This document discusses the treatment of industrial waste water containing cyanides through biological remediation. It provides background information on cyanides, their classification, toxicity, sources in industrial waste streams, and standards for cyanide levels in water. It then summarizes two treatment methods studied - adsorption of cyanides onto activated carbon and their biodegradation by microorganisms. The pathways and various microbes capable of biodegrading cyanides through specific enzymatic reactions are also outlined.

1. TTrreeaattmmeenntt ooff IInndduussttrriiaall WWaassttee WWaatteerr::
BBiioollooggiiccaall RReemmeeddiiaattiioonn ooff CCyyaanniiddeess
DR. CHANDRAJIT BALOMAJUMDER
PROFESSOR
DEPARTMENT OF CHEMICAL ENGINEERING
INDIAN INSTITUTE OF TECHNOLOGY ROORKEE, INDIA

2. CCYYAANNIIDDEE
• Carbon-nitrogen radical and refers to all CN (-CºN) groups that
can be determined analytically as the cyanide ion, CN-
• Highly toxic
• Found in a wide variety of organic and inorganic compounds
• Produced by certain bacteria, fungi, and algae
• Important form of nitrogen for microorganisms, fungi and plants
• Used in various industrial applications
• Produced as wastes and emissions from industries in large
quantities

3. CCLLAASSSSIIFFIICCAATTIIOONN OOFF CCYYAANNIIDDEE CCOOMMPPOOUUNNDDSS
Types of cyanide Examples Remarks
K Ionize easily, 2Zn(CN)4, K2Cd(CN)Weak 4
K Ionize moderately 2Cu(CN)3, K2Ni(CN)4
Moderately
strong
K Don’t ionize easily, very stable 2Fe(CN)6, K3Co(CN)Strong 6
Inorganic SCN-, CNO- Cyanate unstable
Acetonitrile, Acylonitrile, Stable
Organic Aliphatic Adiponitrile, Propionitrile
(Nitriles)
Aromatic Benzonitrile Stable
Complex
Zn(Cn)2, Cd(CN)2Insoluble , AgCN
Ionize in aqueous solution at
low concentration and mostly
present as HCN below pH 8
NaCN, KCN, Ca(CN)Soluble 2
Simple
Equilibrium depends on pH,
HCN, CN (pKa, 9.2 at 25oC) Free -

4. STABILITY AND TTOOXXIICCIITTYY OOFF CCYYAANNIIDDEESS
• The stability of cyanide salts and complexes are pH dependent
• Toxicity depends on their
– chemical form
– stability
– bioavailability to the exposed microbes and animals
• Cyanide compounds remain in the aqueous phase and form
complexes with other metallic contaminants
• Metal-cyanide complexes are much less toxic than free
cyanide, but their dissociation releases toxic free cyanide as
well as the metal cations

5. TTooxxiicciittyy lleevveell ooff VVaarriioouuss CCyyaanniiddee CCoommppoouunnddss
LD50 Physical TLV
form
Compound
Hydrogen cyanide (HCN) Gas 5 mg/m3 1 mg/kg human
Potassium Cyanide (KCN) Solid 5 mg/m3 10 mg/kg rat, 2.85 mg/kg human
Sodium cyanide (NaCN) Solid 5 mg/m3
Cyanogen chloride (CNCl) Gas 0.3 ppm
6.44 mg/kg rat,
2.85 mg/kg human
Sodium Cyanate (NaCNO) Solid 260 mg/kg mice
Potassium Cyanate (KCNO) Solid 320 mg/kg mice
Potassium ferricyanide Solid 1600 mg/kg rat
(K2 [Fe(CN)6])
TLV – threshold limit value is the time-weighted average concentration for an 8-hour workday and 40-hour
workweek to which a worker may be repeatedly exposed without adverse effect.
LD50 – lethal dose to 50% of a specified population.

