Treatment of Daqing oily sludge by thermochemical cleaning method

Cleaning Oily Sludge Using Colloidal Gas Aphrons: Optimizing Process Conditions and Analyzing Mechanisms

Colloidal gas aphrons (CGAs) are applied in pollutant removal due to their large specific surface area and high surface activity. The structure and properties of the prepared CGAs were investigated in the process of oil removal from oily sludge. The prepared CGAs had a liquid film thickness was 5-10 μm with high stability. CGA interfacial tension was as low as 3.157 mN/m. Then it was found that the oil removal rate of CGAs was higher than that of chemical treatments, showing that CGAs could increase the mass transfer surface area and provide additional attachment sites for pollutants, enhancing the oil removal. The treatment conditions of the oil removal were optimized through response surfaces, showing that under optimal treatment conditions, the oil removal rate of oily sludge reached 96.07%. Additionally, the interaction between surfactant concentration and temperature was the most significant of all of the influencing factors. The behavior and mechanism of CGAs in the cleaning process of oily sludge were further investigated using an inverted fluorescence microscope, SEM, FTIR, and two-dimensional fluorescence spectrometer, showing that pollutants transferred from the liquid film surface of CGAs to the inside the film, and CGAs could specifically adsorb negatively charged organic compounds and aromatic hydrocarbons. The results show that CGAs achieved liquid membrane solubilization. Many negatively charged organic compounds and aromatic hydrocarbons are adsorbed onto the CGAs liquid membrane surface via electrostatic and hydrophobic interactions and then migrated to the hydrophobic layer of the CGAs liquid membrane due to the distribution effect, thus enabling rapid pollutant migration between solid and liquid phases.

Mechanism of highly efficient oil removal from spent hydrodesulfurization catalysts by ultrasound-assisted surfactant cleaning methods

The removal of crude oil from spent hydrodesulfurization catalysts constitutes the preliminary stage in the recovery process of valuable metals. However, the traditional roasting method for the removal exhibits massive limitations. In view of this, the present study used an ultrasound-assisted surfactant cleaning method to remove crude oil from spent hydrodesulfurization catalysts, which demonstrated effectiveness. Furthermore, the study investigated the mechanism governing the process with calculation and experiments, so as to provide a comprehensive understanding of the cleaning method's efficacy. The surfactant selection was predicated on the performance in the IFT test, with SDBS and TX-100 finally being chosen. Subsequent calculations and analysis were then conducted to elucidate their frontier molecular orbitals, electrostatic potential, and polarity. It has been found that both SDBS and TX-100 possess the smallest LUMO-HOMO energy gap (ΔE), registering at 4.91 eV and 4.80 eV, respectively, and presenting the highest interfacial reactivity. The hydrophilic structure in the surfactant regulates the wettability of the oil-water interface, and the long-chain alkanes have excellent non-polar properties that promote the dissolution of crude oil. The ultrasonic-assisted process further improves the interface properties and enhances the oil removal effect. Surprisingly, the crude oil residue was reduced to 0.25% under optimal conditions. The final phase entailed the techno-economic evaluation of the entire process, revealing that, in comparison to the roasting method, this process saves $0.38 per kilogram of spent HDS catalyst, with the advantages of operational simplicity and emission-free. Generally, this study shed new light on the realization of efficient oil removal, with the salience of green, sustainable, and economical.

New insights into interaction between oil and solid during hydrothermal treatment of oily sludge

Hydrothermal treatment (HT) can effectively dehydrate and reduce oily sludge (OS) volume, but the resulting hydrothermal oily sludge (HOS) presents greater challenges for washing than the initial oily sludge (IOS). This study examines the effects of HT on OS by analyzing changes in water, oil, and solid. Results indicate that HT considerably decreases the water content in OS while increasing resin and asphaltenes contents. In addition, condensation, side-chain scission, and oxidation reactions occur during the HT process, resulting in coking, agglomeration, and an increase in oxygen-containing groups. This increase, further confirmed by X-ray photoelectron spectroscopy (XPS), enhances the interaction between oil and solids. Calcite, the most prevalent solid-phase component, may form a calcium bridge with the oxygen-containing groups. Moreover, HT reduces the solid particle size, thereby increasing the oil-solid contact area. Interestingly, the process of deasphalting diminishes the interaction between oil and solids, facilitating sludge washing. After washing, the residual oil content in HOS is reduced to less than 0.34%. This study elucidates why HOS is challenging to separate from oil and solids and introduces a novel method that combines dodecylbenzene sulfonic acid (DBSA)-assisted heptane deasphalting with conventional washing techniques. This method shows promise for applications in OS affected by weathering processes.

The methods for improving the biodegradability of oily sludge: a critical review

Biological degradation method, as an environmentally friendly, low-carbon, and clean pollution treatment technology, is widely used for the harmless disposal of oily sludge. The biodegradability of oily sludge with stable emulsification system, high oil, and water content is poor. Therefore, it is necessary to pre-treat the oily sludge to improve its biodegradability, including recover the petroleum resources and remove heavy metals and bio-toxic organic matters. This review systematically summarizes five oily sludge treatment methods and their influences on sludge biodegradability, including pyrolysis, chemical hot washing, solvent extraction, chemical oxidation, and hydrothermal. Pyrolysis at temperatures above 750 °C produces high molecular weight polycyclic aromatic hydrocarbons, chemical hot washing and chemical oxidation would cause secondary pollution, solvent extraction method could not be applied due to the high cost and high toxicity of the extractant, and the oil removal of hydrothermal method is inefficient. Additionally, the principles, advantages, and disadvantages of those treatments and the factors affecting microbial degradation were analyzed, which provide the development direction of pretreatment technology to improve the biodegradability of oily sludge.

