Pretreatment of coal gasification wastewater by adsorption using activated carbons and activated coke

Efficient flocculation pretreatment of coal gasification wastewater by halophilic bacterium Halovibrio variabilis TG-5

The isolated halophilic bacterial strain Halovibrio variabilis TG-5 showed a good performance in the pretreatment of coal gasification wastewater. With the optimum culture conditions of pH = 7, a temperature of 46 °C, and a salinity of 15%, the chemical oxygen demand and volatile phenol content of pretreated wastewater were decreased to 1721 mg/L and 94 mg/L, respectively. The removal rates of chemical oxygen demand and volatile phenol were over 90% and 70%, respectively. At the optimum salinity conditions of 15%, the total yield of intracellular compatible solutes and the extracellular transient released yield under hypotonic conditions were increased to 6.88 g/L and 3.45 g/L, respectively. The essential compatible solutes such as L-lysine, L-valine, and betaine were important in flocculation mechanism in wastewater pretreatment. This study provided a new method for pretreating coal gasification wastewater by halophilic microorganisms, and revealed the crucial roles of compatible solutes in the flocculation process.

Modeling of cadmium(II) removal in a fixed bed column utilizing hydrochar-derived activated carbon obtained from discarded mango peels

Cadmium is found in many underdeveloped countries' aquatic bodies. Therefore, contaminated water should be treated before consumption; henceforth, efficient and customized point-of-use filtration is foreseeable. Traditionally, carbon-based sorbents have been utilized for such treatments, but alternative sources are also being investigated. Hydrochars made from mango peels using a thermal activation process were employed as an adsorbent instead of activated carbon in this investigation. The prepared material was porous with active surface functionalities, and the interaction of cadmium with the surface was possibly ion-exchange in nature. The performance of a material for a candle water filtering system with a 2.5 cm internal diameter and a 30.48 cm column height was determined using the parameters acquired by the Thomas model. The material was found to be highly efficient at 453.5 L/min/Filter water, whereas 31670.6 L/min/Filter can be treated if the break point and exhaustion point are considered, respectively, as the candle replacement time. These findings indicate that activated hydrochar might be a suitable sorbent for removing cadmium ions from contaminated water.

Characteristics of Water Contaminants from Underground Coal Gasification (UCG) Process—Effect of Coal Properties and Gasification Pressure

One of the most important issues during UCG process is wastewater production and treatment. Condensed gasification wastewater is contaminated by many hazardous compounds. The composition of the generated UCG-derived wastewater may vary depending on the type of gasified coal and conditions of the gasification process. The main purpose of this study was a qualitative and quantitative characterization of the UCG wastewater produced during four different UCG experiments. Experiments were conducted using semi-anthracite and bituminous coal samples at two distinct pressures, i.e., 20 and 40 bar. The conducted studies revealed significant relationships between the physicochemical composition of the wastewater and the coal properties as well as the gasification pressure. The strongest impact is noticeable in the case of organic pollutants, especially phenols, BTEX and PAH’s. The most abundant group of pollutants were phenols. Conducted studies showed significantly higher concentration levels for bituminous coal: 29.25–49.5 mg/L whereas for semi-anthracite effluents these concentrations were in much lower range 2.1–29.7 mg/L. The opposite situation occurs for BTEX, higher concentrations were in wastewater from semi-anthracite gasification: 5483.1–1496.7 µg/L, while in samples from bituminous coal gasification average BTEX concentrations were: 2514.3–1354.4 µg/L. A similar relationship occurs for the PAH’s concentrations. The higher values were in case of wastewater from semi-anthracite coal experiments and were in range 362–1658 µg/L while from bituminous coal gasification PAH’s values are in lower ranges 407–1090 µg/L. The studies conducted have shown that concentrations of phenols, BTEX and PAH’s decrease with increasing pressure. Pearson’s correlation analysis was performed to enhance the interpretation of the obtained experimental data and showed a very strong relationship between three parameters: phenols, volatile phenols and CODcr.

Adsorption of ammonia nitrogen and phenol onto the lignite surface: An experimental and molecular dynamics simulation study

Ammonia nitrogen and phenol are typical inorganic and organic pollutants in the coal chemical wastewater, respectively. In this study, the adsorption characteristics of ammonia nitrogen and phenol on lignite were investigated through experimental and molecular dynamics simulations. The results show that the adsorption of ammonia nitrogen was carried out via ion exchange, which was significantly faster than the adsorption of phenol driven by the π-π interaction. In the binary adsorption, the surface electronegativity of lignite decreased with the adsorption of ammonia nitrogen thereby promoting the adsorption of phenol. However, the extent of ammonia nitrogen adsorption was slightly reduced in the presence of phenol. Molecular dynamics simulation results indicated that the adsorption of phenol molecules on the lignite surface was closer than that of ammonium ion. The addition of ammonium ions could enhance the adsorption of phenol molecules on the lignite surface. The simulation results were well consistent with the experimental findings. This study indicates lignite has a promising potential in coal chemical wastewater adsorption pretreatment.

