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TL3101 PFK TL3101 SOLID-FLUID SEPARATION Program Studi Teknik Lingkungan ITB TL3101 PFK Mixtures Types of Mixtures Heterogeneous Homogeneous Coffee Sea Water Heterogeneous or Homogenous? TL3101 PFK Heterogeneous or Homogeneous? TL3101 PFK Heterogeneous or Homogeneous? TL3101 PFK Solid • Floating & Settleable solid/materials • Total Solid: • Total Dissolved Solid (TDS): • Fixed Dissolved Solid (FDS) • Volatile Dissolved Solid (VDS) • Total Suspended Solid (TSS): • Fixed Suspended Solid (FSS) • Volatile Suspended Solid (VSS) • Colloidal solid: categorized as Suspended Solid but in the laboratory classified as Dissolved Solid (size: 0.001 to 1.0 μm) TL3101 PFK Colloidal Solids Medium Material Name Example Liquid Solid Sol Clay turbidity Liquid Liquid Emulsi Oil Liquid Gas Foam Foam/Cream Gas Solid Aerosol Dust, smoke Gas Liquid Aerosol Mist, fog Solid Liquid Gel Jelly TL3101 PFK Solid-Fluids Separation • Physical Separation: Suspended Solids • Sedimentation • Filtration • Floatation Mostly applied in Pollution Prevention • Mechanical Separation • Centrifugation • Distillation • Crystallization • Chromatography • Chemical Separation: Colloidal & Dissolved Solids • Coagulation • Precipitation TL3101 PFK Solid-Fluids Separation TL3101 PFK Sedimentation (Applied to Settling Chamber) • Sedimentation, or clarification, is the process of letting suspended material settle by gravity. • Suspended material may be particles, such as clay or silts, originally present in the source water. • More commonly, suspended material or floc is created from material in the water and the chemical used in coagulation or in other treatment processes, such as lime softening. • Sedimentation is accomplished by decreasing the velocity of the water being treated to a point below which the particles will no longer remain in suspension. • When the velocity no longer supports the transport of the particles, gravity will remove them from the flow. TL3101 PFK TL3101 PFK Settling Velocity Settling velocity can be calculated using a wide variety of formulae that have been developed theoretically and/or experimentally. Stoke’s Law of Settling is a very simple formula to calculate the settling velocity of a sphere of known density, passing through a still fluid. Stoke’s Law is based on a simple balance of forces that act on a particle as it falls through a fluid. TL3101 PFK FG, the force of gravity acting to make the particle settle downward through the fluid. FB, the buoyant force which opposes the gravity force, acting upwards. FD, the “drag force” or “viscous force”, the fluid’s resistance to the particles passage through the fluid; also acting upwards. Force (F) = mass (m) X acceleration (A) DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING DISCRETE (TYPE I) SETTLING TL3101 PFK FG depends on the volume and density (rs) of the particle and is given by: FG 6 d rs g 3 6 r s gd 3 FB is equal to the weight of fluid that is displaced by the particle: FB 6 d rg 3 6 rgd 3 Where r is the density of the fluid. FD is known experimentally to vary with the size of the particle, the viscosity of the fluid and the speed at which the particle is traveling through the fluid. Viscosity is a measure of the fluid’s “resistance” to deformation as the particle passes through it. FD 3dU Where (the lower case Greek letter mu) is the fluid’s dynamic viscosity and U is the velocity of the particle; 3d is proportional to the area of the particle’s surface over which viscous resistance acts. TL3101 PFK Drag Coefficient on a Sphere 4 gd ( r p - r w ) Vt = 3 CD rw 18 Stokes Law 100 10 1 laminar Reynolds Number turbulent 10 00 00 0 10 00 00 00 10 00 00 10 00 0 10 24 Re 10 00 Cd 1 0.1 0. 