Coking Wastewater Treatment Plant Research Articles

Predicting the occurrence of substituted and unsubstituted, polycyclic aromatic compounds in coking wastewater treatment plant effluent using machine learning regression

Organic contaminants such as polycyclic aromatic compounds (PACs) occurring in industrial effluents can not only persist in wastewater but also undergo transformation into more toxic and mobile substituted heterocyclic products during their treatment. Thus, predicting the occurrence of PACs and their heterocyclic derivatives (HPACs) in coking wastewater is of utmost importance to reduce the environmental risks of receiving water bodies. While HPACs can be monitored through sampling and analysis, their characterisation techniques are costly and time-consuming. In this study, we propose 3 distinct kernel-based machine learning (ML) models for predicting PACs including substituted HPACs and alkylated PACs occurring in coking wastewater. By using routinely measured wastewater quality data, as input for our models, we predicted the occurrence of 14 HPACs in the final effluent with an R2 of 0.83. Further performance assessment of the regression model based on support vector machine (SVR) showed a logarithmic error (MALE) of 0.46 and square error (RMSE) of 0.073 ng/L. Comparatively, K-nearest neighbor and random forest models showed an R2 of 0.75 and 0.76 respectively for HPAC prediction. Further model exploration through feature analysis revealed that the superior predictability of SVR model was based on its higher weightage (81%) towards input variables of dissolved organic carbon and total ammonia which could capture the underlying secondary transformations likely occurring in the treatment plant. Based on partial dependence plots, ammonia levels higher than 120 mg/L and DOC levels of 50-60 mg/L were indicative of higher HPACs dissolved in coking effluent. This work highlights the capability of kernel-based ML models in capturing nonlinear wastewater chemistry and offer a tool for monitoring trace organic contaminants released in coking wastewater effluents.

Effective degradation of quinoline by catalytic ozonation with MnCexOy catalysts: performance and mechanism.

Quinoline inevitably remains in the effluent of coking wastewater treatment plants due to its bio-refractory nature, which might cause unfavorable effects on human and ecological environments. In this study, MnCexOy was consciously synthesized by α-MnO2 doped with Ce3+ (Ce:Mn = 1:10) and employed as the ozonation catalyst for quinoline degradation. After that, the removal efficiency and mechanism of quinoline were systematically analyzed by characterizing the physicochemical properties of MnCexOy, investigating free radicals and monitoring the solution pH. Results indicated that the removal rate of quinoline was greatly improved by the prepared MnCexOy catalyst. Specifically, the removal efficiencies of quinoline could be 93.73, 62.57 and 43.76%, corresponding to MnCexOy, α-MnO2 and single ozonation systems, respectively. The radical scavenging tests demonstrated that •OH and •O2- were the dominant reactive oxygen species in the MnCexOy ozonation system. Meanwhile, the contribution levels of •OH and •O2- to quinoline degradation were about 42 and 35%, respectively. The abundant surface hydroxyl groups and oxygen vacancies of the MnCexOy catalyst were two important factors for decomposing molecular O3 into more •OH and •O2-. This study could provide scientific support for the application of the MnCexOy/O3 system in degrading quinoline in bio-treated coking wastewater.

Characteristics and Risk Assessment of PAH Pollution in Soil of a Retired Coking Wastewater Treatment Plant in Taiyuan, Northern China.

