Coal Gasification Wastewater Research Articles

Enhanced anaerobic degradation of selected nitrogen heterocyclic compounds with the assistance of carboxymethyl cellulose

Carboxymethyl cellulose (CMC) is a modified cellulose compound that is dispersible in water. Microbial anaerobic degradation of nitrogen heterocyclic compounds (NHCs) in wastewater treatment may be enhanced by CMC addition, but this remains uncertain due to a lack of experimental evidence. In this study, It was demonstrated that CMC is a suitable co-metabolic matrix in an enhanced anaerobic degradation of quinoline and indole in coal gasification wastewater. When the dosage of CMC was 0.5 mg/L, a reactor exhibited a high degradation efficiency on quinoline and indole, with ratios of 95.23 ± 1.99% and 94.33 ± 3.45%. The addition of CMC increased the concentration of extracellular polymeric substances in anaerobic sludge and increased the particle size of the sludge, which improved the microbial stability and sedimentation of anaerobic granular sludge. Analysis of high-throughput sequencing indicated that the addition of CMC improved the richness and diversity of bacterial and archaea communities. Acetic acid metabolism was the primary mechanism to produce methane during anaerobic degradation of NHCs wastewater.

Two-stage air stripping combined with hydrolysis acidification process for coal gasification wastewater pretreatment.

Coal gasification wastewater is mainly from gas washing, condensation and purification processes in the gas furnace with high NH3-N (nitrogen in water in the form of free ammonia (NH3) and ammonium ion (NH4 +)), TN (total nitrogen) and refractory organics content, which will inhibit the subsequent biological treatment. The 'air stripping - hydrolysis acidification - air stripping' process was proposed as the pretreatment for coal gasification wastewater to improve the biodegradability and nitrogen removal, which could reduce the subsequent biological treatment load. The first-stage air stripping process before hydrolysis acidification could achieve a significant removal of NH3-N (97.0%) and volatile phenol (70.0%), reducing the corresponding toxicity on hydrolysis acidification. The group with air stripping had more abundant microbial communities and a more effective organic degradation performance in hydrolysis acidification than that without air stripping. The second-stage air stripping removed NH3-N released from hydrolysis acidification, and significantly reduced the TN concentration in effluent. The whole process achieved a TN removal from 2,000 ± 100 mg/L to 160 ± 80 mg/L, and a total phenols removal from 700 ± 50 mg/L to 80 ±20 mg/L.

Enhanced treatment of coal gasification wastewater in a membraneless sleeve-type bioelectrochemical system

A bioelectrochemical system (BES) is a technology with potential for accelerating the degradation of recalcitrant compounds, the components and configurations of which are important for treatment performance. In the present work, a membraneless sleeve-type BES (termed BioE) was designed for the treatment of synthetic coal gasification wastewater (CGW, phenol as a model pollutant) and real CGW. Compared with the biological control (termed Bio), the phenol removal rate and COD removal efficiency increased by 2.6 and 2.1 fold in the BioE, respectively. However, the coulombic efficiency of this system was relatively low, ranging from 0.42% to 2.6%. This combination of results indicated that anode respiration was not the main process in the BioE. The increased CH4 production and higher levels of methanogens obtained from the BioE confirmed that the methanogenic process proceeded, possibly facilitated by the diffusion of H2 from the cathode to the anode. This study provides new insight into biocathode function for COD oxidation removal in BESs. Moreover, this study indicates that pursuing a high coulombic efficiency may not be necessary for wastewater treatment, as it consumes less energy at the lower value.

Kinetic insights into removal of indole in aqueous solutions by ozonation: operating parameters, modeling and degradation pathways

Nitrogenous heterocyclic compounds (NHCs) pose a serious threat to human health and ecosystems, and ozonation has been widely applied in the efficient removal of NHCs in water environments. In the present study, the degradation performance of indole in aqueous solutions was investigated. The second-order rate constants of indole reacting with molecular ozone at pH 2 and ·OH at pH 9 were determined to be 223.24 M−1 s−1 and 12.3 × 109 M−1 s−1, respectively. The effect of different operating parameters both on the mass transfer and chemical kinetics was evaluated during the degradation of indole by ozonation. To attain a better removal performance, a pH value around 9 and a temperature of 35.6 °C were preferred. Additionally, the higher initial ozone concentrations were proved to be beneficial for the enhancement of the removal rate. Compared with synthetic solutions, the removal of indole appeared to be more efficient in real bio-treated coal gasification wastewater. A chemical kinetic model was built based on the rate constants and exposures of O3 and ·OH, and experimental results demonstrated that the removal rates can be satisfactorily predicted. The relative contributions of O3 and ·OH measured by the modeling results indicated that the molecular ozone played a dominant role in the reaction system. By further analysis of intermediates with gas chromatography–mass spectrometry (GC–MS), a number of products were detected, and three degradation pathways were tentatively proposed. This work provides a reference for kinetic studies on the treatment of other NHCs using ozone technologies.

