Fenton Pretreatment Research Articles

Enhanced indigenous bacteria-mediated bioremediation of aged petroleum-contaminated soil by Fenton pretreatment: Synergistic effect of soil environmental improvement and microbial community response

Due to the harsh soil environment and low microbial activity, the efficacy of indigenous bacteria-mediated bioremediation is often limited in aged petroleum-contaminated soils. In this study, Fenton pretreatment (H2O2: 200 ∼ 600 mmol/kg, H2O2: Fe2+ = 100: 1) was applied to improve the aged soil environment and rebuild the microbial community to enhance subsequent bioremediation. After pretreated by 400 mmol/kg H2O2 and 4 mmol/kg Fe2+ (T2), the removal efficiency of total petroleum hydrocarbons (TPHs) was elevated to 93.27 %, equivalent to 1.96-fold of the natural attenuation (CK). Additionally, the half-life of biodegradation was shorted to 45.57 d, representing a decrease to 0.29-fold that of CK. Correlation analysis revealed a radar plot comprising five indicators, including bacterial quantification (BQ), dehydrogenase (DHA), polyphenol oxidase (PPO), permeability coefficient (K), and bulk density coefficient (γ), all of which exhibited positive correlations with TPHs degradation. Compared to CK, Fenton pretreatment increased the richness and evenness of the microbial community during incubation, thus facilitating TPHs biodegradation. Moreover, Fenton pretreatment accelerated the shift of the dominant genus in T2 from Pseudomonas (0.599) to Pseudomonas (0.258), Nocardioides (0.109), Dietzia (0.157), and Stenotrophomonas (0.120) throughout the incubation. Based on the analysis of Kyoto Encyclopedia of Genes and Genomes (KEGG), the metabolism and enzymatic functional genes related to the biodegradation of petroleum hydrocarbons in T2 were enhanced during incubation, accounting for the high removal efficiency of TPHs. These findings demonstrated that moderate Fenton pretreatment was an effective approach to stimulate indigenous bacteria for the enhanced biodegradation of aged petroleum-contaminated soil.

Enhanced humification attributed by the integration of Fenton reagent and oxalic acid during a co-composting of swine manure and corn straw: Impacts and the possible mechanisms

To illustrate the role and mechanism of using oxalic acid (OA) and Fenton reagent to enhance carbon transformation and humification in the co-composting of swine manure and corn straw, four different treatments, SW1 (Control), SW2 (Fenton reagent), SW3 (10 % OA), and SW4 (Fenton reagent + 10 % OA) were set up for an 80-day pilot-scale composting. Compared with the Fenton pretreatment, the contents of Fe (II) and hydroxyl radicals (·OH) in the SW4 treatment increased by 20.25 %-54.55 % and 6.39 %-71.00 %, respectively. This confirmed the role of OA in protecting Fe (II) and maintaining the generation of ·OH during the composting. Compared with Control, Fenton-like reagent amendment facilitated decomposition of dissolved organic carbon and total organic matter by 20.53 % and 25.37 %, respectively, which led to a higher content of humic substances (141.81 mg/g) and a higher degree of polymerization (3.51) in SW4. Among all, the dissolved organic carbon in the compost substrate of SW4 treatment showed the highest level of aromatization and more refractory organic matter decomposition. The compact microbial co-occurrence network analysis exhibited the high-metabolic activity in Fenton-like treatment (SW4). Therefore, the probable mechanism of humification facilitation by Fenton-like reagent amendment in co-composting could be controlled by several processes: 1) generation of ·OH for facilitating the decomposition of organic matter, 2) disintegration of refractory lignocellulose substances by promoting the lignin pathway of humification, and 3) increasing the quantity and activity of microbes (i.e., Proteobacteria, Actinobacteriota, Chloroflexi, Ascomycota and Basidiomycota) involved in humification. This study provided a profound understanding of Fenton-like reagent amendments in co-composting of agricultural solid wastes and proposes a solution for enhancing the humification degree of compost products for agricultural use.

