Effects of adding bulking agent, inorganic nutrient and microbial inocula on biopile treatment for oil-field drilling waste

Pilot-scale field studies on activated microbial remediation of petroleum-contaminated soil

Soil contamination by petroleum, including crude oil from various sources, is increasingly becoming a pressing global environmental concern, necessitating the exploration of innovative and sustainable remediation strategies. The present field-scale study developed a simple, cost-effective microbial remediation process for treating petroleum-contaminated soil. The soil treatment involves adding microbial activators to stimulate indigenous petroleum-degrading microorganisms, thereby enhancing the total petroleum hydrocarbons (TPH) degradation rate. The formulated microbial activator provided a growth-enhancing complex of nitrogen and phosphorus, trace elements, growth factors, biosurfactants, and soil pH regulators. The field trials, involving two 500 m3 soil samples with the initial TPH content of 5.01% and 2.15%, were reduced to 0.41% and 0.02% in 50 days, respectively, reaching the national standard for cultivated land category II. The treatment period was notably shorter than the commonly used composting and bioaugmentation methods (typically from 8 to 12 weeks). The results indicated that the activator could stimulate the functional microorganisms in the soil and reduce the phytotoxicity of the contaminated soil. After 40 days of treatment, the germination rate of rye seeds increased from 20 to 90%, indicating that the microbial activator could be effectively used for rapid on-site remediation of oil-contaminated soils.

Human health risk assessment of volatile organic compounds in oil-based drill cuttings of shale gas

Waste oil-based drill cuttings contain dioxins and volatile organic compounds (VOCs), which have the potential to cause serious health effects in humans. Therefore, this paper took oil-based drill cuttings (OBDCs) as the research object and carried out the testing of VOCs and dioxins content by using GC-MS and HRGCS-HRMS and comprehensively evaluated the content, composition and distribution pattern of VOCs and dioxins and the risk to human health posed by the two pollutants in OBDCs. The results showed that the VOCs did not exceed the emission limits in ESPPI (GB 31571-2015), but it is vital to recognise that 1,2-dichloropropane has the potential to cause cancer risk, with soil and groundwater risk control values of 662.95 mg·kg-1 and 0.066 mg·kg-1, respectively. Benzene, 1,2-dichloropropane and 8 other VOCs pose a non-carcinogenic risk to humans. The levels of polychlorinated dibenzofurans (PCDFs) exceeded those of polychlorinated dibenzo-p-dioxins (PCDDs), which accounted for 95.76 percent of the total PCDD/Fs, 2,3,4,7,8-P5CDF (56.00%), 2,3,7,8-T4CDF (9.20%), 1,2,3,6,7,8-H6CDF (8.80%) and 1,2,3,7,8-P5CDF (8.00%) were the main contributing monomers. The findings of the assessment on exposure risk indicate that there is a respiratory risk to oil-based drill cuttings dioxins for adults and children exceeded the World Health Organisation (WHO) acceptable daily intake (ADI) (1-4 pgTEQ/kg/d). Finally, three aspects of solid waste pre-treatment prior to incineration, the incineration process and post incineration were used to reduce the environmental and human health risks from dioxins.

Employing salt-tolerant bacteria Serratia marcescens subsp. SLS for biodegradation of oily kitchen waste

The high oil and salt content of kitchen waste (KW) inhibit bioconversion and humus production. To efficiently degrade oily kitchen waste (OKW), a halotolerant bacterial strain, Serratia marcescens subsp. SLS which could transform various animal fats and vegetable oils, was isolated from KW compost. Its identification, phylogenetic analysis, lipase activity assays, and oil degradation in liquid medium were assessed, and then it was employed to carry out a simulated OKW composting experiment. In liquid medium, the 24 h degradation rate of mixed oils (soybean oil: peanut oil: olive oil: lard = 1:1:1:1, v/v/v/v) was up to 87.37% at 30 °C, pH 7.0, 280 rpm, 2% oil concentration and 3% NaCl concentration. The ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS) method demonstrated that the mechanism of SLS strain metabolizing long-chain triglycerides (TAGs) (C53-C60), especially the biodegradation of TAG (C18:3/C18:3/C18:3) by the strain can reach more than 90%. Degradation of 5, 10, 15% concentrations of total mixed oil were also calculated to be 64.57, 71.25, 67.99% respectively after a simulated composting duration of 15 days. The results suggest that the isolated strain of S. marcescens subsp. SLS is suitable for OKW bioremediation in high NaCl concentration within a reasonably short period of time. The findings introduced a salt-tolerant and oil-degrading bacteria, providing insights into the mechanism of oil biodegradation and offering new avenues of study for OKW compost and oily wastewater treatment.