We analyzed the soil at the site of a former coking wastewater treatment plant on redeveloped land in Taiyuan, northern China, in an attempt to detect the presence of 16 types of priority polycyclic aromatic hydrocarbons (PAHs) listed by the United States Environmental Protection Agency (US EPA) and evaluate the potential pollution risks. The results show that the total proportion of PAHs in the surface soil of the redeveloped land ranged from 0.3 to 1092.57 mg/kg, with an average value of 218.5 mg/kg, mainly consisting of high-ring (5-6 rings) components. Characteristic ratio analysis indicated that the pollution was mainly related to the combustion of petroleum, coal, and biomasses. The wastewater treatment units operated according to the following treatment train: advection oil separation tank, dissolved air flotation tank, aerobic tank, secondary sedimentation tank, and sludge concentration tank. Our study found that pollution resulting from low-ring PAHs mainly appeared in the advection oil separation tank during the pre-wastewater treatment stage, while medium-ring PAH contamination mainly occurred in the dissolved air floatation tank, aerobic tank, and secondary sedimentation tank during the middle stages of wastewater treatment. High-ring PAH contamination primarily appeared in the sludge concentration tank in the latter stage of wastewater treatment. Based on our assessment of the ecological risk using the Nemerow Comprehensive Pollution Index and the toxicity equivalent factor (TEF) method, we determined that individual PAHs in the study area exceeded acceptable levels and the total amount of pollution was potentially harmful to the ecological environment. In addition, the comprehensive lifetime cancer risk for different populations resulting from exposure to the soil in the study area was determined to be within acceptable limits based on the average PAH concentrations.

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.

The significance of resource recycling for coking wastewater treatment: based on environmental and economic life cycle assessment

The sustainability of the coking industry is supported by reasonable production profit and environmental quality requirements. The traditional measures substantially increased the related costs for enterprises to reach standards. This paper aims to develop a comprehensive cost combined environmental impact assessment method that is necessary for the analysis of wastewater treatment systems. Typical three coking wastewater treatment processes in China were evaluated. Results showed that eutrophication dominantly contributed to the overall environmental effect. Improving effluent quality could significantly reduce the total environmental impact. In terms of an economic perspective, the price of raw materials was the main factor that affected the operating cost of comprehensive treatment. Based on subsystem analysis, the pretreatment stage accounted for the majority of environmental and cost burdens, respectively reaching 64%–78% and 64%–86%. Optimizing the pretreatment process by enhancing the efficiency of high concentration raw material recovery and substituting toxic raw materials for extractant could reduce the environmental impact and economic cost by 43.8% and 57%, respectively, which was an effective way to improve the potential performance of coking wastewater treatment plants (WWTPs).

Remediation of cyanide in biologically treated coke plant wastewater by chemical treatment method

ABSTRACT Biological treatment with a stable activated sludge process, followed by chemical treatment is one of the potential and accepted cyanide remediation processes for coke plant wastewater treatment. Biologically treated coke plant wastewater contains free cyanide above permissible limit. Presently, chemical treatment with NaOCl is being used to attenuate free cyanide below permissible limit in biologically treated water. This process increases the TDS and colour content in discharge water. Ca(OCl)2 can be used as an alternative to NaOCl for cyanide remediation in biologically treated coke plant wastewater without increasing TDS. In the present work, cyanide removal efficiency of NaOCl and Ca(OCl)2 for real coke plant wastewater after biological treatment has been studied. Optimisation of chemical dosage, treatment time and pH study has been done for Ca(OCl)2 and NaOCl treatment. It was found that up to 90% of free cyanide removal could be achieved through Ca(OCl)2 treatment without increasing the TDS value. In addition, more than 50% colour of the wastewater was removed. pH elevation step required in NaOCl treatment can be eliminated in Ca(OCl)2 treatment, thereby reducing caustic consumption. The study indicated that the use of Ca(OCl)2 is economically more viable than that of NaOCl in cyanide treatment.

Removal of fluoride from coke wastewater by aluminum doped chelating ion-exchange resins: a tertiary treatment

Coke wastewater is one of the most problematic industrial wastewaters, due to its large volume and complex pollutant load. In this study, ion exchange technology was investigated with the objective of reducing the fluoride content of the effluent from a coke wastewater treatment plant (26.7 mg F-/L). Two Al-doped exchange resins with chelating aminomethyl-phosphonic acid and iminodiacetic groups were assessed: Al-doped TP260 and TP207 resins, respectively. The effect of resin dosage, varying from 5 to 25 g/L, was evaluated. F- removal was within the range 57.8–89.3% and 72.0–92.1% for Al-doped TP260 and TP207, respectively. A kinetic study based on a generalized integrated Langmuir kinetic equation fitted the experimental data (R2 > 0.98). The parameters of the said kinetics met the optimal conditions for the ion exchange process, which seemed to be more favorable with Al-doped TP260 resin than with Al-doped TP207 resin, using the same resin dosage. Furthermore, the experimental data were well described (R2 > 0.98) by Langmuir and Freundlich isotherm models, in agreement with the findings of the kinetic study: the maximum sorption capacity was obtained for the Al-doped TP260 resin.

