By referring this presentation you can gain knowledge on principles of green chemistry and green remediation for environment.

1. Green Chemistry
in Toxicology
V.Vijitha
Lectrurer (Prob.)
Dept. of Biosystems Technology
FoT, UoJ

2. Green Chemistry in Toxicology
• Objective:
• To eliminate the production of hazardous materials
• To design products and processes at all stages of the chemical
life cycle to reduce their intrinsic hazard
• Green toxicology is a framework for integrating the principles of
toxicology into the enterprise for,
• Designing safer chemicals
• Minimizing potential toxicity as early in production as
possible

3. • Green chemistry is based on a framework of a cohesive set of 12
principles
• These principles helps chemists to achieve the intentional goal of
sustainability

4. 1. Prevent waste
• Design chemical syntheses to prevent waste
• Leave no waste to treat or clean up
2. Maximize atom economy
• Design syntheses so that the final product contains the
maximum proportion of the starting materials
• Waste few or no atoms
• Maximizing the incorporation of material from the
starting materials or reagents into the final product
Principles of Green chemistry

5. 3. Design less hazardous chemical syntheses
• Design syntheses to use and generate substances with little or
no toxicity to either humans or the environment
4. Design safer chemicals and products
• Design chemical products that are fully effective yet have little
or no toxicity
5. Use safer solvents and reaction conditions
• Avoid using solvents, separation agents, or other auxiliary
chemicals
• If you must use these chemicals, use safer ones

6. 6. Increase energy efficiency
• Run chemical reactions at room temperature and pressure
whenever possible
7. Use renewable feedstocks
• Use feedstocks that are renewable rather than depletable
• Source of renewable feedstocks: Agricultural products or the
wastes of other processes
• Source of depletable feedstocks: Fossil fuels (petroleum,
natural gas, or coal) or mining operations

7. 8. Avoid chemical derivatives
• Avoid using blocking or any temporary modifications if possible
• Derivatives use additional reagents and generate waste
9. Use catalysts, not stoichiometric reagents
• Minimize waste by using catalytic reactions
• Catalysts are effective in small amounts and can carry out a single
reaction many times
• They are preferable to stoichiometric reagents, which are used in
excess and carry out a reaction only once

8. 10. Design chemicals and products to degrade after use
• Design chemical products to break down to innocuous substances
after use so that they do not accumulate in the environment
11. Analyse in real time to prevent pollution
• Include in-process, real-time monitoring and control during syntheses
to minimize or eliminate the formation of by products
12. Minimize the potential for accidents
• Design chemicals and their physical forms to minimize the potential
for chemical accidents including
• Explosions
• Fires
• Releases to the environment

9. Phytoremediation

10. • It uses plants to clean up contaminated environments
• Plants can help clean up many types of contaminants
Metals
Pesticides
Explosives
Oil
• They work best where contaminant levels are low.
• Because high concentrations may limit plant growth and
take too long to clean up

11. Classification of phytoremediation
on the basis of mechanisms
1. Rhizosphere biodegradation
2. Phytostabilisation
3. Phytoaccumulation (phytoextraction)
4. Rhizofiltration (Hydroponic systems for treating
water streams)
5. Phytovolatilization
6. Phytodegradation

13. • Rhizosphere biodegradation
Plant secrets natural substances from its roots
These are nutrients needed for growth of micro-organisms
in the soil
The micro-organisms grow speedily and stimulate biological
degradation of contaminants present in soil

14. • Phytostabilisation
Certain plant species are used to immobilise the contaminants in
the soil and groundwater is termed as phytostabilisation
Chemical compounds secreted by the plant immobilise
contaminants, rather than degrade them
It takes place through absorption and accumulation in plant tissues
Adsorption onto roots prohibiting their migration in soil

15. • Phytoaccumulation (Phytoextraction)
It is the process of uptake/absorption and translocation of
contaminants by plant roots into the plant shoots
Plant roots absorb the contaminants along with other
nutrients and water
That can be harvested and metabolised to:
gain energy
recycle the metal from the ash
This process is termed as phytoextraction

16. • The contaminant is not detoxified but stored in the part of
plant such as shoots and leaves
• Plant species selected for their ability to take up large
quantities of Pb are seen to uptake water-soluble metals.
• The plants aerial shoots store the metals.
• Those are harvested and either smelted for potential metal
recovery or are disposed of as a hazardous waste.
• Eg: Cd, Ni, Zn, Ar & Se