Achieving Practical Venue Recycle of Waste Oil-Based Drilling Fluids with Vacuum Distillation Technology

Drilling fluids are essential operating additives for extracting oil and shale gas. Thus, their pollution control and recycling utilization are significant to petrochemical development. Vacuum distillation technology was used in this research to handle waste oil-based drilling fluids and achieve reutilization. Briefly, recycled oil and recovered solids can be obtained from waste oil-based drilling fluids whose density is 1.24-1.37 g/cm³ by vacuum distillation under the condition of an external heat transfer oil temperature of 270 ± 5 °C and a reaction pressure below 5 × 10³ Pa. Meanwhile, recycled oil has excellent apparent viscosity (AV, 21 mPa·s) and plastic viscosity (PV, 14 mPa·s), which could be used as a substitute for 3# white oil. Furthermore, PF-ECOSEAL prepared by recycled solids exhibited better rheological properties (27.5 mPa·s AV, 18.5 mPa·s PV, and 9 Pa yield point) and plugging performance (32 mL V₀, 1.90 mL/min^1/2V_sf) than drilling fluids prepared with the conventional plugging agent PF-LPF. Our work confirmed that vacuum distillation is a valid technology in innocuity treatment and resource utilization of drilling fluids and has great value in industrial applications.

Bioremediation of heavy oily sludge: a microcosms study

Oily sludge is a residue from the petroleum industry composed of a mixture of sand, water, metals, and high content of hydrocarbons (HCs). The heavy oily sludge used in this study originated from Colombian crude oil with high density and low American Petroleum Institute (API) gravity. The residual waste from heavy oil processing was subject to thermal and centrifugal extraction, resulting in heavy oily sludge with very high density and viscosity. Biodegradation of the total petroleum hydrocarbons (TPH) was tested in microcosms using several bioremediation approaches, including: biostimulation with bulking agents and nutrients, the surfactant Tween 80, and bioaugmentation. Select HC degrading bacteria were isolated based on their ability to grow and produce clear zones on different HCs. Degradation of TPH in the microcosms was monitored gravimetrically and with gas chromatography (GC). The TPH removal in all treatments ranged between 2 and 67%, regardless of the addition of microbial consortiums, amendments, or surfactants within the tested parameters. The results of this study demonstrated that bioremediation of heavy oily sludge presents greater challenges to achieve regulatory requirements. Additional physicochemical treatments analysis to remediate this recalcitrant material may be required to achieve a desirable degradation rate.

Development and validation of diffusion-controlled model for predicting polycyclic aromatic hydrocarbons from baking-free brick derived from oil - based drilling cuttings

Investigating the release of organic pollutants from bricks made from solid waste is essential. Based on Fick's laws of diffusion, the diffusion model and diffusion-degradation model of polycyclic aromatic hydrocarbon (PAH) emission from the bricks were deduced. The degradation and 64-day emission of PAHs in solid bricks made of oil-based drill cuttings were observed experimentally. The emission and degradation characteristics of 14 PAHs were obtained and fitted with the diffusion and diffusion-degradation models. The emission of most of the PAHs from the bricks at the beginning was in good agreement with the diffusion model, except for benzo[a]anthracene, pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, and benzo[a]pyrene. However, the emission of PAHs after some time was significantly lower than the theoretical value of the diffusion model. Moreover, fitting with the diffusion-degradation model gave better results, indicating that a joint diffusion-degradation mechanism controlled the emission of PAHs. Therefore, the diffusion-degradation model can better predict the long-term emission of PAHs in bricks made of oil-based drill cuttings.

Improved fertilization efficiency of manure compost obtained by using oil shale semicoke as the bulking agent

Oil shale semicoke is a kind of solid waste produced during the retorting process of oil shale, which could cause environmental pollution without reasonable disposing. In our previous study, the abandoned semicoke was recycled as bulking agent to reduce the nitrogen loss and greenhouse gases emission during composting. But influences of the obtained semicoke-blended compost on soil properties and plant growth remained unclear, which would be discussed in this study. Through leaching experiments, it was found that the N/P/K retention capacity of soil mixed with semicoke-blended compost significantly increased for the good nutrients sorption capacity of oil shale semicoke. Subsequently, germination test showed the germination index of semicoke-blended compost could attain 120%, implying its low phytotoxicity. And pot experiments exhibited the biomass of cress and Brassica rapa significantly increased by 2-4 times when applying semicoke-blended compost as fertilizer, exhibiting its great benefits to plants. For the increase of crop yield, it was closely related to their elevated nutrients uptake efficiency, also might be related to the improved soil microbial community and activity as the microbial analysis indicated. Finally, results of pollutant detection showed the concentration of polycyclic aromatic hydrocarbons, Cr, As, Cd and Pb in the mature semicoke-blended compost obtained through composting was 2.82, 95.30, 5.95, 0.34 and 14.45 mg kg^-1 respectively, meeting the standard for soil application. The research suggests composting could be an effective method for the harmless disposing and resource recycling of oil shale semicoke waste.

