details of hazardous component of waste from metallurgy / electroplating industries with information regarding its bio degradation

1. CYANIDE: HAZARDOUS COMPONENT OF
WASTE FROM METALLURGY/ ELECTROPLATING
INDUSTRIES AND ITS BIODEGRADATION
Presented by:
Manju Chhetri
M.Tech (Biotechnology)
Kathmandu University

2. Introduction
 Cyanide, one of the known most toxic chemicals
 as a chemical weapon ; 1st world war
 Depending on the pH, cyanide can be found as
the ion cyanide (CN− ) in dissolution at high pH
OR may evaporate as HCN (cyanhydric acid) at
neutral or acid pH values (pKa 9.2).
 Cyanide is frequently found in metal–cyanide
complexes because of its high affinity for
transition metals .
 Complexes of cyanide with nickel, copper or zinc
are weakly acid-dissociable, whereas strong
complexes with iron and cobalt are very stable
and strong acid dissociable

3.  Cyanide is a natural compound produced by
many organisms, including bacteria, algae,
fungi, and plants, and is bioproduced in some
cases as a defensive metabolite or with
invasive purposes .

4. Cyanide toxicity Mechanism
 the toxicity of cyanide and its compound depends on their
capacity to release free cyanide.
 Cyanide toxicity mainly occurs because it binds to and inactivates
several metalloproteins, such as cytochrome c oxidase, blocking
the mitochondrial electron transport chain.This inhibition of
aerobic respiration results in histotoxic hypoxia and increases
acidosis from the anaerobic reduction of pyruvate to lactic acid,
resulting in depression of the CNS and myocardial activity .
 Cyanide is not stable in blood, but some derivatives such as
thiocyanate and 2-aminothiazoline-4-carboxylate may be
detected in cyanide-induced deaths; the latter of these
compounds is a stable metabolite that acts as an important
forensic cyanide biomarker

5. USES of Cyanide
 Several industries, including
- plastics, electroplating, organic chemicals
production, photographic developing, and
pharmaceuticals, use cyanide.
In gold and silver mining, cyanide is used to recover
these precious metals through the leaching
process.
Cyanide leaching remains the only viable chemical
lixivant for the recovery of gold, accounting for
90% of world production.
 Concerns leads to  (UNEP) international code
for management of cyanide in gold mining

6. Cyanide in effluent (gold
mining) Mike Agbesi et al

7. Method of cyanide degradation
 Cyanides can be removed from industrial wastes by
- Biodegradation , physical and chemical methods
Chemical and physical methods deal with chemical oxidation
through
- alkaline chlorination,
- ozonization in presence of UV
- hydrogen peroxide,
- Air/SO2 process and
- chlorine dioxide gas,
- adsorption on granulated activated carbon
- ion exchange
- membrane concentration,
- air stripping and evaporation (subsequently through thermal
treatment by alkaline chlorination and hydrolysis at high
temperature )

8. Drawbacks of chemical/Physical
process
 All these methods are based on cyanide
recovery by acidification and/or destruction by
chemical oxidation
 These techniques are only effective for free
cyanide (HCN, CN−) and cyanides that are
weakly bonded to metals. Cyanides that are
strongly bonded or complexes with metals
cannot be treated with these methods

9. Why chemical process not
suitable?
 The process is burdened with high capital,
reagent costs and royalty payments.
 Various reagent and chemical used in the
process are toxic itself when released in
environment accidentally also the end
product of these technologies are also
required some additional treatment prior to
disposal

10.  Despite the toxicity of cyanide, cyanotrophic
microorganisms such as the alkaliphilic
bacterium Pseudomonas pseudoalcaligenes
CECT5344 may use cyanide and its derivatives as
a nitrogen source for growth, making
biodegradation of cyanurated industrial waste
possible.
 Plant and various microorganisms have
resistance to cyanide poisoning since they have
developed alternate pathway for ATP
production. Some of them have different oxidase
rather then cytochrome C oxidase
Biodegradation

11. Why bio degradation?
 The biodegradation method of cyanides removal is
better as:
 It is more economical and faster
 It is more efficient and has less capital and
operative cost.
 The sudden increase in input does not affect the
process adversely
 Biological transformation involves cyanide
degradation and assimilation in the form of amino
acids, thiocyanate, -cyanoanaline and vitamins by
the microorganisms and plants

12.  Cyanide is converted to carbon and nitrogen
source by various enzymes present in
microorganism.
 The metabolic pathway for conversion of
cyanide is influenced by :
- its initial concentration, pH, temperature,
availability of other energy source in the form
of organic carbon required for cell
maintenance and growth, presence of
oxygen, ammonia, and various metals ions

13.  Some of the organisms known to oxidize
cyanide include species of the genera
Actinomyces, Alcaligenes, Arthrobacter,
Bacillus, Micrococcus, Neisseria,
Paracoccus, Pseudomonas, and
Thiobacillus (Given et al. 1998, Mudder et al.
1998). and the tried and true nitrifiers,
Nitrosomonas and Nitrobacter

14. Biodegradation of cyanide
 Despite the toxicity of cyanide:
 many organisms, including bacteria, fungi, plants and
certain animals, synthesize cyanide, which is usually a
defence mechanism (cyanogenic organisms),
 and some microorganisms can assimilate cyanide, using it
as nitrogen source for growth (cyanotrophic organisms).
These microorganisms have different cyanide degradation
pathways
hydrolytic,
 oxidative
 substitution/transfer reactions
Therefore, cyanide biodegradation has become a suitable
alternative to the less efficient and economically more
expensive chemical treatments.

