Solubilization of polycyclic aromatic hydrocarbons (PAHs) with phenol in coking wastewater treatment system: Interaction and engineering significance

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 transform into more toxic and mobile, substituted heterocyclic products during treatment. Thus, predicting the occurrence of PACs and their heterocyclic derivatives (HPACs) in coking wastewater is of utmost importance to reduce the environmental risks in water bodies that receive industrial effluents. Although HPACs can be monitored through sampling and analysis, the characterisation techniques used in their analyses 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 of a coking wastewater treatment plant. Support Vector Machine based regression model (SVR) used for HPAC prediction showed the highest R2 of 0.83. Performance assessment of SVR model showed a mean absolute logarithmic error (MALE) of 0.46 and root mean square error (RMSE) of 0.073 ng/L. Comparatively, K-Nearest Neighbor and Random Forest models showed lower R2 of 0.75 and 0.76 respectively for HPAC prediction. Feature analysis attributed the superior predictability of SVR model likely to its higher weightage (81%) towards dissolved organic carbon and total ammonia as input variables. Both these variables could capture the underlying secondary PAC transformations likely occurring in the treatment plant. Partial dependence plots predicted that ammonia levels higher than 120 mg/L and DOC levels of 50-60 mg/L were likely linked to higher HPACs occurring in the final effluent. This work highlights the capability of kernel-based ML models in capturing nonlinear wastewater chemistry and offers a tool for monitoring trace organic contaminants released in coking effluents.

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.

Three-dimensional distribution characteristics of multiple pollutants in the soil at a steelworks mega-site based on multi-source information

Soil pollution at steelworks mega-sites has become a severe environmental issue worldwide. However, due to the complex production processes and hydrogeology, the soil pollution distribution at steelworks is still unclear. This study scientifically cognized the distribution characteristics of polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), and heavy metals (HMs) at a steelworks mega-site based on multi-source information. Specifically, firstly, 3D distribution and spatial autocorrelation of pollutants were obtained by interpolation model and local indicators of spatial associations (LISA), respectively. Secondly, the characteristics of horizontal distribution, vertical distribution, and spatial autocorrelations of pollutants were identified by combining multi-source information such as production processes, soil layers, and properties of pollutants. Horizontal distribution showed that soil pollution in steelworks mainly occurred in the front end of the steel process chain. Over 47% of PAHs and VOCs pollution area were distributed in coking plants and over 69% of HMs in stockyards. Vertical distribution indicated that HMs, PAHs, and VOCs were enriched in the fill, silt, and clay layers, respectively. Spatial autocorrelation of pollutants was positively correlated with their mobility. This study clarified the soil pollution characteristics at steelworks mega-sites, which can support the investigation and remediation of steelworks mega-sites.

Physicochemical pre- and post-treatment of coking wastewater combined for energy recovery and reduced environmental risk

In this study, physicochemical pre- and post-treatment of highly polluting coking wastewater (CWW) for the removal of refractory compounds and recovery of high-energy substances/components was investigated. An economic optimization model targeting the development of a cost-effective and sustainable treatment technology was proposed. At the post-treatment stage, powdered activated carbon (PAC) was used to separate the refractory and toxic pollutants from the bio-treated CWW, with the adsorption capacity ranging from 50 to 120 mg chemical oxygen demand (COD) g^-1 PAC. Then, the spent PAC, together with a coagulant, was reused in the pre-treatment of highly concentrated raw CWW, which lifted the adsorption capacity to 800-1200 mg COD g^-1 PAC. Results showed that the adsorbent's high selectivity towards macromolecular and complicated pollutants could remove 25-65 % of COD in both CWW flows. Analysis of pollutants' molecular weight distribution and GC-MS indicated a good affinity between PAC and high-energy pollutants (phenolic compounds and alkanes), which could transfer 144,555 kJ m^-3 of energy from CWW to the adsorption-coagulation sludge. The economic optimization model suggested that the cost of the adsorbent was compensated by the net benefits of energy recovery and that profit was achieved when the PAC price was less than 5562 CNY t^-1. The proposed two-stage PAC/coagulant approach offers a way to sustainable water quality and sludge management, plus energy recycling, in CWW treatment. It may also be applied to the treatment of other industrial wastewaters.