Regional distribution, properties, treatment technologies, and resource utilization of oil-based drilling cuttings: A review

Oil-based drilling cuttings (OBDC) are hazardous wastes produced during the extensive use of oil-based drilling mud in oil and gas exploration and development. They have strong mutagenic, carcinogenic, and teratogenic effects and need to be properly disposed of to avoid damaging the natural environment. This paper reviews the recent research progress on the regional distribution, properties, treatment technologies, and resource utilization of OBDC. The advantages and disadvantages of different technologies for removing petroleum pollutants from OBDC were comprehensively analyzed, and required future developments in treatment technologies were proposed.

Impact of Petroleum Contamination on the Structure of Saline Soil Bacterial Communities

Petroleum contamination may lead to variations in soil microbial community structure and activities. The bioremediation of petroleum-contaminated soil typically depends on the characteristics and activities of oil-degrading microorganisms, which can be introduced or be part of the native soil microbiota. Thus, analyzing the structure of the microbial community and internal relationships in the bioremediation process is critical. Our study characterized the physical and chemical properties, microbial community structure, and microbial diversity of surface soil collected near an oilfield. The total carbon (TC), total organic carbon (TOC), and microbial diversity in oil-contaminated soil was found higher than in uncontaminated samples. Proteobacteria abundance was inhibited with oil pollution, while Actinomycetes abundance was enhanced. Some indigenous hydrocarbon-degrading bactera were enriched by oil pollution, such as Bacillus, Actinomarinales norank, Balneolaceae uncultured, Marinobacter, and Pseudomonas. Furthermore, Rokubacteria, Nitrospirae, and Entotheonellaeota were significant differences in the contaminated group. There were 16 genera with significant differences in the polluted group, such as Woeseia, Pelagibius, Pontibacillus, IS_44, Aliifodinibius, while Halothiobacillus, Algoriphagus, Novosphingobium, etc. had significant differences in the uncontaminated group. Redundancy analysis demonstrated that the responses of the microorganisms to the evaluated environmental factors were different, and TC was the most important driver of microbial community variation. Moreover, TOC was the largest contributor to operational taxonomic unit (OTU) and Chao index variations. Our results provide a theoretical basis for the enhancement of microbial activity in oil-contaminated soil, which might improve bioremediation efficacy.

Resource utilization from solid waste originated from oil-based shale drilling cutting during shale gas development

With the large-scale development of shale gas, oil-based drilling fluids are widely used, generating significant amounts of solid wastes from oil-based shale drilling cutting (OBSDC). These solid wastes are biologically toxic and are difficult to degrade. The current treatment methods do not meet the requirements for oily sludge. This study begins with pyrolysis of OBSDC in order to use it as an external admixture for preparing cement slurry for resource utilization. The research results showed that when the OBSDC content was increased to 35%, the mechanical properties of developed cement were favourable. Evaluating the cement sheath integrity showed that the OBSDC cement met the subsequent production requirements for a casing with an internal pressure of 50.01 MPa, applicable for cementing surface casings as well as technical casings. The active SiO₂ and feldspar in OBSDC after pyrolysis promoted the hydration reaction of cement and accelerated the crystallization of C-S-H, which in turn complemented the cement mechanical properties. When OBSDC was in the proper dosage range, the particle gradation characteristics further optimized the pore structure of the cement matrix and increased the cement strength.

Organic wastes bioremediation and its changing prospects

Increasing inappropriate anthropogenic activities and industrialization have resulted in severe environmental pollution worldwide. Their effective treatment is vital for general health concerns. Depending on the characteristics of pollutants, the severity of pollution may differ. For sustainable treatment of polluted environments, bioremediation is accepted as the most efficient, economical, and environmentally friendly method hence largely preferred. However, every bioremediation technique has its own unique advantages and limitations due to its defined applications criteria. In bioremediation, microorganisms play a decisive role in detoxification by degrading, mineralizing and accumulating various forms of harmful and biodegradable pollutants from the surroundings and transforming them into less lethal forms. Bioremediation is performed ex-situ or in-situ, based on location of polluted site as well as characteristics, type and strength of the pollutants. Furthermore, the most popular methodologies for bioremediation include bioaugmentation, biostimulation, bioattenuation among others which depend on the prevailing environmental factors into the microbial system. Implementing them appropriately and effectively under ex-situ or in-situ method is extremely important not only for obtaining efficient treatment but also for the best economic, environmental, and social impacts. Therefore, this review aims to analyze various bioremediation methods for organic pollutants remediation from soil/sediments and wastewater, their strength, limitation, and insights for the selection of appropriate bioremediation techniques based on nature, types, degree, and location of the pollution. The novelty aspect of the article is to give updates on several key supporting technologies which have recently emerged and exhibited great potential to enhance the present bioremediation efficiency such as nanobubble, engineered biochar, mixotrophic microalgae, nanotechnology etc. Moreover, amalgamation of these technologies with existing bioremediation facilities are significantly changing the scenario and scope of environmental remediation towards sustainable bioremediation.

