Removal of lead (Pb(2+)) by the cyanobacterium Gloeocapsa sp.

Pb(2+) 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 Pb(2+) was then further studied under pH 4. The results showed that Pb(2+) concentration in the range of 0-20 mg L(-1) was not inhibitory to Gloeocapsa sp. growth but reduced its Pb(2+) removal efficiency (by 4.5% when Pb(2+) concentration increased from 2.5 to 20 mg L(-1)). Pb(2+) removal characteristics followed the Langmuir adsorption isotherm with the maximum removal capacity (q(max)) of 232.56 mg g(-1). Adsorption of Pb(2+) by this cyanobacterium followed the second order rate reaction and intraparticle diffusion was likely the rate-determining step. The initial rate of Pb(2+)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.

Production, composition and Pb2+ adsorption characteristics of capsular polysaccharides extracted from a cyanobacterium Gloeocapsa gelatinosa.

Pb2+ adsorption by the living cells of the cyanobacterium Gloeocapsa gelatinosa was studied. Cyanobacterial cells with intact capsular polysaccharide (CPS) showed 5.7 times higher Pb adsorption capacity than that of cells without CPS. The adsorbed Pb was desorbed by EDTA, indicating that Pb2+ adsorption occurred mainly on cell surface. Production, sugar content and ability of CPS to remove Pb2+ were then studied in details. CPS production by G. gelatinosa increased when culture time was prolonged. The maximum CPS production was 35.43 mg g(-1) dry weight after 30-day cultivation. Xylose, arabinose, ribose, rhamnose, galactose, glucose, mannose and fructose were the neutral sugars presented in CPS of G. gelatinosa. Acidic sugars including galacturonic and glucuronic acids were also found in CPS. The amount and composition of G. gelatinosa's CPS varied according to its growth phase and culture conditions. The highest amount of acidic sugars was produced when cultured under low light intensity. The extracted CPS rapidly removed Pb2+ from the solution (82.22+/-4.82 mg Pb2+ per g CPS), directly demonstrating its roles in binding Pb2+ ions. Its ability to remove Pb2+ rapidly and efficiently, to grow under sub-optimal conditions (such as low pH and low light intensity), and to produce high amount of CPS with acidic sugars, leads us to conclude that G. gelatinosa is a potential viable bioadsorber for mildly acidic water contaminated with Pb2+.