quenching test and electron paramagnetic resonance (EPR) research both indicated that AO7 degradation relied mainly on non-free radical oxidation (primarily singlet oxygen (¹O₂)). A recycling experiment further demonstrated NRSBC800's high stability after recycling three times.

Role of micro-size zero valence iron as particle electrodes in a three-dimensional heterogeneous electro-ozonation process for nitrobenzene degradation

A novel water treatment process (designated E-Fe⁰-O₃ process) was constructed by combining electrolysis, micro-size zero valence iron (Fe⁰) and ozone in this study. Compared with other control processes, the combined process demonstrated a remarkable synergy, and it could obtain 90.5% of NB removal within 20 min. As for the mineralization experiment, the TOC removal efficiency for NB within 120 min was higher in the E-Fe⁰-O₃ process, while the energy consumption was lower than the traditional E-O₃ and E-Fe⁰ process. Interestingly, hydroxyl radicals (OH) acted as a key role for NB removal, and the concentration of OH in different processes were compared. Further study indicated OH, direct anode oxidation, direct ozonation, and zero valence iron catalysis were all responsible for nitrobenzene removal. Besides, the durability of Fe⁰ in the E-Fe⁰-O₃ process was systematically evaluated by reusing Fe⁰ 10 times. Notably, the electric field could protect micro-size zero valence iron from passivation for catalytic ozonation after the long-term reaction. Finally, other ozone-refractory organics pollutants were also investigated in the E-Fe⁰-O₃ process, and the influence of various water matrices on NB removal was discussed. All results demonstrated that the E-Fe⁰-O₃ process was an efficient method to remove refractory organic pollutants in various natural waters.

Enhanced removal of Co(II) and Ni(II) from high-salinity aqueous solution using reductive self-assembly of three-dimensional magnetic fungal hyphal/graphene oxide nanofibers

Layer-structured graphene oxide excellent carrier for modifications; however, its poor recoverability and stability preclude its application in wastewater treatment fields. Herein, three-dimensional magnetic fungal hyphal/graphene oxide nanofibers (MFHGs) were assembled by a reductive self-assembly (RSA) strategy for the efficient capture of Co(II) and Ni(II) from high-salinity aqueous solution. The RSA strategy is inexpensive, eco-friendly and easy to scale up. The obtained MFHGs enhanced the dispersity and stability of graphene oxide and exhibited excellent magnetization and large coercivity, leading to satisfactory solid-liquid separation performance and denser sediment. The results of batch removal experiments showed that the maximum removal capacity of MFHGs for Ni(II) and Co(II) was 97.44 and 104.34 mg/g, respectively, in 2 g/L Na₂SO₄ aqueous solution with a pH of 6.0 at 323 K, and the effects of initial pH and ionic strength on Co(II) and Ni(II) removal were explored. Yield residue analysis indicated that the high porosity and oxygen-containing functional groups of MFHGs remarkably improved their Co(II)- and Ni(II)-removal capacities. According to the analysis, hydroxyl groups and amine groups participated in the chemical reaction of Co(II) and Ni(II) removal, and cation-exchange chemical adsorption was dominant during the Co(II)- and Ni(II)-removal process. Based on the attributes of MFHGs, a continuous-flow recycle reactor (CFRR) was proposed for emergency aqueous solution treatment and exhibited satisfactory removal efficiency and regeneration performance. The combination of MFHGs and the proposed CFRR is a promising water treatment strategy for rapid treatment applications.

Magnetite enhances anaerobic digestion of high salinity organic wastewater

Biological treatment of high salinity organic wastewater is a significant challenge because many microorganisms involved in the anaerobic digestion process cannot survive high osmotic pressures. In order to alleviate some of the stresses associated with the treatment of high salinity wastewater, two lab-scale up-flow anaerobic sludge bed reactors with or without magnetite (100 g/L) were used to treat high salinity organic wastewater. This study showed that the bioreactor amended with magnetite had higher chemical oxygen demand removal efficiencies (90.2% ± 0.54% vs 73.1% ± 1.9%) and methane production rates (4082 ± 334 ml (standard temperature and atmospheric pressure, STP)/d vs 2640 ± 120 ml (STP)/d) than the non-amended control reactor. In addition, the consumption of volatile fatty acids (20.9 ± 3.4 mM vs 61.7 ± 2.0 mM) was accelerated. Microbial community analysis revealed that the addition of magnetite caused the enrichment of many bacterial genera known to form robust biofilms (i.e. Pseudomonas) that are also capable of extracellular electron transfer and methanogens from the genus Methanosarcina which have been shown to participate in direct interspecies electron transfer. These results show that magnetite addition could enhance the performance of anaerobic digesters treating high salinity wastewater.