Bio-treated Coking Wastewater Research Articles

Catalytic ozonation of reverse osmosis concentrate from coking wastewater reuse by surface oxidation over Mn-Ce/γ-Al2O3: Effluent organic matter transformation and its catalytic mechanism

Degradation of organics in high-salinity wastewater is beneficial to meeting the requirement of zero liquid discharge for coking wastewater treatment. Creating efficient and stable performance catalysts for high-salinity wastewater treatment is vital in catalytic ozonation process. Compared with ozonation alone, Mn and Ce co-doped γ-Al2O3 could remarkably enhance activities of catalytic ozonation for chemical oxygen demand (COD) removal (38.9%) of brine derived from a two-stage reverse osmosis treatment. Experimental and theoretical calculation results indicate that introducing Mn could increase the active points of catalyst surface, and introducing Ce could optimize d-band electronic structures and promote the electron transport capacity, enhancing HO• bound to the catalyst surface ([HO•]ads) generation. [HO•]ads plays key roles for degrading the intermediates and transfer them into low molecular weight organics, and further decrease COD, molecular weights and number of organics in reverse osmosis concentrate. Under the same reaction conditions, the presence of Mn/γ-Al2O3 catalyst can reduce ΔO3/ΔCOD by at least 37.6% compared to ozonation alone. Furthermore, Mn-Ce/γ-Al2O3 catalytic ozonation can reduce the ΔO3/ΔCOD from 2.6 of Mn/γ-Al2O3 catalytic ozonation to 0.9 in the case of achieving similar COD removal. Catalytic ozonation has the potential to treat reverse osmosis concentrate derived from bio-treated coking wastewater reclamation.

Application of SO42–/Fe2O3-CuO solid superacid materials in cyclic compounds from wastewater: Performance and mechanism

In wastewater treatment, the degradation of refractory cyclic compounds by catalytic ozonation using sulfated solid superacid has not been thoroughly investigated. The doped S element alters the electronic activity and drives the ozone oxidation of recalcitrant organic pollutants, potentially leading to an increase in catalytic efficiency. This study aimed to develop a novel iron-copper sulfate (SO42–/Fe2O3-CuO) solid superacid composite to strengthen catalytic reactions. According to the characterization results, the embedding of SO42– enhanced the electron transfer inside the material, leading to more Lewis acid sites, which facilitated the catalytic decomposition of O3. The catalytic degradation and reaction kinetics experiments on quinoline verified the superior catalytic performance of the SO42–/Fe2O3-CuO system compared to other systems. Fluorescence, UV–Vis spectrophotometry, and EPR experiments demonstrated that the hydroxyl radicals (OH), superoxide radicals (O2−), and singlet oxygen (1O2) were generated in the SO42–/Fe2O3-CuO system, and their presence accelerated the redox cycling of Fe(III)/Fe(II) and Cu(II)/Cu(I). In addition, the possible degradation pathways of quinoline were verified by density functional theory (DFT) calculations, and the toxicity of intermediates was assessed by quantitative structure–activity relationship (QSAR) analysis. Finally, the applicability of the SO42–/Fe2O3-CuO catalytic system in bio-treated coking wastewater (BTCW) was validated. GC–MS experiments further confirmed that it was mainly the cyclic compounds that contributed to the removal rate during the catalytic process. In summary, this study demonstrated the significant potential of the SO42–/Fe2O3-CuO catalytic system in degrading refractory cyclic compounds, providing valuable technical support for the field of wastewater treatment.

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.

