Oily Sludge Research Articles

Experimental and kinetic study of heavy metals transformation in supercritical water gasification of oily sludge

As an industrial organic waste, oily sludge can be transformed into valuable syngas by supercritical water gasification (SCWG) technology. The transformation behaviors of heavy metals in SCWG of oily sludge must be considered to prevent the secondary pollution attributed to the high contents of heavy metals in oily sludge. In this work, the gasification products distribution after SCWG of oily sludge in a batch reactor under different reaction conditions (550–700 °C, 1–15 min) was studied. The distributions of heavy metals (Cu, Cr and Zn) in different forms including acid-soluble and exchangeable fraction (F1), reducible fraction (F2), oxidizable fraction (F3), residual fraction (F4) and heavy metal ions in liquid residues (M+) were presented and the transformation trend of those five fractions during the SCWG process was demonstrated. A reaction pathway and quantitative kinetic model of Zn transformation in SCWG were proposed. The results indicated that gas yield was enhanced at higher reaction temperature and longer residence time. Heavy metals in oily sludge were mainly composed of F3 and M+, they tended to deposit in F4 with increasing reaction temperature and residence time, which was stable and environmentally harmless. F3 showed better reactivity than F2 and contributed more to the formation of F4. Enhancing the transformation of Zn ions in liquid residues to more stable forms was necessary. This study highlighted that SCWG of oily sludge could realize energy utilization and heavy metals stabilization.

Production of Mesoporous Magnetic Carbon Materials from Oily Sludge by Combining Thermal Activation and Post-Washing.

In this work, the oily sludge (OS) from a local waste oil recycling plant was reused as a precursor for producing porous magnetic carbon composites (CC) by pyrolysis, followed by carbon dioxide activation. Based on the thermogravimetric analysis (TGA) of the OS feedstock, the preparation experiments were performed at 800–900 °C. From the pore analysis of the CC products, it indicated an increasing trend, as the BET surface area greatly increased from about 1.0 to 44.30 m2/g. In addition, the enhancement effect on the pore properties can be consistently obtained from the acid-washed CC products because the existing and new pores were reformed due to the leaching-out of inorganic minerals. It showed an increase from 32.27 to 94.45 m2/g and 44.30 to 94.52 m2/g at 850 and 900 °C, respectively, showing their mesoporous features. These porous and iron-containing features were also observed by the scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). In addition, the adsorption removal of total organic carbon (TOC) in the raw wastewater, by the CC product, showed its high performance (>80%).

A makeup remover-inspired chitosan-based emulsion for heavy oil removal in oily sludge treatment

During oil production processes, oily sludges are inevitably produced and accumulating, which are extremely hazardous to our living environment. Due to their complex compositions mainly containing oil-contaminated solids and emulsified water and oil, it has been always a great challenge to treat oily sludges before solids can be properly disposed, and oil and water can be recycled. In this study, inspired by the makeup remover and for the first time, a chitosan-based emulsion was developed to treat oily sludges. The emulsion can efficiently remove the heavy oil from solids with removal efficiency of ∼94.7%–98.0% varying with solution pH, sludge to emulsion ratio, and settling time. It has been revealed that the oil liberates from solid surfaces resulted from the wettability alteration of the solid surface in emulsion solution due to the decrease in oil/water interfacial tension as well as oil layer softening by the solvent penetration. A rag layer formed after oil liberation due to the unresolved dispersed oil droplets carrying solid particles, which was further treated by the addition of ∼1.4–6.1 wt‰ of HCl to the mixture. With HCl addition, the dispersed oil drops were found to coalesce attributed the charge neutralization and interfacial property change of chitosan molecules at oil/water interfaces evident from the zeta potential measurement. Our work proposes an environmental-friendly approach to treat oily sludges, and provides valuable information on the oil removal mechanisms using emulsion solution shielding lights on the development of emulsion-based treating technology for both oily sludge and oil-contaminated solids treatment.

Synergistic Preparation of Sludge Carbon from Oily Sludge and Walnut Shells.