Olive mill wastewater co-treatment: Effect of (electro)Fenton processes and dilution ratio on moving bed biofilm reactor performance

The treatment of olive mill wastewater (OMW) represents still an open challenge because of its highly polluting load. One of the most affordable methods for small-medium mills is to send OMW to industrial wastewater treatment plants (IWTP). Accordingly, this work explored a strategy consisting of the biological co-treatment of real OMW and simulated urban wastewater by a moving bed biofilm reactor (MBBR), with and without (electro)Fenton pre-treatment, to simulate OMW treatment through a multi-barrier approach in an IWTP. The effluent of the MBBR without pre-treatment, despite the long period of operation of 18 months, was in compliance with the limit for total phenols (TPHs) of 0.5 mg/L only at a really low OMW's dilution ratio (DR) (1/4000 (v/v)). The Fenton oxidation (FO) and the electro-assisted Fenton (EAF) processes were investigated as pre-treatment of diluted OMW. FO resulted in good performances in terms of TPHs removal (81%) and improved biodegradability (final BOD5/COD ratio = 0.35) but in poor COD removal (24%). EAF was more effective (COD removal = 41%, TPHs removal = 85%, and final BOD5/COD ratio = 0.40) than FO. Therefore, EAF was finally investigated on undiluted OMW (COD removal = 56%, TPHs removal = 84%, and final BOD5/COD ratio = 0.62) and subsequently co-treated with simulated urban wastewater by MBBR, identifying 1/1000 as the optimal DR. The investigated multi-barrier approach is an interesting option for OMW co-treatment in IWTPs to successfully address the challenge of TPHs degradation and drastically reduce the volume of the biological process unit (4 times lower than MBBR treatment alone).

Sulfomethylation reactivity enhanced the Fenton oxidation pretreatment of bamboo residues for enzymatic digestibility and ethanol production.

Bamboo is considered a renewable energy bioresource for solving the energy crisis and climate change. Dendrocalamus branddisii (DB) was first subjected to sulfomethylation reaction at 95°C for 3h, followed by Fenton oxidation pretreatment at 22°C for 24h. The synergistic effect of combined pretreatment dramatically improved enzymatic digestibility efficiency, with maximum yield of glucose and ethanol content of 71.11% and 16.47g/L, respectively, increased by 4.7 and 6.11 time comparing with the single Fenton oxidation pretreatment. It was found that the hydrophobicity of substrate, content of surface lignin, degree of polymerization, and specific surface area have significant effects on the increase of enzymatic saccharification efficiency. It also revealed that sulfomethylation pre-extraction can improve the hydrophilicity of lignin, leading to the lignin dissolution, which was beneficial for subsequent Fenton pretreatment of bamboo biomass. This work provides some reference for Fenton oxidation pretreatment of bamboo biomass, which can not only promote the utilization of bamboo in southwest China, but also enhances the Fenton reaction in the bamboo biorefinery.

Hydrodynamic cavitation-assisted acid pretreatment and fed-batch simultaneous saccharification and co-fermentation for ethanol production from sugarcane bagasse using immobilized cells of Scheffersomyces parashehatae

A new alternative for hydrodynamic cavitation-assisted pretreatment of sugarcane bagasse was proposed, along with a simultaneous saccharification and co-fermentation (SSCF) process performed in interconnected columns. Influential variables in the pretreatment were evaluated using a statistical design, indicating that an ozone flow rate of 10 mg min−1 and a pH of 5.10 resulted in 86 % and 72 % glucan and xylan hydrolysis yields, respectively, in the subsequent enzymatic hydrolysis process. Under these optimized conditions, iron sulfate (15 mg L−1) was added to assess Fenton pretreatment, resulting in glucan and xylan hydrolysis yields of 92 % and 71 %, respectively, in a material pretreated for 10 min. In SSCF, ethanol volumetric productivities of 0.33 g L−1 h−1 and of 0.54 g L−1 h−1 were obtained in batch and fed-batch operation modes, achieving 26 g L−1 of ethanol in 48 h in the latter mode.