Selective and efficient removal of emerging contaminants by sponge-like manganese ferrite synthesized using a solvent-free method: Crucial role of the three-dimensional porous structure

Ubiquitous macromolecular natural organic matter (NOM) in wastewater seriously influences the removal of emerging small-molecule contaminants via heterogeneous advanced oxidation processes because this material covers active sites and quenches reactive oxygen species. Here, sponge-like magnetic manganese ferrite (MnFe2O4-S) with a three-dimensional hierarchical porous structure was prepared via a facile solvent-free molten method. Compared with the particle-like structure of MnFe2O4-P, the sponge-like structure of MnFe2O4-S presents an enlarged specific surface area (112.14 m2·g−1 vs. 58.73 m2·g−1) and a smaller macropore diameter (68.2–77.2 nm vs. 946.5 nm). Enlarging the specific surface area increases the exposure of active sites, and adjusting the pore size helps sieve NOM and emerging contaminants. These changes are expected to effectively improve the degradation activity and overcome interference. To confirm the superiority of the sponge-like structure, MnFe2O4-S was used to activate peroxymonosulfate (PMS) for the degradation of multiple emerging contaminants, and its ability to degrade bisphenol A with and without humic acid (HA) was compared with that of MnFe2O4-P. The degradation activity of MnFe2O4-S was 1.6 times greater than that of MnFe2O4-P. Moreover, 20 mg·L−1 HA inhibited the degradation activity of MnFe2O4-S by only 7.1%, which was much lower than that obtained for MnFe2O4-P (53.4%). In addition, the excellent performance was maintained in multiple water matrices. Notably, under lake water matrices, the degradation activity of MnFe2O4-P was inhibited by 35.6% while that of MnFe2O4-S was hardly inhibited. More importantly, the MnFe2O4-S/PMS system was also applicable to the treatment of actual wastewater and 73.0% and 90.1% of total organic carbon and chemical oxygen demand was removed from bio-treated coking wastewater containing non-biodegradable contaminants and NOM. This study provides an alternative route for the green production of high-activity porous spinel ferrites with environmental anti-interference properties.

Identifying the critical activated carbon properties affecting the adsorption of effluent organic matter from bio-treated coking wastewater

Activated carbon is widely used to remove effluent organic matter (EfOM) from bio-treated coking wastewater. However, the critical carbon properties affecting adsorption performance are still unclear. Nine commercial powdered activated carbons (PACs) with different pore structures, surface functional groups, and surface charges were used to adsorb EfOM from bio-treated coking wastewater, which was fractionated according to their molecular weight (MW) and hydrophobicity. Good correlations were observed between the adsorption of biopolymers (MW > 20,000 Da, 7 %) and macropore volume (>50 nm), as well as between the adsorption of humics (MW = 1000 ~ Da, 36 %) and mesopore volume (2–50 nm), suggesting that the adsorption sites of EfOM depended on their molecular size. Higher isoelectric points and fewer acidic groups promoted the adsorption of the most negatively charged hydrophobic acids (HPOA, 39.5 %). According to variation partitioning analysis (VPA), mesopore-macropore greatly contributed to the adsorption capacities of EfOM (71.3 %), whereas the sum of phenolic hydroxyl and carboxyl (26.3 %) and isoelectric point (12.2 %) affected the normalized adsorption capacities of EfOM. In conclusion, PAC with a higher mesopore volume, fewer acidic groups, and a higher isoelectric point was desirable for removing EfOM from bio-treated coking wastewater. This study provides guidance for the selection of PAC for the removal of EfOM from bio-treated coking wastewater.

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.

Fe-Mn-Cu-Ce/Al2O3 as an efficient catalyst for catalytic ozonation of bio-treated coking wastewater: Characteristics, efficiency, and mechanism