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.

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.

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).

Kinetics and molecular mechanism of enhanced fluoranthene biodegradation by co-substrate phenol in co-culture of Stenotrophomonas sp. N5 and Advenella sp. B9

Polycyclic aromatic hydrocarbons (PAHs) and phenol are persistent pollutants that coexist in coking wastewater (CWW). Fluoranthene (Flu) is the predominant PAH species in the CWW treatment system. Our work emphasized on distinguishing the effects of phenol on Flu biodegradation by co-culture of Stenotrophomonas sp. N5 and Advenella sp. B9 and illustrated the molecular mechanisms. Results showed Flu biodegradation by co-culture was enhanced by phenol. According to the first-order degradation kinetic analysis of Flu, phenol significantly increased the biodegradation rate constant and shortened the half-life of Flu. Transcriptome analysis pointed out the up-regulation of DNA repair activity and 3717 significantly differentially expressed genes (DEGs), were triggered by 800 mg/L phenol. GO enrichment analysis suggested these DEGs are mainly concentrated in biochemical processes such as metal ion binding and alpha-amino acid biosynthesis, which are closely associated with Flu biodegradation, indicating that phenol promotes DNA repair activity and reduces Flu genotoxicity. qRT-PCR was performed to detect the gene expression of aromatic ring-opening dioxygenase. Combined with transcriptome analysis, the qRT-PCR results suggested phenol did not induce the expression of related PAHs-degrading enzymes. RNA extraction and microbial growth curves of COC and COC + Ph provided further evidence that phenol serves as co-substrate which increases biomass and the concentration of degrading enzymes, therefore promoting the Flu degradation.

In-situ growth of Co/Ni bimetallic organic frameworks on carbon spheres with catalytic ozonation performance for removal of bio-treated coking wastewater

The Co/Ni-MOFs@CS composite derived from Co/Ni bimetallic organic framework was synthesized and characterized. Compared with a single O₃ system, the synergy between carbon sphere (CS) and metal organic frameworks (MOFs) improved the electron transfer efficiency and the formation rate of •OH. The coexistence of Co and Ni in various valence states might accelerate the cyclic process of Co(II)/Co(III) and Ni(II)/Ni(III), thereby improving the catalytic activity. Taking levofloxacin as a model pollutant, the mechanism of catalytic process was discussed, and the catalytic reaction was successfully applied to the removal of residual organics in bio-treated coking wastewater (BTCW). The removal rates of chemical oxygen demand (COD) and total organic carbon (TOC) in 60 min were 50.85%-53.71% and 39.98%-43.48%. From the perspective of UV absorption and 3D EEM, catalytic ozonation was more conducive to breaking the electronic protection of inert organic molecules such as heterocyclic compounds, and achieving higher efficiency of mineralization. It provides a new idea for catalytic ozonation technology of wastewater treatment in the future from theory, technology and application.

Evolution of biochemical processes in coking wastewater treatment: A combined evaluation of material and energy efficiencies and secondary pollution

The application of advanced biological treatment technology results in improved coking wastewater (CW) effluent quality at lower material and energy input practiced by wastewater treatment plants. In wastewater treatment, the diversity of biological processes combinations affects the variety of microorganisms and biochemical reactions resulting in effluent quality. Four full-scale CW processes, anaerobic-anoxic-oxic (A/A/O), anoxic-oxic-hydrolytic-oxic (A/O/H/O), anoxic-oxic-oxic (A/O/O), and oxic-hydrolytic-oxic (O/H/O) were compared for their consumption of chemicals and energy, emissions of greenhouse gases, and excess sludge production. A new performance indicator combining the above mentioned parameters was proposed to comprehensively evaluate processes in capacity to CW. The O/H/O process showed stable and reliable operation with minimum chemicals cost and the average energy consumption, whereas A/A/O at its good performance in TN removal required a large amount of alkaline chemicals to maintain stability. Besides, a substantial addition of chemicals in A/A/O results in larger average amounts of inorganic sludge. Also, the A/A/O process with a single aerobic unit appeared to be incapable of energy saving when dealing with CW rich in nitrogen and poor in phosphorus. The process with dual aerobic units can achieve more complete carbon and nitrogen removal, which is related to the sequence of biochemical reactions. Diverse sequence combinations can create variation in HRT and DO, whereby contaminants proceed through distinct channels of degradation. In the comparative analysis of CWPIs, it could be seen that O/H/O is the biological treatment process with the least equivalent energy consumption input at present thus exhibiting promising application in CW treatment. The A/O/O and A/O/H/O combinations are good attempts of development; however, more energy-efficient operation modes have to be further investigated.

