Some companies now marker microbial inocula, which are claimed to significantly increase the rate of biodegradation of oil pollutants Another approach has been to utilise and marker white-rot fungi such as Phanaerochytae chrysosporium, a widely used degrader of lignocellulosic matrrials organisms thatcan degrade such complex organic molecules, e.g. lignin, have wide of range of enzymic activities which are capable of degrading many of the most dangerous industrial pollutants, a.g. PCBs. There are presently some constraints on this approach. Vis:
(1) Indigenous degradative microbes are fully adated to the specific environment to be treated.
(2) Introduced or foreign microbes must be able to survive in the new environment and be able compete whit the established indigenous microbes
(3) Added inocula must remain in close contact whit the pollutant and, in aqueous, avoid dilution.
A further possibility in bioremediation is to genetically engineer microorganisms to be able to degrade those organic pollutant molecules that, at present they are unable to do. While this has been achieved in some cases, there are considerable technical problems, including genetic stability and survival of the new microbe in a hostile environment. Furthermore, there are legislative, ethical and perceptional problems concerned with their release into environment such as sewage systems soils and oceans. To date no genetically engineered microorganism has left the laboratory and been tested in the field. There is intense research in progress worldwide. Particularly the USA, and it is believed by many informed industrial scientist that in the near further this is technology may widely and safely used for environmental applications.
The detection and disarming of land mine –a problem of hung dimensions in countries devastated by war – may well, in part, have a biotechnological amelioration for example, certain microorganisms can utilize explosives such as 2,4,6 trinitrotoluene (TNT) as nutrient, and soil contaminated with TNT can be bio remediated. Since longstanding lend mines invariably leak explosives into the near environment, it has been shown that, by inserting a gene for luminescence or fluorescence near the digestive enzyme, the bacteria would glow, thus enhancing recognition of the mine. This process exemplifies the bringing together of biosensor technology and bioremediation
While microorganisms have dominated bioremediation practices there is a groundswell of interest in using plants to remediate some environmental problems. Plants have evolved n exquisite root system that allows efficient acquisition of essential elements from soil. Removing from soil inorganic
Pollutants such as lead, mercury and cadmium could well be a new, potentially low-cost, environmentally sound remediation strategy.
Bioremediation is a new technology and will require time for full development and application. Some of the relative strengths and weaknesses of bioremediation for the treatment of oil spillages are shown in table 9.3
9.7 Detection and monitoring of pollutants
A wide range of traditional methods have long been used to detect pollutants, including microbial and chemical analyses. More recently improved biological detection methods include biosensors and immunoassays. Such sensors can be designed to highly selective or sensitive to a wide range of compounds, e.g. pesticides. Microbial biosensors are microorganisms which produce a reaction (such as luminescence light) upon contact with the substance to be sensed.
Immunoassays use labelled antibodies and enzymes to measure pollutant levels. Such assays have proved very valuable for sensitive and sensitive and rapid field use. Another increasingly used technique for microbial detection is direct isolation and amplification of DNA from soil.
Y recognized as 9.8 Microbes and the geological environment
Microbes are increasingly recognized as important catalytic agents in certain geological processes, e.g. mineral formation, mineral degradation, sedimentation, weathering and geochemical cycling.
One of the most detrimental examples of microbial involvement with minerals occurs in the production of acid mine waters. This occurs from microbial pyrite oxidation when bituminous coal seams are exposed to air and moisture during mining. In many mining communities, the huge volumes of sulphuric acid produced in this way have created pollution on an unprecedented scale. Other examples of the detrimental effects of microbes include the microbial weathering of building stone such as limestone, leading to defacement or structural changes.
