Bioremediation of PAHs - Limitations and soultions

Introduction 1.1 Occurrence of polycyclic aromatic hydrocarbons (PAH) in the environment Worldwide industrial and agricultural developments have released a large number of natural and synthetic hazardous compounds into the environment due to careless waste disposal, illegal waste dumping and accidental spills. As a result, there are numerous sites in the world that require cleanup of soils and groundwater. Polycyclic aromatic hydrocarbons (PAHs) are one of the major groups of these contaminants (Da Silva et al., 2003). PAHs constitute a diverse class of organic compounds consisting of two or more aromatic rings with various structural configurations (Prabhu and Phale, 2003). Being a derivative of benzene, PAHs are thermodynamically stable. In addition, these chemicals tend to adhere to particle surfaces, such as soils, because of their low water solubility and strong hydrophobicity, and this results in greater persistence under natural conditions. This persistence coupled with their potential carcinogenicity makes PAHs problematic environmental contaminants (Cerniglia, 1992; Sutherland, 1992). PAHs are widely found in high concentrations at many industrial sites, particularly those associated with petroleum, gas production and wood preserving industries (Wilson and Jones, 1993). 1.2 Remediation technologies Conventional techniques used for the remediation of soil polluted with organic contaminants include excavation of the contaminated soil and disposal to a landfill or capping - containment - of the contaminated areas of a site. These methods have some drawbacks. The first method simply moves the contamination elsewhere and may create significant risks in the excavation, handling and transport of hazardous material. Additionally, it is very difficult and increasingly expensive to find new landfill sites for the final disposal of the material. The cap and containment method is only an interim solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability. A better approach than these traditional methods is to completely destroy the pollutants, if possible, or transform them into harmless substances. Some technologies that have been used are high-temperature incineration and various types of chemical decomposition (for example, base-catalyzed dechlorination, UV oxidation). However, these methods have significant disadvantages, principally their technological complexity, high cost , and the lack of public acceptance. Bioremediation, on the contrast, is a promising option for the complete removal and destruction of contaminants. 1.3 Bioremediation of PAH contaminated soil & groundwater Bioremediation is the use of living organisms, primarily microorganisms, to degrade or detoxify hazardous wastes into harmless substances such as carbon dioxide, water and cell biomass Most PAHs are biodegradable unter natural conditions (Da Silva et al., 2003; Meysami and Baheri, 2003) and bioremediation for cleanup of PAH wastes has been extensively studied at both laboratory and commercial levels- It has been implemented at a number of contaminated sites, including the cleanup of the Exxon Valdez oil spill in Prince William Sound, Alaska in 1989, the Mega Borg spill off the Texas coast in 1990 and the Burgan Oil Field, Kuwait in 1994 (Purwaningsih, 2002). Different strategies for PAH bioremediation, such as in situ , ex situ or on site bioremediation were developed in recent years. In situ bioremediation is a technique that is applied to soil and groundwater at the site without removing the contaminated soil or groundwater, based on the provision of optimum conditions for microbiological contaminant breakdown.. Ex situ bioremediation of PAHs, on the other hand, is a technique applied to soil and groundwater which has been removed from the site via excavation (soil) or pumping (water). Hazardous contaminants are converted in controlled bioreactors into harmless compounds in an efficient manner. 1.4 Bioavailability of PAH in the subsurface Frequently, PAH contamination in the environment is occurs as contaminants that are sorbed onto soilparticles rather than in phase (NAPL, non aqueous phase liquids). It is known that the biodegradation rate of most PAHs sorbed onto soil is far lower than rates measured in solution cultures of microorganisms with pure solid pollutants (Alexander and Scow, 1989; Hamaker, 1972). It is generally believed that only that fraction of PAHs dissolved in the solution can be metabolized by microorganisms in soil. The amount of contaminant that can be readily taken up and degraded by microorganisms is defined as bioavailability (Bosma et al., 1997; Maier, 2000). Two phenomena have been suggested to cause the low bioavailability of PAHs in soil (Danielsson, 2000). The first one is strong adsorption of the contaminants to the soil constituents which then leads to very slow release rates of contaminants to the aqueous phase. Sorption is often well correlated with soil organic matter content (Means, 1980) and significantly reduces biodegradation (Manilal and Alexander, 1991). The second phenomenon is slow mass transfer of pollutants, such as pore diffusion in the soil aggregates or diffusion in the organic matter in the soil. The complex set of these physical, chemical and biological processes is schematically illustrated in Figure 1. As shown in Figure 1, biodegradation processes are taking place in the soil solution while diffusion processes occur in the narrow pores in and between soil aggregates (Danielsson, 2000). Seemingly contradictory studies can be found in the literature that indicate the rate and final extent of metabolism may be either lower or higher for sorbed PAHs by soil than those for pure PAHs (Van Loosdrecht et al., 1990). These contrasting results demonstrate that the bioavailability of organic contaminants sorbed onto soil is far from being well understood. Besides bioavailability, there are several other factors influencing the rate and extent of biodegradation of PAHs in soil including microbial population characteristics, physical and chemical properties of PAHs and environmental factors (temperature, moisture, pH, degree of contamination). Figure 1: Schematic diagram showing possible rate-limiting processes during bioremediation of hydrophobic organic contaminants in a contaminated soil-water system (not to scale) (Danielsson, 2000). 1.5 Increasing the bioavailability of PAH in soil Attempts to improve the biodegradation of PAHs in soil by increasing their bioavailability include the use of surfactants , solvents or solubility enhancers.. However, introduction of synthetic surfactant may result in the addition of one more pollutant. (Wang and Brusseau, 1993).A study conducted by Mulder et al. showed that the introduction of hydropropyl-ß-cyclodextrin (HPCD), a well-known PAH solubility enhancer, significantly increased the solubilization of PAHs although it did not improve the biodegradation rate of PAHs (Mulder et al., 1998), indicating that further research is required in order to develop a feasible and efficient remediation method. Enhancing the extent of PAHs mass transfer from the soil phase to the liquid might prove an efficient and environmentally low-risk alternative way of addressing the problem of slow PAH biodegradation in soil.

