Solid Separation Method,Coagulation and Sedimentation

Solid Separation Method For IETS

1. Solid Separation Methods Coagulation and Sedimentation W aste water treatment basics JICA Training JEMAI July 2012 1

2. Note JEMAI has been educating PCM/trainees and internal environmental auditors etc. for more than 40 years Specially prepared text books have been published annually by JEMAI since 1970s Following slides include some extracts out of JEMAI text books for PCMs and additional information/comments prepared by the lecturer 2

3. physicochemical treatment 　 3.2.1 Sewage Treatment Planning SS Separation, Characteristics of waste water Gravity Separation and Particle diameter Particle sizes and treatment methods 3.2.2 Sedimentation Settling velocity of spherical particles Stokes ’ law and Settling efficiency in plain settling Inclined-plate 3.2.3 Coagulation ( Chemical Treatment) Flocculation , coagulant, Jar test etc. 3.2.4 Flotation Separation 3.2.5 Clarifying filtration Sand filtration, filtration resistance, cleaning etc. 3.2.6 pH adjustment pH , neutralization curve, pH adjustment, metal hydroxides etc. Other topics 3

4. Introduction & 3.2.1 Sewage Treatment Planning 4

5. 5 Ion, Molecule Colloid Suspended solid Note : industrial effluents: Wastewater is often a mixture, blend ( compound) of the above non-filterable residue Organic Introduction

6. 3.2.1 Sewage Treatment Planning ① Method of sewage treatment can be categorized into physicochemical and biological treatments. Effluent contaminated with organic substances (BOD, COD) are generally processed by biological measures, although physicochemical processes including solid-liquid separation and oxygen absorption are required as steps within the biological treatment. Contaminants interfused in the effluent (industrial wastewater) consist of both suspended solids and dissolved matter, respectively containing organic and inorganic substances. Sewage treatment is conducted for the purpose of decomposing such contaminants, and/or separating the contaminants from water for concentration based on a combination of physicochemical and biological processing methods. 6

7. Major objectives of sewage treatment 7 Processing/dewatering and disposal of sludge

8. 3.2.1 Sewage Treatment Planning ② The objectives of sewage treatment include : Solid-liquid separation [Suspended Solids (= SS); BOD/COD, Soil/Clay, FOG (Fats, oil, & grease) etc . Oxidization/decomposition of organic substances, reducing material (reductive, non-oxide, including BOD , COD, etc.) Adjustment of acidity (pH) Elimination of toxic substances Elimination of inorganic nutrient salts (primarily phosphor/nitrogen compounds) Processing/dewatering and disposal of sludge 8

9. 3.2.1 Sewage Treatment Planning ③ Various processes/steps are combined in sewage treatment The terms primary/secondary/tertiary treatment are often used to indicate the level of processes applied, though the categorization is intended for convenience and the detail is not clearly defined. The cost of sewage treatment increases as the process becomes more elaborate from primary through secondary and to tertiary treatment, corresponding with the sophistication of the technology involved. Solid matter separated in respective processes is collectively referred to as sludge. The processing/ disposal of the sludge are an important aspect of sewage treatment . 9

10. Treatment technology (schematic image) 10 In practice they apply combined processes & various technologies P ollutants should be rejected and collected ‘Primary’ or pretreatment steps. Separate as much as sludge/solid materials by simple treatment technologies

11. 3.2.1 Sewage Treatment Planning ④ The terms primary/secondary/tertiary treatment Primary treatment: Basically involves the physical removal of solids , with the objective of eliminating SS by screening, settling or floatation (separation). Secondary treatment: Collective designation of processes involving the decomposition/ elimination of organic substances (BOD) interfused in the effluent by biological measures such as activated sludge method . In general, over 90% of the BOD is removed in the process. Tertiary treatment: Organic substances (BOD/COD), nutrient salts (nitrogen/phosphorus) and other components remaining after subjection to secondary treatment are removed in this process. Also referred to as advanced water purification . 11

12. Suspended Solids Separation Removal methods, solids handling and processing Screens (Grit Removal for non-putrescible solids) Gravity Separation Flotation and Settlement Inclined-plate clarifiers etc. Chemical Coagulation and flocculation Filtration Cartridge & Bag filtration, Filter Backwash etc. Sludge treatment Solids Thickening and Dewatering Disposal Technologies and Incineration etc. Putrescibe = tend to decay or spoil 12 Introduction

