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The detoxification of cyanide by algae was examined by exposing cultured suspensions of Arthrospira maxima, Chlorella sp. and Scenedesmus obliquus in growth media to varying concentrations in short-time batch tests. In each experiment, the pH was adjusted to 10.3. The effect of pH, initial concentration of algal cells, temperature and cyanide concentration on microbial detoxification were examined. Under the experimental conditions, initial microbial detoxification rates of 50 and 100 mg/L free cyanide were observed for 25 h. A. maxima did not survive due to its sensitivity to the higher cyanide concentrations in the solutions. S. obliquus removed the cyanide to a greater extent than did Chlorella sp. S. obliquus detoxified 99% of the cyanide, while Chlorella sp. removed about 86% in the same time period. For the raised cyanide concentrations between 100 and 400 mg/L, S. obliquus was the only microorganism tested for 67 h. Kinetic studies of cyanide detoxification showed that microbial removal was linearly correlated with concentration.
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Microbial detoxification of cyanide solutions:
a new biotechnological approach using algae
Fatma Gurbuz, Hasan Ciftci, Ata Akcil
*
, Aynur Gul Karahan
BIOMIN Group, Suleyman Demirel University, TR 32260, Isparta, Turkey
Received 24 January 2003; received in revised form 24 October 2003; accepted 28 October 2003
Abstract
The detoxification of cyanide by algae was examined by exposing cultured suspensions of Arthrospira maxima, Chlorella
sp. and Scenedesmus obliquus in growth media to varying concentrations in short-time batch tests. In each experiment, the pH
was adjusted to 10.3. The effect of pH, initial concentration of algal cells, temperature and cyanide concentration on microbial
detoxification were examined. Under the experimental conditions, initial microbial detoxification rates of 50 and 100 mg/L free
cyanide were observed for 25 h. A. maxima did not survive due to its sensitivity to the higher cyanide concentrations in the
solutions. S. obliquus removed the cyanide to a greater extent than did Chlorella sp. S. obliquus detoxified 99% of the cyanide,
while Chlorella sp. removed about 86% in the same time period. For the raised cyanide concentrations between 100 and 400
mg/L, S. obliquus was the only microorganism tested for 67 h. Kinetic studies of cyanide detoxification showed that microbial
removal was linearly correlated with concentration.
D 2003 Elsevier B.V. All rights reserved.
Keywords: Cyanide; Algae; Detoxification; Environmental; Biotechnology
1. Introduction
The concept of ecological chemistry was first
introduced in the beginning of the 1950s (Korte and
Coulston, 1998), while the ecotoxicology and envi-
ronmental fate of hazardous chemicals have been
researched for ov er three decades. It would be bene-
ficial to better integrate and coordinate the efforts of
scientists dealing with the assessment and long-term
prediction of contaminant pathways, environmental
fate, t ransformations and interactions in complex
systems, and remediation of impacts on the biosphere,
through better exchange of this knowledge and its
application in development of sustainable strategies to
assure envir onmen tal saf ety (Twardowska, 2002).
Development of novel technologies for the treatment
of industrial and hazardous wastes is increasing rap-
idly. Particular attention is being focused upon the use
of biological treatment either along with, or in com-
bination with, chemical and physical treatment pro-
cesses. Aerobic and anaerobic m icrobial treatment
processes have been successfully employed in the
destruction and/or removal of organic compounds,
inorganics and metals (Mudder and Botz, 2001).
Cyanide is a known toxic chemical in mining, the
production of plastics, electroplating, tanning, chem-
0304-386X/$ - see front matter D 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.hydromet.2003.10.004
* Corresponding author. Department of Mining Engineering,
Mineral Processing Division, Suleyman Demirel University, TR
32260, Isparta, Turkey. Tel.: +90-246-2111774; fax: +90-246-
2370434.
E-mail address: ata@mmf.sdu.edu.tr (A. Akcil).
www.elsevier.com/locate/hydromet
Hydrometallurgy 72 (2004) 167 176
ical syntheses, etc. The chemistry and toxicology of
cyanide has been well studied in the laboratory.
