BIOLOGICAL CYANIDE DEGRADATION IN AEROBIC FLUIDIZED-BED REACTORS - TREATMENT OF ALMOND SEED WASTE-WATER

The continuous aerobic transformation of synthetic cyanide waste-water , amygdalin solutions and almond seed extract containing cyanide was i nvestigated in several fluidized bed reactors. Various inocula consist ing of activated sludge or soil slurry were used. Successful inoculati on was achieved with simple soil slurry. No significant influence was found between the performance of the systems inoculated with a cyanide contaminated soil and a garden soil. The performance and stability of the reactors with respect to degradation rate were tested for a range of cyanide loading conditions, with feed containing only cyanide, and with different additional carbon sources, as well as various C:N rati os at a hydraulic retention time Of 24 h. No growth with cyanide as th e sole source of carbon and nitrogen was observed. The system with lac tate as the organic C-source was capable of operating at cyanide conce ntrations of 16o ppm cyanide with a conversion rate of 0.125 kg cyanid e/m3 d. Ammonia was the end product and the effluent concentration was 0.5 ppm CN-. The systems with ethanol as the organic C-source could d egrade only 0.05 kg cyanide/m3 d, whose feed concentration was 60 ppm cyanide. Amygdalin, an organic cyanide-containing compound present in stone fruit seeds, was fed as a model substrate. Degradation rates up to 1.2 kg COD/m3 d could be measured with no free or organically bound cyanide in the effluent. These rates were limited by oxygen transfer, owing to the large amount of degradable COD. The further investigatio ns with almond seed extracts, confirmed the applicability of the aerob ic process to treat food-processing waste streams having low concentra tions of cyanide with high COD content.