Enhanced biodegradation of coal gasification wastewater with anaerobic biofilm on polyurethane (PU), powdered activated carbon (PAC), and biochar

The primary objective was to explore the feasibility of anaerobic biofilm on polyurethane (PU), powdered activated carbon (PAC), and biochar in strengthening anaerobic degradation of phenolic compounds and selected nitrogen heterocyclic compounds (NHCs) in coal gasification wastewater (CGW). When total phenols (TPh) was less than 300 mg/L, PAC-based biofilm was more efficient. Whereas, when the TPh concentration was more than 450 mg/L, PU-based biofilm performed the optimal degradation efficiency. Furthermore, microbial community structure analysis showed that PAC and biochar had little effect on the microbial community structure after 120 days of operation, while the addition of PU could lead to the enrichment of Giesbergeria, Caldisericum, Thauera, Methanolinea, and Methanoregula.

Ni-Induced C-Al2O3-Framework (NiCAF) Supported Core-Multishell Catalysts for Efficient Catalytic Ozonation: A Structure-to-Performance Study.

During catalytic ozonation, Al2O3-supported catalysts usually have stable structures but relatively low surface activity, while carbon-supported catalysts are opposite. To encourage their synergisms, we designed a Ni-induced C-Al2O3-framework (NiCAF) and reinforced it with a Cu-Co bimetal to create an efficient catalyst (CuCo/NiCAF) with a core-multishell structure. The partial graphitization of carbon adjacent to Ni crystals formed a strong out-shell on the catalyst surface. The rate constant for total organic carbon removal of CuCo/NiCAF (0.172 ± 0.018 min-1) was 67% and 310% higher than that of Al2O3-supported catalysts and Al2O3 alone, respectively. The metals on CuCo/NiCAF contributed to surface-mediated reactions during catalytic ozonation, while the embedded carbon enhanced reactions within the solid-liquid boundary layer and in the bulk solution. Moreover, carbon embedment provided a 76% increase in ·OH-production efficiency and an 86% increase in organic-adsorption capacity compared to Al2O3-supported catalysts. During the long-term treatment of coal-gasification wastewater (∼5 m3 day-1), the pilot-scale demonstration of CuCo/NiCAF-catalyzed ozonation revealed a 120% increase in ozone-utilization efficiency (ΔCOD/ΔO3 = 2.12) compared to that of pure ozonation (0.96). These findings highlight catalysts supported on NiCAF as a facile and efficient approach to achieve both high catalytic activity and excellent structural stability, demonstrating that they are highly viable for practical applications.

Molecular Composition and Transformation of Dissolved Organic Matter (DOM) in Coal Gasification Wastewater

Coal gasification process generates a huge amount of highly concentrated industrial wastewater. A better understanding of molecular compositions of dissolved organic matter (DOM) is necessary for t...

The feasibility and mechanism of reverse electrodialysis enhanced photocatalytic fuel cell-Fenton system on advanced treatment of coal gasification wastewater

A novel reverse electrodialysis enhanced photocatalytic fuel cell (PREC)-Fenton system is established for advanced treatment of coal gasification wastewater. Results indicate the reverse electrodialysis (RED) stack is crucial to achieve higher electricity production and H2O2 generation. Operational parameters including salinity gradient, air flow rate, solutions flow rate and pH are investigated. The optimal H2O2 production and wastewater treatment are observed at salinity ratio of 100, air flow rate of 16 mL/min, solutions flow rate of 2.0 mL/min and a broaden pH of 2–7. A high coulombic efficiency of 59.6% and cathodic efficiency of 51% is obtained, while the COD, total phenol and NH4+-N removal reach 92.4%, 86.1% and 77.3%. Moverover, the system requires much lower energy consumption of 26.4 kWh/(kg·TOC). The PREC-Fenton system is a more economical and efficient candidate for energy recovery and wastewater treatment.

