Utilization of blue green algae for the removal of some heavy metals from waste water

Abstract

Aphanothece halophytica was able to accumulate lead rapidly and became saturated at 90 ub/mg dry weight within 1 hour. For zinc accumulation, it still increased at a slower rate of 7.8 ug/hr.mg dry weight after a rapid rate in the first 10 minutes. The lead and zinc accumulation by A. halophytica were passive adsorption which were highest at pH 6.5 and increased above 6.0 respectively. Spirulina platensis was able to accumulate lead at a rapid rate in the first 10 minutes and slow down at 15.6 ug/hr.mg dry weight. About 50-70 % of accumulated lead was EDTA non-extractable and was likely to be transported into the cell. Zinc accumulation by S. platensis occurred at the cell surface with the rate of 15.6 ug/hr.mg dry weight and became saturated at 19 ug/mg dry weight within 5 hours. A part of zinc accumulation by S. platensis required energy from metabolic process but not from external glucose. The lead and zinc accumulation increased at pH above 6.5 and 6.0 respectively. Cations affected lead and zinc accumulation differently for the two algae except in the case of lead accumulation by A. halophytica which was not affected by cations. The rates of lead and zinc accumulation by both algae depended on metal concentration in solution but were saturated when the metals were in excess. The total lead and zinc accumulation by both algae increased with increasing cell density but efficiency of the cell did not. Lead accumulation per hr per mg dry weight of A. halophytical was stable and zinc accumulation per hr per mg dry weight decreased with increasing cell density up to 0.5 mg dry weight/ml. The efficiency of S. platensis to accumulate lead and zinc decreased with increasing cell density up to 1 and 0.6 mg dry weight/ml respectively. The age of cells had little effect on lead and zinc accumulation of both algae. Aphanothece halophytica and S. platensis had low efficiency for lead and zinc removal from acid waste water but higher efficiency of 85% was observed for zinc removal from alkaline waste water using A. halophytica at 0.87 mg dry weight/ml. The cell was not available for repeated use by EDTA washing after the removal of zinc from waste water.