Selective removal of thiosulfate from coke oven gas desulfurization wastewater by catalytic wet air oxidation with manganese-based oxide from spent ternary lithium-ion batteries

Selective and efficient removal of thiosulfates (S2O32-) to recover high-purity and value-added thiocyanate products by fractional crystallization process is a promising route for the resource treatment of coke oven gas desulfurization wastewater. Herein, catalytic wet air oxidation (CWAO), with manganese-based oxide synthesized from spent ternary lithium-ion batteries (MnOx-LIBs), was proposed to selectively remove S2O32- from desulfurization wastewater. 98.0 % of S2O32- is selectively removed by the MnOx-LIBs CWAO system, which was 4.1 times that of the MnOx CWAO system. The synergistic effect among multiple metals from spent LIBs induces the enlarged specific surface area, increased reactive sites and formation of oxygen vacancy, promoting the adsorption and activation of O2, thereby realizing high-efficiency removal of S2O32-. The satisfactory selective removal efficiency can be maintained in the proposed system under complex environmental conditions. Notably, the proposed system is cost-effective and applicable to actual wastewater, in which 81.2 % of S2O32- is selectively removed from coke oven gas desulfurization wastewater. More importantly, compared with the typical processes, the proposed process is simpler and more environmentally-friendly. This work provides an alternative route to selectively remove S2O32- from coke oven gas desulfurization wastewater, expecting to drive the development of resource utilization of coke oven gas desulfurization wastewater.

Mn-Co-Ce/biochar based particles electrodes for removal of COD from coking wastewater by 3D/HEFL system: Characteristics, optimization, and mechanism

In this work, the Mn, Co, Ce co-doped corn cob biochar (MCCBC) as catalytic particle electrodes in a three-dimensional heterogeneous electro-Fenton-like (3D-HEFL) system for the efficient degradation of coking wastewater was investigated. Various characterization methods such as SEM, EDS, XRD, XPS and electrochemical analysis were employed for the prepared materials. The results showed that the MCCBC particle electrodes had excellent electrochemical degradation performances of COD in coking wastewater, and the COD removal and degradation rates of the 3D/HEFL system were 85.35% and 0.0563 min-1 respectively. RSM optimized conditions revealed higher COD removal rate at 89.23% after 31.6 min of electrolysis. The efficient degradability and wide adaptability of the 3D/HEFL system were due to its beneficial coupling mechanism, including the synergistic effect between the system factors (3D and HEFL) as well as the synergistic interactions between the ROS (dominated by •OH and supplemented by O2•-) in the system. Moreover, the COD removal rate of MCCBC could still remain at 81.41% after 5 cycles with a lower ion leaching and a specific energy consumption of 11.28 kWh kg-1 COD. The superior performance of MCCBC, as catalytic particle electrodes showed a great potential for engineering applications for the advanced treatment of coking wastewater.

Heterogeneous electro-Fenton treatment of coking wastewater using Fe/AC/Ni cathode: optimization of electrode and reactor organic loading

A self-developed iron-loaded activated carbon-based nickel foam electrode (Fe/AC/Ni cathode) was used to construct electro-Fenton reaction system to treat coking wastewater. To meet the gap between laboratory beaker experiments and field trials for practical applications, we proposed and validated a method for obtaining organic loads, the essential parameters used in the design of electrochemical systems for wastewater treatment. The three influencing factors most relevant to organic loading, the effective surface area of cathode, chemical oxygen demand (COD) concentration of influent, and treatment time, were selected and investigated for their effects on the COD removal rate of coking wastewater by single-factor experiments and further optimized by response surface method. The appropriate electrode area load (La) and reactor volume load (Lv) were calculated by their corresponding intrinsic relationships with the three factors. The optimum application conditions were effective surface area of cathode 28.5 cm2, COD concentration of influent 1.76 kg·m-3, and treatment time 160.43 min. Under these conditions, the maximum COD removal rate was 98.51%. The La and Lv were 8.905 mgCOD·cm-2·h-1 and 0.634 kgCOD·m-3·h-1, respectively. The characterization experiment results showed that the Fe/AC/Ni cathode had a significant effect on the treatment of refractory organic contaminants in coking wastewater.

Biochar inoculated with Rhodococcus biphenylivorans altered microecological regulation by promoting quorum sensing and electron transfer: Up-regulation of related genes and enhancement of phenol and ammonia degradation

Bioaugmentation is an efficient method for improving the efficiency of coking wastewater removal. Nevertheless, how different immobilization approaches affect the efficiency of bioaugmentation remains unclear, as does the corresponding mechanism. With the assistance of immobilized bioaugmentation strain Rhodococcus biphenylivorans B403, the removal of synthetic coking wastewater was investigated (drying agent, alginate agent, and absorption agent). The reactor containing the absorption agent exhibited the highest average removal efficiency of phenol (99.74 %), chemical oxygen demand (93.09 %), and NH4+-N (98.18 %). Compared to other agents, the covered extracellular polymeric substance on the absorption agent surface enhanced electron transfer and quorum sensing, and the promoted quorum sensing benefited the activated sludge stability and microbial regulation. The phytotoxicity test revealed that the wastewater's toxicity was greatly decreased in the reactor with the absorption agent, especially under high phenol concentrations. These findings showed that the absorption agent was the most suitable for wastewater treatment bioaugmentation.

Comparison of ozone-based AOPs on the removal of organic matter from the secondary biochemical effluent of coking wastewater

Advanced oxidation processes (AOPs) based on ozone are gaining continuously growing popularity in wastewater treatment. This study explored the treatment of coking wastewater using a combination of ozonation (O3), ultraviolet (UV), and hydrogen peroxide (H2O2) process expressed by % chemical oxygen demand (COD) removal, % total organic carbon (TOC), % UV254, % fluorescence intensity removal and its electrical energy consumption. The obtained results demonstrated that, the combination of O3, UV, and H2O2 which is denoted by O3/UV/H2O2 in this study achieved great success in COD removal (92.08%), TOC removal (78.25%), and reduction of fluorescence intensity (99.82%). Compared with the O3 and O3/UV processes, O3/UV/H2O2 improved the COD removal by approximately 54-69% and 38-51%, respectively. In addition, the energy consumption was reduced by 53-67%. The TOC removal rate in the effluent ranged 71% and 83%, while the UV254 removal rate was up to 90%. The fluorescence spectroscopy showed that the O3/UV/H2O2 combination process reduced the fluorescence intensity by almost 97% within 10 min. Furthermore, the total polycyclic aromatic hydrocarbons (PAHs) concentration in the effluent was less than 10μg/L (removal efficiency > 80%) and the most toxic benzo(a)pyrene (BaP) was less than 0.03 μg/L (0.018μg/L). In addition, the energy consumption of the O3/UV/H2O2 process was 53-67% lower than those of O3 and O3/UV processes. Furthermore, the energy consumption was 80.26 kWh m-3 after 60 min of reaction time when the COD (69.3 mg/L) met the standard discharge. Finally, the O3/UV/H2O2 process could be an effective method for improving the mineralisation of refractory organic matter.

Advanced treatment of coking wastewater: Recent advances and prospects

Advanced treatment of refractory industrial wastewater is still a challenge. Coking wastewater is one of coal chemical wastewater, which contains various refractory organic pollutants. To meet the more and more rigorous discharge standard and increase the reuse ratio of coking wastewater, advanced treatment process must be set for treating the biologically treated coking wastewater. To date, several advanced oxidation processes (AOPs), including Fenton, ozone, persulfate-based oxidation, and iron-carbon micro-electrolysis, have been applied for the advanced treatment of coking wastewater. However, the performance of different advanced treatment processes changed greatly, depending on the components of coking wastewater and the unique characteristics of advanced treatment processes. In this review article, the state-of-the-art advanced treatment process of coking wastewater was systematically summarized and analyzed. Firstly, the major organic pollutants in the secondary effluents of coking wastewater was briefly introduced, to better understand the characteristics of the biologically treated coking wastewater. Then, the performance of various advanced treatment processes, including physiochemical methods, biological methods, advanced oxidation methods and combined methods were discussed for the advanced treatment of coking wastewater in detail. Finally, the conclusions and remarks were provided. This review will be helpful for the proper selection of advanced treatment processes and promote the development of advanced treatment processes for coking wastewater.

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.

