Treatment Of Coal Gasification Wastewater Research Articles

Electric field coupled with Fe3O4 modified biochar to enhance anaerobic degradation of phenolic compounds in coal gasification wastewater (CGW)

Anaerobic treatment of coal gasification wastewater is usually limited by the inhibition of high concentration of phenolics. In this study, the Fe3O4 loaded biochar (FeBC) coupled with electric field (E-FB) was used to enhance anaerobic phenolics degradation. E-FB significantly accelerated anaerobic removal of phenol, p-cresol and 3,5-xylenol with methane production improved by 84.2 % compared to the control, where FeBC contributed most. E-FB improved anodic oxidation capacity, adsorption-biodegradation and Fe (III) reduction process, which resulted from the synergistic effects between electric field and FeBC. E-FB significantly enhanced the microbial activity and extracellular electron transfer (EET) in the suspended sludge with the maximum electron transfer system activity (132.9 %), cytochrome C (7.2 nmol/g MLSS) and adenosine triphosphate contents (87.8 nmol/ g MLSS) obtained. Compared with FB, E-FB stimulated the secretion of proteins and humic acid-like substances in extracellular polymeric substance, which could contribute to higher EET efficiency. More abundant phenol degrading bacteria, dissimilatory iron reducing bacteria, electroactive bacteria and potential direct interspecies electron transfer (DIET) partners (e.g., Geobacter and Methanobacterium) were enriched in E-FB especially on the anode. The benzoyl-CoA pathway on the anode and CO2-reduction methanogenesis (possibly via DIET) in the suspended sludge and anode were improved in E-FB.

Electrocatalysis coupled heterogeneous electro-Fenton like treatment of coal gasification wastewater using tourmaline as catalyst: process parameters and response surface.

Coal gasification technology is essential for realizing clean and efficient conversion of coal, as well as for reducing carbon emissions. However, coal gasification technology is accompanied by a large amount of coal gasification wastewater that is biodegradable. In this work, tourmaline was applied as a catalyst in electro-Fenton like process for treating coal gasification wastewater. The optimal applied parameters of coal gasification wastewater were investigated as follows: current density of 90 mA cm-2, tourmaline dosage of 8 g L-1, electrode gap of 1 cm, and temperature at 25 °C; the COD removal ratio reached 91.24% after 240-min treatment. In addition, the current density and tourmaline dosage were further optimized by response surface method. The result was about current density with 82.4 mA cm-2 and catalyst with 7.57 g L-1; the predicted COD removal efficiency was 86.91%. Under the optimal parameters the actual COD removal efficiency was 88.25% a little high than the predicted value. To explore the reusability of tourmaline as Fenton reaction catalyst, five cycles of experiments were carried out. The result demonstrated that tourmaline could be used as catalyst for treating coal gasification wastewater by electro-Fenton like process.

Mn-doped carbon-Al2SiO5 fibers enable catalytic ozonation for wastewater treatment: Interface modulation and mass transfer enhancement

Heterogeneous catalytic ozonation is an efficient approach to remove hazardous and refractory organic contaminants in wastewater. It is crucial to design an ozone catalyst with high catalytic activity, high mass transfer and facile separation properties. Herein, easily separable aluminosilicate (Al2SiO5) fibers were developed as carriers and after interface modulation, Mn-doped carbon-Al2SiO5 (Mn-CAS) fibrous catalysts were proposed for catalytic ozonation. The growth of carbon shells on Al2SiO5 fiber surface and the introduction of metal Mn provided abundant Lewis acid sites to catalyze ozone. The Mn-CAS fiber/O3 system exhibited superior reactivity to degrade oxalic acid with a rate constant of 0.034 min−1, which was about 19 times as high as Al2SiO5/O3. For coal gasification wastewater treatment, Mn-CAS fibers also demonstrated high catalytic activity and stability and the COD removal was over 56%. Computational fluid dynamic simulations proved the high mass transfer properties of fibrous catalysts. Hydroxyl radicals (•OH) were identified as the predominant active species for organic degradation. Particularly, the catalytic pathways of O3 to •OH on Mn-O4 sites were revealed by theoretical calculations. This work provides a novel fibrous catalyst with high reactivity and mass transfer as well as easy separation characteristics for catalytic ozonation and wastewater purification.