Treatment of printing and dyeing wastewater using Fenton combined with ceramic microfiltration membrane bioreactor

The release of printing and dyeing wastewater (PDW) into the environment is a concern attributed to its acute, chronic and cytotoxic effects to aquatic life. Two anaerobic/aerobic-membrane bioreactors (A/O–MBRs) were operated continuously to treat raw (untreated) and Fenton oxidized PDW. After about 70 days acclimatization, 67% of the chemical oxygen demand (COD) and 35% of adsorbable organic halogens (AOX) were removed by direct biodegradation in A/O–MBR without Fenton pre-treatment, while 90% of the COD and 79% of AOX were removed in Fenton + A/O–MBR system. Fenton oxidation play a dominate role on the COD and AOX removal of PDW in the combination system. The Fenton pre–treatment of PDW could remarkably reduce membrane fouling. The Shannon indices showed that the microbial diversity in anaerobic flocs were significantly higher than the microbial diversity in aerobic flocs in both two A/O–MBR systems. The metagenomics analysis found that the key functional genes responsible for the AOX biodegradation were EC3.1.1.45, pcaI, and pcpD. The transcript per million (TPM) abundance of EC3.1.1.45 and pcaI significantly up-regulated in both anaerobic and aerobic flocs after 70 days acclimatization. Based on the pilot applications study, the total operation cost of Fenton + A/O–MBR processes for PDW remediation was approximately 1.263–1.384 USD/t. This study provides a promising technique for removing AOX and other organic contaminants from PDW.

Fenton pretreatment to mitigate membrane distillation fouling during treatment of landfill leachate membrane concentrate: Performance and mechanism

Membrane distillation (MD) is regarded as a promising technology for treatment of landfill leachate membrane concentrate (LLMC) due to its merits of low cost and high rejection of non-volatile components. However, the high concentration of pollutants in the wastewater will cause severe membrane fouling, resulting in costly cleaning and maintenance. In this study, Fenton pretreatment was applied to alleviate membrane fouling during MD treatment of LLMC. Compared to rapid flux decline of 88.2% at concentration factor (CF) of 3 for raw LLMC, MD flux only decreased by 17.4% at CF = 6 for treating acidic Fenton effluent without subsequent pH adjustment (Fe2+ and H2O2 concentration were 600 mg/L and 1457 mg/L, respectively). The pH neutralization of Fenton effluent or merely acidification of LLMC could not achieve such excellent fouling mitigation. It was concluded that both oxidation and acidification were critical and the collaboration mechanism was revealed to explain low membrane fouling. Firstly, Fenton oxidation removed organic contaminants, reduced the hydrophobicity of organic substances and increased the percentage of carboxylic group within LLMC. Thus, hydrophobic (HP) attraction was weakened but multivalent cation bridging became dominant fouling mechanism for neutral Fenton effluent. Then, acidification weakened multivalent cation bridging by inhibiting the deprotonation of carboxylic group, further mitigating membrane fouling. However, acidification of LLMC caused more severe organic fouling due to decrease in electrostatic (EL) repulsion. In addition to low membrane fouling, satisfactory total organic carbon (TOC) rejection rate of 96.23% was achieved during combined Fenton-MD process. This study demonstrated that Fenton pretreatment without pH neutralization could effectively alleviate MD fouling and elucidated the synergistic mechanism between oxidation and acidification for fouling mitigation.

Elaborating the role of rhamnolipids on the formation of humic substances during rice straw composting based on Fenton pretreatment and fungal inoculation

Composting is a green and sustainable way to dispose and reuse agricultural wastes, but the low degradation rate during composting hinders its application. This study was conducted to explore the effect of added surfactant rhamnolipids after Fenton pretreatment and inoculation of fungi (Aspergillus fumigatus) into the compost on the formation of humic substances (HS) during rice straw composting, and explored the effect of this method. The results showed that rhamnolipids speeded up the degradation of organic matter and HS formation during composting. Rhamnolipids promoted the generation of lignocellulose-degrading products after Fenton pretreatment and fungal inoculation. The differential products benzoic acid, ferulic acid, 2, 4-Di-tert-butylphenol and syringic acid were obtained. Additionally, key fungal species and modules were identified using multivariate statistical analysis. Reducing sugars, pH, and total nitrogen were the key environmental factors that affected HS formation. This study provides a theoretical basis for the high-quality transformation of agricultural wastes.

Enhanced bio-ethanol production from bamboo residues by alkali-aided Fenton reaction pretreatment and enzymatic saccharification

Alkali extraction was used to assist the Fenton pretreatment for overcoming the recalcitrance of bamboo and producing more sugar-based chemicals and bioethanol. The alkali-aided Fenton pretreatment showed the delignification of 55.33% and xylan removal of 80.76%. The surface lignin coverage, hydrophobicity, specific surface area, and cellulose crystallinity index were obviously changed by the combined pretreatment, which made cellulose accessibility increased by about 2-folds than Fenton pretreatment alone. The cleavage of β-O-4 linkage, the decrease of condensed structure and syringyl unit were observed in the residual lignin from the NaOH-Fenton pretreated D. brandisii, all of which reduced the nonproductive adsorption between enzymes and lignin. When NaOH-Fenton pretreated four bamboo residues were performed enzymatic hydrolysis, glucose yields of 66–74% and ethanol concentration of 11–16 g/L were obtained. The sequential NaOH-Fenton pretreatment should be considered as an environmentally-friendly bamboo biorefinery technology in the future.

