Natural Water Purification Processes

Soil may be viewed as a natnral filter for wastes and one that rates very high in sustainability. Most organic matter is readily degraded in soil, and, in principle, soil constitutes an excellent primary, secondary, and tertiary treatment system for water. Soil has physical, chemical, and biological characteristics that can enable wastewater detoxification, biodegradation, chemical decomposition. 

FIGURE 5.11 Major components of a complete physical-chemical treatment facility for municipal wastewater. 

Early civilizations, such as the Chinese, used human organic wastes to increase soil fertility, and the practice continues today. The ability of soil to purify water was noted well over a century ago. In 1850 and 1852, J. Thomas Way, a consulting chemist to the Royal Agricultural Society in England, presented two papers to the Society entitled Power of Soils to Absorb Manure. Mr. Way s experiments showed that soil is an ion exchanger. Much practical and theoretical information on the ion exchange process resulted from his work. 

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In some cases, technology helps to reduce the natural radiation exposure. For example, when drinking water supplies are drawn from surface waters, the use of water-purification processes brings about a decrease in the concentration of radium and other naturally occurring radioactive elements. Another example is the burning of fossil fuel, which reduces the specific activity of C in the biosphere and therefore lowers the doses from those radionuclides. 

In hemodialysis the dialysis fluids are prepared from the tap water which may contain considerable amounts of trace metals. In the absence of adequate water treatment procedures it must be considered the main source of trace metal dialysate contamination. Some domestic tap water contains aluminum in high concentrations either naturally or as a result of the addition of the element as a flocculant to the water basins, a procedure which is part of the water purification process and has led to an acute, fatal intoxication of a considerable number of patients in a Portuguese dialysis center (see also below) [17,18]. Worth noting is that concentrations of particular elements in tap water may vary seasonally, e.g. silicon, or even on a day-to-day... 

Before the explosion of the human population and the advent of the Industrial Revolution, natural purification processes were quite adequate to provide ample water of very high purity in all but desert regions. Nature s purification processes can be thought of as massive but somewhat delicate. 

Which water purification process is not a natural process (a) Distillation, (b) Aeration, (c) Filtration, (d) Reverse osmosis, (e) Settling. 

Low levels of radionuclides have been found in the piping. Based on analyses of piping scale, the material was determined to be naturally occurring thorium found in alum used during the water purification processes (DOE-RL 1990). 

First Carbonation. The process stream OH is raised to 3.0 with carbon dioxide. Juice is recycled either internally or in a separate vessel to provide seed for calcium carbonate growth. Retention time is 15—20 min at 80—85°C. OH of the juice purification process streams is more descriptive than pH for two reasons first, all of the important solution chemistry depends on reactions of the hydroxyl ion rather than of the hydrogen ion and second, the nature of the C0 2 U20-Ca " equiUbria results in a OH which is independent of the temperature of the solution. AH of the temperature effects on the dissociation constant of water are reflected by the pH. 

Other Uses. The quantity of coal used for purposes other than combustion or processing is quite small (2,6). Coal, especially anthracite, has estabHshed markets for use as purifying and filtering agents in either the natural form or converted to activated carbon (see Carbon). The latter can be prepared from bituminous coal or coke, and is used in sewage treatment, water purification, respirator absorbers, solvent recovery, and in the food industry. Some of these markets are quite profitable and new uses are continually being sought for this material. 

The number and complexity of unit processes and in turn unit operations comprising a water purification or wastewater treatment facility are functions of the legal and operational requirements of the treated water, the nature and degree of contamination of the incoming water (raw water to the plant), and the quantities of water to be processed. This means then, that water treatment facilities from a design and operational standpoints vary, but they do rely on overlapping and even identical unit processes. 

Demineralization Processes As in dealkalization, there are various IX demineralization process configurations possible depending on the nature of the supply water, the final water quality needs, and the operating preferences. Demineralization may take place in anywhere from one to four vessels per train, depending on the specific purification process. 

Surfactant concentrations in polluted natural water bodies interfere with the self-purification process in several ways. First, certain detergents such as ABS are refractory or difficult to biodegrade and even toxic or inhibitory to microorganisms, and influence the BOD exhibited by organic pollution in surface waters. On the other hand, readily biodegradable detergents could impose an extreme short-term burden on the self-purification capacity of a water course, possibly introducing anaerobic conditions. 

The link between colloids and surfaces follows naturally from the fact that particulate matter has a high surface area to mass ratio. The surface area of a 1cm diameter sphere (4jtr ) is 3.14 cm, whereas the surface area of the same amount of material but in the form of 0.1 pm diameter spheres (i.e. the size of the particles in latex paint) is 314 000 cm. The enormous difference in surface area is one of the reasons why the properties of the surface become very important for colloidal solutions. One everyday example is that organic dye molecules or pollutants can be effectively removed from water by adsorption onto particulate activated charcoal because of its high surface area. This process is widely used for water purification and in the oral treatment of poison victims. 

The traditional application of adsorption in the process industries has been as a means of removing trace impurities from gas or liquid streams. Examples include the removal of H2S from hydrocarbon streams before processing, the drying and removal of C02 from natural gas, and the removal of organic compounds from waste water. In these examples the adsorbed component has little value and is generally not recovered. Such processes are generally referred to as purification processes, as distinct from bulk separations, in which a mixture is separated into two (or more) streams, each enriched in a valuable component, which is recovered. The application of adsorption to bulk separations is a more recent development that was stimulated to a significant extent by the rapid... 

Industrial separation membranes and ion-exchange resins can be made from chitin, especially for water purification. Chitin is also used industrially as an additive to thicken and stabilize foods and pharmaceuticals. Since it can be shaped into fibres, the textile industry has used chitin, especially for socks, as it is claimed that chitin fabrics are naturally antibacterial and antiodour (www.solstitch.net). Chitin also acts as a binder in dyes, fabrics and adhesives. Some processes to size and strengthen paper employ chitin. 

Ammonia is found in the environment as the result of natural and industrial processes. It is released into the environment by the breakdown of organic wastes, and it is a constituent of the soil, the atmosphere, and bodies of water. Ammonia is also a key intermediate in the nitrogen cycle and is a product of amino acid metabolism (WHO 1986). Anhydrous ammonia is used in the production of nitric acid, explosives, synthetic fibers, and fertilizers (Budavari 1989). It is used as a refrigerant as a corrosion inhibitor in the purification of water supplies in steel production as a catalyst for polymers as a preservative for latex and in the production of nitrocellulose, urea formaldehyde, sulfite cooking liquors, and nitroparaffins (ACGIH 1991 Lewis 1993). Ammonium hydroxide (10-35% ammonia) is a major constituent of many cleaning solutions. Ammonia... 

Gas Purification. The best-known purification process using 4A is that of natural gas this involves two benefits, namely, peak-shaving whereby the calorific value of fhe gas is adjusted by CO2 (and water) removal, and sweetening by H2S removal. The latter purification also is used in LPG treatment. Another example is the trapping of hydrocarbons in gas and vacuum circuits. 

Some water purification and sewage treatment plants use oxygen. The gas is pumped through water to increase the rate at which naturally occurring bacteria break down organic waste materials. A similar process has been found to reduce the rate at which eutrophication takes place in lakes and ponds and, in some cases, to actually reverse that process. 

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