17. • Rhizofiltration
The process in which adsorption of contaminants occurs onto
plant roots or absorption and sequestration in the roots is
known as rhizofiltration
Hydroponic systems for treating water streams
Contaminants that are found in solution form encloses in the
root zone by formation of wetland
It is used to cleaning up contaminated wastewater
Roots become soaked with contaminants, they are harvested
and disposed

18. • Phytovolatilization
Def: Release of the contaminant or a modified form of the
contaminant to the atmosphere from the plant during
transpiration is termed as phytovolatilization
Plants uptake water containing organic contaminants
Then release the contaminants into the air through their
leaves as volatile components at comparatively low
concentrations

19. • Phytodegradation
Specific plant species is used for a particular contaminant on the
basis of the degradation capability of plant species.
Plants actually metabolise and deteriorate contaminants within
plant tissues.
The plants absorb hydrocarbons and other complex organic
molecules.
Then metabolize or mineralize them in chemical reactions
energized by sunlight

20. Application of phytoremediation
• It is used to clean up contaminants present in soil and
groundwater
• It is applied for the elimination/treatment of
Metals
Radionuclides
Pesticides
Explosives
Fuels
Volatile Organic Compounds and Semi Volatile Organic Compound

21. Limitations of phytoremediation
• Needs a wide range of land for remediation
• If high concentration of contaminant - plants may die
• The plant’s capacity to reach the depth, determines the
treatment zone
• It is limited to streams and groundwater
• The high contamination of metals in harvested plants can
be a problem during its disposal

22. Wet Lands

23. Definition for Wetland
“Areas of land where the water table is at or near the surface for at least
part of the year and are characterized by the presence of adapted
vegetation types and soil characteristics that have developed in response to
the wet and saturated conditions”
Natural wetlands
• Land areas of transition region between terrestrial and aquatic systems
(eg. Swamps, marshes bogs)
• Wet areas exist in the landscape due to natural processes rather than
created as a result of anthropogenic influences

24. • What are constructed wetlands?
– Man-made/Engineered wetlands artificially created for
treating anthropogenic discharges
– Designed to mimic functions and processes found in natural
wetlands within a more controlled environment to treat and reuse of
wastewater
• Control the direction of flow
• Regulate the water level
• Regulate the retention time

25. • Why constructed wetlands for wastewater treatment?
– Economical
– Efficient (moderate)
– Simple technology
– Low or no energy requirement
– Pleasing environment
– Performances are expected to be high in tropical
environment

26. Advantages and disadvantages
Advantages
– Simple operation and maintenance: Less skilled man-power
requirement
– Tolerance for shock loads (hydraulic and pollutant load)
– Less rigorous pre-treatment requirement
– Flexibility in site location (compared to natural wetlands): Can
be integrated to land spaces
– Ecological values such as green space, wild life habitats,
recreational and educational areas
– Social benefits

27. Disadvantages
– Large land area requirement
– Mosquito and other pest breeding possibility
– Start-up problems
– Variable performance possibilities

28. Compartments of wetlands
• Wetland vegetation
• Bed media/sediment
• Root zone/pore water
– Roots
• Litter/detritus
• Water
• Air
• Micro-organisms growing in biofilms
Treatment is a result of complex interaction between all these compartments
Vegetation
Bed Media
Root zone
Air
detritus

29. Key features of a constructed wetland
• Inlet zone
• Water column
• Bed-media/substrate
• Micro-organisms
• Outlet zones
• Subsurface barrier/liner
• Wetland plants

30. Different groups of macrophytes
Emergent macrophytes (Helophytes) Submerged macrophytes (Hydrophytes)
Floating leaved macrophytes (Pleustophytes) Free floating macrophytes (Pleustophytes)

31. Common Plant Types
Water lily
Phragmites australis
Common Reeds
Iris pseudacor
Yellow flag Iris
Typha latifolia
Cattail
Scirpuss spp
Bulrush.
Lumna spp.
Duck weeds
Commonrus
h
Canna Lily Hydrilla verticillata bladderwort
Carrex spp.
Sedges.
Umbrella Palm
Cyperus
alternifolius
Rooted Emerged
Rooted Emerged
Floating
Submerged

