Refinery Sludge Research Articles

Factors influencing demulsification of refinery oily sludge via ultrasonic treatment

Ultrasonic demulsification treatment is essential to dehydrate refinery sludge with complex composition, high water content, and demulsification difficulty. Herein, the influencing factors and the demulsification mechanism are studied in oily sludge treatment. The effects of initial temperature, ultrasonic amplitude, and time, as well as a diversity of additives on the ultrasonic dehydration rate of oily sludge demulsification, are investigated. The optimal demulsification conditions are confirmed (temperature: 20 °C, ultrasonic amplitude: 100 %, and ultrasonic time: 5 min), based on the effectiveness and economy of dehydration. The combined ultrasonication and pyrolysis of the solid residue of sludge shows a dehydration rate of 60.49 %, beneficial for the green transformation and utilization of subsequent demulsification products. Moreover, the mechanism of ultrasonic emulsification is proposed, as well. This work provides an important reference for the subsequent resource utilization of oily sludge in the industry.

Removal and stabilization of As and Cd in water/soil using silicate-supported nano zero-valent iron composites: Preparation, behavior, mechanism and cost analysis

A novel silicate-supported nano zero-valent iron composite material (nZVI@SS) for the removal and stabilization of arsenic (As) and cadmium (Cd) in water/soil had been developed through the modification of low-grade oolitic iron ore (OI) by reduction, while refinery sludge (RS) as reductant, manganese carbonate (MC) as additive in this work. The As and Cd adsorption capacity of nZVI@SS reached 93.91 mg·g−1 and 265.81 mg·g−1, respectively. Its specific surface area and pore volume increased by 19.28 m2·g−1 and 0.24 cm3·g−1, respectively when compared with unmodified OI. In the actual soil leaching process, using 2 % nZVI@SS for 30 days, the leaching concentrations of As and Cd decreased by 87.86 % and 85.51 % respectively, while their bioavailable contents were reduced by 15.59 mg·kg−1 and 1.40 mg·kg−1, correspondingly. The formation of chemical precipitates as Fe-As, Ca-As compounds, and Cd(OH)2 was the main mechanism of their adsorption process. Therefore, HMs adsorbed by nZVI@SS were difficult to desorb, making it more suitable for passivation/stabilization of HMs in groundwater/soil. Furthermore, the production cost of nZVI@SS was approximately 50 $/T, below the average market value of comparable adsorption materials. This method made low-grade minerals into environmentally friendly materials with high added value, significantly reduced the environmental risk of HMs in water/soil, and provided a new approach for the development of sustainable environmentally friendly materials using hazardous waste RS as a resource.

Aqueous extracts of composted oil refinery sludge and their possible environmental impacts

ABSTRACT Oil refinery sludge (ORS) management is a global concern, yet information on its low-cost biotransformation possibility is fairly limited. We present a novel approach for ORS mitigation by Eisenia fetida and Eudrilus eugeniae and aerobic composting (AC) in producing clean aqueous extracts (compost teas). Detailed physicochemical characterization, phytotoxicity assays, economic feasibility comparisons, and mathematical equation-based environmental and human health hazard prediction studies were done for all the earthworm and non-earthworm processed compost teas. The E. eugeniae-compost tea reduced Cr, Pb, Cu, Cd, and Zn contents by 52.7, 61.2, 41.8, 80, and 93.8%, respectively. The earthworm-sourced teas showed lower ecological risk (<300) than their aerobic counterparts. Seed germination in Pisum sativum and Cicer arietinum was 2–2.5 folds higher with vermi-derived tea application. Economic assessments illustrated the superiority of E. eugeniae-based biotransformation with higher cash flow and a lower payback time of 1.53 years. The mathematical predictions on human health showed no alarming status for any of the vermi/aerobic compost teas. Overall results implied that vermicomposting is safer and more beneficial than AC in the ORS bioconversion. However, this study warrants further research in exploring the efficiency of other earthworm species, feedstock selection, or seasonal variability in ORS management.