The preparation process of synergistic preparation of sludge carbon by oily sludge and walnut shells are divided into two stages: carbonization preparation of a carbon precursor and activation preparation of sludge carbon. The preparation conditions of the carbon precursor are 2.5:1 mass ratio of oily sludge and walnut shells, carbonization temperature is 450°C, and time is 2 h. There are some pores on the surface of the prepared carbon precursor, the heavy metal content of leachate does not exceed the standard, and the use process will not cause heavy metal pollution. Intensive research is carried out on factors affecting the preparation of sludge carbon by activation of the carbon precursor by the orthogonal experiment and single-factor experiment. The optimal activation conditions are determined by using ZnCl2 as an activator, mass ratio of the carbon precursor to ZnCl2 is 1:4, activation temperature is 800°C, heating rate is 15°C/min, and activation holding time is 1 h. The surface of sludge carbon is distributed with many pores, several layers of small pores can be seen deeply in the large holes, and pore size distribution is dominated by micropores and mesopores. BET Specific surface area, pore volume, average pore, and iodine value are 1772.69 m2/g, 1.98 cm3/g, 1.64 nm, and 1011.65 mg/g, respectively, which surpasses commercially available activated carbon comprehensively.

Effect of the Anode Structure on the Performance of Oily Sludge Sediment Microbial Fuel Cells.

The anode is considered to be a key factor to improve the single-chamber bioelectrochemical system’s efficiency to degrade oily sludge in sediment while generating electricity. There are few studies on the effect of the anode structure on the performance of oily sludge MFCs systematically. In this paper, an oily sludge bioelectrical system was constructed using carbon felt and carbon plate as anode materials, adjusting the anode material arrangement as transverse and longitudinal, and using different anode materials from single to sextuple anodes. The results of this study showed that the rate of degradation of oily sludge was greater with carbon felt (17.04%) than with the carbon plate (13.11%), with transverse (23.61%) than with the longitudinal (19.82%) arrangement of anodes, and with sextuple anodes (33.72%) than with a single anode (25.26%) in the sediment microbial fuel cells (SMFCs). A similar trend was observed when the voltage, power density, and electromotive force (EMF) of SMFCs were estimated between the carbon felt and carbon plate, transverse and longitudinal arrangements, single and sextuple anodes. It is concluded that the proper adjustment of anode arrangements, using carbon felt as an anode material, and increasing the number of anodes to six may accelerate the rate of degradation of oily sludge in oily sludge sediment microbial fuel cells (SMFCs). Furthermore, the electricity generation performance was also improved.

An electricity-generating bacterium separated from oil sludge microbial fuel cells and its environmental adaptability.

Electricity-generating bacteria as biocatalysts for microbial fuel cells (MFCs), their species, and power generation performance determine the pollution control and power generation performance of MFCs. And there are few studies on the types and performance of electricity-generating bacteria isolated from oily sludge microbial fuel cells. For improving the power generation performance of oily sludge MFCs, an electricity-generating bacterium was isolated from the oily sludge. More importantly, the adaptability of nitrogen to phosphorus ratio, temperature, and pH of the electricity-generating bacteria were adjusted by a controlled variable method. The results of this study showed that the electricity-generating bacterium was identified as Bacillus cereus, with a rod-shaped cell, about 0.5-1.0μm in length. The optimal nitrogen-phosphorus ratio, temperature, and pH of MFCs were 4.67:1, 25 ℃, and pH = 7, respectively. Its maximum power density, COD, and oil removal rate was up to 65 mW·m-3, 90.51%, and 87.76%, respectively. The study of this functional bacterium will provide beneficial assistance for the improvement of oil removal and power generation performance of oily sludge MFCs.

Iron-biochar production from oily sludge pyrolysis and its application for organic dyes removal.