It is important to develop a catalyst that has high catalytic activity and can improve the degradation efficiency of refractory organic pollutants in the catalytic ozonation process. In this study, Fe-Mn-Cu-Ce/Al2O3 was synthesised via impregnation calcination for catalytic ozonation of bio-treated coking wastewater. The physical and chemical characteristics of the catalysts were analysed using X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller nitrogen adsorption–desorption methods. The effects of catalyst dosage, pH, and reflux ratio on the degradation efficiency of wastewater were examined in laboratory-scale experiments. The chemical oxygen demand (COD) removal rate of bio-treated coking wastewater was estimated to be 52.76 % under optimal conditions. The experiments on the catalytic mechanism demonstrated that the surface hydroxyl formed by the Lewis acid sites on the surface of the catalyst can react with ozone as the active site forming the active oxygen (·OH, ·O2–, and 1O2), thereby efficiently degrading the organic pollutants in coking wastewater. Furthermore, a pilot-scale experiment on the catalytic ozonation of bio-treated coking wastewater was carried out using an Fe-Mn-Cu-Ce/Al2O3 catalyst, while the effects of the initial pollutant concentration, ozone concentration, and gas flow on the COD removal rate were studied on a pilot scale. It was found that the COD removal rate of the wastewater was ∼ 60 % under optimal parameters. After the treatment, the wastewater steadily reached the coking wastewater discharge standard (COD < 80 mg/L), while the operating cost of catalytic ozonation reached ∼ 0.032$/m3, thereby paving the way toward economic engineering applications. The COD degradation kinetics in the bio-treated coking wastewater followed pseudo-second-order kinetics. Three-dimensional fluorescence and gas chromatography–mass spectrometry revealed that macromolecular organic pollutants in the bio-treated coking wastewater were greatly degraded. In summary, Fe-Mn-Cu-Ce/Al2O3 exhibited good reusability, high catalytic activity, and low cost and has a wide application prospect in the treatment of coking wastewater.

Efficient Removal of Organic Matter from Biotreated Coking Wastewater by Coagulation Combined with Sludge-Based Activated Carbon Adsorption

Coagulation–adsorption can be effective in the removal of the organic matters remaining in biotreated coking wastewater (BTCW), and cheap and efficient adsorbents benefit the widespread application of this technology. In this study, a sludge-based activated carbon (SAC) was prepared using zinc chloride to activate sludge pyrolysis carbon for the treatment of BTCW with coagulation as the pretreatment process. According to Brunauer-Emmett-Teller (BET) and the scanning electron microscope (SEM) analysis, the SAC exhibited a specific surface area of 710.175 m2/g and well-developed pore structure. The removal characteristics of the organic matter in BTCW were systematically studied. The results show that 76.79% of the COD in the BTCW was removed by coagulation combined with SAC adsorption, and the effluent COD was below the discharge limit (80 mg/L) (GB16171-2012), with the optimal dosages of polyaluminum chloride and SAC being 150 mg/L and 4 g/L, respectively. Compared with a commercial powdered activated carbon (PAC) (48.26%), the SAC achieved a similar COD removal efficiency (47.74%) at a higher adsorption speed. The removal efficiencies of the hydrophobic components (77.27%) and fluorescent components by SAC adsorption were higher than those by PAC adsorption. The SAC also had an excellent removal effect on complex organic compounds and colored substances in the BTCW, as revealed by UV-vis spectra analyses.

Performance and membrane fouling mitigation for bio-treated coking wastewater treatment via membrane distillation: Effect of pre-treatment

A large amount of coking wastewater is generated from the coal coking industry in China. As the coking wastewater containing high concentration of hazardous substances is harmful to the environment and health, it is necessary to be properly treated before being discharged. In this work, direct contact membrane distillation (DCMD) is explored to deeply treat the real bio-treated coking wastewater (BCW). DCMD system performance and membrane fouling are evaluated. Results showed that the serious membrane fouling caused by the brown fulvic and humic acid-like organics in the BCW occurred, resulting in permeate flux decline sharply. Various pre-treatment approaches including coagulation, ozonation and electrocoagulation (EC) were selected to alleviate membrane fouling. It was noteworthy that the long-time steady flux and low permeate conductivity was kept during DCMD filtration of the BCW pre-treated by EC. Moreover, the membrane surface remained clean at the conclusion of the DCMD experiment. In contrast, permeate flux declined quickly due to membrane pores plugging during DCMD treatment of the BCW pre-treated via ozonation. More pollutants penetrated into the permeate, which was caused by the removal of humic acid from the fouling layer during DCMD treatment of the BCW pre-treated via coagulation. Our work suggested that DCMD process combined with EC can be used as an advanced treatment to treat the BCW effectively.

