Selected cyanobacteria and green algae species as phycoremediation agent for toxic metal pollutants

Abstract

Water is an essential environmental element and vital in the Islamic value system for purification in performing Ibadah. Cleanliness is not only on application of water to worship but also from safety aspect for daily usage like drinking water and recreation. Regrettably, this tiny volume of water that available on earth is under severe stress because of speedy rise in populace, urbanisation, and untenable utilisation of water in agricultural and industrial setups. Thus, this research has aimed to explore various groups of selected algae that can be employed as potential biosorption agent for inorganic contaminants in polluted aquatic ecosystem. The research was conducted by developing two phases which were algae culturing and phycoremediation model system. In algae culturing, the research has been undertaken by investigating two green algae species of Chlorella vulgaris and Pandorina morum as well as two blue-green algae species (Cyanobacteria) of Pseudanabaena sp. and Synechococcus sp. cell culture growth exposed to different medium formulation, pH and photoperiod. In the second phase, phycoremediation model system was performed by assessing heavy metal sequestration of the same group of algae species exposed to various concentrations and period of time. Two species from group of green algae; C. vulgaris and P. morum and cyanobacteria; Pseudanabaena sp. and Synechococus sp were tested in four different medium; Chu-10, Bold’s Basal medium, Bristol, and BG-11 in different pH (3.8, 5.8, 6.8 and 7.8) in six different photoperiods (24:0, 12:12, 18:6, 6:18 and 0:24 day/dark cycle) condition. Range of green and blue green algae species cells density growth in different pH, photoperiod and medium formulation varies between species. The highest cells density growth for both P. morum and C. vulgaris were detected under photoperiod of 24 h light in BG11 medium at pH 7.8 with the amount of 170 x104 mL-1 and 161 x104 mL-1 respectively, whereas in cyanobacteria species cells density growth were found varied. Pseudanabaena sp. was identified to have yielded the highest amount of cells density growth at 115 x104 mL-1 in BBM medium under photoperiod of 24 h light at pH 7.8. Meanwhile, Synechococus sp. highest amount of cells density growth was detected in BG11 medium at pH 7.8 and 24 h light at 481 x104 mL-1. Marked differences were observed between green and blue-green algae species in cells density growth rate. Therefore, all four selected algae species were analysed over bioconcentration factor (BCF) to further investigate the phycoremediation capability between green and blue green algae species. Three different concentrations of 1mg/L, 2mg/L and 3mg/L of heavy metals (Pb, Fe, Cr, Cd, Al and Cu) were tested for four weeks and the samples were analysed every week via Inductively Coupled Plasma (ICP). Highly significant differences were observed between the species, the heavy metals, the time duration, and all combinations of interactions, which emphasises that changes in BCF value are complex and the responses are not consistent across species. The magnitude of these effects depends on the algae species, time duration, and the concentration and type of heavy metal. Although these factors had an effect on the BCF value, the most influential factor appeared to be the algae species selection. Amongst the selected algae, C. vulgaris and Synechococus sp. were great candidates as good heavy metal accumulator but the cyanobacteria species were the best alternative instead of green algae species for phycoremediation agent.