Energy, exergy, economic and environmental comprehensive analysis and multi-objective optimization of a sustainable zero liquid discharge integrated process for fixed-bed coal gasification wastewater

For a long time, China's regional water resource imbalance has restricted the development of coal chemical industry, and it is imperative to achieve zero liquid discharge (ZLD). Therefore, the game relationship between technical indicators, costs and emissions in ZLD process of fixed-bed coal gasification wastewater treatment process should be explored in detail. According to the accurate model, the simulation for ZLD of fixed-bed coal gasification wastewater treatment process is established, and this process is assessed from the perspective of thermodynamics, economy, and environment. The total energy consumption of ZLD process before optimization is 4.032 × 108 W. The results of exergy analysis show exergy destruction of ZLD process is 94.55%. For economic and environmental results, the total annual cost is 1.892 × 107 USD·a−1 and the total environmental impact is 4.782 × 10−8. The total energy consumption of the optimal six-step ZLD process based on multi-objective optimization is 4.028 × 108 W. The CO2 content in the treated wastewater is 0.1%. This study will have an important role in promoting the establishment of the ZLD process for coal chemistry industry.

Enhanced biodegradation of coal gasification wastewater (CGW) by a novel integration of powdered activated carbon treatment (PACT) coupled with wet air regeneration (WAR)

This study illustrated the advanced degradation of coal gasification wastewater (CGW) by powdered activated carbon treatment (PACT) coupled with wet air regeneration (WAR). The results demonstrated that the PACT-WAR process achieved high efficiencies on the removal of COD (92.58%), Tph (96.56%), NH4+-N (99.52%), and TN (71.52%). The PACT process was more favorable to improving the structural stability of activated sludge (AS) and the biodiversity of specific functional microbial communities. Among them, the relative abundance of Sphingopyxis, Flavobacterium, Nitrosomonas and Terrimonas was enriched to facilitate the degradation of phenolic and nitrogen compounds. More importantly, the regeneration efficiency of spent PAC was 83.33% by the WAR process, which would effectively reduce the addition of fresh PAC. The regeneration solution displayed better denitrification capacity as the additional carbon source. Therefore, the PACT-WAR process was an excellent practical process for enhancing CGW treatment.

Analysis of the differential metabolic pathway of cultured Chlorococcum humicola with hydroquinone toxic sludge extract

Microbe inhibition produces intermediate metabolites and toxic substances that accumulate significantly in residual sludge toxicity after continuous treatment of coal gasification wastewater with activated sludge. To address this issue, Chlorococcum humicola was cultured with sludge extract. Proteomics analysis was used to investigate the mechanism of stress response in microalgae to sludge toxicity. Upon completion of growth, microalgae treated with sludge extract produced 0.725 ± 0.036 g/L of biomass. The total organic carbon concentration and toxicity removal rates on microalgae were 75.1 ± 3.8% and 47.4 ± 2.1%, respectively. The proteomics analysis revealed that under stress conditions, microalgae altered cellular components such as the nucleus and plasma membranes, affecting the photosynthetic and respiratory processes. The logarithmic phase was characterized by a down-regulation of oxidative phosphorylation and an increase in energy synthesis regulated by the isopropyl phosphate isomerase. The results demonstrate a proteomic basis for the reduction and utilization of waste sludge, as well as provide a molecular mechanism reference for optimizing the model of cultivating microalgae using sludge.