Sorption of benzo[a]pyrene by Chernozem and carbonaceous sorbents: comparison of kinetics and interaction mechanisms

Benzo[a]pyrene (BaP) is a polycyclic aromatic hydrocarbon, highly persistent and toxic and a widespread environmental pollutant. Although various technologies have been developed to remove BaP from the environment, its sorption through solid matrixes has received increasing attention due to cost-effectiveness. The present research compares the adsorption capacity of Haplic Chernozem, granular activated carbon and biochar in relation to BaP from water solution. Laboratory experiments with different initial BaP concentrations in the liquid phase and different ratios of the solid and liquid phases show that Freundlich model describes well the adsorption isotherms of BaP by the soil and both sorbents. Moreover, the BaP isotherm sorption by the Haplic Chernozem is better illustrated by the Freundlich model than the Langmuir equation. The results reveal that the sorption capacity of the carbonaceous adsorbents at a ratio 1:20 (solid to liquid phases) is orders of magnitude higher (13 368 ng mL^-1 of activated carbon and 3 578 ng mL^-1 of biochar) compared to the soil (57.8 ng mL^-1). At the ratio of 0.5:20, the adsorption capacity of the carbonaceous sorbents was 17-45 times higher than that of the soil. This is due to the higher pore volume and specific surface area of the carbonaceous sorbents than soil particles, assessed through scanning electron microscopy. The sorption kinetic of BaP by Chernozem was compared with the adsorption kinetics by the carbonaceous sorbents. Results indicate that the adsorption dynamic involves two steps. The first one is associated with a fast BaP adsorption on the large available surface and inside macro- and meso-pores of the sorbent particles of the granular activated carbon and biochar. Then, the adsorption is followed by a slower process of BaP penetration into the microporous space and/or redistribution into a hydrophobic fraction. The effectiveness of the sorption process depends on both the sorbent properties and the solvent competition. Overall, the granular activated carbon and biochar are highly effective adsorbents for BaP, whereas the Haplic Chernozem has a rather limited capacity to remove BaP from contaminated solutions.

Advances in treatment of coking wastewater - a state of art review

Coking wastewater poses a serious threat to the environment due to the presence of a wide spectrum of refractory substances such as phenolic compounds, polycyclic aromatic hydrocarbons and heterocyclic nitrogenous compounds. These toxic substances are difficult to treat using conventional treatment methods alone. In recent years much attention has been given to the effective treatment of coking wastewater. Thus, this review seeks to provide a brief overview of recent developments that have taken place in the treatment of coking wastewater. In addition, this article addresses the complexity and the problems associated with treatment followed by a discussion on biological methods with special focus on bioaugmentation. As coking wastewater is refractory in nature, some of the studies have been related to improving the biodegradability of wastewater. The final section focuses on the integrated treatment methods that have emerged as the best solution for tackling the highly unmanageable coking wastewater. Attention has also been given to emerging microwave technology which has tremendous potential for treatment of coking 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.

Synergy between autotrophic denitrification and Anammox driven by FeS in a fluidized bed bioreactor for advanced nitrogen removal