In this study, a single-step pyrolysis approach was developed to directly convert oily sludge (OS) with high iron content into a magnetic iron-char catalyst for organic dyes removal. Magnetic iron-char catalysts were employed to degrade crystal violet (CV), methylene blue (MB), and sunset yellow (SY). The OC800 iron-char catalyst prepared from OS was not only rich in iron (mainly stable Fe3O4), but also showed favorable pore structures. Effects of operation parameters like temperature, H2O2 dosage, and pH on dye removal based on Fenton degradation were examined. In OC800 Fenton system (0.5mL H2O2, 500mg/L dye concentration, and pH=2 in 50mL solution), the maximum dye removal capacities of SY, CV, and MB were 83.61, 639.19, and 414.25mg/g, respectively. In dyes degradation experiments, the prepared catalyst could be reused (more than 3 successive cycles) due to higher stability and less leaching of iron. One-step pyrolysis of OS with high iron content thereby represents a promising approach to transform sludge waste to functional biochar that removes hazardous dyes.

Carbonaceous material prepared by pyrolysis of refinery oily sludge for removal of flotation collectors in wastewater.

The carbonaceous material (CM) prepared by refinery oily sludge was proposed to remove flotation collectors, butyl xanthate (BX), and diethyldithiocarbamate (DDTC) in synthetic wastewater. The effects of the CM on removal efficiency, adsorption kinetics, and isotherms were experimentally carried out. The surface structure and composition of CM were characterized by BET isotherm, XRD, and SEM-EDS, and the concentration of BX and DDTC was tested by UV-VIS spectrometer. The adsorption behavior and removal mechanism were investigated by zeta potential, ToF-SIMS, FTIR, etc. The removal efficiencies of BX and DDTC were both more than 99%, and the maximum adsorption capacity peaked when the pH of the solution was neutral. The two collectors were heterogeneous adsorption on the surface of CM. BX, DDTC, and related metal compounds were found on the surface of carbonaceous material, confirming the existence of both physical and chemical adsorption, and physical adsorption accounted for the main mechanism. It is proved that BX and DDTC can be removed by carbonaceous material and realize the high-effective utilization of refinery oily sludge.

Analysis of Pyrolysis Characteristics of Oily Sludge in Different Regions and Environmental Risk Assessment of Heavy Metals in Pyrolysis Residue.

As a resource treatment method, pyrolysis realizes the recovery of oil and immobilization of heavy metals in oily sludge (OS). The results showed that the composition of OS had little effect on the trend of the whole pyrolysis process, but it had different effects on the mass loss and maximum weight loss rate at each pyrolysis stage. SEM–EDS results showed that the pyrolysis residue had a porous internal structure, which was similar to that of activated carbon. The elements S, Ca, O, Fe, Al, and Si were embedded in the carbon skeleton. After OS pyrolysis, the oil content of the solid residue was far less than 2%, which met the pollution control requirements for comprehensive utilization specified in China’s oil and gas industry standard. At the same time, the ratio of exchangeable fraction decreased and the ratio of residual fraction increased after OS pyrolysis. The potential ecological hazard coefficient (Er) of Cd in OS2, OS2-500, and OS2-600 was greater than 40, which were strong and medium hazards. The Er values of OS2-700 and other metals were far lower than 40, which were low hazards. With the increase of pyrolysis temperature, the comprehensive ecological hazard index (RI) of heavy metals in the residue gradually decreased and the RI value of OS2-700 decreased to 28.01. Therefore, the pyrolysis residue had an internal porous structure and controllable environmental risk. It could be used as an adsorption material for heavy metals to realize the comprehensive utilization of OS.

Assessment of palladium nanoparticles as chemical modifier for lead determination in leached extracts from petroleum waste by high-resolution continuum source atomic absorption spectrometry

ABSTRACT Palladium nanoparticles were evaluated as a potential chemical modifier for lead determination by high-resolution continuum source graphite furnace atomic absorption spectrometry. Hydrophilic palladium nanocubes and palladium nanospheres were synthesised with sizes varying from 3 to 22 nm. Positive effects in terms of sensitivity and thermal stability upon the use of palladium nanoparticles were observed, especially using the 3 nm spherical-shaped. The mass of modifier influenced the thermal stability and relative signal intensity of the analyte, although the effectiveness of the modifier appeared to be suppressed to an important extent in the presence of matrix components of the leached extracts obtained from petroleum wastes. The optimised pyrolysis and atomisation temperatures were, respectively, 800 °C and 2300 °C, using 200 ng of 3 nm palladium nanoparticles. The limit of detection (4 µg L−1) and the precision (better than 18 %) were considered satisfactory for the proposed analysis. The method accuracy, evaluated by recovery tests and by comparison with the results obtained using inductively coupled plasma mass spectrometry, was proven adequate to enable the determination of Pb in leached extracts from petroleum waste. The method was successfully applied to determine lead in leached extracts obtained from oily sludge and drill cuttings and the obtained concentrations ranged from <13 to 354.4 µg L−1.

