Process "docked" physical-chemical and biotechnology for the treatment of wastewater contaminated with cyanide

Abstract

This investigation contributes to the study and development of a new photochemical degradation technique (solar and artificial light) and biological process for the treatment of non biodegradable highly toxic substances present in wastewater. Efficient pretreatments as the photocatalytic process are necessary to modify the structure of the pollutants, by transforming them into less toxic substances of easy biodegradation allowing a biological treatment to complete the degradation.
The behavior of cyanide concentration present in a effluent wastewater (400 mg/L of CN -) is evaluated to laboratory scale, by the techniques of heterogeneous photocatalytic with artifi cial and solar light, titanium dioxide and hydrogen peroxide in a Compound Parabolic Cylindrical photo-reactor (CPC) and bioremediation with an isolated native stump; with the purpose of obtaining permissible cyanide concentrations by national legislation(1 mg/L).

Several bacterial species as Pseudomonas sp can effectively degrade cyanide into less toxic products. During the metabolism, they use the cyanide as a nitrogen source and glucose as a carbon source to transform it to ammonia and carbon dioxide.

Bacterium is isolated and identified of a mud coming from the industry of metallic compounds recovery, thenit is adapted in a solution of cyanide of 15 mg/L. During biodegradation the cyanide efficiency removal and percentage of degradation are quantified and curves of biomass growths are elaborated to the time.

In the biological process, the effects of initial concentration of cyanide and agitation on the percentage of reduction of the cyanide concentration by means of a factorial design of experiments are analyzed.
In this biodegradation process is determined that the most significant variable is agitation and initial concentration of cyanide is not as outstanding for this. The kinetic study of cyanide degradation is adjusted to fi rst order kinetics, following a Langmuirian regime and growth biomass kinetics is model by the Monod equation.
Optimal conditions of cyanide biodegradation are pH 9.5, temperature 28 ºC, inoculum size 1.21 x105 UFC/ml, agitation of 200 rpm and initial concentration of cyanide 15 mg/L. Tests indicate that the biological treatment with Pseudomonas sp might be competitive with other chemical treatment process.

Using both techniques together (photocatalytic and biotechnology) a 99.86% of reduction of cyanide concentration is achieved; the results indicate that using the two techniques together could be used to remove toxic organic pollutants from the wastewater.