13. Items to be considered when planning a waste water treatment process 1 Preliminary studies Exact and detailed analyses and assessment about raw material, secondary material and by-products etc. Production processes, step by step assessment The qualities and quantities of waste water Conditions of original water (industrial water) Conditions of discharging rivers, lakes, and any other waters Vulnerability ; source of drinking water, aquatic fauna and flora etc. The above changes or fluctuations with time, days, seasons, and years etc. Other parameters including from climate , weather, - - - to the ecological systems 13 Introduction

14. Items to be considered when planning a waste water treatment process 2 Accurate estimation The material balances of raw material and water to be used Waste water volume and its quality generated in each process Manufacturing waste water Cooling water Domestic wastewater (sewage) etc. S eparate or joint treatment? Highly polluted but small quantity Slightly polluted and huge volume Scheduled wastes? Prevent rainwater/run-off water from being mixed with waste water to be treated 14

15. Characteristics of waste (waste water) 15 Law Concerning Reporting, etc. of Releases to the Environment of Specific Chemical Substances and Promoting Improvements in Their Management (Law No. 86 of 1999, hereinafter referred to as “PRTR Law ”) Under the PRTR : 462 Chemical substances are regulated in Japan MSDS: 100 chemical substances Introduction

16. Characteristics of waste water 1 Low concentrations of pollutants in general A great variety of coexisting substances Fluctuations found in the concentrations and compositions of the targeted substances Changes in raw materials, processes, storages, products, by-products, and wastes etc. T he waste water will be influenced by above parameter changes Fats, oils, and greases (FOG) Washing and cleaning chemical material etc. Jointly it makes more complicated 16 Introduction

17. Characteristics of waste water 2 Concentration of solids in the wastewater SS; Particles ’ size? Colloid? Or Solution? By-products The desired final concentration Settle-ability Thickening characteristics Discrete (scatter) or flocculent nature http://www.chem.utsunomiya-u.ac.jp/lab-Nov/index.html 17 Introduction

18. Gravity Separation and Particle diameter Plain Sedimentation 18 Introduction

19. Particle diameter and treating method Dimension of particles in waste water and their treatment procedures Dissolved and small colloidal solids are non-filterable residue, in general. Metal solvent ( ion) would be chemically treated – to be deposited as particles. Note: The above is just estimated value in 1990s, not actual one. 19

20. ＵＦ ＭＦ Ion, Molecule Colloid Suspended solid Virus Bacteria, Small algae 1 millimeter 1 micrometer 1 nanometer 10 - 7 10 - 6 10 - 9 10 - 8 10 - 5 10 - 4 10 - 10 10 - 3 (M) Particle sizes and treatment methods [Schematic diagram, not actual results] Sedimentation Chemical treatment and/or Coagulation Note: The above is just estimated value in Japan, not actually measured one. 20 Introduction

21. Points to be considered by enforcement officers Waste water treatment facilities Understand the outline ( Pollutants’ quality and quantity, Input – Output, Treatment capacity etc . ) Appropriate maintenance and trainings Record keeping (monitoring record) Ex . electricity cost, chemicals consumed, and analysis cost W orking standard manuals and staff competency 21 Introduction

22. Separation of solid matters Screening Removal of comparatively large solid particles Storage and Adjustment Equalization Adjustment of the volume and concentrations (flow, SS & pollutant concentration, temperature etc.) Settling or floating solid matters  Advanced treatment Sludge management 22 Introduction

23. Separation of solid matters Screening Removal of comparatively large solid particles FOG; Oil and water separation Equalization 　 Adjustment of treating volume and concentrations Settling or floating solid matters Sedimentation of sand and other fine suspended substances Flotation of FOG, oily component or light suspended substances Neutralization = Adjust of pH Then, to the Secondary and/or to the Tertiary Treatment process 23 Introduction

24. Separation of solid matters Coagulation and Sedimentation Pressurized-air flotation Aerobic biological treatment To the Tertiary Treatment D ischarge treated water Filtration, Reverse Osmosis (RO) or Chemical treatment incl . oxidation, UV, or Activated carbon adsorption Anaerobic treatment 24 Introduction

25. Oil Separators 25 Oil Separators are utilized based on the tank velocity, oil droplet velocity, and oil content etc. API (American Petroleum Institute, rectangular shape ) PPI (Parallel Plate Interceptor, a number of inclined plates set in parallel ) CPI (Corrugated Plate Interceptor, a plate pack consisting of inclined corrugated plates ) Introduction