Field studies have assessed cyanide toxicity to wa-
terfowl and epidemiological studies have evaluated
acute and chronic human health effects. Exposures to
cyanide in mining solutions have been generally
controlled with physical exclusion methods, chemi-
cal treatment and recovery of cyanide, or by mai n-
taining the levels of weak acid dissociable (WAD)
cyanide below 50 mg/L.
The most common forms of cyanide in the envi-
ronment are free cyanide and its metal complexes.
Free cyanide, especially HCN gas at pH 9.31 and
lower, is the primary toxic agent in the environment
(Mudder and Botz, 2001; Huiatt et al., 1983). The
toxicity of metal cyanide complexes is related to their
ability to release cyanide ions in solution with rela-
tively small fluctuations in pH. Total cyanide meas-
urements include not only free cyanide but also the
weakly and strongly complexed metal cyanides. The
relationship between total cyanide and free cyanide in
natural waters varies with receiving-water conditions,
the degree of aeration, the type of cyanide compounds
present, exposure to daylight and the presence of other
compounds (Hagelstein and Mudder, 1998).
Chemical and physical processes have been ap-
plied in most cases for cyanide destruction from
tailings slurries and wastewaters. However, there are
still problems facing the mining industry because of
stringent environmental regulations and the cost of
compliance with those regulations. Det oxification
of cyanide by microorganisms from tailings slurry
and wastewaters is an alternative to the chemical
processes. Biological degradation or attenuation of
cyanide and its related species such as ammonia and
thiocyanate is a natural process and can be engineered
to treat larger flows and higher cyanide concentrations
found at a gold mining operation (Happold et al.,
1954; Lawrence et al., 1998; Mudder et al., 2001;
Whitlock and Mudder, 1998). The operating costs for
destruction of cyanide by chemical and physical
treatment are generally higher than for biological
processes, but chemical and physical proces ses typi-
cally yield more rapid detoxification and are less
susceptible to tem perature upsets. Nonetheless, appli-
cation of biological processes is a viable and well-
proven approach to cyanide destruction and overall
management of this chemical at mining operations
(Akcil, 2003; Akcil and Mudder, 2003; Botz, 2001;
Given et al., 1998).
Microbial detoxi fication of cyanide in mine waste-
waters has an advantage over conventional chemical
methods because of its low treatment cost, in-situ
treatment, complete detoxificati on and its natural
non-toxic products (Adams et al., 2001; Thompson
et al., 1994).
2. Brief description of microbial treatment
Aerobic and anaerobic biological processes have
been successfully employed in the treatment of a
wide variety of industrial and hazardous liquid
wastes. The microorganisms primarily responsible
for biological degradation include a diver se group
of anaerobic and aero bic bacteria. These single-
celled microorganisms exhibit a wide range of met-
abolic functions and are capable of degrading a wide
range of chemical s tructures and concentrations.
Bacteria utilize a combination of extracellular and
intracellular adaptive and constitutive enzymes in the
biochemical breakdown and assimilation of the or-
ganic and inorganic compounds present in liquid
wastes. These compounds, along with various
nutrients (i.e. nitrogen, phosphorous and trace met-
als), are d egraded and/or assimilated for the purposes
of energy production and cell synthesis. The extra-
cellular enzymes found on the cell wall or in the
capsule layer surrounding the cell wall aid in the
breakdown of larger and more complex molecules,
converting these compounds to smaller, more soluble
by-products. The breakdown products are then trans-
ported into the bacterial cell for conversion to
cellular ma terial and energy t hrough the use o f
intracellular enzymes. The chemical composition of
the cell wall and capsule layer also account s for the
properties responsible for adsorption and absorption
of various refractory organics and heavy metals.
Extracellular and intracellular enzymes are either
adaptive and constitutive in nature. Constitutive
enzymes are present at all times and have evolved
following many successive generations and muta-
tions resulting from exposur e of a bacterial species
to specific compounds. The production of adap tive
enzymes that are not normally present may be
stimulated by the presence of a particular compound
F. Gurbuz et al. / Hydrometallurgy 72 (2004) 167–176168
or class of compounds, that the bacteria utilize as
alternative carbon and/or energy sources if preferred
substrates are not available.