Interaction Mechanisms of Fouling and Cleaning Protocol for A/O-Mbr Treatment of Coal Gasification Wastewater

Interaction Mechanisms of Fouling and Cleaning Protocol for A/O-Mbr Treatment of Coal Gasification Wastewater

Advanced treatment of coal gasification wastewater by O3/Fenton in a rotating packed bed in tandem with coagulation

In this study, the O3/Fenton system in a rotating packed bed (RPB) in tandem with coagulation process was applied to the advanced treatment of coal gasification wastewater (CGW). The removal of COD reached 35.4% in the O3/Fenton@RPB process, and the total removal of COD rose to 47.8% after the effluent of the O3/Fenton@RPB process was further treated with coagulation. The O3/Fenton@RPB + coagulation tandem process also demonstrates good effect on enhancing biodegradation and removing color of the CGW, with the BOD5/COD and decolorization in the tandem process reaching 0.49 and 87.5%, respectively. In addition, an artificial neural network model was established to predict the mass transfer performance of the O3/Fenton system in the RPB and exhibited a good predictability. The O3/Fenton@RPB + coagulation tandem process shows the application potential in the advanced treatment of CGW.

Binary TiO2/RGO photocatalyst for enhanced degradation of phenol and its application in underground coal gasification wastewater treatment

In this work, we synthesized the TiO2/reduced graphene oxide (TiO2/RGO) binary nanohybrids through the sol-anaerobic calcination method, the TiO2 nanoparticles belonging to anatase type were evenly loaded on RGO surface in the form of Ti–O–C bond. The enhanced photocatalytic performance can be ascribed to the existence of RGO that can effectively promote the transfer of photo-induced electron-hole pairs to generate more hydroxyl radicals (·OH) and superoxide anion (O2·-) degrading phenol. The TiO2/RGO nanocomposite with weight ratio of RGO to TiO2 (37.0%–55.7%) had achieved maximum degradation of phenol from aqueous solution, and about 97.87% of phenol had been removed within 180 min under UV-light illumination. Through GC-MS tracking of phenol degradation process, it can be observed that long-chain intermediates will be generated, and these intermediates will eventually be degraded, confirming that phenol can be completely removed. Additionally, around 67% TOC of simulated underground coal gasification (UCG) wastewater can be removed after 10 h degradation using TiO2/RGO binary composites as photocatalysts. All these results demonstrate that the binary nanohybrids possess great potential for the organic contaminants destruction from the actual coal chemical wastewater.

Effects of polyurethane foam carrier addition on anoxic/aerobic membrane bioreactor (A/O-MBR) for coal gasification wastewater (CGW) treatment: Performance and microbial community structure

Coal gasification wastewater (CGW) is a typical toxic and refractory industrial wastewater with abundant phenols contained. Two identical anoxic/aerobic membrane bioreactors (with (R2) and without (R1) polyurethane (PU) foam) were carried out in parallel to investigate the role of PU foam addition in enhancing pollutants removal in CGW. Results showed that both systems exhibited effective removal of chemical oxygen demand (>93%) and total phenols (>97%) but poor ammonia nitrogen removal (<35%) constrained by ammonia oxidation process. GC–MS analysis revealed that aromatic and other refractory intermediates were dramatically reduced in R2. Moreover, the PU addition had negligible influence on the total soluble microbial products and extracellular polymeric substances contents but significantly alleviated membrane fouling with the operating time 33% prolonged. Microbial community revealed that Flavobacterium, Holophaga, and Geobacter were enriched on PU. Influent type might be a main driver for microbial community succession.

Simultaneously autotrophic denitrification and organics degradation in low-strength coal gasification wastewater (LSCGW) treatment via microelectrolysis-triggered Fe(II)/Fe(III) cycle

