IT202100016004A1 - METHOD FOR THE IN SITU IMPLEMENTATION OF BIOREMEDIATION WORKS - Google Patents

Description

Description of the invention entitled:

?METHOD FOR THE IN SITU IMPLEMENTATION OF BIOREMEDIATION WORKS?

Description

field of technique

The present invention relates to the chemical sector and in particular to the environmental chemistry sector. Pi? in detail, the present invention concerns a peculiar methodology for implementing bioremediation works which is substantially based on an accurate study of the site to be treated and on the targeted choice of the most suitable remediation technique. suited to its level of contamination. All with the result of optimizing the efficiency of the reclamation intervention in terms of effectiveness of the treatment and targeted investment of resources associated with it.

Known art

Contamination of soils, groundwater, sediments, surface waters and air? one of the major problems facing the industrialized world. The large-scale production of a variety of chemical compounds is causing the deterioration of the quality? environmental. Among these, xenobiotic compounds together with natural organic compounds are the most? toxic and resistant to biodegradation and tend to accumulate in food webs causing biomagnification and serious health problems for humans. While many pollutant compounds are effectively degraded by microorganisms, others persist and pose a serious environmental threat.

At present, public and private clients of reclamation interventions tend to move towards the removal of the contaminated matrix or obsolete technologies such as the ?Pump and Treat? of groundwater. However, new innovative technologies are being developed, aimed at the destruction of polluting compounds, which can already represent a viable alternative to this approach. One of these techniques, bioremediation, uses the metabolic potential of microorganisms to decontaminate polluted environments.

In general, bioremediation techniques involve environmental modifications obtained through the addition of nutrients, forced aeration and the addition of appropriate degrading organisms.

Bioremediation frequently affects multiphase and heterogeneous environments, such as soils in which the contaminant is present in association with soil particles, dissolved liquids and gases. Because of this complexity, effective bioremediation requires a multidisciplinary approach involving microbiology, engineering, ecology, geology and chemistry.

Bioremediation offers many advantages over chemical-physical technologies, especially for contaminants that are diluted and spread over a large surface area.

Treatment in situ ? one of the most effective of this technology as it does not involve the transport of contaminants and has a minimal environmental impact. Furthermore, the in situ treatment can be inexpensive, can? selectively destroy organic pollutants without harming flora and fauna, and can be used for pollutants that are present at low but environmentally relevant concentrations.

Bioremediation techniques have been successfully used to decontaminate sites affected by petroleum, polychlorinated biphenyls (PCBs), trichlorethylene (TCE), perchlorethylene (PCE), trinitrotoluene (TNT), and BTEX (benzene, toluene, ethylene, and xylene) pollution. still an immature technology.

Although microorganisms play a key role in biogeochemical cycles and bioremediation processes, knowledge of community variations microbial changes during bioremediation ? in fact still limited.

This why? Many bacteria of environmental interest cannot yet be cultured with conventional laboratory techniques. has slowed down the development of bioremediation in the field.

Not ? It is still known how to evaluate the biological contribution to the effectiveness of bioremediation and how to ascertain its environmental impact.

Because of the difficulty technique in monitoring bacteria that degrade contaminants, bioremediation often encounters the difficulty to identify the measures to follow in case of failure of the technique.

Furthermore, the limited knowledge of the variations of the communities? microbial growth during bioremediation makes it difficult to assess the impact of these techniques on ecosystems. Fortunately, rapid advances in molecular biology methods have made it easier to study the structure of human communities. microbial without introducing interference and will allow? in the future the optimization of bioremediation techniques.

Bioremediation techniques can be classified as ex situ or in situ. The former are treatments that involve the physical removal of the contaminated material for the treatment processes, while the latter involve the treatment of the contaminated material on site.

Bioremediation offers many advantages over conventional techniques as it can be done on the site, ? often inexpensive and has minimal environmental impact, eliminates waste permanently, ? well received by? public opinion and pu? be applied in conjunction with physical or chemical treatments. In addition, in situ techniques have further advantages because they eliminate transport costs, permanently degrade pollutants, have minimal impact on the ecosystem, can be applied for diluted contaminants and are not excessively expensive.

