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of Alternative Technologies for Freshwater Augumentation
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4.3 Biological Pretreatment of Raw Water
This technology is being used in China to pre treat slightly
polluted water sources which have to be used as raw water sources for
water treatment works. Generally, such sources are polluted by wastewater,
and the primary concerns relate to the presence of carbonaceous and
nitrogenous compounds in the raw water which may not satisfy water source
standards. Most water treatment works commonly use a
coagulation-sedimentation-filtration-disinfection process. However, when
polluted water is used as a source water to produce water for public
consumption, reactions between carbonaceous compounds in the raw water and
Cl2 used in the disinfection stage, and between Cl2 and nitrogeneous
compounds in the raw water, results in formation of compounds such as
trihalomethanes which are harmful to human health. These compounds also
consume greater volumes of Cl2, beyond those necessary for disinfection,
resulting in a waste of Cl2. In such cases, bio pretreatment is one
options for improving the safety and quality of the water produced by the
waterworks. Various kinds of commercial plastic products may be used as
growth substrates to promote biological pretreatment of the raw water.
Alternatively, sometimes local materials such as the shells of shellfish
can be used for this purpose in coastal cities. The treatment process is
shown diagrammatically in Figure 24.
Extent of Use
This technology has been used by small municipalities and industries.
Operation and Maintenance
Biological pretreatment of raw water feeds to waterworks requires good
operational and maintenance supervision by qualified staff. Constant
monitoring of the water quality parameters is also necessary. Such
monitoring requires a fully equipped laboratory and trained staff to
operate the laboratory equipment.
Level of Involvement
This technology is typically implemented at the municipal level or at
the level of individual large industries.
Table 17 summarises the costs associated with the use of this
TABLE 17. Cost of the Biotreatment Process in China
Figure 24. A Process Diagram for Biological
Effectiveness of the Technology
This is an effective technology for ensuring the quality of raw water
for municipal and industrial purposes. Tables 18 and 19 present an example
of the effectiveness of this technology from a glass factory in Zhejiang
Province, China. Table 18 shows the water quality parameters of the water
source used by the glass factory, and the industrial water standards.
Table 19 shows the water quality of the product water at various points in
the treatment process (refer to Figure 24).
TABLE 18. Source Water Quality and Industrial Water
Standards for Industrial Use.
This technology is effective in reducing the concentrations of
pollutants in natural waters, thereby improving water quality for a
variety of water uses after application of conventional water treatment
The primary disadvantage of this technology is that it requires trained
staff to implement. The biological pretreatment technology needs to be
carefully controlled and closely monitored to ensure consistent quality
product water is produced.
This technology is acceptable, with no known cultural problems.
TABLE 19. Effluent Water Quality Using Biological
Pretreatment Processes in China.
Further Development of the Technology
This technology is considered to be fully developed. Pilot projects are
needed to popularize the use of this technology.
Professor Chi Bute, Tingji University, 1239 Shiping
Road, Shanghai 200009, China, Fax: 86 21 650 28965.