Utilization of bacteria to degrade cyanide and
thiocyanate on a scale larger than laboratory bench
scale has not been previously accomplished even
though the available literature indicated that certain
strains of bacteria possessed the capacity to degrade
cyanides. Many of these biological reactions, such
as degradations, oxidations and metal accumulation
or ingestion, cannot be d uplicated by chemical
processes, or at least not at the very rapid react ion
rates accomplished by microorganisms. Biological
treatment is also advantageous in that chemical
compounds acting as a food source may be degrad-
ed without alteration of the liquid matrix to the
degree ca us ed b y ch e mic al processes . Thu s, the
effluent is more likely to be compatible with the
natural water of a receiving stream (Mudder and
Botz, 2001).
Bacteria are capable of utilizing cyanide as a
carbon and nitrogen source (Knowles, 1976; Rangas-
wami and Balasubramanian, 1963; Skowronski and
Strobel, 1969). Biological treatment can be applied in
many situations, under many conditions, and in many
configurations including in-situ, aerobic and anaero-
bic, active and passive, and suspended and attached
growth. It has been employed in full-scale facilities
worldwide both in conventional cyanidation and heap
leach applications. The microbial species can thrive
in multiple environmen ts allowing for uptake, treat-
ment, sorption and/or precipitation of cyanide, its
related compounds and metals (Adams and Gardener,
1994; Akcil, 2002; Akcil et al., 2003; Arps et al.,
1993; Babu et al., 1996; Chapatwala et al., 1998;
Cellan et al., 1998; Finnegan, 1992; Finnegan et al.,
1991a,b; Mosher and Figueroa, 1996; Nelson et al.,
1998; Oudjehani et al., 2002; Trapp et al., 2003;
White and Schnabel, 1998). However, it is known
that the toxicity of cyanide can limit a microorga-
nism’s ability to use it as a substrate for growth.
Therefore, microorganisms capab le of de tox ifying
cyanide and metal cyanide complexes were isolated
from soil samples uncontaminated with metal or
cyanide (Patil and Paknikar, 1999).
It has been demonstrated, under anaerobic con-
ditions, that cyanide is hydrolysed to ammonia and
formate, which is converted to bicarbonate (Hubb et
al., 2000). Cyanide could also be incorporated into
microorganisms by pathways utilized by the cyano-
genic organism (Blumenthal et al., 1968). Cyanide
is produced by oxidative decarboxylation of glycine
in a process, which is stimulated by methionine or
other methyl-group donors. Cyanogenesis usually
occurs in mic roorganisms at the end of the growth
phase and it is affected by the iron and phosphate
content of the medium. These factors suggest that
cyanogenesis is a secondary metabolism. Two likely
mechanisms for cyanogenesis in bacteria, fungi and
algae are discussed in several articles by Knowles
(1988) and Kleid et al. (1995). When Chlorella
pyrenoidosa was fed with cyanide, it forms h-
cyanoalanine and g-glutamyl-h-cyanoalanine. Many
plants transform cyanide into asparagine or the di-
peptide g-glutamyl-h-cyanoalanine (Knowles, 1976).
Eriksen and Lewitus (1999) clearly demonstrated that
the respiration rate of some algae was stimulated by
KCN.
A remarkabl e number of plants are also cyanogen-
ic, utilising cyanide in the soil (Knowles, 1976;
Seigler, 1975). Microbial cell wall contains functional
groups of protein lipopolysaccharides and lip ids.
These functional groups are capable of adsorbing ions
in cyanide solutions. Nui and Volesky (2000) demon-
strated the main mechanism of gold biosorption,
including the adsorption of anionic Au(CN)
2
species,
was onto N-containing functional groups on biomass,
through ion-pairing. This study demonstrated that
Bacillus subtilis, Penicillium chrysogenum and Sar-
gassum fluitans biomass could extract gold from
cyanide solution.
Whilst bacteria and fungi have often been iden-
tified as cyanide detoxifying microorganisms, cya-
nide detoxification by algae has been shown in only
afewstudies( Gur buz et a l., 2 002).Microbial
detoxification of cyanid e by algae species was
significantly influenced by the various factors, in-
cluding initial concentration of cyanide, initial cell
density and time. The pH was k ept at 10.3 to
prevent loss of cyanide as HCN, due its volatile
nature. Kinetic studies on cyanide detoxification at
various initial cyanide concentrations showed it to
follow a pseudo first order reaction rate. This paper
presents further laboratory studies of microbial cy-
anide detoxification by three different natural algae
species.