26. Tertiary Treatment (manufacturers) Reason for the advanced treatment When discharging to the water area where particularly strict regulations are in force When containing pollutants that cannot be removed by the treatment up to the secondary one When recycling of waste water is to be attained Activated carbons Ion exchange resins, chelate resin etc. Membrane separation Electro-dialysis (osmotic process), Reverse osmosis, Microfiltration, Ultrafiltration Ozone , UV etc. 26 Introduction

27. Sludge Screened residue, sediments , floating sludge (scum) Coagulated precipitates and surplus sludge generated by biological treatment (activated sludge) Dehydration (dewater), drying, solidification, or incineration In case of organic sludge (not chemically polluted) it will be recycled as manure or animal feed 27 Introduction

28. 3.2.2 Sedimentation Physical Treatment 28

29. 3.2.2 Sedimentation ① In effluent treatment processing, the initial stage of treatment involves the separation of organic and inorganic contaminants interfused in the water as insoluble suspended solids . For example, metallic hydroxide or sulfide sedimentation is commonly separated out in a solid-liquid separation process; First, the adjustment of the pH ( hydroxide ) or addition of sulfides ( sulfide precipitation ) to the effluent in order to eliminate toxic metallic ions dissolved in the water. 29 Sedimentation

30. 3.2.2 Sedimentation ② Biological sewage treatment They state that organic contaminants are generally decomposed by microorganisms http://www.pref.ibaraki.jp/bukyoku/doboku/01class/class33/xhtml/qanda9.html 30 Sedimentation

31. 3.2.2 Sedimentation ③ Contrary to the descriptions for biological sewage treatment stating that organic contaminants are generally decomposed by microorganisms; About 40 to 60% of the BOD requiring elimination is actually transformed into SS in the form of microbial cells, and the separation/disposal of the resulting sludge becomes the most important component of the treatment process . BOD SS microbial cells Physical Treatment 31 Sedimentation

32. Plain sedimentation ( being allowed to settle without coagulation) 　 If the density of particles is smaller than water’s density ‘floating’ method can be applied In case of a small SS or colloidal solution 　　　　　　 ‘Coagulating sedimentation’ will be applied 　　　 Sedimentation velocity of particles 　 　　 32 Japan Agency for Marine-Earth Science and Technology: JAMSTEC Density=Specific gravity Sedimentation: 1.Plain sedimentation or natural settlement Ex .; a primary sedimentation tank/basin 2. Coagulating sedimentation with the flocculation process The rate of descent gradually accelerates in the initial stage then - - - - - - - Molecule or metal ion ? Sedimentation

33. 3.2.2 Sedimentation ④ However , the inverse resistance force acting on the particle with the power proportional to the square of the speed eventually stops the acceleration once the resistance force working on the particle becomes equivalent to the gravitational force. Thereafter , the particle begins to descend at a fixed rate. This rate of descent is referred to as the terminal sedimentation rate, which is generally referenced as ‘the sedimentation rate of particles’. the resistance force S edimentation rate gravitational force 33 (1) Particle sedimentation rate Terminal sedimentation rate (terminal settling velocity) When particles suspended in water sediment under 　 the influence of gravity, the rate of descent gradually accelerates in the initial stage of the process.

34. Equation of motion is used in calculating the sedimentation rate of particles, with the resistance force segmented into three regions as a function of the Reynolds number. The resistance force is represented as indicated below: Settling velocity of spherical particles; Stokes' law 　 　　 34

35. If the particles are falling in the viscous fluid such as waste water by their own weight due to gravity ( g ) , then a terminal velocity*, also known as the settling velocity ( V ), is reached when this frictional force combined with the buoyant force exactly balance the gravitational force. The resulting settling velocity (or terminal velocity) is given by Stokes’ law. The Stokes’ law V = g （ ρ － ρ ） d 2 18μ Settling velocity of spherical particles; Stokes' law 　 　　 35 v is the particles' settling velocity, sedimentation velocity (cm/s ) g is the gravitational acceleration, acceleration of gravity (cm/s 2 ) ρ is the mass density of the particles, density of particle (g/m3) ρ is the mass density of the fluid, density of water (g/cm3) ( vertically downwards if ρ  >  ρ , upwards if ρ  <  ρ   ) μ is the dynamic viscosity, viscosity of water (g/cm/s) d is the diameter of the spherical object/particle ( c m) *Terminal Velocity: A free-falling object achieves its terminal velocity when the downward force of gravity equals the upward force of drag (frictional force).