6. EFFECT OOFF CCYYAANNIIDDEE CCOOMMPPOOUUNNDDSS
• Exert direct toxicity to fish and higher forms of life including
human (acute and chronic effects)
• Acute effect of cyanide include
– rapid breathing
– Gasping
– Arrhythmia
– Coma
– eventual death
• Chronic effects include
– acute effects
– neurological changes
– impairment of thyroid function
– demyelization of nerve fibers

7. • Potent inhibitors of cellular metabolism - causing problem in
sewage treatment
• The biological activity of microorganisms that digest sewage
and sludge is lost at 0.3 mg/l cyanide
• Binding of cyanide to metallic cofactor cause inhibition to
activities of metalo-enzymes
• Free cyanides inhibit cytochrome oxidase and suppress
aerobic respiration
• Free cyanide found to be highly toxic to methanogenic bacteria,
causing problem for anaerobic degradation of cyanide

8. INDUSTRIES USE CYANIDE ARE
 Electroplating
 Mining (extraction of Gold, Silver etc.)
 Case Hardening
 Automobile Manufacturing
 Printed Circuit Board Manufacturing
 Steel and Cock plant
 Petrochemical Refining
 Synthesis of Organic Chemical and Synthetic Fibers
 Paint, Ink formulation and Plastics
 Aluminum Works
 Explosives manufacture
 Pesticides etc.

9. Malononitrile
(lubricating oil
additive)
Propionitrile
(solvent)
Petroleum
Fumigant poison Cyanogen,
gas,
Zinc cyanide
Copper cyanide
Calcium cyanide
Hydrogen cyanide
Ammonium
thiocyanate
(pesticides)
parasiticide
Cyanogen
bromide
insecticides,
Cvanogen
chloride
pesticides,
Sodium cyanide,
Malononitrile
Cyanogen bromide
Barium cyanide
Calcium cyanide
Ferrocyanide (used
as a flotation agent
for copper and
lead/zinc
separation)
Ammonium Mining
thiocyanate
Potassium- or sodium- Herbicides
cyanide
(degreasing)
Propionitrile (solvent,
dielectric fluid)
Nickel cyanide
Silver cyanide
Barium cyanide
Zinc cyanide
Copper cyanide
Hydrogen cyanide
Cyanogen chloride (metal
cleaner)
Mercuric potassium
cyanide (mirror
manufacturing)
Electroplating
Potassium
ferrocyanide
Adhesives Ammonium thiocyanate Cement stabiliser Calcium cyanide Fire retardant
Primary cyanide
compounds used in
the process
Primary cyanide Industry
compounds used
in the process
Primary cyanide Industry
compounds used in the
process
Industry
Use of cyanide compounds in various industries

10. Primary cyanide
compounds used in
the process
Ferricyanide
Ferrocyanide
Propionitrile
Ammonium
thiocyanate
(ingredient in
antibiotic
preparations)
Ammonium
thiocyanate
Potassium
ferrocyanide
Primary cyanide Industry
compounds used
in the process
Pharmaceuticals
(includes
antibiotics, and
nonprescription
prescription
steroids, drugs)
Rocket and missile
propellant
Cyanogen
Wine
Ferricyanide,
Ferrocyanide
Ferric
ferrocyanide
(Prussian blue,
Malononitrile
Mercuric cyanide
(germicidal soap)
Copper cyanide
(marine paint)
Sodium
ferrocyanide
Ferric
ferrocyanide
(Prussian blue,
Potassium
ferrocyanide
Primary cyanide Industry
compounds used in the
process
Pigments, paints,
dyes, ink,
personal
care products
Ferricyanide bleach
Mercuric cyanide
Hydrogen cyanide
Malononitrile Adiponitrile Road salt
(intermediate in the
manufacture of nylon)
Cyanogen bromide
Cyanogen chloride
Hydrogen cyanide
(production of nylon
and other synthetic
fibers and resins)
Ammonium thiocyanate
(improve the
strength of silks)
Industry
Photography
Synthetic fiber
acrylic fiber,
nylon,
synthetic
rubber
Source: Data from MPI, Final Technical Memorandum: Summary of cyanide investiation a SRWTP and preliminary conclusions and
reconmiendations, report by Malcolm Pirnie. Inc. Emeryville, CA to the Sacramento Regional County Sanitation District,
Sacramento Reg:c: Wastewater Treatment Plant, Regulatory Compliance Group, Sacramento, CA, 2004.