F. Gurbuz et al. / Hydrometallurgy 72 (2004) 167–176 169
3. Materials and methods
3.1. Reagents and conditions
Stock solutions of sodium cyanide (NaCN) (Merck)
were prepared fresh each day with deionised water
being used throughout the tests. A 1-L stock solution
of cyanide was prepared by dissolving 1.885 g sodium
cyanide with NaOH (solid). All glassware was washed
by soaking 10% HNO
3
and rinse d with deionised
water. All reagents were analytical grade. Initial solu-
tion temperature was maintained at 24 jC. The pH of
the solutions was maintained 10.3 and was adjusted
by using 1 N NaOH, before and after stirring. Tempe-
rature was maintained at 30 jC throughout the pro-
cess. During the test period, cyanide concentrations
(CN
WAD
) were monitored periodically.
Cyanide was analysed as CN
WAD
in the samples.
Free cyanide and weak acid cyanide reacts with the
picric acid reagent to produce an orange colour that
can be measured colorimetrically at a wavelength of
520 nm (Shimadzu UV/VIS 1601) using known
standards for quantification. The dissolved alkali
metal picrate was converted by cyanide to the col-
oured salt of iso-purpuric acid and its concentration
was measured. Calibration curves were prepared for
each test. Con trol experiments containing growth
medium and CN
solution but no algal cells were
carried out under identical conditions. All tests were
conducted in duplicates according to colorimetric
picric acid method.
3.2. Micro algae and growth conditions
The three species of algae investigated were Ar-
throspira maxima, Scenedesmus obliquus and Chlo-
rella sp. The cult ures were aerated with filtered air
and were illuminated at 4000 lux light inte nsity with
a ligh t/dark cycle of 16/8 (Wong et al., 2000). A.
maxima was purchased from CCAP in England and
cultured in Zorrouk medium (Vonshak, 1986). S.
obliquus was isolated from Lake Egirdir, Turkey and
cultured in modified SAG medium (Richmond, 1986).
Chlorella sp. wa s isolated from the Mediterranean
seawater and cultured in Erdschreiber medium (Hem-
erick, 1978). The cultures were centrifuged and then
inoculated to the synthetic medium of cyanide at
different levels.
3.3. Measurement of algal growth
Algal growth in the flasks was monitored by
measuring the chlorophyll-a concentration (Becker,
1994)—along with the cyanide levels. Acetone was
used to extract the pigments from the separa ted algal
cells. The chlorophyll-a concentration in the extract
was calculated by reading the absorption (A) of the
pigment extract in a spectrophotometer at the given
wavelength against a solvent blank using the follow-
ing equation:
Chlorophyll-a ¼ð12:7 A
663
Þð2:69 A
645
Þ
4. Results and discussion
4.1. Control tests for algal selection
The first phase of the study was to control the
cyanide detoxification ability of algae. Two laboratory
scale tests were conducted to determine the effect of
cyanide concentrations (50 and 100 mg/L) and incu-
bation period on the destruction performance of the
three algal cultures (Fig. 1). The concentration of
inoculated algal cultures was measured as 5 mg/L.
A wide variation in cyanide detoxification efficiency
amongst the algal species was noted. By measuring
the chlorophyll content and by microscopic examina-
tion, A. maxima was found to be inhibited by the
effect of cyanide. A. maxima cells lysed and foamed at
the surface of the medium. However, S. obliquus and
Chlorella sp. detoxified cyanide at approximately the
same level in a 50 mg/L cyanide-containing medium.
The detoxification of the cyanide occu rred during the
17-h incubation period of the two algae. As there was
no significant difference between them for this con-
centration, Chlorella sp. was determined to destruct
the cyanide slightly better than S. obliquus. However,
when the detoxification of cyanide was tested in a 100
mg/L medium, S. obliquus decreased the cyanide to
5.25 mg/L at the end of 17 h and detoxified all the
cyanide within 25 h. The percentage removal of cya-
nide in a one-hour incubation period was 31% and
27%, increasing to 95% and 75% after 17-h incubation
for S. obliquus and Chlorella sp., respectively. It was
observed that >99.9% detoxification of cyanide oc-
curred within a period of 25 h (Fig. 1).