Use microalgae to treat coke wastewater for producing biofuel: Influence of phenol on photosynthetic properties and intracellular components of microalgae

Using microalgae to treat coking wastewater has important application prospects and environmental significance. Previous studies have suggested that phycoremediation of pollutants from coking wastewater is feasible and can potentially enhance biodiesel production. This work investigates the effects of phenol in coking wastewater on C. pyrenoidosa and S. obliquus growth, photosynthesis activity, and intracellular components. The results indicated that when the phenol concentration was lower than 300 mg L-1, both microalgae maintained good photosynthetic and physiological activity, with a maximum quantum yield potential ranging from 0.6 to 0.7. At the phenol concentration of 300 mg L-1, the biomass of C. pyrenoidosa was 2.4 times that of the control group. For S. obliquus, at the phenol concentration of 150 mg L-1, the biomass was approximately 0.85 g L-1, which increased by 68% than that of the control group (0.58 g L-1). The lipid content in both microalgae increased with the phenol concentrations, with the maximum content exceeding 40%. The optimal phenol concentrations for C. pyrenoidosa and S. obliquus growth were determined to be 246.18 and 152.73 mg L-1, respectively, based on a developed kinetic model. This work contributes to further elucidating the effects of phenol on microalgae growth, photosynthesis, and intracellular components, and suggests that using microalgae to treat phenol-containing coking wastewater for producing biofuel is not only environmentally friendly but also holds significant energy promise.

A combined process model for wastewater treatment based on hydraulic retention time and toxicity inhibition

Hydraulic retention time (HRT), as an important parameter in the wastewater treatment process, has a great impact on water quality and energy consumption. With the rapid advances in computer technology and deepened understanding of in microbial metabolism, a series of activated sludge models (ASMs) have been developed and applied in wastewater treatment. However, ASMs simulation based on the nexus of HRT, water treatment process, water quality and energy consumption has yet to be verified. In this study, HRT was creatively linked to water treatment process variation. And a novel combined process model (CPM) was developed based on the operational data and treatment performance data from 4 full-scale coking wastewater treatment processes. In the CPM, an array of biological treatment processes were represented by setting the HRT in respective treatment units of the anaerobic-oxic-hydrolytic & denitrification-oxic (A/O/H/O) process. The relationships between HRT, effluent quality and energy consumption were systematically analyzed. Results showed that: (i) for A/O/H/O process, the HRT of first oxic (O1) reactor has a key effect on the effluent water quality and energy consumption, while the impact of the anaerobic (A) reactor HRT was limited; (ii) the O/H/O process has a clear advantage in treating coking wastewater due to the carbon removal and detoxification function of O1 reactor; (iii) the lowest energy consumption (with the total system HRT below 210 h) to meet the biological effluent quality requirements (COD = 200 mg/L, TN = 50 mg/L) is 4.429 kWh/m³. Since the CPM could effectively work out the optimal process configuration and break the boundaries between HRT and process variation, it has enormous potential to be extended to the design of other wastewater treatment processes.

Determining the degradation mechanism and application potential of benzopyrene-degrading bacterium Acinetobacter XS-4 by screening

In industrial wastewater treatment, organic pollutants are usually removed by in-situ microorganisms and exogenous bactericides. Benzo [a] pyrene (BaP) is a typical persistent organic pollutant and difficult to be removed. In this study, a new strain of BaP degrading bacteria Acinetobacter XS-4 was obtained and the degradation rate was optimized by response surface method. The results showed that the degradation rate of BaP was 62.73% when pH= 8, substrate concentration was 10 mg/L, temperature was 25 °C, inoculation amount was 15% and culture rate was 180 r/min. Its degradation rate was better than that of the reported degrading bacteria. XS-4 is active in the degradation of BaP. BaP is degraded into phenanthrene by 3, 4-dioxygenase (α subunit and β subunit) in pathway Ⅰ and rapidly forms aldehydes, esters and alkanes. The pathway Ⅱ is realized by the action of salicylic acid hydroxylase. When sodium alginate and polyvinyl alcohol were added to the actual coking wastewater to immobilize XS-4, the degradation rate of BaP was 72.68% after 7 days, and the removal effect was better than that of single BaP wastewater (62.36%), which has the application potential. This study provides theoretical and technical support for microbial degradation of BaP in industrial wastewater.

Catalytic ozonation of hard COD in coking wastewater with Fe2O3/Al2O3-SiC: From catalyst design to industrial application

Development of robust, reactive, and inexpensive catalyst for pollutants abatement with catalytic ozonation is of great significance. Herein, the effect of a robust and easy-recovery catalyst, Fe₂O₃/Al₂O₃-SiC, for the catalytic ozonation of hardly biodegradable COD (hard COD) in coking wastewater had been explored. Al-O-Si bond formed on modified SiC through the substitution of hydrogen in surficial Si-OH groups by Al³⁺. The Lewis acid sites improved the adsorption of ozone and facilitated the formation of ·OH and O₂·^-. For coking wastewater treatment, the removal ratio of hard COD and the generation speed of hydroxyl radical (R_ct) in the catalytic ozonation process were 71% and 253% higher than those in the ozonation group, respectively. Ozone utilization increased from 0.44 g COD removed/g O₃ in the ozonation group to 1.42 g COD removed/g O₃ in the Fe₂O₃/Al₂O₃-SiC catalytic ozonation group. In a full-scale application, Fe₂O₃/Al₂O₃-SiC catalytic ozonation decreased the consumption of O₃ to 60 mg L^-1 and decreased the operation cost by 50%. These results provided an approachable way for sharing the extraordinary capacity of ozone for contaminants remediation in industrial applications.

Treatment of coking wastewater by a novel full-scale microaerobic-anoxic-oxic (M/A/O) system: Performance and microbial community analysis

The aim of this study was to investigate the relationship between system removal performance and microbial community structure in a novel full-scale microaerobic-anoxic-oxic (M/A/O) system for coking wastewater (CWW) treatment. The results showed that 93% of chemical oxygen demand (COD) and 99% of NH4+-N removal efficiency were achieved via M/A/O process, meanwhile, main organic pollutants in CWW including phenolic compounds, heterocyclic compounds and polycyclic aromatic hydrocarbons were basically removed. Four dominant phyla of Proteobacteria, Firmicutes, Bacteroidetes and Nitrospirae were demonstrated distributed in the system and played significant roles in M/A/O biological treatment process. Major function of the microaerobic process was to partly remove the biodegradable substances such as phenols and hydrolyze the refractory contaminants such as N-heterocyclic compounds to improve the biological oxygen demand/chemical oxygen demand (BOD5/COD) ratio and release ammonia. This work illustrated the structure and function of microbial community in M/A/O system and provided a new choice for high-strength CWW treatment.

Distribution characteristics, air-water exchange, ozone formation potential and health risk assessments of VOCs emitted from typical coking wastewater treatment process

Coking industry has been considered as important source of volatile organic compounds (VOCs) emissions. However, few studies have emphasized the occurrence and adverse effects of VOCs from coking wastewater treatment processes. In this research, pollution profiles of both air and water phase VOCs in a typical coking wastewater treatment plant were investigated in terms of distribution characteristics, air-water exchange, ozone formation potential (OFP) and associated human health risks. Thirty VOCs were detected in the air phase, in which benzene and naphthalene were found to be the major VOCs with total contribution of 87.81 %. Nineteen VOCs were detected in the water phase, in which benzene, naphthalene and toluene contribute most to total VOCs with total contribution of 75.1 %. The regulating tank (RT) was the major source of VOCs, and the emission rate of total VOCs from all unites was 2711.03 g/d with annual emission of 0.99 t. The emission factor was estimated to be 1.36 g VOCs/m³ wastewater. The air-water exchange was assessed using the Fugacity model, and water-to-air volatilization was predominant based on the net flux of air-water exchange. OFP evaluated by emission factor indicated that the total OFP in RT was the highest (1.52 g O₃/m³ wastewater), and toluene contributed 41.8 % of the total OFP, followed by naphthalene accounting for 38.7 % The total carcinogenic risks were in the range of 8.60 × 10^-6 to 2.18 × 10^-3, in which the RT exceeded the significant risk threshold (>1 × 10^-4). The non-carcinogenic risks of hazard quotient value in RT also exceeded the risk threshold (>1), and naphthalene was the major contributor accounting for 79.02 %. These results not only provided comprehensive knowledge on pollution profiles and environmental risks of VOCs during coking wastewater treatment processes, but also facilitated the implement of VOCs regulation and occupational health protection strategies in coking industries.