Characterization and treatment of oily sludge: A systematic review

Oily sludge is a prevalent hazardous waste generated in the petroleum industry, and effectively treating it remains a key challenge for the petroleum and petrochemical sectors. This paper provides an introduction to the origin, properties, and hazards of oil sludge while summarizing various treatment methods focused on reduction, recycling, and harmlessness. These methods include combustion, stabilization/solidification, oxidation and biodegradation techniques, solvent extraction, centrifugation, surfactant-enhanced oil recovery processes as well as freezing-thawing procedures. Additionally discussed are pyrolysis, microwave radiation applications along with electrokinetic method utilization for oily sludge treatment. Furthermore explored are ultrasonic radiation techniques and froth flotation approaches. These technologies have been thoroughly examined through discussions that analyze their process principles while considering influencing factors as well as advantages and disadvantages associated with each method. Based on the characteristics of oily sludge properties and treatment requirements, a selection methodology for choosing appropriate oily sludge treatment technology is proposed in this study. The development direction of processing technology has also been explored to provide guidance aimed at improving efficiency by optimizing existing processing technologies. The paper presents a comprehensive treatment method for oily sludge, ensuring that all the parameters meet the standard requirements.

Advances in ultrasonic treatment of oily sludge: mechanisms, industrial applications, and integration with combined treatment technologies

In the petroleum sector, the generation of oily sludge is an unavoidable byproduct, necessitating the development of efficient treatment strategies for both economic gain and the mitigation of negative environmental impacts. The intricate composition of oily sludge poses a formidable challenge, as existing treatment methodologies frequently fall short of achieving baseline disposal criteria. The processes of demulsification and dehydration are integral to diminishing the oil content and reclaiming valuable crude oil, thereby playing a critical role in the management of oily sludge. Among the myriad of treatment solutions, ultrasonic technology has emerged as a particularly effective physical method, celebrated for its diverse applications and lack of resultant secondary pollution. This comprehensive review delves into the underlying mechanisms and recent progress in the ultrasonic treatment of oily sludge, with a specific focus on its industrial implementations within China. Both isolated ultrasonic treatment and its combination with other technological approaches have proven successful in addressing oily sludge challenges. The adoption of industrial-scale systems that amalgamate ultrasound with multi-technological processes has shown marked enhancements in treatment efficacy. The fusion of ultrasonic technology with other cutting-edge methods holds considerable potential across a spectrum of applications. To fulfill the goals of resource recovery, reduction, and neutralization in oily sludge management, the industrial adoption and adept application of a variety of treatment technologies are imperative.

Nocardioides limicola sp. nov., an alkaliphilic alkane degrading bacterium isolated from oilfield alkali-saline soil

A Gram-stain-positive, rod-shaped, non-spore-forming, alkane degrading bacterium, designated DJM-14T, was isolated from oilfield alkali-saline soil in Heilongjiang, Northeast China. On the basis of 16 S rRNA gene sequencing, strain DJM-14T was shown to belong to the genus Nocardioides, and related most closely to Nocardioides terrigena KCTC 19,217T (95.53% 16 S rRNA gene sequence similarity). Strain DJM-14T was observed to grow at 25-35 °C, pH 7.0-11.0, in the presence of 0-6.0% (w/v) NaCl. The predominant respiratory quinone was MK-8 (H4) and LL-diaminopimelic acid was the diagnostic diamino acid in the cell-wall peptidoglycan. The major fatty acids were identified as iso-C16:0 and C18:1 ω9c. It contained diphosphatidylglycerol, phosphatidylglycerol and phosphatidylinositol as the polar lipids. The genome (3,722,608 bp), composed of 24 contigs, had a G + C content of 69.6 mol%. Out of the 3667 predicted genes, 3618 were protein-coding genes, and 49 were ncRNAs. Digital DNA-DNA hybridization (dDDH) estimation and average nucleotide identity (ANI) of strain DJM-14T against genomes of the type strains of related species in the same family ranged between 18.7% and 20.0%; 68.8% and 73.6%, respectively. According to phenotypic, genotypic and phylogenetic data, strain DJM-14T represents a novel species in the genus Nocardioides, for which the name Nocardioides limicola sp. nov. is proposed and the type strain is DJM-14T (= CGMCC 4.7593T, =JCM 33,692T). In addition, novel strains were able to grow with n-alkane (C24-C36) as the sole carbon source. Multiple copies of alkane 1-monooxygenase (alkB) gene, as well as alcohol dehydrogenase gene and aldehyde dehydrogenase gene involved in the alkane assimilation were annotated in the genome of type strain DJM-14T.