15. cyanidase (P. fluorescens, E. coli )
cyanide hydratase
formamidase
(P. stutzeri and
pathogen fungi);
cyanide dioxygenase
(Pseudomonas and
Bacillus)
rhodanase
Thiocyanate
hydrolase
(Bacillus and
Thiobacillus
3-cyanoalanine synthase
nitrilase or nitrile
hydratase/amidase
(Bacillus)

16. Pseudomonas pseudoalcaligenes
 The bacterial strain, Pseudomonas pseudoalcaligenes
CECT5344, can grow under alkaline conditions with cyanide,
cyanate, different metalcyanide complexes, and wastewaters
from jewellery industry as the sole nitrogen source.
 This strain has an optimal pH for growth of 9.5, and it has
tolerance to metals, making it a suitable candidate for
bioremediation of cyanide-containing industrial wastes .
 In this bacterium, cyanide induces a cyanide insensitive
respiratory chain that is associated with a malate:quinone
oxidoreductase that converts L-malate into oxaloacetate.This
ketoacid/oxoacids reacts with cyanide to produce a
cyanohydrin (nitrile) that is further converted into its
respective carboxylic acid and ammonium by the nitrilase
NitC, which is essential for cyanide assimilation


17. History and Example
 Cyanide destruction by microorganisms was first
examined in the early twentieth century and was
first commercially demonstrated in the gold
mining industry at the Homestake Gold Mine,
USA in the middle 1980s (Mudder &Whitlock
1984)
( leading mining company in the development
and implementation of biological treatment
systems for cyanide destruction.)

18. The Homestake Mine pit in Lead,
South Dakota

20. The first step in the Homestake MiningCo. biological treatment process is
the oxidative breakdown of cyanides and thiocyanate, and subsequent
sorptionand precipitation of free metals into the biofilm. Cyanide and
thiocyanate are degraded to a combination of ammonia, carbonate, and
sulfate.
The second step converts ammonia to nitrate through the conventional
two-step nitrification process with nitrite as the intermediate.Various
Pseudomonas species are responsible for complete assimilation of the
wastewater, including oxidation of cyanide, thiocyanate and ammonia.

22.  At the end of the process nearly all of the
cyanide is removed from the wastewater
resulting in an effluent that is safe enough to
be discharged into a receiving stream.The
removal rates of cyanide from the
wastewater, depending on plant operations,
vary from 91 – 99.5% of the total cyanide
(Baxter and Cummings 2006)

25. Cyanomics; a new era
 Cyanomics: new generation techniques for cyanide
biodegradation New generation ‘omic’ techniques
have revolutionized our knowledge of biological
processes by generating substantial data for the
global analysis of these processes.
 Genomic, transcriptomic and proteomic techniques
applied to cyanide biodegradation (‘cyan-omics’)
provide a holistic view that increases the global
insights into the genetic background of
cyanotrophic microorganisms that could be used for
biodegradation of industrial cyanurated wastes and
other biotechnological applications.

26.  Although many microorganisms can use cyanide
as a nitrogen source, only the genomes of three
cyanide- degrading bacteria have been
sequenced,
Pseudomonas pseudoalcaligenes CECT5344
 Pseudomonas fluorescens NCIMB 11764 and
 Azotobacter chroococcum NCIMB 8003
Due to the chemical heterogeneity of the different
cyanide-containing industrial wastewaters,
identification of new cyanotrophic bacterial
strains with different catabolic capacities is also
of interest.

27.  In contrast to cyanide-assimilating bacteria,
many cyanogenic bacteria, including
Chromobacterium violaceum, Burkholderia
cepacia and different strains of
Pseudomonas, have been sequenced .These
bacteria produce cyanide by a hydrogen
cyanide synthase complex that is encoded by
the hcnABD genes, and they share cyanide
resistance mechanisms with cyanotrophic
microorganisms.

28. Conclusion
 As mentioned previously, cyanide is the most
important gold-extracting chemical; therefore,
cyanogenic bacteria could be useful for biomining,
an attractive, environmentally friendly technology
that applies biological systems to facilitate the
extraction and recovery of metals from ores, as an
alternative to conventional methods.
 Destruction of cyanide by microorganisms in gold mill
effluents is a natural process that can be readily
exploited and engineered to accommodate both large
flows and the elevated cyanide containing solutions
generated at commercial precious metals operations

29. Reference
 Biodegradation of cyanide wastes from mining and jewellery
industries, Vıctor M Luque-Almagro, Conrado Moreno-
Vivian and Marıa Dolores Roldan
 Bacterial cyanide degradation is under review:
Pseudomonas pseudoalcaligenes CECT5344, a case of an
alkaliphilic cyanotroph , Vıctor M Luque-Almagro,
Conrado Moreno-Vivian and Marıa Dolores Roldan;
Departamento de Bioquımica y Biologı´a Molecular, Spain
 Enzymatic mechanism and biochemistry for cyanide
degradation: A review Neha Gupta∗, Chandrajit
Balomajumder,V.K. Agarwal, Journal of Hazardous
Materials
 Physico-chemicalCharacteristics of a Gold MiningTailings
DamWastewater MikeAgbesiAcheampong1 , Jackson
Adiyiah2 and Ebenezer DavidOkwaning Ansa; Journal of
Environmental Science and Engineering