Synergistic effects of simultaneous coupling ozonation and biodegradation for coking wastewater treatment: Advances in COD removal, toxic elimination, and microbial regulation

Coking wastewater contains high concentrations of cyanide, phenols, pyridine, quinoline, and polycyclic aromatic hydrocarbons. Its high toxicity and low biodegradability leads to long hydraulic retention time of biological process and high cost of advanced oxidation process. In this study, the simultaneous combination of ozonation and biodegradation (SCOB) was proposed to treat coking wastewater. Through this process, ozonation breaks the refractory organics, and the biodegradable intermediates are rapidly mineralized by microorganisms protected by porous carriers. Thus, the performances of SCOB, individual biodegradation and ozonation systems were compared. The long-term stability of the SCOB system was evaluated, the contributions of ozonation and biodegradation were analyzed, and their synergistic mechanisms were elaborated. Results showed that biological activity was inhibited in the biodegradation system, and chemical oxygen demand (COD) removal was only 27.6% for the ozonation system. COD and total phenol removal of SCOB system reached 48.5% and 79.3%, respectively, and its kinetic degradation constant of COD was 55.6% higher than that of the ozonation system. Ozonation contributed to the oxidation of organics with unsaturated functional groups as well as soluble microbial products (SMPs), causing the effluent toxicity and chroma to decrease by 82.7% and 270 times, respectively. The higher abundances of microorganisms and functions were enriched in the core of carrier, which became dominant region for biodegradation. Consequently, COD removal of the SCOB system stabilized at >80% for real coking wastewater treatment, confirming its promising potential for the treatment of highly polluted industrial wastewater.

Carbon dot-based molecularly imprinted fluorescent nanopomegranate for selective detection of quinoline in coking wastewater

Quinoline, as a refractory and toxic organic pollutant in coking wastewater, causes great harm to the environment and human health even in trace amount. To realize the selective and sensitive detection of quinoline in coking wastewater, a novel molecularly imprinted fluorescent nanopomegranate with carbon dots (CDs) as seeds and fluorescence source (CD-MIP) was prepared, using quinoline as the template, and N-(β-aminoethyl)-γ-aminopropyl trimethoxysilane (KH792) as the monomer. The preparation and detection conditions of CD-MIP were systematically optimized. The structure and detection performance of CD-MIP were investigated in detail. The resulting CD-MIP exhibits excellent photoluminescence performance, high detection sensitivity, good selectivity and reproducibility towards quinoline. Under the optimized conditions, the fluorescence intensity of CD-MIP shows a satisfying linearity with quinoline concentration in the range of 20-200 mg/L with a detection limit of 6.7 mg/L. Owing to the existence of imprinted cavities that highly match with quinoline, a high imprinting factor (3.46) for CD-MIP was obtained. In addition, CD-MIP represents a greater affinity towards quinoline than towards other analogues, as well as an outstanding anti-interference capability. For trace analysis in real coking wastewater, CD-MIP also gives satisfactory results. Therefore, CD-MIP shows promising application in the selective detection of trace quinoline in wastewater.

Biodegradability enhancement of phenolic wastewater using hydrothermal pretreatment

A novel hydrothermal pretreatment was applied for the biochemical treatment of phenolic wastewater with high concentrations of phenolic substances. The results demonstrated that 250 °C was the reaction temperature dividing point for complete oxidation, hydrothermal gasification, and amino release from carbonaceous organics in phenolic wastewater. Before the dividing point reached, some of the large molecules were hydrolyzed into small molecules of volatile phenolic substances that were easily adsorbed by the activated sludge. After the integrated hydrothermal pretreatment and anaerobic/aeration process, the removal rate of volatile phenolswas respectively reached by 97 % and 88 % with hydrothermal temperature of 250 °C and without pretreatment. Functional microorganisms (i.e., Chloroflexi) responsible for aromatic compounds degradation were enriched, thus the dioxygenases, dehydrogenase reactions, and meta-cleavage of catechol were enhanced. This work provided an innovative approach to remove phenolic substances from phenolic wastewater, and in-depth understandings of microbial responses in biochemical systems.

Diverse and distinct bacterial community involved in a full-scale A/O1/H/O2 combination of bioreactors with simultaneous decarbonation and denitrogenation of coking wastewater

Taking into account difficulties in exhaustive simultaneous decarbonation and denitrogenation in biological treatment of coking wastewater (CWW), a novel full-scale CWW biological treatment sequentially combining anaerobic, aerobic, hydrolytic, and aerobic reactors (A/O1/H/O2) was designed performing excellent removal of carbon-containing pollutants in the bioreactors A and O1, while the nitrogen-containing compounds in the bioreactors H and O2. To provide an effective tool for the CWW treatment monitoring and control, the succession of microbial community in this unique toxic CWW habitat should be established and characterized in detail. The results of 16S rRNA genes revealed Acidobacteria dominating in the unique CWW habitat. The dominant groups in bioreactors A and O1 include Proteobacteria, Firmicutes, and Acidobacteria, while Proteobacteria, Acidobacteria, Nitrospirae, and Planctomycetes dominate in reactors H and O2. The genera of Rhodoplanes, Bacillus, and Leucobacter are rich in genes responsible for the xenobiotics biodegradation and metabolism pathway. The Mantel test and PCA results showed the microbial communities of A/O1/H/O2 sequence correlating strongly with SRT, and COD load and removal. The co-occurrence network analysis indicated decarbonation and denitrogenation driven by two network modules having the keystone taxa belonging to the Comamonadaceae and Hyphomicrobiaceae families. The results significantly expanded the knowledge on the diversity, structure, and function of the CWW active sludge differentiating the relationships between bacterial communities and environmental variables in CWW treatment.

Preparation of Fe-loaded needle coke particle electrodes and utilisation in three-dimensional electro-Fenton oxidation of coking wastewater

Novel iron-loaded needle coke spherical electrodes were fabricated for the first time using the sintering method. With DSA as the anode, nickel foam as the cathode and the spherical electrodes as the particle electrodes, a three-dimensional (3D) electro-Fenton system was constructed to treat coking wastewater. Using the chemical oxygen demand (COD) removal efficiency of coking wastewater as an indicator of electrode performance, the optimal conditions for particle electrode preparation were determined by single-factor experiments as consisting of a 4:1 catalyst-to-binder ratio, Fe²⁺ loading for the preparation of the particle electrodes of 2.5%, a particle size of 5.5 ± 0.5 mm, and a sintering temperature of 400 °C. Response surface methodology was applied to model and optimise the 3D electro-Fenton process for treating coking wastewater. Under the optimal conditions of an electrode spacing of 5 cm, applied voltage of 11.15 V, initial pH of 2.62, and particle electrode dosing of 12.23 g L^-1, the removal rates of COD, NH₃-N, NO₃^--N, total nitrogen, colour, and UV₂₅₄ were 87.5%, 100%, 72.2%, 84.8%, 95%, and 72.4%, respectively. Spectral analysis revealed that the 3D electro-Fenton system strongly degraded coking wastewater, causing decomposition of large molecules of organic compounds and residuals primarily consisting of olefins and alkanes. Because the prepared particle electrodes exhibited stable physical and chemical structure, they have great potential for engineering applications due to their resistance to water flow erosion, stable catalytic reaction activity, and reusability.

Advanced aromatic organic compounds removal from refractory coking wastewater in a step-feed three-stage integrated A/O bio-filter: Spectrum characterization and biodegradation mechanism

Extensive presence of aromatic organic compounds (AOCs) is a major course for the non-biodegradability of coking wastewater (COW). In-depth understanding of bio-degradation of AOCs is crucial for optimizing the design and operation of COW biological treatment systems in practical applications. Herein, the behavior and fate of AOCs were explored in a lab-scale step-feed three-stage integrated A/O biofilter (SFTIAOB) treating synthetic COW. Long-term operation demonstrated that COD, phenol, indole, quinoline and pyridine could be simultaneously removed. Phenol and indole were chiefly removed by anoxic zones, while quinoline and pyridine removal occurred in both anoxic and aerobic zones. Ultraviolet-visible spectrum observed that initial carboxylation and subsequent ring cracking and mineralization. Infrared spectroscopy also confirmed that key functional groups were cracked and produced during AOCs bio-degradation. Three-dimensional fluorescence spectrum indicated that significant transformation and elimination of tryptophan and humic acid with high molecular weight. Ring cleavage, distinct degradation and even complete mineralization of complex AOCs were further verified by gas chromatography-mass spectrometry. Moreover, functional degrading bacteria and aromatic ring-cleavage enzymes was successfully identified. Finally, AOCs biodegradation mechanisms by alternating anoxic and aerobic treatment was unraveled. This research provides thorough insights on AOCs biodegradation using a step-feed multi-stage alternating anoxic/oxic COW treatment process.

A rational strategy of combining Fenton oxidation and biological processes for efficient nitrogen removal in toxic coking wastewater

Effective removal of nitrogen from coking wastewaters is a great challenge, since conventional biological technologies commonly suffer from concentrated bio-toxic components such as phenolic compounds and thiocyanide (SCN^-). This study has successfully developed a novel ternary process for efficiently removing nitrogen from a practical coking wastewater, by rationally combined biological pretreatment, Fenton sub-pretreatment and final partial nitrification-denitrification (PN) process. It was noted that the oxic biological pretreatment (OP) could degrade above 80 % of COD and SCN^- in the wastewater, by adopting the pristine coking wastewater sludge. Fenton sub-pretreatment would further degrade the residual toxic organics and protect the metabolic activity of nitrobacteria and denitrobacteria, realizing the efficient removal of NH₄⁺-N and TN that occurred in the final PN process with self-cultivated sludge. This work can provide an interesting strategy by rationally combining biological-physicochemical processes for nitrogen removal in toxic industrial wastewaters.