New insight into desorption behavior and mechanism of oil from aged oil-contaminated soil in microemulsion

The intractable nature of oil-contaminated soil (OS) constitutes the chief limiting factor for its remediation. Herein, the aging effect (i.e., oil-soil interactions and pore-scale effect) was investigated by analyzing the properties of aged OS and further demonstrated by investigating the desorption behavior of the oil from the OS. XPS was performed to detect the chemical environment of N, O, and Al, indicating the coordination adsorption of carbonyl groups (oil) on the soil surface. Alterations in the functional groups of the OS were detected using FT-IR, indicating that the oil-soil interactions were enhanced via wind-thermal aging. SEM and BET were used to analyze the structural morphology and pore-scale of the OS. The analysis revealed that aging promoted the development of the pore-scale effect in the OS. Moreover, the desorption behavior of oil molecules from the aged OS was investigated via desorption thermodynamics and kinetics. The desorption mechanism of the OS was elucidated via intraparticle diffusion kinetics. The desorption process of oil molecules underwent three stages: film diffusion, intraparticle diffusion, and surface desorption. Owing to the aging effect, the latter two stages constituted the major steps for controlling oil desorption. This mechanism provided theoretical guidance to apply microemulsion elution for remedying industrial OS.

Highly Efficient Treatment of Oily Sludge by a Novel High-Speed Stirring Method at Room Temperature

Oily sludge is one of the main hazardous wastes which seriously endangers the ecological environment and human health. In this paper, in order to effectively treat oily sludge, a novel high-speed stirring (HSS) method was proposed to clean oily sludge, and the main parameters affecting the residual oil rate of oily sludge were studied experimentally. Firstly, the cleaning time and stirring speed were optimized in the one-stage HSS cleaning, and then the optimal cleaning time of two-stage HSS cleaning was determined by the response surface method. The results suggested that the oil can be efficiently separated by high-speed stirring at room temperature, and that the two-stage cleaning with a circular-hole outlet (Rotor-C) followed by a vertical hole-outlet (Rotor-V) presented the best effect. The optimal stirring speed was 6000 r/min, and the optimal cleaning times of the two-stage cleaning were 7 min and 8 min, respectively. After cleaning, the residual oil rate of the treated oily sludge was 1.65%, and the removal rate of the petroleum hydrocarbons was 84.3%.

Study on the thermal washing of oily sludge used by rhamnolipid/sophorolipid binary mixed bio-surfactant systems

Demulsification and crude oil desorption are usually a necessary step for the treatment of oily sludge in the petroleum industry. In this study a binary mixed bio-surfactant (rhamnolipid / sophorolipid, RL/SL) was used to strengthen the removing oil efficiency for oily sludge by thermal washing method. Surface tension values of the single and the mixed surfactants were carried out to investigate the effect of mixing systems on reducing critical micelle concentrations (CMC) value. The models proposed by Clint, Rubingh and Gibbs et al. had been employed to interpret the formation of mixed micelles and synergism and found out in case of the mass ratios of 4:6 the synergism was the strongest in RL and SL mixed surfactant systems, which was selected as the washing agents to treat the oily sludge produced from Huabei oilfield. Through the optimization of oil washing process parameters, the oil removal rate reached the maximum value (95.66%, residual oil rate 1.98%) at the condition of heating temperature of 45 °C, detergents concentration of 500 mg/L, washing time of 3 h, liquid/solid mass ratio of 1:4, stirring speed of 300 r/min, and washing 4 times. The factors affecting the oil washing effect were analyzed from the composition and performance characteristics of oily sludge samples, washing oil system and washing process parameters. The results showed that low oil content of oily sludge, small specific surface area, strong wetting and solubilization of the oil-washing system all can increase the oil-washing effect and the washing time and temperature had a great influence on the oil-washing effect. Compared with the results of other researchers, the oil washing temperature and the concentration of oil washing agent were significantly lower and high oil removal rate and low residual oil rate were obtained in this study. It was confirmed that thermal oil washing method using RT/SL binary bio-surfactant mixing system was proved to a high-efficiency, low-consumption and wide range of applications technology.

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.

Effects of Different Heat Treatment Methods on Organic Pollutants and Heavy Metal Content in Oil Sludge Waste and Ecotoxicological Evaluation

The discharge of large amounts of oily sludge heat treatment residues constitutes a severe threat to the environment. However, little is known about the toxicity of these heat-treated residues. Current research has mainly focused on the toxic effects of single heavy metals or single hydrocarbons on plants, whereas the phytotoxic effects of hydrocarbon–metal mixtures have remained largely unexplored. In this study, pot experiments were conducted to evaluate the effects of different proportions of heat treatment residues (pyrolysis, heat-washing, and high-temperature oxidation residues) from three kinds of oily sludge on the physiological and biochemical parameters of mung bean plants. Higher proportions of residues decreased the germination rates and enzyme activity of mung beans compared to uncontaminated soil. When pyrolysis residue, hot-washing residue, and high-temperature thermal oxidation residue are used in green planting soil, their content must be lower than 30%, 90%, and 70%, respectively. Additionally, our findings indicated that the accumulation level of pollutants in oily sludge heat treatment residues was not high. However, the three kinds of residues exhibited different degrees of plant toxicity. The pyrolysis residue still exhibited strong ecotoxicity, even at low concentrations. In contrast, the toxicity of the hot-washing residue was much lower than that of the pyrolysis residue and the high-temperature thermal oxidation residue. Our findings indicated that mung bean is highly tolerant of contaminated soil and is therefore well suited for phytoremediation applications.