On the basis of the metabolic synergy between autotrophic denitrification (AuDen) and anaerobic ammonium oxidation (Anammox), the feasibility of a novel ferrous sulfide (FeS)-driven AuDen and Anammox coupled system (FS-DADAS) was investigated. The nitrogen removal performance of FS-DADAS was investigated in a lab-scale fluidized bed bioreactor fed with synthetic wastewater containing NH₄⁺-N and NO₃^--N. The results of long-term operation (120 days) demonstrated the promising performance of the system with 100% NO₃^--N removal and NH₄⁺-N concentrations lower than 8.11 mg L^-1 in the effluent at a nitrogen loading rate of 0.20 g-N·(L·d)^-1. Sufficient NO₂^--N was provided by the AuDen for Anammox where a high removal rate of total nitrogen (TN) was achieved. The contribution of Anammox to TN removal was at >80%. The reactor could maintain a stable pH with less SO₄^2- production owing to the fact that Fe(II) and S acted as electron donors. FeS gradually transformed into a sheet-like secondary mineral, FeOOH. AuDen (Thiobacillus) and Anammox bacteria (Candidatus Kuenenia) were successfully retained in the bioreactor, with relative abundance values of 18.82%-23.64% and 3.52%-8.67%, respectively. FS-DADAS is a promising technology for the complete removal of TN from wastewaters with low C/N ratios at low energy consumption.

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.

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.

Enhancement of PAHs biodegradation in biosurfactant/phenol system by increasing the bioavailability of PAHs

The poor bioavailability of polycyclic aromatic hydrocarbons (PAHs) is the main limiting factor for their biodegradation in contaminated sites. The addition of biosurfactant is an effective method for enhancing the bioavailability of PAHs. Suitable low molecular weight (LMW) organic matters have been shown to increase the bioavailability of PAHs. Therefore, we investigated the effect of phenol, which often co-exists with PAHs, on the biodegradation of PAHs in biosurfactant solution. The results show that the critical micelle concentration (CMC) of the biosurfactant decreased after phenol was added. The formation of mixed micelles resulted in enhancement of PAHs dissolution. The weight solubilization ratio (WSR) values of biosurfactant for Phe, Pyr and BaP in phenol solution are approximately 1.34, 1.40 and 1.67 times that of the control group, respectively. Phenol, therefore, can assist biosurfactant to increase the availability of PAHs by microbes. The bioavailability of PAHs in sludge increased from 27.7% to 43.1% after the biosurfactant was added, and reached a maximum of 49.2%, following the simultaneous addition of phenol and biosurfactant. Phenol also improved the degradation of PAHs by Stenotrophomonas sp. N5 in biosurfactant solution.

Effects of Nrf2-Keap1 signaling pathway on antioxidant defense system and oxidative damage in the clams Ruditapes philippinarum exposure to PAHs

NF-E2-related factor 2 (Nrf2) is a master regulator of antioxidant defense system which can maintain the oxidation balance in the cell. In our previous study, we first cloned the Nrf2 gene in clams and preliminarily explored the role of the Nrf2 at the transcription level. In this study, RNA interference (RNAi) technology was used to interfere with the expression of Nrf2 after being exposed to benzo(a)pyrene (BaP) for 5 days to verify the role of Nrf2 in the antioxidant defense system. Besides, we examined the mRNA expression and enzyme activities of antioxidases and the oxidative damage. The positive correlations between the Nrf2 with the mRNA expression and the enzyme activities of antioxidases indicated that Nrf2 was required for the induction of these antioxidant genes. Additionally, the mRNA expression and the enzyme activities of the glutathione peroxidase (GPx) in the Nrf2-dsRNA group were significantly higher than those in the control groups on the fifth day, indicating that the GPx is more sensitive to oxidative stress. Moreover, the oxidative damage in the RpNrf2-dsRNA group was markedly increased than control groups, indicating that Nrf2 transcriptional regulation may play an essential role in defending against oxidative damage. This study provides a foundation for further research on the mechanism of detoxification and antioxidation of polycyclic aromatic hydrocarbons (PAHs) in the clams at the transcription level and the protein level.

Biodegradation of phenol by a highly tolerant strain Rhodococcus ruber C1: Biochemical characterization and comparative genome analysis

A novel phenol-degrading strain was isolated and identified as Rhodococcus ruber C1. The degradation analysis shows that 1806 mg/L of phenol can be completely degraded by strain C1 within 38 h, and the maximum specific growth rate (μ_max=1.527 h^-1) and maximum specific phenol degradation rate (q_max=3.674 h^-1) indicate its excellent phenol metabolism capability. More importantly, phenol can be degraded by strain C1 in the temperature range of 20-45 °C within 72 h, and with longer degradation time, phenol can be completely degraded even at 10, 15 and 50 °C. The whole genome of strain C1 was sequenced, and a comparative genome analysis of strain C1 with 36 other genomes of Rhodococcus was performed. A remarkable gene family expansion occurred during the evolution of Rhodococcus, and a comprehensive evolutionary picture of Rhodococcus at genomic level was presented. Moreover, the copy number of genes involved in phenol metabolism was compared among genus Rhodococcus, and the results demonstrate high phenol degradation capability of strain C1 at genomic level. These findings suggest that Rhodococcus ruber C1 is a bacterium capable of degrading phenol efficiently in the temperature range of 10-50 °C.

