Advanced waste water treatment

Advanced wastewater Treatment - Ion exchange - Reverse Osmosis - Electrodialysis - Adsorption and oxidation. Removal of Nutrients - Constructed wetlands.

1. ADVANCED WASTE WATER TREATMENT By, ANITHA V PhD. Research Scholar Department of Environmental Sciences Bharathiar University, Coimbatore .

2. Steps of Wastewater Treatments Collection of waste water Preliminary Treatment : Physical treatment & clarification of large particles Primary Treatment : Physical treatment & clarification of large particles Secondary Treatment : Biological treatment Tertiary Treatment : Chemical Treatments – Chlorination, Filtration, Ozonization . Sludge Processing: Biological + chemical + Physical Effluent discharge

3. Why We Need Tertiary Treatment To remove TSS and OM. To remove specific organic and inorganic components. To make treated wastewater suitable for reuse, safe discharge. To remove residual nutrients. To remove pathogens. To reduce TDS and meet reuse quality standards.

4. One or more of the unit operation/ process will be used for achieving this tertiary treatment. Nutrient Removal Disinfection Nitrification & Denitrification Ion Exchange Membrane Process Filtration Carbon adsorption Primary Treatment Secondary Treatment Tertiary Wastewater Treatment

5. Ion Exchange Undesirable ionic contaminants are removed from water by exchange with another non-objectionable, or less objectionable ionic substance. A typical example of ion exchange is a process called “water softening” aiming to reduce calcium and magnesium content. It also is used to remove other substances from the water in processes such as dealkalization , deionization,  denitrification , and disinfection. Ion exchange is also efficient in removing toxic metals from water.

6. There are two different groups of ions: Positively charged cations Negatively charged anions

7. Ion exchange process

8. Cationic resins Cation exchangers can be classified as either strong acid cation (SAC) resins or weak acid cation (WAC) resins, both of which are extensively used for demineralization . SAC resins are also commonly used for softening , while WAC resins are used for dealkalization applications. Contaminants removed by cation resins typically include: Calcium (Ca 2+ ) Chromium (Cr 3+  and Cr 6+ ) Iron (Fe 3+ ) Magnesium (Mg 2+ ) Manganese (Mn 2+ ) Radium (Ra 2+ ) Sodium (Na + ) Strontium (Sr 2+ ) Anionic resins Anion exchangers can be classified as either  strong base anion (SBA) resins  or weak base anion (WBA) resins . SBA resins are frequently used for demineralization , while WBA resins are often used for acid absorption . Contaminants removed by anion resins typically include: Arsenic Carbonates (CO 3 ) Chlorides (Cl – ) Cyanide (CN – ) Fluoride Nitrates (NO 3 ) Perchlorate (ClO 4- ) Perfluorooctane sulfonate anion (PFOS) Perfluorooctanoic acid (PFOA) Silica (SiO 2 ) Sulfates (SO 4 ) Uranium

9. Advantages One of the most appropriate technologies to removes dissolved inorganic ions effectively Possibility to regenerate resin Relatively inexpensive initial capital investment Disadvantages Does not remove effectively bacteria High operation costs over long-term The process of regenerating the ion exchange beds dumps salt water into the environment (regeneration)

10. Application Water softening (remove calcium and magnesium ions) Water demineralisation (removal of all ions) De-alkalisation (removal of bicarbonates) Cation exchange resins can also remove: iron, lead, radium, barium, aluminium and copper among others. Anionic exchange units can remove: nitrate, sulfate, and other negatively charged atoms (called anions). Ion exchangers are also used to remove or recover metal ions from wastewater in the chemical industry. Some contaminants (such as arsenic, fluoride, lithium ions) are difficult to remove with ion exchange due to a poor selectivity of the resins.

11. Reverse Osmosis RO is a water purification technology that uses semi permeable membrane It works on the concept of diffusion RO is also known as hyperfiltration RO can remove many types of molecules and ions from solution. M.W greater than 200 is likely to reject.

12. OSMOSIS The solvent naturally moves from an area of low solute concentration to an area of high solute concentration called osmosis Reverse osmosis Reverse osmosis is the process of forcing a solvent from region of high solute concentration through semipermeable membrane to a region of low solute concentration by applying a pressure

13. Use of RO technology Drinking water purification Waste water purification Hydrogen production Maple syrup production in food industry Deionized water Desalination of brackish water Desalination of seawater Production of ultrapure water

14. Removals  Removes Pesticides  Removes salt  Removes microorganisms  Removes suspended solids  Removes dissolved solids  Removes toxic material

15. Advantages E nergy requirements are low. Less space requirement. Fully automated and designed to start-up and shutdown automatically. Thus, RO plants usually require little labour . E asy m aintenance E xpansion an easy option.

