Page 2 Plant-Bacteria Interactions Edited by Iqbal Ahmad, John ...

290j 15 The Use of Rhizospheric
and fecal coliform bacteria [27,74–84]. A number of industrial wastes such as dairy
waste, sugar industry waste, tannery waste, electroplating industry waste, textile
industry waste, paper and pulp mill waste and domestic waste have been treated
by water hyacinth [55,72,85,86]. Treatment efficiency cannot be summarized as it
varies with wastewaters having different chemical properties; however, the method
can attain high treatment efficiencies. For example, water hyacinth reduced 87% of
chemical oxygen demand (COD), 95% of total suspended solids (TTS) and 98.6% of
fecal bacteria in 7 days in municipal wastewater treatment [79].
Water hyacinth has attracted considerable attention because of its ability to grow
in heavily polluted water together with its capacity for metal ion accumulation [87–
91]. It removes nutrients and pollutants in wastewater through a complex array of
physicochemical processes, including absorption, flocculation, precipitation and
sedimentation, and biological mechanisms including plant and bacterial processes
[53,44,92,93]. Water hyacinth can grow in heavily polluted water and has a high
capacity of metal ion accumulation, even with relatively toxic metal ions such as Hg 2
+ and Pb 2+ [87–91,94]. Sutton and Blackburn [95] studied Cu 2+ uptake by water
hyacinth from Hoagland nutrient solution. Many data have been accumulated on the
uptake of metal ions including As 3+ ,Cu 2+ ,Cd 2+ ,Cr 6+ ,Hg 2+ ,Ni 2+ ,Pb 2+ ,Se 2+ ,Eu 2+
and Zn 2+ by this species [92,96–106]. The highest levels of Cd 2+ ,Cr 2+ and Cu 2+ found
in roots were 6103, 3951 and 2655 mg l 1 , respectively [90]. Water hyacinth can also
extract metal ions at low concentrations. The bioconcentration factors (BCFs) of the
roots of water hyacinth for Cu 2+ , Ni 2+ and Zn 2+ were 2.5 · 10 3 , 1.6 · 10 3 and
6.1 · 10 3 , respectively, and were comparatively higher than those of other biological
systems [104]. Thus, water hyacinth can be used as an efficient biofilter for metal
ions and has been widely used in plant-based wastewater treatment systems [55].
15.4
Biology of Water Hyacinth
Water hyacinth is a free-floating aquatic plant, which has spread throughout the
world by human activity. It is a successful invader of freshwater and eutrophic
environments having the property of rapid vegetative growth and multiplication,
wide ecological amplitude and great phenotypic variation [87]. The dramatic growth
of water hyacinth has deteriorated the utilization of water resources [55,87,107] and
ranks first among the aquatic plants as a nuisance weed [87]. Nowadays, however,
scientists and engineers have turned this nuisance to merit and are using water
hyacinth to combat water pollution as it removes nutrients and inorganic pollutants
from wastewater [55].
15.4.1
Scientific Classification
Water hyacinth belongs to the family Pontederiaceae. The scientific name is Eichhornia
crassipes. The genus Eichhornia was named in 1843 by Kunth in the honor of