A Novel Method on Contaminant Degradation in Coal-gasification Wastewater

An alternative method of wastewater recycle in coal-gasification process was proposed and evaluated. The experiment was performed using lab-scale entrained-flow reactor system to study thermal degradation of COD and NH3-N contained in wastewater with the variant of temperature and reaction atmosphere. The results showed that reaction temperature has a significant effect on COD and NH3-N degradation, and degradation efficiency is obviously increased with temperature in the range of 400~1000 °C. The degradation efficiency of COD and NH3-N in different atmospheres ranks: oxidative > inert > reductive. The practical operation can meet the requirement to obtain high degradation efficiencies and the cost of facility reconfiguration will be reduced.

Fate of potentially hazardous trace elements during the entrained-flow coal gasification processes in China

With the rapid and wide application of the coal gasification technology in China, the corresponding environmental issues require increasing attention. In this study, the feed coal, coal gasification wastewater samples at key technical links, and the coal gasification residues were collected from three entrained-flow coal gasification plants in Northwest China and were characterized to understand the migration and partition of 21 potentially hazardous trace elements (PHTEs) in coal gasification process and their potential environmental impacts.Compared with Chinese coal, the concentrations of the PHTEs in the feed coals are mainly at the level of “depleted” and “normal”. Undergoing the heating process in the gasifier, purification procedure for the syngas, and the residue-wastewater separation, the PHTEs in the feed coals are transferred into gaseous phase, wastewater, and gasification residues. The PHTEs are easier to be released into the gaseous phase during the GSP gasification process compared with the OMB and GE gasification processes. The chalcophile elements Zn, As, Se, Cd, Sb, Tl, Pb, and Hg tend to be enriched in the fine residues, and the retention capability of Hg by the residues is the lowest. With the grey water circulation and the use of additives, the black water samples have higher PHTEs concentrations than other water samples. Except for Sr, Mo, Sb, and Cs, most of the elements in the original water samples can be reduced effectively by removing the particulate matters. In some cases, Cr6+, Zn, As, Se, Cd, and Pb in the original wastewater samples exceed the limit for industrial use as indicated in the Chinese Environmental Quality Standards for Surface Water and the Emission Standard for Pollutants from Coal Industry. The potential environmental impacts of As and Se in the water cannot be reduced by filtration. The environmental impacts of the coal gasification residues should be further evaluated.

Characterization of cometabolic degradation of p-cresol with phenol as growth substrate by Chlorella vulgaris

To investigate the potential application of Chlorella vulgaris in the treatment of coal gasification wastewater, the characteristics of phenol and p-cresol cometabolism by Chlorella vulgaris were studied, including phenol degradation, ammonia nitrogen removal, antioxidant enzyme activities, and phenol hydroxylase activity. The results showed that the highest tolerable concentrations of phenol and p-cresol for Chlorella vulgaris were 800 and 400 mg/L, respectively. During cometabolism, phenol at low concentrations (100 mg/L) significantly promoted the degradation of p-cresol. Meanwhile, the removal efficiency of ammonia nitrogen was approximately 60% and was not affected by variations in phenol concentration. Furthermore, the cometabolism of phenol and p-cresol was enhanced by improvement of phenol hydroxylase activity of Chlorella vulgaris after the addition of NaHCO3 as an exogenous nutrient. Therefore, Chlorella vulgaris has a great potential for the biochemical treatment of coal gasification wastewater.

Potential of the integration of coagulation and ozonation as a pretreatment of reverse osmosis concentrate from coal gasification wastewater reclamation

Combination of coagulation and ozonation was used to treat brine derived from a three-stage reverse osmosis (RO) process during coal gasification wastewater reclamation. Effects of operating parameters on the removals of total organic carbon (TOC), color and UV absorbance at 254 nm (A254) were investigated during coagulation and ozonation. All the removal efficiencies of TOC, A254 and color of FeCl3 coagulant are about twice those of AlCl3 coagulant at the same molar dose since almost all the molecular weight fractions of RO concentrate (ROC) could be removed effectively by FeCl3 coagulant while only the fractions of molecular weight > 3 k Da could be removed effectively by AlCl3 coagulant. The TOC removal increases with the increasing of ozone dose and reaction temperature during ozonation of ROC after coagulation pretreatment. TOC and color of ROC after pretreated by coagulation could be further removed effectively during ozonation since ozonation can significant reduce the fluorescence response of all the fractions of effluent organic matter in ROC. It is unexpectedly found that the increase of A254 is observed after ozonation, this is because the intensity of absorbance at 254 nm by the low molecular weight transformation products (<2 k Da) increases significantly with the reaction time after 30 min. The coagulation coupling with ozonation is efficient in the removals of both TOC and color of ROC.