Mitigation of petroleum-hydrocarbon-contaminated hazardous soils using organic amendments: A review

The term "Total petroleum hydrocarbons" (TPH) is used to describe a complex mixture of petroleum-based hydrocarbons primarily derived from crude oil. Those compounds are considered as persistent organic pollutants in the terrestrial environment. A wide array of organic amendments is increasingly used for the remediation of TPH-contaminated soils. Organic amendments not only supply a source of carbon and nutrients but also add exogenous beneficial microorganisms to enhance the TPH degradation rate, thereby improving the soil health. Two fundamental approaches can be contemplated within the context of remediation of TPH-contaminated soils using organic amendments: (i) enhanced TPH sorption to the exogenous organic matter (immobilization) as it reduces the bioavailability of the contaminants, and (ii) increasing the solubility of the contaminants by supplying desorbing agents (mobilization) for enhancing the subsequent biodegradation. Net immobilization and mobilization of TPH have both been observed following the application of organic amendments to contaminated soils. This review examines the mechanisms for the enhanced remediation of TPH-contaminated soils by organic amendments and discusses the influencing factors in relation to sequestration, bioavailability, and subsequent biodegradation of TPH in soils. The uncertainty of mechanisms for various organic amendments in TPH remediation processes remains a critical area of future research.

Characteristics of organic carbon metabolism and bioremediation of petroleum-contaminated soil by a mesophilic aerobic biopile system

An innovative mesophilic aerobic biopile technology was explored to improve the bioremediation efficiency of petroleum-contaminated soil. Under the suitable soil conditions (C:N:P at 100:5:1 and soil moisture content at 18%), the soil pH was hold in the range of 7.4 to 6.8 throughout the bioremediation process, the mesophilic (30 °C-40 °C) and forced aeration (3 h-on/1 h-off) conditions were the critical factors to enhancing petroleum biodegradation. The consumption of bioavailable organic carbon (BAC) which was one of the most important factors regulating microbial metabolism, was positively related (R² = 0.85, 40 °C) with the rate of petroleum removal. The 50% threshold of BAC could be regarded as the signal for supplementing the soil nutrients in the mesophilic aerobic biopiles to favor petroleum removal. The optimal conditions (40 °C, 3 h-on/1 h-off) maximized the utilization of BAC, promoted the petroleum degradation, and remained the microbial abundance and community composition stable to the greatest extent. In addition, the accumulation of aliphatic acids affected the microbial activity, which limited the efficiency of petroleum degradation to a certain extent. Jointly considering the energy consumption, time cost and soil conditions maintenance, a cost-effective biopile technology was obtained by temperature and aeration regulation and BAC supplementation, which could be applied to engineering application.

Bioremediation of oily sludge by solid complex bacterial agent with a combined two-step process

In the present research, a bioremediation process was developed using solid complex bacterial agents (SCBA) through a combined two-step biodegradation process. Four isolated strains showed high efficiency for the degradation of total petroleum hydrocarbons (TPH) and the reduction of COD of the oily sludge, at 96.6% and 92.6%, respectively. The mixed strains together with bran prepared in form of SCBA exhibited improved performance compared to individual strains, all of which had an optimal temperature of around 35 °C. The use of SCBA provided advantages over commonly used liquid media for storage and transportation. The two-step process, consisting of firstly biosurfactant-assisted oil recovery and secondly biodegradation of the remaining TPH with SCBA, demonstrated the capability for treating oily sludge with high TPH content (>10 wt%) and short process period (60 days). The large-scale (5 tons oily sludge) field test, achieving a TPH removal efficiency of 93.8% and COD reduction of 91.5%, respectively, confirmed the feasibility and superiority of the technology for industrial applications.

