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TECHNOLOGICAL OPTIONS FOR THE
MANAGEMENT OF SALINE STREAMS
Dr. G. Sekaran Chief Scientist& Cluster Chairman
IWWA 2014
Environmental Technology Division
CSIR- Central Leather Research Institute
Adyar, Chennai
24TH MARCH , 2014
Leather manufacturing and wastes
Soaking
Liming
Unhairing
Reliming
Deliming including washing
Pickling
Tanning
Wastewater Major issue
Soak liquor
Lime liquor
Lime liquor
Delime liquor
Pickle liquor
Tan liquor
Ammonia
H2S
Hair
High TDS, COD, BOD
High COD, BOD ,Sulphide,fleshing
High TDS
High TDS
Dusting of salt Salt
Leather manufacturing and wastes
Retanning
Neutralization including washing
Wet-finishing
Trimming
Buffing
Wastewater Major issues
Shavings
Waste water
Waste water
Trimmings
Shaving
Finishing
Waste water
Buffing dust
High COD, Low BOD , Low BOD/COD
High COD, Low BOD , Low BOD/COD
Inorganic TDS
Sodium chloride is the major contributor of TDs
Sodium sulphide
Chromium
Calcium hydroxide
Zinc chloride
Mercuric Chloride
Magnesium salt, phosphate , nitrate
Organic TDS in tannery wastewater [natural organics and synthetic organics]
• Organic compounds employed in the tanning process
• Synthetic tanning agents, Sulphonated polyphenols,Modified Glutardialdehyde
• Acrylic acid condensates Anionic surfactants aliphatic sulfonates
• Aliphatic sulphates Non ionic surfactants Aromatic ethoxylates
• Aliphatic ethoxylates Preservatives
• Benzo azol- derivatives Hologenated alkanes
• Chlorinated fatty acids, Aliphatic thiols
• Dyes
Parameters Raw
effluent
pH 8.5
Turbidity, NTU 850
Total Dissolved Solids , mg/l 16000
Total Suspended Solids , mg/l 4200
Chemical Oxygen Demand , mg/l 4750
Biochemical Oxygen Demand, mg/l 1100
Total hardness , mg/l 1600
Chromium , mg/l 180
Sulphide , mg/l 120
Chloride , mg/l 9500
Characteristics of wastewater discharged from leather industry
OBJECTIVES OF BIOLOGICAL TREATMENT
To reduce the BOD and COD To reduce the refractory organic compounds To reduce foulants in the treated wastewater To reduce reject volume in the R.O unit To increase rate of evaporation in evaporator
Impact of TDS on secondary Biological treatment The raw wastewater contains large amounts of easily degradable aliphatic biogenic orgnaic matter which might be prefrentially degraded in the anaerobic step The degradation of aromatic compounds is energetically and kinetically less favourable under anaerobic conditions The organic removal efficiency decreased with increased in sodium chloride content in the influent wastewater.
Effluent turbidity increased significantly when the sodium chloride concentration in the wastewater was increased.
High concentration of salts cause cell plasmolysis and death of micro organisms due to the increase in osmotic pressure
The flux decline profile becomes more prominent with increasing Ca2+ concentration
The flux profiles become more significant when the ionic strength of the feed solution is increased to 10 mM
Membrane fouling results in an increase in feed pressure and requires frequent cleaning of membranes. This leads to a reduction in overall facility efficiency and a shorter membrane life.
The increase in effluent turbidity could be caused by the release of nondissolved cellular components due to plasmolysis of microorganisms
Distribution of TDS in sectional streams of wastewater
Soak Liquor –
47.1 %
Pickilng - 12.5 %
Chrome Tanning -
13.7 %
Others - 26.66 %
0
5000
10000
15000
20000
25000
R R - S R - (S + P) R - (S + P +C)
R - (P + C)
21000
15857 12962
9122
16923
R - Raw; S - Soak; P - Pickle; C - Chrome
Total Dissolved solid(mg/L) content of wastewater after segregation
0
2000
4000
6000
8000
10000
12000
14000
R R - S R - (S + P) R - (S + P +C)
R - (P+C)
12500
5000
3585 1836
11095
R - Raw; S - Soak; P - Pickle; C - Chrome
Chloride(mg/L) content of wastewater after segregation
Option 1
Management of soak
liquor
Conventional Method: segregation and solar evaporation
Issues: The evaporated residue is poor in quality It lacks reusable option due to the presence of dissolved organics ( derived from the raw material) suspended impurities ( derived during solar evaporation )
Magnified issue: Disposal onto secured land fill is not recommended due to difficulty in handling the leachate . The salt is heaped in industries [for how long?]