Laboratory study of grouted macadams impregnated with mine waste geopolymeric binder

A new type of pavement has been gaining popularity over the last few years in Europe. It comprises a surface course with a semi-flexible material that provides significant advantages in comparison to both concrete and conventional asphalt, having both rut resistance and a degree of flexibility. It also provides good protection against the ingress of water to the foundation, since it has an impermeable surface. The semi-flexible material, generally known as grouted macadam, comprises an open-graded asphalt skeleton with 25% to 35% voids into which a cementitious slurry is grouted. This hybrid mixture provides good rut resistance and a surface highly resistant to fuel and oil spillage. Such properties allow it to be used in industrial areas, airports and harbours, where those situations are frequently associated with heavy and slow traffic. Grouted Macadams constitute a poorly understood branch of pavement technology and have generally been relegated to a role in certain specialist pavements whose performance is predicted on purely empirical evidence. Therefore, the main objectives of this project were related to better understanding the properties of this type of material, in order to predict its performance more realistically and to design pavements incorporating grouted macadam more accurately. Based on a standard mix design, several variables were studied during this project in order to characterise the behaviour of Grouted Macadams in general, and the influence of those variables on the fundamental properties of the final mixture. In this research project, one approach was used to the design of pavements incorporating Grouted Macadams: a traditional design method, based on laboratory determined of the stiffness modulus and the compressive strength.

Industrial accidents triggered by lightning: causes and consequences

Natural hazards affecting industrial installations could directly or indirectly cause an accident or series of accidents with serious consequences for the environment and for human health. Accidents initiated by a natural hazard or disaster which result in the release of hazardous materials are commonly referred to as Natech (Natural Hazard Triggering a Technological Disaster) accidents. The conditions brought about by these kinds of events are particularly problematic, the presence of the natural event increases the probability of exposition and causes consequences more serious than standard technological accidents. Despite a growing body of research and more stringent regulations for the design and operation of industrial activities, Natech accidents remain a threat. This is partly due to the absence of data and dedicated risk-assessment methodologies and tools. Even the Seveso Directives for the control of risks due to major accident hazards do not include any specific impositions regarding the management of Natech risks in the process industries. Among the few available tools there is the European Standard EN 62305, which addresses generic industrial sites, requiring to take into account the possibility of lightning and to select the appropriate protection measures. Since it is intended for generic industrial installations, this tool set the requirements for the design, the construction and the modification of structures, and is thus mainly oriented towards conventional civil building. A first purpose of this project is to study the effects and the consequences on industrial sites of lightning, which is the most common adverse natural phenomenon in Europe. Lightning is the cause of several industrial accidents initiated by natural causes. The industrial sectors most susceptible to accidents triggered by lightning is the petrochemical one, due to the presence of atmospheric tanks (especially floating roof tanks) containing flammable vapors which could be easily ignited by a lightning strike or by lightning secondary effects (as electrostatic and electromagnetic pulses or ground currents). A second purpose of this work is to implement the procedure proposed by the European Standard on a specific kind of industrial plant, i.e. on a chemical factory, in order to highlight the critical aspects of this implementation. A case-study plant handling flammable liquids was selected. The application of the European Standard allowed to estimate the incidence of lightning activity on the total value of the default release frequency suggested by guidelines for atmospheric storage tanks. Though it has become evident that the European Standard does not introduce any parameters explicitly pointing out the amount of dangerous substances which could be ignited or released. Furthermore the parameters that are proposed to describe the characteristics of the structures potentially subjected to lightning strikes are insufficient to take into account the specific features of different chemical equipment commonly present in chemical plants.

Waste management in Forlì-Cesena province: Life Cycle Assessment (LCA) of Forlì incinerator

This work assesses the environmental impact of a municipal solid waste incinerator with energy recovery in Forlì-Cesena province (Emilia-Romagna region, Italy). The methodology used is Life Cycle Assessment (LCA). As the plant already applies the best technologies available in waste treatment, this study focuses on the fate of the residues (bottom and fly ash) produced during combustion. Nine scenarios are made, based on different ash treatment disposing/recycling techniques. The functional unit is the amount of waste incinerated in 2011. Boundaries are set from waste arrival in the plant to the disposal/recovery of the residues produced, with energy recovery. Only the operative period is considered. Software used is GaBi 4 and the LCIA method used is CML2001. The impact categories analyzed are: abiotic depletion, acidification, eutrophication, freshwater aquatic ecotoxicity, global warming, human toxicity, ozone layer depletion, photochemical oxidant formation, terrestrial ecotoxicity and primary energy demand. Most of the data are taken from Herambiente. When primary data are not available, data from Ecoinvent and GaBi databases or literature data are used. The whole incineration process is sustainable, due to the relevant avoided impact given by co-generator. As far as regards bottom ash treatment, the most influential process is the impact savings from iron recovery. Bottom ash recycling in road construction or as building material are both valid alternatives, even if the first option faces legislative limits in Italy. Regarding fly ash inertization, the adding of cement and Ferrox treatment results the most feasible alternatives. However, this inertized fly ash can maintain its hazardous nature. The only method to ensure the stability of an inertized fly ash is to couple two different stabilization treatments. Ash stabilization technologies shall improve with the same rate of the flexibility of the national legislation about incineration residues recycling.