Characterization of non-volatile organic contaminants in coking wastewater using non-target screening: Dominance of nitrogen, sulfur, and oxygen-containing compounds in biological effluents

While abundant volatile compounds (VOCs) have been identified in coking wastewater, the structures and occurrence of non-volatile organic compounds (non-VOCs) have remained unknown. In this study, 3966 non-VOCs belonging to 24 groups were tentatively identified for the first time in wastewater from four biological coking wastewater treatment systems in northern China using a non-target screening technique. A total of 227 compounds with CHNO, CHO, CHOS, and CHNOS elemental compositions were assigned with level 2 identification confidence, and 19 of them were confirmed with authentic standards, with 9-methyl-9H-carbazole-3-carbaldehyde (1706.3-2032.7 μg/L) and 3-Indolyl acetic acid monomethyl terephthalate (773.7-1449.9 μg/L) as the top two compounds in the influents, and 9-methyl-9H-carbazole-3-carbaldehyde (31.8-130.1 μg/L) and monomethyl terephthalate (13.9-196.6 μg/L) as the top two in the effluents. The four groups of substances accounted for 93.4% and 71.5% of the total responses of tentatively identified compounds in the influents and biological effluents, respectively, and were estimated to contribute 32.3-48.9% of the chemical oxygen demand in the biological effluents. In comparison with those in the influent, abundant S-containing compounds (CHOS and CHNOS, 35.2% of the total responses) were observed in the biological effluents, suggesting their highly bio-refractory characteristics. The advanced treatment process using synchronized oxidation-adsorption could almost completely remove the CHOS and CHNOS compounds from the biological effluents.

Bioaugmentation of quinoline-degrading bacteria for coking wastewater treatment: performance and microbial community analysis

Ochrobactrum sp. XKL1, previously found to have the ability to efficiently degrade quinoline, was bioaugmented into a lab-scale A/O/O system to treat real coking wastewater. During the bioaugmentation stage, the removal of quinoline and pyridine of the O1 tank could be enhanced by 9.88% and 7.96%, respectively. High-throughput sequencing analysis indicated that the addition of XKL1 could significantly affect the alteration of microbial community structure in the sludge. In addition, the relative abundance of Ochrobactrum has demonstrated a trend of increasing first followed by decreasing with the highest abundance of 7.87% attained on the 94th day. The bioaugmentation effects lasted for about 14 days after the strains was inoculated into the reactor. Although a decrease in the relative abundance of XKL1 was observed for a rather short period of time, the bioaugmented A/O/O system has been proven to be more effective in the removal of organic pollutants than the control. Hence, the results of this study indicated that the bioaugmentation with XKL1 is a feasible operational strategy that would be able to enhance the removal of NHCs in the treatment of coking wastewater with complex composition and high organic concentrations.

Visible light assisted FeOOH/CeO2/C deep degradation of organic matter in coking wastewater

In order to degrade hard-to-degrade organic pollutants such as amines, phenols, naphthalenes, pyrroles and pyridazines in coking wastewater, the nano-FeOOH/CeO₂/C composite catalysts (FCHCoke) were prepared. Firstly the catalysts were characterized by XRD, TEM, BET, BJH and UV/Vis/NIR. Then UV-Vis and GC-MS were used to detect the products in the degradation process of organic pollutants, respectively. The results showed that the average pore size of FCHCoke was 2-6 nm and the carrier coke enhanced the ability of the catalyst to absorbs visible light. Each intermittent light exposure for 2 h showed a better photodegradation. Under the intermittent irradiation of visible light of for a total of 8 h, 100µg۰mL^-1aniline and phenol were completely degraded. Dihydronaphthalene, esters, pyrrole, pyridazine, oxime and macromolecular alkanes in coking wastewater were also completely degraded. The acidity of pH=6 is more suitable for the photodegradation reaction of the catalyst. Organic degradation is the result of a combination of chemical catalysis and photocatalysis.

Microbial community composition and function prediction involved in the hydrolytic bioreactor of coking wastewater treatment process

The hydrolytic acidification process has a strong ability to conduct denitrogenation and increase the biological oxygen demand/chemical oxygen demand ratio in O/H/O coking wastewater treatment system. More than 80% of the total nitrogen (TN) was removed in the hydrolytic bioreactor, and the hydrolytic acidification process contributed to the provision of carbon sources for the subsequent nitrification process. The structure and diversity of microbial communities were elaborated using high-throughput MiSeq of the 16S rRNA genes. The results revealed that the operational taxonomic units (OTUs) belonged to phyla Bacteroidetes, Betaproteobacteria, and Alphaproteobacteria were the dominant taxa involved in the denitrogenation and degradation of refractory contaminants in the hydrolytic bioreactor, with relative abundances of 22.94 ± 3.72, 29.77 ± 2.47, and 18.23 ± 0.26%, respectively. The results of a redundancy analysis showed that the OTUs belonged to the genera Thiobacillus, Rhodoplanes, and Hylemonella in the hydrolytic bioreactor strongly positively correlated with the chemical oxygen demand, TN, and the removal of phenolics, respectively. The results of a microbial co-occurrence network analysis showed that the OTUs belonged to the phylum Bacteroidetes and the genus Rhodoplanes had a significant impact on the efficiency of removal of contaminants that contained nitrogen in the hydrolytic bioreactor. The potential function profiling results indicate the complementarity of nitrogen metabolism, methane metabolism, and sulfur metabolism sub-pathways that were considered to play a significant role in the process of denitrification. These results provide new insights into the further optimization of the performance of the hydrolytic bioreactor in coking wastewater treatment.

Insight into the effects of biological treatment on the binding properties of copper onto dissolved organic matter derived from coking wastewater

Biological treatment can remove more than 89.8% of total organic carbon (TOC) and 94.4% of fluorescent dissolved organic matter (DOM) in the coking wastewater, thereby affecting the migration, transformation and bioavailability and binding characteristics of heavy metals (HMs). The results of parallel factor analysis (PARAFAC) show that protein-like materials accounted for 97.53% in the coking wastewater DOM, a large number of humic-like substances are produced and accounted for more than 55.40% after biological treatment. A new spectral data processing method, the 1/n-th power transformation after two-dimensional correlated spectroscopy (2D-COS) in combination with synchronous fluorescence spectra (SFS), can identify small features obscured by strong peaks, and reveal more binding sites as well as preserve the sequential order information. The result indicates that the preferential bonding of Cu(II) is at 306 nm (protein-like) for coking wastewater DOM, and at 514 nm (humic-like) for effluent DOM. The C-O group of esters and alcohols can preferentially complexate with Cu(II) in the coking wastewater and effluent DOM. The log K_M values of PARAFAC components with Cu(II) are in the range of 3.59-5.06 for coking wastewater DOM, and in the range of 4.80-5.64 for the effluent DOM. Log K_M values for protein-like materials with Cu(II) are higher than these for fulvic- and humic-like substances. Humic-like substances can form more stable complexes with Cu(II) in the effluent DOM. Biological treatment increases the chemical stability of DOM-Cu(II) complexes, thereby further reducing the environmental risk of Cu(II).

Preparation of Tin-Antimony anode modified with carbon nanotubes for electrochemical treatment of coking wastewater

To improve the electrocatalytic activity, carbon nanotubes (CNTs) were used to modify a titanium-supported tin-antimony anode (Ti/SnO₂-Sb). Compared to a Ti/SnO₂-Sb anode, the Ti/SnO₂-Sb-CNTs anode exhibited a higher oxygen evolution potential (1.62 V), smaller crystalline volume (71.23 Å³), larger active surface area (0.371 mC cm^-2), lower charge transfer resistance (8.24 Ω), and longer service life (291 h). The CNTs provided the Ti/SnO₂-Sb anode with effective electrocatalytic activity, conductivity and stability. To evaluate its performance, the Ti/SnO₂-Sb-CNTs anode was utilized for the treatment of coking wastewater. The chemical oxygen demand (COD) and total organic carbon (TOC) removal yields of the coking wastewater reached 83.05% and 74.56% under the optimal current density of 25 mA m^-2, Na₂SO₄ concentration of 35 mM, and plate spacing of 10 mm. UV₂₅₄, ultraviolet-visible absorption spectroscopy, excitation-emission matrix spectra spectroscopy, and Fourier-transform infrared spectroscopy analyses showed that the aromatic and nitrogenous compounds in the coking wastewater were degraded. Furthermore, the electrochemical treatment could effectively reduce the toxicity of the coking wastewater. The energy consumption of the coking wastewater treatment was reduced to 396.56 kWh (kg COD)^-1. This study provides a basis engineering application of the electrochemical oxidation of coking wastewater.