36. Laminar Flow Spherical particles Homogeneous (uniform in composition) material Smooth surfaces Particles do not interfere with each other George Stokes (1819–1903) The settling velocity is directly proportional to; the square of particle diameter the difference in density between solid and liquid Q: Steel ball bearings or plastic balls in water or glycerin/syrup-----? Stokes' law (1851) makes the following assumptions for the behavior of a particle in a fluid 36 Stokes' law

37. 3.2.2 (1 ) Particle sedimentation rate Particles addressed in the treatment of effluents generally maintain small diameter (d) and sedimentation rate (ν), and therefore, the Re is also insignificant ( i.e., less than 1 ), allowing for the assumption that the behavior corresponds with the Stoke’s equation for the most part. As indicated in the formula, the sedimentation rate is proportional to the particle diameter squared . Although the equation indicated below is drawn upon the hypothesis that the particle is spherical in shape, particles actually suspended in the effluent may not be spherical with difference in diameter, configuration and density, rendering the measurement of such individual particles impractical. Accordingly , the distribution of sedimentation rate should be measured in real situations as indicated next slide: g （ ρ － ρ ） d 2 18μ V = 37 Stokes' law

38. By the Andreasen pipet the particle concentrations are measured and the plotting results will indicate the curve in Fig.2. Fig.2: Smaller particles with settling velocities lower than 2 cm/h occupy 30% of the total distribution. The distribution of sedimentation rate should be measured in real situations as indicated above 38 Stokes' law They measure the velocity distribution by using an Andreasen pipet or the like, and to select a proper precipitator matching to a particular purpose.

39. Settling efficiency in plain settling Up-flow type settling tank The efficiency is determined by the settling velocity distribution of suspended solids and the up-flow rate (m3/m2 ・ d) of the precipitator (clarifier) if the flow of water in the precipitator is very ideal, i.e., No turbulence No short current etc. When the separation surface area of the precipitator is taken as A and the flow rate of water as Q, then the up-flow velocity ( U ) is Q/A. U =Q/A To improve the settling efficiency: Larger surface area of A, less flow rate of Q, and increasing SS particle sedimentation rate 39 Sedimentation

40. In an up-flow type settling tank as shown in Fig.3 ( a ) all the particles with sedimentation velocities larger than u can be settled, but those with smaller velocities than u will flow out from the tank. (a) U =Q/A In a level flow type settling tank , Fig. 3( b ) , if the volume of tank is taken as V, the depth of water as h , the residence time as t , L-M velocity as V , that is, t = V/Q V = A h then h = V/A Fig(b ); t = time to pass between L-M L-M sedimentation velocity, V , is “ h / t =(V/A)/(V/Q)= Q/A ” *Even such lower velocity than V as L-E, all SS below F-M can be settled before reaching the outlet point in theory . U =Q/A = W Flow M 3 day /surface area m 2 (V =Q/A) volume of tank Surface area 40 Q = flow rate * * * * * * * * * Sedimentation

41. S ettling velocity = Q/A Water Surface area : A Q = flow rate To achieve a higher settling efficiency , Q/A must be reduced, for example , i f Q is constant A must be increased Where the available space is limited, it is common practice to build a number of inclined plates in parallel inside the precipitator/clarifier to increase the effective separation area, instead of increasing the actual water surface area. Inclined plates Settled sludge 41 Sedimentation

42. 42 Inclined plates (Fukuoka pref.) Inclined pipes Sedimentation

43. Inclined plates/pipes and advanced one (C) 2009 Suido Kiko Kaisha,LTD . All rights reserved Fluid drag 流体抗力 Swirling current Gravitational pull + ラビリンス（固液分離装置 ） Sedimentation

44. Q:Why they do not use Inclined-plate clarifiers for biological sludge tank? Activated sludge treatment - bacteria As long experience has proved bacteria and other biomass can grow on the plates, plugging or reducing the settling area. Gradual plugging between the plates may occur in general, so clean-up is recommended. Oily or sticky SS may also creates plugging problems between the plates. Piled sludge on the plates may break and collapse thin Inclined- plates. 44 Sedimentation