Impact of necrophytoremediation on petroleum hydrocarbon degradation, ecotoxicity and soil bacterial community composition in diesel-contaminated soil

Hydrocarbon degradation is usually measured in laboratories under controlled conditions to establish the likely efficacy of a bioremediation process in the field. The present study used greenhouse-based bioremediation to investigate the effects of natural attenuation (NA) and necrophytoremediation (addition of pea straw (PS)) on hydrocarbon degradation, toxicity and the associated bacterial community structure and composition in diesel-contaminated soil. A significant reduction in total petroleum hydrocarbon (TPH) concentration was detected in both treatments; however, PS-treated soil showed more rapid degradation (87%) after 5 months together with a significant reduction in soil toxicity (EC50 = 91 mg diesel/kg). Quantitative PCR analysis revealed an increase in the number of 16S rRNA and alkB genes in the PS-amended soil. Substantial shifts in soil bacterial community were observed during the bioremediation, including an increased abundance of numerous hydrocarbon-degrading bacteria. The bacterial community shifted from dominance by Alphaproteobacteria and Gammaproteobacteria in the original soil to Actinobacteria during bioremediation. The dominance of two genera of bacteria, Sphingobacteria and Betaproteobacteria, in both NA- and PS-treated soil demonstrated changes occurring within the soil bacterial community through the incubation period. Additionally, pea straw itself was found to harbour a diverse hydrocarbonoclastic community including Luteimonas, Achromobacter, Sphingomonas, Rhodococcus and Microbacterium. At the end of the experiment, PS-amended soil exhibited reduced ecotoxicity and increased bacterial diversity as compared with the NA-treated soil. These findings suggest the rapid growth of species stimulated by the bioremediation treatment and strong selection for bacteria capable of degrading petroleum hydrocarbons during necrophytoremediation. Graphical abstract.

Material flow analysis and heavy hydrocarbon removal in a full-scale biopile and soil washing plant in northern Italy

This study aimed to assess the mass fluxes and removal efficiencies of heavy hydrocarbons in a full-scale plant located in northern Italy. This plant receives and treats contaminated soil, soils and rocks from construction and demolition activities, incineration slags and street cleaning residues. The plant has three sections, consisting of bioremediation using biopile, a soil washing stage and a stabilization/solidification unit, which can perform independently or together with the others. The material flow analysis showed how the crisis in the construction industry changed the final destination of waste after the treatment: as the market demand for coarse material decreased, waste was sent directly to landfills for inert waste, instead of being recovered. Hydrocarbon mass fluxes showed that a considerable amount of pollutants was removed. In the period 2009-2014, the removal efficiencies of the bioremediation, the soil washing section and the entire plant were respectively 73%, 58% and 62%. The percentages of removal attained at the facility in study were sufficient to ensure the possibility of recovering the waste or disposing of it in different landfill categories, according to the national regulations.

Preparation of non-sintered lightweight aggregates through co-mechanochemical treatment of oil-contaminated drill cuttings, circulation fluidized bed combustion fly ash, and quicklime

This work investigates the feasibility of co-mechanochemical treatment of oil-contaminated drill cuttings (OCDC), circulation fluidized bed combustion (CFBC) fly ash, and quicklime to prepare non-sintered lightweight aggregates (NSLWAs). The NSLWAs with high cylinder compressive strength and low water absorption could be obtained under the condition of optimal water addition and appropriate steam-curing temperature, as well as steam-curing time. Co-mechanochemical treatment could enhance the pozzolanic reactivity of CFBC fly ash effectively, which is beneficial to the strength development of NSLWAs. Moreover, co-mechanochemical treatment also can degrade the petroleum hydrocarbon of OCDC, greatly reducing the leaching concentrations of total petroleum hydrocarbons (TPH) of NSLWAs. The final leaching concentrations of TPH are much lower than the requirements of Chinese National Standard GB 31571-2015. Graphical abstract.

Physicochemical characteristics of oil-based cuttings from pretreatment in shale gas well sites

Understanding the physicochemical characteristics of oil-based cuttings (OBCs) is an important foundation for subsequent treatment and management. The macro- and microscopic properties of white oil-based cuttings (WOBCs) and diesel-based cuttings (DBCs) after the different pretreatment steps have been assessed using scanning electron microscopy. The organic and inorganic compositions of OBCs have been analyzed using X-ray diffraction, Fourier-transform infrared spectrometry, and gas chromatography-mass spectrometry. Inorganic matter (SiO₂, BaSO₄, and CaCO₃), alkanes, aromatic compounds, and water were the main components of OBCs. The organic content (26.14%) and alkane content of the WOBCs were higher than that of the DBCs, whereas for the inorganic content (70.87%), the reverse was true. The macro- and micromorphologies of OBCs were quite different because their oil and water contents were different. The oil contents of OBCs decreased in the order A1 (14.64%) > A3 (12.67%) > A2 (11.06%) and B1 (9.19%) > B3 (8.94%) > B2 (4.66%); the water contents decreased in the order A1 (2.99%) > A3 (2.19%) > A2 (1.09%) and B1 (2.30%) > B3 (1.87%) > B2 (1.09%). Moreover, a skid-mounted treatment technology for OBCs was proposed. The results can be a scientific guidance for the treatment and management of OBCs.

