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

Multi-stage oxic biofilm system for pilot-scale treatment of coking wastewater: Pollutants removal performance, biofilm properties and microbial community

A multi-stage oxic biofilm system based on hydrophilic polyurethane foam was established and operated for advanced treatment of coking wastewater, in which distinct gradient variations of pollutants removal, biofilm properties and microbial community in the 5 stages were evaluated. The system rapidly achieved NH4+-N removal efficiency of 97.51 ± 2.29 % within 8 days. The biofilm growing attached on the carriers exhibited high biomass (≥10.29 g/L), which ensured sufficient microbial population. Additionally, the rising extracellular polymeric substance and declining proteins/polysaccharides ratios across stages suggested a dense-to-loose transition in the biofilm's structure, in response to the varying pollutant concentrations. The dominance of Nitrosomonas cluster in the first 3 stages and Nitrospira lineage in the following 2 stages facilitated the complete depletion of high NH4+-N concentration without NO2--N accumulation. Overall, the distinct biofilm property and community at each stage, shaped by the multi-stage configuration, maximized the pollutants removal efficiency.

Seasonal dynamics of bacterial composition and functions in biological treatment of coking wastewater

Seasonal dynamics of bacterial composition and functions were demonstrated for the biological fluidized-bed bioreactors combined in the anoxic/aerobic1/aerobic2 (AOO) coking wastewater (CWW) treatment sequences. The bacterial composition and functions in the CWW activated sludge samples were revealed by 16S rRNA genes amplicon sequencing. Thiobacillus, Cloacibacterium, Alkaliphilus and Pseudomonas were determined as core genera with seasonal changes. Mutable microbial community composition fluctuated in different seasons in same bioreactor. Distributions of predicted KEGG pathways along four seasons consistently demonstrated enrichment in biodegradation of carbon- and nitrogen-containing compounds. The major contaminants were removed from CWW by biochemical pathway of xenobiotics biodegradation and metabolism. This Level 2 pathway mainly owned the Level 3 pathways of benzoate degradation, drug metabolism-other enzymes, drug metabolism-cytochrome P450, metabolism of xenobiotics by cytochrome P450, and aminobenzoate degradation. The RDA results showed that dissolved oxygen with seasonal fluctuation was the main parameter shaping the microbial community. The observed dynamics within the microbial community composition, coupled with the maintained stability of CWW treatment efficiencies and a consistent profile of microbial functional pathways, underscore the presence of functional redundancy in the AOO bioreactors. The study underscored stable and effective operational performances of bioreactors in the AOO sequences, contributing the knowledge of microbiological basics to the advancement of CWW biological treatment. KEY POINTS: • Seasonal fluctuations of bacterial composition described for the AOO system. • Seasonal distributions of metabolic functions focused on carbon and nitrogen removal. • Functional redundancy was revealed in the AOO microbial community.

Theoretical insight into the removal process of isoquinoline by UV/Cl and UV/PDS: Oxidation mechanism and toxicity assessment

Isoquinoline (IQL), as a typical nitrogen-containing heterocyclic contaminant in coking wastewater, poses a serious threat to the aquatic environment and human health. Due to its chemical stability, traditional sewage treatment technology is not highly efficient in IQL removal. Advanced oxidation processes (AOPs) driven by ultraviolet radiation could be an effective treatment method, but it could generate toxic byproducts. In this work, the removal of IQL initiated by HO•, ClO•, Cl•, and SO4•- in UV/chlorine and UV/persulfate (PDS) process was comprehensively investigated, clarifying the degradation mechanism, reaction kinetics, and ecological toxicity. The findings indicate that the dominant oxidation mechanism of IQL by HO•, ClO•, and Cl• is radical adduct formation (RAF), while single electron transfer (SET) is the main reaction pathway of SO4•- with IQL. At 298 K and 1 atm, the order of rate constants for the reactions of IQL with active radicals is Cl• (6.23 × 1010 M-1 s-1) > SO4•- (8.81 × 109 M-1 s-1) > HO• (1.66 × 109 M-1 s-1) > ClO• (1.62 × 108 M-1 s-1). The acute and chronic toxicity of IQL and its degradation byproducts at three different trophic levels were evaluated using ECOSAR program. The byproducts produced by the oxidative degradation of IQL by HO• and SO4•- are mostly "not harmful", and their toxicity shows a decreasing trend compared to that of IQL. The byproducts derived from the reaction of IQL with Cl• are all "toxic" or "harmful", and the ranking of harm to three types of aquatic organisms is green algae > fish > daphnia. Hence, UV/PDS process could be more secure in pollutant disposal in wastewater. In actual water treatment process, merit attention should be paid to the potential hazards of the byproducts generated by various contaminants.