Chemically and Physically Pretreated Straw in Moderate Conditions: Poor Correlation between Biogas Production and Commonly Used Biomass Characterization

Straw is a substantial agricultural by-product for biogas production. Hydrolysis of straw is found to be a rate-limiting step during its anaerobic digestion and could be enhanced by pretreatment. In this paper, the effect of various combinations of particle size reduction, autoclaving, and low-level Fenton reaction was studied on straw for biogas production. Grinding of straw contributed to the maximum increase in the biomethane potential. Only Fenton or only the autoclave process improves the kinetics slightly but does not considerably improve the biomethane potential. Combining autoclaving and low-concentration Fenton pretreatment considerably improves the BMP values. Lignin content, CHNSO elemental analysis, Scanning Electronic Microscopy (SEM), Simon’s staining, infrared spectroscopy (DRIFT and ATR), Nuclear magnetic resonance spectroscopy, and wide-angle X-ray diffraction analysis (WAXD) were used to characterize the physical and chemical changes of straw due to pretreatment. Results show a poor correlation between biogas production and the different physical and chemical biomass characteristics. It makes it difficult to explain the outcome of various pretreatment methods applied to biomass. Without further improvement and development of analytical techniques, the prediction of the biomethane potential of a feedstock with the aid of pretreatment can only be considered in case-by-case studies.

Synergistic effect of Fenton pretreatment and hydrothermal carbonization of lignin on the physicochemical properties of the resulting hydrochar

Mechanistic description of the synergistic effect of Fenton pretreatment and hydrothermal carbonization on lignin.

Study on the effect of biochar combined with Fenton oxidation on the aerobic composting of sludge

ABSTRACT Biochar was derived from rice straw pyrolyzed at 400°C, and biochar was added to the excess sludge at the ratio of 10% DS, 25% DS, and 50% DS as a supplementary skeleton for sludge Fenton pre-treatment. Rice husk biochar mixed with fungus residue as compost conditioner. In this study, we explored the effects of seven groups of composting materials on the composting effect and fertilizer quality under different pre-treatment methods of Fenton-pretreated sludge cake and conventional dewatered sludge cake, and different biochar additions. Specifically, we conducted a 22-day composting experiment using a composting reactor to investigate the effect of rice husk biochar combined with Fenton oxidation on the physicochemical properties of sludge composting. The results of this study showed that the FB50 group significantly increased the composting rate. Nutrient analysis showed that the FB50 group was rich in fertilizer nutrients, such as available phosphorus, and alkali-hydrolyzable nitrogen content increased. Heavy metals (Cu, Cd, Cr, Pb, Zn, Ni) met China’s ‘Agricultural Sludge Pollutant Control Standard’ GB 4284-2018 Grade A standard, with obvious passivation and significantly reduced bioavailability. All these results suggested that biochar coupled with Fenton oxidation was more beneficial to sludge composting.

Improving enzymatic saccharification of corn stover via thioglycolic acid-mediated Fenton pretreatment

Fenton pretreatment is known as a green and mild approach, but it is usually time-consuming and inefficient in promoting lignocellulose enzymatic hydrolysis. Here we demonstrate that thioglycolic acid (TA) significantly accelerates Fenton pretreatment (FP) of corn stover (CS) and improves enzymatic hydrolysis of cellulose and xylan. The results showed that the reducing sugar yield of CS reached 77.0% with TA-assisted FP in only 16 h, while it was only 34.1% and 38.0% with FP alone in 16 h and 72 h, respectively. Via examination of the changes of composition, physical and chemical characteristics of CS before and after pretreatment, it was found that TA-assisted FP greatly improved the removal of hemicellulose and lignin, resulting in increment of the pore volume, pore size and cellulose exposure of CS substrate, which together promoted the enzymatic saccharification of CS.