Review on polycyclic aromatic hydrocarbons (PAHs) migration from wastewater

Rapidly increasing global population and increased civilization has increased burden on potable water resources and results in larger volumes of wastewater. Physical wastewater management techniques has advanced for domestic usage and commercial effluent new conceptions about imminent wastewater treatment have been acclaimed for highly carcinogenic polycyclic aromatic hydrocarbon (PAH) compounds. The present review study emphasis on the assessment of several accessible PAHs treatment methods used in wastewater management. The elementary principles, contextual remediation mechanisms and recent development in PAHs removal practices have also been precisely explained. The comprehensive information regarding sources, dispersal, classification, physicochemical properties, PAHs toxicity for humans and aquatics life, conventional treatment procedures, and advanced oxidation processes specified can assist us to identify the PAHs problem and their intensity. The performance evaluation of different removal techniques are discussed in details and found that highest PAHs' reduction for 5-or 6-ring (99%,) while 3-ring (79% reduction) with oxidant dose of 1.64 mL/L using titanium catalyst. In case of MWTPs, with secondary techniques, the average removal efficiency found in the range of 81.1-92.9% while for AOPs are 32-99.3%. Here, overall yield through AOPs most suitable if process used with some catalyst enhanced the yield as well and suitable for high ring as well as low ring PAHs. Among various processes, advanced oxidation and catalytic oxidation processes are the most valuable and promising techniques for PAHs removal. Based on the given evidences, the AOPs coupled with catalysts have been decided as the most competent design for wastewater PAHs treatment.

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.

Enhancement of phenol biodegradation: Metabolic division of labor in co-culture of Stenotrophomonas sp. N5 and Advenella sp. B9

The aim of this work is to study the synergistic effect of Stenotrophomonas sp. N5 and Advenella sp. B9 co-culture (COC) on enhancement of phenol biodegradation. These two strains utilizing phenol as sole carbon and energy source were isolated from phenol-containing coking wastewater. The results of biodegradation experiment showed the COC of N5 and B9 has stronger capability to degrade phenol than either of mono-culture (MOC). Growth kinetics studies indicated inhibitory effect of phenol on COC was reduced by the interaction of N5 and B9 in COC. The RNA-Seq results demonstrated that phenol biodegradation was enhanced by metabolic division of labor (DOL) in COC based on the expression of key genes for phenol degradation. GO enrichment analysis of differentially expressed genes (DEGs) indicated DEGs between COC and MOC degradation systems are mainly concentrated in the synthesis of cell components, microbial growth and metabolism, and catalytic activity. The expression of 3 transcriptional factors (LysR, Two-component system response regulator, and TetR families) which can regulate degradation of aromatic compounds, was identified beneficial to phenol degradation.

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.

An Overview and Evaluation of Highly Porous Adsorbent Materials for Polycyclic Aromatic Hydrocarbons and Phenols Removal from Wastewater

Polycyclic aromatic hydrocarbons (PAHs) and phenolic compounds had been widely recognized as priority organic pollutants in wastewater with toxic effects on both plants and animals. Thus, the remediation of these pollutants has been an active area of research in the field of environmental science and engineering. This review highlighted the advantage of adsorption technology in the removal of PAHs and phenols in wastewater. The literature presented on the applications of various porous carbon materials such as biochar, activated carbon (AC), carbon nanotubes (CNTs), and graphene as potential adsorbents for these pollutants has been critically reviewed and analyzed. Under similar conditions, the use of porous polymers such as Chitosan and molecularly imprinted polymers (MIPs) have been well presented. The high adsorption capacities of advanced porous materials such as mesoporous silica and metal-organic frameworks have been considered and evaluated. The preference of these materials, higher adsorption efficiencies, mechanism of adsorptions, and possible challenges have been discussed. Recommendations have been proposed for commercialization, pilot, and industrial-scale applications of the studied adsorbents towards persistent organic pollutants (POPs) removal from wastewater.

