Phytoremediation of Industrial Wastewater using Water Hyacinth 253
14.6.2 Removal of Organic Pollutants from Industrial Wastewater
WH tissues contain many enzymes that perform various biochemical processes to transfer and
degrade organic compounds in joint action with rhizosphere bacteria (Lu et al. 2017, Anipeddi et al.
2022). The developed root system of water hyacinth is crucial in removing organic pollutants from
water through two mechanisms:
1. Roots can absorb PCBs, PAHs as well as other organic pollutants from the aquatic environment
and/or transfer pollutants to other parts of the plant, where they can be degraded into harmless
molecules (Voudrias and Assaf 1996, Xia et al. 2003).
2. The root system provides a habitat for various microorganisms by releasing exudates and
enzymes to stimulate microbial activity and strengthen mineralization and other forms of
biotransformation by rhizosphere microorganisms (Voudrias and Assaf 1996, Xia et al. 2003).
Unlike heavy metals, the assimilation of organic pollutants by the roots of remediation plants
accounts only for a small portion of the total removal (Liu et al. 2003, Zhang et al. 2011, Lu et al.
2014). Most organic pollutants, especially non-ionic ones, could enter the root system of plants via
diffusion, and only some (for instance, systemic pesticides) enter plant roots via a transpiration pull
of leaves (Xia 2002, Paraíba 2007, Al-Qurainy and Abdel-Megeed 2009). There are several steps
in the uptake. Firstly, the organic pollutants in the water get absorbed in the “apparent free space”
in the external root tissues, which account for 10 ~ 20% of the volume of the plant root system
(Nye and Tinker 1977); then, the organic pollutants could be transferred through the cell walls and
intercellular spaces (apoplastically) all the way to endodermis. Endodermis which blocks apoplastic
pathway as it contains highly-suberinized Casparian band impermeable to water; to bypass the
casparian band, ions and molecules should be taken into root cells, and then continue symplastically
from the cell interior to another cell interior via plasmodesmata (Wild et al. 2005).
A case study by Gamage and Yapa (2001) observed the phytoremediation capacity of WH in
textile mill effluent of Sri Lanka. The study has shown a substantial reduction in VS 72.6, TDS 60,
TSS 46.6, 75 BOD and 81.4% COD. Another study by Roy et al. (2010) on textile industry effluent
has shown a 60% reduction in COD and the pH reduction from 11.2 to 8.6. On the other hand,
Munavalli and Saler (2009) worked on dairy industry wastewater, where WH alone contributed to
30 – 45% COD removal. It has also shown a significant reduction of organic strength and has the
tendency to neutralize the pH of dairy industry wastewater. Similarly, another study by Bhavsar
et al. (2010) on the dairy industry wastewater observed the removal of COD levels from 810 mgL–1
to 200 mgL–1. They also observed a pH reduction from 8.3 to 7.04 and alkalinity reduction from
600 mgL–1 to 480 mgL–1. Safauldeen et al. (2019) conducted a phytoremediation experiment on batik
textile effluent using water hyacinth, where treatment achieved 83 and 89% removal of COD and
TSS, respectively (Table 14.9).
14.7 Conclusion
Water hyacinth has a high potential for removing many organic pollutants and heavy metals from
wastewater under different climatic conditions. Apart from the organic pollutants, N, P, Na, Ca, N,
it helps to reduce many toxic non-essential heavy metals like Al, As, Au, Cd, Cr, Hg, Pb, Pd, Pt,
Sb, Te and Tl from different industrial effluents. Moreover, the study presents characteristics of
the wastewater produced from the different lignocellulosic wastewater-producing industries, i.e.,
paper and pulp mills, dairy and textile industries. However, the dairy industry wastewater has fewer
heavy metals and other pollutants than textile and paper and pulp industries. Different treatment
approaches are taken for removing/minimizing the pollutants. Phytoremediation using water
hyacinth would be one of the cheapest, most cost-effective and environment-friendly approaches to
remediate organic and inorganic pollutants, including heavy metals. Some additional investigation
on uptake efficiency, appropriate climatic conditions and post-harvest treatment processes are
required to develop practical large-scale approaches to phytoremediation using water hyacinth.