In order to improve bioremediation techniques in the field and estimate its impact on ecosystems, ? Is it necessary to analyze the communities? microbials taking part in bioremediation.

To pursue this goal, molecular biology techniques have recently been developed and applied to identify microorganisms by means of molecular markers.

Over the past two decades, molecular technologies, such as DNA analysis, have been employed to study microbial ecology. These new techniques have facilitated the analysis of microbial populations in natural environments, thus decreasing the need? to use microbial cultures. In fact, microbiologists have understood that natural microbial populations are very different from those deriving from isolated microorganisms. This ? also the case of microorganisms that degrade polluting compounds. There? implies that natural environments host a wide range of unidentified microorganisms that exhibit catalytic towards pollutants and which therefore have a crucial role in bioremediation.

Bioremediation? a developing technology. One of the biggest difficulties? ? that bioremediation ? conducted in natural environments, which contain many organisms not yet characterized. Another impediment to bioremediation techniques consists in the fact that almost never two environmental problems occur under completely identical conditions: usually, in fact, the type and quantity? of pollutants, climatic conditions and hydrogeochemical dynamics are always different.

With the growing attention paid to the environment by governments and public opinion, the concept of sustainability? ? was quickly extended to environmental issues as well. Particularly in the remediation sector? more and more the GSR (Green and Sustainable Remediation) approach is frequently used, which aims to eliminate unacceptable risks to human health and the environment, while minimizing the negative environmental, social and economic impacts caused by the remediation interventions themselves.

With this approach ?is the design of a remediation intervention extended from how to remediate to if and how much to remediate? (Winsconsin Initiative for Sustainable Remediation & Redevelopment, A Practical Guide to Green and Sustainable Remediation in the State of Wisconsin, Jan 2012).

Yes ? in fact, sometimes in the past it reached the absurd point of intervening in situations that did not pose particular environmental problems, using systems for remediation that have generated an overall impact far greater than the benefit deriving from the elimination of the residual contamination removed. Furthermore, are there ?technical limits to the remediation interventions that often exceed the desired objectives, and which cannot be achieved with traditional techniques, particularly in the case of very large and diluted contaminations? (Ellis & Hadley, Sustainable Remediation White Paper? Integrating Sustainable Principles, Practices, and Metrics Into Remediation Projects, Remediation 2009).

The concept of sustainability? of a reclamation intervention is based on the evaluation of all the main aspects relating to the Social, Environmental and Economic spheres, which increasingly? frequently they form the ?pillars? of national policies in terms of remediation (Wisconsin 2012).

Purpose of the present invention? that of defining a method for implementing a sustainable remediation intervention based on bioremediation techniques with the aim of optimizing the effectiveness of the intervention through a careful choice of the type of intervention, a choice which is based, first of all, on the type of portion to be treated/reclaimed.

Description of the invention

The method for implementing a bioremediation process according to the present invention has as its objective that of guaranteeing a particular effectiveness and rapidity? in the process of restoring and repairing deteriorated ecosystems, in particular contaminated groundwater and therefore, on the one hand, to maximize bioremediation interventions ? in terms of their benefits? and on the other hand, to offer potentially better results with externalities? positive directed to an improvement from a point of quality? and safety in the final stage of rehabilitation.

Pi? in detail, the method for implementing a bioremediation process according to the present invention ? first of all a method which requires that the reclamation takes place in situ, and consists of various sequential phases which include:

a) Identification of the site to be reclaimed. This phase involves the morphological study of the site with known technologies as well as the study of the history of the activities? industrial activities carried out there;

b) The implementation of environmental investigations which include the execution of activities? sampling;

c) Study of the site, typically of the groundwater, and definition of the extent of contamination of the same or of the soil and groundwater;

d) Analysis and definition of contamination levels with known techniques of molecular microbiological analysis and characterization;

e) Identification, choice and implementation of the in situ remediation intervention technique. Said technique? choice between Reductive Biological Dechlorination (BRD), Biospreading, In situ Chemical Oxidation (ISCO), Reactive Permeable Barriers (Zerovalent Iron), Pump & Treat, Monitored Natural Attenuation (MNA).

For the purpose of greater exhaustiveness? Some of the main degradation processes of contaminants, especially hydrocarbons, involved in in situ remediation are described below.