A novel iron-based composite modified by refinery sludge for fixing Pb, Zn, Cu, Cd, and As in heavy metal polluted soil: Preparation, remediation process and feasibility analysis

In this study, we prepared a novel iron-based composite (NIC) via a one-step reduction method utilizing refinery sludge (RS) as the reducing agent and iron ore (IO) as the iron source, allowing for the concurrent stabilization of multiple heavy metals (HMs) in soil. The loose, porous structure of NIC provided ample active sites, including Fe0, CaAl2Si2O8, fixed carbon, and a small amount of active amorphous substances. After 60 days of soil remediation using 5% NIC, the bioavailable content of HMs Cu, Zn, Pb, Cd, and As was reduced by 71.55%, 49.62%, 91.35%, 61.37%, and 41.45%, respectively. Upon magnetic recovery and analysis of NIC in soil, HMs were found to have been enriched in the material, forming new phases like FeAsO4, ZnFe2O4, among others. Thus, the immobilization mechanism of HMs included adsorption, co-precipitation and complexation etc. Furthermore, NIC enhanced soil pH and cation exchange capacity, elevating the soil's ability to retain heavy metal cations. Lastly, cost-benefit analysis revealed that RS as a reducing agent could lower the production cost of environmental remediation materials. Furthermore, HM leaching toxicity analysis verified the safety of its usage. Overall, our findings offer a promising procedure for both the resource utilization of refinery sludge and multi-metal co-contaminated soil remediation.

Unleashing synergistic potential of microbially enhanced anaerobic co-digestion of petroleum refinery biosludge and yard waste: Impact of nutrient balance and microbial diversity

Petroleum refinery sludge, an egregious solid residue generated from the wastewater treatment plants poses an environmental hazard owing to its intricate hydrocarbon composition, necessitating competent treatment for secure disposal. The study proposes a green solution through anaerobic co-digestion of nitrogen-rich petroleum refinery sludge (PS) with carbon-rich yard waste (YW), balancing the nutrients and moisture content for efficient microbial proliferation. Using Central Composite Design-Response Surface Methodology, 1 L batch experiments were conducted with varying carbon/nitrogen (C/N) ratios and pH to achieve maximum biogas yield within 50 days of co-digestion. However, the sluggish biogas recovery (40%) indicated a slow rate-limiting hydrolysis, necessitating pretreatment. Feedstock incubation with Bacillus subtilis IH1 strain, isolated from the microbially-enriched PS, at 108 colony forming units (CFU) per mL for 5 days maximized the soluble chemical oxygen demand and volatile fatty acids by 2.2 and 1.4 folds respectively compared to untreated feedstock. Scale-up Bacillus subtilis aided co-digestion studies further augmented biogas by 76% against untreated monodigestion of PS with significant total petroleum hydrocarbons, emulsions, and lignocellulosic degradation. Further identification of major organic pollutants in the batch digestate revealed significant degradation of the toxic organic hydrocarbon pollutants apotheosizing the efficacy of the synergistic sustainable technique for the management of PS. Environmental implicationThe effluent treatment plants (ETPs) of petroleum refining industries generate sludge which is a complex mixture of petroleum hydrocarbons, oil–water (O/W) emulsions and heavy metals. These petroleum hydrocarbon constituents can be linear/cyclic alkanes, polyaromatics, resins and asphaltenes, whose intricate composition is reportedly carcinogenic, cytogenic and mutagenic, classifying it as hazardous waste. Biological treatment of these sludge through anaerobic digestion leads to utilization of petroleum hydrocarbons with subsequent energy recovery. Co-digestion of these sludge with competent co-substrates leads to nutrient balance, diverse microbial proliferation and toxicant dilution. Microbially aided co-digestion further augments methane rendering a digestate with utmost pollutant degradation.