SRIOM
PROCESS
[CLRI PATENTED
PROCESS]
R.O Salt
NaCl
HCl
H2O
Neutralisation
Ca SO4 (solid lumps)
OPTION FOR SPECIATION OF SALT FROM REJECT
CO2
Ca (OH)2
Ca Cl2 (crystals)
Sand
filter
Organic
destruction
Semi Pilot plant for SRIOM Process
in Envt. Tech. Division, CLRI
Option 2
Management of soak
liquor
Conventional Method: segregation and solar evaporation
Issues: Poor rate of evaporation due to microbial mat ( cynobacteria and thiobacillus) on the surface of water preventing the diffusion of thermal and light radiations Rate is very much reduced during winter
and Rainy season Spill over around solar evaporation pan Causing ground water pollution. Recommendation: Mechanical evaporation Bottleneck : Presence of natural organic compounds (
protein , fat, muco poly saccharides, blood,
dirt , dung )
S.No.
Parameters
Min
Max
Ave.
Standard
Deviation
1
pH
5.72
7.25
6.56
0.439
2
BOD
360
720
460
108.16
3
COD
882
1581
1327
269.30
4
TOC
164
328
273
62.30
5
Dissolved protein
470
916
709
128.86
6
Total Dissolved
Solids
14390
31250
23452
6406.98
7
Bacterial count
6X104
1.12X108
2.13X107
-
Characteristics of clarified soak wastewater
All the values except pH and Bacterial count are expressed in mg/l
Bacterial count is expressed in CFU/ml
Molecular oxygen has low oxidation
potential and thus difficult to degrade
synthetic orgnics In tannery
wastewater.
Hence, oxidants with high oxidation
potential for the oxidation of
inorganics may improve the
environmental management in Leather
sector.
Compound Oxidation Potential
(V)
Relative Power of
Chlorine
Fluorine 3.06 2.25
Hydroxyl Radical 2.80 2.05
Ozone 2.07 1.52
Hydrogen
Peroxide
1.77 1.30
Permanganate 1.67 1.23
Hypochlorous acid 1.49 1.10
Chlorine 1.36 1.10 Hydroxyl radical may be considered as the oxidising agent with oxidation potential of 2.8V Reduction potential O2 + 4H+ + 4e- --> 2H2O (l) ; 1.23 V
insitu generation of highly
potent chemical oxidant
hydroxyl radical (OH•)
with a high electrochemical
oxidation potential
(2.8V versus normal hydrogen
electrode)
for the destruction of wide
range of organic compounds in
soak wastewater FACCO technology in
TNPL, Karur, Tamilnadu
Fenton’s reagent , releases hydroxyl radicals on mixing with wastewater facilitating the oxidation of organics. During the Fenton reaction , hydrogen peroxide is catalysed by ferrous ions to produce hydroxyl radicals
Fe2+ + H2O2 Fe3+ + OH- + HO (k176.5 mol-1 s-1)
The generated Fe3+ can react with H2O2 to regenerate
back Fe2+ to sustain the reaction
Fe3+ + H2O2 Fe2+ + H+ + HO2 (k2 1 x 10-2 mol-1 s-1)
The OH• species formed through Eq (1) attack the organic substrates present in the wastewater.
FACCO technology for refractory laden
wastewater
Hydroxy radicals are
generated by Fenton’s reagent, a mixture of Ferrous iron and hydrogen peroxide
Hydroxy radicals react with organics and break them down gradually into smaller fragments .
FACCO technology
in CETP, VAPI
Nano Porous Activated carbon has been proved
to generate hydroxyl radicals using molecular
oxygen
S.no Parameters Values
1 SBET (m2/g) 438.9
2 Smic (m2/g) 214.9
3 Smeso (m2/g) 224.0
4 Vmeso /Vtot (%) 69.23
5 Average pore diameter (nm ) 3.528
6 Carbon (%) 37.96
7 Hydrogen (%) 2.40
8 Nitrogen (%) 0.50
9 Moisture (%) 13.56
10 Ash (%) 45.58
11 Decolorizing power (mg/g) 69.32
12 Point of zero charge (PZC) 7.1
13 Apparent density (g/cm3) 0.32
Characteristics
of the
Nanoporous
carbon
SBET: BET surface
area;
Smic: micropore
surface area;
Smeso: mesopores
surface area.
