Phytoremediation of Industrial Wastewater using Water Hyacinth 241

The phytoremediation consists of four major processes, i.e., phytoextraction, phytostabilization,

phytovolatilization and rhizofiltration where the pollutants are directly accumulated and metabolized

in plant tissues or transported and released as exudates by biochemical mechanisms (Schnoor et al.

1995).

In the phytoextraction process, plants and roots extract the metals and translocate them to shoots.

The shoots and roots are harvested to remove the contaminants. Phytoextraction is considered a low-

impact technique, having 10 times lower operational cost per hectare as compared to conventional

remediation techniques (Jadia and Fulekar 2009, Salt et al. 1995). In phytostabilization, plant roots

limit the bioavailability and mobility of the contaminants. As a result, it is referred to as inactivation

and is used to remediate soil, sediment and sludge contaminants (Jadia and Fulekar 2009, USEPA

2000). Plants involved in phytovolatilization uptake the contaminants and transform them into volatile

forms. The converted less toxic substances are released into the atmosphere through transpiration

(USEPA 2000, Jadia and Fulekar 2009). In the phytofiltration or rhizofiltration process, plants are

used to remediate water and wastewater with a low concentration of contaminants (Ensley 2000)

(Figure 14.2). Both terrestrial and aquatic plants absorb, concentrate and precipitate contaminants

in the roots. Heavy metals like Pb, Cd, Cu, Ni, Zn and Cr can be accumulated through this process

and are primarily retained within the roots (USEPA 2000).

Phytodegradation

Figure 14.2. Types of phytoremediation.

14.4 WH: An Aquatic Macrophyte

WH is a free-floating, invasive aquatic macrophyte abundant in the South and northern regions

of India (Kumar and Chauhan 2019). The temperature of 28°C to 30°C (Malik 2007) with pH

ranging from 6.5 to 8.5, and salt concentration less than 2%, are suitable for its optimum growth.