Magnetically separable NiFe2O4/sepiolite catalyst for enhanced ozonation treatment of quinoline and bio-treated coking wastewater in a catalytic ozonation system

In a quest to eliminate the bio-refractory organic pollutants in industrial wastewater, the NiFe2O4/SEP composites were synthesized via a sol-gel method and investigated by XRD, SEM, XPS, FTIR, VSM. The TOC removal increased from 16.82% to 69.35% in NiFe2O4/SEP+O3 system using quinoline as a target contaminant after 30 min, which is about 4.12 times as that in O3 system. The evolution of acetic acid, oxalic acid and formic acid in quinoline degradation was analyzed, saturated carboxylic acids were inertia to ozone molecules. However, 93.54% of oxalic acid was removed after 10 min, and 77.66% of acetic acid was degraded after 30 min in catalytic ozonation. The generation of small molecular organic acids could promote the Fe3+/Fe2+ redox cycle by complexing with Fe3+ on NiFe2O4/SEP, and then accelerated the formation of reactive oxygen species. In the presence of NiFe2O4/SEP, the high oxidation potential of •OH and •O2- contributed to an excellent TOC removal rate. Meanwhile, NiFe2O4/SEP was proved to be active for bio-treated coking wastewater in catalytic ozonation. The naturally fluorescent constituents in bio-treated coking wastewater were almost entirely removed by NiFe2O4/SEP+O3 system in 60 min. These findings indicated the good potential of NiFe2O4/SEP for practical applications in industrial wastewater treatment.

Impacts of Activated Carbon and Organic Matter Characteristics on the Adsorption of Effluent Organic Matter from Bio-Treated Coking Wastewater

Impacts of Activated Carbon and Organic Matter Characteristics on the Adsorption of Effluent Organic Matter from Bio-Treated Coking Wastewater

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.

Removal efficiency and mechanism of bio-treated coking wastewater by catalytic ozonation using MnO&lt;sub&gt;2&lt;/sub&gt; modified with anionic precursors

In this paper, MnO&lt;sub&gt;2&lt;/sub&gt; catalyst were firstly prepared and modified by four kinds of anionic precursors (i.e., NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;, AC&lt;sup&gt;-&lt;/sup&gt;, SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt; and Cl&lt;sup&gt;-&lt;/sup&gt;) through redox precipitation method. After that, bio-treated coking wastewater (BTCW) was prepared and employed as targeted pollutants to investigate the catalytic ozonation performance of prepared-MnO&lt;sub&gt;2&lt;/sub&gt; catalyst was investigated and characterized by the removal efficiencies and mechanism of the prepared bio-treated coking wastewater (BTCW), which was employed as the targeted pollutants. Specifically, the effects of specific surface area, crystal structure, valence state of Mn element and lattice oxygen content on catalytic activity of MnO&lt;sub&gt;2&lt;/sub&gt; materials were characterized by BET, XRD and XPS, respectively. Results showed that COD of BTCW could be removed 47.39% under MnO&lt;sub&gt;2&lt;/sub&gt;-NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; catalyst with 2 h reaction time, which was much higher than that of MnO&lt;sub&gt;2&lt;/sub&gt;-AC&lt;sup&gt;-&lt;/sup&gt; (3.94%), MnO&lt;sub&gt;2&lt;/sub&gt;-SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt; (12.42%), MnO&lt;sub&gt;2&lt;/sub&gt;-Cl&lt;sup&gt;-&lt;/sup&gt; (12.94%) and pure O&lt;sub&gt;3&lt;/sub&gt; without catalyst (21.51%), respectively. So, MnO&lt;sub&gt;2&lt;/sub&gt;-NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt; presented the highest catalytic performance among these catalysts. The reason may be attributed to a series of better physiochemical properties including the smaller average grain, the larger specific surface area and active groups, more crystal defect and oxygen vacancy, higher relative content of Mn&lt;sup&gt;3+&lt;/sup&gt; and adsorbed oxygen (O&lt;sub&gt;ads&lt;/sub&gt;) than that of another three catalysts.