Alternated biodegradation of naphthalene (NAP), acenaphthylene (ACY) and acenaphthene (ACE) in an aerobic granular sludge reactor (GSBR)

The paper presents quantitative changes of selected 2- and 3-ring PAHs after process phases of GSBR reactor. The studies have been carried out for 264 cycles of GSBR reactor, during which concentration of naphthalene was increased in the range of 3.00-710.00 μg/L, acenaphthylene 1.00-160.00 μg/L, acenaphthene 3.00-440.00 μg/L. GSBR operating cycle consisted of filling (30 min), mixing (90 min), aeration (540 min), sedimentation (10 min), decanting (30 min) and downtime (20 min) phases. Activated sludge dry mass concentration was 4.00 kg/m³. Conducted studies showed that in GSBR reactor naphthalene was degraded with the highest intensity. Results of the statistical analysis confirmed that naphthalene concentrations were statistically significantly different (α = 0.05) after each individual GSBR process phase, while in case of acenaphthene and acenaphthylene, the differences were observed only between mixing and aeration phases. Additionally, equations estimating concentrations of PAHs in treated wastewater were developed. Selected activated sludge technological parameters (sludge volume index, sludge and hydraulic retention time) and concentration of PAHs were used for equations. The R² coefficients of equations were above 0.99, which indicates a good adjustment of estimation to observed values.

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.

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.

Characterization of polycyclic aromatic hydrocarbons in urban-rural integration area soil, North China: Spatial distribution, sources and potential human health risk assessment

The promotion of urbanization has accelerated the development of small manufacturing workshops and brought serious environmental problems. In this study, spatial distribution, sources and potential health risk for polycyclic aromatic hydrocarbons (PAHs) in urban-rural integration area soil in North China (800 km²) were discussed. The average total concentration of 16 PAHs was 225 μg kg^-1, and range from 25 to 15155 μg kg^-1 (n = 250). According to the European soil quality standards, more than 70% of the samples don't reach the pollution level, while around the small workshop concentration area and non-ferrous metal smelter were more contaminated than other area. The spatial distribution of soil PAHs concentration shows that low molecular weight, medium molecular weight and high molecular weight is very similar to the distribution of total PAHs, indicating that is likely to be caused by point source pollution. The sources of PAHs were identified by positive matrix factorization. The main six sources in the region are coal and biomass combustion, creosote, coke tar, vehicle and oil, which is consistent with the local energy consumption structure. Finally, a deterministic assessment of the cancer risk showed that the range for children was 5.94 × 10^-8 to 2.53 × 10^-5, and adults it ranged from 2.11 × 10^-8 to 9.01 × 10^-6. There is not a carcinogenic risk value greater than 10^-4 in the entire region, but potential carcinogenic risks persisted in some areas. We conclude that PAHs pollution of soil in the area is an issue that deserves urgent attention for the relevant departments.

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.

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.

A biosurfactant-producing Pseudomonas aeruginosa S5 isolated from coking wastewater and its application for bioremediation of polycyclic aromatic hydrocarbons

Although polycyclic aromatic hydrocarbons (PAHs) are considered as toxic and refractory pollutants, their biodegradation can be facilitated by biosurfactants. However, few studies have been performed to understand the potential isolation and application of biosurfactant-producing microorganism for promoting the in-situ removal of PAHs from wastewaters. In this work, a biosurfactant-producing strain S5 isolated from coking wastewater was identified as Pseudomonas aeruginosa. The biosurfactant produced by strain S5 was determined as glycolipid with a critical micelle concentration (CMC) of 96.5 mg/L, and reduced the surface tension from 72.2 to 29.6 mN/m. Addition indigenous P. aeruginosa S5 to coking wastewater effectively promoted the biodegradation of high weight molecular (HWM) PAHs (reduction from 9141.02 to 5117.16 µg/L in 15 days) in sludge phase. The results showed that the removal of PAHs in the sludge was enhanced by inoculating indigenous biosurfactant-producing microorganism in coking wastewater serving as an in-site remediation technology.

