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CHEMICAL TREATMENT PROCESSES

ERT 417/4 WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011). CHEMICAL TREATMENT PROCESSES. By; Mors Hafiza Binti Shukor. At the end of these topic, students should be able to acquire these ability:.

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CHEMICAL TREATMENT PROCESSES

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  1. ERT 417/4 WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011) CHEMICAL TREATMENT PROCESSES By; Mors Hafiza Binti Shukor

  2. At the end of these topic, students should be able to acquire these ability: • INTERPRET, COMPARE, JUSTIFY and CHOOSE the chemical treatment methods for waste treatment in industries. • CALCULATE and DESIGN the basic structure of waste treatment unit operations By; Mrs Hafiza Binti Shukor

  3. Chemical methods of wastewater treatment take advantage of two types of properties: (1)the chemical characteristics of the pollutants, regarding their tendency to react with, or interact with, treatment chemicals; (2)the chemical characteristics of the products of reaction between pollutants and treatment chemicals, regarding their solubilities, volatilities, or other properties that relate to the inability of the product to remain in water solution or suspension. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  4. Role of Chemical Unit Processes in Wastewater Treatment • The principle chemical unit processes used for ww treatment include: • Chemical coagulation • Chemical precipitation • Chemical disinfection • Chemical oxidation • Advanced oxidation processes • Ion Exchange • Chemical neutralization, scale control and stabilization ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  5. In general, six chemical processes can be taken advantage of to remove substances from wastewater: 1. Reaction to produce an insoluble solid 2. Reaction to produce an insoluble gas 3. Reduction of surface charge to produce coagulation of a colloidal suspension 4. Reaction to produce a biologically degradable substance from a nonbiodegradable substance 5. Reaction to destroy or otherwise deactivate a chelating agent 6. Oxidation or reduction to produce a Non objectionable substance or a substance that can be removed more easily by one of the methods listed above ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  6. 1) NEUTRALIZATION @ pH ADJUSTMENT Neutralization – the removal of excess acidity or alkalinity with a chemical of opposite site composition. Chemical Stabilization is often required for highly treated wastewaters to control the aggressiveness with respect to corrosion. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  7. Chemicals used most commonly for the control of pH (neutralization) Adapted from Eckenfelder,2000 ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  8. 2)CHEMICAL COAGULATION & FLOCCULATION Coagulation? • Employ ofremoval of waste materials in suspended @ colloidal form. • Is destabilization of colloids. • (particles are essentially coated with a chemically sticky layer that allows them to flocculate @ agglomerate and settle in a reasonable period of time). ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  9. Coagulant? • Chemical that is added to destabilize the colloidal particles in ww so that floc formation can result. Flocculent? • Chemical typically organics, that is added to enhance the flocculation process. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  10. Flocculation? • Term used to describe the process whereby the size of particles increases as a result of particle collisions. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  11. When coagulants such as Al2(SO4)3 are added to the water supply, they form solid precipitates (green) • Theseprecipitates catch other impurities (red)in the water, forming a solid mass containing the precipitate formed by coagulation and the trapped impurities. • This mass will settle to the bottom by sedimentation, and the water (with the trapped impurities now removed) can be drained off of the top. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  12. Colloids? • Are presented by particle over a size range of 1nm to 0.1 nm (do not settle on standing & cannot removed by conventional physical treatment process) • Colloids in WW can be either: • HYDROPHOBIC (eg. Clay) • No affinity for the liquid medium • Lack stability in the present of electrolytes and thus, readily susceptible to coagulation. • HYDROPHILLIC (eg. Protein) • Affinity for water • The absorbed water retards flocculation and frequently required special treatment to achieve coagulation • Colloids posses electrical properties which create a REPELLING FORCE and PREVENT agglomeration and settling ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  13. As a coagulant (+ve) dissolved, the cation serves to neutralize the negative charge of the colloids. • This occur before visible floc formation • Rapid mixing which “COATS” the colloid is effective in the phase. • Micro flocs are then formed which retain a positive charge in the acid range because of the ADSORPTION of H+. • This micro flocs serve to neutralize and coat the colloidal particles. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  14. MECHANISM OF COAGULATION • Coagulation results from 2 basic mechanism: • PERIKINETIC @ ELECTROKINETIC COAGULATION • In which the repulsive force between the particles is reduced by ions @ colloids of apposite charge to level below the Van Der Waals attractive force. Aggregation of particles in the size range from 0.01 to 1µm. • ORTHOKINETICS COAGULATIONS the micelles aggregate & form clumps which agglomerate the colloidal particles. ERT 417/3WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2009/2010)