Treatment of Bio-Treated Coking Wastewater by Catalytic Ozonation with Semi-Batch and Continuous Flow Reactors

In this work, the treatment of bio-treated coking wastewater (BCW) by catalytic ozonation was conducted in semi-batch and continuous flow reactors. The kinetics of chemical oxygen demand (COD) removal were analyzed using BCWs from five coking plants. An integral reactor with catalytic ozonation stacked by ozone absorption (IR) was developed, and its efficiency was studied. The catalyst of MnxCe1-xO2/γ-Al2O3 was efficient in the catalytic ozonation process for the treatment of various BCWs. The chemical oxygen demand (COD) removal efficiencies after 120 min reaction were 64–74%. The overall apparent reaction rate constants were 0.0101–0.0117 min−1, which has no obvious relationship with the initial COD of BCW and pre-treatment biological process. The IR demonstrated the highest efficiency due to the enhancement of mass transfer and the utilization efficiency of ozone. Bypass internal circulation can further improve the reactor efficiency. The optimal results were obtained with the ozone absorption section accounting for 19% of the valid water depth in the reactor and 250% of circulation flow ratio. The long-term and full-scale application of the novel reactor in a continuous mode indicated stable removal of COD and polycyclic aromatic hydrocarbons (PAHs). The results showed that the system of IR is a promising reactor type for tertiary treatment of coking wastewater by catalytic ozonation.

Simultaneous anti-fouling and flux-enhanced membrane distillation via incorporating graphene oxide on PTFE membrane for coking wastewater treatment

To overcome the limitations of existing hydrophobic membranes for membrane distillation (MD) to treat industrial wastewater with complex contaminants, a composite membrane was developed in this study via incorporating graphene oxide (GO) on commercial polytetrafluoroethylene (PTFE) membrane. The dual-layer GO/PTFE membrane demonstrated asymmetric wettability, which transformed the membrane from in-air hydrophobic and underwater superoleophilic pristine surface to in-air hydrophilic and underwater oleophobic surface. The composite membrane displayed excellent salt rejection (>99.9%) and organic rejection (99.4%) during MD of bio-treated coking wastewater, outperforming the pristine PTFE membrane with apparent fouling and wetting phenomenon. The flux of GO/PTFE membrane reached 20.1 kg/m2·h, which is 44% higher than that of the pristine membrane. These improvements were attributed to the specific morphological and physicochemical characteristics of the composite membrane, such as high water affinity, strongly negative charges on membrane surface, reduced temperature polarization and screening effect to large molecules by the GO layer. This study suggests that GO/PTFE composite membrane has great potential in enhancing the permeate flux and fouling resistance simultaneously, which could be a competitive option for MD to treat challenging wastewaters enriched with salts and hydrophobic organics.

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

In this study, the performance of catalytic ozonation in the treatment of bio-treated coking wastewater (BCW) using pilot- and full-scale systems was investigated. Additionally, the removal efficiency of organic pollutants from BCW, the deactivation mechanism of MnxCe1-xO2/γ-Al2O3, and backflushing optimization for in-situ catalyst regeneration, which have not been previously investigated, were analysed. Results of the 12-month pilot scale experiments showed that catalytic ozonation resulted in the effective removal of organic pollutants when backflushing was applied as an in-situ catalyst regeneration strategy. The effluent chemical oxygen demand (COD) content decreased from 150 to 78 mg L−1, and remained below a discharge limitation of 80 mg L−1, and the stable COD removal efficiencies (from 56.0% to 47.9%) indicated that catalyst deactivation, which primarily resulted from the deposition of inorganic salts on the surface of the catalyst that limited interaction between ozone and active sites and/or prevented electrons transfer, was primarily inhibited by backflushing. The catalyst regeneration via in-situ air- and water-backflushing was attributed to the scrubbing, collision, and/or the loosing effect. Additionally, in the full-scale experiment, the catalytic ozonation process with in-situ alternative backflushing exhibited a stable COD removal efficiency (above 45.6%) for 885 days when water- and air-flushing strengths of 10 L m−2 s−1 and 15 L m−2 s−1, respectively, were applied with a 7-day regeneration interval. Therefore, the results of this study provide new insights into catalytic ozonation and support its engineering application in BCW treatment.