45. Inclined-plate clarifiers in USA 1 The inclined-plate clarifier reduces the necessary settling depth, so it reduces the necessary settling area by up to 90% and highly effective in removing suspended solids In conventional sedimentation, the overflow rate is used to calculate the required surface area of the sedimentation basins. So, all particles with a settling rate equal to or greater than the overflow rate will be removed. 　　　　　 The tank depth does not affect solids removal effectiveness. Water Environment Federation, USA 2008 45 Sedimentation

46. Inclined-plate clarifiers in USA 2 Not usually used to clarify biological sludges because bacteria (and other biomass) can grow on the plates, plugging or reducing the settling area. Oily ‘sticky’ solids may also create plugging problems between the plates. Conventional sedimentation or flotation should be considered in these cases. Water Environment Federation, USA 2008 46 Sedimentation

47. Settling Tanks ( clarifier) The rectangular clarifier The radial flow or circular clarifier Simpler mechanism for sludge scraping and discharging settled sludge Less frequency of mechanical breakdown Minimize turbulent flow at the inlet and outlet ends and to eliminate the short current of water flow through the tank φ19.5M Tank, Matsushima-town, Miyagi-ken Above photo: http ://www.seiwa-matsushima.co.jp/work7.html 47

48. Advanced RO & MBR method Good quality treated water can be produced by utilizing MBR and/or RO method 排水 の再利用を目的とした膜分離活性汚泥法（ MBR ）及び RO 膜を利用することに より良質 な処理水が得られます。 MBR The dipping ( soaking) membrane (pore space 0.1 ～ 0.4μm) rejects small bacteria so that the treated water can be used for car washing, toilet and plat watering etc. 浸 漬膜（孔径 0.1 ～ 0.4μm ）の処理水は清澄で細菌類も除去されており、洗車、トイレ、散水等への再利用ができます。膜分離装置は曝気槽内に設置できるため省スペースとなります。膜カートリッジはユニット式で点検・交換が簡単です 。 (C) 2009 Suido Kiko Kaisha,LTD . All rights reserved

49. 3.2.3 Coagulative separation 49

50. Coagulation sedimentation Particles bigger than 1 - 10 μm can be separated by spontaneous settling (plain sedimentation) and/or by filtration Particles less than 1 μm (up to 0.001 μm ) shall be applied ‘Coagulation sedimentation’ Coagulant helps to form flocs Target pollution control COD, Color, Oil etc. W ater treatment level Floc size and settling velocity Cost and expenses Sludge generation Management/control Fate of the coagulant 50 Coagulant must be cheap and must not be hazardous substances Coagulation

51. The inorganic flocculating agents positively charged, such as Fe/Al, neutralize the particle surface electric charges, however, High-polymer coagulants induce coagulation by bridging particles in addition. 51 Coagulation

52. 3.2.3 Coagulative separation While large-sized suspended particles with diameters of up to 10 μm are separable by plain sedimentation and normal filtration , smaller particles with diameter of less than 1 μm cannot be processed mechanically without the use of coagulation, i.e., coagulative separation . Furthermore , particles smaller than 0.001 μm are distributed within the water in molecular form and does not respond to coagulative separation without prior chemical precipitation. Particulates in the range of 0.001 to 1 μm are referred to as colloidal particles or simply colloids, and subjected to coagulative separation . 52 1 micrometer 1 nanometer 1 millimeter Coagulation

53. Ion, Molecule Colloid Suspended solid Virus Bacteria, Small algae 1 millimeter 1 micrometer 1 nanometer 10 - 7 10 - 6 10 - 9 10 - 8 10 - 5 10 - 4 10 - 10 10 - 3 (M) Particle sizes and treatment methods [Schematic diagram, not actual results] Sedimentation Chemical treatment and/or Coagulation Note : The above is just estimated value , not actually measured one. 53 Coagulation

54. Under normal circumstances, colloidal particles are governed by Brownian motion, evenly distributed within the medium due to the repulsive force of the negative charge present on the particular surface. 54 Colloidal particles are assumed to be moving within the medium with a hydrated layer of water molecules adhered to the surface. Electrical potential created along the shear plane of this hydrated layer is called zeta-potential and can be measured. repulsive force 　斥力、反発力。　水和層のせん断面 http ://www.horiba.com/ jp /scientific/products- jp /pa... Zeta-potential Negatively charged at the surface

