Enzymatic degradation of oxalic acid for prevention of scaling

Abstract

Formation of calcium oxalate incrusts, scaling, may cause severe problems in the pulp and paper industry. Enzymatic degradation of oxalic acid provides a novel approach to eliminate the problems with calcium oxalate precipitation. The performance of two oxalate-degrading enzymes, oxalate oxidase from barley and oxalate decarboxylase from Aspergillus, was tested in model experiments with respect to catalytic efficiency under different conditions, including pH, temperature and enzyme concentration. Oxalate decarboxylase was found to be more sensitive to temperature variations than oxalate oxidase, which was selected for further experiments. Authentic samples from pulp bleach plants were used to test the performance of oxalate oxidase. The results showed that oxalic acid could be degraded enzymatically also in the industrial bleaching filtrates, which were obtained from D-, E-, O-, OP-, PO-, Q-, QP-, and Z-stages. The bleaching filtrates contained compounds that inhibited the action of oxalate oxidase. The degree of inhibition was strongly dependent on the filtrate and could be alleviated by dilution. (Less)