Biochar performance for preventing cadmium and arsenic accumulation, and the health risks associated with mustard (Brassica juncea) grown in co-contaminated soils

Cadmium (Cd) and arsenic (As) in co-contaminated soil can enter the human body harming health via the food chain, such as vegetables. Biochar derived from waste has been used to reduce heavy metal uptake by plant, but long-term effects of biochar under Cd and As co-contaminated soil needs to be investigated. A following mustard (Brassica juncea) was grown on co-contaminated soil amended with different raw materials of biochar including biochars pyrolyzed by lignite coal (LCB), rice straw (RSB), silkworm excrement (SEB), and sugar refinery sludge (SSB). The results showed that compared to the control, Cd and As contents of mustard shoot in SSB treatment decreased by 45–49% and 19–37% in two growing seasons, respectively, which was the most effective among 4 biochars. This probably due to SSB owns more abundant Fe-O functional groups. Biochar also altered the microbial community composition, specifically SSB increased proteobacteria abundance by 50% and 80% in the first and second growing seasons, thereby promoted the simultaneous immobilization of Cd and As in soils which may reduce the potential risks to humans. In summary, considering the long-term effects and security of SSB application on mustard, not only is it an effective waste recycle option, but it should also be promoted as a promising approach for safe vegetable production in Cd and As co-contaminated soils.

Effect of noble bacteria Ochrobactrum intermedium (Alhpa-22) on decolorization of methyl orange dye in a bioreactor

Abstract In this study Ochrobactrum intermedium (Alhpa-22) was isolated from petroleum refinery sludge and characterized by using 16rRNA. In experimentation, for decolrization of methyl orange dye an indigenous noble bacterial ochrobactrum intermedium (Alhpa-22) at 35 °C has been used in a bioreactor. The ochrobactrum bacterial decolorized methyl orange dye having the concentration of 50 mgL−1 by 87 % within 9 days, which is a very encouraging result. decolorization of methyl orange dye by the isolated bacteria was elucidated using a UV–Vis spectrophotometer. The experimental data were fitted first and zero order kinetics models which show degradation of dye follows first order kinetics in presence of Lysinibacillus fusiformis KLm1, bacterial ochrobactrum intermedium (Alhpa-22) and mix consortia of Lysinibacillus fusiformis KLm1 and ochrobactrum intermedium (Alhpa-22). The rate constant were estimated to be 0.017 h−1, 0.020 h−1 and 0.014 h−1 respectively. Due to its higher decolorizing capability these may be used for the bioremediation of methyl orange dye (azo dye).

Preparation of carbonaceous adsorption composite with refinery sludge for butyl xanthate and diethyldithiocarbamate removal in flotation wastewater

Preparation of carbonaceous adsorption composite with refinery sludge for butyl xanthate and diethyldithiocarbamate removal in flotation wastewater

Microbial pretreatment using Kosakonia oryziphila IH3 to enhance biogas production and hydrocarbon depletion from petroleum refinery sludge

Petroleum refinery sludge (PRS) from the biological treatment unit was assessed for the extent of anaerobic biodegradability and pollutant removal through microbial pretreatment utilizing a novel lignin peroxidase (LiP) enzyme-producing bacterial strain, Kosakonia oryziphila to optimize the accelerated solubilization of PRS. K. oryziphila was incubated at different dosages (107, 108 and 109 CFU/mL) for 6 d resulting in maximum soluble chemical oxygen demand (3-fold increment) and volatile fatty acids concentration (2.53-fold increment) against untreated for dosage 108 CFU/mL on 4th d. The maximum LiP activity (20.52 IU/mL) was obtained at optimum conditions. The interactive effect of pretreated substrate and inoculum (S/I) ratios and pH on accumulated biogas yield was optimized using central composite design-response surface methodology in 1 L batch assay. This resulted in significant interaction of independent variables to obtain an optimal condition (S/I = 2.69 and pH = 7.38) for maximum biogas (5.15 L/g VSadded) with 1.56-fold increment against untreated PRS. During process scale-up (20 L study), total petroleum hydrocarbon, oil and grease, and total phenol removals were 56.2%, 62.5% and 88.4% respectively within 50 d of digestion. The digestate phytotoxicity assay revealed a significant reduction in seed-germination inhibition with an increase in seedling and biomass growth suggesting improved decontamination during the digestion process.

