A method and system for the biological disposal of oxalate is described in which a biological reactor having an alkalophilic oxalate-degrading aerobic micro-organism in aqueous solution is employed. The biological reactor comprises a vessel containing the aqueous solution and having an input for receiving dissolved oxalate from a dissolver tank. Sodium oxalate, as a by-product or the Bayer process in an alumina refinery, can be introduced into the dissolver tank in solid form together with trace elements and nutrients for biological growth. The system operates as a continuous feed process with dissolved oxalate being pumped from the dissolver tank into the biological reactor vessel continuously in a controlled manner. The biological reactor further comprises an aerator, including an oxygen probe for monitoring the level of dissolved oxygen in solution. Biological degradation of the sodium oxalate in a highly alkaline solution occurs in the biological reactor with sodium carbonate and bicarbonate formed as end products in an effluent. The effluent is then pumped to a causticiser reaction tank and settler tank for converting the sodium carbonate and bicarbonate in the effluent to useful sodium hydroxide which can be recycled in the Bayer process. The alkalophilic oxalate-degrading aerobic micro-organism is preferably Bacillus AGAL N91/005579.