Perpustakaan Digital ITB

Rapid nutrient removal from municipal wastewater can be achieved by algae immobilised in beads of alginate. The use of immobilised algae has been limited by the additional costs of immobilisation, hence the selection of an alginate with appropriate properties can improve its viability. Nutrient (nitrogen and phosphorus) removal, biomass productivity, bead stability, and production cost were criteria used to compare the immobilisation of Chlorella vulgaris in three alginate products: food grade, and two laboratory products with low and medium viscosity. Algal biomass productivity was greater for low viscosity (47 mg/L/d) than both medium viscosity (37 mg/L/d) and food grade (36 mg/L/d) alginate while nutrient removal was independent of alginate product in batch culture. As such, the criteria for alginate selection could be narrowed to bead stability and alginate price. Beads prepared from medium viscosity alginate were the least stable as they lost the most strength over four weeks exposure to wastewater, swelled and released more organic carbon than the other two products. This was attributed to the lower proportion of L-guluronate in the polymer for medium viscosity alginate which led to the Ca-alginate having less cross-linking. Greater cross-linking in the structures of the food and low viscosity Caalginates was associated with higher porosity (96.7–96.8%) and higher immobilisation efficiency (95–97%). As immobilisation in food grade alginate led to similar nutrient removal and little loss of stability in wastewater, despite lower algal growth, its lower cost means it presented as an effective alternative to the laboratory products.