16. Disadvantage Hardness not removed Does not remove dissolved gases Removes beneficial healthy minerals too Disposal of Concentrate RO process cannot be applied without pre-treatment Household RO units use a lot of water

17. ELECTRODIALYSIS Electrodialysis is an electrochemical process in which ion transfer separates salt from water. It is effective only for substances that can be ionized E xample, salt (NaCl) becomes, in solution, a mixture of Na +  and Cl −  ions. When electrodes, connected to a suitable direct current supply, are immersed in a salt solution, current will flow, carried by the ions.

18. The ions with a positive charge are attracted towards the negative cathode and are called cations . Negatively charged anions flow towards the positive anode. In electrodialysis, filters or membranes selectively impervious to cations or anions are placed alternately between the electrodes. Cation filters permit the flow of anions but act as a barrier to positively charged cations. Conversely, anions are held back by the anion filter while cations pass through.

19. In certain compartments of the tank, ions will collect as their flow is checked by an appropriate filter. Cells of increasing salt concentration thus alternate with cells of salt depletion. Water that is sufficiently desalinated is extracted from the appropriate compartments. Electrodialysis is only generally used with brackish waters as it is uneconomic for sea water desalination. It is used together with ion exchange and activated carbon to produce ultra-pure water for the electronics and pharmaceutical industries.

20. Advantages No phase change, which results in relatively low energy consumption. Needs only limited pre-treatment. Separating non-ionised from ionised components. Osmotic pressure is not a factor in ED system, so the pressure can be used for concentrating salt solutions to 20% or higher .

21. Disadvantage Organic matter, colloids and SiO2 are not removed. P re-treatment is necessary to prevent ED stacks fouling. C ontrols are required for optimum condition. Selection of membranes materials must be compatibility with the feed stream.

22. Applications Desalination of water Small and medium scale drinking water production. Stabilize wine Food and beverage industries Glycerin purification Glycol desalting

23. DISTILLATION Distillation is the process of converting liquid into its vapours by heating and reconverting it again into liquid by condensing the vapours. It is method of separating substances which differ in their vapour pressures. The distillation process is carried out in an apparatus which consists of (a) Still, in which volatile material is boiled. (b) Condenser, in which vapours are condensed. (c) Receiver, in which distillate is collected.

24. TYPES OF DISTILLATION PROCESSES The following are the various types of distillations: 1. Simple distillation 2. Distillation under reduced pressure 3. Fractional distillation 4. Steam distillation 5 . Destructive distillation

25. Advantages of Distillation It is an efficient method of water softening for smaller purposes. It is relatively cheap. It can also be reused. Disadvantages of Distillation Some of the unwanted elements may be found in the distilled water. Unfortunately, liquids such as herbicides which have a boiling point of 100% which is equal to that of water will tend to condense with water and therefore, separation of this two can be tough. As a process of water softening, distillation requires a keen eye, so that unwanted elements do not mix with water. When distillation is done on a larger scale, a very high amount of energy needed. The distilled water does not contain any oxygen and is also very tasteless. It has very high levels of acidity.

26. ADSORPTION Adsorption can be defined as a process in which atoms or molecules move from a bulk phase ( ie solid, liquid or gas ) onto a solid or liquid surface.  In other words, it is adhesion of atoms, ions or molecules from a gas liquid or dissolved solid to a surface.  Adsorbate – The substance which is adsorbed on the surface.  Adsorbent – The substance on which surface the adsorbate is adsorbed.  Adsorption is a surface phenomenon & consequence of surface energy

27. TYPES OF ADSORPTION Types of Adsorption Characteristics Physical Adsorption (Physisorption) Unselective. Low energy of adsorption. Associative Chemical Adsorption(Chemisorption) Selective ,strongly dependent on both gas & solid surface. Higher energies of adsorption than those of physisorption Dissociative Chemical Adsorption(Chemisorption) Selective, strongly dependent on both gas & solid surface. Higher energies of adsorption than those of physisorption.

28. Factors Affecting Adsorption  Temperature  Pressure  Surface Area  Activation Of Solid Adsorbent  Agitation  pH  Characteristics Of Adsorbent  Dose Of Adsorbate & Adsorbent

29. LIST OF COMMERCIAL ADSORBENTS  Activated Carbon  Silica Gel  Activated Alumina  Synthetic Zeolite  Clay  Polymers & Resins

30. APPLICATIONS OF ADSORPTION  Effective in heterogeneous catalysis.  Effective in removing coloring material.  Effective as ion exchange resins.  Used as adsorption indicators.  Used in gas masks.  Used in dyeing of cloth.  Used as de- humidizers .

