PhD

An investigation entitled ―Phytoremediation of inorganic contaminants in
Vellayani wetland ecosystem‖ was carried out at the Department of Soil Science and
Agricultural Chemistry, College of Agriculture, Vellayani, during 2013-16. The
objective of the study was to track the potential sources of contaminants threatening
the Vellayani wetland ecosystem and suggest a viable phytoremediation technology.
The experiment comprised of four parts.
The first part involved a peripatetic survey in the catchment of Vellayani lake
along the rivulets that contribute water to Palappoor, Pallichalthodu, Reservoir bund,
Arattukadavu RB, Valiyavilagam, Mannamvarambu and Manamukku sites. Three
rivulets per site were identified, and geocoded water and sediment samples were
drawn from five sampling points under each rivulet during pre and post monsoon
seasons of 2014-15. Among the physical properties of water colour, turbidity and
suspended solids were above the maximum permissible limit (MPL).
Chemical
properties viz., pH, EC, NO3-N, NH4-N, P, Fe, Al, Pb, Cd and BOD of water showed
significant difference among the sites during both the seasons but COD was
significant only for post monsoon. P content and BOD exceeded the MPL and Al the
desirable limit. Coliforms were detected at all sites during both seasons and were
above the MPL. Texture of the sediment varied from sandy clay to sandy clay loam.
EC, OC, NO3-N, NH4-N and P contents of sediment showed a decreasing trend
during the post monsoon season. Arattukadavu RB was the most contaminated site
followed by Palppoor and Manamukku the least contaminated site preceeded by
Mannamvarambu and Valiyavilagam with respect to water and sediment quality. No
pesticide residue was detected in water and sediment. The highest plant density was
noticed for Cynadon dactylon L.
In the second part, potential sources of contaminants were identified as
automobile workshops/servicing centres, domestic wastes from hotels/houses and
sewage.
Out of the 29 species of dominant macrophytes, highest biomass was
recorded by Limnocharis flava L. (Buch.). In shoot, the highest concentration for Fe
was recorded by M. vaginalis, Panicum repens L. for Aland S. trilobata for Pb and
Cd.
In root, the highestconcentration for Fe, Al, Pb and Cd was showed by
Eichhornea crassipes Mart., Monochoria vaginalis (Burm.f.), Colacasia esculenta L.
and Sphagneticola trilobata L. respectively. Sediment from Arattukadavu recorded
the highest contents for Fe, Al, Pb and Cd and count for bacteria, fungi and
actinomycetes. It was observed from the study that concentration of Fe, Al, Pb and
Cd decreased with the distance from the source of contamination. Higher quantities
of Fe was extracted by E.crassipes and M.vaginalis; Al by M. vaginalis and L. flava
and Pb and Cd by L.flava and E.crassipes from the wetland ecosystem.
In the third part, four pot culture experiments were carried out with graded
doses of Fe (1000, 2000 and 3000 mg kg-1), Al (750, 1000 and 1250 mg kg-1)and Pb
and Cd (50, 75 and 100 mg kg-1) to determine the hyperaccumulation ability of
selected macrophytes based on a screening trial. The macrophytes were grown in
sediment and water collected from the Vellayani wetland ecosystem for a period of
45 days.
From the study it was observed that E. crassipes was the best
hyperaccumulator for Fe, M. vaginalis for Al and L. flava for both Pb and Cd and can
be identified as the best phytoextractors for the same. Root was the major retention
site for all the metals. Among the rhizosphere microbes, fungi maintained a positive
relation with levels of of Fe, Al, Pb and Cd and a negative relation by bacteria and
actinomycetes.
In the fourth part, the macrophytes showing highest hyperaccumulation ability
for each metal (based on part III) were raised in pots containing the respective metals
(2000 mg Fe kg-1, 1000 mg Al kg-1 and 75 mg Pb /Cd kg-1) for 60 days. The plants
were harvested and the biomass was put to different disposal methods viz.,
composting, vermicomposting, ashing and production of biochar and was used for the
pot culture experiments with amaranthus. The treatment effects were significant for
biomass production and metal extraction.
Among the four disposal methods,
vermicomposting had resulted the highest biomass production for all except Pb.
Regarding the metal extraction by amaranthus, application of ash (T4) showed the
highest removal and the least by the biochar (T5). The metal retention in soil was
highest for biochar and least for ash. Loss of metals from the processed materials was
also lowest for biochar.
Thus the best disposal technique of phytoextractors
/hyperaccumulators is conversion to biochar.
The viable phytoremediation technology is to raise suitable phytoextractors /
hyperaccumulators in the contaminated area and dispose them through biochar
production.