11. Cyanide levels in wastewaters
Industrial waste water source Simple Complex Total % Simplec Ref. No
Coke-oven waste water 54.8b [5]
Coke plant 100-1000 [6]
Coke plant 1.6-6.0
Coke plant 0.1-0.6
Coke plant 0.1-0.7
25.4a 25.7 a 1.17
Coke plant 0.3
Coke oven plant 10-150a [7]
Coke plant waste 10-38.1 [8]
Coke plant waste 91-110 [9]
Coke plant waste streams [10]
Coke oven liquor 0-8
Decantation tank 8
Final cooler condensate 196
Benzole separator 2736
Oil generation plant separator 104
Spent limed liquor 4
Coke plant ammonia liquor 2-44.5 [11]
Coke plant ammonia liquor 20-60 [9]
Coal conversion (synthane) 1-6 [9]
Coal conversion wastes 2-30 [9]

12. Industrial waste water source Simple Complex Total % Simplec Ref. No
0.0-0.2a 0.03-0.27a 26-100 [12]
Electroplating plants 0.03-0.07
Electroplating plants 0.01-14.24b [13]
Electroplating plants/PCB plants 3.0-59.0b [14]
Electroplating plants 3.6-6.6 [15]
Plating rinse 0.3-4 [8]
32.5 [8]
25 [9]
60-80 [16]
30-50 [17]
1.4-256 [8]
Plating industries(rising waste) 1.4-256 b [18]
Plating industries (plating bath) 4000-100 000b [12]
Plating bath 30000 [19]
Plating bath 45000-100000 [20]
Plating bath [11,21,22]
Brass 16000-48000
Bronze 40000-50000
Cadmium 20000-67000
Copper 15000-67000
Silver 12000-60000
Tin-zinc 40000-50000
Zinc 4000-64000
Alkaline cleaning bath 4000-8000 [17]

13. Industrial waste water source Simple Complex Total % Simplec Ref. No
Blast furnace scrubber water [9]
Steel making segment (range) 0.2-1.4
Steel making segment (max) 2.4
Blast furnace gas wash 48.5
Steel mill Coke plant liquor 7.5-39.6 [9]
Color film bleaching process 71 [23,24]
Paint and ink formulation 0-2 [9]
Bright dip 15-20 [17]
10.4-50.9a 10.4-50.9a 0-0.3 [25]
Chemical industry 0-0.03
Gold ore extraction 18.2-22.3 [9]
Explosives manufacture 0-2.6 [9]
2.25a 2.25a 0 [12]
Oil refinery 0.0
Petroleum refining 0-1.5 [9]
a Includes thiocyanate.
b Unspecified whether thiocyanate included.
c % of total cyanide concentration

14. Standards for cyanide level in water and wastewater:
US-health service cites 0.01mg/l as guideline and 0.2 mg/l as
permissible limit for cyanide in effluent
Minimal national standard (MINAS) for cyanide in effluent - 0.2
mg/l in India
U.S.EPA standard for drinking and aquatic-biota waters
regarding total cyanide are 200 and 50 ppb respectively
Limit for cyanide In Mexico is 0.2 mg/l
German and Swiss regulations have set limit of 0.01 mg/l for
cyanide for surface water and 0.5 mg/l for sewers

15. CYANIDE REMOVAL TTEECCHHNNOOLLOOGGIIEESS
 Alkaline-chlorination-oxidation
 Hydrogen peroxide oxidation
 Ozonation
 Electrolytic oxidation
 Ion exchange
 Acidification
 AVR Process
 Lime-sulfur method
 Reverse osmosis
 Activated carbon adsorption
 Caro’s Acid method
 Thermal hydrolysis
 INCO Process (by SO2/Air)
 Biological Treatments

16. METHODS USED IN TTHHEE PPRREESSEENNTT SSTTUUDDYY
Adsorption
Biodegradation
Simultaneous Adsorption and Biodegradation

17. AADDSSOORRPPTTIIOONN
• Effective method for cyanide removal
• Used mostly as a polishing process
• Cyanide species exhibit surface reactivity with certain mineral
solids and with activated carbon
• Granular/Powered activated carbon is the most widely used
adsorbent for cyanide complexes
• Activated carbon particle has a porous structure consisting of a
network of inter connected microspores and macrospores that
provide a good capacity for the adsorption due to its high
surface area

18. BBIIOODDEEGGRRAADDAATTIIOONN
• Natural approach
• Relatively inexpensive
• No chemical handling equipment or expensive control needed
• Cost is fixed with greater volumes of waste also
• Biomass can be activated by aeration
• Can treat cyanides without generating another waste stream
• No toxic byproducts, hence environmental friendly
• Used as nitrogen or both carbon and nitrogen source by
microbes
• Microbes convert cyanide enzymatically to ammonia, which is
readily assimilated into cellular nitrogen

