Treatment of cyanide-containing wastewater from the food industry in a laboratory-scale fixed-bed methanogenic reactor.
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.
Siller
H
H
Institut für Ingenieurbiologie und Biotechnologie des Abwassers, Universität Karlsruhe.
Winter
J
J
D000641:Ammonia / Q000494:pharmacology; D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D019149:Bioreactors; D003486:Cyanides / Q000032:analysis / Q000378:metabolism*; D019605:Euryarchaeota / Q000378:metabolism*; D019649:Food Industry; D005524:Food Technology; D005618:Fresh Water / Q000032:analysis; D007220:Industrial Waste; D002365:Manihot / Q000378:metabolism; D008697:Methane / Q000032:analysis; D013447:Sulfites / Q000494:pharmacology; D018505:Waste Management; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000378:metabolism*
D003486:Cyanides; D007220:Industrial Waste; D013447:Sulfites; D014874:Water Pollutants, Chemical; D000641:Ammonia; D008697:Methane