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.

Bioremediation of coke plant wastewater from steel industry with mixed activated sludge–microalgal consortium in lab‐scale semi‐continuous mode

AbstractBACKGROUNDRemoval of toxicities from wastewater has always demanded great attention as it has life‐threatening impacts on every living being and the environment. In the present study, bioremediation of ammonia and cyanide from coke plant wastewater (CPWW) by using bacterial consortia with activated sludge (AS) supplemented with microalgal (MA) biomass in semi‐continuous mode was performed. Parameters such as pH, total dissolved solids (TDS), dissolved oxygen (DO) and bacterial cell viability, along with any significant effect on the growth of microalgal cells in wastewater, was investigated by determining its specific growth rate (μ).RESULTSWith pH values remaining constant for the system, the ammonia removal rate with microalgae additions was approximately 38.3% lower than that with AS. Similarly, the cyanide removal rate after addition of microalgae to the system showed a difference of 43% with AS treatment. TDS levels dropped by 22.18% and the concentration of DO increased by 21.91% in comparison to the values obtained by treatment of CPWW with AS and MA to CPWW with AS alone.CONCLUSIONMicroalgae additions effectively increase the efficiency of AS treatment of CPWW and thus can be taken to field trials for developing a cost‐effective and environmentally friendly strategy of wastewater treatment. © 2021 Society of Chemical Industry

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.

Two-stage anoxic-oxic (A/O) system for the treatment of coking wastewater: Full-scale performance and microbial community analysis

• A full-scale AOAO coking wastewater treatment system was investigated. • Various pollutants were removed efficiently after the AOAO process. • The biodegradation dynamics of refractory organics was explored by GC × GC-TOF MS. • Composition and function of microbial community greatly altered in AOAO process. Coking wastewater (CWW) is one of the most challenging industrial wastewaters to treat, due to its complex chemical composition, high organic load, and potential toxicity to human and environmental health. A full-scale coking wastewater treatment plant with a two-stage anoxic-oxic-anoxic-oxic (A1/O1/A2/O2) process was investigated systematically. The experimental results showed that the AOAO process exhibited an excellent removal capacity of COD, ammonia, nitrate, and total nitrogen. The GC × GC-TOF MS analysis investigated that the majority of refractory organic compounds, such as phenols, quinolines, polycyclic aromatic hydrocarbons, hydrocarbons, etc., were either fully decomposed or exhibited significant decreases in concentration during the full-scale AOAO process, which offered insights to the biodegradation dynamics of CWW organic components. Microbial community analysis showed that bacterial communities were remarkably altered in the four bioreactors of the AOAO process: Proteobacteria dominated during the whole AOAO process, while Nitrospirae and Bacteroidetes enriched in the primary and secondary AO process, respectively. Moreover, metagenomic sequencing found that the relative abundances of amino acid metabolism and carbohydrate metabolism in the primary AO process were both higher than that in the secondary AO process. It indicated that as the AOAO process progressed, the changes in operational characteristics could remarkably affect the variations of functional microorganisms responsible for organics and nitrogen removal and metabolic functions of microbial community. Through this study, a comprehensive assessment of the AOAO biological processes of coking wastewater treatment was achieved, which provided valuable insights to the operation and evaluation of relevant real treatment plants.