19. • Biodegradation can be possible under both anaerobic and
aerobic conditions
• Aerobic conditions are maintained due to the toxicity of cyanides
to methanogenic bacteria under anaerobic conditions
• Attach growth processes have better toxicity tolerance than
suspended growth
• Various strains of microorganisms have been found for the
degradation of cyanide and metal cyanides
• Biodegradation occurs through specific enzymes and pathways

20. Microbes for Cyanide biodegradation studies
P.putida
Fusarium solani
P.fluorescens immobilized on Calcium Alginate
P.fluorescens in presence of Glucose (conc=.465g/l)
Klebsiella oxytoca
Mixed culture of bacteria
P.putida immobilized on sodium alginate
Fusarium oxysporum & F solani
P.putida immobilized on Ultrafiltration membranes
Citrobacter sp , Pseudomonas sp
Fusarium oxysporum immobilized on Sodium alginate,
Methylobacterium sp
Strains of Trichoderma spp

21. Microbes for Cyanide biodegradation studies
P.fluorescens immobilized on zeolite
Burkholderia Capcia stain C-3
B. stearothermophilus NCA 1503
Mix of (1) F.Solani T.polysporum, (2)F.oxyspoum, Scytalidium
themophilum, Pencillium miczynski
Granular Cyanidase
Bacillus magaterium
E.Coli BCN6
Stemphilium loti
Pseudomonas fluorenscens NCIB11764 (CN) Pseudomonas
gr (phenol)
S. loti, G. Sorgi
Pseudomonas putida BCN3
Bacillus pumilis (clay,purchage, filamentous develp)
Pseudomonas Acidovorans

22. PATHWAYS FOR BIODEGRADATION OF CYANIDE AND THIOCYANATE
Hydrolytic reactions
Cyanide hydratase
HCN + H2O → HCONH2
Cyanidase
HCN + 2H2O → HCOOH
Nitrile hydratase
R-CN + H2O → R-CONH2
Nitrilase
R-CN + 2H2O → R-COOH
Oxidative reactions
Cyanide monoxygenase
HCN + O2 + H+ + NAD(P)H → HOCN + NAD(P)+ + H2O
Cyanide dioxygenase
HCN + O2 + 2H+ + NAD(P)H → CO2 + NH3 + NAD(P)+
Reductive reactions
HCN + 2H++ 2e– → CH=NH + H2O → CH2=O
CH2=NH + 2H+ + 2e– → CH3-NH + 2H+ + 2e–
→ CH4 + NH3
Substitution/Transfer reactions
Cyanoalanine synthase
Cysteine + CN– → β-cyanoalanine + HS
2OAS + CN– → β-cyanoalanine + CH3COO–
Thiosulfate:cyanide sulfurtransferase
CN– + SO2– → SCN– + SO2–
23
3
Thiocyanate biodegradation
Carbonyl pathway (thiocyanate hydrolase)
SCN– + 2H2O → COS + NH3 + OH–
Cyanate pathway (cyanase)
SCN– + 3H2O + 2O2 → CNO– + HS– → HS– + 2O2 → SO4
2– + H+
CNO– + 3H+ + HCO3
– → NH4
+ + 2CO2
The general categories of chemical reactions responsible for the biodegradation of cyanide and thiocyanate. For the hydrolytic reaction
involving nitriles, R represents either an aliphatic or aromatic group. The substitution/transfer reaction catalyzed by cyanoalanine synthase
can also use O-acetylserine (OAS) as a substrate. The cyanate formed by cyanide monoxygenase is converted to NH4þ and CO2 by the
same pathway as the cyanate from thiocyanate. The reductive pathway is derived from the action of nitrogenase and the products
resulting from the transfer of pairs of electrons.

