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Tham khảo tài liệu 'waste water treatment and reutilization part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Using Wastewater as a Source of N in Agriculture Emissions of Gases and Reuse of Sludge on Soil Fertility 379 In spite of these advantages their use can be restricted by the high content of salts heavy metals bacteria and virus that can be present in residual waters Zekri and Koo 1994 reason why developed and developing countries have decided to establish rules for their use. The use of residential waters for crop irrigation has increased in several communities although some factors that limit the use of residual waters for irrigation include the following Bhatnagar et al. 1992 1. water availability at the time of irrigation 2. water quality according to the standards of use 3. disease transmission potential 4. accumulation of toxic substances This is demonstrated by Cortés 1989 who points out that residual waters can be considered unhealthy at the time they reach the parcel because they exceed the limits of microbe contamination suggested in Engelberg Switzerland 1995 which should be of no more than 1000 fecal coliforms per 100 ml of water and should not have more than one helminth L-1 of water WHO 1989 . The presence of these microorganisms in residual waters soils and fruits as is the case of coliforms Escherichia coli and Klebsiella pneumoniae Pseudomonas spp and helminth eggs Ascaris lumbricoides and Trichuris trichuria among others which cause real and potential risks to public health. In Mexico the specific and non-specific sources of residual water discharges that come from population centers industry and agriculture exercise a heavy pressure over most of the superficial bodies of water 29 monitored hydrologic regions out of a total of 37 reach an acceptable category of water quality. Out of the total load of oxygen biochemical demand OBD 89 is concentrated in just 15 basins and almost 50 specifically in the Pánuco Lerma San Juan and Balsas rivers causing heavy contamination in them INEGI 2001 . Organochloride pesticides stand out since 1948 because of the