Internal Micro-electrolysis Using Fe/C Material for Pre-Treatment of Concentrated Coking Wastewater

Untreated coking effluent presents a great challenge for sustainable development of the steel industry and environment preservation. In this study, an internal micro-electrolysis method using Fe/C materials was employed for pretreatment of real coking wastewater with high mass concentration. The Fe/C materials were prepared by Fe powder and graphite powder; and the characteristics of surface morphology, structure, composition of the synthesized materials were examined by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDS). The effects of factors namely dosage of Fe/C material, treatment time, initial pH and temperature were investigated via chemical oxygen demand (COD) and phenol removal efficiencies. Optimal treatment efficiency was attained at pH of 4, Fe/C dosage of 40 g/L, treatment time of 360 minutes and temperature of 25°C. After the internal electrolysis process, the values of COD, BOD5, and phenol of the wastewater were 6500, 4850 and 0.1 mg/L, respectively.

Fate of antibiotic resistance genes during high-solid anaerobic co-digestion of pig manure with lignite

Lignite could be used to promote methane production during high-solid anaerobic co-digestion (HS-AcoD) of pig manure, however, the effects of lignite amendment on the fate of ARGs during HS-AcoD are unknown. Here, we explored the influence of lignite (0%, 8%, 16%, 32%, and 64%) on the fate of ARGs during HS-AcoD of pig manure. The results showed that 16% lignite reduced the absolute abundance of ARGs by 28.71% compared with the 0% lignite treatment. Variation partitioning analysis suggested the combined effect of microbial community, mobile genetic elements (MGEs) and environmental factors was the major driver shaping the pattern of ARGs. The potential hosts of ARGs were Bifidobacterium, Lactobacillus, Tissierella and Streptococcus. Structural equation models analysis suggested lignite indirectly impacted the pattern of ARGs by significantly reducing the abundance of microbial community and MGEs. These findings give an insight into the mechanistic understanding of the lignite influence on the reduction of ARGs during HS-AcoD.

New insights of enhanced anaerobic degradation of refractory pollutants in coking wastewater: Role of zero-valent iron in metagenomic functions

Coking wastewater (CWW) has long been a serious challenge for anaerobic treatment due to its high concentrations of phenolics and nitrogen-containing heterocyclic compounds (NHCs). Herein, we proposed and validated a new strategy of using zero-valent iron (ZVI) to strengthen the anaerobic treatment of CWW. Results showed that COD removal efficiencies was increased by 9.5-13.7% with the assistance of ZVI. GC-MS analysis indicated that the removal of phenolics and NHCs was improved, and the intermediate 2(1H)-Quinolinone of quinoline degradation was further removed by ZVI addition. High-throughput sequencing showed that phenolics and NHCs degraders, such as Levilinea and Sedimentibacter were significantly enriched, and the predicted gene abundance of xenobiotic degradation and its downstream metabolic pathways was also increased by ZVI. Network and redundancy analysis indicated that the decreased oxidation-reduction potential (ORP) by ZVI was the main driver for microbial community succession. This study provided an alternative strategy for strengthening CWW anaerobic treatment.

Effective adsorption of diclofenac sodium from neutral aqueous solution by low-cost lignite activated cokes

Activated cokes have attracted great interest inwater treatment to remove organic pollutants due to their low cost and specific textural properties. In this study, adsorptive removal of diclofenac sodium (DCF) from neutral aqueous solution by available lignite activated cokes (LACs) was reported for the first time. Diclofenac sodium could be quickly removed from aqueous solution by LAC-2, with the maximum Langmuir adsorption capacity q_m of 224 mg/g at pH 6.5. Characterization results (including scanning electron microscopy, transmission electron microscopy, elemental analyses, Boehm titrations, N₂ adsorption-desorption isotherms and Fourier transform infrared spectroscopy) and a series of adsorption kinetics, adsorption isotherms model studies revealed that high porosity with developed macro- and micropore structures on LAC-2, as well as high content of phenolic groups, could obviously enhance the DCF adsorption capacity and rate. Moreover, LAC-2 showed high affinity towards DCF at low concentrations, as well as good reusability after three adsorption-desorption cycles. pH effect studies revealed that hydrogen-bonding interaction plays an important role during adsorption, accompanied with certain contribution from electrostatic interaction and π-π interaction. This study indicates the promising potential of LAC-2 as an efficient, low-cost and recyclable material for DCF removal from water bodies.

Valorization of poly(ethylene)terephthalate wastes into nanoporous carbons for the adsorption of 1,3-diphenylguanidine from an aqueous solution

Carbon prepared by using MgO templating and KOH activation has a better absorption capacity for DPG.