The autotrophic iron-depended denitrification (AIDD), triggered by microelectrolysis, was established in the microelectrolysis-assistant up-flow anaerobic sludge blanket (MEA-UASB) with the purpose of low-strength coal gasification wastewater (LSCGW) treatment while control UASB operated in parallel. The results revealed that chemical oxygen demand (COD) removal efficiency and total nitrogen (TN) removal load at optimum current (2.5 A/m3) in MEA-UASB (83.2 ± 2.6% and 0.220 ± 0.010 kg N/m3·d) were 1.42-fold and 1.57-fold higher than those (58.5 ± 2.1% and 0.139 ± 0.011 kg N/m3·d) in UASB, verifying that AIDD and following dissimilatory iron reduction (DIR) process could offer the novel pathway to solve the electron donor-deficient and traditionally denitrification-infeasible problems. High-throughput 16S rRNA gene pyrosequencing shown that iron-oxidizing denitrifiers (Thiobacillus and Acidovorax species) and iron reducing bacteria (Geothrix and Ignavibacterium speices), acted as microbial iron cycle of contributors, were specially enriched at optimum operating condition. Additionally, the activities of microbial electron transfer chain, electron transporters (complex I, II, III and cytochrome c) and abundance of genes encoding important enzymes (narG, nirK/S, norB and nosZ) were remarkably promoted, suggesting that electron transport and consumption capacities were stimulated during denitrification process. This study could shed light on better understanding about microelectrolysis-triggered AIDD for treatment of refractory LSCGW and further widen its application potential in the future.

Process Design and Economic Analysis of Coal Gasification Wastewater Treatment and Solid Oxide Cells Coupling System

Process Design and Economic Analysis of Coal Gasification Wastewater Treatment and Solid Oxide Cells Coupling System

Selectively photoelectrocatalytic reduction of oxygen to hydroxyl radical and singlet oxygen: Mechanism and validation in coal wastewater

The fine-tuning of generating hydroxyl radical (OH) and singlet oxygen (1O2) was firstly proposed via the selectively photoelectrochemical (PE) reduction of oxygen with Cu-coordinated carbon-nitride-electrode (CuCN). Complete removal efficiency and trace Cu leaching (<0.01 ppm) were achieved during treatment of dimethyl phthalate and atrazine, which were mainly oxidized by OH and 1O2, respectively. Besides, no toxic intermediates was detected in the whole degradation process. The overall oxygen reduction pathway in PE system was demonstrated by electron paramagnetic resonance measurements and quenching tests. The valence band position of CuCN was designed to be more negative (−1.5 VSHE) for favoring the photocatalytic oxygen reduction. Specifically, Cu-N2-C as active sites optimized the Gibbs free energy of intermediate *OOH (ΔG*OOH = 3.99 eV) to improve the reactivity of two-electron oxygen reduction. The CuCN/photoelectrochemical system is applied for treatment of coal water slurry gasification (CWS) wastewater with high concentration of salt. The TOC of CWS was successfully decreased from 127 to 1.9 mg·L−1 in 3 h with a low specific energy consumption of 0.024−0.05 kW·h·g−1·TOC−1. The treated CWS wastewater can be used for recovery and utilization of salt as chemical raw materials. This work highlights the important role of synergistic photo-electro-catalytic effect in regulating the generation of active oxygen species via oxygen reduction pathway, which can be a promising way especially for salinity coal wastewater remediation.

Removal of Solid Impurities from Coal Gasification Wastewater by Sand Filtration

Coal gasification wastewater has complex pollutant components and high COD value, and contains a variety of toxic and harmful substances. The treatment of coal gasification wastewater has always been one of the important problems in the development of coal gasification industry in China. In this paper, aiming at the removal of fine particle pollution in coal gasification wastewater, the sand filtration method was used to explore the changes of parameters such as solid content removal, separation accuracy, grade efficiency under the conditions of separating different bed thicknesses. With this separation method, the fine particle pollutants in coal gasification wastewater can be effectively removed by more than 95%, the separation accuracy can reach 0.46 μm. The operation conditions are optimized for further industrial application.

