Removal of lead (Pb2+) by the Cyanobacterium Gloeocapsa sp.

Pb2+ removal ability of the viable-freshwater cyanobacterium Gloeocapsa sp. was studied in batch experiments. Gloeocapsa sp. was cultured in the Medium 18 with pH adjusted to 3, 4, 5, 6 and 7. Growth was subsequently determined based on the increase of chlorophyll-a content. Gloeocapsa sp. was able to grow at all pH levels tested, except at pH 3. Removal of Pb2+ was then further studied under pH 4. The results showed that Pb2+ concentration in the range of 0–20 mg L−1 was not inhibitory to Gloeocapsa sp. growth but reduced its Pb2+ removal efficiency (by 4.5% when Pb2+ concentration increased from 2.5 to 20 mg L−1). Pb2+ removal characteristics followed the Langmuir adsorption isotherm with the maximum removal capacity (qmax) of 232.56 mg g−1. Adsorption of Pb2+ by this cyanobacterium followed the second order rate reaction and intraparticle diffusion was likely the rate-determining step. The initial rate of Pb2+adsorption during intraparticle diffusion was slower under light than under dark conditions, indicating that light probably slowed down the initial rate of intraparticle diffusion through the repulsion effects on cell membrane.