23. SIMULTANEOUS AADDSSOORRPPTTIIOONN AANNDD
BBIIOODDEEGGRRAADDAATTIIOONN ((SSAABB))
• Adsorption onto adsorbent reduces the inhibitory effect of the
cyanides for microbial mass
• Presence of activated carbon increases liquid-solid surfaces, on
which
microbial cells
enzymes
organic materials
oxygen
are adsorbed providing an enriched environment for microbial
metabolism
• Activated carbon can be partially regenerated by
microorganisms while the carbon bed is in operation

24. • Carbon adsorption capacity, controlled by the bioregeneration,
highly increased
• Carbon adsorption column cycle prolonged as compared to pure
adsorption system alone
• Stable performance of the combined process during peak load
because the reserve of adsorption capacity due to
bioregeneration
• The adsorbed cyanides desorbed back in to the biofilm and also
through it into the liquid phase and become accessible to the
microbial degradation
• Both processes in one unit results in a better removal and
process performance
• SAB process has been utilized for treatment of lots of
substances, but fate of cyanide removal is not established

25. OBJECTIVE OF PRESENT
WORK

26. Effect of process parameters such as:
• pH
• Temperature
• Contact time
• Initial concentration of cyanide
on removal of Sodium, Zinc and Iron Cyanide from
aqueous solutions by
• Adsorption
• Biodegradation
• Simultaneous adsorption and biodegradation

27. MMAATTEERRIIAALLSS AANNDD
MMEETTHHOODDSS

28. Sodium Cyanide [NaCN]
• Simple alkali salt of cyanide
• Highly soluble in water and dissociate to release CN-
• Highly toxic due to ionization in aqueous solutions
• Produced largely from Electroplating (for degreasing) and
Mining industries
• Stock solution of 1 g/L was prepared by dissolving 1.88 g/L
NaCN
in Milli-Q water (Q-H2O, Millipore Corp. with resistivity of
18.2MΩcm)

29. Zinc cyanide [Zn(CN)4
2- ]
• Weakly stable complexes of metal cyanide
• Classified as weak-acid dissociable (WAD) as they are easily
dissolved under mildly acidic conditions (pH = 4 - 6)
• Dissociation to release free cyanide
• Produced from Electroplating, Pesticide industries
• Stock solution of 1 g/L was prepared by mixing
3.57 g/L of autoclaved Zinc sulphate salt solutions
and 3.25 g/L of filter-sterilized KCN solution
in Milli-Q water (Q-H2O, Millipore Corp. with resistivity of
18.2MΩcm) to obtain K2Zn(CN)4

30. Ferro cyanide [Fe(CN)6
4- ]
• Highly stable complex
• Dissociate in highly acidic condition (pH<2-3) and in UV light
• Relatively Less toxic
• Produced in Pesticide, fire resistant herbicide industries,
mining, pharmaceutical, paint, dye, wine industries
• Stock solution of 1 g/L was Prepared by dissolving 2.7 g/L
K4[Fe(CN)6].3H2O in Milli-Q water (Q-H2O, Millipore Corp. with
resistivity of 18.2MΩcm)

31. Properties of granular activated carbon
Elemental
analysis
C=75.11 %
H= 1.913%
N=S= 0.0 %
Micro-pore (<2nm)
volume (cm3/g)
BET Surface
area (m2/g)
Particle size
(mm)
2.0-5.0 583.35 0.2112
Bulk density = 400 g/l
GAC was Purified with Millie-Q water
and dried at 110 °C for 24 h

32. Culture: Stemphilium loti
• Source : IMTECH, Chandigarh, India
• Growth conditions : Aerobic
• Temperature : 30 oC
• pH : 7.2
• Incubation Time : 24 hrs
• Subculture : 30 days
• Culture was revived in Nutrient Broth media and Agar Plates
Photo of Petriplate Gram stain by microscope Photo of by SEM

33. • Biodegradation medium :
Glucose : 5.0 g/L
K2HPO4 : 0.5 g/L
KH2PO4 : 0.5 g/L
MgSO4·7H2O: 0.05 g/L
for growth medium the following content was added to
biodegradation medium:
Peptone : 1.0 g/L
Yeast Extract : 1.0 g/L
NH4SO4: 0.5 g/L

34. METHODOLOGY
• GAC doses (Dc) of 20 g/L were used for adsorption and SAB
study
(GAC dose was optimized from previous experiments, results not
mentioned here)
• Cultures were grown in suitable nutrient broths and agar plates
for revival
• Sterilization of the medium was performed in an autoclave at 121
°C for at least 20 min
• Biologically activated carbon (BAC) was prepared by immobilising
S. loti was initially immobilized on GAC and then added to
biodegradation medium to maintain 20 g/L BAC for SAB study
• For adaptation of the microbe, cyanide was added stepwise in
10-50 mg CN-/L as only source of carbon and nitrogen