Characterization and biodegradability assessment of water-soluble fraction of oily sludge using stir bar sorptive extraction and GCxGC-TOF MS

Percolation of water through oily sludge during storage and handling of the sludge can cause soil and groundwater contamination. In this study, oily sludge from a refinery was equilibrated with water to obtain the water-soluble fraction (WSF) of oily sludge. The WSF had dissolved organic carbon (DOC) of 166 mg/L. Human cell line-based toxicity assay revealed IC50 of 41 mg/L indicating its toxic nature. The predominant compounds in WSF of oily sludge included isomers of methyl, dimethyl and trimethyl quinolines and naphthalenes along with phenol derivatives and other polynuclear aromatic hydrocarbons (PAHs). Biodegradation of WSF of oily sludge was studied using a consortium of Rhodococcus ruber, Bacillus sp. and Bacillus cereus isolated from the refinery sludge. The consortium of the three strains resulted in 70% degradation over 15 days with a first-order degradation rate of 0.161 day−1. Further analysis of the WSF was performed using the stir-bar sorptive extraction (SBSE) followed by GCxGC-TOF MS employing a PDMS Twister. The GCxGC analysis showed that Bacillus cereus was capable of degrading the quinoline, phenol and naphthalene derivatives in WSF of oily sludge at a faster rate compared to pyridine and benzoquinoline derivatives. Quinoline, phenol, biphenyl, naphthalene, pyridine and benzoquinolines derivatives in the WSF of oily sludge were reduced by 87%, 92%, 88%, 77%, 40% and 62%, respectively with respect to the controls. The WSF of oily sludge contained, n-alkanes, ranging from n-C12 to n-C18 which were removed within 2 days of biodegradation.

BIOTREATABILITY OF PETROLEUM REFINERY SLUDGE USING LAND - FARMING AND ANAEROBIC DEGRADATION TECHNIQUES

One of the major problems faced by oil industries and the environment, is the safe disposal of oily sludge generated during the processing of crude oil. Biotreatability of petroleum refinery sludge using bioremediation and anaerobic degradation techniques was studied. Analysis of the Nigerian Petroleum Refinery sludge used for this research indicated that the sludge is slightly acid with high total petroleum hydrocarbon (TPH) content of 340,000mg/kg and polyaromatic hydrocarbon (PAH) content of 0.075mg/kg. The heterotrophic bacterial and fungal counts were 5.86 x 105 and 4.72 x 105cfu/g respectively while the hydrocarbon degrading bacterial and fungal count were 2.85 x 102 and 2.75 x 102 cfu/g respectively. Results from biotreatability studies revealed that the sludge contamination at lower concentration 10,000 (1%) mg/kg, recorded high percentage degradation than the treatment with higher sludge concentration, 50,000 (5%) mg/kg. Biostimulation treatments enhanced the sludge degradation better than the natural attenuated treatment. Volume of biogas produced in the anaerobic microcosm was highest in the treatment with compost in both 1% (10.73 l/kg) and 5% (9.27 l/kg) sludge treatments. Though the NPK treated soil enhanced the biodegradation of sludge most, degradation started declining by the 9th week while that of compost continued to rise steadily till the 12th week. Anaerobic process was quite slow and did not degrade the sludge as much as the aerobic land – farming method.

