Zero liquid discharge history, why required, how to achieve?

1. ZERO LIQUID
DISCHARGE
Guided By
Dr. Mrs Anjali K. Khambete
Associate Professor,
Department of Civil Engineering.
SARDAR VALLABHBHAI NATIONAL INSTITUTE OF
TECHNOLOGY
Presented By
Tulsi Makwana
P17EN011
M-Tech (Environmental
Engineering)

2. INTRODUCTION
 Water scarcity is going to be a major issue for industries in coming days. With
continuous increase in water demand the only option would be to conserve
treat and reuse the water to a extent possible. ‘Zero Liquid Discharge (ZLD)’
is one strategy to address this challenge.
 India with a growing population and rising water consumption is going to face
water stress. Per capita availability of water is likely to go down from 1545 m3
per year in 2011 to 1341 m3 per year in 2025.
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3. HISTORY
 ZLD was initially developed for power plants in USA and later was
implemented globally. In a early 70’s, increased salinity of the Colorado river,
created the need to impose ZLD.
 First ZLD installed was of 114-454 m3 / hour, based on evaporation /
crystallization.
 Worldwide construction of ZLD plants represent an average of 200 million
USD of investment annually.
 Countries like India, China, where water is scarce and industrial water
recovery ratio is vey low, are potential candidates of development of ZLD
solutions.
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4. ZERO LIQUID DISCHARGE
 Zero Liquid Discharge (ZLD) refers to the recycling and treatment process in
which the plant discharges no liquid effluent into surface waters, completely
eliminating the environmental pollution to water bodies.
 Zero Liquid Discharge refers to installation of facilities and system which
enables industrial effluent for absolute recycling of permeate and converting
solute into residue in the solid form by adopting method of concentration and
thermal evaporation. (CPCB Draft Guidelines, January, 2015.)
 ZLD process makes effective use of wastewater treatment, recycling, and
reuse, thereby contributing to water conservation through reduced intake of
fresh water.
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5. ZERO LIQUID DISCHARGE
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6. DRIVERS OF ZLD
 Stringent environment regulations on discharge of specific pollutants.
 Water scarcity in the area.
 Economics.
 Recovery of useful materials.
 Growing social responsibilities towards environmental issues.
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7. CHALLENGES FOR ZLD
 Technical guidance not available.
 Technology selection is big challenge.
 Difficulty in dealing with very complex streams.
 Need of integration of suitable technologies to achieve reduce, recycle,
recovery and reuse.
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8. ZLD TECHNOLOGIES
 Main aim of ZLD is to recover useful products, and salts from rejects, apart
from recovery of maximum water for recycle.
 Major ZLD Technologies:
• Solvent extraction / Stripper.
• Membrane Bio-Reactor Technology (MBR).
• Ultra filtration / Reverse Osmosis.
• Evaporation Technologies
• Agitated Thin Film Dryer (ATFD).
• Incinerator.
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9. SOLVENT EXTRACTION
 Objective is to either recovery of solvent or removal of solvents from
wastewater for easy treatment and disposal.
 Carried out by two methods :
• Air stripping.
• Steam stripping.
 Factors contributing to the economics in ZLD process:
• Treated water reuse / recycle potential.
• Value of recovered solvent.
• Treatment cost.
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10. AIR/STEAM
STRIPPER
10Source: ZLD Technology Guidance Manual (GPCB)

11. MEMBRANE BIO-REACTOR
 Vital resource for the treatment and reuse of Municipal water and wastewater.
 Process where microfiltration and ultrafiltration is used.
 MBR consists of combination of membrane a biological reactor systems.
 An aerobic biological system where air is provided through diffuser
membranes for growth of biomass.
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12. MBR
12Source: SUEZ water technologies and solutions

13. EXTERNAL
MEMBRANE
S
SUBMERGE
D
MEMBRANE13
Source: ZLD Technology Guidance Manual (GPCB)

14. Advantages
 Secondary clarifier no required.
 Small footprint.
 Post treatment can be eliminated.
 High loading rate capabilities.
 Combined solids, COD and nutrient
removal.
 Low sludge production.
 Bulking or rising sludge is not a
problem.
 Disinfection takes place.
Disadvantages
 Energy consumption is 2-3 times the
conventional treatment.
 Membrane costs are very high.
 Operational problems due to
membrane complexity and fouling.
 Pre-treatment.
 High maintenance cost due to high
replacement costs.
 Aeration limitations.
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MEMBRANE BIO-REACTOR

15. EVAPORATION
TECHNOLOGIES
 Rejects from previous treatments is treated by evaporation and crystallization.
 During these processes, the condensate is recovered while contaminated
elements are separated as solids with some moisture in it.
 The effluent is salty solution and thermal separation is the final step of ZLD.
 Most commonly used technique for reduction of waste volume, recovery of
salts and to recycle the condensate.
 Types:
• Falling Film
• Forced Circulation
• Natural Circulation
• Plate type 15

16. FALLING FILM
EVAPORATOR
 Requires only very low temperatures.
 Can be used as a pre-concentrator in a combined multi-effect plant.
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Advantages
 Low power requirement.
 Low pressure drop.
 High heat transfer rate.
 Less capital cost.
 Fast start up and shut down.
Disadvantages
 Very sensitive to saturation of ions
present.
 Frequent scaling in case of effluent
and crystalline product.
 More down time.
 Higher cleaning frequency.