Ultrahigh-purity ammonia recovery from synthetic coke wastewater via membrane contactor: Overcoming phenolic interference and assessing cost efficiency

Ammonia recovery from industrial wastewater using membrane contactor processes is emerging as a promising method owing to the diverse applications of ammonia. This study uniquely addressed ammonia recovery from coke plant wastewater, which is challenging due to the presence of numerous toxic and volatile phenolic compounds. Experiments were conducted using a synthetic coke plant effluent to assess the effects of various pH levels and temperatures on ammonia recovery. Specifically, the aim was to achieve high-purity ammonia recovery while minimizing the permeation of phenolic compounds. The results demonstrate that ammonia recovery in the membrane contactor processes is highly efficient, even in the presence of phenolic compounds. During temperature variations at 25 °C and 40 °C, the recovery of ammonia increased from 42.36% to 52.97% at pH 11. Additionally, increasing the pH of a feed solution from 7 to 12 significantly increased the ammonia content to 58.3%. At this pH, the recovered ammonia was of exceptional purity (>99%), with phenol, p-Cresol, and 2,4-xylenol present at negligible concentrations (0.001%, 0.002%, and 0.004%, respectively). This was attributed to the ionization of phenolic compounds at higher pH levels, which prevents their permeation through the hydrophobic membrane. The estimated cost analysis revealed that the membrane contactor process at pH 12 was approximately 1.41 times more cost-effective than conventional air-stripping processes over eight years of operating period (pH-12 membrane contactor: $19.79; pH-12 air stripping: $23.75). This study provides a detailed analysis of the optimal conditions for selective ammonia recovery from complex wastewater, highlighting both effective treatment and sustainable resource recovery and offering a superior alternative to traditional methods.

E-peroxone with a novel GDE decorated with hydrophobic membrane for the degradation of pyridine: Stability, byproducts and toxicity

E-peroxone process is an emerging electrochemical oxidation process, based on ozone and the in-situ cathodic generation of H2O2, but the stability of cathode is one of the key restraining factors. In this study, we designed a multilayer gas diffusion electrode (GDE) decorated with a commercial hydrophobic membrane for the degradation of pyridine. It was found that a proper control of membrane pore sizes and hot-pressing temperature can significantly promote the GDE stability. Subsequently, key operational parameters of the constructed E-peroxone system were investigated, including the ozone concentration, current density, pH value, electrolyte type and initial concentration of pyridine. The degradation pathways were proposed according to six identified transformation products. The toxicity variation along the degradation progress was evaluated with microbial respiration tests and Toxicity Estimation Software Tool (T.E.S.T.) calculation and an efficient detoxification capacity of E-peroxone was observed. This research provides a theoretical basis and technical support for the development of highly efficient and stable E-peroxone system for the elimination of toxic organic contaminants.