F. Gurbuz et al. / Hydrometallurgy 72 (2004) 167–176170
Another experiment was set at 100 mg/L of cya-
nide concentration for two algae species, S. obliquus
and Chlorella sp., to observe the effect of cyanide on
the cell density (Table 1). The algae population of
Chlorella sp. and the control group of S. obliquus
dropped at 24 h due to a high pH level. But the cell
density rose after adaptation. There are other reports
describing the cyanide degrading ability of Chlorella
sp. (Knowles, 1976). However, no other data on the
degradation of cyanide by S. obliquus was noted in
the literature.
4.2. Effect of cyanide concentration
Since differences in cyanide removal by each algal
were observed, only S. obliquus was examined in
detail due to its greater ability to degrade cyanide.
Kinetic experiments were carried out at different
cyanide concentrations. It can be conclu ded from
these results that the algae grew in all cyanide con-
centrations tested. The initial level of cyanide was 100
mg/L and the measured NH
4
concentration was 10
mg/L. The measured end products were NO
3
(56 mg/
Fig. 1. The effect of cyanide concentration during incubation period (feed solutions (a) = 50 mg/L, (b) = 100 mg/L).
F. Gurbuz et al. / Hydrometallurgy 72 (2004) 167–176 171
L), CO
3
(36 mg/L), HCO
3
(237.9 mg/L), NH
4
(3 mg/
L) and CN
WAD
(0.1 mg/L) at the end of the tests. Fig.
2 summarizes the results of CN
removal by S.
obliquus obtained at the different cyanide concentra-
tions (100, 200 and 400 mg/L).
Depending on the cyanide concentration, degrada-
tion was completed after 67 h and was influenced by a
low inoculation rate. Better results were obtained with
a high inoculation rate. Compared to the experiment
conducted for the selection of the algae, cyanide
degradation of S. obliquus was higher than the experi-
ments at different cyanide concentrations. For exam-
ple, the CN
level was reduced by S. obliquus to
below 1 mg/L in 25 h using an initial 100 mg/L of
CN
concentration. Although a low inoculation rate
resulted in a long incubation period and low cyanide
degradation rate, cyanide was still reduced by 97
99%. Cyanide concentration above 300 mg/L can
become toxic to microorganisms (Adams et al.,
2001). However, S. obliquus tolerated 400 mg/L
CN
without adaptation to the medium. The maxi-
mum tolerable cyanide concentration will be exam-
ined in further experiments.
Different results have been reported in the literature
about the maximum degradable cyanide concentra-
tions attained with bacteria and fungi. The maximum
degradable cyanide concentration for two Burkholde-
ria cepacia strains was 520 mg/L CN
. The results
showed that bacteria levels higher than 10
4
cells/mL
were able to resist a concentration of 100 mg/L free
cyanide, while 10
8
cells/mL were required to resist a
concentration of 750 mg/L free cyanide in the medi-
um. At concentration levels higher than 750 mg/L free
cyanide, the toxicity of the media did not allow
bacterial survival. On the other hand, Akcil et al.
(2003) reported that Pseudomonas sp. reduced cya-
nide from 200 to below 1 mg/L in 70 h without
adaptation. In a sequencing batch biofilm reactor
(SBBR) with a 48-h cycle time, 20 mg/L free cyanide
was removed from a waste stream provided with 156
mg/L glucose substrate, by cyanide degrading
microbes enriched from a municipal wastewater treat-
ment plant (White and Schnabel, 1998).
In this work, S. obliquus biomass was determined
via spectrophotometric analysis of chlorophyll-a dur-
ing cyanide degradation assays and the results are
given in Fig. 3. While the biomass of the control
Table 1
Influence of cyanide on algal population
Cyanide Algal type Population (cell/mL)
(mg/L)
Time (h)
02448
100 S. obliquus 9.24
10
6
1.02
10
7
1.30
10
7
S. obliquus
(control)
8.23
10
6
7.92
10
6
8.55
10
6
Chlorella sp. 1.07
10
7
7.87
10
6
9.00
10
6
Chlorella sp.
(control)
1.02
10
7
9.09
10
6
1.02
10
7
Fig. 2. The effect of cyanide concentration on detoxification by S. obliquus.
