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Methods and Means of Water Treatment
Among the research programmes, developed by AQUA PLUS Ltd. are technologies and equipment for emergency water supplies.
For preparation of water under emergency conditions (natural disasters and industrial failures, civilisation problems and in areas without central or local water supply) the ultimate task is to ensure disinfection of water, i.e. elimination or separation of all microbial and biological growth in the water.
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Mechanical treatment of water (removing undissolved particles, turbidity, colour, etc.), or possible adjustment of chemical composition of water (ionic composition, removal of organic substances, etc.) can be considered as a following step.
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It is claimed that the main cause of human disease is due to natural water sources and their biological activity. Hence, just by thorough elimination of this contamination, majority of problems ascribed to consumption of untreated water can be avoided.
If the disinfected water exhibits odour, turbidity or does not meet the requirements of chemical composition, it does not comply with generally accepted hygienic standards or the consumer´s desires, nevertheless it will not result in acute or chronic health disorders.
There are three principal methods of water disinfection usually implemented under emergency conditions; boiling of water, physical methods of separation of microbial organisms and chemical treatment.
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Boiling of water is the oldest, well-known and still widely applied method, which with keeping the recommended time of heat treatment secures safe elimination of micro-organisms. However this method presents high energy demands and technical problems, resulting from boiling (limited volume of water, cool-down period required, storage in non-sterile containers, etc.).
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Microbial filtration is one of physical methods. It should be pointed out that very recent methods, unfortunately difficult to carry out, like UV sterilization, ozone treatment or membrane separation processes, have to be disregarded.
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A number of companies manufacture and offer mechanical filters, made from various materials (metal, ceramic, plastic or their combination), which reportedly should retain bacteria in pores of construction material, of less than 0.2 µm ( which is a diameter of the smallest bacteria). The problems incountered are mechanical impurities contained in water, clogging and fouling the pores and diminishing the product water flow and a real danger of retro-contamination on the product side. These bacteria are flushed to disinfected water in repeated, multiple applications of such filters. Moreover, commercially available filters are permeable for viruses, with 0.025 - 0.075 µm size.
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Critical comments in efficiency assessment studies stress the absence of long-term disinfection efficiency testing, and the fact that mechanical defects or missing spare parts can leave the user without any treatment means, completely in the hands of the manufacturer, who should guarantee that the filtration material is pin-hole free and that any leakage to the product water can occur.
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The third group represents chemical method of disinfection. Most of the agents used are iodine or chlorine based chemicals.
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Disinfection capability of individual systems is limited by a number of factors (concentration of active component, time of exposure, temperature of water, pH, organic substances, turbidity, resistance of organisms present, etc.). Concentration level of active component can be easily altered. The problem is in the unreacted disinfectant. Both iodine and chlorine exhibit characteristic ( an unpleasant) sensoric properties; odour and taste (some iodine agents even colour). The elevated concentrations of iodine and active chlorine may have negative impact on human health.
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Some world companies apply a neutralising agent, which has negative influence on taste or health effects (e.g., sodium thiosulphate) and does not allow the increase of concentration of the active component to a desirable level.
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Therefore the manufacturers of such water treatment systems attach an instruction leaflet, warning that the disinfection efficiency need not be sufficient (if the water is turbid, and/or cool and/or resistant micro-organisms are present and/or high concentration of organic substances, etc.).
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A recommendation follows, instructing that in similar cases a multiple dose of disinfecting agent and/or prolonged exposure to the agent should be used. A decision making process is transferred to the user and the disinfecting agents need not always have sufficient disinfection effect.
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