Study on the Effect of Petroleum Components on the Elution of Oily Sludge by a Compound Biosurfactant

Currently, research on oily sludge treatment mainly focuses on optimizing the deoiling effect and research on the deoiling mechanism, and the influence of petroleum components on the properties and treatment of oily sludge is rarely considered. Therefore, in this study, petroleum substances in three types of oil sludge were eluted using the biosurfactant cleaning technology, and the influence of petroleum components on the cleaning process was explored. The results showed that the biosurfactants rhamnolipid and sophorolipid had a synergistic effect, and the oil-removal rate was as high as 92.2% when the SL mass fraction was 0.4 in the compound biosurfactant. Three types of oily sludge, wellsite-landing sludge, pipeline-landing sludge, and tank-bottom sludge, were cleaned by the compound biosurfactant; the results showed that the residual petroleum substance in liquid and solid phases, the turbidity value, and the zeta-potential value of the supernatant of oil sludge samples after cleaning increased with the increase in the heavy components of the oily sludge, and the oil-removal rate decreased gradually. After cleaning, the average relative molecular weight of the three oil phases increased with the heavy components, which was increased by 1.83, 4.83, and 10.72%, respectively, and the increase in molecular weight increased the difficulty of cleaning. After cleaning, the retention time and peak intensity of the oil sample changed significantly, and it had a stronger elution effect on low-molecular-weight alkanes. It was found that the compound biosurfactant had a good elution effect on polycyclic aromatic hydrocarbons, but the increase in the content of heavy components and the increase in aromatic rings increased the difficulty of cleaning. Moreover, it was found that the compound biosurfactant could not completely elute the petroleum substances on the surface of solid particles, and the asphaltene components in the oil phase were more difficult to elute than other components.

Alcanivorax limicola sp. nov., isolated from a soda alkali-saline soil

An alkaliphilic and aerobic bacterium, designated as strain JB21^T, was isolated from a soda alkali-saline soil sample in Heilongjiang, Northeast China. Strain JB21^T is a Gram-stain-negative, rod-shaped, non-motile and amylase-positive bacterium. Growth occurred at 15-45 °C (optimum, 35-37 °C), in the presence of 0-15.0% (w/v) NaCl (optimum, 1.0%) and at pH 6.5-10.5 (optimum, pH 8.5-9.5). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain JB21^T was most closely related to type strains of the genus Alcanivorax, with the highest sequence similarity to Alcanivorax indicus SW127^T (96.3%), and shared 95.4-93.1% sequence identity with other valid type strains of this genus. The major cellular fatty acids identified were C_16:0 and summed feature 8 (C_18:1ω6c and/or C_18:1ω7c). The polar lipids comprised phosphatidylethanolamine, phosphatidylglycerol and one unidentified phospholipid. The genomic G + C content of strain JB21^T was 61.3 mol%. The digital DNA-DNA hybridization (dDDH) estimation and average nucleotide identity (ANI) between strain JB21^T and type strains of the genus Alcanivorax were 18.3-23.2% and 69.2-79.0%, respectively. On the basis of its phenotypic and phylogenetic characteristics, we suggest the creation of a new species within the Alcanivorax genus, named Alcanivorax limicola sp. nov., type strain JB21^T (= CGMCC 1.16632^T = JCM 33717^T).

Compound Cleaning Agent for Oily Sludge from Experiments and Molecular Simulations

This paper reported a new oily sludge compound cleaning agent formula, which used a combination of molecular simulation and experimental methods to study its interfacial formation energy (IFE), and exciting results were obtained. From a total of 24 surfactants in five categories, sodium silicate (Na₂SiO₃), sodium dodecylbenzene sulfonate, and fatty alcohol polyoxyethylene polyoxypropylene ether (JFC-SF) were screened out because of their excellent washing oil effect. Under a reasonable orthogonal system, when the mass ratio of the three surfactants was 3:1:1, the oil desorption effect was the best, the oil residual rate could reach 2.13%, and the oil removal efficiency could reach 93.53%. Verified by the molecular dynamics simulation module, the absolute value of the interface binding energy was the largest at this compound ratio, which was 465.71 kcal/mol. More importantly, we have discussed in depth the mechanism of adsorption and permeation of oily sludge by cleaning agents. Through single-factor influence experiments, the following optimized working condition parameters of the cleaning agent were determined: cleaning conditions with an agent content of 4%, a temperature of 70 °C, a stirring speed of 400 rpm, a cleaning time of 30 min, and a liquid-solid ratio (L/S) of 4:1. The research results laid the foundation for resource utilization, harmlessness, and reduction of oily sludge in the Liaohe oilfield.

Enhanced Separation of Oil and Solids in Oily Sludge by Froth Flotation at Normal Temperature

Oily sludge (OS) contains a large number of hazardous materials, and froth flotation can achieve oil recovery and non-hazardous disposal of OS simultaneously. The influence of flotation parameters on OS treatment and the flotation mechanism were studied. OS samples were taken from Shengli Oilfield in May 2017 (OSS) and May 2020 (OST), respectively. Results showed that Na2SiO3 was the suitable flotation reagent treating OSS and OST, which could reduce the viscosity between oil and solids. Increasing flotation time, impeller speed and the ratio of liquid to OS could enhance the pulp shear effect, facilitate the formation of bubble and reduce pulp viscosity, respectively. Under the optimized parameters, the oil content of OST residue could be reduced to 1.2%, and that of OSS could be reduced to 0.6% because of OSS with low heavy oil components and wide solid particle size distribution. Orthogonal experimental results showed that the impeller speed was the most significant factor of all parameters for OSS and OST, and it could produce shear force to decrease the intensity of C-H bonds and destabilize the OS. The oil content of residue could be reduced effectively in the temperature range of 24–45 °C under the action of high impeller speed.