55. For molecules and particles that are small enough, a high zeta potential will confer stability, i.e., the solution or dispersion will resist aggregation. When the potential is low, attraction exceeds repulsion and the dispersion will break and flocculate. 55 From Wikipedia The significance of zeta potential is that its value can be related to the stability of colloidal dispersions. The zeta potential indicates the degree of repulsion between adjacent, similarly charged particles in a dispersion. Source: Wikipedia Zeta-potential

56. When suspended particles are too small to be separated by spontaneous settling, a coagulant will be added to coagulate the fine particles into large flocs (increasing the settling velocity) In general, fine particles are negatively charged at their surfaces and repel each other , which can be lowered by a coagulant bearing positive charges (to be electric neutralization). Excessive coagulant supply under too vigorous agitation, may cause surface covering, the whole surface of the particles, and defeat the bridging effect. Coagulation sedimentation Separation by Coagulation 56 Zeta-potential Bridging effect Electric neutralization

57. ζ potential 　　 When the Z eta potential is low (less than ±10mV) with coagulant, attraction exceeds repulsion and the dispersion will break and flocculate. Colloids with low zeta potentials tend to coagulate or flocculate and become larger particles. Z eta potential : - 20 ～ -30mV ( electrokinetic potential) Colloidal particles (dispersion) flocculate 57 Zeta-potential

58. The zeta-potential generated by colloidal particles evenly distributed within the water is in the range of - 20 to -30 mV. Upon neutralizing the electric charge of the hydrated layer by adding colloids or ions partaking an opposite (generally positive) charge, thereby adjusting the zeta-potential of the suspended particle to within ± 10 mV, the attractive force acting among the particles (van der Waals attraction) overwhelms the repulsive force of the charged shear plane, thus causing the particles to coagulate. 58 Coagulation

59. Substances used for such purposes are called flocculating agents. The agents are generally water soluble with hydrolysis nature, i.e., hydrolytic cleavaging (break down) properties . Any metallic salt with the appropriate properties and allowing for the generation of positively charged metal hydroxide colloids will suffice as coagulant, although iron or aluminum salts are used exclusively in the field of water treatment because of their inexpensiveness and non-toxicity . These metals hydroxides form gelatinous ( gel, gelled) sedimentation with porous structure providing for significant surface area. Dispersion 分散 hydrolysis 加水分解 59 cleavaging 裂け、分割、 Gelatinous / dʒəlˈæṭənəs / ゼラチン状 / 質の ; ゲル状の Coagulation

60. This has a significant influence on the surface charge of the suspended particles, and the gelatinous structure of the sedimentation works favorably toward enhancing the coagulation. Additional efficacy of physicochemical attachment is also to be expected . The large agglutinates of suspended particles formed in the process are referred to as “ flocs ”. agglutinate 膠着 [ 接合 ] させる . する 60 Coagulation

61. 3.2.3 (1) Flocculating agents Aluminum sulfate [Al 2 (SO 4 ) 3 ・ 18H 2 O] is one of the most commonly used inorganic flocculating agents. When aluminum sulfate is dissolved in water, the substance hydrolyzes (undergo hydrolysis) as colloidal coagulation of aluminum hydroxide. The hydroxide takes on many different forms depending on the acidity of the water, but generally expressed as Al(OH) 3 . Please see next slide. 61 Coagulation

62. Hydrolysis (hydrolyzing effects, reaction with water molecules ) Aluminum sulfate chemical reaction: Al 2 (SO 4 ) 3 ・ 18H 2 O + 3Ca(HCO 3 ) 2 → 2Al(OH) 3 + 3CaSO 4 + 6CO 2 + 18H 2 O 62 Colloidal coagulation of aluminum hydroxide Alkali, 3Ca(HCO 3 ) 2 will be consumed under the process pH must be adjusted ; pH 6 – 8 Coagulation

63. Hydrolytic Cleavage 1 加水分解開裂 ; 加水分解的開裂 As indicated in the above slide, the hydrolytic cleavage (hydrolysis) of the flocculating agent consumes the alkali content of the water, changing its pH level. There is a most suitable range of pH for the promotion of the agglutination (conglutination) reaction depending on the type of effluent and flocculating agent used, and the agent may be used with acidic or alkali additives for the adjustment of pH. Alkali additives are used more frequently than acidic additives . 63 Coagulation