Combination of Coagulation and Ozone Catalytic Oxidation for Pretreating Coking Wastewater

In this study, coagulation, ozone (O₃) catalytic oxidation, and their combined process were used to pretreat actual coking wastewater. The effects on the removal of chemical oxygen demand (COD) and phenol in coking wastewater were investigated. Results showed that the optimum reaction conditions were an O₃ mass flow rate of 4.1 mg min⁻¹, a reaction temperature of 35 °C, a catalyst dosage ratio of 5:1, and a O₃ dosage of 500 mg·L⁻¹. The phenol removal ratio was 36.8% for the coagulation and sedimentation of coking wastewater under optimal conditions of 25 °C of reaction temperature, 7.5 reaction pH, 150 reaction gradient (G) value, and 500 mg·L⁻¹ coagulant dosage. The removal ratios of COD and phenol reached 24.06% and 2.18%, respectively. After the O₃-catalyzed oxidation treatment, the phenols, polycyclic aromatic hydrocarbons, and heterocyclic compounds were degraded to varying degrees. Coagulation and O₃ catalytic oxidation contributed to the removal of phenol and COD. The optimum reaction conditions for the combined process were as follows: O₃ dosage of 500 mg·L⁻¹, O₃ mass flow of 4.1 mg·min⁻¹, catalyst dosage ratio of 5:1, and reaction temperature of 35 °C. The removal ratios of phenol and COD reached 47.3% and 30.7%, respectively.

Tracking multiple aromatic compounds in a full-scale coking wastewater reclamation plant: Interaction with biological and advanced treatments

Aromatic compounds are widely contained in coking wastewater (CWW), drawing great attention due to their potential risks to environment and human health. Integrated systems combining biological processes with advanced treatments are the current trend of CWW reclamation. However, the variations of aromatic composition throughout these processes are poorly understood. This study investigated the occurrence, fate and removal of aromatic compounds in a full scale CWW reclamation plant with eight treatment stages by gas chromatography-mass spectrometry and optical spectrum. The results showed that polycyclic aromatic hydrocarbons (PAHs), phenols and heterocyclic compounds accounted for 38.9%, 33.5% and 22.6% of the total organics in CWW, respectively. Among them, PAHs were more sensitive to anaerobic digestion, while phenols and heterocyclics had higher bioavailability in aerobic process. Although more than 90% DOC could be removed in biological processes, the bio-effluent was still brown in color, implying the residues of aromatics to the advanced treatments. The interaction between the bio-refractory organics and the advanced treatments suggested that multiple aromatic compounds were selectively removed along the treatment train. Specifically, coagulation, sand filtration, ultrafiltration, adsorption, nanofiltration and reverse osmosis were found to be highly related to the elimination of residual isoquinoline, phenol, cresol, fluoranthene, benzene and humic-like organics, correspondingly. Findings in this study indicated that adsorption was a key step for removing chromophoric PAHs with more aromatic rings, while fouling control in the end-point membrane systems should be focused on the elimination of BTEXs and humic-like substances.

Modelling PAH partitioning during sludge disintegration: The key role of dissolved and colloidal matter

The partitioning between solids and the aqueous phase largely controls the fate of PAH compounds in biological treatment. The prediction of PAH sorption behaviour into activated sludge was investigated here. The suitability of a three-compartment model to describe partitioning in such a complex matrix was first evaluated by adding increasing quantities of dissolved and colloidal matter (DCM) (from 0 to 34.9% of the total matter). In a range of DCM concentrations varying from 0 to 1.4 g L^-1, the PAH aqueous fraction, including both freely dissolved and sorbed to DCM molecules, increased from 9.9% to 33% for naphthalene (the most soluble PAH) and from 0.29% to 13.3% for indeno(1,2,3,c,d)pyrene (the least soluble PAH tested). The sorption of PAHs on dissolved and colloidal matter (DCM) was assessed by determining two partitioning constants (K_PART and K_DCM) for the 16 PAHs listed by the US EPA. New experiments were carried out for model validation and show that the model properly predicts the PAH partitioning following sludge disintegration by sonication.