F. Gurbuz et al. / Hydrometallurgy 72 (2004) 167–176172
group increased with time and reached a steady value
after 43-h incubation, the biomass passed through a
maximum level after 43 h in 100 and 200 mg/L
cyanide containing media. During this time, there
was no additional nutrient supplement, such as phos-
phorus, which would limit growth.
Although the biodegradation process continued
in 400 mg/L cyanide concentration, biomass rapidly
decreased during the 43-h incuba tion period. How-
ever, it was found that there was an increase in
biomass after 67 h. To determine changes of the
cells in this high cyanide medium, microscopic
examination of S. obliquus was undertaken. Swollen
cells and loss of pigment were observed. It was
also observed that aggregation of biomass most
likely occurs after introducing cyanide. Some im-
Fig. 3. Changes of S. obliquus biomass at different cyanide concentrations.
Fig. 4. The aggregation and loss of pigmentation (LP) of S. obliquus cells after introducing NaCN.
F. Gurbuz et al. / Hydrometallurgy 72 (2004) 167–176 173
portant changes and aggregates of algae are shown
in Fig. 4.
4.3. Effect of temperature and light
Experiments were conducted to de termine the
influence of temperature and incubation in dark and
light periods. The results showed that cyanide detox-
ification rates increased at 20 jC in the light compared
to combined light and dark. However, during growth
in the combined light and dark periods, the degrada -
tion was faster at 30 jC than at 20 jC (Fig 5). Adams
et al. (2001) found that, when the temperature was
decreased, the cyanide detoxification rate increased
with some microorganisms. Other microorganisms
have optimum cyanide degradation rates at higher
temperatures. It has been reported that optimum
cyanide degradation temperatures for various Applied
Biosciences microorganisms range from 4 to >30
jC, e.g., complete cyanide reduction by B. cepacia
required a few hours but as expected was more rapid
at 30 jC than at 15 jC (Blumenthal et al., 1968).
4.4. Effect of pH
The results in Table 2 indicate that the optimal pH
conditions for detoxification of cyanide is pH 10.3.
The loss of cyanide by natural degradation in control
groups is especially high at pH 8 and 9 due to volatile
nature of HCN. However, algal detoxification was
significantly less at pH 11. The best result was
obtained at pH 10.3. Therefore, pH level appears to
Fig. 5. The effect of temperature on detoxification rate by S. obliquus (*light, **light and dark).
Table 2
Influence of pH on the detoxification of S. obliquus in cyanide solution
Cyanide
(mg/L)
pH Population
(cell/mL)
Detoxification
time (h)
Algal detoxification
(mg/L)
Natural degradation
(mg/L)
200 8 1.0
10
7
64 <1 64
9 1.2
10
7
64 5.6 85
10.3 1.2
10
7
120 2.9 130
11 1.5
10
7
168 52.3 148
F. Gurbuz et al. / Hydrometallurgy 72 (2004) 167–176174
play a very important role on cyanide existence and
algae growth.
5. Conclusions
This paper reports on the results of an evaluation of
the degradation of cyanide by algal species, particu-
larly by S. obliquus. Under the test conditions, bio-
detoxification of 50 and 100 mg/L free cyanid e were
observed over 25 h. S. obliquus was better adapted to
reduce cyanide concentration than Chlorella sp. S.
obliquus, degrading the cyanide by 99% while Chlo-
rella sp. was able to detoxify only 86% of the cyanide
in the same time period.
For higher cyanide concentrations between 100
and 200 mg/L, S. obliquus was the only microorgan-
ism exposed to cyanide and tested for 67 h. Kinetic
studies on cyanide detoxification showed that bio-
detoxification was linearly related to cyanide concen-
tration and time.
One of the main objectives of this work was to
examine the effects of pH. It was found that S.
obliquus was capable of removing cyanide at pH 8
10 much more efficiently than natural degradation
through loss of volatile HCN.
The use of algae reported in this work offers a
process for removing cyanide without pH adjustment
at minimal cost as only trace amounts of nutrients are
required to be added. Algae can be easily obtained and
cult ivated and require less nutrien ts than bacteria.
Thus, the process has the potential of becoming an
economical and an eco-friendly alternative to the
conventional chemical processes. Further w ork is
justified to demonstrate a sustainable continuous pro-
cess for typical gold mining effluents.