In contrast to these harmful effects, microbes are increasingly used beneficially to extract commercially important elements by solubilisation (bioleaching) .For example, metals like cobalt, copper, zinc, lead or uranium can be more easily separated from low-grad ores using microbial agents – mining with microbes
The biological reactions in extractive metal leaching are usually concerned with the oxidation of mineral sulphides. Many bacteria, fungi, yeasts, algae and even protozoa are able to carry our specific reactions. Many minerals exist in close association with other substances, e.g. sculpture, and iron sulphide with must be oxidised to free the valuable metal. A widely used bacterium thiobacillus ferrooxidans can oxidised both sulphur and ion, the sulphur in the ore wastes being converted by the bacteria or sulphuric acid. Simultraneously, the oxidation of iron sulphide to iron sulphate is enhanced
The commercial process involves the repeated washing of crushed ore (normally in large heaps, fig. 9.8) with a bioleaching solution containing live microorganisms and some essential nutrients (phosphate/ammonia) to encourage their growth. The leach liquor collected from the heaps contains the essential metal, with can easily be separated (downstream processing) sulphuric acid extraction.
In the USA almost 10% total copper production is obtained by this method. Countries such as India, Canada, the USA, Chile and Peru are routinely extracting copper at a worldwide annual rate of 300000 tonnes using microbes; whith low-Grade ores, bioleaching costs a half to a third as much as direct smelting.
Large-scale bioleaching of uranium ores is widely practiced in Canada, India, the USA, the USSR. By means of bacterial leaching it is possible to recover uranium from low-grade ore (0.01-0.5% U3 O8), which would
Be uneconomic by any other known process. The USA alone extracts 4000 tonnes of uranium per year in this manner. Uranium is primarily used as a fuel in nuclear power generation, and microbial recovery of uranium from otherwise useless low-grade ores can be considered as an important contribution to energy production (Table 9.4). Bioleaching of uranium ores is seen to have an important contribution to the economics of nuclear power stations by providing also a means of recovery of uranium from low-grade nuclear wastes.
Continuous processes have been developed, and the control of the essential bacterial population is easily achieved because of the acidity and limited substrate availability leaching technology will continue to offer more efficient and cheaper ways of extracting the increasingly scarce metals necessary for modern industry. The principal disadvantage of bioleaching is the relative slowness of the process
Another important application for bacterial bioleaching is the removed of the sulphur-containing pyrite from high-sulphur coal. Little use is now mate of high-sulphur coal because of the sulphur dioxide pollution that occurs with burning. However, as more and more reserves of coal are brought into use, high-sulphur coals cannot be overlooked. Thus the bacterial removal of pyrite (which contains most of the sulphur) from high-sulphur coal could well have huge economic and environmental significance.
Aliphatic hydrocarbon-utilizing bacteria are also being used fir prospecting for petroleum deposits. Microbes will soon be commercially used to release petroleum products from oil shelf and tar sand. In all these system there is rarely any formalized containment vessel or bioreactor. Instead, the natural geological site becomes the bioreactor, allowing water and microorganisms to flow over the ore and to be collected after natural seepage and outflow. Recycling by mechanical pumping can also be used.
Microorganisms can also be used as metal (bio) accumulators from dilute solution. The microorganisms, bacteria, yeasts and moulds can activity uptake the metals in various ways and, such processes have a potential use in extracting rare metals from dilute solution, bus it is still to be seen whether it will become an important technology.
In a similar way, microorganisms are being used to extract toxic metals from industrial effluents and reduce subsequent environmental poisoning.
Some plants have been shown to accumulate heavy metals such as nickel, cobalt, cadmium, nickel and even gold, and studies are now being carried out to assess whether such plans could be used to extract metal from soil or ores that are sub economic for conventional mining. This area of study is celled ‘phytomining’ and will depend on the use of hyper accumulating plants. It is envisaged that hyper accumulating plants would be harvested from soil containing metal, the plant material burnt to give a small volume of plant ash (bio-ore) containing high concentrations of the target metal, and the final bio-ore smelted to yield metal. Such processes are not yes commercially viable. Phytomining could well appeal to conservation as an alternative to opencast mining of low-grade ores.
In all these activities, multidisciplinary approaches are necessary, and new biotechnological techniques, such as designing an organisms for a specific function, could yield further benefits. The overall picture of this area of biotechnology is