A novel phenol and ammonia recovery process for coal gasification wastewater altering the bacterial community and increasing pollutants removal in anaerobic/anoxic/aerobic system

Coal gasification wastewater (CGWW) is a typical toxic and refractory industrial wastewater. Here, a novel phenol and ammonia recovery process (IPE) was employed for CGWW pretreatment, and the coupled system assemble by the IPE process with A2/O system (IPE-A2/O) were operated to enhance the treatment performance of CGWW. The results showed that the IPE pre-treated effluent had a higher BOD5/COD ratio and lower refractory compounds compared to a typical process (MIBK). Subsequent A2/O biological treatment indicated that the A2/O-p system (A2/O system followed IPE process) obtained a higher average COD removal of 92% compared to 87.7% of the control (A2/O-m, A2/O system followed MIBK). The GC–MS analysis suggested that the content of alkanes in the IPE-A2/O effluent was lower than that of the MIBK-A2/O. The high-throughput sequencing revealed Levilinea, Alcaligenes, Acinetobacter, Thauera and Thiobacillus were the core genera in A2/O system. The genera Alcaligenes, Acinetobacter, Thauera and Thiobacillus in the degrading consortium were enriched in the A2/O-p system, leading to increased removals of organic pollutants and TN. These results suggested that the IPE process was a feasible pretreatment method, and the coupled IPE-A2/O system was an alternative technique for treating CGWW.

Catalytic performances of Ni-based catalysts on supercritical water gasification of phenol solution and coal-gasification wastewater

Activity and stability of the supported Ni-based catalysts for the gasification performances of phenol solution and coal-gasification wastewater in supercritical water were studied in a continuous reactor at 480 °C, 25 MPa and oxygen ratio of 0.2 for 50 h operation. The influences of the supports (γ-Al2O3, active carbon (AC) and carbon nanotube (CNT)) on gas yields, gasification efficiencies for phenol solution were investigated, and the loading amount of Ni were optimized. Results showed that the catalytic activity and the stability of the catalysts followed the order of Ni/CNT > Ni/AC > Ni/γ-Al2O3. The activity of Ni/AC and Ni/γ-Al2O3 decreased after 30 h continuous operation, and there occurred significant leaching of Ni2+. For Ni/CNT catalyst, H2 yield increased obviously when the loading amount of Ni lower than 15 wt%, while increased little at higher loading amount. Then, 15 wt% Ni/CNT with a thickness of 1.5 mm was coated on 316 L stainless steel (SS316L, an economic material usually used as the reactor material), which can act as a "catalytic tube wall" in reactor. The catalytic activity and corrosion resistance of Ni/CNT/SS316L for the gasification of real coal-gasification wastewater were studied. Results showed that Ni/CNT/SS316L gave a great positive effect on H2 production. H2 yield increased from 25.36 mmol/g (total organic carbon) without catalyst to 75.12 mmol/g (total organic carbon) with Ni/CNT/SS316L after operated for 20 h, respectively. However, obvious pealing of the coating was found after 50 h operation. Further study is necessary for the improvement of the coating preparation method.

Anaerobic bioaugmentation hydrolysis of selected nitrogen heterocyclic compound in coal gasification wastewater

Anaerobic bottle experiments were conducted in parallel for 120 consecutive days to perform the bioaugmentation hydrolysis of selected nitrogen heterocyclic compounds (NHCs) in coal gasification wastewater. Due to enhancement with PAC and Fe(OH)3@PAC, quinoline, pyridine, and indole were hydrolyzed more effectively. The addition of PAC and Fe(OH)3@PAC improved the coagulation capacity of microorganisms, which laid a solid foundation for the removal of selected NHCs and the adverse environmental conditions. Anaerobic degradation of the NHCs occurred first through hydrogenation, then through the opening of the nitrogen heterocycles, followed by the release of ammonia nitrogen and finally the opening of the benzene rings. Enriched Acinetobacter, Levilinea, Comamonas, and Longilinea were the main functional groups responsible for the anaerobic biodegradation of the selected NHCs.