Binary TiO 2/RGO Photocatalyst for Enhanced Degradation of Phenol and its Application in Underground Coal Gasification Wastewater Treatment

In this work, we synthesize the TiO2/RGO binary nanohybrids through the sol-anaerobic calcination method, the TiO2 nanoparticles belonging to anatase type were evenly loaded on RGO surface in the form of Ti-O-C bond. The enhanced photocatalytic performance can be ascribed to the existence of RGO that can effectively promote the transfer of photo-induced electron-hole pairs to generate more hydroxyl radicals (·OH) and superoxide anion (O2·-) degrading phenol. The TiO2/RGO nanocomposite with weight ratio of RGO to TiO2 (37.0% to 55.7%) has achieved maximum degradation of phenol from aqueous solution, and about 97.87% of phenol has been removed within 180 min under UV-light illumination. Through GC-MS tracking of phenol degradation process, it can be observed that long-chain intermediates will be generated, and these intermediates will eventually be degraded, confirming that phenol can be completely removed. Additionally, around 67% TOC of simulated underground coal gasification (UCG) wastewater can be removed after 10 h degradation using TiO2/RGO binary composites as photocatalysts. All these results demonstrate that the binary nanohybrids possess great potential for the organic contaminants destruction from the actual coal chemical wastewater.

Activated carbon catalytic ozonation of reverse osmosis concentrate after coagulation pretreatment from coal gasification wastewater reclamation for zero liquid discharge

To fulfil the requirement of zero liquid discharge in the coal gasification wastewater treatment plant, evaporation and crystallization are usually adopted to treat reverse osmosis concentrate (ROC). However, their efficacies and the quality of their products are greatly affected by the organic matter concentration in coal gasification-ROC (CG-ROC). In the present study, ozonation with a commercial activated carbon (AC) as catalyst was conducted to further remove the organic matter in the concentrate originated from a three-stage RO after coagulation pretreatment. The kinetic model calculations were used for the first time to quantitatively evaluate the effect of matrix components on the performance of ozonation of CG-ROC at initial pH 9 and 11. The TOC removal difference among ozonation alone, ozonation alone followed by AC adsorption, and AC catalytic ozonation indicates that AC has a certain catalytic effect during ozonation of CG-ROC. The ΔO3/ΔTOC can be significantly reduced from 43.2 mg O3/mg TOC of ozonation alone to 16.2 mg O3/mg TOC of AC catalytic ozonation under the goal of achieving a similar TOC removal. The change of initial pH has little effect on the TOC removal during ozonation with AC, however, it has a remarkable effect on the TOC removal during ozonation alone. According to the results obtained in kinetic model calculations, high concentration of CO3•- would be generated from the reaction between HO• and CO32− with a high concentration in solution, leads to the delay on the TOC removal in the early reaction stage during ozonation alone at initial pH 11. The results of A254 and molecular weight (MW) distribution indicate that ozonation with AC is more efficient in removing the low MW intermediates absorption at 254 nm compared to that of ozonation alone. Ozonation with AC is more suitable for CG-ROC treatment since it is more energy saving, more efficient in organic matter removal, and more tolerated pH change and wastewater matrix compared to ozonation alone.

Comprehensive analysis of diverse biochemical treatment technologies of fixed-bed coal gasification wastewater from the perspective of different weight dimensions

Assessing the comprehensive performance of coal chemical wastewater process is an intricate and important task due to different biochemical treatment technologies. In this work, a 3E triangle model is developed to evaluate biochemical and advanced treatment technologies for zero liquid discharge of fix-bed coal gasification wastewater treatment process. In 3E triangle model, 19 key performance indicators are considered. In engineering performance aspect, up-flow anaerobic sludge blanket reactor case shows the best performance. In the life cycle environmental impact aspect, sequence batch reactor case shows the best performance through life cycle assessment, especially freshwater aquatic ecotoxicity potential and global warming potential. Generally, due to the higher fixed cost and power consumption of other technologies, the depreciation and variable cost of up-flow anaerobic sludge blanket reactor case are lower. Overall, the up-flow anaerobic sludge blanket reactor case shows excellent performance in 3E comprehensive performance. In addition, membrane bioreactor has better development prospects and its weight has a greatest impact which COD removal accounts for the majority.