Pi? in detail, among the degradative processes which fall within the field to which the present invention pertains and which concern the method in question, there are the degradation processes of chlorinated aliphatic hydrocarbons.

even more in detail, the three main microbiological processes that lead to the transformation and reduction of the mass of chlorinated aliphatic hydrocarbons (CAHs), are: reductive dechlorination; direct aerobic oxidation; aerobic cometabolism (Frascari et al., 2015). In reductive dechlorination CAHs are utilized by specialized bacteria, as final acceptors of the electron transport chain. The process leads to the reduction of the number of chlorine atoms in the molecule and ? very efficient on molecules with a high degree of chlorination as they are characterized by high redox potential (i.e. they are strong oxidants). This implies that the process takes place under redox-reducing conditions, generally in the absence of oxygen and when the electron acceptors that compete with the dechlorination process have been consumed or removed.

Direct aerobic oxidation occurs when CAHs are used by microorganisms as the sole source of carbon and energy and molecular oxygen is used as the final oxidant and acceptor of the electron transport chain. In this process, the microorganisms recognize the presence of substrates (e.g. CAHs) and synthesize the enzymes necessary for their mineralization. The process of direct aerobic oxidation ? more efficient in compounds with a low degree of chlorination as they are more electron-donor than their high-chlorinated counterparts.

Aerobic cometabolism instead occurs when microorganisms synthesize specific enzymes, normally oxygenases (enzymes that catalyze the incorporation into an organic molecule of one or two oxygen atoms such as hydroxyl), for the degradation of one of their growth compounds (substrate) and, incidentally, these enzymes also catalyze the oxidation of non-growth substrates (co-substrate) for the organism. However, usually necessary the presence of the substrate why? the microorganisms synthesize the enzymes for the transformation of the co-substrate. In other words, microorganisms oxidize CAHs even if they are unable to use these compounds as a source of carbon and energy and need a different substrate to activate the synthesis of the necessary enzymes. The degradation process proceeds through the formation of an epoxide through the catalytic action of the oxygenases and continues through biological and abiological transformations until the complete degradation of the substrate. For the site in question, cometabolic processes are therefore considered possible on the entire series of chlorinated ethylenes present (from PCE to VC).

As regards the processes of degradation of aromatic hydrocarbons (BTEX) there? it should be said that the two main microbiological processes that lead to the transformation of aromatic hydrocarbons (i.e. BTEX) are: anaerobic oxidation and aerobic oxidation.

The anaerobic microbial oxidation process of BTEX does not involve the involvement of molecular oxygen (O2) nor? as the final electron acceptor n? as a reagent/activator in the biodegradation process. In fact, in general, the biodegradation mechanism provides for an initial activation of the compound with oxygen-independent mechanisms such as addition of fumarate, carboxylation, oxygen-independent hydroxylation and the subsequent formation of the common central intermediate benzoyl-CoA. The latter then undergoes a reduction of the aromatic ring catalyzed by benzoyl-CoA reductase, which precedes ring cleavage and subsequent oxidation (Chakraborty and Coates, 2004). In anoxic conditions, the first step in the catabolism of toluene ? mediated by the enzyme benzylsuccinate synthetase (Bss) whose subunit? alpha ? encoded by the bssA gene (Foght, 2008).

In aerobic biodegradation, molecular oxygen plays the dual role of final electron acceptor and reagent in the biodegradation pathways. The main enzymes involved in these processes are the oxygenases which, starting from <O>2, catalyze the incorporation of one oxygen atom (monooxygenase) or two oxygen atoms (dioxygenase) as hydroxyl groups in the aromatic ring. Dioxygenases are divided into opening and activating dioxygenases depending on whether they also catalyze the opening of the aromatic ring or not and are defined according to the substrate (e.g. benzene dioxygenase, toluene dioxygenase (TOD) and benzoate dioxygenase) (Ouyang et al ., 2007). Specifically, toluene dioxygenase (TOD) in turn comprises three enzymatic components, one of which ? a dioxygenase consisting of two subunits? encoded by the todC1 and todC2 genes (Ouyang et al., 2007).

As mentioned above, the method for the implementation of bioremediation of contaminating sites takes place in situ and is characterized by the fact that it applies specifically specific technologies, per se? notes, and specified in detail below, of bioremediation based on the site to be treated.