Strategic implementation of integrated bioaugmentation and biostimulation for efficient mitigation of petroleum hydrocarbon pollutants from terrestrial and aquatic environment

Release of petroleum hydrocarbon pollutants poses a serious problem to the terrestrial as well as marine ecosystem. This study investigated and compared the potency of different biodegradation strategies for mitigating total petroleum hydrocarbon (TPH) of petroleum refinery sludge by an integrated action of bioaugmentation and biostimulation vis-à-vis separate bioaugmentation and biostimulation approaches. The implementation of a concomitant bioaugmentation-biostimulation strategy (BABSS) involving the indigenously developed bacterial consortium and poultry litter extract showed the best performance by mitigating the TPH up to 90.3 ± 3.7% in 21 days. The GC-FID analysis confirmed the efficacy of different TPH degradation strategies. The kinetic study of TPH degradation of BABSS resulted first-order with rate 0.11 day−1. Thus, the BABSS proved to be more efficient in degrading TPH in an eco-friendly manner and hence, may pave the way for better management of petroleum hydrocarbon pollutants, while providing a sustainable solution to the disposal of poultry wastes.

Simultaneous biodegradation of BTX by isolated degrading bacterial strains in a newly designed modulated bio-scrubber assisted to airlift parallel bioreactors.

A new approach in this present study, isolated bacteria from refinery sludge were used in a laboratory-scale bio-scrubber, connecting with two parallel airlift bioreactors to eliminate harmful and toxic fumes of BTX. One of the main features of this bio-scrubber is using porous mineral pumice fillers (Lava Rock) inside poly-urethane foam (PUF)module tower, connecting with agitator bio-phasic continuously stirred tank bio-reactor (CSTbR) to increase retention time and contact surface. The bio-scrubber and airlift plug flow bio-reactor(PFbR) were used in parallel with cooling flow to be more efficient in preservation of the corresponding heater and endothermic from removal reactions. Performance of bio-scrubber in removing BTX vapors with 10 % silicone oil and grade 350 poise as organic phase in the inlet concentration range of 180 ± 0.3 to 1950.5 ± 0.1mg /m3 (ppmv) for up to 6 months in two air flow rate's 2.5 and 3.5 (lit/min) that each treatment lasted about 2 months. The rate of biodegradation in this study was carried out by mixing 3 isolated bacteria, obtaining from refinery sludge, named DBIS-03, DTIS-12, and DXIS-09, which they had highest biodegradability than all the isolated strains. The results of BTX biodegradation at each EBRT (Empty Bed Retention Time) showed that the removal efficiency of BTX with isolated bacterial samples was able to grow and multiply on porous fillers and regenerate the growth medium of autotrophic bacterial strain with O2 gas and micronutrients from contaminated air flow with minimum concentration. Benzene, toluene and xylene inputs maximum concentration over a period of 20 days loading, respectively: B :99.2 % (at 2.5 lit/min and 183.2 ± 0.2mg /m3 (ppmv)), T: 98 % (at 2.5 lit/min and 327.1 ± 0.1mg /m3 ( ppmv)) and X: 85.9 % (at 2.5 lit/min and 296.8 ± 0.8mg /m3 (ppmv)) compared to 3.5 lit/min and so show the best performance in removing BTX from polluted air in period of 30 days.

Adsorption of the Petrochemical Pollutants Released at the Small Vehicle-Service Facilities on the Coal Refinery Sludge/Pyrocarbon Compositions

It has been proven that the use of coal-like adsorbents with the mosaic and hydrophobic surface structure is efficient in cleaning thewastewater from a wide range of pollutants under the condition of their uncontrolled release from various small enterprises. Thisrange includes such environmentally dangerous agents as petrochemicals and other pollutants formed at car filling, carwash stationsor other similar facilities. Technical pyrocarbon and the coal refinery sludges are readily available waste materials with high porosity,which exhibit some adsorption activity and can be utilized in water/wastewater treatment solutions. Then the adsorbents can be eitherdisposed of at the landfill areas or incinerated as components of some secondary fuels. The highest adsorption performance is achievedfor the sorbent mixture of the refinery sludges and technical pyrocarbon with the ratio of the components 4:1.If the wastewater is flowing through this composition, the degree of petrochemicals removal reaches 75-80% for the mixture sludge/technical pyrocarbon, while the pure pyrocarbon ensures the removal degree of 15-20% only. Though adsorption efficiency under stationary conditions (keeping the adsorbent and the wastewater in contact inside some decontamination pond/vessel for at least 24 h) ishigher, this option is hard-to-realize for a small car service/wash station. As an alternative, comparatively small wastewater cleaningcartridges filled with the 4:1 mixture of coal sludge and technical pyrocarbon can be recommended for preliminary decontaminationof the wastewater formed at such enterprises before their discharge to the local municipal sewerage lines.