Characteristics and kinetic analysis of the catalytic pyrolysis of oily sludge under new nickel-ore–based catalysts

Characteristics and kinetic analysis of the catalytic pyrolysis of oily sludge under new nickel-ore–based catalysts

Behavior Study of Migration and Transformation of Heavy Metals during Oily Sludge Pyrolysis

Behavior Study of Migration and Transformation of Heavy Metals during Oily Sludge Pyrolysis

Investigation and prediction of co-pyrolysis between oily sludge and high-density polyethylene via in-situ DRIFTS, TGA, and artificial neural network

Oily sludge (OS), a hazardous waste produced in a large amount in petroleum industries, has raised great interest in research, and thermal treatment method such as pyrolysis is promising to achieve the goal. This research studied the pyrolysis behavior during co-pyrolysis of OS and high-density polyethylene (HDPE, plastic waste model component) with different blend ratios. The changes of functional groups against pyrolysis temperature were detected via in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The interactive effect between the two feedstocks during co-pyrolysis was analyzed via thermogravimetric analysis (TGA). The DRIFTS showed that the pyrolysis of HDPE can provide abundant •CH3 free radicals which may accelerate the pyrolysis of OS. The disparities between theoretical and experimental thermogravimetric/derivative thermogravimetry (TG/DTG) curves of mixtures indicated a synergistic interaction during co-pyrolysis. Besides, the activation energy of co-pyrolysis was obtained based on kinetic analysis, which showed that the average activation energy followed the trend of O3H1 < OS < O1H1 < HDPE < O1H3. In addition, two artificial neural network (ANN) models, namely ANN model Ⅰ with training and testing R2 of 0.99 (for prediction of interactive effect) and ANN model Ⅱ with training and testing R2 of 0.92 (for prediction of activation energy), were established and validated by comparing with the experimental data, which showed satisfied credibility. Ultimately, the two ANN models were used to reversely guide and optimize experiment design for the highest synergistic effect and the minimum activation energy. This study offers a new insight and strategy to aid pyrolysis experimental studies.

Fe-NX-C material with excellent supercapacitor performance prepared through oleic acid acidification pretreatment—Oily sludge pyrolysis process

Heteroatom-doped carbon materials derived from oil-bearing sludge exhibit excellent supercapacitor performance due to their unique electronic and chemical properties. However, the complex composition of heteroatoms in oil-bearing sludge makes it difficult to achieve sufficient and directional doping by direct pyrolysis. In this paper, an oleic acid pretreatment-roasting-secondary activation strategy was developed to make full use of hydrocarbons, iron- and nitrogen-containing compounds in oil-bearing sludge to prepare Fe-NX-C materials with excellent electrochemical properties. Characterization results such as transmission electron microscopy (TEM) and N2 adsorption analysis showed that the best sample had a hierarchical pore structure and uniform Fe and N element loading. X-ray photoelectron spectroscopy (XPS) analysis found that the addition of oleic acid can promote the formation of Fe-Nx, and the dosage of oleic acid will affect the content of Fe-Nx in the carbon materials. Electrochemical characterization of this supercapacitor material was conducted. The best sample's specific capacitance was as high as 293.6 F g−1 at the current density of 0.5 A g−1, and the capacitance retention rate could still reach 71.5% at the current density of 10 A g−1. The assembled button-type symmetrical supercapacitors had an energy density of 8.68 Wh kg−1 and a power density of 137.53 W kg−1, which is much higher than those of most other waste-based carbon materials. This work presents a new idea for the preparation of heteroatom doped carbon materials with excellent capacitive properties from oily sludge, which provides a new reference for the treatment and resource utilization of oily sludge.

Efficient Separation and Recovery of Petroleum Hydrocarbon from Oily Sludge by a Combination of Adsorption and Demulsification.