Acknowledgements
In this paper, most of the study is based on the
results of biological treatment research and was
carried out by BIOMIN Group since 2000. One of
the authors (A. Akcil) would like to speci ally thank
Dr. Terry Mudder and Dr. Karen Hagelstein, TIMES
Ltd., USA for their invaluable comments. The authors
would also like to thank the referees for his/her
invaluable discussion during the critical reading,
which helped improve the quality of this original
article.
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... Phycoremediation finds its application owing to its several advantages such as (i) it can remove the pollutants in an environmentally and eco-friendly manner to ppm levels, (ii) generated biomass can be used for the production of value-added products which makes the process profitable one. Gurbuz et al. (2004) tested three microalgal cultures such as Chlorella sp. Arthrospira maxima, and Scenedesmus obliqus for the biological detoxification of cyanide from the mining process wastewater. ...
... Time variation studies on: (a) the removal of pollutants from SSTCW solution (M4) and variation of pH of the SSTCW, (b) the production of biomass and biomolecules during treatment of SSTCW solution (M4), (c) Proposed pathways for pollutants removal from SSTCW(Gurbuz et al. 2004;Wang et al. 2019;Rai et al. 2020). ...
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... After which, cyanase, in presence of bicarbonate, induced to reduce cyanate into ammonia and CO 2 . Gurbuz et al. (2004) pointed out the detoxification of CN 2 by algal cells was efficiently high for the CN 2 initial concentration, as found in this study. This may be related to KCNO accumulation by algal cells (Trinelli et al. 2013). ...
... This may indicate the efficiency of the cyanate removal by C. vulgaris to the relatively low concentrations only. Also, Gurbuz et al. (2004) indicate the initial cyanate concentration has a direct effect on the biological detoxification process by algal cells. This may be due to the saturation attained by the KCN accumulation at specific concentrations by algal cells (Jin et al. 2012). ...
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... Vascular plants and algae possess the enzymes betacyanoalanine synthase and beta-cyanoalanine hydrolase, which convert free cyanide to the amino acid asparagine. Thus, cyanide is detoxified and the nitrogen conserved as the amide nitrogen of asparagine (Goudey et al. 1989;Gurbuz et al. 2004). ...
... It is catalyzed by the alternative oxidase (AOX). In microorganisms, AOX can act as a terminal electron acceptor in the presence of inhibitors of the cytochrome c oxidase complex of electron transport chain (ETC), such as cyanide (Gurbuz et al. 2004). In various plant species AOX are known to play a key role in the biochemical reactions that occur after activation of mitochondrial retrograde signaling (Rhoads and Subbaiah 2007;Giraud et al. 2009). ...
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... In general HCN is produced by the plant as a defense mechanism against herbs. Various algae like Cyanobacteria, Chlorella valgaris, Scenedesmus and Nostoc muscorum (Gurbuz et al. 2004(Gurbuz et al. , 2009) bacteria like Chromobacterium violaceum and certain Pseudomonas species (Fairbrother et al. 2009) and fungi like Actinomycetes and Tricholoma produce and metabolize cyanide. In bacteria normally HCN is produced during transition stage of growth and in fungus when fruiting bodies are formed or during damaged or stress condition as a mechanism to provide nitrogen and carbon source (Ezzi and Lynch 2005). ...
Chapter
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... The pH range of the present study was chosen based on literature. Gurbuz et al. (2004) reported a pH of 10.3 as an effective pH for microalgal detoxification, while Khamar et al. (2015) showed a pH of 9.5 as suitable for the action of two bacterial strains (BN1 and DNB). In another study, Diaz and Caizaguano (1999) reported a pH of 8 is effective for the biodegradation as well as for the growth of Pseudomonas bacteria. ...
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... Rhodanese has been thoroughly studied with regard to animals and microorganisms [16], but not that well at all in the context of plants. ...