Biodegradation of pyrene by a novel strain of Castellaniella sp. under denitrifying condition

Pyrene, a four-ring PAHs, is a typical pollutant in coking wastewater, which is difficult to biodegrade in the conventional biological wastewater treatment processes. Biodegradation of pyrene coupled with denitrification process is an effective approach for treating coking wastewater due to simultaneous removal of toxic organic pollutants and nitrate. In this study, a novel strain capable of degrading pyrene was isolated from the activated sludge of a local coking wastewater treatment plant and identified to be Casterllaniella sp. based on 16S rRNA gene sequence analysis. It can degrade pyrene under denitrifying condition. The degradation efficiency of pyrene reached 97.2% when pyrene concentration was 100 mgL−1. According to the analysis of electron transformation process, about 50% of pyrene was degraded using nitrate as electron acceptor. During pyrene degradation process, almost no intermediate products were detected by GC-MS with the detection limit of 0.1 ngL−1 perhaps due to the complete degradation of pyrene. The SDS-PAGE analysis showed that the proportion of 6 proteins increased during pyrene degradation, and 4 proteins could be considered as enzymes involved in pyrene degradation. The analysis of intermediate products and proteins suggested that pyrene degradation under anoxic condition by Castellaniella sp. Pyr2 was different from other aerobic pathways. Furthermore, this strain has potential for the practical application of simultaneous removal of pyrene and nitrate from coking wastewater.

Coking wastewater treatment plant as a sources of polycyclic aromatic hydrocarbons (PAHs) in sediments and ecological risk assessment

The spatial and temporal distribution of polycyclic aromatic hydrocarbons (PAHs) was investigated in sediments of Maba River, a major tributary of Beijiang River (South China). A total of 13 samples from Maba River and its tributary, Meihua River, were analyzed for 16 PAHs. The total concentration of 16 PAHs (ΣPAH) in high and low water period ranged between 47.61 to 25480.98 ng g−1, with a mean concentration of 4382.98 ng g−1, and 60.30 to 15956.62 ng g−1 with a mean concentration of 3664.32 ng g−1, respectively. Three-ring and four-ring PAHs were the dominant species. It was concluded that a pattern of pyrolytic input as a major source of PAHs in sediments through the molecular ratio method for the source identification, such as HMW/LMW PAHs, Flu/(Flu+Pyr), IcdP/(IcdP+BghiP) and BaA/(BaA+Chr). It is suggested that the pollution emission from the iron and steel plant might be the most important sources of PAHs into Maba River water system. The threat of PAHs contamination to biota of the river was assessed using effect range low (ERL) and effect range median (ERM) values, which suggested that PAHs in Maba River and its tributary had already caused ecological risks.

Distribution Characteristics of Volatile Organic Compounds and Contribution to Ozone Formation in a Coking Wastewater Treatment Plant.

Ozone pollution, which can be caused by photochemical reactions, has become a serious problem. The ozone formation potential (OFP) is used to describe the photochemical reactivity. Volatile organic compounds (VOCs) are main precursors of ozone formation, and wastewater treatment plants (WWTPs) are important sources of VOCs. Therefore, it is necessary to study the concentration level and OFP of VOCs from WWTPs. In this work, a coking WWTP with anaerobic-oxic-oxic (A/O/O) processes in Shaoguan city, Guangdong province, China, was selected to investigate the characteristics of VOCs at wastewater treatment areas and office areas. The OFP of VOCs was estimated by the maximum incremental reactivity (MIR) coefficient method. Results showed that 17 VOCs were detected, and the total concentration of VOCs was the highest at the raw water tank (857.86 μg m−3). The benzene series accounted for 69.0%–86.9% and was the main component of VOCs in the WWTP. Based on OFP data, the top six VOCs contributing most to the OFP were m-xylene, toluene, p-xylene, o-xylene, styrene, and benzene. This study provides field data and information on the environmental risk of VOCs for coking companies and environmental departments. We found that the priority control sources of VOCs were wastewater treatment units because of their larger OFP contributions.

Tertiary treatment of coke plant effluent by indigenous material from an integrated steel plant: a sustainable approach.