The treatment of oily sludge (OS) can not only effectively solve environmental pollution but also contribute to the efficient use of energy. In this study, the separation effect of OS was analyzed through sodium lignosulfonate (SL)-assisted sodium persulfate (S/D) treatment. The effects of SL concentration, pH, temperature, solid–liquid ratio, revolving speed, and time on SL adsorption solubilization were analyzed. The effects of sodium persulfate dosage, demulsification temperature, and demulsification time on sodium persulfate oxidative demulsification were analyzed. The oil removal efficiency was as high as 91.28%. The results showed that the sediment was uniformly and finely distributed in the S/D-treated OS. The contact angle of the sediment surface was 40°, and the initial apparent viscosity of the OS was 56 Pa·s. First, the saturated hydrocarbons and aromatic hydrocarbons on the sediment surface were adsorbed by the monolayer adsorption on SL. Stubborn, cohesive oil agglomerates were dissociated. Sulfate radical anion (SO4−·) with a high oxidation potential, was formed from sodium persulfate. The oxidation reaction occurred between SO4−· and polycyclic aromatic hydrocarbons. A good three-phase separation effect was attained. The oil recovery reached 89.65%. This provides theoretical support for the efficient clean separation of oily sludge.

Catalytic pyrolysis of oily sludge with iron-containing waste for production of high-quality oil and H2-rich gas

Oily sludge (OS), as a kind of organic hazardous waste with complex components, is suitable for treatment by pyrolysis. To attain effective removal of petroleum hydrocarbons and explore synergistic disposal for multi-source solid wastes, the catalytic effects of steel slag (SS) and red mud (RM) were investigated in this work. They could reduce the activation energy, accelerate OS degradation and shift the degradation of petroleum hydrocarbons towards lower temperature. What’s more, RM with higher iron content worked better, gained more pyrolytic gas and higher H2 production as well. More pyrolytic gas production was obtained when RM addition was at a low proportion. However, excessive catalyst would play a certain inhibitory role. The addition of RM promoted oil recovery at low temperature (400–500 °C) but brought more gas originating from oil cracking at high temperature (600 °C). At 400 °C, the oil yield elevated continuously with prolonging retention time. Nevertheless, even if the retention time was long enough, the harmless disposal for OS could not be completed with the catalysis of RM. Finally, the pristine minerals in RM were co-pyrolysis with OS individually to explore catalytic contributions. Metal oxides could enhance the gas yield and reduce the oil yield. The order of catalytic capacities was Fe2O3＞CaO＞SiO2＞Al2O3. Fe2O3 promoted H2 production and conversion from heavy oil into light fuels. Besides, Fe2O3 was reduced into Fe3O4 with part of [O] shifting into oil. CaO, SiO2, and Al2O3 could reduce the oxygen content in the pyrolytic oil through their acid-base properties to improve the oil quality. This work summarized the functions of various components in RM, might provide inspiration for getting insight into the application of collaborative treatment of different solid wastes.

Study on amino-directed modification of oil sludge-derived carbon and its adsorption behavior of bisphenol A in water

In order to remove bisphenol A (BPA) in wastewater, this paper reported an amino-functionalized oily sludge-derived carbon (GP-H-OSC) obtained by grafting amino groups using oily sludge as a precursor, which could quickly adsorb BPA in the wastewater. The adsorption results showed that the grafting modification method was more likely to form effective adsorption sites on the surface than the impregnation modification. FT-IR and Boehm titration results indicated that the oxidation modification strategy was beneficial in generating more carboxyl groups on the surface of the oily sludge-derived carbon, which could provide intermediate connection groups for the subsequent grafting. The SEM and BET results revealed that the polyethyleneimine (PEI) would form a dense mesoporous structure on the surface during the grafting process, which was conducive to the transport of pollutants. The adsorption process of BPA by GP-H-OSC conformed to the pseudo-second-order kinetic model and the Langmuir isotherm model. The maximum extent of BPA adsorption was 393.2 mg/g based on the Langmuir isotherm model. Based on the analysis of FT-IR and XPS, GP-H-OSC mainly trapped BPA in water through the formation of hydrogen bonds between the functional amino groups on the surface and the hydroxyl groups on BPA. Moreover, primary amines were more likely to form hydrogen bonds with hydroxyl groups on BPA than imines. The removal rate of GP-H-OSC for low concentration BPA wastewater could reach 95% within 1 h, and it still had strong adsorption performance after recycling experiments. In summary, it was feasible to graft PEI on the surface of sludge-derived carbon, and the obtained amino-functionalized carbon material could adsorb BPA quickly and efficiently, showing great potential in practical wastewater treatment.