Application of coke breeze for removal of colour from coke plant wastewater

Treatment of coking waste water has always been a challenge because of its complex and toxic nature. Numbers of technologies like biological treatment, advanced oxidation processes, activated carbon treatment etc. are available for removal of color and organic contaminants from wastewater. However, challenges and problems associated with application of biological, advanced oxidation methods for removal of color, chemical oxygen demand (COD), cyanides led to thrust for the development of new promising technologies. In this study, the application of coke breeze for the treatment of wastewater through adsorption has been demonstrated. A pseudo second order reaction kinetics has been observed through batch process adsorption study. Furthermore, adsorption data has found to be best fitted with the Freundlich adsorption isotherm model. Color removal efficiency of 80-90% along with COD removal efficiency of 40-50% was observed within 30 min by 120 g/L dosage of the adsorbent. The removal of phenolic and other organic compounds from coking wastewater has been measured through UV-Vis spectroscopy. The morphological changes of the adsorbent coke breeze have been captured through scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. However, because of the significant abundance in the steel plant, cost effectiveness and applicability of the post-treated coke breeze in sintered plant as fuel, turn it into a suitable adsorbent despite of having much lower specific surface area compared to commercial activated carbon (AC). Therefore, application of the coke breeze turns it into a very promising material and the technique is sustainable towards the coke quenching effluent treatment.

Correlating bacterial and archaeal community with efficiency of a coking wastewater treatment plant employing anaerobic-anoxic-oxic process in coal industry

Coking wastewater (CWW) contains various complex pollutants, and biological treatment processes are frequently applied in the coking wastewater treatment plants (CWWTPs). The present work is to evaluate the contaminants removal of a full-scale CWWTP with an anaerobic-anoxic-oxic process (A/A/O), to reveal function of bacterial and archaeal community involved in different bioreactors, and to clarify the relationship between the performance and microbial community. Illumina Miseq sequencing of bacteria showed that β-proteobacteria dominated in three bioreactors with relative abundance of 60.2%~81.7%. 75.2% of sequences were assigned to Petrobacter in the bioreactor A1, while Thiobacillus dominated in A2 and O with relative abundance of 31.8% and 38.7%, respectively. Illumina Miseq sequencing of archaea revealed a high diversity of methanogens existed in A1 and A2 activated sludge. Moreover, Halostagnicola was the dominant archaea in A1 and A2 activated sludge with relative abundance of 41.8% and 66.5%, respectively. Function predicted analysis explored that function of bacteria was similar to that of archaea but the relative abundance differed from each other. A putative biodegradation model of CWW treatment in A/A/O process indicated that A1 and A2 activated sludge mainly reduced carbohydrate, protein, TN, phenol and cyanide, as well as methane production. Bacteria in the bioreactor O were responsible for aerobic biotransformation of residual carbohydrates, refractory organics and nitrification. The redundancy analysis (RDA) further revealed that removal of COD, TN, and NO₃^--N, phenol and cyanides were highly correlated with some anaerobic bacteria and archaea, whereas the transformation of NH₄⁺-N was positively correlated with some aerobic bacteria.

Removal of F- and organic matter from coking wastewater by coupling dosing FeCl3 and AlCl3

Coagulation and precipitation is a widely applied method to remove F^- from wastewater. In this work, the effect of coagulation on the removal of F^- and organic matter from coking wastewater was studied using AlCl₃ and FeCl₃ as compound coagulants. The removal rates of F^- and organic matter under different coagulant doses and pH conditions were investigated. The results show that the highest removal rates of F^- by AlCl₃ and FeCl₃ are 94.4% and 25.4%, respectively; when the dosage is 10 mmol/L, the TOC removal rates of FeCl₃ and AlCl₃ reach 20.4% and 34.7%, respectively. Therefore, the removal rate of F^- by AlCl₃ is higher than that of FeCl₃, but the removal rate of organic matter by FeCl₃ is relatively higher. The addition of Ca²⁺ can promote the removal of F^-, but the removal rate of organic matter decreases. In addition, by investigating the effects of different pH and Fe-Al ratio on the removal rate, the removal effect of adding FeCl₃ and AlCl₃ at the same time was discussed. The results show that the most suitable working condition for the removal of organic matter and F^- is that the pH is 6.5 and the molar ratio of Al/Fe is 8:2. Overall, the removal mechanism of F^- and organic matter in coking wastewater by FeCl₃ and AlCl₃ was explored in this study. The experimental results can provide reference for the advanced treatment of coking wastewater.

An integrated biological-electrocatalytic process for highly-efficient treatment of coking wastewater

Coking wastewater is typically refractory, mainly due to its biological toxicity and complex composition. In this study, a novel integrated biological-electrocatalytic process consisting of two three-dimensional electrochemical reactors (3DERs), two biological aerated filters (BAFs), and a three-dimensional biofilm electrode reactor (3DBER) is developed for the advanced treatment of coking wastewater. 73.21% of chemical oxygen demand (COD), 38.02% of ammonium nitrogen (NH₄⁺-N) and 91.46% of nitrate nitrogen (NO₃^--N) are removed by 3DERs. BAFs mainly convert NH₄⁺-N to NO₃^--N through microbial nitrification. The 3DBER removes the residual NO₃^--N by bio-electrochemical denitrification. The integrated system can eliminate 74.72-83.27% of COD, 99.38-99.74% of NH₄⁺-N, and 69.64-99.83% of total nitrogen from coking wastewater during the continuous operation, as well as significantly reducing the toxicity of the wastewater. The superiorities of the integrated 3DERs/BAFs/3DBER system recommend the application of such biological-electrocatalytic technology in the treatment of highly toxic wastewater.

Performance and microbial community dynamics relationship within a step-feed anoxic/oxic/anoxic/oxic process (SF-A/O/A/O) for coking wastewater treatment

A step-feed anoxic/oxic/anoxic/oxic (SF-A/O/A/O) was developed and successfully applied to full-scale coking wastewater treatment. The performance and microbial community were evaluated and systematically compared with the anoxic/oxic/oxic (A/O/O) process. SF-A/OA/O process exhibited efficient removal of COD, NH₄⁺-N, TN, phenols, and cyanide with corresponding average effluent concentrations of 317.9, 1.8, 46.2, 1.1, and 0.2 mg·L^-1, respectively. In particular, the TN removal efficiency of A/O/O process was only 7.8%, with an effluent concentration of 300.6 mg·L^-1. Furthermore, polycyclic aromatic hydrocarbons with high molecular weight were the dominant compounds in raw coking wastewater, which were degraded to a greater extent in SF-A/OA/O. The abundance in Thiobacillus, SM1A02, and Thauera could be the main reason why SF-A/O/A/O was superior to A/O/O in treating TN. The microbial community structure of SF-A/O/A/O was similar among stages in system (P ≥ 0.05, Welch's t-test) and was less affected by environmental factors, which may have been one of the important factors in the system's strong stability.

Occurrence, fates, and carcinogenic risks of substituted polycyclic aromatic hydrocarbons in two coking wastewater treatment systems

This paper reports for the first time the occurrence, fates, and carcinogenic risks of 20 substituted polycyclic aromatic hydrocarbons (SPAHs) and 16 priority PAH species in two coking wastewater treatment plants (WWTPs) (plant E and central WWTP). The measured total concentrations of PAHs and SPAHs in raw wastewater of coking plant E were 3700 and 1200 μg·L^-1, respectively, with naphthalene (1400 μg·L^-1), and fluoranthene (353 μg·L^-1) as dominant PAH species and 2-methylnaphthalene (167 μg·L^-1), anthraquinone (133 μg·L^-1), and 1-methylnaphthalene (132 μg·L^-1) as dominant SPAHs. For the 11 methyl-PAHs (MPAHs), 4 oxygenated-PAHs (OPAHs), and 5 nitrated-PAHs (NPAHs) investigated, the biological wastewater treatment process removed 98.6% MPAHs, 83.9% OPAHs, and 89.1% NPAHs. Mass balance analysis result revealed that transformation was the major mechanism to remove low-molecular-weight (LMW) MPAHs (59.9-77.3%), a large part of OPAHs, including anthraquinone, methylanthraquinone, and 9-fluorenone (46.7-49.6%), and some NPAHs, including 2-nitrofluorene and 9-nitroanthrancene (52.9-59.1%). Adsorption by activated sludge mainly accounted for removing high-molecular-weight (HMW) SPAHs (59.6-71.01%). The relatively high concentrations of SPAHs in excess sludge (15,000 μg·g^-1) and treated effluent (104 μg·L^-1) are of great concern for their potential adverse ecological impacts. SPAHS exhibited similar behaviors in central WWTP, though the influent concentrations were much lower. The concentration levels of SPAHs in the ambient air of coking plant E and central WWTP may also pose potential lung cancer risks (LCR) to the workers through inhalation, where all studied SPAHs except 3-nitrofluoranthene and 7-nitrobenz[a]anthracene exceeded the acceptable cancer risk standards (>10^-6) recommended by U.S EPA. This study could help identify the ecological and healthy risks during coking wastewater treatment and provide useful information for policy-making.

