Removal of viruses from sewage, effluents and waters. 2. Present and future trends.
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Because large variations occur in the concentrations of viruses that enter treatment plants from season to season and from place to place, and even during a 24-hour period, field studies on the removal of viruses by treatment processes require temporal coordination of sampling. Quantitative methods for concentrating viruses must be developed to measure accurately the efficiency of virus removal by treatment processes in field situations. Extended settling, and storage of sewage and raw waters, reduce virus levels and deserve further study. Oxidation ponds must be reevaluated with regard to temporal matching of influent and effluent samples and with special care to prevent short-circuiting. Conventional and modified activated sludge plants must be reassessed with temporal matching of samples. Coagulation of viruses with metal ions requires field evaluation, and virus removal by filtration through sand and other media, under constant salt and organic loadings, needs both laboratory and field evaluation. A comparative study of water disinfectants related to specific conditions is needed. The toxicity, carcinogenicity, and teratogenicity of products resulting from disinfection must also be assessed. Other matters for investigation are: methods for quantitatively detecting viruses adsorbed on solids, the virus-removal capability of soils, better virus indicators, virus concentration in shellfish, the frequency of infection in man brought about by swallowing small numbers of viruses in water, the epidemiology of virus infection in man by the water route, the effect of viruses of nonhuman origin on man, and the occurrence of tumour-inducing agents in water. (+info)
Water-borne typhoid fever caused by an unusual Vi-phage type in Edinburgh.
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Investigation of a small series of cases of typhoid fever infected in a river between 1963 and 1970 revealed that all were caused by a single source, a carrier of a rare phage type of Salmonella typhi. The contamination of the river resulted from an incorrect sewage connexion with a surface water drain outfall into the river. (+info)
Removal of viruses from sewage, effluents, and waters. I. A review.
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All sewage and water treatment processes remove or destroy viruses. Some treatment methods are better than others, but none is likely to remove all of the viruses present in sewage or in raw water. Primary settling of solids probably removes a great many of the viruses in sewage because viruses are largely associated with the solids. Long storage of effluents or water is destructive to viruses. Activated sludge is the best biological method for removing viruses from sewage. Trickling filters and oxidation ponds are erratic, the latter probably because of short-circuiting. Coagulation with metal ions is the most effective single treatment method for removing viruses from sewage and from raw waters, according to laboratory studies at least. Lime is the best coagulant for these purposes in the rapidly virucidal high pH range. Polyelectrolytes also can sediment viruses. Rapid filtration through clean sand does not remove viruses, but filtration of coagulated effluents does, probably because the layering floc itself adsorbs viruses. Clays and carbon adsorb viruses to some extent, but the process is not efficient. Ultimately, disinfection should help to produce virus-free waters for drinking and virus-free effluents for discharge into waters with which man may come into contact. Because disinfection is not a simple matter, disinfectants must be selected according to need. Effluents and waters containing solids can probably be disinfected only by heat or by penetrating radiation, waters discharged into streams should not be disinfected with anything that will injure or kill aquatic life (unless the toxic products can be neutralized), and drinking-waters should carry a disinfecting residue. (+info)
New factors in the design, operation and performance of waste-stabilization ponds.
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In the developing countries, the unit costs of waste-stabilization ponds are generally low. Moreover, in the tropics and subtropics, the environmental conditions are conducive to a high level of pond performance. In view of this, the theory, operation and performance of such ponds under these conditions have been studied.It is shown that the Hermann & Gloyna and Marais & Shaw theories of the degradation action in oxidation ponds can be integrated, and that account can be taken of the effect of the sludge layer. In Lusaka, Zambia, anaerobic conditions are much more likely to occur in summer than in winter, because of intense stratification. It is confirmed that a series of maturation or oxidation ponds is more efficient than a single pond of equivalent volume.When aqua privies and septic tanks are used as anaerobic pretreatment units, the area of the primary oxidation ponds can be reduced and there is less likelihood that anaerobic conditions will develop in them in summer. The use of self-topping aqua privies, discharging through sewers to oxidation ponds, has made possible the economic installation of water-carriage systems of waste disposal in low-cost high-density housing areas.In the oxidation ponds, typhoid bacteria appear to be more resistant than indicator organisms; helminths, cysts and ova settle out; there are no snails and, if peripheral vegetation is removed, mosquitos will not breed. (+info)
Water borne viral infections and their prevention.
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Unless special measures are taken, community water supplies are likely to contain enteric viruses which may lead to sporadic cases, or even epidemics, of such diseases as infectious hepatitis or poliomyelitis. After a general discussion of waterborne viral infections, in which it is pointed out that subclinical infections may considerably outnumber clinical cases, the author proposes a method for the concentration and detection of enteric viruses in water by means of membrane filtration and growth on monkey-kidney-cell or other tissue cultures.The various methods of disinfection of water which can reduce the virus concentration to an acceptable level are discussed, and it is concluded that flocculation and filtration followed by chlorination, or ozonation followed by chlorination, are adequate methods where large volumes of water are to be treated. In developing countries where relatively small volumes of water have to be treated, iodination appears to offer certain advantages, allowing the construction of a simple water-treatment plant requiring little supervision. However, until the long-term effects of iodine, in particular on pregnant women and young children, are known iodination plants should be used only on an experimental basis. (+info)
Floc sizing techniques.
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In the study of mass transfer of substrate through floc particles, it is essential to have an estimate of floc size. This study presents floc size measurements made on pure culture bacterial floc and shows their applicability to mass transfer studies. A critical review of the biological literature on methods to size biological floc and determine wet floc density is also presented. (+info)
Distribution of lead in body fluids after ingestion of soft solder.
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Blood, serum, cerebrospinal fluid, and urine obtained from a patient before and after chelation therapy showed that (1) the ratio of Pb in his cerebrospinal fluid to that in his serum varied from 0.4 to 0.9 and was independent of serum Pb concentration; (2) the fraction of Pb in his serum fell linearly with decreasing blood Pb concentration and changed from 1.6% to 0.33% as his blood Pb concentration changed from 116 micrograms/dl (5.6 mumol/l) to 31 micrograms/dl (1.5 mumol/l); and (3) his renal clearance of Pb from serum varied from 5 ml/min to 36 ml/min. This high value was obtained 11 days after chelation and is attributed to large quantities of Sn in his urine promoting the excretion of Pb. Solder was identified in his stool after discovery of radio-opaque material in his bowel. The Pb isotope ratios of the solder were different from those in his urine when he was first admitted, and showed that he had ingested solder when he had returned home on weekend passes. (+info)
Significance of losses in water distribution systems in India.
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Effective management of water supply systems consists in supplying adequate quantities of clean water to the population. Detailed pilot studies of water distribution systems were carried out in 9 cities in India during 1971-81 to establish the feasibility of a programme of assessment, detection, and control of water losses from supply systems. A cost-benefit analysis was carried out. Water losses from mains and service pipes in the areas studied amounted to 20-35% of the total flow in the system. At a conservative estimate, the national loss of processed water through leaks in the water distribution systems amounts to 10(12) litres per year, which is equivalent to 500 million rupees.It is possible to bring down the water losses in the pipe mains to 3-5% of the total flow, and the cost incurred on the control programme can be recovered in 6-18 months. Appropriate conservation measures will help in achieving the goals of the International Water Supply and Sanitation Decade to provide clean water for all. (+info)