Thermogravimetric-infrared analysis and performance optimization of co-pyrolysis of oily sludge and rice husks

In this paper, thermogravimetric-infrared spectroscopy was used to analyze co-pyrolysis of oily sludge (OS) from oil penetration and rice husks (RH) at various ratios (1:0; 3:1; 1:1; 1:3; 0:1), obtaining pyrolysis weight-loss behaviors, the laws of mutual synergy, and gas volatilization characteristics. The Coats-redfern and response surface method were employed to analyze kinetics and optimize pyrolysis, respectively. The Ti, Tmax, and Tf increase as the heating rate increases, and the weight loss increases in the second stage. With the increase of the proportion of RH, the Ti and Tmax of the mixture increase, while the Tf and residual content decrease. The co-pyrolysis of the OS and RH has synergistic effects. The addition of RH is beneficial to reduce the E of OS pyrolysis. The mixing ratio affects the strength of small-molecular-gases volatilization. When the RH ratio is 58.9% at 10K/min, the minimum predicted E and residual amount of co-pyrolysis are 58.602 kJ/mol and 42.6%, respectively.

Microwave catalytic co-pyrolysis of chlorella vulgaris and oily sludge: Characteristics and bio-oil analysis

Co-pyrolysis of Chlorella vulgaris (CV) and Oily sludge (OS) under different mixing ratios were investigated by microwave furnace. NiO, activated carbon (AC) and their 1:1 compound (N1A1) with different additions (5%, 10%, 15% and 20%) were selected as microwave additives to study the effects on optimum mixing ratio of co-pyrolysis. The results indicated that mixing ratio of CV/OS = 1:1 (C1O1) was optimum for co-pyrolysis. Besides, 10% AC was optimal on improving pyrolysis characteristics of the C1O1 group. The most significant synergistic interaction of NiO and AC occurred in the 10% N1A1 group. Moreover, hydrocarbons in bio-oil of the C1O1 group increased by 31.84% compared with theoretical values, while nitrogenous, oxygenated compounds decreased by 74.18% and 19.01%. Addition of 10% N1A1 in the C1O1 group increased aliphatic hydrocarbons by 22.44%, and decreased nitrogenous, oxygenated compounds by 41.79% and 36.58%. Overall, 10% N1A1 was conducive for the C1O1 group to obtain high-quality bio-oil.

Removal of Cr(VI) by biochar derived via co-pyrolysis of oily sludge and corn stalks

The co-pyrolysis of oily sludge with biomass to prepare carbon materials is not only an effective way to mitigate oily sludge pollution, but it is also a method of obtaining carbon materials. In this study, a carbon material (OS-CS AC) was obtained by the direct co-pyrolysis of oily sludge (OS) and corn stalks (CS) and then applied to Cr(VI) removal. According to the hydroxy and carboxy masking experiments and the characterization of OS-CS AC by FT-IR, SEM, XPS, XRD, and N2 physical adsorption–desorption, Cr(VI) can be adsorbed efficiently through pore filling, the surface oxygen-containing functional groups can promote the reduction of Cr(VI) to Cr(III) through electron donors, and the greater the electrostatic attraction between the electron-donating functional groups of OS-CS AC and the Cr(VI) is, the stronger the ability to remove Cr(VI). In addition, the removal process was discussed, and the results indicated that the McKay kinetic model, Langmuir isotherm model and Van't Hoff thermodynamic model were the most suitable models for removal. The main factors affecting the removal of Cr(VI) were discussed, and the removal of Cr(VI) reached 99.14%, which gives a comprehensive utilization way of oily sludge and corn stalks.