  15. CHEMICAL COAGULANTS • A coagulant has 3 key properties; • TRIVALENT CATIONS (eg. Al3+ or Fe 3+) • naturally occurring colloids are most commonly –ve charge hence cation are required to achieve charge neutralization. • more effective than monovalent (eg. Na+) or @divalent simple cation (eg. Ca2+) • NON TOXIC • especially for the production of portable water • INSOLUBLE IN NEUTRAL pH RANGE • increase concentration of the coagulant in treated water is undesirable. • therefore, the coagulant is usually relatively insoluble at pH value desired. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  16. Coagulant Agent a) ALUMINUM SULFATE (ALUM) • The most popular coagulant in ww treatment application. • Commercial alum has an average molecular weight of 594, which approximately14 water of hydartion. • Alum reacts with; • Alkalinity • Acidity • The optimal pH range for alum is 5.5 to 6.5 • The aluminum hydroxide is actually in the chemical form of Al203.xH2O and amphotheric (can react acid @ base) • The floc charge is +ve (below pH 7.6) and –ve (above pH8.2). • Between this limit, the floc charges are mixed. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  17. b) FERRIC SALTS • Ferric salts have the disadvantages of being more difficult to handle. • A insoluble hydrous ferric oxide is produce over pH range of 3.0-13.0 • The floc charge is positive in the acid range and negative in alkaline range with mixed charged over the pH range 6.5-8.0 • Ferric cations can be supplied by adding either ferric sulfate (Fe2 (SO4)3.H2O) or ferric chloride (FeCl3.7H2O) • The reaction of ferric chloride in the presence of alkalinity is, • FeCl3.7H2O + 3HCO3- -------Fe(OH)3(s) +3CO2 +3 Cl- +7H2O • And without alkalinity, • FeCl3 + 3H2O ---------Fe(OH)3 (s) + 3H+ + Cl- ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  18. If the alkalinity is insufficient, the addition of ferric chloride results in the release of 3 moles of H+ for every mol of ferric chloride to lower the pH of the solution • Ferric salts generally have wider pH range for effective coagulation than aluminum (eg; pH range from 4 to 9) c) OTHER COAGULANTS • Lime (Ca(OH)2) is not a true coagulant. (but calcium with bicarbonate alkalinity to precipitate calcium carbonate at high pH level) • Lime sludge can frequently be thickened, dewatered and calcined to convert calcium carbonate to lime for reuse. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  19. d) COAGULANT AIDS • The addition of some chemicals will enhance coagulation by promoting the growth of large settling sludge. • Activated silica • is a short chain polymer that serves to bind together particles of microfine aluminum hydrate. • At high dosage, silica will inhibit floc formation because of its electronegative properties. • The usual dosage is 5-10mg/L. • . ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  20. Polyelectrolyte • are high molecular weight polymers which contain absorbable groups and form ridges between particles or charged flocs • Large flocs (0.3-1.0mm) are created when small dosages of polyelectrolyte (1mg/L) are added in conjunction with alum or FeCl3 • is uneffecting by pH and can serve as a coagulant itself by reducing the effective charge of the colloid. