Zero liquid discharge

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 m 3 per year in 2011 to 1341 m 3 per year in 2025. 2

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 m 3 / 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. 3

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. 4

5. Zero Liquid Discharge 5

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. 6

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. 7

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. 8

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. 9

10. AIR/STEAM STRIPPER 10 Source: 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. 11

12. MBR 12 Source: SUEZ water technologies and solutions

13. External membranes submerged membranes 13 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. 14 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. 16 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 evaporator 17 Source: ZLD Technology Guidance Manual (GPCB)

18. Forced recirculation Used for processing liquors which are susceptible to scaling and crystallizing. 18 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 recirculation 19 Source: 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. 20 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 recirculation 21 Source: ZLD Technology Guidance Manual (GPCB)

22. Plate type evaporator Provide flexible capacity by adding more plate units. Offers full accessibility to heat transfer surfaces. 22 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 evaporator 23 Source: ZLD Technology Guidance Manual (GPCB)

24. Evaporation technologies 24 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 , Na 2 SO 4 , NH 4 Cl, 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. 25

26. Single effect evaporator 26 Source: nptel.ac.in

27. multiple effect evaporator 27 Source: nptel.ac.in

28. Forward feed multiple effect evaporator 28 Source: nptel.ac.in

29. backward feed multiple effect evaporator 29 Source: nptel.ac.in

30. mixed feed multiple effect evaporator 30 Source: nptel.ac.in

31. parallel feed multiple effect evaporator 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. 32

33. Mechanical vapour re-compressor 33 Source: 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. 34 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. 35

36. Agitated thin film dryer 36 Source: 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. 37 Agitated thin film dryer

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