Effect of competition between petroleum-degrading bacteria and indigenous compost microorganisms on the efficiency of petroleum sludge bioremediation: Field application of mineral-based culture in the composting process

The effect of competition between isolated petroleum-degrading bacteria (PDB) and indigenous compost microorganisms (ICM) on the efficiency of composting process in bioremediation of petroleum waste sludge (PWS) was investigated. After isolating two native PDB (Acinetobacter radioresistens strain KA5 and Enterobacter hormaechei strain KA6) from PWS, their ability for growth and crude oil degradation was examined in the mineral-based culture (MBC). Then, the PDB isolate were inoculated into the composting experiments and operated for 12 weeks. The results showed that the PDB degraded 21.65-68.73% of crude oil (1-5%) in the MBC after 7 days. The PDB removed 84.30% of total petroleum hydrocarbon (TPHs) in the composting bioreactor containing the initial TPH level of 20 g kg^-1. Removal of petroleum hydrocarbons (PHCs) in the composting experiments proceeded according to the first-order kinetics. The computed values of degradation rate constants and half-lives showed a better performance of the PDB than ICM for TPHs removal. This finding suggests that simultaneous application of the PDB and ICM in the composting reactors resulted in a decline in the effectiveness of the PDB which is due to competition between them. The study also verified that the capability of PDB in degrading PHCs can be successfully scaled-up from MBC to composting process.

Continuous supercritical water oxidation treatment of oil-based drill cuttings using municipal sewage sludge as diluent

Oil-based drill cuttings (OBDC) is a characteristic hazardous waste that is generated in oil and gas exploration. In this study, two typical OBDCs from shale gas fields were treated in a continuous supercritical water oxidation (SCWO) for the first time. Because both heat value and ash content (AC) in the OBDCs were well beyond the capacity of continuous operation, municipal sewage sludge (MSS) was innovatively adapted as the diluent. A mixed sludge with OBDC addition levels of 10%, 20%, and 30% was tested using a novel SCWO reactor. Mean residence times of reactants in different reaction zones were specifically calculated. Results indicated the organic carbon removal efficiency could reach up to 98.44%. Eight detected heavy metals were found to be almost completely removed into solid products, and the concentrations in liquid products were all below the discharge limits. It was also found that the SCWO reactor exhibited good anti-plugging and anti-corrosion performance. The AC in the feedstock was up to 28.58%. To the best of our knowledge, this has, hitherto, not been achieved in a continuous SCWO operation. This study provides a new approach for harmlessly and completely degrading OBDC, and is also helpful for the industrialization of SCWO technology.

Effect of immature and mature compost addition on petroleum contaminated soils composting: kinetics

PURPOSE

The kinetic studies and effect of amendment addition on the performance of the composting process in reduction of total petroleum hydrocarbons (TPH) from petroleum contaminated soils (PCS) were investigated in the present research.

METHODS

Seven composting experiments containing various mixing ratios of PCS to unfinished compost (UC) and finished compost (FC) were set up and operated for 14 weeks. The mixing rations consisted of 1:0 (as control experiment), 1:0.3, 1:0.6, and 1:1. The initial C/N/P and moisture contents of the composting piles were adjusted to 100/5/1 and 50-55%, respectively.

RESULTS

Results showed that 50.09-79.49% of TPH was removed in the composting experiments after 14 weeks. The highest and lowest removal rates were achieved in the ratios of 1:1 and 1:0.3, respectively. Moreover, application of UC as amendments and bulking agent is more efficient than FC. The biodecomposition of TPH was fitted to the first-order kinetic with the half lives and rate constants of 5.63-11.55 days and 0.060-0.123 d^-1, respectively. The bacteria detected from the composting treatments were Staphylococcus sp., Bacillus sp., and Pseudomonas sp.

CONCLUSIONS

The study confirmed the suitability of composting process for PCS bioremediation and superiority of UC than FC as bulking agent.

Biodegradation of high concentrations of petroleum compounds by using indigenous bacteria isolated from petroleum hydrocarbons-rich sludge: Effective scale-up from liquid medium to composting process

The scale-up of petroleum hydrocarbons-rich sludge (PHRS) bioremediation from liquid medium to a composting method bioaugmentated with two indigenous bacteria, capable of degrading high levels of crude oil, was surveyed. After isolating the strains (Sphingomonas olei strain KA1 and Acinetobacter radioresistens strain KA2) and determining their biomass production, emulsification index (E₂₄), bacterial adhesion to hydrocarbon (BATH), and crude oil degradation in liquid medium, they were inoculated into the composting experiments. In liquid medium, the removal rate of crude oil were 67.25, 70.86, 61.77, 42.13, and 27.92%, respectively for the initial oil levels of 1, 2, 3, 4, and 5% after 7 days. Degradation of 10, 20, 30, 40 and 50 g kg^-1 concentrations of total petroleum hydrocarbons (TPH) were also calculated to be 91.24, 87.23, 84.69, 74.08, and 60.14%, respectively after a composting duration of 12 weeks. The values of the rate constants (k) and half-lives (t_1/2) of petroleum hydrocarbons degradation were 0.083-0.212 day^-1 and 3.27-8.35 days for the first-order and 0.003-0.089 g kg^-1day^-1 and 1.12-6.67 days for the second-order model, respectively. This study verified the suitability of the isolated strains for PHRS bioremediation. Successful scale-up of PHRS bioremediation from a liquid medium to a composting process for degrading high amounts of TPH was also confirmed.

