Coastal Marine Environment Sustainability - Sustainable Practices in Geoenvironmental Engineering - page 292

Suspended solids with toxic and
hazardous substances
Recovery
Hazardous and toxic
substances
Clean seawater
Adsorption of
more substances
FIGURE 8.13
Concept of removal of suspended solids (SS).
8.5.1.2 Large Bodies of Water
To treat large bodies of seawater, ilter units consisting of beach sand and steel slag have
been used successfully to remove the suspended solids. These units were installed on a
vessel (approximately 2500 tonnes), as shown in Figure 8.14. The case study conducted
with thirty eight ilter units (1.5 × 3.6 m) for puriication of seawater in closed sea area
achieved a puriication capacity of about 6000 m 3 /day. The quality of the treated (puri-
ied) seawater satisied the regulatory requirements for allowable SS, COD, pH, DO, etc.
(Fukue et al., 2004). A comparison of the nature of the suspended solids showed that these
contained large amounts of substances, as much as the underlying sediments. Figure 8.15
shows the results of removal of the suspended solids. The left-hand plastic cylinder with a
height of 30 cm contains the seawater with suspended solids. That is why no circular lines
on the bottom of the cylinder can be seen. The right-hand picture shows that removal of
almost 100% of suspended solid from the contaminated seawater produced transparent
seawater that, to all intents and purposes, was devoid of suspended solids and all the sub-
stances adhering to the suspended solids. Studies show that this technique can be used for
puriication treatment water in various kinds of marine applications including dredging,
and treatments to prevent development of red tide and blue tide.
8.5.1.3 Continuous Removal of Suspended Solids
In some closed sea areas, land-based hazardous substances are continuously discharged
and delivered by rivers, etc., to the coastal marine waters. Filter units similar to those used
in the puriication vessel, mounted on semipermanent pier ixtures can function well to
remove the hazardous substances adhering to the suspended solids.