35. • Effect of pH (4-11), Temperature (20-45 °C) and agitation time
on percentage removal of cyanide was observed for all
processes with initial concentration of 100 mg CN-/L
• Percentage removal was measured for various initial
concentrations of cyanide (50, 100, 200, 300, 400, 450, 500,
550, 600, 650 mg CN-/L )
• Cyanide removal efficiency for various concentrations in all the
3 processes were compared
• All studies were conducted in batch reactors (250 ml
conical/spherical flask) in incubator shakers at 150 rpm for an
agitation period (ta) of 120 h
• Total cyanide was determined by pyridine–barbituric acid
colourimetric method (578 nm) after distillation

36. Instruments/Apparatus used
Incubator Shakers Batch reactors
Laminar Hood Autoclave Cyanide distillation apparatus

37. Instruments used
Mili Q Elemental Analyser
Scan Electron Microscope Spectrophotometer Microscope

38. RREESSUULLTTSS

39. pH
% removal of cyanide
Adsorption Biodegradation SAB
NaCN ZnCN FeCN NaCN ZnCN FeCN NaCN ZnCN FeCN
4 45.2 71.6 81.68 84.8 46.2 73.9 91.8
5 50.16 80.2 83.3 36.4 53.84 94.1 72.1 89.8 98.7
6 52.4 84.2 82.6 73 88.4 94.4 92.6 98.5 99.9
7 53.68 84.4 79.6 89.1 93.4 93.8 99.9 99.9 99.2
8 59.92 82.48 72.8 89 90.8 82.6 99.9 98.1 87.6
9 63.2 79.44 64.2 85.28 84.88 69.4 99.5 87.6 68.9
10 63.2 66 43.3 75.4 67.44 43.6 88.3 74.5 47.7
11 61.68 42.4 31.2 44 23.2 32.8 84.6 56.3 33.8
Table 1. Effect of pH on removal of cyanides by adsorption, biodegradation
and SAB

40. • Percentage removal of metal cyanide complexes were
maximum at neutral and slight acidic pH (i.e. at pH 6-7) for
adsorption.
• There was increase in percentage removal for sodium cyanide
in alkaline conditions.
• In case of biodegradation No significant removal was observed
below pH 5 or above pH 10 for all the three cyanide
compounds.
• For biodegradation as well as SAB process a similar trend was
found as in the case of adsorption.
• For all processes, the percentage removal of CN- was found to
be more at alkaline, neutal and acidic pH conditions for sodium,
zinc and iron cyanide complexes respectively.

41. Temp.
(oC)
% removal of cyanide
Adsorption Biodegradation SAB
NaCN ZnCN FeCN NaCN ZnCN FeCN NaCN ZnCN FeCN
20 62.6 81.6 78.92 89.6 91.4 92.3 95.3 93.7 96.4
25 65.8 83.7 80.8 96.4 93.4 94.3 99.9 99.9 99.9
30 67 83.9 82.6 96.4 93.4 94.4 99.2 99.5 99.7
35 67.2 83.9 82.6 94.4 91.3 93.6 95.7 97.1 98.0
40 67 84.1 83.5 80.2 85.7 90.4 93.7 95.7 94.9
45 67.3 84.2 83.5 89.7 90.7 92.2
Table 2. Effect of temperature on removal of cyanides by adsorption,
biodegradation and SAB

42. • The difference was not great at different temperatures, but
adsorption increased slightly with rise in temperature.
• Here the rise of temperature favours the adsorbate transport
within the pores of the adsorbent.
• The increase in adsorption with temperature was mainly due to
an increase in number of adsorption sites caused by breaking of
some of the internal bonds near the edge of the active surface
sites of the adsorbent
• In case of biodegradation and SAB maximum growth and
removal of CN- was observed at temperature 25-30 °C and
growth of S. loti ceased above 40 oC.
• 30 °C was taken as the optimal temperature for all the studies.