Thermochemical Recycling of Oily Sludge by Catalytic Pyrolysis: A Review

The main methods of treating oily sludge at home and abroad and the current research status of oily sludge pyrolysis technology are briefly described, and four commonly used catalysts are introduced: metals, metal compounds, molecular sieves, metal-supported molecular sieves, and biomass catalysts for oily sludge. The influence of pyrolysis, the pyrolysis mechanism, and the product composition of oily sludge with the addition of different catalysts are also discussed. Finally, the development direction of preparing new catalysts and the mixed use of multiple catalysts is proposed as a theory to provide for the efficient and reasonable utilization of oily sludge.

A review of the interfacial stability mechanism of aging oily sludge: Heavy components, inorganic particles, and their synergism

Oily sludge is widely produced in the processes of petroleum exploitation, storage, transportation, and refining, and becomes more stable during aging. The interfacial stability of aging oily sludge hinders the recovery and disposal of oil resources. This review summarizes the interfacial film stability of aging oily sludge, which occurs through the formation of viscoelastic and rigid bilayer interfacial films between heavy components (asphaltenes and resins) and inorganic particles. The bilayer interfacial films enhance interfacial film strength and hinder the aggregation of droplets, contributing to the formation of a stable and high-viscosity oil-water-solid three-phase mixture. Recent demulsification technologies for reducing the stability of interfacial films have been classified as follows: removing heavy components, changing asphaltene aggregate structure, and reducing inorganic particle content. More efficient demulsification technologies are expected to be developed by deeply analyzing the microstructure and interfacial properties of asphaltenes and resins, as well as comprehensively studying the complex interactions among various components. This review constructs a bridge between the stability mechanism and the corresponding destabilization methods, which would promote future studies in aging oily sludge treatment.

The sludge-based adsorbent from oily sludge and sawdust: preparation and optimization

Sludge-based adsorbent (S-AB) converted by oily sludge can make full use of the precious resource. In this paper, oily sludge and discarded sawdust are used to prepare adsorbent through chemical activation. The adsorbent prepared is used to adsorb raw petroleum. Firstly, the most reasonable chemical activator ZnCl₂ is ascertained through parallel comparative experiments. The characterization results of N₂-adsorption are consistent with adsorption experiment results, which shows that higher mesopore surface area and volume are benefitted by the adsorption process. Secondly, the optimization of preparation technology is investigated through orthogonal experiments after parallel comparative experiments. The adsorption capacity of S-AB-ZnCl₂ is stronger when the preparation conditions are as follows: an activation temperature of 550°C, an activation time of 3.5 h, a solid-liquid ratio of 1:1.5, a sludge-sawdust ratio of 1:0.5 and the heating rate of 15°C/min. The maximum quantity adsorbed Q₀ = 434.78 mg/g, calculated through the Langmuir adsorption isothermal models, of S-AB-ZnCl₂ prepared under optimized condition is higher than that before optimization. In addition, the most reasonable kinetics fits were of the second-order model.

Comprehensive characterization of an oily sludge from a petrol refinery: A step forward for its valorization within the circular economy strategy

Refinery treatment plants produce large quantities of oily sludge during the petroleum refining processes. The hazardousness associated with the disposal of these wastes, make necessary the development of innovative technologies to handle it adequately, linked to the concepts of circular economy and environmental sustainability. This work provides for the first time a methodology for the deep characterization of this kind of wastes and consequently new insights regarding its valorization. A review of works dealing with the characterization of this type of wastes has been addressed evidencing the complexity and variability of these effluents. The oily sludge under study contains a high concentration of Chemical Oxygen Demand of 196 g COD/L, a Total Kjeldahl Nitrogen of 2.8 g TKN/kg, a phosphorous content as PO₄^3- of 7 g/kg, as well as a great presence of heavy metals in a different range of concentrations. This sludge is composed of three different phases: oily, aqueous and solid. The oily and the solid phases present high percentages of carbon content (84 and 26%, respectively), related to the presence of alkanes ranged from n-C₉ to n-C₄₄. Therefore, it could be possible their valorization by the synthesis of catalyst and/or adsorbents. A dark fermentation process could be also proposed for the oily phase to obtain H₂ as an alternative energy source. Finally, the aqueous phase contains low carbon and nutrients concentration. A previous thermal pre-treatment applied to the oily sludge might increase nutrient and organic loading in the aqueous phase due to solid destruction, making this aqueous effluent suitable for a further conventional biological treatment.