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For over a century now, the mining industry has been using cyanides for gold and silver recovery. Cyanides are highly toxic for human beings, animals, and aquatic organisms. The available physical and chemical methods of wastewater treatment are cost-ineffective. Certain microorganisms are capable of use cyanides as sources of carbon and nitrogen and turn those into ammonia and carbonate. Some plants are also efficient for the processes of cyanides destruction. Phytoremediation of cyanides may be efficient, cost-effective, environmentally friendly, and be used as an attractive alternative to traditional physical and chemical processes. This article considers the capability of aquatic plants, which grow in the valley of Zerafshan River on the territory of Uzbekistan, to dispose of cyanides and recover the cyanides-contaminated tailings of Navoi Mining & Metallurgical Combinat. Such aspects as the mechanisms of enzymatic detoxification of cyanides by aquatic plants and microorganisms are discussed. The most promising plants to be bedded in the tailings dump are selected.
Chapter
Occurrence of huge quantity of cyanide in the environment is due to extensive use in metal-finishing and mining industries. The strong affinity of cyanide with metals makes it favorable as an agent for metal-finishing and lixivant for metal leaching. For many years, cyanide has been used as a leaching reagent for the extraction of precious metals, particularly gold and silver. As a high toxicity of the cyanide it appears on the international priority pollution list. Considering the lethal impact of cyanide on the environment as well as human health, environmental authorities have taken a more stringent attitude toward the presence of cyanide in water. The researchers are trying to investigate best removal techniques for treating hazardous materials like cyanide from metal-finishing industrial wastewater and also strive to reuse of this water for agricultural or other purposes. Although cyanide can be removed and recovered by several processes, while biological treatment process gained an impetus of efficient degradation ability. Biological treatment of cyanide has often been offered as a potentially economical, environmentally friendly alternative to conventional methods. For the treatment of cyanide-containing wastewater, the adsorption and biodegradation are two significant methods. The first one, that is, adsorption is better to other wastewater treatment techniques in terms of efficiency, ease of operation, and low cost. The second, biodegradation method of cyanides removal is better than physical and chemical methods. In cyanide biodegradation process; the cyanide is converted to carbon and nitrogen source by various enzymes present in microorganisms. Biological treatments with bacterial whole cells is another important route for cyanide removal from water in which whole cells are used either in bulk phase or are immobilized on a solid support (bioadsorbent). Immobilized whole cells produce biolayer on bioadsorbent surface and when treated with solution having cyanide, the bacterial cells biodegrade it within the cell as well as it gets adsorbed on bioadsorbent surface. This process is termed as simultaneous adsorption and biodegradation process. In this chapter, we are aimed to make comprehensive description about sustainable bioremoval techniques on the removal of most hazardous materials like cyanide which are released from metal-finishing industrial effluents.
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Environmental pollution is increasing day by day due to anthropogenic activities and different types of toxic contaminants such as heavy metals, chemicals, dyes, pesticides etc enter the environment from different sources such as municipal, industries and agricultural. Among wastewater treatment techniques, bioremediation is one of promising techniques, which utilize the inherent biological mechanism of plant and microorganism for the remediation of diverse pollutants. Microalgae have been applied to mitigate the toxic and recalcitrant pollutants in the effluents. Microalgae have the capacity to remove different types of contaminants through different methods such as biosorption, bioaccumulation and biodegradation. It has been observed that microalgae can remove the pollutants originated from the domestic effluents, agricultural runoffs, textile, leather, pharmaceutical and electroplating industries etc. Additionally, the microalgae have the ability to mitigate the carbon dioxide in their growth process and utilize the micronutrients in the effluents. This review paper critically analysed the application of microalgae for the remediation of diverse types of pollutants commonly present in the environment through different mechanisms.
Article
In activated sludge system, without mixed liquor suspended solids, in which CN served as only source of carbon and nitrogen, it was found that (1) more than 99% of CN was metabolized, (2) suspended solids were maintained, (3) approximately 98% of cyanide-carbon was converted to CO2, and (4) from 75% to 90% of cyanide-nitrogen was converted to ammonia and nitrite.
Article
Cyanidation tailings disposed of in a surface impoundment experience a loss of cyanide due to natural attenuation, which frequently reduces the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed-solution chemistry has been largely empirical in spite of the fact that, in many cases, mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared with data collected for a North American tailings impoundment in 1998.
Article
Cydnidation tailings disposed of in a surface impoundment experience a loss of cyanide due to natural attenuation, which frequently reduces the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed-solution chemistry has been largely empirical in spite of the fact that, in many cases, mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared with data collected for a North American tailings impoundment in 1998.