published on 10 March 2006 in ecosystems
Biotechnology can be defined as the application of microbiology, genetic engineering and biochemistry for the treatment of waste materials by means of micro-organisms, vegetable cells, animal cells and enzymes, and for the production of goods and services in the health sector, food sector, chemical industry, energy and waste elimination.
The constant progress that is taking place in biotechnology know-how has surely opened the way to new applications in sectors of health care, agriculture, food production and the environment.
Environmental biotechnologies are an “emerging” area of application of biotechnology, in which organisms, cells and parts of the same are used to purify the air, treat polluted waters, carry out waste disposal, monitor and rehabilitate contaminated areas.
Research in this sector is greatly oriented towards the development of cleaner industrial products and methods, based on the use of enzymes. Funds have been invested in public research centres and through private initiatives, for the study and updating of biosensors: simple vegetable and microbe organisms that are used to monitor the environment because their behaviour in the presence of polluting substances is known.
Great attention is paid to bacterial organisms, biocatalysts that can carry out the biodegradation and detoxification of xenobiotic compounds, such as synthetic products that normally are not found in nature.
Some activities (as for example intensive pig farming, the production of fodder, blast furnaces, industries for manufacturing polystyrene) produce gaseous waste that must be treated before being disposed in the atmosphere.
Since the Sixties, biofiltering methods have been used for the disposal of gaseous industrial waste. This method uses filters filled with compost to remove bad odours and small amounts of foul-smelling biodegradable substances. The biofiltering system is not very expensive, however it is not very efficient because the overall procedure is slow and the filters must often be replaced. Consequently research has been oriented towards the development of processes that biologically break down the gaseous polluting substances and, specially in northern Europe, many resources have been used to study and realize materials that are suited for the biofilters, and to identify the more efficient micro-organisms for the biofiltering process. Progress in this sector is opening the possibility of treating an ever increasing number of pollutants.
How does biofiltering work?
The air containing undesired gases is passed through the biofilter, which contains organisms that are able to use the polluting substances as a source of nourishment. The micro-organisms used in the biofilter can be fungi, yeasts, moulds and bacteria. The parameters that influence the efficiency of the biofiltering process are temperature and humidity of the flow of air that must be decontaminated, because the micro-organisms require specific environmental conditions in order to live and carry out their normal metabolic activities.
When the plant remains inactive, the organisms that are present must be fed periodically so that all the colonies do not die.
Most oxidation biofilters operate well with mesophile bacteria, that live in optimum conditions at temperatures ranging between 20°C and 40°C. The communities of micro-organisms formed by different strains (microbial flora) that are used, are also able to degrade particular substances made of non natural chemical compounds that may be present in the gaseous effluents.
The inert materials that form the biofilter are supports made using substances like turf, compost or wood shavings. In order to construct filters that are more resistant to wearing, there is a tendency to use materials such as polymer foams and cellulose.
The breaking-down efficiency of a biofilter is its capacity to eliminate the volatile organic compounds that are present in the air. In most cases the result is over 95% and they are greatly used to remove substances with a characteristic nauseating odour (alcohols, ethers, aldehydes, ketones and alkali).
Fungi and lichens
In nature, there are organisms that are defined as bioindicators, that are sensitive to the presence of polluting compounds that alter the environmental equilibrium of their habitat.
Lichens react to the presence of a polluting agent with determined “symptoms” that can be measured precisely, by evaluating the morphological changes (appearance, colour, shape), the physiological and the genetic changes in the cells that the lichens are subjected to after the intake of a harmful compound. Lichens are also able to behave as “sponges” that absorb both the useful and the harmful substances that are present in the environment and concentrate them in their organism. Through chemical analyses it is possible to identify and evaluate the concentrations of substances accumulated in the organism of the lichens.
Lichens are used as bioindicators of atmospheric pollution because of some characteristics that make them particularly suited : poor mobility in the environment, diffuse presence in the examined area, high resistance to environmental stress, inability to eliminate the intoxicated parts, their long life-span and their constant metabolic activity.
Also some fungi are used as contamination bioindicators for heavy metals in the soil, due to their capacity to concentrate harmful substances like silver, lead, mercury and radioactive isotopes in their organism. In fact studies are being carried out in order to understand which fungi genes determine the presence of some proteins that enable a tolerance to these metals. In case of a positive result, thanks to the biotechnologies, the tolerating capacity could be transferred to heavy metals, from the fungi to the bacteria which would then be used more easily in treatment plants.
Land and sea environments can be polluted by a large concentration of natural organic contaminants or as a consequence of industrial processes.