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%).

Solidification/stabilization remediation of heavy metal from petroleum Al-Dura sludge with Portland cement

The aim of this research is to evaluate the method of stabilization/solidification in the treatment of cadmium and iron from Al-Dura Oil Refinery sludge. In addition, the effect of organic matter was studied by using treated and untreated sludge. The procedure was applied in three treatments, where the cement was added to a mixture of sludge/sand prepared at three ratios (i.e., 1:2, 1:3, and 1:4) and also without any sludge (as the control), with the treated and untreated sludge used in proportions of 7, 15, and 25% by weight of sand. Tests of unconfined compression strength and a toxicity characteristic leaching procedure were used to evaluate the stabilization/solidification matrix. The highest unconfined compression strength was 3 Mpa for the samples with untreated sludge, while it was 2.1Mpa for samples with treated sludge. However, the results of the leaching test showed that the samples with the untreated sludge had more retention efficiency compared to the samples with treated sludge. The cadmium retention efficiency was 99.1%, while for iron, it was 97.5%. The organic matter (especially aromatic) had no effect on the leaching of either Iron or cadmium. Therefore, this method seems to be highly successful in the treatment of both Iron and cadmium with untreated Al-Dura Oil Refinery sludge.

Enhanced methane production and hydrocarbon removal from petroleum refinery sludge after Pseudomonas putida pretreatment and process scale-up

The influence of Pseudomonas putida 7525 strain on the pretreatment of petroleum refinery sludge was optimized at different dosages to maximize solubilization for improved biodegradability. Laccase-producing P. putida strain at a dosage of 108 CFU/mL resulted in 249% and 121.57% increments in soluble chemical oxygen demand and volatile fatty acids production respectively as compared to untreated within 6 days of incubation. 1L biochemical methane potential test conducted for optimization of different inoculum and pretreated substrate ratios (0.3, 0.4, 0.5, 0.7 and 1.0) revealed maximum methane augmentation (62%) and volatile solids degradation (66.7%) at ratio 0.5. Scaled-up study (20L) for ratio 0.5 resulted in 57.07% total petroleum hydrocarbon, 62.98% oil and grease and 91.9% phenol removal within 50 days of digestion of pretreated PS. Kinetic modelling of cumulative methane yield indicated that modified Gompertz model showed the best fit thereby, evincing the potency of bacterial species for bioremediation of PS.

Optimization of electrokinetic pretreatment for enhanced methane production and toxicity reduction from petroleum refinery sludge

This study examined the effect of electrokinetic pretreatment on petroleum sludge (PS) released from the wastewater treatment plants of petrochemical industries for enhanced biodegradation and contaminant removal. The application of electric field on PS through direct current is optimized with the combined variation of applied voltage (40–80 V), exposure duration (20–120 min) and distance between graphite electrodes (8–16 cm) using central composite design-response surface methodology (CCD-RSM). The optimization study revealed significant interaction among the response variables to obtain an optimum condition (60 V, 83.5 min, 11.6 spacing) for maximization of solubilization in terms of soluble chemical oxygen demand (230% increment against untreated) and volatile fatty acids (172% increment against untreated) concentrations for accelerated hydrolysis of complex PS. BMP batch assays were performed at different inoculum and sludge ratios (0.3, 0.4, 0.5 and 0.7) based on volatile solids content after pretreatment at the optimized condition which resulted in accumulated methane ranging from 5.16 to 6.61 L/gVSadded (untreated - 3.9 L/gVSadded). The mixing ratio of 0.4 showed the maximum methane enhancement of 69.2% compared to untreated. The maximum removal of organic content (62.8%), oil and grease (71.74%), and total petroleum hydrocarbon (52.9%) were also observed for the mixing ratio of 0.4. The FTIR study showed the efficacy in hydrocarbon dissociation and decomposition after pretreatment of PS. The net energy gain (3508 kJ) and phytotoxicity reduction of batch digestate after the anaerobic digestion suggest the economic feasibility and decontamination efficiency of the electrokinetic pretreatment technique respectively. Further research could be performed to evaluate the viability of this pretreatment for enhanced methane recovery at field-scale levels to relate to these lab-scale postulations.

