Decolorisation of methylene blue using Lactuca and Sophora species.
Thesis DisciplineEnvironmental Sciences
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The world is facing numerous environmental problems, and water pollution is being amongst the major ones. Water quality has worsened dramatically due to various pollution sources. Textile industry effluents, containing a variety of natural and synthetic dyes, is one of the chief sources of pollutants. The diverse structures of these dyes lead to many challenges for their degradation. Certain plants have inbuilt potential to remediate these dyes. The aim of this study is to assess the potential of a non-native New Zealand plant (Lactuca sativa L. var. Great Lakes) and New Zealand native plants (for example, Kowhai) for phytoremediation of methylene blue (MB) as the model dye. Spectrophotometric analysis showed that 10 seeds of Lactuca spp. and pre-germinated Sophora spp. were able to decolorize 40 mg/L MB up to 78% in first 48 hours of incubation under non-sterile as well as aseptic conditions. Lactuca spp. showed up to 86% decolorisation within 96 hours of incubation. The decrease in the radicle lengths by about 20% indicated toxicity of MB towards plants. Increasing the number of seeds from 10 to 20 resulted in 88% decolorisation within first 48 hours of seed incubation. The decolorisation potential was inversely proportional to the increase in MB concentration with 81% decolorisation of 40 mg/L in 48 hours, whereas 400 mg/L showed only 28% decolorisation in the same time period. Under repeated stress conditions the seeds still had a capacity to decolorise MB but the efficiency decreased from 80% in the first cycle to about 43% in third cycle. Pre-germinating the seeds had a positive effect on their decolorisation capacity at higher MB concentrations, while the presence or absence of seed coat and controlled pH did not significantly affect the decolorisation capacity of lettuce seedlings. Using UV-Vis spectroscopy and cyclic voltammetry, the total absence of MB from the system was confirmed, suggesting degradation of the dye. Significant activity induction of marker bio-transformation enzymes from lettuce radicles indicated their probable role in the metabolism of MB. Phytotoxicity assays using ryegrass seeds and seedlings demonstrated the non-toxic nature of the metabolites following decolorisation of MB by lettuce seedlings, suggesting that lettuce seedlings had dye detoxification capacity.