Biotechnologies offer a method to decrease or eliminate pollution, using a modern technique that is considered sustainable because its application is considered at a low risk of side effects on the ecosystems; which is bioreclamation or bioremediation.
Micro-organisms, fungi or plants are used to clean an area from the presence of polluting compounds by isolating the bacteria that are most efficient in degrading the substance that has to be eliminated, and then creating the living conditions that are most suited for the same bacteria.
The practical realization of this biotechnological technique takes place in various stages, that are summarized here below:
- determine the state of pollution, defining the type of pollutant, evaluating its concentration in the environment and determining the level of danger for the ecosystem in which it is present;
- identify the species of bacteria that are able to attack the polluting substance and remove it efficiently;
- isolate the specific strain of the micro-organism or microbe community to be used for the decontamination, from other organisms living in the same environment ;
- provide the optimum quantity of nutrients in order to obtain the required number of colonies of bacteria selected for the decontamination;
- inoculate the bacteria in the polluted area and monitor the speed of degradation of the polluting substance, and identify the refuse products that are formed at the end of the process.
The biodegradation process can take place through an aerobic or anaerobic type of metabolic mechanism.
Bioremediation is a method that makes use of biological systems (algae and micro-organisms). In the last 15 years it has been used successfully and more and more easily as research in this field has led to increasingly practical solutions. This method is preferred to the traditional soil reclamation techniques, such as incineration or the use of chemical solvents, because they have a very costly impact on the environment. In fact, generally, the residues of bioremediation that accumulate in the soil or in the polluted waters consist of carbon dioxide, water and biomass. By applying bioremediation, it is also possible to carry out cleaning interventions in areas of the sea, or soil that have been polluted by oil or other hydrocarbons, or areas of land that are contaminated by benzene or other compounds that are harmful for the environment.
During the past decades a “biotechnological solution” that is able to remove pollutants from the waters is being used successfully: phytopurification, which is based on the capacity of self-purification of the water environment through physical, chemical and biological processes carried out by vegetable and bacterial organisms. The plants involved are macrophytes and microphytes that are specially selected depending on particular characteristics like the capacity to adapt to the environment that needs to be decontaminated and their rapid growth with the formation of a biomass. However the species that are used for phytopurification are aquatic or hygrophytic plants, in other words they are able to live in humid environments. In particular, depending on the type of phytopurification system that is required, different types of floating or submerged macrophytes, that are emersed individually or in association, are used. Water purification takes place due to the joint activity of the macrophytes and some micro-organisms that are associated to them, the algae on one hand find nourishment from the pollutants that are present and favour the development of bacteria that can transform the harmful substances by metabolizing them.
The types of plants of the phytopurification systems depend on the direction of the water-flow. Superficial flow systems are formed by tanks or channels that are 40 to 60 cm deep, which create environments that are similar to ponds covered with floating hydrophytes. Instead, in sub-superficial flow systems, running water does not come into contact with the atmosphere and an inert support is added in the tanks, on which the roots of the macrophytes can develop. The water runs under the inert support, and to favour its movement, the tank, that is 70 to 80 cm deep, is in a slanting position. Phytopurification systems offer an alternative for treating waste waters in small sized rural communities and seasonal waste, as in the case of camping sites, hotels and tourist villages, for the treatment of industrial waste, or percolated waste from the dumps, or waste water washed away from roads and highways. The costs for the realization of these systems are very variable, however they are not greater than for the conventional treatment systems, while instead their management costs are quite modest as energy consumption is practically inexistent.
Biotechnological waste disposal
The traditional methods of disposing industrial waste (oily mud or mud containing hydrocarbons etc.) provide for stocking the same in controlled dumps or their destruction by heat in ovens. These solutions are not easily sustainable and their economic expenses are great. In the Nineties the first biotechnological disposal plants for industrial waste and mud were installed in the United States. These solutions were also adopted in Europe and in Italy. Also in this case the principle was to use communities of aerobic bacteria that could metabolize the waste materials that had to be processed, such as aromatic polycyclic hydrocarbons.
Urban waste disposal is widespread and well developed and since a few years there are various plants operating in Italy. Waste composting is widely diffused. This process involves the aerobic fermenting of the organic part of the urban waste.
Composting operations are carried out on an industrial scale in large plants, and also on a domestic scale and on farms, where dung is replaced by compost. Generally, different types of compost can be obtained depending on the original organic materials : green compost (vegetable waste such as leaves, pruned branches, fruits, vegetables, flowers, wood scraps and paper), selected organic matter compost (from specific and univocal differentiated waste collection, treatment plant mud or food industry waste), and finally mixed compost.
Written by Eliana Marchisio