64. Hydrolytic Cleavage 2 加水分解開裂 ; 加水分解的開裂 Typical inorganic flocculating agents are provided in table 3.2.3-1. As the floc produced with inorganic flocculating agents are rather fragile in terms of mechanical strength, the size and sedimentation speed is subject to certain limitations. The introduction of water soluble polymers with extended chain molecular configuration will enhance the binding power of the floc , consequently yielding larger flocs with a higher rate of sedimentation. Various types of such high-polymer coagulant are available in Japan, and being utilized in a broad range of effluent treatment . 64 Coagulation

65. Table 3.2.3-1 Types and properties of inorganic flocculating agents Type Name Formula Applicable pH for coagulation Applicability to drinking water Remarks Aluminum Aluminum sulfate Al 2 (SO 4 ) 3 ・ 18H 2 O 6 to 8 ○ Most common. Occasionally used with iron salts, also called "Alum". Sodium aluminate NaAlO 2 ○ Said to increase potency when used together with alum. Basic aluminum chloride Polymerized Al n (OH) m Cl 3n-m ○ Effective in elimination of chromatic component (color), and capable of reaction without significant alteration of the pH. Iron Iron (II) sulfade FeSO 4 ・ 7H 2 O 9 to 11 ○ May leave iron residue under unsuitable conditions, coloring water. Iron (III) chloride FeCl 3 ・ 6H 2 O ○ Iron (III) sulfade Fe 2 (SO 4 ) 3 ・ n H 2 O ○ Copperas chloride Fe 2 (SO 4 ) 3 ・ FeCl 3 ○ Polysilicato-Iron (SiO 2 ) n ・ (Fe 2 O 3 ) ○ 65

66. The addition of minor (small) quantities of high-polymer coagulants is sufficient against suspended colloidal particles, successfully yielding larger flocs . Depending on the charge attributed upon introduction to water, high-polymer coagulants are categorized into cationic, anionic and nonionic agents, with more meticulous differences based on the molecular mass and bifurcation ( bunshi-ryo , bunki ). Coagulation effect exhibited by cationic polymer agents are basically assumed to be derived from the neutralization and cross-linking of the negatively charged surface potential of suspended particles . 66 Coagulation

67. Anionic and nonionic polymers are often used in conjunction with inorganic flocculating agents (ex. Al, Fe), and considered to have their effect on enlarging the floc size by attaching and cross-linking between particles . 67 The selection of a specific flocculating agent from among many available products for the purification of effluents is an exclusively trial-and-error dependent process. Coagulation

68. Coagulation sedimentation method sees applications in the elimination of specific categories of contaminants including COD, tainting ( color), oil and phosphoric salts as well as being used in the clarification of effluents. To this end, specific flocculating agents suited for the intended purpose should be selected. Within this section, descriptions of generic selection criteria are described as follows: 68 Coagulation

69. Coagulant/ flocculating agent selecting factors (examples) 69 Coagulation

70. Goal: To select agents capable of yielding results compliant with the intended purpose of the treatment. To select agents capable of yielding flocs facilitating the process (in terms of floc size, sedimentation characteristics, etc ). To select agents capable of minimizing the types and quantities of chemicals involved, thereby reducing the running cost of the process. 70 Selecting factors (examples ) 1 Coagulation

71. To select agents capable of reducing the volume of sludge, while concurrently yielding superior properties in the context of sedimentation thickening and dehydration. To select agents facilitating the transportation, storage, dissolution and addition of chemicals. To select agents capable of preventing any adverse impacts on the natural environment or the usage of the treated water in the event residues of the agent remain within the water or generated sludge. 71 Typical types of high-polymer coagulants are indicated in table 3.2.3-2. Selecting factors (examples ) 2 Coagulation

72. Table 3.2.3-2 High-polymer coagulants 72 Coagulation

73. 73 Table 3.2.3-2 High-polymer coagulants Coagulation

74. 3.2.3 (2) Jar Test Coagulation efficiency varies depending on the kinds and the amount of coagulant added, pH of the process, the ions coexisting in the system and other factors The optimum conditions should be decided in advance by a jar test (Beaker test with Jar tester) Predetermined amounts of sample liquid are taken in individual beakers with different formulations (amount of coagulant, pH, coexisting ions, etc.), stirred under the same conditions, and allowed to settle. Coagulation efficiency is estimated by visual observation or by analyzing the clarified liquor. 74 Jar Test

75. Coagulation testing method Coagulation is typically tested using equipments similar to the unit (jar tester) indicated on figure 3.2.3-1, according to the procedures described below. Figure 3.2.3-1 Jar tester 75 Jar Test