17. FALLING
FILM
EVAPORAT
OR
17Source: ZLD Technology Guidance Manual (GPCB)

18. FORCED RECIRCULATION
 Used for processing liquors which are susceptible to scaling and crystallizing.
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Advantages
 Can handle slurry.
 Very less fouling.
 Minimum down time.
 Very high heat transfer rate.
 Extended cleaning cycle.
 Most rugged kind of evaporator.
Disadvantages
 High power requirement.
 Higher capital cost.

19. FORCED
RECIRCUL
ATION
19Source: ZLD Technology Guidance Manual (GPCB)

20. NATURAL RECIRCULATION
 Larger evaporation capacities can be obtained.
 Most common application is as a re-boiler at the base of distillation column.
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Advantages
 Minimum power cost.
 Easy operation.
 Can handle viscous material.
Disadvantages
 Very sensitive to saturation of ions.
 Frequent scaling in case of effluents
and crystalline products.
 Higher cleaning frequency.
 Low heat transfer coefficients.
 Higher capital cost.

21. NATURAL
RECIRCUL
ATION
21Source: ZLD Technology Guidance Manual (GPCB)

22. PLATE TYPE EVAPORATOR
 Provide flexible capacity by adding more plate units.
 Offers full accessibility to heat transfer surfaces.
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Advantages
 Less pressure drop.
 High heat transfer.
 Less height required.
 Compact construction.
 Less capital cost.
 Physical cleaning is easy.
Disadvantages
 Gaskets required to replace
periodically.
 Not suitable for slurry and crystalline
products.

23. PLATE
TYPE
EVAPORAT
OR
23Source: ZLD Technology Guidance Manual (GPCB)

24. EVAPORATION
TECHNOLOGIES
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Technology Application
Falling film • Suitable for clear liquors, feeds with low hardness and non-
crystalline concentrates with low viscosities.
• Useful for concentrating milk, juices if hardness < 150 ppm.
Forced
circulation
• Suitable for that containing high hardness levels, silica, suspended
solids and crystalline slurries.
• Salt recoveries like NaCl, Na2SO4, NH4Cl, KCl, etc.
Natural
circulation
• Suitable for concentrations of viscous liquids below saturation
without hardness.
• Solid slurry with high hardness.
• Liquid where solids will settle down.
Plate type • Application is same as forced circulation and falling film designs.
• Used for low level installations.

25. MULTIPLE EFFECT
EVAPORATOR
 An evaporator system in which the vapour from one effect is used as a heating
medium for a subsequent effect boiling at a lower pressure.
 The evaporator denotes the entire system of effects not necessarily one body or
effect.
 Considered as number of effects in series, to the flow of heat.
 The driving force of heat is the temperature difference between the steam
condensing in the first effect and the temperature of the heat sink.
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26. SINGLE
EFFECT
EVAPORAT
OR
26
Source: nptel.ac.in

27. MULTIPLE
EFFECT
EVAPORAT
OR
27
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28. FORWARD
FEED
MULTIPLE
EFFECT
EVAPORATO
R
28
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29. BACKWARD
FEED
MULTIPLE
EFFECT
EVAPORATO
R
29
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30. MIXED
FEED
MULTIPLE
EFFECT
EVAPORATO
R
30
Source: nptel.ac.in

31. PARALLEL
FEED
MULTIPLE
EFFECT
EVAPORATO
R
31
Source: nptel.ac.in

32. MECHANICAL VAPOUR RE-
COMPRESSOR
 Has been used for over 100 years.
 Significantly reduce energy required for evaporation.
 Water vapour generated in the evaporator is compressed to high pressure.
 Compressed vapour acts as a heat source for evaporation.
 Similar to a conventional single effect, except that the vapour released from the
boiling solution is compressed in a mechanical compressor. The compressor
adds energy to the vapour to raise the saturation temperature of the vapour
above the boiling temperature of the solution.
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33. MECHANICAL
VAPOUR RE-
COMPRESSOR
33Source: ZLD technology guidance manual (GPCB)

34. Advantages
 Steam and overall energy
consumption reduces.
 Lower operational cost.
 Reduction in cooling water quantity.
 Higher condensate temperatures
provide additional steam savings.
Limitations
 Very high capital costs.
 Alone cannot be used for all streams
due to its limitation of temperature
difference.
 Energy consumption is more in
compressor.
 Not suitable when steam is readily
available.
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MECHANICAL VAPOUR RE-
COMPRESSOR

35. AGITATED THIN FILM
DRYER
 Used for drying solutions with high TDS water or recovery of products.
 Outcome is in the form of powder having moisture content of 10–15 %.
 Ideal apparatus for continuous processing of concentrated material to dry
solids.
 The system evaporates the solution by thin layer formation on the surface.
 ATFD is evaporation of water / solvents to make concentrated liquid to dry
powder or flakes.
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36. AGITATED
THIN
FILM DRYER
36Source: nptel.ac.in

37. Advantages
 Good heat transfer.
 Can work for highly viscous products.
 Low operating cost.
 Continuous mechanical cleaning of heating surface.
 High evaporation rates.
 Reduced need for maintenance.
 No recirculation.
 High flexibility for variation in requirements.
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AGITATED THIN FILM
DRYER

38. 38
The city of Cape Town was warned!
(9th July.)