Enzyme cocktail containing NADH regeneration system for efficient bioremediation of oil sludge contamination

Oil sludge is one kind of toxic and persistent contamination to ecology system from petroleum industry. In order to recycle contaminated sands and reduce environmental impacts at a lower operating cost, enzyme cocktail 21/CbFDH including NADH regeneration system for oily sludge bioremediation was constructed for the first time. The intracellular enzymes of oil-degrading strain Acinetobacter calcoaceticus 21 were prepared and the formate dehydrogenase gene Cbfdh from Candida boidinii was cloned and functionally expressed in E.coli BL21 induced by lactose. The activity and stability of CbFDH was enhanced through self-induction medium optimization using Box-Behnken design. The CbFDH activity was 12.2 times increased and was only decreased 3.9% upon storage at 30 °C for 5 d. The CbFDH increased the degradation rate of oil in high concentration. For the sludge with 10% oil (w/w), the degradation rate achieved 35.6% after 12 h using enzyme 21/CbFDH with the protein ratio of 1:4. The results will provide novel perspectives for creation and operation of petroleum-degrading enzymes involving formate dehydrogenase with higher efficiency and lower cost comparing to current microbial strains or consortium.

Design and shelf stability assessment of bacterial agents for simultaneous removal of methane and odors

Two types of solid bacterial agents for the simultaneous removal of methane and odor were designed using humic soil (De-MO-1) and the mixture of humic soil and tobermolite (De-MO-2) as biocarriers. The bacterial consortium, having the removability of methane and dimethyl sulfide (DMS), was immobilized in the biocarriers, and then stored at room temperature for 375 days without additional treatment. Although the lag period, of which the incubation time required for removing methane and DMS, tended to increase over the storage period, the removability of methane and DMS was maintained during 375 days in both bacterial agents. Key bacteria associated with the removal of methane and odors (Streptomyces, Promicromonospora, Paracoccus, Lysobacter, Sphingopyxis and Methylosystis) could keep their abundance during the storage period. The richness and evenness values of the bacterial communities in De-MO-1 and De-MO-2 ranged 4.89 ∼ 6.50 and 0.89 ∼ 0.98, respectively, indicating that high bacterial diversity was maintained during the storage period. The results suggest that De-MO-1 and De-MO-2, designed for the simultaneous removal of methane and odors, had shelf stabilities over one year.

Static decontamination of oil-based drill cuttings with pressurized hot water using response surface methodology

Separating organic pollutants from oil-based drill cuttings (OBDC) is the current trend for its safe disposal. In this study, pressurized hot water extraction (PHWE) was adapted to decontaminate OBDC for the first time. Two typical OBDC samples, i.e., diesel-based drill cuttings (OBDC-A) and white oil-based drill cuttings (OBDC-B), were statically extracted in a homemade batch autoclave. Response surface methodology (RSM) with a central composite design (CCD) was applied to investigate the effects and interactive effects of three independent operating parameters (temperature, extraction time, and water volume) and to ultimately optimize the PHWE process. The results suggested that temperature is the dominant parameter, followed by water volume and extraction time. Interactive effects among the three parameters are present in the PHWE of OBDC-A but absent in the PHWE of OBDC-B. The suitable conditions for the effective PHWE of OBDC-A were found to be a temperature of 284-300 °C, water volume of 15-35 ml, and extraction time of 20-60 min. The corresponding conditions were 237-300 °C, 15-35 ml, and 20-60 min for the PHWE of OBDC-B. These different phenomena are caused by the different characteristics of the two OBDC samples. All of the polynomial models obtained from the RSM experiments are very valid and can adequately describe the relationship among the three independent operating parameters and responses. The experimental results also confirmed that PHWE is a more efficient separation technique for decontaminating OBDC than single organic solvent extraction or low-temperature thermal desorption because PHWE integrates the advantages of both these processes.

