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Brown seaweed Ecklonia biomass was used for the treatment of electroplating wastewater that contains chromium and zinc ions. Batch experiments showed that Cr(VI) was removed from the wastewater through reduction to Cr(III) by contact with the biomass, whereas Cr(III) and Zn(II) were removed through adsorption to the binding sites of the biomass. Among various parameters, the solution pH most significantly affected the biosorptive capacity of the biomass. As the solution pH increased, the removal efficiency of Cr(VI) decreased, whereas that of Cr(III) and Zn(II) increased, for pH <5. This divergence of efficiency, because of the removal mechanisms of chromium and zinc ions, necessitated a two-stage biosorption process for the complete removal of both ions from the wastewater. The first stage comprises the removal of Cr(VI) by reduction into Cr(III) and of total chromium by partial adsorption at a low pH (1.5-2.5), and the second stage the removal of residual total chromium and Zn(II) by adsorption at elevated pH (4-5). A series of two columns that contain the Ecklonia biomass with a pH adjustment step between column operations was successfully used as a feasibility test of the proposed process. In conclusion, the abundant and inexpensive Ecklonia biomass can be used in the two-stage biosorption process for the treatment of electroplating wastewater that contains Cr(VI) and other metal ions, because it shows the promise of being environmentally friendlier than any existing chemical treatment process.

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Biological hydrogen production by the green alga Chlamydomonas reinhardtii under sulfur-deprived conditions has attracted great interest due to the fundamental and practical importance of the process. The photosynthetic hydrogen production rate is dependent on various factors such as strain type, nutrient composition, temperature, pH, and light intensity. In this study, physicochemical factors affecting biological hydrogen production by C. reinhardtii were evaluated with response surface methodology (RSM). First, the maximum specific growth rate of the alga associated with simultaneous changes of ammonium, phosphate, and sulfate concentrations in the culture medium were investigated. The optimum conditions were determined as NH(4+) 8.00 mM, PO(4)(3-) 1.11 mM, and SO(4)(2-) 0.79 mM in Tris-acetate-phosphate (TAP) medium. The maximum specific growth rate with the optimum nutrient concentrations was 0.0373 h(-1). Then, the hydrogen production rate of C. reinhardtii under sulfur-deprivation conditions was investigated by simultaneously changing two nutrient concentrations and pH in the medium. The maximum hydrogen production was 2.152 mL of H(2) for a 10-mL culture of alga with density of 6 x 10(6) cells mL(-1) for 96 h under conditions of NH(4)(+) 9.20 mM, PO(4)(3-) 2.09 mM, and pH 7.00. The obtained hydrogen production rate was approximately 1.55 times higher than that with the typical TAP medium under sulfur deficiency.

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