43. Effect of Agitation time on percentage removal of cyanide
• Fig. 1: (a), (b) and (c) represent the percentage removal of 100
mg/L of sodium, zinc and iron cyanide complexes respectively
with increase in agitation time by adsorption, biodegradation
and SAB at 30 °C and pH 7.
• In physical adsorption most of the adsorbate species are
adsorbed within a short interval of contact time.
• However, strong chemical binding of adsorbates with adsorbent
required longer contact time for the attainment of equilibrium.

44. 100
80
60
40
20
0
Adsorption Biodegradation SAB
0 24 48 72 96 120
Cyanide removed (%)
Time (h)
Fig. 1 (a). Effect of agitation time on removal of NaCN

45. 100
80
60
40
20
0
Adsorption Biodegradation SAB
0 24 48 72 96 120
Cyanide removed (%)
Time (h)
Fig. 1 (b). Effect of agitation time on removal of ZnCN

46. 100
80
60
40
20
0
Adsorption Biodegradation SAB
0 24 48 72 96 120
Cyanide removed (%)
Time (h)
Fig. 1 (c). Effect of agitation time on removal of FeCN

47. • Adsorption results reveal that the uptake of adsorbates species
were fast at the initial stage of contact period, and thereafter, it
became slower near the equilibrium.
• From the plots it was observed that the adsorptive removal
cyanide ceases after 24-30 h with adsorbent concentration of
20 g/L.
• From the figures it was evident that no biodegradation or growth
of microbe was found in the staring 12-18 h of agitation. This
may be due the lag phase of microbe.
• Biodegradation started at 24 h, but after 72 h of agitation there
was no significant increase in the percentage removal of
cyanide.
• In SAB the presence of activated carbon increases the liquid-solid
surfaces, on which microbial cells, enzymes, organic
materials and oxygen are adsorbed providing an enriched
environment for microbial metabolism.

48. • Activated carbon can be partially regenerated by
microorganisms while the carbon bed is in operation.
• The carbon adsorption capacity, controlled by the
bioregeneration, is highly increased and the carbon adsorption
column cycle is prolonged as compared to pure adsorption
system alone.
• Biodegradation delayed for a few hours due to delayed growth
of microbes in the presence of cyanide ions, but in SAB process
the percentage removal of cyanide was started earlier.
• This may be due to adsorption occurred in the first phase
followed by biodegradation.
• In case of SAB, a stationary condition reached at 36-42 h. After
stationary condition there was possibility of increase in cyanide
removal due to bioregeneration of BAC and biodegradation in
the medium, which theoretically explains the non-arrival of
equilibrium condition.

49. Effect of initial concentration of cyanide on its percentage
removal
• Fig. 2: (a), (b) and (c) represent the effect of initial concentration
of sodium, zinc and iron cyanides respectively on percentage
removal by adsorption, biodegradation and SAB.
• From the experimental results it was observed that, the removal
efficiency decreased with increase in initial cyanide
concentration for all processes.

50. 100
80
60
40
20
0
Adsorption Biodegradation SAB
0 100 200 300 400
Cyanide removed (%)
Initial cyanide concentration (mg CN-/L)
Fig. 2 (a). Effect of Initial Cyanide Concentration on Removal of NaCN

51. 100
80
60
40
20
0
Adsorption Biodegradation SAB
0 100 200 300 400 500
Cyanide removed (%)
Initial cyanide concentration (mg CN-/L)
Fig. 2 (b). Effect of Initial Cyanide Concentration on Removal of ZnCN

52. 100
80
60
40
20
0
Adsorption Biodegradation SAB
0 100 200 300 400 500 600 700
Cyanide removed (%)
Initial cyanide concentration (mg CN-/L)
Fig. 2 (c). Effect of Initial Cyanide Concentration on Removal of FeCN

53. • At a particular environment the percentage removal of an
adsorption process depends upon the ratio of the number of
adsorbate moiety to the available active sites of adsorbent.
• This ratio, also related to the surface coverage of the adsorbent
(number of active sites occupied/ number of active sites
available) increases with the increase in the number of
adsorbate moiety per unit volume of solution at a fixed dose of
adsorbent.
• Less is the value of this ratio more is the percentage removal.
• At higher cyanide concentration this ratio is high and decreases
gradually with the decrease in cyanide concentration as a result
the percentage removal increases with the decrease in initial
concentration of cyanide.
• At the starting of the experiment the presences of active sites
was more and get saturated with the increase in agitation time.
Hence the percentage removal increased rapidly at the initial
stage and decreased after a certain period