Treatment of Biotreated Coking Wastewater by a Heterogeneous Electro-Fenton Process Using a Novel Fe/Activated Carbon/Ni Composite Cathode

Treatment of Biotreated Coking Wastewater by a Heterogeneous Electro-Fenton Process Using a Novel Fe/Activated Carbon/Ni Composite Cathode

Dissolved organic matter (DOM) removal from biotreated coking wastewater by chitosan-modified biochar: Adsorption fractions and mechanisms

To effectively remove dissolved organic matter (DOM) from actual biotreated coking wastewater (BTCW), a reusable and low-cost chitosan-biochar (CB) was prepared. From the results, CB (52%) exhibited superior removal efficiency compared to that of biochar (12%) and a faster adsorption rate. Analysis of the DOM fractions, molecular weight distribution, fluorescent components, and molecular compositions indicated that chitosan modification made more kinds of DOM components (e.g., hydrophilic substances) have an affinity with biochar. The material characterization and removal characteristics jointly proved that the adsorption efficiency was promoted by the change in pore size distribution and increase in functional groups that provide bonding sites for DOM via hydrogen bonding, acid-base reactions, and electrostatic interactions. Moreover, compared to traditional adsorbent activated carbon, CB exhibited superior removal efficiency and cost-effectiveness. These results demonstrated that CB is a potential alternative adsorbent for advanced DOM treatment of BTCW.

Enhanced removal of nitrate and refractory organic pollutants from bio-treated coking wastewater using corncobs as carbon sources and biofilm carriers

The quality of the bio-treated coking wastewater (BTCW) is difficult to meet increasingly stringent coking wastewater discharge standards and future wastewater recycling needs. In this study, the pre-treatment process of BTCW was installed including the two up-flow fixed-bed bioreactors (UFBRs) which were separately filled with alkali-pretreated or no alkali-pretreated corncobs used as solid carbon sources as well as biofilm carriers. Results showed that this pre-treatment process could significantly improve the biodegradability of BTCW and increase the C/N ratio. Thus, over 90% of residual nitrate in BTCW were removed stably. Furthermore, GC-MS analysis confirmed that the typical refractory organic matters decreased significantly after UFBRs pre-treatment. High-throughput sequencing analysis using 16S rRNA demonstrated that dominant denitrifiers, fermentative bacteria and refractory-organic-pollutants-degrading bacteria co-existed inside the UFBRs system. Compared with no alkali-pretreated corncobs, alkali-pretreated corncobs provided more porous structure and much stable release of carbon to guarantee the growth and the quantity of the functional bacteria such as denitrifiers. This study indicated that the UFBRs filled with alkali-pretreated corncobs could be utilized as an effective alternative for the enhanced treatment of the BTCW.

Chemical oxygen demand (COD) removal from bio-treated coking wastewater by hydroxyl radicals produced from a reduced clay mineral

Removal of chemical oxygen demand (COD) from wastewater has been of considerable interest for several decades, but detailed mechanisms are poorly known. Here we present an environmental friendly method for removing COD from coking wastewater by using chemically reduced nontronite (rNAu-2). Hydroxyl radicals (·OH) produced from oxidation of structural Fe(II) in rNAu-2 in phosphate buffer at pH 6.5, oxidized various compounds in wastewater and thus significantly decreased COD (from 199.10 ± 0.90 to 80.4 ± 1.97 mg/L) within 120 h. The amount of COD removal was positively correlated with the amount of ·OH production, with removal efficiency depending on pH and buffer type. Mass spectrometric analysis of dissolved organic matter (DOM) suggested an oxidative pathway for COD removal. Excitation-emission matrix (EEM) fluorescence spectroscopy showed that aromatic protein-like compounds accounted for a large fraction of DOM in initial wastewater, but after rNAu-2 treatment, their proportion decreased. A sequential treatment of wastewater by rNAu-2 and a common wastewater bacterium Alcaligenes faecalis demonstrated that different orders of chemical and biological treatments affected COD removal efficiency, likely because chemical and microbial treatments targeted different compounds in coking wastewater.