Microalgal diversity in relation to the physicochemical parameters of some Industrial sites in Mangalore, South India.

This study is undertaken to understand the microalgal species composition, diversity, abundance and their association with the polluted sites of an industrial area. The microalgae and the wastewater samples collected from these sites were preserved and analysed using standard methods. One hundred and eight species of the microalgae, belonging to Cyanophyceae, Chlorophyceae, Euglenophyceae, Bacillariophyceace and Desmidaceae, were identified. Of these, the members of Cyanophyceae formed the dominant flora. It was observed that the family Oscillatoriaceae was the most diverse family. In this family, the most diverse genus was found to be the Oscillatoria, with 13 species. Further, the abundance of Oscillatoria princeps indicated that these species are tolerant to the pollution and therefore considered as the 'marker species' of the habitat. The abundance of the Cyanophyceae in these sites was found to be due to the favourable contents of the oxidizable organic matter and the presence of the nutrients, such as the nitrates and the phosphates, in abundance, with less dissolved oxygen. The lesser percentage of the Bacillariophyceae (14%), and the negligible number of the euglenoids (2%) indicated that the sites were rich in the inorganic pollutants and poor in the organic pollutants. The range of Shannon diversity indices was found between 2.10 and 3.50, while the dominance index was found between 0.03 and 0.14, the species evenness between 0.73 and 0.93 and the Margalef index between 1.8 and 6.3. The diversity indices indicated that there is light to moderate level of pollution in the studied sites, with moderate diversity level. The principal component analysis (PCA) of the physicochemical parameters identified the four possible groups, which were responsible for the data structure, explaining the 74% of the total variance of the data set. In the PCA performed using all the variables, the first principal component showed the positive correlation with the total dissolved solids (TDS), salinity, conductivity, temperature, biochemical oxygen demand (BOD) and the sulphates and the negative correlation with the dissolved oxygen (DO) and Pb2+. The second principal component showed the positive correlation with the pH, dissolved oxygen, chemical oxygen demand (COD), nitrates and phosphates, and the negative correlation with the TDS, salinity, conductivity, temperature and BOD. The canonical correspondence analysis (CCA) showed that there were significant (p<0.05) positive and negative relationships between some of the physicochemical parameters and the microalgal species at these sites. The results showed that Calonies bacillum and Pseudanabaena amphigranulata were in close positive association with the pH, DO, COD, chlorides, nitrates and Cu+2 at the third and the fifth sites; the Navicula sphaerophora, Stigonema minutum and Chlamydomonas sphagnicola were in close positive association with the phosphates and the lead at the first, second and the fifth sites; the Anabaena spiroides, Anabaena constricta, Oscillatoria curviceps, Oscillatoria princeps, Spirogyra pratensis, Spirogyra crassa, Aulosira laxa and Micrasterias foliacea were in close positive association with the conductivity and the BOD levels at the fourth site, while the Phormidium acutum, Oedogonium decipiens, Oscillatoria trichoides and Parapediastrum biradiatum were in close positive association with the TDS, salinity, temperature, sulphate and Cr+6 levels at the first and the second sites. Therefore, the variations in the physicochemical parameters in the waters of these habitats are attributed to be the reasons for the differences in the diversity and the distribution of the species. Further, the significant correlations observed between the microalgal species and the physicochemical parameters studied here suggest that the type of pollution can be predicted, based on the structure of the microalgal community.

Removal of Pb²âº from aqueous system by live Oscillatoria laete-virens (Crouan and Crouan) Gomont isolated from industrial effluents.

Cyanobacteria have been found to be potential biosorbents of metal ions from waste water. The Pb²âº removal capacity of growing cells of indigenous cyanobacterium Oscillatoria laete-virens (Crouan and Crouan) Gomont was studied under batch experiments and it was found capable of removing Pb²âº of lower concentrations (below 100 mg L⁻¹). The effects of different concentrations of Pb²âº, on the growth rate of alga were also evaluated. The research parameters include the pH of the solution, contact time, initial concentration of Pb²âº, and culture density. Of the parameters studied, the pH of the solution was found to be the most crucial. The removal of Pb²âº peaked at an initial pH of 5. The data obtained from the equilibrium experiments were found well fitting with the Langmuir isotherm with a maximum sorptive capacity (q(max)) of 20.36 mg g⁻¹, indicating a good biosorbtive potential of growing cells. This was confirmed using scanning electron microscope and energy dispersive X-ray analysis, which showed the adsorption of lead on the surface of the cell. The species could tolerate a concentration as high as 60 mg L⁻¹ of Pb²âº. It was observed that the removal obeyed the pseudo-second-order kinetics. The percentage removal was found to decrease with increasing metal concentration, from 10 to 100 mg L⁻¹. FTIR analysis indicates the involvement of amino, carboxylic and amide groups in the sorption process. Among the desorbing agents evaluated, an efficient recovery of 90.2 % was achieved by HCl, in 24 h. Thus Oscillatoria laete-virens (Crouan and Crouan) Gomont seems to be a promising metal biosorbent for the treatment of Pb²âº, in waste waters.