Study on the treatment of oily sludge in oil fields with lipopeptide/sophorolipid complex bio-surfactant

A systematic study had been carried out to get insight into the micellar behavior of anionic lipopeptide (LT) and nonionic sophorolipid (SL) in their different mass ratio mixed state using the technique of tensiometry. The models proposed by Clint, Rubingh and Gibbs et al. had been employed to interpret the formation of mixed micelles and found out synergism. The obtained experimental critical micelle concentrations (CMC) were lower than the ideal CMCs, indicating negative deviation from ideal behavior for all multi-component mixed micelles formation. A suited binary bio-surfactant mixing system was selected as the washing agents to treat the oily sludge produced from Huabei oilfield by the thermal bio-surfactant washing method. The results showed that in case of the mass ratios of 8:2 the CMC was dramatically decreased and synergism was the strongest in LT and SL bi mixed surfactant systems. The studied binary mixed bio-surfactant system showed higher washing efficiency for oily sludge than single surfactant system. In addition, the washing power of binary mixed bio-surfactants towards oily sludge was the best at below washing conditions: (a) the concentration of the mixed system (100 mg/L), (b) temperature (55 ℃), (c) ratio of sludge/liquid (1:3), (d) washing time (3 h), and (e) stirring speed (300 rpm). Certainly, the washing abilities of the selected surfactants not only depend on their mixing ratio and washing conditions but also associate with microstructure and mineral components of oily sludge.

A critical review on energy recovery and non-hazardous disposal of oily sludge from petroleum industry by pyrolysis

This review systematically reports the pyrolysis of oily sludge (OS) from petroleum industry in regards to its dual features of the energy recovery potential and the environmental risks. The petroleum hydrocarbons are the nonbiodegradable fractions in OS that possess hazardous properties, i.e. ignitability and toxicity. Besides, complicated hazardous elements (i.e. N, S and Cl) and heavy metals inherently existing in OS further aggravate the environmental risks. However, the high oil content and heating value of OS contribute to its huge energy resource potential. Considering the energy demand and the environmental pressure, the ultimate purposes of the OS management are to enhance the oil recovery efficiency to minimize the oil content as well as to stabilize the hazardous elements and heavy metals into the solid residue. Among various OS management technologies, pyrolysis is the most suitable approach to reach both targets. In this review paper, the pyrolysis principle, the kinetics and the product distribution in three-phases are discussed firstly. Then the effects of operating parameters of the pyrolysis process on the quality and the application potential of the three-phase products, as well as the hazardous element distribution are discussed. To further solve the dominant concerns, such as the oil content in the solid residue, the pyrolytic oil quality and the migration of hazardous elements and heavy metals, the potentials of the catalytic pyrolysis and the co-pyrolysis with additives are also summarized. Also, the typical pyrolysis reactors are then presented. From the perspective of the energy efficiency and the non-hazardous disposal, the integrated technology combining the pyrolysis and the combustion for the OS management is recommended. Finally, the remaining challenges of OS pyrolysis encountered in the research and the industrial application are discussed and the related outlooks are itemized.

Ecotoxicity of oil sludges and residuals from their washing with surfactants: soil dehydrogenase and ryegrass germination tests

Oil sludge washing (OSW) with surfactants and co-solvents is used to recover the oil, and this process leaves some residuals (sediments and surfactant solution). Currently, there are no data on the ecotoxicological effects of these OSW residuals from different sludges. This study evaluated the toxicity of OSW residuals from washing four types of oil sludges with five surfactants (Triton X-100 and X-114, Tween 80, sodium dodecyl sulphate (SDS) and rhamnolipid) and a co-solvent (cyclohexane). The toxicity of the residuals was evaluated with the impact on the soil microbial dehydrogenase activity (DHA) and ryegrass (Lolium perenne) seed germination. There was a high DHA detected directly in the sludges and all OSW residual combinations, but this activity could not be attributed to the DHA itself but to some chemical interferences. The DHA was then tested in the soils amended with the OSW residuals to simulate a bioremediation scenario. There were no chemical interferences in this case. In general, the INTF concentrations were significantly higher at low concentrations, 1 and 5% (p < 0.01). There were no significant differences in the DHA at high concentrations of OSW residuals (10, 25 and 50%) which implied that the concentration of the contaminants is not directly proportional to the levels of ecotoxicity. Unexpectedly, the INTF values of the 10, 25 and 50% rhamnolipid-OSW residuals were significantly lower than the Triton X-100 residuals. The ryegrass germination rates were higher than 70% with no apparent phytotoxicity symptoms in the seedlings. Particularly, there was a highly significant negative effect of the residuals on the germination rates at high concentrations (p < 0.01). Given that the extractable petroleum hydrocarbon (EPH) concentrations in the OSW residual-amended soils in both DHA and germination tests were very low (13-21 ppm), other co-contaminants could be contributing to the toxicity. These findings implied that biotreatment techniques can be applied to treat the OSW residuals if necessary.

Oil sludge washing with surfactants and co-solvents: oil recovery from different types of oil sludges

Different physicochemical and biological treatments have been used to treat oil sludges, and oil recovery techniques are preferred such as oil sludge washing (OSW) with surfactants and co-solvents. Toluene is commonly used as co-solvent, but it is non-benign to the environment. This study tested alternative co-solvents (n-pentane, n-hexane, cyclohexane, and isooctane) at 1:1 and 2:1 C/OS (co-solvent to oil sludge ratio). Also, this study evaluated the effect on the oil recovery rate (ORR) of three main parameters in the washing: type, concentration, and application ratio (S/OS) of surfactants to oil sludges. To date, no study has assessed these parameters in the washing of oil sludges from different sources. Four types of oil sludges and five surfactants (Triton X-100 and X-114, Tween 80, sodium dodecyl sulphate (SDS), and rhamnolipid) were used. The results showed that cyclohexane had high ORR and could be used instead of toluene because it is more benign to the environment. The S/OS ratio had a high effect on the ORR and depended on the type of oil sludge. Rhamnolipid, Triton X-100, and Triton X-114 had the highest oil recovery rates (40 - 70%). In addition, it was found that the surfactant concentration had no effect on the ORR. Consequently, the addition of surfactant was not significantly different compared to the washing with no surfactants, except for one sludge. The use of the surfactant in the washing solution can help in the selective extraction of specific oil hydrocarbon fractions in the recovered oil to assess its potential reuse as fuel. Further recommendations were given to improve the OSW process.