Detailed description of the invention

The method for implementing an in situ bioremediation work according to the present invention comprises a series of sequential phases which provide for a prior accurate assessment of the site to be treated, i.e. the aforementioned phases of:

a) Identification of the site to be reclaimed. Said phase provides for the morphological study of the site with known technologies (and therefore omitted from the present description assuming that the person skilled in the art implies their technology) as well as? the study of the history of the activities? industrial activities carried out there;

b) Implementation of environmental investigations which include the execution of activities? sampling (also known to a person skilled in the art);

c) Study of the site, typically of the groundwater, and definition of the extent of contamination of the same or of the soil and groundwater;

d) Analysis and definition of contamination levels with known techniques of molecular microbiological analysis and characterization;

and is characterized by the fact that it includes the following phase:

e) Identification, choice and implementation of the in situ remediation intervention technique. Said technique? choice between Reductive Biological Dechlorination (BRD), Biospreading, In situ Chemical Oxidation (ISCO), Reactive Permeable Barriers (Zerovalent Iron), Pump & Treat, Monitored Natural Attenuation (MNA).

Pi? in detail, on the basis of the characteristics of the site, at least six potentially applicable technologies have been identified for achieving the remediation objective in compliance with the principles of sustainability. social, environmental and economic.

Pi? in detail the method in question provides, on the basis of a prior and accurate screening of the site to be treated, to choose between at least six bioremediation techniques described in detail below:

- reductive biological dechlorination (BRD): The degradation of organo-chlorinated contaminants, in the case in which the optimal redox conditions are present, can occur naturally through a process of reductive dechlorination which takes place through a process of hydrogenolysis, i.e. through the substitution, mediated by microorganisms naturally present in the environmental matrix, of chlorine atoms with hydrogen atoms in anaerobic conditions. In this process the organic pollutant is reduced by acting as an electron acceptor while the electrons are supplied by an electron donor usually produced by the fermentation of organic material naturally present in the aquifer (molecular hydrogen and volatile fatty acids recognized as electron donors par excellence in biological reductive dechlorination). Consequently, the molecules pi? high chlorinated gradually lose the chlorine atoms, until the formation of simple and non-toxic aliphatic hydrocarbons such as ethane and ethylene. Typical and well known ? the tetrachlorethylene degradation pathway, which sequentially degrades to trichlorethylene, dichloroethylene, vinyl chloride and finally to ethylene. The degradation of compounds with a high number of chlorine atoms can? be performed by numerous bacterial strains, but the degradation of less oxidized chlorinated organs can? continue only in the presence of a small number of bacterial strains (e.g. the classic Dehalococcoides sp, which proliferates exclusively in strictly anaerobic conditions and with neutral or slightly acidic pH). The absence of this bacterium in situ entails a risk of accumulation of dichloroethylene and, above all, vinyl chloride, the latter compound being carcinogenic and very volatile. Another generally limiting factor in biological reductive dechlorination processes? just the lack of donor of electrons and also the existence of redox conditions are not appropriate with concentrations of dissolved oxygen incompatible with the? activity? metabolism of dechlorinating microorganisms. This natural process of degradation can? be favored by the addition of amendments which, by means of anaerobic fermentation processes, lead precisely to the formation of molecular hydrogen and volatile fatty acids, electron donors of choice for biological reductive dechlorination. On the other hand, the competition from naturally present substances and electron acceptors such as nitrates, iron, sulphates, etc. must be considered in the planning of the injection intervention. This competition does s? that the degradation is maximum only in a given range of hydrogen ion concentration and in a given range of negative redox potential. - Bio-spreading (BS) ? a technique that consists in the introduction of pressurized air in the groundwater with the aim? to oxygenate the aquifer by increasing the redox potential and stimulating the aerobic biodegradation of the contaminants and, at the same time, favoring the precipitation of some metals. The BS technique finds its ideal application in homogeneous soils with high permeability and in layers at least 2 m thick and not confined.