Evaluation of electro-oxidation and Fenton pretreatments on industrial fruit waste and municipal sewage sludge to enhance biogas production by anaerobic co-digestion

This study presents the effect of electro-oxidation and Fenton pre-treatment on anaerobic co-digestion (AnCoD) of fruit-juice industrial waste (FJW) and municipal sewage sludge (MSS). Biogas production increased from 767 mL to 857 mL and 918 mL after EO and Fenton pretreatment, respectively. The methane amount increased by 28% and 39% for EO and Fenton processes. The removal efficiencies of soluble COD, carbohydrate, and protein for the conditions with the highest biogas production as a result of the pretreatment process were 48%, 65%, 61% for the Fenton pre-treatment, and 37%, 52%, and 39% for the EO pre-treatment, respectively. Cumulative biogas production efficiency for all pre-treated mixtures was estimated with kinetic models. In addition, an evaluation has been made regarding cost, economic gain, and energy consumption of the pre-treatment processes.

Pine sawdust modification using Fenton oxidation for enhanced production of high-yield lignin-containing microfibrillated cellulose

Sawdust is an abundant high-quality residue from sawmills, representing 20–30 % of sawn products by volume. In this study, the chemical pre-treatment of pine sawdust with Fenton’s reagent, formed from hydrogen peroxide and iron catalyst under moderately acidic conditions, was found to intensify the microfibrillation process in terms of energy consumption and improve the grade of the high-yield lignin-containing microfibrillated cellulose (LMFC) produced.With a minor yield loss of 5.5 wt.%, Fenton pre-treatment increased the microfibrillation rate and bonding potential of LMFC, indicating that the ultrastructure of the lignocellulose cell walls had been modified. Linear dependency between the growth of specific surface area and energy consumption was seen, i.e. microfibrillation followed Rittinger’s law of comminution. In comparison with the reference without any pretreatment,the total grinding energy consumption to a particle size of 14 µm was about 30 % lower (10.7 vs. 15 MWh/t) while the tensile strength and stiffness of LMFC films were 50 % (100 vs. 66 MPa) and 35 % higher (6.6 vs. 4.9 GPa), respectively. The advantageous effects of Fenton chemistry were assumed to originate from the cleavage of lignin-carbohydrate bonds, mainly between lignin and hemicelluloses. This phenomenon was supported by the substantially increased solubility of polysaccharides in dilute alkali.The calculated manufacturing costs of LMFCs (using the above-mentioned specifications) was € 850/t, of which the raw material, chemical and electricity costs accounted for 10 %, 2 % and 88 %, respectively. Without any chemical pre-treatment, manufacturing costs were € 1100/t of which raw material accounted for 7 % and electricity 93 %.

Environmental and economic performances of incorporating Fenton-based processes into traditional sludge management systems

Municipal and industrial wastewater treatment plants produce a tremendous amount of sludge containing organic and toxic components. One of the advanced oxidation processes (AOP) - Fenton process has demonstrated great prospect in reduction of sludge organics and toxicity. Fenton pretreatment could ameliorate the sludge dewaterability and biodegradability for anaerobic digestion (AD) process, and enhance the sludge lower heating value for incineration process, thus stimulating sludge dewatering, reduction and energy recovery. However, doubts remain about whether the incorporation of the Fenton process into the traditional sludge management systems brings environmental benefits. Hence, a life cycle environmental impact calculation model was established for sludge with various organic contents (60%, 70%, 80%) under the effect of Fenton and US/UV/Electro-Fenton processes. Noteworthy mitigation of environmental load was observed for the Fenton process coupled with incineration system, which involves high dewatering demand. Conversely, as for the AD system with high biomass transformation rate, Fenton process failed to attain the assumed promotion of environmental benefit. Hydrogen peroxide (H2O2) prominently attributed to the weakness of Fenton process combined with AD (F-AD) scenario, compared with the AD scenario in terms of environmental impact. Summarily, the F-AD scenario acts as the preponderant system when weighing up the pros and cons of environmental impact, energy balance and life cycle cost. Contrary to the mainstream view, the proven technical advantages of Fenton process cannot compensate for the additional environmental loads in the life cycle of sludge. It provides valuable reflection for environmental managers and scholars that we should be more cautious in the application of cutting-edge technologies.

