科研之友
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摘要
Cities in the developing countries have multiple modes of human and animal waste treatment and disposal that finally decide the overall impact on the urban ecosystem, and these have been studied for the city of Bangalore. Four modes are found, namely underground sewage systems, decentralized soak pits and septic tanks, open defecation and a miniscule effort at composting. The extent of N released per unit area is high, ranging between 0.44 and 1.4 t ha(-1) of the urban landscape. In this study the N release and outflow have been estimated. The N entering or flowing in the lithosphere, hydrosphere and in wastewater streams forms the major component. The pool size has first been determined. The size and movement through these pools were estimated with a view to determine the state of the N cycle and if there is a cause for alarm in similar cities in other developing countries. N contribution from human waste (exereta and urine) forms the single largest influx and sewage flowing out of the city forms the single largest efflux of N pool. Owing to a seemingly large use of soak pits and open conveyance of sewage in some parts of the city, coliforms and NO(3)-N have seeped into shallow and deep-ground aquifers and show up in ground- and sub-soil waters in the city. The level of N in these waters at a few places is slightly higher than the permissible limits. This suggests that there is a need to rind alternatives to modes like the ubiquitous soak pit, such that pollution of shallow and deep aquifers is avoided in the future. Currently, there is little effort in stripping the waste water off N. Also, there is no significant effort in recovery and reuse of nutrients, and this is required to increase the sustainability levels.
- 出版日期2008-6-10