1 Drag Coefficient 1000 10 0 Vt d 2 g r p r w Re turbulent boundary Vt d r Regraph CDsphere TL3101 PFK Floc Drag Flocs created in the water treatment process can have Re exceeding 1 and thus their terminal velocity must be modeled using 100 10 CDsphere CDtransition Rek Stokes Rek 1 0.1 0.1 1 10 100 110 3 Regraph Rek 110 4 110 5 110 6 110 7 TL3101 PFK Example: A spherical quartz particle with a diameter of 0.1 mm falling through still, distilled water at 20°C d = 0.0001m rs= 2650kg/m3 = 1.005 ´ 10-3 Ns/m2 g = 9.806 m/s2 r = 998.2kg/m3 2 r r gd S 18 Under these conditions (i.e., with the values listed above) Stoke’s Law reduces to: 8.954 105 d 2 For a 0.0001 m particle: = 8.954 ´ 103 m/s or 9 mm/s TL3101 PFK Effect of Temperature TL3101 PFK Flotation • Flotation is an operation that removes not only oil and grease but also suspended solids from wastewater • The wastewater flow or a portion of clarified effluent is pressurized in the presence of sufficient air to approach saturation TL3101 PFK Waste flow is pressurized to approach saturation released to the atmospheric pressure Minute air bubbles are released from the solution SS, oil & grease, sludge flocs are floated attachment with air bubbles Enmeshed in the floc particles Air-solids mixture rises to the surface TL3101 PFK AIR SOLUBILITY AND RELEASE • The saturation of air in water is directly proportional to pressure and inversely proportional to temperature. • The quantity of air that will theoretically be released from solution when the pressure is reduced to 1 atm: TL3101 PFK AIR SOLUBILITY AND RELEASE • The actual quantity of air released will depend • upon the turbulent mixing conditions at the point pressure reduction • on the degree of saturation obtained in the pressurizing system • The performance of a flotation system depends upon having sufficient air bubbles present to float substantially all of the suspended solids • An insufficient quantity of air will result in only partial flotation of the solids, and excessive air will yield no improvement FLOTATION UNIT • The performance of a flotation unit terms of effluent quality and solids concentration in the float can be related to an air/solids ratio: TL3101 PFK TL3101 PFK Air to Solid Ratio TL3101 PFK Filtration • Conceptually, filtration is like sedimentation: solid-fluids separation • Filtration is configured mostly for solids that are small enough to be removed in sedimentation or flotation processes • Filtration: • Depth Filtration: • Rapid sand filtration: 2 – 5 m3/m2/hr • Slow sand filtration: 0.15 – 0.35 m3/m2/hr • Surface Filtration: • Filter cloth • Membrane TL3101 PFK Depth Filtration Mechanisms • Straining: • Mechanical: solids larger than pore space • Chance contact: solids smaller than pore size are trapped within the filter • Sedimentation: solids settling on the filtering medium • Impaction: heavy solids will not follow the flow streamlines • Interception: solids move along the flow streamline are removed when they come in contact with the surface of filtering medium • Adhesion: solids become attached to the surface of filtering medium as they pass by • Flocculation: Solids growth • Biological growth, especially in slow sand filtration TL3101 PFK TL3101 PFK Depth Filtration (Rapid Sand Filtration) • Solids need a pre-treatment to destabilize the electrical charge • The most important things is not the straining process, but the the removal of solids adhere to grains in the filter medium • Head loss in filter increases with time as filter clogs and gets lower hydraulic conductivity TL3101 PFK TL3101 PFK Rapid Sand Filtration • Medium • Single: sand • Dual: anthracite and sand • Multi/Triple: anthracite, sand, and garnet TL3101 PFK • Porosity: TL3101 PFK Surface Filtration (Membrane Filtration) • Solid-fluid separation by means of surface filtration: • Disc Filter • Membrane Process • Membrane Filtration removes: • Colloidal solid • Dissolved Solid • Membrane Selectivity be base on its porosity: • Micro Filtration (MF) : 0.02 – 10 um • Ultra Filtration (UF) : 0.01 – 0.02 um • Nano Filtration (NF) : 0.0001 – 0.001 um • Reverse Osmosis (RO) : 0.0001 um TL3101 PFK TL3101 PFK TL3101 PFK TL3101 PFK Chemical Solid-Fluid Separation TL3101 PFK Colloidal Particles • Colloid: small particles and disperse homogenously. Colloid particles size around 10-6 mm – 10-3 mm (bigger than atom). • In terms of their affinity In water, colloid particles are divided into: • Hydrophylic: organic colloid particles because of polar