Nitrogen metabolism network in the biotreatment combination of coking wastewater: Take the OHO process as a case

As steel production increases, large volumes of highly toxic and nitrogen-rich coking wastewater (CWW) are produced, prompting the development of a novel oxic-hydrolytic-oxic (OHO) biological treatment combination designed for highly efficient removal of nitrogen-contained contaminants. However, previous studies have not comprehensively explored the CWW biotreatment from the perspective of nitrogen metabolism functional genes and pathways. Based on the investigation of taking the full-scale OHO biotreatment combination as a case, it was found that the O1 and O2 bioreactors remove nitrogen through the ammonia assimilation accounting for 33.87% of the total nitrogen (TN) removal rate, while the H bioreactor removes nitrogen through the simultaneous nitrification-denitrification accounting for 61.11% of the TN removal rate. The major ammonia assimilation taxa include Thauera, Immundisolibacter and Thiobacillus; the major nitrifying taxa include Nitrospira and Nitrosomonas; and the major denitrifying taxa include Thiobacillus, Lautropia and Mesorhizobium. Additionally, the H bioreactor exhibits the potential to be optimized for simultaneous nitrification-denitrification coupled with anaerobic ammonium oxidation (Anammox). These understandings will guide the optimization of engineering design and operational practices, contributing to more effective and sustainable wastewater treatment strategies.

Long-term evaluating the strengthening effects of iron-carbon mediator for coking wastewater treatment in EGSB reactor

Coking wastewater (CWW) treatment is difficult due to its complex composition and high biological toxicity. Iron-carbon mediators was used to enhance the treatment of CWW through iron-carbon microelectrolysis (ICME). The results indicated that the removal rate of COD and phenolic compounds were enhanced by 24.1 % and 23.5 %, while biogas production and methane content were promoted by 50 % and 7 %. Microbial community analysis indicated that iron-carbon mediators had a transformative impact on the reactor's performance and dependability by enriching microorganisms involved in direct and indirect electron transfer, such as Anaerolineae and Methanothrix. The mediator also produced noteworthy gains in LB-EPS and TB-EPS, increasing by roughly 109.3 % and 211.6 %, respectively. PICRISt analysis demonstrated that iron-carbon mediators effectively augment the abundance of functional genes associated with metabolism, Citrate cycle, and EET pathway. This study provides a new approach for CWW treatment.

Further treatment of coking wastewater treated in A2O-MBR by the nanofiltration-powder activated carbon hybrid system

In this study, further treatment of coking wastewater treated in anoxic-oxic-membrane bioreactor (A2O-MBR) was investigated to meet the standards of the ministry by means of nanofiltration (NF) (with two different membranes and different pressures), microfiltration -powder activated carbon (MF-PAC) hybrid system and NF-PAC (with two different membranes and five different PAC concentrations) hybrid system. In addition to the parameters determined by the ministry, other parameters such as ammonium, thiocyanate (SCN-), hydrogen cyanide (HCN), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), color were also examined to evaluate the flux performance and treatment efficiency of the hybrid processes. According to the results, chemical oxygen demand (COD) in the NF process, COD and total cyanide (T-CN) in the MF-PAC process could not meet the discharge standards. As for the NF-PAC hybrid system, XN45 membrane met the discharge standards in all parameters (COD = 96±1.88 mg/L, T-CN =<0,02 mg/L, phenol =<0.05 mg/L), with a recovery rate of 78% at 0.5 g/L PAC concentration.

Constructed wetland as a green remediation technology for the treatment of wastewater from underground coal gasification process

The wastewater from underground coal gasification (UCG) process has extremely complex composition and high concentrations of toxic and refractory compounds including phenolics, aliphatic and aromatic hydrocarbons, ammonia, cyanides, hazardous metals and metalloids. So, the development of biological processes for treating UCG wastewater poses a serious challenge in the sustainable coal industry. The aim of the study was to develop an innovative and efficient wetland construction technology suitable for a treatment of UCG wastewater using available and low-cost media. During the bioremediation process the toxicity of the raw wastewater decreased significantly between 74%-99%. The toxicity units (TU) ranged from values corresponding to very high acute toxic for raw wastewater to non-toxic for effluents from wetland columns after 60 days of the experiment. The toxicity results correlated with the decrease of some organic and inorganic compounds such as phenols, aromatic hydrocarbons, cyanides, metals and ammonia observed during the bioremediation process. The removal percentage of organic compounds like BTEX, PAHs and phenol was around 99% just after 14 days of treatment. A similar removal rate was indicated for cyanide and metals (Zn, Cr, Cd and Pb). Concluded, in order to effectively assess remediation technologies, it is desirable to consider combination of physicochemical parameters with ecotoxicity measurements. The present findings show that wetland remediation technology can be used to clean-up the heavily contaminated waters from the UCG process. Wetland technology as a nature-based solution has the potential to turn coal gasification wastewater into usable recycled water. It is economically and environmentally alternative treatment method.