A review of the application of different treatment processes for oily sludge

Oily sludge contains high concentrations of total petroleum hydrocarbons and heavy metals, which seriously impact the environment and human health. How to dispose of and use the oily sludge has attracted an increasing amount of attention. This study introduces harmless and resource-based oily sludge treatment technologies. It summarizes the technologies from various aspects, such as the process principle, influencing factors, advantages, and disadvantages, and analyzes and summarizes the status quo of the development of the technologies. In comparison, the direction of processing technology development is discussed to provide reference for processing technology improvements, optimization, and efficiency improvements.

A systematic review on options for sustainable treatment and resource recovery of distillery sludge

Distillery sludge generated from the alcohol production plants is considered as a nuisance. It is one of the main sources of environmental pollution because of the presence of high amount of sulphate, phenolic compounds (500.3 ± 26.46 mg/kg), melanoidins, organic matter (14%) and heavy metals (like 18% Mn, 6% Ni and 4% Pb). Hence, advancement in the available techniques for managing this sludge is a prerequisite for its safe and sustainable disposal. The article delivers an assessment of the challenges involved in the treatment of distillery sludge, existing practices, disposal and possible routes for energy recovery. Considering the high nutritional and energy values of the distillery sludge, the associated limitations and challenges of the available sludge management options, it was aimed to highlight alternative methods of its treatment. The present review also compares the current distillery sludge management solutions concerning their environmental sustainability. The most widely used methods, including treatment and disposal techniques considering the current legislation in different countries, have also been dealt with. Furthermore, the study also deals with the resource recovery approaches in order to recover value-added products and available nutrients from distillery sludge. Resource and energy recovery options are therefore considered as sustainable solutions to fulfill the present and future energy requirement and visualize it as a potential opportunity instead of a nuisance.

Optimization of Process Parameters of Rhamnolipid Treatment of Oily Sludge Based on Response Surface Methodology

Oily sludge is a hazardous waste. If not handled properly, it can not only pollute the environment but also endanger human health. This study is the first to use a response surface method to optimize the main parameters of rhamnolipid-based recovery of oil from oily sludge. Using rhamnolipids as the cleaning agent and the oil recovery fraction as the evaluation index, the factors affecting the cleaning efficiency of oily sludge were optimized. The aforementioned sludge was obtained from the Tarim Oilfield. A single-factor experiment was conducted to determine the optimal range of the dosage, liquid-solid ratio, pH value, and time. The Box-Behnken response surface method was used to investigate the influence of each variable on the residual oil fraction of the oily sludge, and the dosage, pH value, and time were found to have a significant impact. The model optimization results show that the best process conditions for rhamnolipid-based recovery of oil are as follows: rhamnolipid dosage = 167.785 mg/L; liquid-solid ratio = 4.589:1; pH = 9.618; time = 1.627 h. Under optimal conditions, the model-predicted oil recovery fraction and the actual oil recovery fraction were 85.15 and 82.56%, respectively; the relative error between the predicted and the actual values was 2.59%. These results indicate that the model results are reliable. The solid residue after the cleaning was also analyzed to gain an in-depth understanding of the cleaning process. This study determined the feasibility of a rhamnolipid-based solution for the treatment of oily sludge and oil-contaminated soil.

Energy and Resource Utilization of Refining Industry Oil Sludge by Microwave Treatment

The oily sludge from crude oil contains hazardous BTEX (benzene, toluene, ethylbenzene, xylene) found in the bottom sediment of the crude oil tank in the petroleum refining plant. This study uses microwave treatment of the oily sludge to remove BTEX by utilizing the heat energy generated by the microwave. The results show that when the oily sludge sample was treated for 60 s under microwave power from 200 to 300 W, the electric field energy absorbed by the sample increased from 0.17 to 0.31 V/m and the temperature at the center of the sludge sample increased from 66.5 °C to 96.5 °C. In addition, when the oily sludge was treated for 900 s under microwave power 300 W, the removal rates were 98.5% for benzene, 62.8% for toluene, 51.6% for ethylbenzene, and 29.9% for xylene. Meanwhile, the highest recovery rates of light volatile hydrocarbons in sludge reached 71.9% for C3, 71.3% for C4, 71.0% for C5, and 78.2% for C6.

