Degradation of cyanide in agroindustrial or industrial wastewater in an acidification reactor or in a single-step methane reactor by bacteria enriched from soil and peels of cassava

Abstract

During cassava starch production, large amounts of cyanoglycosides were released and hydrolysed by plant-borne enzymes, leading to cyanide concentrations in the wastewater as high as 200 mg/l. For anaerobic degradation of the cyanide during pre-acidification or single-step methane fermentation, anaerobic cultures were enriched from soil residues of cassava roots and sewage sludge. In a pre-acidification reactor this culture was able to remove up to 4 g potassium cyanide/l of wastewater at a hydraulic retention time (tHR) of 4 days, equivalent to a maximal cyanide space loading of 400 mg CN- 1(-1) day-1. The residual cyanide concentration was 0.2-0.5 mg/l. Concentrated cell suspensions of the mixed culture formed ammonia and formate in almost equimolar amounts from cyanide. Little formamide was generated by chemical decay. A concentration of up to 100 mmol ammonia/l had no inhibitory effect on cyanide degradation. The optimal pH for cyanide degradation was 6-7.5, the optimal temperature 25-37 degrees C. At a pH of 5 or lower, cyanide accumulated in the reactor and pre-acidification failed. The minimal tHR for continuous cyanide removal was 1.5 days. The enriched mixed culture was also able to degrade cyanide in purely mineralic wastewater from metal deburring, either in a pre-acidification reactor with a two-step process or in a one-step methanogenic reactor. It was necessary to supplement the wastewater with a carbon source (e.g. starch) to keep the population active enough to cope with any possible inhibiting effect of cyanide.

Two‐phase anaerobic digestion processes: a review

“…58 Zinc and nickel were not bound well, lead was bound strongly and copper was bound between these two extremes. 59 determined the optimal pH and temperature range for cyanide degradation during pre-acidi®cation, as 6±7.5 and 25°C±37°C, respectively. Cyanide accumulated and pre-acidi®cation failed at a pH of 5 or lower.…”

Bacterial Degradation of Cyanide and Its Metal Complexes under Alkaline Conditions

“…According to the current knowledge, all of the microorganisms able to assimilate cyanide can use it only as a nitrogen source, but not as the sole carbon source. By contrast, under anaerobic conditions, cyanide may be used as an alternative electron acceptor producing methane and ammonia, either in mixed (45) or axenic (25) cultures.…”

Solid and liquid residues as raw materials for biotechnology

“…Starch-and fibre-containing wastewater from cassava production in Indonesia could also be stabilized anaerobically with COD removal efficiencies of more than 90% at space loadings of 12 kg COD/m 3 per day and 50 mg CN -/m 3 per day in upflow fixed-bed recirculation reactors (Siller 1998;Siller and Winter 1998a). The same range of space loadings was reported for a UASB reactor with tapioca starch wastewater, operated in Malaysia, but it was not reported whether the wastewater contained cyanide (Annachhatre and Amatya 2000).…”