Ammonia nitrogen removal from coking wastewater and high quality gypsum recovery by struvite recycling by using calcium hydroxide as decomposer

This study deals with the highly significant and cost-effective pretreatment of the high concentration of the Total Ammonia Nitrogen (TAN) in coking wastewater to improve the biodegradability. Struvite crystallization is a promising process for TAN removal, but the high operating cost hinders its application. To solve this problem, a novel struvite recycling process was proposed for pre-treating TAN present in the coking wastewater, within which struvite was decomposed in the solid-liquid system using Ca(OH)₂ as the decomposer. The results indicates that 91% of ammonium in struvite could be stripped out from the decomposition solution, with Ca(OH)₂:NH₄⁺ in the molar ratio of 2:1, temperature at 35 °C and a gas to liquid volume ratio of 3500. The resulting solution, post the escape of the ammonia, was dissolved by sulfuric acid. Approximately 100% of the phosphate and magnesium were observed to be released from the insoluble phosphate compounds, resulting in the formation of high-purity gypsum. A TAN removal efficiency of 89% could be achieved by reusing the supernatant after the dissolution of the decomposition product, at pH 9.5 and the Mg:TAN:PO₄-P molar ratio of 1.2:1:1. The pilot-scale test demonstrated that approximately 86% TAN was removed from the coking wastewater and the purity of recovered could reach over 99%. Further economic analysis proves that the operation cost of the proposed process is 0.55$ per m³ of coking wastewater, showing a 73% cost reduction when compared to struvite crystallization without recycling.

Biodegradation of phenol by a halotolerant versatile yeast Candida tropicalis SDP-1 in wastewater and soil under high salinity conditions

In this study, a novel halotolerant phenol-degrading yeast strain, SDP-1, was isolated from a coastal soil in Jiangsu, China, and identified as Candida tropicalis by morphology and rRNA internal transcribed space region sequence analysis. Strain SDP-1 can efficiently remove phenol at wide ranges of pH (3.0-9.0), temperature (20-40 °C), and NaCl (0-5%, w/v), as well as the tolerance of Mn²⁺, Zn²⁺ and Cr³⁺ in aquatic phase. It also utilized multiple phenol derivatives and aromatic hydrocarbons as sole carbon source and energy for growth. Free cells of SDP-1 were able to degrade the maximum phenol concentration of 1800 mg/L within 56 h under the optimum culture conditions of 10% inoculum volume, pH 8.0, 35 °C and 200 rpm agitation speed. Meanwhile, SDP-1 was immobilized on sodium alginate, and the capability of efficiently phenol degradation of free cells and immobilized SDP-1 were evaluated. Shortened degradation time and long-term utilization and recycling for immobilized SDP-1 was achieved compared to free cells. The 1200 mg/L of phenol under 5% NaCl stress could be completely degraded within 40 h by immobilized cells. In actual industrial coking wastewater, immobilized cells were able to completely remove 383 mg/L phenol within 20 h, and the corresponding chemical oxygen demand (COD) value was decreased by 50.38%. Besides, in phenol-contained salinity soil (3% NaCl), 100% of phenol (500 and 1000 mg/kg) removal efficiency was achieved by immobilized SDP-1 within 12 and 26 days, respectively. Our study suggested that versatile yeast Candida tropicalis SDP-1 could be potentially used for enhanced treatment of phenol-contaminated wastewater and soil under hypersaline or no-salt environmental conditions.

The preparation of black titanium oxide nanoarray via coking fluorinated wastewater and application on coking wastewater treatment

Coking wastewater is extremely toxic with poor biodegradability owing to the presence of refractory organics. Black titanium oxide nanotube array (BTN), not only photocatalyst but also electrocatalyst, is with definite potentiality in organic wastewater treatment. Here, we firstly developed an electrochemical method, using fluorinated coking wastewater as electrolyte rather than traditional fluorinated ethylene glycol, to prepare titanium oxide nanoarray economically. Unexpectedly, suspended pollutants and ammonia nitrogen in coking wastewater were removed in BTN preparation. Moreover, the as-prepared BTN could be further employed as photocatalyst or electrocatalyst to degrade dissolved organic matter in coking wastewater. As an electrocatalyst, BTN possessed the comparable •OH production activity about 9.9 × 10^-15 M S^-1 to boron-doped diamond, high oxygen evolution potential around 2.75 V, and high selectivity of chlorine production. Moreover, the biodegradability of treated coking wastewater could be effectively improved by using BTN as electrocatalyst in electrochemical oxidation, and the BOD/COD was from 0.19 to above 0.3 in 4 h at current density of 2 mA cm^-2. The energy consumption was about 63-68 kWh kgCOD^-1, lower than that of various reported electrodes. This study provided an economical and environmentally friendly method to prepare BTN, which was with positive application prospect in the field of coking wastewater treatment.

Understanding the toxicity effect and mineralization efficiency of in-situ electrogenerated chlorine dioxide for the treatment of priority pollutants of coking wastewater

Oxidation of phenol, cyanide and aniline have been analyzed by the enhanced electro-oxidation process in which sodium chlorite was used as an electrolyte and results were validated using statistical tool based on Box-Behnken design. The mineralization efficiency of 78.4%, and 98.18% were predicted at optimized variables condition for phenol, and aniline respectively, whereas complete mineralization has been observed for the cyanide at the optimized conditions, which describes the significance of the design model approach.The process mineralizes the higher phenol concentration revealing a drastic reduction in power consumption in comparison of direct oxidation, i.e., 799.36 kWh/kg to 138.18 kWh/kg for more than 90% mineralization of phenol even at a higher current density of 13.63 mA/cm². The kinetic modelling approach justified that higher current density has also played a role in higher mineralization of pollutants at the specific operating conditions. The by-product formation and toxicity effect on microalgae in wastewater were assessed by the full scan mass spectrometry and microalgae pigment inhibition test after the electro-oxidation of coking wastewater. The pigment growth inhibition rate of Chlorella sp. NCQ and Micractinium sp. NCS2 suggests that sodium chlorite as an electrolyte aid can also effectively used as an oxidizing agent and algal inhibiter in the coking wastewater.

Cathodes of membrane and packed manganese dioxide/titanium dioxide/graphitic carbon nitride/granular activated carbon promoted treatment of coking wastewater in microbial fuel cell

A more practical microbial fuel cell system with both catalytic cathode membrane and packed cathode of modified granular activated carbon with manganese dioxide/titanium dioxide/graphitic carbon nitride/(MnO₂/TiO₂/g-C₃N₄/GAC) was tested in treating high COD coking wastewater (>3000 or >6000 mg L^-1). The decreased system internal resistance promoted treatment efficiency and electricity generation. With microbes acclimated, the system achieved both high removals of COD and NH₄⁺-N (>96%), decreased UV₂₅₄ from 23.80 to 34.50 cm^-1 in influent to 1.11-1.42 cm^-1 in effluent. The capacity in COD removal reached 3.07 kg COD m^-3d^-1 and the maximum power density was 1680 mW m^-3 much higher than those without the packed cathode. This system is feasible for sustainable treatment of coking wastewater.

Treatment of coking wastewater in biofilm-based bioaugmentation process: Biofilm formation and microbial community analysis

Coking wastewater (CWW) containing complicated organic compositions and strong toxicity cause potential hazards to natural water bodies as well as human health. The aim of this study was integrating newly isolated Comamonas sp. ZF-3, biofilm-based bioaugmentation and fluidized bed reactor into an anoxic filter-fluidized bed reactor (AF-FBR) system to treat actual CWW. The results showed that 93 % of chemical oxygen demand (COD) and 97 % of ammonia nitrogen (NH₄⁺-N) removal efficiency were achieved with hydraulic retention time of 70 h. The main pollutants including phenolic compounds, heterocyclic compounds and polycyclic aromatic hydrocarbons could be removed via biofilm-based process in AF-FBR. The formation of carrier biofilm was consistent with the system performance as well as the biofilm community evolution, during which the microbial community was gradually dominated by some functional genus (e.g., Comamonas, Thiobacillus, Pseudomonas and Thauera), meanwhile, ammonium-oxidizing bacteria Nitrosomonas, nitrite-oxidizing bacteria Nitrospira and denitrifiers (e.g., Pseudomonas, Thiobacillus and Bacillus) coexisted in biofilm to form a microbial community for biological nitrogen removal. Such microbial community structure explained the observed simultaneous removal of COD and NH₄⁺-N in the AF-FBR.