32. Constructed
wetlands
Surface Flow
Sub-surface flow
Vertical flow
Emergent plants
Submerged plants
Floating plants
Horizontal flow
Hybrid wetlands
Upflow/downflow
Floating Wetlands
Types of Constructed wetlands

33. Different substrate types
• Rock media/Gravel
• Sand
• Aggregate
• Crushed limestone
• LWA – Light weight aggregate
• LECA – Light expanded clay aggregate
• Oil-shale ash
• Coir pith

34. Free water surface (FWS) wetland
• Water surface is exposed to the atmosphere
• Water flows over the soil media (depth < 50 cm)
• This is a land intensive system (5 – 10 m2 per PE)

35. Horizontal Sub-Surface Flow (HSSF) CWs
• Water flows below substrate media (medium of sand, gravel, soil
or rock) in horizontal direction.
• Less land area than FWS (3 – 5 m2)

36. Vertical sub-surface flow constructed wetlands
• Water is applied to the surface and flows down through the filter
media
• Water is applied intermittently, hence O2 transferring capability is
high
• VSSF wetlands produce higher treatment
• Amount of land is minimal (2 – 3 m2)

37. Hybrid systems
• Two step constructed wetland consisting a HSSF and a VSSF
system
• Hybrid systems are generally more effective, compromising each
others different removal pathways

38. Pollutant Removal Processes
• Biological
– Microbial
degradation
– Plant uptake
– Natural die off
Physico-chemical
— Adsorption
— Sedimentation
— Filtration
— Volatilization
— Precipitation
• Wetlands remove
– Organics (BOD5 and COD)
– Total suspended solids (TSS)
– Microorganisms (Fecal coliform)
– Nutrients (nitrogen and phosphorus)
– Heavy metals

39. Pollutant removal mechanisms
• BOD removal
– Particulate BOD by settling and filtration, then converted to soluble
BOD by hydrolysis
– Soluble BOD degrade by microbial growth (biofilms on stems,
roots, gravel particles etc)
• Suspended solid removal
– Removal occurs by settling and filtration within few meters near the
inlet
• Pathogen removal
– Adsorption, sedimentation and/or filtration
– Die-off from unfavorable environmental conditions (UV-light, pH
and temperatures)
– Predation by protozoa

40. • Nitrogen removal
– Very complex, due to many forms of nitrogen in wastewater (Org. N,
ammonia and nitrate)
– Main processes
• Volatilization as ammonia (at pH > 9)
• Nitrification/denitrification
• Plant uptake
• Adsorption

41. • Phosphorus removal
– Plant uptake
– Adsorption
– Precipitation with Ca, Al and Fe
• Heavy metal removal
– Precipitation and adsorption
– Plant uptake

42. Operation and Maintenance
• Inlet and outlet structures should clean periodically
• Adjusting water level
• Frequent harvesting of plant material
• Elimination of weeds

43. Basic wetland design considerations
• What kind of water is to be treated?
• What is the pollution level of the influent water?
• How much water is to be treated?
• Daily loads
• What are the water levels?
• GW table, surface water level etc.
• What type of wetland?
• HSSF, VSSF, Hybrid
• What is the media to be?
• Soil, sand, gravel

44. Design calculations
• First order plug flow model (k-c model)
Where,
Ce = Effluent BOD5 (mg/L) Ci = Influent BOD5 (mg/L)
KT = Temperature dependent rate constant (d-1)
t = Hydraulic retention time (d)
T = Temperature of liquid in the system 0 C
K20 = Rate constant at 200 C (for BOD removal – 1.104)
Ɵ = temperature coefficient (for BOD removal – 1.06)
= e -K T t
i
C e
C
(20)
(T )
(T 20)
K = K Ɵ

47. By rearranging

48. AS
AC

49. Cross-sectional area
Where;
KS = Hydraulic conductivity in the medium
S = slope of the bed, or hydraulic gradient (as a fraction or
decimal)

50. If the width of the bed is W
Bed cross sectional area and bed width are independent of
temperature (climate) and organic loading since they are controlled
by the hydraulic characteristics of the media.
Length of the bed

51. Sustainable wastewater treatment

52. THANK YOU