Adsorption of Organic Constituents from Reverse Osmosis Concentrate in Coal Chemical Industry by Coking Coal

To solve the unwieldy problem of coal chemical wastewater reverse osmosis concentrate (ROC), a novel treatment method in which coking coal was used to adsorb the organic from ROC and the adsorption mechanism involved was investigated. The results showed that the organic components in the ROC of coal chemical industry can be effectively absorbed by the coking coal and the total organic carbon, UV254 and chromaticity of treated ROC reduced by 70.18%, 70.15% and 59.55%, respectively, at the coking coal dosage of 80 g/L. The isothermal adsorption data were fitted to the Langmuir model well. The kinetics were expressed well by the quasi-second-order kinetic model. The intragranular diffusion model and the BET (Acronym for three scientists: Brunauer–Emmett–Teller) test showed that the adsorption occurred mainly on the surface of the coking coal and its macropores and mesopores. When the pollutants further diffused to the mesopores and micropores, the adsorption rate decreased. The result of X-ray photoelectron spectroscopy and fourier transform infrared spectroscopy spectra showed that the coking coal mainly adsorbed the nitrogen and oxygen species and the halogenated hydrocarbon organic compounds in the ROC. The chlorinated hydrocarbons and heterocyclic organics in ROC are adsorbed on the surface of coking coal.

Overview of the state of the art of processes and technical bottlenecks for coal gasification wastewater treatment

CGWW is major waste stream resulting from a number of activities of the low/medium temperature gasification unit that occurs during the production of natural gas. The resulting effluent contains a broad spectrum of organic and inorganic contaminants and exerts a negative influence on the environment, mainly due to the presence of toxic and refractory compounds. So far, various technologies have been applied for treatment of CGWW, while few reviews are available in the literature. Thus, this review attempts to offer a comprehensive picture about CGWW. An overview about pretreatment, biological and advanced processes for treatment of CGWW is presented, and the degradation mechanism of toxic and refractory pollutants is also elaborated. Technical bottlenecks existing in the operation of coal chemical industries, including foam proliferation, odors and biotoxicity risk, are detailed analyzed. Finally, the prospects of treatment for CGWW are discussed based on the concept of "wastewater is money". The review can be provided as an effective technical support for the construction and operation of coal gasification industries.

Influence of surface modification by sulfuric acid on coking coal's adsorption of coking wastewater

Coking coal, the raw material of a coke plant, was applied to the adsorption of coking wastewater. In this study, coking coal was directly treated with sulfuric acid to improve its surface properties and adsorption ability. Acid treatment was carried out at various concentrations, by varying from 0.001 to 1 mol/L. The samples were characterized by ash content analysis, scanning electron microscope (SEM), N₂ adsorption-desorption analysis, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), wettability analysis, and zeta potential analysis. These results demonstrated that H⁺ could react with inorganic minerals, which resulted in a significant variation of the chemical composition and the structure of coal surface. Furthermore, both the ash content and the surface content of O = C-O, C = O and C-O groups declined gradually as the concentration of sulfuric acid increased, while the surface area and pore volume of micropore, the lipophilic and hydrophobic properties, and zeta potential magnitude increased, resulting in enhanced hydrophobic and Van der Waals' forces between the fine coal and organic pollutants. Characterization modification showed a better performance in adsorption, the removal rate enhanced from 23% to 42% after treated by 1 mol/L sulfuric acid. It was concluded that the acid activation modified the lipophilic and hydrophobic properties, the surface charge properties, surface area and pore volume, the content of oxygen functional groups, all of which could be potentially useful in wastewater adsorption.

An advanced anaerobic biofilter with effluent recirculation for phenol removal and methane production in treatment of coal gasification wastewater

An advanced anaerobic biofilter (AF) was introduced for the treatment of coal gasification wastewater (CGW), and effluent recirculation was adopted to enhance phenol removal and methane production. The results indicated that AF was reliable in treating diluted CGW, while its efficiency and stability were seriously reduced when directly treating raw CGW. However, its performance could be greatly enhanced by effluent recirculation. Under optimal effluent recirculation of 0.5 to the influent, concentrations of chemical oxygen demand (COD) and total phenol in the effluent could reach as low as 234.0 and 14.2mg/L, respectively. Also, the rate of methane production reached 169.0mLCH4/L/day. Though CGW seemed to restrain the growth of anaerobic microorganisms, especially methanogens, the inhibition was temporary and reversible, and anaerobic bacteria presented strong tolerance. The activities of methanogens cultivated in CGW could quickly recover on feeding with glucose wastewater (GW). However, the adaptability of anaerobic bacteria to the CGW was very poor and the activity of methanogens could not be improved by long-term domestication. By analysis using the Haldane model, it was further confirmed that high effluent recirculation could result in high activity for hydrolytic bacteria and substrate affinity for toxic matters, but only suitable effluent recirculation could result in high methanogenic activity.

Effect of effluent recirculation rate on the performance of anaerobic bio-filter treating coal gasification wastewater under co-digestion conditions

In this study, anaerobic biofilter (AF) was adopted for anaerobic co-digestion of potato starch wastewater (PSW) and coal gasification wastewater (CGW).