Prediction and Optimization of Biogas Production from OMW Digestion Using Fenton Pre-Treatment Process with Particle Swarm Optimization

Prediction and Optimization of Biogas Production from OMW Digestion Using Fenton Pre-Treatment Process with Particle Swarm Optimization

Study on the evolution pattern of the chemical structure of Fenton pretreated lignin during hydrothermal carbonization

Two new lignin feedstocks (HLF and DALF) were obtained by Fenton pretreatment of herbal lignin (HL) and de-alkalized lignin (DAL), and hydrothermal carbonization of each lignin sample was carried out at 290 °C with different holding times to investigate the impact of Fenton pretreatment on the physicochemical properties of the hydrothermal materials. The analyses based on 13C solid-state NMR, XPS, FTIR, SEM and fully automated calorimetry showed that the optimal holding time for hydrothermal carbonization of lignin at 290 °C was 30 min. The two types of lignin were treated with Fenton pretreatment to remove some methoxy groups and make the aromatic structural units more compact. Hydrothermal carbonization removed a small amount of αO4 and βO4 bonds from the structure, increased the guaiacyl units [G], decreased the syringyl units [S], and formed more stable 4-O-5 and CC bonds, which in turn polymerized into 10–300 µm irregular spherical carbon particles or porous honeycomb carbon blocks. The calorific values of HLF290-30 and DALF290-30 were increased to 31.04 MJ/kg and 32.17 MJ/kg, respectively, by the combination of Fenton pretreatment and hydrothermal carbonization. Overall, the Fenton pretreatment of lignin enhanced the degree of aromatization and removal of methoxylation during hydrothermal carbonization of lignin. This study provides a sustainable and green strategy for the preparation of high calorific value hydrochar as well as all-round utilization of lignin.

Influence of fenton pretreatment on anaerobic digestion of sugarcane vinasse: effect of H2O2 dosage

Sugarcane vinasse is one of the resources with a high potential for biogas production. However, its high value of COD (>100 g/L) and poor biodegradability could present substrate inhibition during anaerobic digestion. Thus, pretreatment techniques seem necessary for improving the process efficiency and enhancing biogas yield from sugarcane vinasse. In this study, the pretreatment process has been carried out using Fenton reagent, which utilizes the hydroxyl radical produced from the catalyzing reaction between hydrogen peroxide and Fe2+ or Fe3+. Sugarcane vinasse as substrate was pretreated using Fenton reaction at different doses of 30% H2O2 within the range of 15 to 80 g/L. Through Fenton pretreatment, the biodegradability of sugarcane vinasse and biogas production was markedly increased. The optimum dose of H2O2 for Fenton pretreatment of biogas production from sugarcane vinasse was 60 g/L. At this pretreatment condition, the cumulative biogas yield was 124.39 mL/g sCOD, and the methane content was 52.6%. The methane content of biogas from Fenton-pretreated vinasse increased approximately four times higher (from 11.3% to 52.6%) compared to the untreated sugarcane vinasse as control. These results indicate that Fenton pretreatment can be applied to improve substrate biodegradability and enhance biogas production from sugarcane vinasse.

Application of a Fenton process for the pretreatment of an iron-containing oily sludge: A sustainable management for refinery wastes

The feasibility of a Fenton-type process for the pretreatment of an oily refinery sludge has been explored taking advantage of the iron contained in the own sludge. This process reduces the content of total petroleum hydrocarbons (TPHs) accompanied by an increase in the total organic carbon concentration in the liquid phase. The effect of the temperature and the hydrogen peroxide loading was thoroughly studied in this work being the oxidant concentration the most critical parameter. Under 60 °C and 90 g/L of initial hydrogen peroxide concentration, the Total Organic Carbon (TOC) of the liquid phase was increased up values of 1336 mg/L and with a remarkable contribution of acetic acid as final oxidized compound (396 mgC/L). Additionally, nitrogen and phosphorous compounds were also dissolved in the aqueous phase achieving values of 250 mg/L and 7 mg/L for total Kjeldahl nitrogen and total phosphorous, respectively. Respirometry assays of the aqueous phase after the Fenton pretreatment have evidenced an increase of biodegradability up to 49% which makes this phase suitable for further biological processing in the refinery scheme. The reduction of the content of TPHs (61%) of the oily sludge, has also improved the settleability of the treated effluent (reducing the capillary suction time (CST) in ca. 88%).