FENTON ACTIVATED
CARBON CATALYTIC
OXIDATION
[FACCO]
Hydroxyl radicals are generated from molecular oxygen and adsorb
onto the MAC800 through the following sequential reactions. The free
electrons present in the MAC800 (this was confirmed using ESR
spectroscopy, the value reported was calculated by spin density of the
carbon = 16.052 x 1021 spins/g) initiate reaction
-C (e-cb) + O2 -C (O2
●)ads
-C (O2●)ads + H+
(aq) -C(HO2●)ads
The adsorbed hydro peroxyl radicals are converted into hydroxyl
radicals and remain adsorbed on the surface of MAC800
-C(HO2●)ads + H+
aq -C(2OH●)ads
The positive charged centers in MAC 800 serves to adsorb the
organic substrate as expressed interms of COD (The existence of
energy gap in MAC800 was confirmed through UV-Reflectance
spectroscopy and the value was found to be 1.55eV conforming
to extrinsic semiconductor grade).
-C(h+vb) + (COD) -C (COD)ads
FACCO technology saline (3% TDS)
wastewater
Karthikeyan et al ., Environ Sci
Pollut Res, 2012.
The adsorbed COD and hydroxyl radicals present at the proximate position
undergo constructive overlapping to produce CO2 and H2O and regenerating
back to bare nano activated carbon surface.
(COD)ads
H2O + CO2 + -C (h+vb) + e-
cb
-C (2OH●)ads
where
h+vb - electron hole in the valence band
e-cb - electron in the conduction band
-C - refers to the excited carbon active site
FACCO technology in CETP, VAPI
Sekaran et al., Environmental Chemistry Letters 9 ( 2011) ,
Concentration of pollution parameters after treatment using
extreme halophiles after immobilization in mesoporous activated carbon
S.No
Pollution
Parameters
Concentration (mg/l)
Initial
Final
1
COD
2559
67-148
2
BOD
720
15-51
3.
Protein
Nil
709
Segregation , Treatment and Reuse of Soak liquor
Reject volume
50%
Treated soak wastewater
Water
recovery
Option 3
Integrated solid waste
and
soak liquor
Management
MAJOR ISSUE WITH OPTION 2 IS
ENERGY REQUIREMENT FOR MECHANICAL
EVAPORATION OF SALINE STREAM IS VERY
HIGH
RECOMMENDATION:
EXTRACTION OF ENERGY FROM HAZARDOUS
SOLID WASTE THROUGH PYROLYSIS PROCESS
MSPM
hopper
Residual ash
Condensate oil
Condenser
Wet scrubb
er
Dehydration
Unit, Silica gel
Gas pump
O2 cylinder
Clean gas
Gate valve
Pyrolytic gas
Energy recorder
Temperature programmer
O2 flow controller
Gas sampling port
Screw conveyer
Induction Furnace
Oxygen
MSPM
Road
application
materials
Evaporation
of saline
streams
using energy
from solid
waste
Option 2
Management of Spent
Chrome Liquor
[low COD and High TDS]
0
1000
2000
3000
4000
5000
6000
7000
R R - S R - (S + P) R - (S + P +C)
R - (P+C)
5300
6271 5841
4933
3863
R - Raw; S - Soak; P - Pickle; C - Chrome
Sulphate(mg/L) content of wastewater after segregation
Segregation of chrome liquor to reduce sulphate
content in the composite stream and to increase
COD/SO4
Anaerobic digestion is improved by
suppressing SRB and promoting the activity MB
PUMP
collection
TANK
Liquor
Chrome
Recovery of Chromium hydroxide from spent chrome liquor S
pe
nt
ch
rom
e
liq
uo
r MgO
H2SO4
Issues:
Management of supernatant
liquor ( Magnesium sulphate)
in chromium precipitation .
Increases TDS content of
treated wastewater
Retards evaporation rate in
evaporators due to
hygroscopic nature [ hydration
energy is -91.2 kj/mole)
PUMP
AIRBLOWER
PRESSURE
SAND
FILTER
CACCO
REACTOR
AA
EXCESS
AIR
TREATED
MgSO4 solution
For resale AA: AIR AQUA SYSTEM
collection TANK
Liquor
Chrome
MgSO4 + COD
Recovery of Chromium hydroxide and MgSO4 from spent
chrome liquor S
pe
nt
ch
rom
e liq
uo
r
MgO
H2SO4
Textile industry
The bottlenecks in adopting the technology are high cost of operation
for MEE and maintenance of RO membrane module.
Multi effect evaporation is a costly system for concentration of the
effluents before crystallization.
It requires more maintenance in terms of consuming more fuel
The recovered salt has poor purity and market value of salt is also very
less.
When the availability of land has become constraint, the MEE would be
preferable.
A common MEE set-up as joint ventures may be an economical
recommendation.
Proper preliminary treatments should be followed to reduce the
maintenance cost of RO membrane.
CONCLUSIONS The saline streams have to be segregated for the
better management of other streams in biological
treatment .
The saline streams have to be treated for reuse
purpose to overcome the solid waste disposal
issues.
Pyrolysis integrated saline water management
could be a better choice to manage both liquid and
solid wastes