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  21. There are 3 types of polyelectrolyte; • CATIONIC Which adsorbed on a negative colloid or floc particles • ANIONIC Which replaces the anionic group on a colloidal particle and permit hydrogen bonding between the colloid and polymer • NON ANIONIC Which adsorbs and flocculates by hydrogen bonding between the solid surfaces and the polar groups in the polymer ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  22. COAGULANT EQUIPMENT 2 basic types of equipment adaptable to coagulant and flocculant of industrial WW. 1) CONVENTIONAL SYSTEM Uses rapid mixed-tank followed by a flocculation tank 2) AN UPFLOW SOLID CONTACT UNIT Known as a Sludge Blanket Unit combines MIXING, FLOCCULATION and SETTLING in a single unit. The influent raw water and chemical are added in the centre cone. As the water flow upward, the solid settle to form a sludge blanket that can provide further oppurtinity to drive the precipitation to completion Main advantage – reduce size ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  23. AN UPFLOW SOLID CONTACT UNIT ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  24. 3)ION EXCHANGE • Objectives; • Used for the removal of undesirable anion and cations • Cation are exchanged for hydrogen or sodium (H+ or Na+) • Anions are exchanged for hydroxyl ions ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  25. ION EXCHANGE RESINS • – consist of an organic or inorganic network structure with attached functional groups • - made by POLYMERIZATION of organic compounds into porous 3D structure • -increase cross linking between organic chains gives smaller pore sizes. • -the functional ionic group usually introduced by reacting the polymeric metric with a chemical compound containing the desired group. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  26. Resins • their exchange capacity is determined by the number of functional groups per unit mass of resin. • cationic resin ----if they exchange +ve ions (acidic functional group) • (eg. Sulfonic) • anionic resin ------if they exchange –ve ions (basic functional group) • (eg. Amine) • the strength of the acidic @ basic character depends on the degree of ionization of the fuctional group ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  27. ION EXCHANGE REACTIONS • The reaction depends upon chemical equilibrium situations in which one ion will selectively replace another on the ionized exchange site. • Cation exchange on the sodium cycle can be given as • Na2.R + Ca2+ Ca.R + 2Na+ (R=resin) ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  28. When all the exchange sites have been replaced with calcium, the resin can be regenerated by passing a concentrated solution of sodium ions through the bed. This reverses equilibrium, • 2Na+ + Ca.R Na2.R + Ca2+ • Similar reactions occur for ‘CATION EXCHANGE” on hydrogen cycle • Ca2+ + H2.R Ca.R + 2H+ • Regeneration with 2-10% H2SO4 • Ca.R + 2H+ ----------------H2R + Ca+ (R=resin) ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  29. Anion exchange replaces anion with hydroxyl ions • SO42- + R.(OH)2 R.SO4 + 2OH- • Regeneration with 5-10% NaOH • R.SO4+ 2OH- R.(OH)2+ SO42- ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  30. The capacity of Ion Exchange Bed usually expressed as equivalents perliter of bed volume. • Resin Utilization is defined as the ratio of the quantity of ions removed during treatment to the total quantity of ions that could be removed at 10% efficiency. • The regeneration efficiency is the quantity of ions removed from the resin compared to the quantity of ions present in the volume of regenerate used. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  31. ION EXCHANGE OPERATION UNIT • It involves a sequence of operating steps. • The ww is passed through the resin until the available exchange sites are filled and the contaminants appear in the effluent. • This stage is defined as the breakthrough and the treatment is stopped and the bed is washed to remove dirt and to regenerate the resin. • The bed is then regenerated and rinsed with water to wash out residual regenerant. Effluent conc. No regeneration breakthrough Regeneration Volume of waste treated Ion removal

