Degradation Of Coal Gasification Wastewater Research Articles

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.

Enhanced degradation of phenolic compounds in coal gasification wastewater by an iron‑carbon micro-electric field coupled with anaerobic co-digestion

Coal gasification wastewater contains many refractory and toxic pollutants, especially high concentrations of total phenols, which are difficult to degrade by microorganisms. The aim of our study is to explore the anaerobically enhanced degradation of coal gasification wastewater by an iron‑carbon micro-electric field coupled with anaerobic co-digestion. The optimal ratio of activated carbon to iron and the optimal dosage of co-substrate (glucose = 1500 mg/L) were investigated by batch tests. In the long-term operation of the iron‑carbon reactor, 1500 mg/L glucose was added into the influent, and carbon and iron in a ratio of 2:1 were added to the anaerobic sludge. The average effluent COD and total phenols concentrations were kept at approximately 455 and 56.3 mg/L, respectively, and removal rates of both reached 90% after treatment with the iron‑carbon micro-electric field coupled with anaerobic co-digestion in the iron‑carbon reactor. Moreover, compared with the control reactor, the methane production from the iron‑carbon reactor increased to 200 mL/day, with an increase in the methane production rate by 90%. Microbial community analysis indicated that hydrogenotrophic methanogens were enriched, and syntrophic metabolism via interspecies hydrogen transfer was enhanced. Direct interspecies electron transfer might occur between the potential electroactive bacteria Clostridium, Bacteroidetes, and Anaerolinea and the methanogens Methanosaeta, Methanobacterialies, and Methanobacterium for syntrophic metabolism through the iron‑carbon process coupled with anaerobic co-digestion.

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.

Performance, mechanism and stability of nitrogen-doped sewage sludge based activated carbon supported magnetite in anaerobic degradation of coal gasification wastewater

In current study, the UASB reactor was enhanced by nitrogen-doped sewage sludge based activated carbon supported Fe3O4 (Fe3O4/N-SBAC) for coal gasification wastewater treatment. The results showed that COD removal efficiency was increased to 64.4% with Fe3O4/N-SBAC assistance and the corresponding methane production rate achieved up to 1093.6 mL/d. Fe3O4/N-SBAC promoted microbial growth and enzymatic activity, leading to high extracellular polymeric substances and coenzyme F420 concentrations. Fe3O4/N-SBAC also facilitated the sludge granulation process with high particle size, substantial interspecific signal molecules and low diffusible signal factor. Microbial community analysis revealed that Fe3O4/N-SBAC might support direct interspecies electron transfer process, in which the enriched Geobacter was likely to communicate with Methanothrix via electrical connection, improving anaerobic degradation of coal gasification wastewater. Total phenols shock and pH impact revealed that reactor stability was enhanced in the Fe3O4/N-SBAC-supplemented system.

Effective oxidative degradation of coal gasification wastewater by ozonation: A process study

Coal gasification wastewater (CGW) has attracted considerable industrial attention because of its high toxicity and poor biodegradability. Ozonation is a promising process for CGW treatment. In this study, the effects of ozone concentration, pH, and ozonation time on CGW treatment were investigated. The results confirmed that CGW was degraded effectively and that the chemical oxygen demand (COD) was reduced from 1057 to 362 mgL−1, utilizing 50 mgL−1 ozone for 90 min. Further, the color of CGW changed from brown to clear and colorless, and the pH decreased from 8.5 to 4.7. Importantly, molds were observed in the oxidized CGW after 14 d at room temperature (23 ± 2 °C), indicating that CGW is significantly biodegradable by ozonation. The CGW components were extracted with three different organic solvents (chloroform, n-hexane, and benzene), and their compositions were analyzed by gas chromatography–mass spectrometry (GC–MS) before and after ozonation. The results proved that considerable amounts of highly toxic refractory compounds in CGW, such as phenolic compounds, polynuclear aromatic hydrocarbons (PAHs), and nitrogenous heterocyclic compounds (NHCs), were degraded to compounds that included olefins, carboxylic acids, and cycloalkanes, or minerals, which are relatively environmentally benign. Moreover, the number of substances in CGW decreased significantly from 127 to 74 after ozonation. Summarily, ozonation is a promising approach for the treatment of highly toxic refractory wastewater, such as CGW.

Potential enhancement of direct interspecies electron transfer for anaerobic degradation of coal gasification wastewater using up-flow anaerobic sludge blanket (UASB) with nitrogen doped sewage sludge carbon assisted

Waste sewage sludge was converted into the novel conductive material of nitrogen doped sewage sludge carbon (N-SC) to enhance anaerobic degradation of coal gasification wastewater (CGW). The results indicated that N-SC played a significant role in enhanced efficiencies, with chemical oxygen demand (COD) removal efficiency increased by 25.4%, methane production rate improved by 68.1% and total volatile fatty acids (VFA) decreased by 37.5% than that of controlled reactor. The conductivity, activity of electron transport, and extracellular polymeric substances (EPS) of anaerobic sludge were remarkably enhanced with N-SC, which promoted sludge granulation and supplied better conductive environment for microorganisms. The microbial community analysis revealed that potential enhancement of direct interspecies electron transfer (DIET) was achieved by electrical connection between enriched Geobacter, Pseudomonas and Methanosaeta with N-SC assisted, which enhanced the anaerobic degradation of CGW. Moreover, anaerobic degradation with N-SC had higher capacity to resist acidic shocks, facilitating the process stability.

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

The up-flow anaerobic sludge blanket (UASB) system with graphene assisted was developed for coal gasification wastewater (CGW) treatment. Short-term results showed that optimal graphene addition (0.5 g/L) resulted in a more significant enhancement of methane production and chemical oxygen demand (COD) removal compared with that of the optimal activated carbon addition (10.0 g/L). Long-term results demonstrated that COD removal efficiency and methane production rate with graphene assisted achieved 64.7% and 180.5 mL/d, respectively. In addition, graphene could promote microbes accumulation and enzymes activity, resulting in higher extracellular polymeric substances (EPS) and coenzyme F420 concentrations. X-ray Diffraction (XRD) analysis indicated that chemical of graphene changed insignificantly during the experiment. Meanwhile, with graphene assisted, cells were attached together to form microbial aggregates to facilitate sludge granulation process. Furthermore, the enriched Geobacter and Pseudomonas might perform direct interspecies electron transfer (DIET) with Methanosaeta via biological electrical connection, enhancing the anaerobic degradation of CGW.