Study On Biological Treamtment Of Cyanide-Containing Waste Waters By Alcaligenes Sp.

Cyanide must be handled properly and safely to avoid harm to people orthe environment. In this paper removal of cyanide in wastewater through anAlealigenes sp strain is studied.A cyanide analytical method was established at first. Photospectrometerwas employed to determine cyanide concentration in wastewater because ofaccuratation, rapidness and simpleness. It is also effective when concentrationsof NH₄⁺,S^2- and SS in cyaide waste waters, respectively, are lower than 400mg·L^-1.The cyanide-degradation enzyme was extracted from an Alcaligenes sp.strain DN25, which has been screened and preserved in our lab, and itsdegradation properties were studied in this paper. The results showed that theendoenzyme of strain DN25 played a main role in degradating cyanide andectoenzyme also behaved a little activity. The degradation rate was 39.6% and15.3% respectively for the endoenzyme and ectoenzyme under the sameconditions. The endoenzyme was found to have a good thermal and pH stabilityand could be preserved in 30℃and alkaline condition. The optimal degradationconditions for the endoenzyme were 35℃and pH 7.0. During degradationprocess, the reaction rate appeared higher at the beginning and decreased with the reaction time. The cyanide removal could reach 98.5% after 35 h when theendoenzyme amount was OD1.5. The Mickaelies constant and maximundegration rate values ware determined to be 267.8mg·L^-1 and 6.71mg·(L·min)^-1,respectively. NH₃ was proved to be the final degradation product and theinhibition of urea on enzyme activity suggests the existence of cyanidehydratase in crude enzyme extracted from Alcaligenes sp. strain DN25.Alcaligenes sp. strain DN25 was directly employed to treat the cyanidewastewater. When some pollutants such as NH₄⁺, S^2-and SS were added to thesystem, free cell was shown to be effective to biodegradation of cyanide. As forthe biodegradation process in 5L bioreactor, the reactor had a good adaptation toloading of cyanide. During the first 40th day, high removal efficiency of above90% was kept for cyanide-degradation. In the following 40-60d, removalefficiency of cyanide was decreased to be 85% in immobilized cell bioreactorwith NH₄⁺—N added. The reason may be the decrease of buffer capacity due toadding of NH₄⁺ and accumulation of product-formic acid, which results inactivity decrease.Some strains which can biodegrade cyanide complexe K₄Fe(CN)₆ werescreened. The rate of K₄Fe(CN)₆ degradation by seven strains was evaluated.Studies also demonstrated that the strains can use cyaide as the sole of carbonand nitrogen. The cyanide-degradation ability of strains Y6 and Y1 were betterthan others. Their rates to 100 mg·L^-1CN^- were 55.9% and 48.6 at 7d and dry cellweights were 7.15 and 7 g·L^-1 respectively.