Selection of optimum biological treatment for coking wastewater using analytic hierarchy process

The design of biological treatment process for the coking wastewater (CW) is complicated since wastewater treatment demand is gradually increasing lacking the systematic strategy in efficiency evaluation and advisable selection. Therefore, this study develops a holistic approach by means of the analytic hierarchy process (AHP) that uses numerical representation to rank the preferences of each participating alternatives for evaluation of the advanced biological technologies in CW treatment. Based on survey results, six types reactor combinations were selected as the alternatives, which were further classified as two group according to COD load. The AHP methodology consists of weighting and ranking procedures considering technical, economic, environmental and administration factors defined as criteria layers. Eighteen indicators were chosen as sub-criteria layers. Inclusively beneficial and sustainable biological processes were assessed and ranked along the AHP implementation. The results placed technical indicators to the top position among the criteria layers in the weighting descending order 'technical indicators > economic indicators > environmental indicators > administrative indicators', whereas the weight of indicators in sub-criteria layers fitted in the range of 0.005 to 0.151. The inclusive priority calculation integrating all weight indices of criteria and sub-criteria layers resulted in the anaerobic-anoxic-oxic (A/A/O) combination rising in the hierarchy of the low load group, whereas the oxic-hydrolytic-oxic (O/H/O) process was prioritized in the high load group. The accuracy and objectivity of AHP application was also supported by sensitivity and variability analyses that examines a range for the weights' values and corresponding to alternative scenarios.

Catalytic ozonation of bio-treated coking wastewater in continuous pilot- and full-scale system: Efficiency, catalyst deactivation and in-situ regeneration

In this study, the performance of catalytic ozonation in the treatment of bio-treated coking wastewater (BCW) using pilot- and full-scale systems was investigated. Additionally, the removal efficiency of organic pollutants from BCW, the deactivation mechanism of Mn_xCe_1-xO₂/γ-Al₂O₃, and backflushing optimization for in-situ catalyst regeneration, which have not been previously investigated, were analysed. Results of the 12-month pilot scale experiments showed that catalytic ozonation resulted in the effective removal of organic pollutants when backflushing was applied as an in-situ catalyst regeneration strategy. The effluent chemical oxygen demand (COD) content decreased from 150 to 78 mg L^-1, and remained below a discharge limitation of 80 mg L^-1, and the stable COD removal efficiencies (from 56.0% to 47.9%) indicated that catalyst deactivation, which primarily resulted from the deposition of inorganic salts on the surface of the catalyst that limited interaction between ozone and active sites and/or prevented electrons transfer, was primarily inhibited by backflushing. The catalyst regeneration via in-situ air- and water-backflushing was attributed to the scrubbing, collision, and/or the loosing effect. Additionally, in the full-scale experiment, the catalytic ozonation process with in-situ alternative backflushing exhibited a stable COD removal efficiency (above 45.6%) for 885 days when water- and air-flushing strengths of 10 L m^-2 s^-1 and 15 L m^-2 s^-1, respectively, were applied with a 7-day regeneration interval. Therefore, the results of this study provide new insights into catalytic ozonation and support its engineering application in BCW treatment.

An integrated three-dimensional electrochemical system for efficient treatment of coking wastewater rich in ammonia nitrogen

Coking wastewater is highly toxic and refractory industrial wastewater, and is thus extremely challenging to treat. Currently, most treatment technologies focus on degrading carbonaceous pollutants, while insufficient attention is placed on ammonium nitrogen (NH₄⁺-N), the most important nitrogenous contaminant in coking wastewater and with a high biological toxicity. In the current study, we developed an integrated electrochemical system comprising two three-dimensional electrochemical reactors (3DERs), two three-dimensional biofilm electrode reactors (3DBERs) and one three-dimensional biofilm electrode reactor for denitrification (3DBER-De) to treat coking wastewater rich in NH₄⁺-N. Our integrated system is able to remove 70.7% of total nitrogen (TN) at the low energy consumption of 1.29 kWh m^-3, and can reduce COD by 55.8%. The 3DERs primarily degrade NH₄⁺-N, nitrate nitrogen (NO₃^--N), and COD by electrochemical redox reactions, while the 3DBERs convert residual NH₄⁺-N to NO₃^--N by fusing biofilm and electricity. Moreover, the 3DBER-De further eliminates NO₃^--N by bio-electrochemical denitrification. The coking wastewater is purified as it flows through the integrated treatment system, with only a few hydrocarbon residuals detected that are able to be readily biodegraded by conventional biological treatments. The proposed 3DERs/3DBERs/3DBER-De system provides a new solution for coking wastewater with high concentrations of NH₄⁺-N.

ZF-3 involved in typical organics degradation in coking wastewater

The aim of this study was to investigate the characteristic of a newly isolated strain Comamonas sp. ZF-3 involved in typical organics degradation in coking wastewater (CWW). The results showed that the isolated strain had efficient biodegradability of phenolic compounds and heterocyclic compounds in CWW, meanwhile, phenol and indole could be respectively used as sole carbon source for its growth, which demonstrated the bioaugmentation potential of the isolated strain in CWW treatment. During phenol and indole degradation processes, part of metabolites (e.g., 2,3-hexanedione, 2-ethyl-1-hexanol, nonanal, 2-propyl-1-heptanol, butanoic acid, butyl ester and butanoic acid, anhydride) remained in effluents, with NH₄⁺-N concentration having no obvious reduction, which implied the biological treatment of CWW should be accomplished by complex microbial communities in many steps.

A pilot-scale three-dimensional electrochemical reactor combined with anaerobic-anoxic-oxic system for advanced treatment of coking wastewater

Coking wastewater is highly concentrated and extremely toxic, greatly challenging the treatment technologies. Conventional biological technology such as anaerobic-anoxic-oxic (A²O) system is inefficient, since various biological reactions are inhibited by toxicants in coking wastewater. In this work, a pilot-scale three-dimensional electrochemical reactor (3DER) is integrated into the A²O system as a pretreatment unit to improve the treatment efficiency of coking wastewater. The results indicate that 3DER pretreatment increased the biodegradability of coking wastewater, promoting the degradation of coking wastewater in A²O system. The integrated 3DER-A²O system can remove 94.4% of COD and 76.2% of TN from coking wastewater, and the energy consumption was only 0.22 kWh/kg COD and 4.69 kWh/kg TN. The components of coking wastewater were significantly simplified and the acute toxicity was reduced from 99% to 12% after the treatment. The integrated 3DER-A²O system provides a new solution for coking wastewater treatment, showing a promising application potential.

New insights of enhanced anaerobic degradation of refractory pollutants in coking wastewater: Role of zero-valent iron in metagenomic functions

Coking wastewater (CWW) has long been a serious challenge for anaerobic treatment due to its high concentrations of phenolics and nitrogen-containing heterocyclic compounds (NHCs). Herein, we proposed and validated a new strategy of using zero-valent iron (ZVI) to strengthen the anaerobic treatment of CWW. Results showed that COD removal efficiencies was increased by 9.5-13.7% with the assistance of ZVI. GC-MS analysis indicated that the removal of phenolics and NHCs was improved, and the intermediate 2(1H)-Quinolinone of quinoline degradation was further removed by ZVI addition. High-throughput sequencing showed that phenolics and NHCs degraders, such as Levilinea and Sedimentibacter were significantly enriched, and the predicted gene abundance of xenobiotic degradation and its downstream metabolic pathways was also increased by ZVI. Network and redundancy analysis indicated that the decreased oxidation-reduction potential (ORP) by ZVI was the main driver for microbial community succession. This study provided an alternative strategy for strengthening CWW anaerobic treatment.

Simultaneous decarburization, nitrification and denitrification (SDCND) in coking wastewater treatment using an integrated fluidized-bed reactor

There are two problems in biological treatment of coking wastewater (CWW): incapability of pre-anaerobic treatment to eliminate the toxicity in wastewater, and the lack of carbon source for subsequent denitrification in pre-aerobic treatment. To achieve simultaneous decarburization, nitrification and denitrification (SDCND) in CWW treatment, biological carrier materials was used to build an integrated fluidized-bed reactor (Reactor B, RB). A conventional fluidized-bed reactor (Reactor A, RA) was used as a control reactor under the same condition. The results showed that RB was more advantageous since its removal efficiencies of COD and TN were 90% and 87%, respectively, which were significantly higher than these in RA (82% and 45%), at a hydraulic retention time (HRT) of 60 h. Microelectrode measurement indicated that oxygen transfer was limited inside the carrier where the formation of a dissolved oxygen (DO) concentration gradient was observed. Microbial community analysis showed that the aerobic and anoxic microenvironments in RB promoted the co-existence of a wider variety of bacteria, thus achieving SDCND. These results indicated the integrated fluidized-bed reactor exhibited promising feasibility for simultaneous carbon and nitrogen removal in CWW treatment under the same aeration driven conditions. The SDCND process realized by fluidized-bed reactor provided a reference for the treatment of toxic industrial wastewater with high carbon to nitrogen ratio.