The efficiency and mechanism in a novel electro-Fenton process assisted by anodic photocatalysis on advanced treatment of coal gasification wastewater

A novel dual-chamber photo-electrochemical oxidation system with Fe@Fe2O3/CF cathode was constructed bycombining cathodic electro-Fenton and anodic photocatalysis for advanced treatment of biologically pretreated coal gasification wastewater (CGW). In the electro-Fenton cathode chamber, maximal chemical oxygen demand (COD) removal efficiency of 84.2% was arrived within 120 min at current density 10 mA/cm2, initial pH 3 and air flow rate 0.4 L/min for its initial concentration of 200 mg/L. Correspondingly, the effluent concentration of COD, BOD5, TOC and total phenols were 31.5, 3.9, 8.4 and 13.8 mg/L respectively, satisfying the stringent wastewater discharge standard. Moreover, the H2O2 concentration change and wastewater acute toxicity were analyzed. Furthermore, a reasonable degradation mechanism was proposed based on the contribution of hydroxyl radicals (OH), and thus degradation pathway of phenol as typical pollutant was also speculated. The integrated system is confirmed to be high-effective and stable, and thus it is a potentially promising alternative for treatment toxic refractory industrial wastewater.

Enhanced anaerobic biodegradation efficiency and mechanism of quinoline, pyridine, and indole in coal gasification wastewater

Anaerobic bottle experiments were operated in parallel for 160 consecutive days for raw (R1), Polyurethane (R2), and Fe3O4@Cu/Polyurethane (R3) biodegradation of selected nitrogen-heterocyclic (NHCs) in coal gasification wastewater. The addition of Fe3O4@Cu/Polyurethane absolutely had an enhancement of microorganism for the degradation of NHCs. The results of GC–MS showed that the first step of anaerobic degradation of NHCs was the opening of nitrogen heterocyclic ring, the second step was the release of ammonia nitrogen and the opening of benzene ring. In R3, direct interspecies electron transfer (DIET) guided by Fe3O4@Cu could realize the rapid transfer of electrons and avoid the accumulation of electrons in the degradation of the NHCs. Furthermore, acute toxicity analysis showed that under the enhancement of Fe3O4@Cu/Polyurethane, the selected NHCs was degraded effectively and the toxic inhibition of selected NHCs on living organisms decreased effectively. Finally, high-throughput 16S rRNA pyrosequencing showed that the dominant strains were dispersed more balanced with the assist of Fe3O4@Cu/Polyurethane.

Development of synergistic extraction process for highly efficient removal of phenols from coal gasification wastewater

Due to the limitation of the existing solvents, the phenols recovery process cannot control phenols concentration to less than 300 mg/L. Therefore, this study presented a synergistic phenols extraction process by using optimal design solvent mixture. The solvent mixture was proposed with the volume ratio of methyl isobutyl ketone (MIBK) to n-pentanol 6:4. The synergistic extraction process was simulated to acquire the parameters with treatment 130 t/h coal gasification wastewater. The removal efficiencies of phenols and treatment costs for the synergistic extraction process had been addressed. The removal efficiency of total phenols can reach to 97.0% after two-stage extraction, and the concentration of total phenols can be decreased from 6273 mg/L to 190 mg/L. Compared with single solvent MIBK, the reduction of phenols emissions is 47.2% by proposed solvent mixture. The operation cost and income of crude phenols showed that synergistic extraction process realized profit about 3.35 CNY/t. Given the removal efficiencies and treatment costs, the solvent mixture (60% MIBK, 40% n-pentanol) is very promising for phenols removal.

Complex Mechanism of Phenol Extraction of Coal Gasification Wastewater

Complex Mechanism of Phenol Extraction of Coal Gasification Wastewater

Shortcut Biological Nitrogen Removal from Coal Gasification Wastewater in Three-Stage MBBRs.

A lab-scale aerobic-anoxic-aerobic (AE1-AN-AE2) MBBR system was tested for the removal of COD, <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="01977-ilm01.gif"/>, SCN-, phenols, and nitrogen from coal gasification wastewater, using a shortcut biological nitrogen removal process. Dissolved oxygen concentration in AE1 was maintained at 1.0 to 2.0 mg/L to ensure stable <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="01977-ilm12.gif"/> accumulation. Adding methanol wastewater to AN guaranteed denitrification efficiency. AE2 ensured high removal rates of <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="01977-ilm23.gif"/>, SCN-, and phenols. The effects of influent pollutant concentration and hydraulic retention time (HRT) on nitrogen removal were studied. Improving the dissolved oxygen concentration in AE1 eliminated the negative effect of increased organic loading on nitrification, but it affected the stability of nitrosation. Shortening the HRT had negative effects on the performance of the system and performance recovered after it was extended. The average total nitrogen removal rate was 82.6% with a CODmethanol/<inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="01977-ilm34.gif"/> ratio of 3.5. Biomass and activity of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria were measured to understand the evolution of nitrification.