Evaluation of fatty acid derivatives in the remediation of aged PAH-contaminated soil and microbial community and degradation gene response

In this study, derivatives of two common fatty acids in plant root exudates, sodium palmitate and sodium linoleate (sodium aliphatates), were added to an aged Polycyclic aromatic hydrocarbons (PAHs) contaminated soil to estimate their effectiveness in the removal of PAHs. Sodium linoleate was more effective in lowering PAHs and especially high-molecular-weight (4-6 ring) PAHs (HMW-PAHs). Principal coordinates analysis (PCoA) indicates that both amendments led to a shift in the soil bacterial community. Moreover, linear discriminant effect size (LEfSe) analysis demonstrates that the specific PAHs degraders Pseudomonas, Arenimonas, Pseudoxanthomonas and Lysobacter belonging to the γ-proteobacteria and Nocardia and Rhodococcus belonging to the Actinobacteria were the biomarkers of, respectively, sodium linoleate and sodium palmitate amendments. Correlation analysis suggests that four biomarkers in the sodium linoleate amendment treatment from γ-proteobacteria were all highly linearly negatively related to HMW-PAHs residues (p < 0.01) while two biomarkers in the sodium palmitate amendment treatment from Actinobacteria were highly linearly negatively related to LMW-PAHs residues (p < 0.01). Higher removal efficiency of PAHs (especially HMW-PAHs) in the sodium linoleate amendment treatment than in the sodium palmitate amendment treatment might be ascribed to the specific enrichment of microbes from the γ-proteobacteria. The bacterial functional KEGG orthologs (KOs) assigned to PAHs metabolism and functional C23O and C12O genes related to cleavage of the benzene ring were both up-regulated. These results provide new insight into the mechanisms of the two sodium aliphatate amendments in accelerating PAHs biodegradation and have implications for practical application in the remediation of PAHs-contaminated soils.

Experimental study on catalytic pyrolysis of oil sludge under mild temperature

The pyrolysis performance of oil sludge (OS) was studied using a thermal gravimetric analysis apparatus and a tube furnace reactor. The oil recovery rate of OS pyrolysis showed a rapid growth trend at 450 °C. Moreover, the co-pyrolysis experiments of the OS and catalysts, including walnut shells, Fe₂O₃, K₂CO₃, polyvinyl chloride (PVC), and OS pyrolysis char with addition ratios of 5, 7, and 9 wt%, respectively, were conducted in a tube furnace reactor at 450 °C. The experiments demonstrated that all catalysts increased the oil recovery rate, but the optimal addition ratios differed. The pyrolysis chars produced above 450 °C had a well-developed pore structure, and the catalytic pyrolysis of OS at 450 °C could increase the yield of pyrolysis oil and reduce the potential ecological risk of heavy metals in the pyrolysis char. Therefore, catalytic pyrolysis is an inexpensive and highly efficient approach for treating solid waste.

Chemisorption mechanism of crude oil on soil surface

One of the main challenges in cleaning crude oil-contaminated soil is the unknown adsorption mechanism between residual oil and soil. Herein, infrared spectrometer (IR) is used to detect the existence of dibutylphthalate (DBP) and pelargonamide on montmorillonite (MMT) surface. In addition, after the adsorption of DBP and pelargonamide on MMT, the bands in fingerprint region of the two IR spectra are almost identical, indicating coordination bonds were formed on the surface of MMT. X-ray photoelectron spectroscopy (XPS) is employed to detect the chemical environment of N, O and Al. The reverse migration of Al^2p spectrum and forward migration of N^1s and O^1s spectra indicate the coordination adsorption of carbonyl and amine groups on MMT surface. Then, density functional theory (DFT) calculations are applied to make a further explanation of the bonding mechanisms of DBP and pelargonamide onto MMT surfaces. The result shows that there are two types of aluminum on the surface of MMT acting as Lewis acid sites in coordination adsorption, namely Al³⁺/Si⁴⁺ isomorphic substitutions and Al³⁺ adsorbed on MMT by means of electrostatic adsorption. Meanwhile, the oxygenium on the surface of MMT acts as Brønsted bases in hydrogen bonding adsorption.

Maximisation of oil recovery from an oil-water separator sludge: Influence of type, concentration, and application ratio of surfactants

Worldwide the generation of oil sludges is approximately 160 million metric tonnes per annum. The washing of oil sludge with surfactant solutions can be used to recover the oil and reused as a feedstock for fuel production. There is a need to establish the influence of the surfactant type, concentration, and application (surfactant to oil sludge, S/OS) ratio to oil sludge for the maximisation of oil recovery. This study presented the oil recovery rates from the washing of an oil-water separator sludge using surfactants, Triton X-100, sodium dodecyl sulphate (SDS), Tween 80, rhamnolipid, and Triton X-114. The surfactants were characterised by critical micelle concentration (CMC), micelle size, and surface activity. A Taguchi experimental design was applied to reduce the number of experimental runs. In general, Triton X-100 and X-114, and rhamnolipid had higher micelle sizes and surfactant activities which resulted in higher oil recoveries. The key role of the surfactants in the washing was evidenced because the ORR values with the surfactants were significantly higher than the value with the control with no surfactant solution. The S/OS ratio was the factor with the largest effect on the Taguchi signal-to-noise ratio (an indicator of variation) of the oil recovery rate. The levels with the maximum recovery rate were 1:1 S/OS, 2CMC of surfactant concentration and Triton X-100 (32% ± 5), Triton X-114 (30% ± 7), and rhamnolipid (29% ± 8). In conclusion, less surfactant solution (1:1 S/OS) and low surfactant concentration (≤2CMC) provided the maximum oil recovery from this type of oil sludge. To our knowledge, no previous study with surfactants has reported low oil recovery values at high S/OS ratios in the oil sludge washing.