Abstract
During the process of producing cassava starch from Manihot esculenta roots, large amounts of cyanoglycosides were released, which rapidly decayed to CN− following enzymatic hydrolysis. Depending on the varying cyanoglycoside content of the cassava varieties, the cyanide concentration in the wastewater was as high as 200 mg/l. To simulate anaerobic stabilization, a wastewater with a chemical oxygen demand (COD) of about 20 g/l was prepared from cassava roots and was fermented in a fixed-bed methanogenic reactor. The start-up phase for a 99% degradation of low concentrations of cyanide (10 mg/l) required about 6 months. After establishment of the biofilm, a cyanide concentration of up to 150 mg CN−/l in the fresh wastewater was degraded during anaerobic treatment at a hydraulic retention time of 3 days. All nitrogen from the degraded cyanide was converted to organic nitrogen by the biomass of the effluent. The cyanide-degrading biocoenosis of the anaerobic reactor could tolerate shock concentrations of cyanide up to 240 mg CN−/l for a short time. Up to 5 mmol/l NH4Cl (i.e. 70 mg N/l = 265 mg NH4Cl/l) in the fresh wastewater did not affect cyanide degradation. The bleaching agent sulphite, however, had a negative effect on COD and cyanide removal. For anaerobic treatment, the maximum COD space loading was 12 g l−1 day−1, equivalent to a hydraulic retention time of 1.8 days. The COD removal efficiency was around 90%. The maximum permanent cyanide space loading was 50 mg CN− l−1 day−1, with tolerable shock loadings up to 75 mg CN− l−1 day−1. Under steady-state conditions, the cyanide concentration of the effluent was lower than 0.5 mg/l.
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Received: 15 August 1997 / Received revision: 10 October 1997 / Accepted: 14 October 1997
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Siller, H., Winter, J. Treatment of cyanide-containing wastewater from the food industry in a laboratory-scale fixed-bed methanogenic reactor. Appl Microbiol Biotechnol 49, 215–220 (1998). https://doi.org/10.1007/s002530051161
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DOI: https://doi.org/10.1007/s002530051161