Eastlund and Gough (1969) have made a novel suggestion for solving the problems of depletion of raw materials and huge accumulations of wastes on earth. They suggest a properly regulated use of thermonuclear reactions in controlled fusion reactors to produce cheap electricity without radioactive wastes. During this process, thin and very hot gases called ‘plasmas’ are produced and the superheated plasmas could perhaps be made use of to completely vaporize the waste products, thereby converting them to electri­fied particles of their constituent elements. The latter could then be recovered and recycled. Researches to translate these suggestions into action and to test their efficacy are now underway in American laboratories. Plasmas—the fourth state of matter after solids, liquids, and gases—could conceivably have as profound an effect on tomorrow’s world as the advent of nuclear energy has caused in the world of yesterday and today.

Plasmas are most commonly generated by methods involving thermal or electrical energy. In fact, more than 99.9% of all the matter in the universe is ultimately comprised of plasmas. The ionized gas in fluorescent tubes and in neon tubes is really plasma.

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Most gas lasers depend on plasmas for their operation. Some current motivations for plasma research include the generation of energy by the fusion of nuclei of light elements, space exploration, electrical generation, ore extraction, and propulsion techniques and pollution prevention. Plasmas could well constitute the major energy source of the future. The most reliable way to control pollution and improve water quality is undoubtedly to stabilize the ecosystem by balancing the input and output of energy and nutrients. Some reasonable ways to increase stability of aquatic ecosystems include reduction in waste inputs, harvesting and removal of biomass, trapping of nutrients, fish management, and aeration. Similar ways applicable to land conservation include reforestation, restricting monoculture productivity, erosion control and use of detritus agriculture. Methods com­mon to both kinds of ecosystems are enhancement of biological complexity through establishment of ecological niches, seeding diverse populations and recirculating certain organisms, maintenance of fairly high biomasses com­patible with energy flow, maintenance of stratification and maintenance of high chemical buffer intensity including weathering of rocks, etc. In general, pollution means instability whereas a non-polluted habitat is equivalent to a stable ecosystem that resists perturbation.

Waste treatment is by no means the only major consideration in pollution control; various physical and biological methods of stream management can be adopted with a view to restoring an ecological balance and restoring diversification in the ecosystem to control pollution. Although pollution from known and specific outlet points can be con­trolled relatively easily, that resulting from nonpoint sources is extremely difficult to control. Nonpoint sources are mostly those sources which result in ninoff, seepages, and percolation of pollutants to surface and groundwaters via diffuse and undefined routes. Some important kinds of nonpoint pollution sources are agriculture, silviculture, mining, groundwater salinity (irrigation, oil field brines, natural de-icing, municipal and industrial effluents, etc.), urban runoff, rural sanitation, land development and heavy construction works.

Sediments, nutrients and biocides are the major kinds of pollutants from non-irrigated farming whereas salinity is the major problem from ungated fanning. Many construction and building activities create problems related to erosion and the resulting sediment runoff to surface waters. Kumar et al. (1974) have produced certain pollution-tolerant strains of unicellular algae isolated from effluents of oil refineries and fertilizer facto­ries. Comparisons of these strains with wild strains with respect to growth characteristics and the capacity to absorb phosphates and nitrates indicated faster growth and consistently greater uptake of phosphate by mutant strains of Anacystis nidulans. Pollution-tolerant strains of a nidulans and Chlorella vulgaris showed enhancement of nitrate uptake capacity as compared to wild type cells. Studies such as these were prompted by the consideration that natural populations of algae may harbour heterogeneous mixtures of geneti­cally distinct strains differing from one another in respect of pollution toler­ance. The tolerance of algae isolated from polluted habitats, to high concen­trations of nitrate, urea and phosphate was investigated as also the capacity of the algal cells to glean or strip the nutrients from the culture medium (Kumar and Sharma, 1975).

Pollution-tolerant strains of algae can have great signifi­cance in pollution abatement. Aquatic algae and other microbes and lower forms of life are efficient accumulators of radioactive substances from polluted habitats and some of these organisms can concentrate them within their cells to concentrations much higher than those in the ambient water. One advantage of algae, especially the blue-green algae, in this context lies in their generally higher level of resistance to radiations as compared to higher plants and animals (see Kumar, 1963). The complexities of the aquatic ecosystem, including biologi­cal diversity, strongly influence the concentration and translocation of radio­active materials in aquatic communities.

Microbes can also absorb such elements as strontium, caesium and lithium which do not seem to be essential for growth but which do have radioactive forms. The following general aspects about the significance of radioactive wastes are noteworthy: (1) They may be ingested by aquatic animals and predators and go directly into body tissues, or (in lower organisms) they are mostly absorbed on cell or body surfaces. (2) The complexity of body organization is inversely proportional to the direct concentration of the radio-element; e.

g., algae and protozoa can con­centrate relatively more of these pollutants than vertebrates. (3) Certain radionuclides (and their non-radioactive forms) tend to be­come preferentially deposited in specific tissues or organs. Thus, Sr90 is a bone seeker, radioisotopes of iodine go mostly to the thyroid, and silicon goes to frustules of diatoms, etc. At its 16th Symposium held in Zurich in 1972, the European Federation for Water Protection (EFWP) has concluded that: (a) greater importance should be given to water bodies, both flowing and stationary, used for recreation, nautical sports, bathing, fishing, etc.