Emission characteristics and associated health risk assessment of volatile organic compounds from a typical coking wastewater treatment plant

Coking wastewater is a typical industrial wastewater and contains a number of toxic and harmful organic pollutants which threaten human health. However, emission of volatile organic compounds (VOCs) from coking wastewater treatment plants (WWTPs) is rarely studied. Here, the emission characteristics of VOCs were investigated in a full-scale coking WWTP composed of an anaerobic-oxic-oxic (A-O₁-O₂) treatment system. Furthermore, the potential health risks were assessed in this study. VOC emission rates were estimated at each unit of the coking WWTP and the influencing factors of emissions were discussed. Seventeen VOCs were identified in the air phase by gas chromatography-mass spectrometry combined with Tenax adsorption-thermal desorption method; benzene, toluene, and xylenes were predominant, and the concentration of total VOCs decreased gradually from the raw water tank (857.86 ± 131.30 μg m^-3) to the effluent tank (28.56 ± 3.96 μg m^-3). The total VOC emission rate from all units was 1773.42 g d^-1, corresponding to an annual emission of 0.65 tons year^-1. Since the treatment capacity of this coking WWTP was about 1500 m³ d^-1, it was estimated that 1.18 g of VOCs are emitted during the treatment of 1 m³ wastewater. Influencing factors of VOC emission mainly include the background concentration of VOCs in wastewater, operational parameters of the treatment processes, and physicochemical properties of VOCs. The carcinogenic risk of VOCs for workers in this coking WWTP ranged from 3.0 × 10^-5 to 7.8 × 10^-4, which exceeded an acceptable level (1.0 × 10^-6). The non-carcinogenic risk hazard ratio of benzene exceeded 1, indicating that benzene has an obvious non-carcinogenic risk. Understanding VOCs emission characteristics and emission rates can help to identify the adverse effects of coking WWTPs on human health and provide relevant information for policy-making.

Structure and function of microbial community involved in a novel full-scale prefix oxic coking wastewater treatment O/H/O system

A novel full-scale prefix oxic coking wastewater (CWW) biological treatment O/H/O system had been operated steadily six years with the effluent quality meeting national discharge standard. Comparing to the traditional CWW biological treatment process, which usually have an anaerobic unit at the start of the process, here the O/H/O system has obvious advantages in COD removal, total nitrogen removal and reduced energy consumption. It is very necessary to illustrate the structure and function of the microbial community involved in different bioreactors of the O/H/O system. High-throughput MiSeq sequencing was used to examine the 16S rRNA genes in this system. Results revealed a contrasting microbial composition among the activated sludge samples of three sequential bioreactors: the β-Proteobacteria related sequences dominated in the O₁ activated sludge with the relative abundance of 56.44% while 7.53% of the sequences were assigned to Thiobacillus; Rhodoplanes related sequences dominated in the bioreactor H and O₂ activated sludge with relative abundance of 8.86% and 8.92%, respectively. The physico-chemical characteristics of CWW were analyzed by standard methods and the operational parameters were routinely monitored to examine their effects on the microbial communities. The bioinformatics software package of phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) was used to predict the microbial community functional profiling and found three dominant genera of Rhodoplanes, Lysobacter and Leucobacter enriched the xenobiotics biodegradation and metabolism pathway. The diverse and distinct microbial community involved in biological treatment processes of CWW treatment indicating that water characteristics and operational parameters determined the microbial community composition. These results significantly expanded our knowledge of the biodiversity and population dynamics of microorganisms and discerned the relationships between bacterial communities and environmental variables in the biological treatment processes. Moreover, in this study, we proposed a comprehensive biodegradation model of CWW treatment and defined as O/H/O system.

Investigation of the fate of heavy metals based on process regulation-chemical reaction-phase distribution in an A-O1-H-O2 biological coking wastewater treatment system

Regulation mechanism of typical substances including OH^-, CN^-, SCN^-, S^2-, NH₃ on the distribution of heavy metals was investigated in coking wastewater treatment plant with our self-designed Anaerobic-Oxic-Hydrolytic-Oxic (A-O₁-H-O₂) system through engineering data exposure and computational density functional theory (DFT) verification. The results showed that coking sludge had superior enrichment ability for heavy metals, especially for the sludge from the A and H tanks. The enrichment ratio of the 8 heavy metals including Cd, Pb, Ni, Zn, Cu, Hg, Cr and As in coking waste sludge was found to be 6232 (comparing to these in the influent wastewater of A-O₁-H-O₂ system). The distribution of 8 heavy metals was closely related to their chemical (precipitation and/or complexation) and biochemical reaction potential with OH^-, CN^-, SCN^-, S^2-, NH₃ in the A-O₁-H-O₂ system. The regulation mechanism of these precipitation and/or complexation agents on heavy metals was confirmed by DFT calculation. The stable energy of complexes formed between typical compounds and common heavy metal ions follow the order: OH: Cu²⁺>Pb²⁺>Zn²⁺>Cd²⁺>Hg²⁺>Ni²⁺; S^2-: Pb²⁺>Cu²⁺>Zn²⁺>Cd²⁺>Hg²⁺>Ni²⁺; CN^-: Zn²⁺>Cu²⁺>Cd²⁺>Hg²⁺>Pb²⁺>Ni²⁺; SCN^-: Zn²⁺>Cd²⁺>Pb²⁺>Hg²⁺>Cu²⁺>Ni²⁺; NH₃: Cu²⁺>Zn²⁺>Cd²⁺>Pb²⁺>Hg²⁺>Ni²⁺, providing reference for the judgement of which metal ions were preferentially combined with the typical compounds in coking wastewater. The results of this paper indicated that the enrichment of heavy metal ions in coking wastewater can be achieved by process design combined with the control of operating conditions (dissolved oxygen, hydraulic retention time, sludge retention time and pH), basing on the nature of heavy metal ions. Finally, the separation and differential management of heavy metals can be achieved.

Highly active and durable carbon electrocatalyst for nitrate reduction reaction

The development of a new class of carbon electrocatalysts for nitrate reduction reaction (NRR) that have high activity and durability is extremely important, as currently reported metallic electrocatalysts show a main drawback of low stability owing to leaching and oxidation. Herein, we demonstrate that a unique N-doped graphitic carbon-encapsulated iron nanoparticles can be utilized as a promising NRR electrocatalyst. The resulting Fe(20%)@N-C achieves a better nitrate removal proportion of 83.0% (attained in the first running cycle) compared to the efficiencies of other reference catalysts, including those with lower entrapped Fe content. The nitrogen selectivity is 25.0% in the absence of Cl^- and increases to 100% when supplemented with 1.0 g L^-1 NaCl. More importantly, there is no statistically significant difference (at a 95% confidence interval) regarding the removal percentage recorded over 20 cycles for the Fe(20%)@N-C cathode. We propose that the iron nanoparticles could attenuate the work function on the neighboring carbon atoms, which are the reactive sites for NRR, and that the graphitic shells hinder the access of the electrolyte, thus protecting the iron particles from dissolution and oxidation. Testing with the real industrial wastewater further demonstrates the superiority of Fe(20%)@N-C cathode towards NRR, as evidenced by efficient removal of nitrate available in the biological effluent from a local coking wastewater treatment plant.

Structure and function of microbial community associated with phenol co-substrate in degradation of benzo[a]pyrene in coking wastewater

Coking wastewater (CWW) contains high contents of phenols and other toxic and refractory compounds including polycyclic aromatic hydrocarbons (PAHs) with the most carcinogenic benzo[a]pyrene (BaP) among them. The mechanism of PAHs/BaP degradation in activated sludge of CWW treatment with phenol as co-substrate was studied. For characterizing the structure and functions of microbial community associated with BaP degradation with phenol as co-substrate, high-throughput MiSeq sequencing was used to examine the 16S rRNA genes of microbiology, revealing noticeable shifts in CWW activated sludge bacterial populations. Major genera involved in anaerobic degradation were Tissierella_Soehngenia, Diaphorobacter and Geobacter, whereas in aerobic degradation Rhodanobacter, Dyella and Thauera prevailed. BaP degradation with phenol as co-substrate induced bacterial diversification in CWW activated sludge in opposite trends when anaerobic and aerobic conditions were applied. In order to predict the microbial community functional profiling, a bioinformatics software package of phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) was run to find that some dominant genera enriched in the BaP pathway may own the ability to degrade PAHs/BaP. Further experiments should focus on testing the dominant genera in BaP degradation at different oxygen levels.