side (OH, COOH, NH2) on colloids surface. Characteristics: water soluble and having boundwater (water envelope). • Hydrophobic: Inorganic colloid particles. Having no or very small affinity to water: no bound water occurred TL3101 PFK Zeta Potensial • Colloid stability is very much affected by “ionic charge” working on the colloids surface • Hydrophylic colloid: electric charge due to dissociation of polar group. Example: COOCOOH COO OH- R OHR + NH3 H+ R H+ NH3+ Isoelectric point NH3OH pH • Hydrophobic colloid: Adsorption of ionic molecule from the solution. Ionic Charge of hydrophobic colloid is switchable by altering the solution pH. It is suggested that the ionic charge of hydrophobic colloid is formed from either hydroxyl or hydrogen ions TL3101 PFK Zeta Potential • Colloid in medium attract opposite charge ions (counter ions) to form double layer: • Fixed or Stern layer • Diffuse or Gouy layer • Shear of plane: interface between solution as a part of particles and • • • • solution Shear of plane of hydrophobic colloid overlap and enclose fixed layer Shear of plane of hydrophylic colloid overlap and working on the surface bound water Zeta potential: electrostatic force working on the surface of “shear of plane” Zeta potential: resultant between attraction force (van der Waals) repulsion force TL3101 PFK TL3101 PFK Colloid Stability • Colloid stability indicate by the magnitude of zeta potential. The stronger the zeta potential, the more stable the colloid. • Basically, zeta potential is the magnitude of ionic charge working on the colloid • Device: zeta meter • Zeta Potential Equation: = 4qd/D Where: q = charge per unit area d = thickness of “shear surface” interface D = Dielectric constant • Hydrophylic colloid stability is also affected by bound water that behaves as elastic barrier TL3101 PFK Colloid Destabilization • Zeta Potential Reduction: • pH adjustment • Counter ions addition • Bivalent ions: 50x stronger than monovalent • Trivalent ions: 1000x stronger than monovalent • Hydrophylic colloids destabilization: not only zeta potential reduction, but also to destroy bound-water: “salting out” (the addition of high concentration salt: SO4, Cl-, NO3-, I-) • Coagulation : colloid particles destabilization • Solid-Fluid Separation by Chemical Process: • Zeta potential reduction (electrokinetic): addition of coagulant agent • Particles interaction and bounding (orthokinetic): flash mixing • Floc formation: slow mixing (floculation) TL3101 PFK Coagulation Reaction - 1 • Al2(SO4)3xH2O: • Sufficient alkalinity: Al2(SO4)3xH2O + 6HCO3- 2Al(OH)3 + 3SO4- + 6CO2 + xH2O reduction of bicarbonate and formation of CO2, causing the drop of pH • No bicarbonate available, alkalinity should be added: Al2(SO4)3xH2O + 6OH- 2Al(OH)3 + 3SO4- + xH2O • Al(OH)3 is amphoteric compound and insoluble at pH between 5 – 7. At pH below 5, this compound dissociates to form aluminium ion and at pH above 7 to form AlO2 ion TL3101 PFK Coagulation Reaction - 2 • Ferro sulphate (FeSO47H2O) : • FeSO47H2O + 2OH- Fe(OH)2 + SO4-2 + 7H2O Fe(OH)2 is formed at high pH (above 9,5). To increase pH normally Ca(OH)2 is added • If O2 available: 4Fe(OH)2 + O2 + 2H2O Fe(OH)3 At neutral pH, Fe(OH)3 is more insoluble than Fe(OH)2. • Fe(OH)3 is not an amphoteric compound TL3101 PFK Coagulation Reaction Pathway • Dissociation of coagulant agent to form metallic ion • Hydrolysis of metallic ion to form hidroxo-metallic ion complexes that tend to polimerisize as Meq(OH)p+z: • Al6(OH)15+3 • Al7(OH)17+4 • Al13(OH)34+5 • Fe2(OH)2+4 • Fe2(OH)4+5 • Those polyvalent ions interact and agregate with colloid as a result of zeta pontetial reduction and the increase of van der Waals force • Remaining coagulant continue to dissociate and polimerize to form insoluble metallic hydroxide (Fe(OH)3 or Al(OH)3): sweep coagulation (enmeshment process) TL3101 PFK Other Coagulant Agent • Polymeric Coagulant as Coagulant aid: • Cationic : behave as coagulant • Anionic : to form floc • Dosage: 1/100 of Inorganic Coagulant (Salt) • Coagulant types and dose determination in laboratory : • jar-test • zeta potential measurement