, and more particularly for their value as sources of industrial and drinking water supplies; (b) groundwa­ter should be suitably conserved and protected; (c) it is not necessarily always true that biodegradable pollutants alone cause the major pollution load; several kinds of ingredients such as heavy metals, refractory chemical com­pounds, mineral oil, exist which cannot be decomposed by mechanical or biological means; inorganic fertilizers and various biocides are also responsi­ble for contributing to this load; (d) preventive measures against possible future detrimental effects of pollution are even more important than the repair of damage already inflicted; further efforts should be made to reduce the amounts of solids and liquid wastes by reutilizing or recycling some of their components; and (e) control of water bodies and of plants serving the purpose of water protection should be reinforced and carried out by all available means, including legal enforcement. The World Health Organization (WHO) has proposed International Stan­dards for Drinking Waters (see WHO, 1970) on the basis of which five classes of quality are distinguished, viz., biological pollutants, e.

g., microbes and pathogens; radioactive pollutants, toxic substances, specific chemicals affect­ing health, and characteristics affecting the acceptability of water. The maxi­mum permissible concentrations of various kinds of pollutants have been prescribed and the characteristics for water acceptability include such proper­ties as colour, smell, taste, turbidity, pH, hardness, etc. Various techniques are currently being devised to control water pollution by removing various chemical, biological and radiobiological pollutants through such physicochemical methods as absorption, electrodialysis, ion exchange and reverse osmosis. In most such methods, the high costs consti­tute the main hurdle and are the limiting factor for general and wider application to control of water pollution. Of these various techniques, reverse osmosis deserve special mention.

This can, in principle, be used to separate any substance in liquid or gaseous solution. It involves the use of a porous membrane whose chemical nature can be made such that it has a preferential attraction for the solvent and a similar repulsion for the solute. This technique was originally developed to purify seawater but is now playing a significant role in water pollution control, water renovation, water purification, and waste reclamation. The technique is also very valuable in the treatment of hard waters rich in calcium and magnesium. Reverse osmosis offers an economical and effective method for upgrading sewage water to a quality suitable for most water uses. In recent years, ozonation has been used to disinfect drinking water in Switzerland and some other countries. There has been growing concern at potential pollution of drinking water by organic and organometallic com­pounds.

Treatment of such polluted waters with ozone can oxidize the pollutants, disinfect the water, and improve its taste and odour, thereby making it suitable for drinking. Some of the pollutants are directly oxidized by ozone whereas others react slowly with ozone decomposition. For many industrial effluents, reverse osmosis has proved to be very effective for reclaiming or concentrating specific chemical or materials. In contrast, much less attention has been paid to the employment of reverse osmosis as a municipal wastewater treatment technique where the concentra­tions of toxicants and heavy metals are relatively low. Reverse osmosis has been found to be able to remove essentially all viral and bacterial particles (cells) as well as most suspended and dissolved inorganic and organic chemicals from water. This technique also permits effective separation of heavy metals from water and secondary municipal effluents and pesticides and organic phosphates can some time be virtually completely removed from water by employing this method.

The removal efficiencies of various toxi­cants vary with their chemical nature. Because of growing scarcity of land for the ultimate disposal of sewage sludge, the sludge is being incinerated in many urban areas now. Require­ments for phosphorus removal from municipal waste-water treatment efflu­ents have caused an increase in sludge volumes with considerably higher concentrations of phosphorus and its associated precipitant metals (e.g., iron, aluminium and calcium). These elements survive the incineration process and appear in the ash. Increased shortages of landfill sites are forcing many countries to seek alternative waste disposal methods. One such promising alternative is incineration in energy-from-waste (EFW) facilities.

These facil­ities provide two benefits: a significant reduction in the volume of waste for disposal and some income from energy production. Incineration can reduce the volume of waste to be landfilled by up to 90% extending the life of present landfill sites and reducing the need for new sites. It shows the sketch of a currently popular incinerator being used in Canada. Very little information is available concerning the environmental impact of chemical sewage sludges (resulting from chemical additions to sewage sludge for phosphorus removal) in either fluid or dry forms when applied to a wide variety of agricultural soils producing many different crops. Proper assessment of long-term risks of applying chemical sludges to farmland is desirable, since these sludges could produce potentially deleterious effects on soils, groundwater, and vegetation.

Until recently the main emphasis of pollution control in many countries has been on sanitary and industrial wastes. Increasing attention is now being given to the problems of urban drainage. The importance of urban water shed management is being increasingly felt in controlling pollution from street runoff. The requirements and methods for possible storm water treatment are now beginning to be considered. In recent years storm-generated pollution has become recognized as one of the greatest offenders in the area of water pollution.

It can contribute heavily to BOD, COD, total suspended solids, total N and orthophosphate loads of water. An effective means of managing storm-generated pollution involves source control of storm water runoff by detention and natural treatment in a lake (Oliver and Grigoropoulos, 1981). This procedure can bring about an immediate improvement of rurtoff quality and make it possible to remove pollutants on a long-term basis.