  32. Example : Ion Exchange An industrial ww ion exchange unit has a resin volume of 0.1m3 and need to process 1600 L/day of ww. The influent contains 340mg/L of hardness as CaCO3 and it is desirable to soften it to achieve a total hardness of 100mg/L as CaCO3. What should the bypass flowrate be? Ans: 470.6L/day ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  33. 4)ADSORPTION • Objectives: • Process of collecting soluble substances that are in solution on a suitable interface (liq phase transfer to solid phase). • Chemical adsorption • results from molecular condensation in the capillaries of the solid. • In general, substance of low molecular weight are more easily adsorbed. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  34. TERMS IN ADSORPTION PROCESS ADSORBATE Substance that is being removed from the liquid phase at the interface ADSORBENT Solid, liquid, or gas onto which adsorbate accumulate ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  35. ACTIVATED CARBON IN WASTEWATER TREATMENT • Is polishing process for water that has receive Normal Biological Treatment. • Carbon is used to removed a portion of the remaining dissolved organic matter. • The overall rate of adsorption is controlled by ‘the rate of diffusion’ of solute molecules within the square of the particle diameter • ----increase with increasing temperature, concentration of solute • ---decreases with increasing MW of solute. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  36. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  37. ACTIVATED CARBON (AC) • Produced by 1st making a char from materials such as coconut and wall nut hulls, wood and coal. • The ‘char’ • – produced by heating (<700oC) the materials to a red heat to drive off the hydrocarbon but with insufficient supply of air to sustain the combustion. • - Char particle is then activated by exposure to an oxidizing gas at high temperature(800-900oC) (the gas develops a porous structure in the char and thus creates a large internal surface area) • After certain amount of time for contact, the AC is allowed to settle to the bottom of the tank. • A coagulant such as polyelectrolyte may be needed to aid the removal of the carbon particle. • Carbon regeneration is done once the adsorption capacity has been reached.(rate of adsorption=rate of desorption) ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  38. before Activated (making pore) after Figure 2; sketch of activated carbon before and after activation ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  39. 2 size classification of AC are; • GRANULAR AC (GAC) • diameter >0.1mm • a fixed column is often used • the water is applied to the top of the column • regeneration in a furnace by oxidizing the organic matter • POWDERED AC (PAC) • diameter <200mesh • is added to the effluent from biological treatment process • or directly to the various biological treatment processes or • in physical-chemical treatment processes. • methodology for regeneration is not well defined. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  40. ANALYSIS OF THE ADSORPTION PROCESS • Freundlich and Langmuir isotherm are most commonly used to describe the adsorption characteristics of the AC in WW treatment. Equilibrium concentration of adsorbate in solution after adsorption A) Freundlich Isotherm Amount of adsorbate per unit wt. of AC Empirical constant • The constant in Freundlich isotherm can be determined by plotting (x/m) vs C and making the equation as; ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  41. B) Langmuir Isotherm Empirical constant Equilibrium concentration of adsorbate in solution after adsorption Amount of adsorbate per unit wt. of adsorbent (AC) • Langmuir isotherm assumes that; • A fixed number of accessible sites are available on the AC, all of which have the same energy. • Adsorption is reversible. Equilibrium is reached when the rate of adsorption is the same as the rate of desorption from the surface. • The constant in the Langmuir isotherm can be determined by plotting C/(x/m) vs Ce ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  42. BREAKTHROUGH ADSORPTION CAPACITY • The fixed breakthrough adsorption capacity, (x/m)bof the GAC is some % of the theoretical adsorption capacity found from the isotherm. • The (x/m)b of a single column is approximately 25-50% of the theoretical capacity (x/m)o. • Once (x/m)b is known, the time to breakthrough can be calculated by solving the equation for tb. Influent organic concentration (mg/L) Mass of organic material adsorbed in GAC column at breakthrough(g) Time to breakthrough (d) Equation 1 breakthrough organic concentration (mg/L) Mass of carbon in the column Flow rate ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  43. Equation 1 was developed assuming that Ci is constant and that the effluent concentration increase linearly with time from 0 to Cb • Rearranging equation 1, tb can be calculated; ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  44. Example : Adsorption (a) Determine the Freundlich and Langmuir isotherm coefficients for the following GAC adsorption test data. The liquid volume used in the batch adsorption test was 1L. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  45. Example : Adsorption (b) Determine the breakthrough time for the GAC filter column when operated at a filtration rate of 0.203 m3/m2.min. Assume that the surface area of the filter column is 0.929 m2, the depth of filter is 1.524m. The influent TOC concentration is 3.25mg/L and the breakthrough TOC conc has been set at 0.75mg/L. The density of the GAC to be used in the filter column is 604kg/m3. Given that, ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  46. 5)CHEMICAL OXIDATION • Objectives; • Reduction of BOD and COD • The oxidation of ammonia and non- biodegradable organic compound, Chemical oxidation in ww treatment typically involves the use of oxidizing agent such as ozone,hydrogen peroxide, permanganate, chloride dioxide, chlorine or oxygen to bring about change in the chemical composition of a compound or a group of compounds. ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  47. a) Chemical oxidation of BOD and COD Cl2, O3, H2O2 Cl, O3, H2O2 Intermediate oxygenated molecules Simple end product (eg. CO2, H2O, etc) Organic molecule (eg. BOD) ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  48. b) Chemical oxidation of Biodegradable Organic Compounds Usually using chlorine and ozone. Typical chemical dosage for the oxidation of organics in ww ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  49. c) Chemical oxidation of Ammonia • Chlorine is used to oxidize the ammonia nitrogen in solution to nitrogen gas and other stable compounds (breakpoint chlorination) • Disadvantages of the process including the buildup of acid (HCl) which will react with the alkalinity, buildup of TDS and the formation of unwanted chloro-organic compounds. • Therefore, this process is seldom use today ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

  50. Chlorination • Chlorine has been applied for a wide variety of objectives other than disinfection including; • Pre chlorination for hydrogen sulfide control • Activated sludge bulking control • Odor control • The principle chlorine compounds used are chlorine (Cl2), chlorine dioxide (ClO2), calcium hypochlorite (Ca(OCl)2) and sodium hypochlorite (NaOCl). ERT 417/4WASTE TREATMENT IN BIOPROCESS INDUSTRY SEM 1 (2010/2011)

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