- In Situ Chemical Oxidation (ISCO): Is ISCO or Chemical Oxidation? a technique that involves the injection of oxidizing chemical substances into the subsoil, with the aim of breaking the molecules of polluting substances, transforming them into less toxic compounds for humans and the environment. There are several possible oxidants, each of which is characterized by its own oxidation potential (strength of the oxidant), by the reaction kinetics and by the characteristic thermodynamic conditions of activation and ? therefore, or less suitable for certain pollutants and/or contexts. Other fundamental parameters that govern the chemical oxidation processes in the subsoil, determining whether or not the success of the intervention is, are the temperature, the pH, the concentration of natural organic matter, the presence of any catalysts and the concentration of the reagents. Some reagents have extremely short residence times in the subsoil (a few days), and require a series of very punctual interventions throughout the area to be treated, as they lose their effectiveness shortly after being injected. Organic contaminants are ideally degraded to carbon dioxide and water, passing through the formation of intermediate products typically characterized by a very rapid decay. ? however it is probable that the reaction with the oxidants leads to a modification of the oxidation potential of some heavy metals naturally present in the subsoil, with their solubilisation and the formation of plumes of metals in solution in the groundwater; at the exit from the reaction zone the restoration of the original state of oxidation of the metals does not necessarily occur, and consequently the plume of metal contamination can extend well beyond the reaction zone (think for example of the oxidation of Chromium III to Chromium VI, much more toxic and mobile than the previous one). The introduction of oxidants into the subsoil normally takes place with direct injection from specially constructed wells or drillings, even if numerous other systems can be applied, such as direct mixing with the soil. In order to effectively degrade contaminants, ? however, it is necessary that the molecules of oxidants come into contact with the molecules of pollutants, and therefore that the reagents are injected and dispersed in the most? homogeneous as possible in the area to be treated. In general, the ISCO must be used in correspondence with active secondary sources of contamination, as a system for reducing the mass of contaminants in the source for the reduction up to the possible elimination of the emission of contaminants in the groundwater. Its use in areas not affected by the presence of evident and well-identified sources is hardly reasonable precisely because, after the loss of reactivity? of the injected oxidants, there would certainly be phenomena of rebound of the contaminants which could only be contrasted with repeated, and in any case unpredictable, subsequent reinjection phases.

- Permeable Reactive Barriers (Zerovalent Iron): A Permeable Reactive Barrier (PRB) ? defined as ?an underground reactive material installation designed to intercept a contaminated plume, permit flow through the reactive medium, and transform the contaminants into environmentally acceptable forms in order to achieve concentration values appropriate for remediation downstream of the barrier?. The principle on which PRBs are based? relatively simple: a reactive and permeable medium is placed inside the aquifer system by creating a continuous trench or reactive zones contained in Funnel & Gate type systems, so as to be crossed by the contaminated water which moves due to the natural hydraulic gradient. Reactive material? chosen in such a way that the chemical-physical and/or biological processes that take place inside the barrier allow the contaminant to be degraded, immobilized or absorbed during the crossing phase. Among the various reactive materials currently available, the one most used? certainly the granular zero valent iron (ZVI, zero valent iron). The zero-valent iron, by creating an extremely reducing environment, allows to implement an abiotic reductive dehalogenation of the chlorinated aliphatic hydrocarbons with the formation of ethylene and/or ethane, as non-toxic final products. The degradation process of chlorinated solvents on ZVI occurs through two parallel pathways, a hydrogenolysis (least important pathway) and a dichlorobeta elimination (main pathway). Unlike the biological reduction process, essentially a hydrogenolysis, the reduction on iron appears decidedly more? rapid and takes place with the formation of very unstable and rapidly degraded intermediates (chlorine acetylene and acetylene) which do not accumulate but rapidly degrade to ethylene and ethane.

- Pump & Treat/Stock: The Pump & Treat ? a consolidated technique which consists in the pumping and surface treatment of polluted groundwater. The technique involves the installation of fenestrated wells throughout the aquifer, with pumps that carry the pumped water to a collection network, up to the treatment plant and the delivery point, frequently represented by the sewage system. The treatment of P&T ? normally realized as a hydraulic containment system, or for the barrier of the underground flow of contaminated groundwater, due to its rapidity? and versatility installation. Can? in any case, it can also be used advantageously for the treatment of localized concentration hot spots where the presence of contaminants is in any case deriving from recent primary contamination phenomena or from the presence of active secondary sources from separate phases in still mobile form. Where contamination comes from slow back diffusion processes from low permeability layers? or from material flows deriving from historical sources that are not clearly identified, the P&T ? widely demonstrated to be highly ineffective and decidedly unsustainable both from an economic and an environmental point of view.

