Reclamation of DPK hydrocarbon polluted agricultural soil using a selected bulking agent

Techno-economic analysis of phytoremediation: A strategic rethinking

Phytoremediation is a cost-effective and environmentally sound approach, which uses plants to immobilize/stabilize, extract, decay, or lessen toxicity and contaminants. Despite successful evidence of field application, such as natural attenuations, and self-purification, the main barriers remain from a "promising" to a "commercial" approach. Therefore, the ultimate goal of this paper is to examine factors that contribute to phytoremediation's underutilization and discuss the real costs of phytoremediation when the time and land values are considered. We revisit mechanisms and processes of phytoremediation. We synthesize existing information and understanding based on previous works done on phytoremediation and its applications to provide the technical assessment and perspective views in the commercial acceptance of phytoremediation. The results show that phytoremediation is the most suitable for remote regions with low land values. Since these regions allow a longer period to be restored, land vegetation covers can be established in more or less time like natural attenuation. Since the length of phytoremediation is an inherent limitation, this inherent disadvantage limits its adoption in developed business regions, such as growing urban areas. Because high land values could not be recovered in the short term, phytoremediation is not cost-effective in those regions. We examine the potential measures that can enhance the performance of phytoremediation, such as soil amendments, and agricultural practices. The results obtained through review can clarify where/what conditions phytoremediation can provide the most suitable solutions at a large scale. Finally, we identify the main barriers and knowledge gaps to establishing a vegetation cover in large-scale applications and highlight the research priorities for increased acceptance of phytoremediation.

Bioaugmentation as a green technology for hydrocarbon pollution remediation. Problems and prospects

Environmental pollution mitigation measure involving bioremediation technology is a sustainable intervention for a greener ecosystem biorecovery, especially the obnoxious hydrocarbons, xenobiotics, and other environmental pollutants induced by anthropogenic stressors. Several successful case studies have provided evidence to this paradigm including the putative adoption that the technology is eco-friendly, cost-effective, and shows a high tendency for total contaminants mineralization into innocuous bye-products. The present review reports advances in bioremediation, types, and strategies conventionally adopted in contaminant clean-up. It identified that natural attenuation and biostimulation are faced with notable limitations including the poor remedial outcome under the natural attenuation system and the residual contamination occasion following a biostimulation operation. It remarks that the use of genetically engineered microorganisms shows a potentially promising insight as a prudent remedial approach but is currently challenged by few ethical restrictions and the rural unavailability of the technology. It underscores that bioaugmentation, particularly the use of high cell density assemblages referred to as microbial consortia possess promising remedial prospects thus offers a more sustainable environmental security. The authors, therefore, recommend bioaugmentation for large scale contaminated sites in regions where environmental degradation is commonplace.

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.

Principal component analysis reveals microbial biomass carbon as an effective bioindicator of health status of petroleum-polluted agricultural soil

We investigated a number of microbiological activities in the soil to serve as biomonitoring tools in assessing the ecotoxicity of diesel-contaminated soil samples during the different periods of bioremediation. Sawdust was used as the biostimulant for the biodegradation of artificial diesel-polluted soil samples. Soil microbial population, soil microbial enzymatic activities (catalase, lipase, dehydrogenase, urease, phosphatase and β-glucosidase), soil microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP), soil microbial respirometric index and total petroleum hydrocarbon (TPH) concentration were monitored to evaluate the efficiency of the bioremediation process. After a period of 56 d, total petroleum hydrocarbon content reduced from 14,221 to 270 mg/kg. The parameter estimation using the nth-order kinetic model revealed that the first-order rate constants (k) for TPH removal were 4.417 d^-1 and 0.2670 d^-1 for sawdust-amended and unamended soil, respectively. This implied that, the sawdust amendment resulted in reaction rate 16.5 times faster than unamended soil. Thus, the biological indicators were generally more pronounced in biostimulated soil than the attenuated soil. However, to evaluate the efficiency of the sawdust-assisted bioremediation, principal component analysis, which was used in selecting the most sensitive bioindicators. It was observed that microbial biomass carbon, catalase, lipase and dehydrogenase were the most responsive bioparameters. A positive relationship between TPH removal and the four most sensitive bioparameters suggests that the use of four biological activities have proven to be effective monitoring tools for evaluating the efficiency of a bioremediation strategy.

Kinetic modelling of total petroleum hydrocarbon in spent lubricating petroleum oil impacted soil under different treatments

The integration of first and second order kinetic model in parameter estimation for the degradation pattern of total petroleum hydrocarbon (TPH) in spent lubricating petroleum oil (SLPO) over a four-month period was the subject of the present investigation. Study design considered four treatment microcosms notably; sewage sludge (SB), monitored natural recovery (MNR), surfactant (SA) and control (SO). The rate of TPH degradation using sewage sludge as amendment material depicted effective TPH removal within ten weeks. A maximum allowable concentration of residual TPH (4300 mg kg^-1) was obtained through an amendment with sewage sludge. Degradation constant (k) produced by both first and second order rates significantly demonstrated the performance of sewage sludge biomass over the other three treatments applied, however, experimental data adequately fitted into the first order kinetics (k = 0.27 d^-1, t½ = 3.0 d). TPH removal efficiency of sewage sludge and detergent were 96.0% and 81.0% respectively. The use of sewage sludge biomass significantly (p < .05) improved soil biological characteristics and produced optimum dehydrogenase activity (DHA ≥ 8.8 TPFg^-1 d), germination index (%IG ≥ 88%), and chlorophyll content (chl ≥ 100 µg cm^-2), thus, recommended for field scale application in soil hydrocarbon pollution remediation.

