Membrane and Desalination Technologies - TCE Moodle Website

Desalination of Seawater by Thermal Distillation and Electrodialysis Technologies 553
high-pressure pumps in RO process, which produce noise during operations. Various technological
measures can be utilized to reduce noise levels so that the risk to the operators can be
minimized (26). The operations should be kept away from population centers.
The more important form of emission from desalination that raises environmental concerns
comprises the discharge of concentrated saltwater after the desalination process is completed
(27). The TDS of wastewater from a conventional DWTP is approximately 3–5 times higher
than that in the feed; the flow rate is 20–50% of feed flow. The waste also contains chemicals
used in the pretreatment of feed water, such as antiscalants, surfactants, and acid.
Major disposal alternatives for the water pollution are given in Table 12.4. Each method
varies in complexity and costs. Sewer discharge is commonly the least complex and least
Table 12.4
List of disposal alternatives for water pollution in DWTP
Technology Brief description
Ocean disposal Ocean disposal is typically done several miles offshore with diffusers.
Dilution by seawater can reduce the contents of the waste. The
treatment plant outfall location may be affected by water quality rules
Discharge to sewer and
surface waters
and regulation.
Sewer discharge is the simplest; however, it depends on the ability of the
wastewater treatment plant to accept high salinity discharge. Surface
water discharge involves discharge to a point of outfall such as tidal
lake or brackish canal. Dilution by surface waters can reduce the
contents of wastes. The location of discharge and the pretreatment
requirement are determined by state and regulatory agencies; water
quality testing (e.g. bioassay toxicity) is required.
Land application Irrigation is sometimes used for the waste streams with relatively lower
salinity. Saline tolerant vegetation and habitat are required. This is
usually determined by site-specific soil and drainage characteristics
Evaporation pond Desalting concentrate is discharged to ponds and evaporated to dryness
for final disposal. It is land intensive and requires relatively dry
climates. Dry salt is the final waste product, which must be
characterized and disposed of accordingly as solid waste. This is
generally applicable only in arid environments and then usually in an
inland location
Deep well injection In deep well injection, the waste streams are injected to the ground and
are permanently stored in the injection zone. It is very commonly used
Zero discharge and
industrial reuse
by the desalination water treatment plants
Zero discharge of wastes can be achieved by thermal processes, which
greatly reduce or eliminate the waste stream. The thermal processes are
energy intensive and very costly. Wastes must be characterized and
disposed of accordingly. Marketable salts for general industrial uses
can be recovered. This is still in the development stages, but past
attempts indicate that recovery of marketable byproducts is
economically difficult