Comparative study of different ultrasound based hybrid oxidation approaches for treatment of real effluent from coke oven plant

The present study investigates the treatment of real coke plant effluent utilising several ultrasound-based hybrid oxidation approaches including Ultrasound (US) alone, US + catalyst, US + H2O2, US + Fenton, US + Ozone, and US + Peroxone, with main objective as maximizing the reduction of chemical oxygen demand (COD). Ultrasonic horn at power of 130 W, frequency as 20 kHz and duty cycle as 70% was applied. Study with varying catalyst (TiO2) dose from 0.5 g/L - 2 g/L revealed 1 g/L as the optimum dose resulting in 65.15% reduction in COD. A 40 ml/L dose of H2O2 was shown to be optimal, giving an 81.96% reduction in COD, based on the study of varied doses of H2O2 from 20 ml/L to 60 ml/L. US + Fenton reagent combination at optimum Fe2+/H2O2 (w/v) ratio of 1:1 resulted in a COD reduction of 85.29% whereas reduction of COD as 81.75% was obtained at the optimum flow rate of ozone as 1 LPM for US + Ozone approach. US + Peroxone demonstrated the best efficiency (90.48%) for COD reduction. To find the toxicity effects, the treated (US + peroxone) and non-treated samples were tested for the growth of bacterial cultures. It was observed that the toxicity of the treated sample increased only marginally after treatment. High-resolution liquid chromatography mass spectrometry (HR-LCMS) analysis was also performed to establish intermediate compounds. Overall, the coupling of ultrasound with oxidation processes produced better results with US + Peroxone established as best treatment approach for coke plant effluent.

Advanced treatment of coking wastewater: Recent advances and prospects

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

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

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

Insights into current bio-processes and future perspectives of carbon-neutral treatment of industrial organic wastewater: A critical review

With the rise of the concept of carbon neutrality, the current wastewater treatment process of industrial organic wastewater is moving towards the goal of energy conservation and carbon emission reduction. The advantages of anaerobic digestion (AD) processes in industrial organic wastewater treatment for bio-energy recovery, which is in line with the concept of carbon neutrality. This study summarized the significance and advantages of the state-of-the-art AD processes were reviewed in detail. The application of expanded granular sludge bed (EGSB) reactors and anaerobic membrane bioreactor (AnMBR) were particularly introduced for the effective treatment of industrial organic wastewater treatment due to its remarkable prospect of engineering application for the high-strength wastewater. This study also looks forward to the optimization of the AD processes through the enhancement strategies of micro-aeration pretreatment, acidic-alkaline pretreatment, co-digestion, and biochar addition to improve the stability of the AD system and energy recovery from of industrial organic wastewater. The integration of anaerobic ammonia oxidation (Anammox) with the AD processes for the post-treatment of nitrogenous pollutants for the industrial organic wastewater is also introduced as a feasible carbon-neutral process. The combination of AnMBR and Anammox is highly recommended as a promising carbon-neutral process for the removal of both organic and inorganic pollutants from the industrial organic wastewater for future perspective. It is also suggested that the AD processes combined with biological hydrogen production, microalgae culture, bioelectrochemical technology and other bio-processes are suitable for the low-carbon treatment of industrial organic wastewater with the concept of carbon neutrality in future.

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.