54. • In case of biodegradation, the decrease in removal of cyanide
with increase in initial concentration may be due to the toxicity of
cyanide compounds to S. loti at higher concentration.
• No significant biological activity was found in the medium above
350, 350 and 450 mg/L for sodium, zinc and iron cyanides
respectively.
• Although metal-cyanide complexes by themselves are much
less toxic than free cyanide, their dissociation releases free
cyanide as well as the metal cation, which can also be toxic.
• The initial concentration up to which biodegradation was
possible is more in iron cyanide as compared to other
compounds may be due to the toxicity of easily dissolved free
cyanide ions in sodium and zinc cyanide solutions.
• It could be easier to utilize cyanide as a source of nitrogen in the
presence of another source of carbon and energy, as the
amount of nitrogen needed for the growth is less than the
requirement for carbon.

55. • In the presence of microbial film, the removal of substances is
mechanistically complex involving
(i) transport of substances from the bulk liquid to the surface of microbial film,
(ii) simultaneous mass transfer, adsorption, and biochemical reaction within
microbial film
(iii) simultaneous mass transfer and adsorption within adsorbent.
• The complexity increases due to dynamic nature of the
microbial film.
• Efficiency of SAB process was more as compared to adsorption
and biodegradation alone.
• In SAB process, due to attach growth and combined process
performance, resistance to cyanide toxicity by S. loti was more
and could achieved good efficiency even at higher
concentrations.
• SAB process has been used successfully for degradation of
various compounds such as phenol, toxic metals, dye etc.,
however its fate was not known for removal of cyanide
compounds, hence this study is the 1st of this kind

56. SEM after adsorption on GAC SEM of biodegradation medium
SEM of biologically activated carbon in SAB process

57. Mixing
chamber
Column
Stirrer-motor reactor
0.22μm Filter
for air
Rotameters
(upto 2 lpm)
Probe ports (pH,
ORP, DO &
thermometer)
Probe ports (pH, ORP
&DO)
0.45μm
Filter for
water
Peristaltic pump
Compressor
Sample
addition
Probe port
(temp)
0.22μm Filter
Samp
ling
ports
Washing
0.22μm
Filter
Pressure
gauge
Pressure
gauge
Pressure
gauge
Level
indicator
Level
indicator
Level
indicator
drainage
Feed
tank
Steam
generator
P5
P4
P3
P2
P1
Details of Column Experimental set-up

58. Electric plug
fitting for cooler
or hot air blower
Wood Chamber for Temperature Control
4’
Thermostat arrangement
Switch and socket point
4’
7’
2’6”
Inside light point and
light arrangement
Electric wiring
6’
2’ 6”
6’
6”x1’ window for hot
and cool air blower
1’
6”
1’6”
1’6”x1’6” side bracket arrangement
for keeping hot and cool air blower
6”x1’6” door to close
window when not in use
4’x4’x7’ wooden box
made of 12mm
waterproof plywood and
inside of white matt
One side wooden door 2’6”x6’ made of 12mm waterproof
Opening 2’6”x 30cm
finish lamination
plywood and inside of white
door 5 cm
matt finish lamination

59. Column
reactor

60. Constant
temperature
environmental
chamber for
Feeding Tank
Air compressor Autoclave reactor

62. CCOONNCCLLUUSSIIOONNSS

63. • Percentage removal efficiency and rate of removal with respect to time
was found better in SAB process as compared to adsorption and
biodegradation alone
• Removal of iron cyanide was found more by suspended as well as
immobilised S. loti as compared to sodium and zinc cyanide
• SAB process was used successfully for removal of high concentrated
cyanide in water and wastewater
• Due to the monolayer adsorption of cyanide on the BAC, there was
possibility of reduction of toxicity of cyanide and metal ions to microbes
• During SAB there was possibility of bioregeneration of carbons, which
increased the adsorption capacity and prolong the time of adsorption
process
• Cyanide adsorbed on the BAC surface could be easily biodegraded by
microbes as GAC act as enrichment surface and attached growth gave
better efficiency
• SAB is more efficient and prolonged process for removal of cyanide

64. BBIIBBLLIIOOGGRRAAPPHHYY

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67. TThhaannkk yyoouu