Enhanced Degradation of Phenolic Compounds in Coal Gasification Wastewater by Methods of Microelectrolysis Fe-C and Anaerobic-Anoxic—Oxic Moving Bed Biofilm Reactor (A2O-MBBR)

The coal gasification wastewater figures prominently among types of industrial effluents due to its complex and phenolic composition, posing great difficulty for conventional water treatment processes. Since the coking wastewater is toxic and mutagenic to humans and animals, treatment of coal gasification wastewater is genuinely necessary. In this study, we established a lab-scale A2O (Anaerobic-Anoxic—Oxic) with moving bed biological reactor (MBBR) system and evaluated some water indicators of wastewater pretreated with internal electrolysis, of wastewater output of the established A2O-MBBR system, and of the wastewater treated by the combination thereof. The wastewater was taken from a coking plant at Thai Nguyen Iron and Steel Joint Stock Company in Vietnam. COD, BOD5, NH4+-N, phenol, and pH of the input coal gasification wastewater were 2359, 1105, 319, 172 mg/L, and 8 ± 0.1, respectively. The conditions of internal electrolysis were as follows: 720 min of reaction time, pH = 4, 25 g/L Fe-C dosage, and 100 mg/L PAM dosage. After internal electrolysis process, the removal of COD, BOD5, NH4+-N, and phenol were 53.7%, 56.7% 60.5%, and 73.3%, respectively. After 24 h of treatment, the treatment efficiencies of the combined treatment process are as follows: 100% phenol removal, 71.3% of TSS removal; 97.7% reduction of BOD5, and 97.1% reduction of COD; total N content reduced by 97.6%; total P content decreased by 81.6%; and NH4+-N content decreased by 97.5%. All above indicators after treatment have met QCVN 52: 2017/BTNMT (column A) Vietnamese standard for steel industry wastewater.

New insights into enhanced anaerobic degradation of coal gasification wastewater (CGW) with the assistance of magnetite nanoparticles

Magnetite nanoparticles (Fe3O4 NPs) was firstly used to enhance pollutants removal during coal gasification wastewater (CGW) treatment in anaerobic digestion (AD) system. Bench-scale results revealed that 200 mg/L and 20–40 nm of Fe3O4 NPs addition resulted in a maximum removal capacity of total phenol (TPh) at a temperature of 36 °C and hydraulic retention time (HRT) of 36 h. Meanwhile, Fe3O4 NPs addition reduced the oxidation reduction potential (ORP) values and biological toxicity, and enhanced the stability of AD system. Pilot-scale results showed that the TPh and chemical oxygen demand (COD) removal efficiency (53% and 49%) were obtained with the optimal dosage of Fe3O4 NPs. Moreover, electron nanowires may be established with Fe3O4 NPs assisted to perform direct interspecies electron transfer (DIET) among Geobacter, Pseudomonas and Methanosaeta species, and finally enhanced the pollutants removal efficiency.

Economic Analysis of Syngas Production by Coupling Coal Gasification Wastewater Treatment and Solid Oxide Cell System

Coal is the main energy source in China, and coal chemistry wastewater treatment has always been a research hotspot. For the large amount of concentrated organic wastewater, high cost caused by complex treatment process is the key issue. In this paper, the fixed bed Lurgi gasifier wastewater coupled with solid oxide cells (SOCs) system is employed for its treatment. Based on Aspen Plus software, the purified methane from marsh gas is sent to solid oxide fuel cell (SOFC) for electricity generation. While carbon dioxide separated from biogas purification and acid gas removal enters solid oxide electrolysis cell (SOEC) to produce syngas by co-electrolysis with steam.The simulation results show that the efficiency of SOFC is 48.5 %. The generated electric energy can be used for auxiliary equipment in wastewater treatment and SOEC to produce syngas, recycling of carbon dioxide. SOEC with wind power of 12.84 MW is enough to treat the waste gas generated by the 1,100 t/h Lurgi gasification wastewater treatment process. Economically, the cost of producing syngas, with high purity and fewer contaminant contents, is about 0.126 $/Nm3. It can be used to produce various chemicals, so as to further improve the economic benefit of wastewater treatment.