- Monitored Natural Attenuation (MNA): The term MNA (Monitored Natural Actuation) refers to cases in which the reduction of the level of contamination is based on the processes that naturally occur in groundwater; these are all those physical, chemical and/or biological phenomena which, under favorable conditions, act without human intervention to reduce the concentrations of pollutants in groundwater. The reduction of contamination is controlled through monitoring aimed at verifying the efficiency of the process. Interest in the MNA technique? increased in recent years following the difficulties? found in the definition of the processes that intervene in the subsoil and the related problems and costs that arose in using more techniques? conventional under complex site-specific conditions. In particular, in the international technical literature, MNA is considered, especially for contamination by chlorinated solvents, as the technology of choice for managing diffuse plumes, at contained concentrations, deriving from historical contaminations with the absence of well-identified active secondary sources, and in the absence of health risks, once its capacity has been ascertained? to contain the extension of the plume.

Claims (8)

Claims 1. Method for the implementation of an in situ bioremediation work comprising a series of sequential phases which provide for a prior assessment of the site to be treated, these phases being: a) Identification of the site to be reclaimed, this phase foreseeing the morphological study of the site and the study of the history of the activities? industrial activities carried out there; b) Implementation of environmental investigations which include the execution of activities? sampling; c) Study of the site and definition of the extent of contamination of the same, said site being land or aquifers; d) Analysis and definition of contamination levels with molecular microbiological analysis and characterization techniques; said method being characterized in that it further comprises the following step: e) Identification, choice and implementation of the in situ reclamation intervention technique, called technique ? choice between at least reductive biological dechlorination, Biospreading, In situ Chemical Oxidation, Reactive Permeable Barriers, Pump & Treat, Monitored Natural Attenuation. 2. Method for the implementation of an in situ bioremediation work according to the previous claim in which the technique for the reclamation intervention is reductive biological dechlorination, said method providing for the use in the site to be reclaimed of bacterial strains such as Dehalococcoides sp where the treated site has contaminants represented by hydrocarbons with a high number of chlorine atoms. 3. Method for the implementation of an in situ bioremediation work according to claim 1 in which the technique for the remediation intervention ? Bio-spreading, said method providing that the site to be treated is a stratum with a thickness of at least 2 m, or permeable and homogeneous soil, said method providing for the introduction of pressurized air, oxygenating the aquifer, increasing the redox potential and stimulating the aerobic biodegradation of contaminants and, at the same time, favoring the precipitation of metals. 4. Method for the implementation of an in situ bioremediation work according to claim 1 in which the technique for the remediation intervention ? in situ chemical oxidation, said method involving the injection of oxidizing chemical substances into the subsoil, with the aim of breaking the molecules of polluting substances, transforming them into less toxic compounds for humans and the environment, said injection taking place in correspondence of active secondary sources of contamination. 5. Method for the implementation of an in situ bioremediation work according to claim 1 in which the technique for the remediation intervention provides for the use of Reactive Permeable Barriers, said method providing for the introduction of a reactive medium into the subsoil , said medium being a zerovalent metal, said metal creating a reducing environment and allowing to carry out a reductive dehalogenation by abiotic way of the chlorinated aliphatic hydrocarbons with the formation of ethylene and/or ethane, as non-toxic final products. 6. Method for the implementation of an in situ bioremediation work according to the previous claim in which the reactive medium is? zerovalent granular iron. 7. Method for the implementation of an in situ bioremediation work according to claim 1 in which the technique for the remediation intervention ? the Pump & Treat, this method consists in the pumping and surface treatment of polluted groundwater. 8. Method for the implementation of an in situ bioremediation work according to claim 1 in which the remediation technique ? the Monitored Natural Attenuation, said method providing for the monitoring of the efficiency of the contamination reduction process which when this is based on the processes that naturally occur in groundwater; these processes being those physical, chemical and/or biological phenomena which, under favorable conditions, act without human intervention to reduce the concentrations of pollutants in groundwater.