Numerical Analysis of Heat Transfer Performance of In Situ Thermal Remediation of Large Polluted Soil Areas

In recent years soil contamination has become a global problem because of industrial development. In situ thermal remediation has been proposed recently to not only lower costs, but also reduce the environmental impact compared to other soil remediation technologies such as chemical remediation. During the soil thermal remediation process, factors such as soil type and water content affecting the heat transfer pose challenges. In this study, a simple mathematical model is presented and the heat transfer performance during the soil heating process is researched via COMSOL Multiphysics 5.3 software (COMSOL Inc., Stockholm, Sweden). The temperature distribution and heating period under different operating conditions are evaluated. The simulation results show that the average soil temperature exhibits three stages during the heating process. First, soil is heated from the ambient temperature to the water boiling temperature (100 °C). Then, the soil stays at the water boiling temperature for a while before reaching the target temperature. Simultaneously, the effects of initial water content and groundwater flow on heat transfer are also studied. In addition, the results of a simulation can provide a reference for in situ heating remediation technology.

Harmful algal blooms under changing climate and constantly increasing anthropogenic actions: the review of management implications

The present review reports all management approaches (physical, chemical, and biological) traditionally adopted in mitigating the global impact of harmful cyanobacterial blooms (cyanoHABs). It recognizes that each mitigation strategy shows characteristic associated limitations and notes that no remedial step has provided a sustainable solution to HABs on a global scale. It emphasizes that the putative anthropogenic N&P inputs reduction through improved wastewater treatment and regulation of point and non-point sources-agricultural fertilizers only offer a short term solution. These approaches are rather preventive than curative hence, do not address concerns relating to the recovery of already-eutrophic and hypereutrophic systems. It raises new concerns on the implications of non-agricultural pollutants such as hydrocarbon fractions in bloom accretions often neglected while addressing HAB triggers. It also accesses the global impacts of HABs as it pertains to socio-economic implications in the geographically diverse world. It, therefore, proposes that Integrated Management Intervention involving the merging of two or more mitigation steps be administered across the aquatic continua as a prudent management solution to complement the current N&P dual management paradigm. It stresses that the contemporaneous adoption of management options with both preventive and curative measures is a key to sustainable HAB management. This review provides sufficient advances and current scenarios for approaching cyanoHABs. Further, it advocates that future research perspectives tackle the mitigation design beyond the short-term nutrient regulations and the parochial attention to the point and non-point N&P input sources.

Thermophilic composting of hydrocarbon residue with sewage sludge and fish sludge as cosubstrates: Microbial changes and TPH reduction

The hydrocarbon residue in petroleum product storage tanks is waste generated in large quantities that must be properly managed to reduce its risk to the environment. By comparing the effect of two organic cosubstrates, the aim of our research is to determine the feasibility of composting as a bioremediation method for the treatment of the solid phase of the hydrocarbon residue. For this purpose, four treatments of the pollutant waste were established in triplicate: waste only; waste with bulking agent (1:2); waste with fish sludge and bulking agent (1:2:6); and waste with municipal sewage sludge and bulking agent (1:2:6). The composting system consisted of 12 reactors with a capacity of 30 L, each equipped with aeration and temperature control. Both at the beginning and the end of the experiment (20 days), we evaluated the physicochemical parameters, the structure of the microbial community through phospholipid fatty acid analysis, and the total petroleum hydrocarbon content (TPH). Treatments with cosubstrates maintained thermophilic temperatures, during 14 and 8 days in fish and municipal sludge respectively, while in the controls mesophilic conditions were maintained. The incorporation of fish sludge decreased TPH present in the initial mixture by 39.5%. The municipal sludge treatment resulted in a lower of temperatures and a TPH decrease close to 23.9%. In the control treatments, there was a slight TPH decrease, mainly due to the forced ventilation. Although, both composting treatments with cosubstrates proved adequate for the bioremediation of residue from hydrocarbon storage tanks, fish sludge presented best bioremediation conditions. Municipal sewage sludge provided a bioaugmentation effect due to its rich diversity and microbial biomass. Fish sludge could have biostimulant and surfactant effect producing an aliphatic mixture of pollutant waste with the nutritional requirements to promote the development of fungal communities.

Whole Genome Sequence Analysis of an Alachlor and Endosulfan Degrading Micrococcus sp. strain 2385 Isolated from Ochlockonee River, Florida

We recently isolated Micrococcus sp. strain 2385 from Ochlockonee River, Florida and demonstrated potent biodegradative activity against two commonly used pesticides- alachlor [(2-chloro-2`,6`-diethylphenyl-N (methoxymethyl)acetanilide)] and endosulfan [(6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9methano-2,3,4-benzo(e)di-oxathiepin-3-oxide], respectively. To further identify the repertoire of metabolic functions possessed by strain 2385, a draft genome sequence was obtained, assembled, annotated and analyzed. The genome sequence of Micrococcus sp. strain 2385 consisted of 1,460,461,440 bases which assembled into 175 contigs with an N₅₀ contig length of 50,109 bases and a coverage of 600x. The genome size of this strain was estimated at 2,431,226 base pairs with a G+C content of 72.8 and a total number of 2,268 putative genes. RAST annotated a total of 340 subsystems in the genome of strain 2385 along with the presence of 2,177 coding sequences. A genome wide survey indicated that that strain 2385 harbors a plethora of genes to degrade other pollutants including caprolactam, PAHs (such as naphthalene), styrene, toluene and several chloroaromatic compounds.