Tuesday, April 20, 2010
10-12

Enzymatic prevention of calcium oxalate scaling: Effects of anionic and cationic substances on oxalate oxidase

Sandra Winestrand, Department of Chemistry and Biomedical Sciences, Karlstad University, SE-651 88, Karlstad, Sweden, Simona Larsson, Faculty of Civil Engineering, Riga Technical University, LV 10483, Riga, Latvia, Pierre Cassland, Novozymes, Krogshøjvej 36, 2880, Bagsværd, Denmark, Nils-Olof Nilvebrant, Department of Chemical Engineering, Karlstad University, SE-651 88, Karlstad, Sweden, and Leif J. Jönsson, Department of Chemistry, Umeå University, SE-901 87, Umeå, Sweden.

Oxalic acid is present in lignocellulosic feedstocks and may also form during industrial processes, such as cooking and bleaching. Together with calcium, oxalate forms precipitates that cause problems in industrial processes. Oxalate-degrading enzymes have potential as agents for prevention of calcium oxalate scaling in the pulp and paper industry and in lignocellulose-based biorefineries. The concentrations of selected anionic and cationic substances in seven authentic industrial filtrates were determined and the effects of charged substances on oxalate degradation by oxalate oxidase were investigated by treatments with ion-exchange resins. Treatment of the filtrates with anion exchanger, cation exchanger or uncharged resin increased the oxalic acid degradation rates. The anion-exchange treatment resulted in a major increase (>10 times) in the degradation rates for two filtrates and in an intermediate increase (2-10 times) for four filtrates. The cation-exchange treatment resulted in a major increase in the degradation rates for two filtrates and in an intermediate increase for three filtrates. Treatment with uncharged resin resulted in an intermediate increase in the degradation rates for three filtrates, while the increase for the other filtrates was low (<2 times). The effect of lignosulfonates, which were present in one of the filtrates, on the oxalate oxidase activity was studied in separate experiments. The results show that modification of the ionic environment can dramatically improve the rate of enzymatic degradation of oxalic acid in industrial process water.

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