Assessment of ecotoxical state of technologically modified edaphotopes with waste of oil refinery with the Allium-test method

The ecotoxic state of technologically modified edaphotopes by waste of refinery was investigated with the Allium-test method. Material for the investigations was samples of edaphotopes which were selected at a depth of 15–20 cm from seven research areas of different locations. The last ones were 10–200 m away in relation to the surface storages of oil sludge and other waste of refinery. It has been detected in Allium-test that edaphotopes of the research areas located at a distance of 10–50 m relative to the storages of waste are toxic. Particularly, their aqueous extracts cause a medium and high level of phyto-, cyto- and genotoxic effects on the growing and proliferative activity of Allium cepa Stuttgarter Riesen variety meristem. Test extracts of edaphotopes in growing Allium-test caused darkening of rootlets and blackening of their tips (contrary to the light rootlets with light tips in control). In addition to it the growing activity of A. сepa bulb roots that were grown on the aqueous extracts of edaphotopes was decreased in 1.71–3.5 times depending on the location and measure of remoteness of the research area from the storage of waste of the refinery. Phytotoxicity of aqueous extracts of those edaphotopes regarding to A. сepa is above average and higher levels, and tolerance of onion rootlets to the test extracts decreases up to 29–52 % comparing to control. The mitotic activity of apical meristem of rootlets also decreased. Particularly, mitotic indexes diminished to 51.05–63.57 % (in control – 82.34 %) and cytotoxicity ones were in the range of 22.8–48.0 % that confirms the medial level of cytotoxicity of the investigated edaphotopes. Ana-telophase method and micronucleus test have shown that the chromosome aberrations frequency and appearance of micronuclei in the cells of the apical meristem of the test object A. cepa is higher in 3.34–5.20 times comparing to control. It indicates the average and the high level of genotoxicity of the investigated edaphotopes. The edaphotopes, which are located at the distance of 100–200 m in relation to the surface storages of waste of refinery have a slight phyto-, cyto- and genotoxic effects which are close to the background level.

Enhanced biodegradation of total petroleum hydrocarbons by implementing a novel two-step bioaugmentation strategy using indigenous bacterial consortium

In the present study, a two-step bioaugmentation strategy (TSBS) was implemented by using indigenous bacterial consortium to enhance the degradation of total petroleum hydrocarbons (TPH) from petroleum refinery sludge (PRS). A bacterial consortium was developed using four indigenous isolated strains, Dietzia sp. IRB191, Dietzia sp. IRB192, Staphylococcus sp. BSM19 and Stenotrophomonas sp. IRB19 from PRS. The optimum conditions of pH, temperature, and sludge concentration were 7, 34 °C, and 2% (w/v), respectively, for maximum TPH degradation, obtained using one variable at a time approach. Under the optimal culture conditions, the developed consortium was inoculated twice to the culturing medium, at the beginning (0th day) and again on the 10th day for implementing a novel TSBS. The maximum TPH degradation of 91.5 ± 2.28% was found with TSBS, which was 1.18 times higher than that of SSBS (77.3 ± 2.6%) in 15 days of incubation. GC-FID study also confirmed that the TPH present in the PRS was effectively degraded by the bacterial consortium with TSBS. The TPH degradation by using TSBS proceeded according to the first-order kinetics with a rate constant of 0.155 d−1. Hence, biodegradation using a TSBS can be considered an effective and eco-friendly process for safe disposal of petroleum refinery sludge.