Biological process is an important and integral part of the coke plant wastewater treatment. Increasing pressure to meet more stringent discharge limits has led to adopt tertiary treatment for biologically treated coke plant (BTCP) effluent which contains intense colour along with many residual toxic pollutants like phenol, cyanide, thio-cyanate and COD. A sustainable process has been developed to remove these pollutants from BTCP effluent by using an indigenous material coke breeze which is abundantly available in integrated steel plant. Based on the developed process, a full-scale (200 m3/h) treatment plant has been designed for installation. The designed data has been obtained from a continuous demo plant treating 10 m3/h BTCP effluents. The utilised coke breeze is entirely used for sinter making. The process is highly efficient for the removal of colour above 95% and other residual pollutants like phenol, cyanide and COD to a safe level for discharge or reuse. This process neither incurs any additional chemical cost nor generates any secondary pollutants or products. Moreover, the developed process is very sustainable as it has some great advantages like less investment and low maintenance cost; therefore, the method is good in economics. The treated wastewater contains very less amount of chemical residues therefore meets the standards for reuse as industrial water resource. Hence, this developed technology has significant economic, social and environmental benefits. Graphical Abstract .

Ozonation of Coking Wastewater Effluent to Remove Disinfection By-Product Precursors Using an O3 Fluidized Bed Reactor

Various types of dissolved organic matter (DOM) exist in the effluent of coking wastewater treatment plants. These can become precursors for disinfection by-products (DBPs) during chlorination in downstream drinking water treatment plants, representing a significant threat to the water supply. In this study, an O3 fluidized bed reactor (FBR) process is proposed to stabilize and reduce the number of precursors of haloacetonitriles (HANs) and trihalomethanes (THMs) in coking wastewater effluent. It was found that higher O3 concentrations resulted in lower amounts of precursors. Analysis of dissolved organic carbon (DOC) and total organic carbon (TOC), as well as three-dimensional excitation-emission matrix (3D EEM) fluorescence spectroscopy, showed that O3 preferentially decomposed DOM containing unsaturated and aromatic components. Ozonation also changed the species of organic compounds in the effluent. Furthermore, nitrogenous organic compounds such as nitrogen-containing heterocyclic compounds and nitrile were quickly oxidized. Amines were first increased then decreased, while the olefin and phenol, which contain unsaturated functional groups, were also selectively oxidized by ozonation. Organic acids and alkanes were formed during ozonation; however, these intermediate compounds showed relatively low formation potential for HANs and THMs. Therefore, the precursors can be mineralized or converted to organic compounds, which are less likely to form disinfection by-products. These results indicate that the ozonation treatment of coking wastewater effluent can effectively minimize disinfection by-product formation potential (DBPFP), reducing risks to the downstream water supply.

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.

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−, S2−, 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−, S2−, 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+; S2−: 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.

Optimization and validation of headspace solid-phase microextraction method coupled with gas chromatography-triple quadrupole tandem mass spectrometry for simultaneous determination of volatile and semi-volatile organic compounds in coking wastewater treatment plant.

Industrial wastewater could be an important source for the emission of volatile (VOCs) and semi-volatile organic compounds (SVOCs), but little is known about it. In this study, a method for the identification and quantitation of 43 VOCs and SVOCs in coking wastewater was developed using a solvent-free equilibrium extraction method on the basis of headspace solid-phase microextraction accompanied by gas chromatography-triple quadrupole tandem mass spectrometry (HS-SPME-GC-MS/MS). To ensure good extraction efficiency, the parameters that have an effect on the HS-SPME-GC-MS/MS process were carefully optimized, in terms of fiber exposure time and temperature, pH, salt additives, sample volume, and desorption time. The HS-SPME method showed good linearity range with coefficients of determination (R2) ≥ 0.991 and achieving a satisfactory recoveries value (70-120%) with good relative standard deviations (RSDs) < 20% (precision). Furthermore, the purposed approach proved to be sensitive with low detection limits, where the values ranged from 0.03 to 3.01μg/L. The real sample analysis result showed that 43 of VOCs and SVOCs were detected in raw coking wastewater, with 3-cresol as the dominant ones. Further, the method revealed that seven phenols, 11 polycyclic aromatic hydrocarbons, and five BTEX were detected even in the treated effluent. In conclusion, the HS-SPME method developed in this study is simple in sample preparation, convenient, sensitive, and could satisfy the requirement of the analysis of VOCs and SVOCs in coking wastewater.

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.