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Urban Wastewater Treatment  289


              of small-scale farmers use wastewater for high-value crops because there is
              no alternative irrigation (Asano et al. 1985). In a conventional process setup,
              sewage is collected in a large network of pipes usually known as sewers. It is
              then transported to the centralized treatment plants and treated. Efforts are
              also being directed at treating sewage by a decentralized method, whereby it
              is treated locally with the aim of reusing the treated wastewater (CPCB,
              2009). Depending on the characteristics of the sewage, various techniques
              have been used in various treatment plants operating under favorable local
              conditions. In most of the Class I cities, the ASP is commonly used in sewage
              treatment. This covers around 59.5% of the total installed capacities; upflow
              anaerobic methods cover about 26% of the installed capacity.
                 Sector demands for water are reaching new heights where irrigation,
              household supply, energy, and industry seek increased volumes to meet
              growing needs. The 2050 projections for India report that there will be a
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              requirement of 1447 cubic kilometers (km ) of water, of which 74% is iden-
              tified for irrigation purposes, while the rest is for drinking water (7%), indus-
              try (4%), energy (9%), and other uses (6%; CPCB, 2009). However, with
              rapid urban growth with 498 Class I cities and 410 Class II towns (GOI,
              2008), the demand for drinking water is also rising and has a high priority,
              competing with rural water needs, including irrigation. The current water
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              supply to these cities is estimated at about 48 million m per day and is pro-
              jected to increase further with the increased demand from different sectors
              (CPCB, 2009). A large number of these growing cities are located in major
              river basin catchments, taking fresh water away and discharging wastewater
              back into the catchments, thus polluting irrigation water. The urban return
              flow is seen not only as a hazard but also as an asset. From the past experience
              of urban/municipal wastewater treatment, it is quite evident that the indus-
              trial sector requires a huge volume of fresh water for increased productivity
              (Asano and Levine, 1996). The withdrawal of fresh water by industries fur-
              ther depletes the availability of resources. Realizing this, and for long-term
              sustainability, urban sectors can join with industry to share its water potential
              from treated secondary sewage or cooling water for primary/secondary
              industrial uses. Newer technologies offering significantly higher removal
              rates should be designed and implemented. Membrane technologies, which
              were formerly restricted to water desalination applications, are now being
              tested for the production of high-quality water for indirect potable reuse,
              and they are expected to lead current treatment technologies in the near
              future.
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