Bioremediation of storage tank bottom sludge by using a two-stage composting system: Effect of mixing ratio and nutrients addition

The effect of mixing ratio and nutrients addition on the efficiency of a two-stage composting system in removal of total petroleum hydrocarbons (TPH) from storage tank bottom sludge (STBS) was investigated. The system consisted of ten windrow piles as primary composting (PC) followed by four in-vessel reactors as secondary composting (SC). Various initial C/N/P and mixing ratios of STBS to immature compost (IC) were examined in the PC and SC for 12 and 6weeks, respectively. The removal rates of TPH in the two-stage system (93.72-95.24%) were higher than those in the single-stage one. Depending on the experiments, TPH biodegradation fitted to the first- and second-order kinetics with the rate constants of 0.051-0.334d^-1 and 0.002-0.165gkg^-1d^-1, respectively. The bacteria identified were Pseudomonas sp., Bacillus sp., Klebsiella sp., Staphylococcus sp., and Proteus sp. The study verified that a two-stage composting system is effective in treating the STBS.

Supercritical water oxidation of oil-based drill cuttings

Oil-based drill cuttings (OBDC) are a typical hazardous solid waste that arises from drilling operations in oil and gas fields. The supercritical water oxidation (SCWO) of OBDC was comprehensively investigated in a batch reactor under the conditions of various oxygen coefficients (OC, 1.5-3.5), temperatures (T, 400-500°C) and reaction times (t, 0.5-10min). Preheating experiments indicated that most of the organic compounds in the initial OBDC sample were distributed within gaseous, oil, aqueous and solid phases, with no more than 9.8% of organic compounds converted into inorganic carbon. All tested variables, i.e., OC, T and t, positively affect the transformation of carbon compounds from the oil and solid phases to the aqueous phase and, ultimately, to CO₂. Carbon monoxide is the primary stable intermediate. The total organic carbon (TOC) removal efficiency can reach up to 89.2% within 10min at 500°C. Analysis of the reaction pathways suggests both homogeneous and heterogeneous reactions exist in the reactor. The homogeneous reaction is a typical SCWO reaction that is governed by a free radical mechanism, and the heterogeneous reaction is dominated by mass transfer. The information obtained in this study is useful for further investigation and development of hydrothermal treatment procedures for OBDC.

Bioremediation of hydrocarbon degradation in a petroleum-contaminated soil and microbial population and activity determination

Bioremediation of hydrocarbon degradation in petroleum-polluted soil is carried out by various microorganisms. However, little information is available for the relationships between hydrocarbon degradation rates in petroleum-contaminated soil and microbial population and activity in laboratory assay. In a microcosm study, degradation rate and efficiency of total petroleum hydrocarbons (TPH), alkanes, and polycyclic aromatic hydrocarbons (PAH) in a petroleum-contaminated soil were determined using an infrared photometer oil content analyzer and a gas chromatography mass spectrometry (GC-MS). Also, the populations of TPH, alkane, and PAH degraders were enumerated by a modified most probable number (MPN) procedure, and the hydrocarbon degrading activities of these degraders were determined by the Biolog (MT2) MicroPlates assay. Results showed linear correlations between the TPH and alkane degradation rates and the population and activity increases of TPH and alkane degraders, but no correlation was observed between the PAH degradation rates and the PAH population and activity increases. Petroleum hydrocarbon degrading microbial population measured by MPN was significantly correlated with metabolic activity in the Biolog assay. The results suggest that the MPN procedure and the Biolog assay are efficient methods for assessing the rates of TPH and alkane, but not PAH, bioremediation in oil-contaminated soil in laboratory.

Bioremediation of diesel and lubricant oil-contaminated soils using enhanced landfarming system

Lubricant and diesel oil-polluted sites are difficult to remediate because they have less volatile and biodegradable characteristics. The goal of this research was to evaluate the potential of applying an enhanced landfarming to bioremediate soils polluted by lubricant and diesel. Microcosm study was performed to evaluate the optimal treatment conditions with the addition of different additives (nutrients, addition of activated sludge from oil-refining wastewater facility, compost, TPH-degrading bacteria, and fern chips) to enhance total petroleum hydrocarbon (TPH) removal. To simulate the aerobic landfarming biosystem, air in the microcosm headspace was replaced once a week. Results demonstrate that the additives of activated sludge and compost could result in the increase in soil microbial populations and raise TPH degradation efficiency (up to 83% of TPH removal with 175 days of incubation) with initial (TPH = 4100 mg/kg). The first-order TPH degradation rate reached 0.01 1/d in microcosms with additive of activated sludge (mass ratio of soil to inocula = 50:1). The soil microbial communities were determined by nucleotide sequence analyses and 16S rRNA-based denatured gradient gel electrophoresis. Thirty-four specific TPH-degrading bacteria were detected in microcosm soils. Chromatograph analyses demonstrate that resolved peaks were more biodegradable than unresolved complex mixture. Results indicate that more aggressive remedial measures are required to enhance the TPH biodegradation, which included the increase of (1) microbial population or TPH-degrading bacteria, (2) biodegradable carbon sources, (3) nutrient content, and (4) soil permeability.