Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 291

marine ecosystems. The methods used include (a) removal of the contaminants and
hazardous substances by various techniques, (b) immobilization and isolation of these
substances, and (c) neutralization and detoxiication. The techniques for treatment of
seawater include aeration, iltration, adsorption, accumulation, isolation, etc. Common
treatment techniques for contaminated sediments include dredging and capping. Other
lesser-used techniques include cultivation and lime strewing. The essence of the various
techniques, together with present capabilities, economics of operation, and requirements
are also briely noted in the table. The ultimate aim of sediment and seawater treatment
procedures is to remove the threat posed by contaminants and hazardous substances in
the water and sediments.

8.5.1 Removal of Contaminated Suspended Solids

8.5.1.1 Conined Sea Areas

In conined sea areas, accumulation of hazardous substances and eutrophication are sig-
niicant problems. A major factor in the constitution of seawater quality is the amount
of suspended solids in the seawater. These solids include mineral particles, plankton,
organic matter, and others kinds of particulate matter. The sorption characteristics and
properties of suspended solids make them useful tools for sorption of hazardous sub-
stances such as heavy metals, PAHs, chlorinated organic compounds, etc., in the sea-
water. Bacteria such as colon bacilli may also be found on the surfaces of suspended solids.
Table 8.5 provides an example of the concentration of heavy metals adhering to some
typical suspended solids. Removal of the contaminated suspended solids will be a step
toward obtaining better seawater quality. Together with the process of bioaccumulation,
these suspended solids can be removed from the seawater using pumping and iltration
techniques, e.g., released phosphorus (into the sea) initially taken by phytoplankton and
algae will be removed when the phytoplankton and algae are themselves subsequently
removed. Figure 8.13 gives a schematic illustration of this simple concept. The ultimate
aim is to ensure that the concentrations of the hazardous substances are lower than the
allowed values in the guidelines. Improved seawater quality provides for (a) greater
transmission of light to sea bed, (b) acceptable water quality for leisure use by the local
coastal community, (c) reduction of potential for eutrophication and reduced capability
for development of red tide, and (d) better sediment quality and also further reduction
in potential for eutrophication, benthic contamination, and development of blue tide.
Technology and procedures for removal of suspended solids in closed sea areas using
iltering techniques should be determined by the targeted inal requirements and results
of site investigation.

TABLE 8.5
Examples of Metal Concentrations in the SS of a Coastal Sea Area (mg/kg dry)
Element Concentration Element Concentration Element Concentration

Fe 8000-30,000 Cu 240-500 P 2600-3000

Al 14,000-44,000 Pb 26-97 Mg 9600-14,000

Ti 1000-32,000 Cd 2.6-3.0 Ca 9000-90,000

V 40-53 Ni 2.8-36 K 9500-15,000

Zn 350-940