31. Advantages High performance Low cost Wide pH range Easy operation Disadvantages W aste product Weak selectivity

32. Oxidation Ultimate aim is to mineralize convert constituents of an organic pollutant into simple, harmless and inorganic molecules Carbon to carbon dioxide Hydrogen to water Phosphorus to phosphates or phosphoric acids Sulfur to sulfates Nitrogen to nitrates Halogens to halogen acids

33. Adavnced Oxidation Processes Ozone based Fenton Photochemical Oxidation Processes UV Photolysis H2O2/UV Ozone/UV TiO2 Photocatalysis PhotoFenton

34. Classical Oxidants Oxygen: moderate oxidant with small solubility in water that needs high investments in installations, but its low operation costs may do the process attractive. Chlorine: strong oxidant and cheap. Possibility of producing chlorinated organic compounds, more toxic than the initial ones. It has good enough solubility in water. Permanganate: strong enough oxidant, but expensive. It is selective, no easy to handle and not desirable manganese is added to the treated water. Hydrogen peroxide: multipurpose oxidant soluble in water that could be applied directly or with a catalyst (without it some organic compounds are not attacked). Ozone: strong oxidant that as oxygen and hydrogen peroxide does not introduce new ions to the medium. It is more soluble in water than oxygen. Its difficult handling. Necessary to generate it on-site. Process, normally, is controlled by mass transfer.

35. REMOVAL OF NUTRIENTS

36. Removal of Nitrogen  PHYSICAL METHODS Electrodialysis Re verse osmosis  CHEMICAL METHODS Ammonium precipitation as struvite Carbon sorption Breakpoint chlorination Ion exchange Oxidation

37.  PHYSICOCHEMICAL METHOD Ammonia stripping  BIOLOGICAL METHODS Nitrification – Denitrification Nitrogen Removal Via Sulphate Oxidising Bacteria IFAS (Integrated Fixed Film And Activated Sludge System)

38. Ammonia removal Air stripping Biological nitrification and denitrification

39. Phosphorus Removal A) Physical Filtration For Particulate Phosphorus Membrane Technologies B) Chemical Precipitation C) Biological Enhanced Biological Phosphorus Removal (EBPR)

40. Biological Nutrient Removal ( BNR ) is a process used to remove nitrogen and phosphorus using micro-organisms. BNR Process Biological Nitrogen Removal Biological Phosphorous Removal

41. BIOLOGICAL PHOSPHOURUS REMOVAL The treatment process can be designed to promote the growth of PAOs. PAOs convert available organic matter to PHAs. PAOs - Polyphosphate –accumulate organisms – are a group of bacteria that, under certain conditions, facilitate the removal of large amounts of phosphorous from wastewater in a process, PHAs - Polyhydroxyalkanoates – are linear polyesters produced in nature by bacterial fermentation of sugar or lipids.

42. Integrated Fixed Film Activated Sludge Process(IFAS) Combines fixed film technology with conventional activated sludge. Immerse a solid support media into an aeration basin. Media can be fixed or floating. Textile mesh material, floating sponges or plastic media. Provides surface area for biological growth to attach. Creates additional biomass. Provides additional biological activity. Increases solids settling. Increases waste water treatment facilities.

43. Sequential Batch Reactor Process(SBR) Continuous flow system. Primarily for nitrogen removal. Flexible, inexpensive and efficient. Operational cost is high. Three phases Fill phase React phase Settle phase

44. Step Feed Process Continuous flow process. Influent flow is split to several feed locations. Recycle sludge stream is sent to the beginning. Higher solids retention time is achieved providing enhanced treatment. Phosphorus removal is limited

45. Moving Bed Biofilm Reactor Process (MBBR) Direct derivative of fixed film activated sludge process. Provide sites for bacteria attachment. Allows higher concentration of active biomass. More treatment capacity. Phosphorus removal requires additional stages.

46. Conclusion of BNR BNR is an established technology. Implementation and operation is a challenge. Complex and high cost. Requires trained design engineers and operators. BNR process modelling is a useful tool for design and operation of WWTPs

47. Wetland ■ A wetland is a land area that is saturated with water, either permanently or seasonally , such that it takes on the characteristics of a distinct ecosystem. ■ The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique hydric soil. WETLAND FUNCTIONS AND VALUES CONSTRUCTED WETLANDS Small artificial WWTS One or more shallow treatment cells More suitable for warmer climates COMPONENTS OF CONSTRUCTED WETLANDS

48. SUBSURFACE FLOW WETLAND

49. SURFACE FLOW WETLAND

50. Horizontal Flow Constructed Wetland