76. Jar test process Prepare the necessary quantity of 500 mL beakers filled with sample of the water to be treated. 500 mL of the sample shall be accurately measured into each beaker. Load the beakers onto the jar tester, lower the agitation axis into the beakers, immersing the agitation blade in the water. Turn on power switch and activate timer. The agitation blade shall be set to a rotation of 120 to 150 min -1 and operate. Concurrently introduce the chemicals as indicated. Promptly introduce the specified amount of chemical (for example, aluminum sulfate solution) into respective beaker using measuring pipettes. For example, on order to prepare a 1% solution of aluminum sulfate on quantities of 20/40/60/80 mg/L with the specimen quantity of 500 mL, 1/2/3/4 mL of the chemical shall be introduced into the beakers respectively . 76 Jar Test

77. Generation of flocs 1 to 5 minutes after the introduction of the chemical, reduce speed of the agitation blade to 30 to 60 min -1 . The faster rotation used during the initial phase of the test is intended to facilitate the formation of minute flocs by uniform mixing, and the speed is then reduced to allow the created flocs to gradually grow larger. Stop the agitation after 10 to 20 minutes of gradual rotation, then take out the agitation blade. Promptly observe the flocs , noting their condition and rate of sedimentation. The type and quantity of agents capable of creating large flocs with high sedimentation speed while maintaining the clarity of the supernatant (upper clear water) should be selected for use in treating the sample water. 77 Jar Test

78. Jar test Analyze the water quality of the supernatant. By conducting an analysis of the water filtered using a filtration paper type 5-A, the water quality achieved upon executing sand filtration as a post-process to the coagulation can also be estimated. In evaluating the measurement and design of the treatment system, it is advisable to observe the time required for the flocs to grow to visually identifiable proportions after the rapid agitation phase, as well as whether the generated flocs are easily damaged during the gradual agitation. 78 Jar Test

79. Jar test Items analyzed in water quality evaluation differ depending on the type of effluent and purpose of treatment, but generally include visual inspection, temperature, turbidity, chromaticity, transparency, pH and suspended solids. COD, BOD and oil content may also be gauged as needed. 79 Jar Test

80. 3.2.3 (3) Components of the coagulation system Coagulating sedimentation is very important process most commonly used in the field of waste water treatment. In ordinary precipitating separation, the design of the system is based on the sedimentation rate or distribution of the particle diameter of the suspended particle to be separated. However , the suspended solids subject to the coagulating sedimentation process consist of colloidal distributions incapable of settling by precipitating separation within a limited amount of time . 80 Coagulation

81. Accordingly, the distribution of particle diameter within the pre-treatment water is not so importance, and the efficiency of the separation process is determined by the capability of the system to coagulate the solids into coarse particles ( flocs ).  time savings Although ”coagulation” and “sedimentation” are quite different processes, there are systems capable of performing both operations. Coagulating sedimentation systems must be capable of performing the following procedures : 81 Coagulation

82. ① Introduction of the appropriate flocculating agent The type of agent to be deployed is not determined by systematic demand, but by the water quality of the suspended substances subjected to the treatment. In any form of coagulating sedimentation, the types and quantities of flocculating agents are defined solely based on the water quality regardless of the system employed. As methods to estimate the quantity of agent to be deployed from the result of water quality analysis are yet to be developed, the determination of agent deployment involves a trial-and-error with the jar testing procedure. 82 Coagulation

83. ② Particle concentration In order for the suspended particles to coagulate into flocs after the surface potential is neutralized by the introduction of flocculating agents, particles need an opportunity to contact each other. The probability of particle osculation increases as the concentration gets higher. Numerous theoretical formulas are proposed concerning the representation of the rate of coagulation, and can be summarized into the following: 83 Coagulation

84. 84 Where n : quantity of particles within a specified volume of water (SS particle concentration) t : time k : coefficient In the formula above, the value “k” is a coefficient determined by the agitating condition and diameter of the particle during the initial stages of coagulation and the growth stage of the flocs generated. Based on this formula, the rate of coagulation increases corresponding to the concentration of the particles . d =differentiate Coagulation

85. ③ Appropriate agitation The rate of floc generation relates to the value G signifying the strength of agitation (average velocity gradient of fluids). Value G is determined from the motivity W per unit volume with the relationship of G = √W/μ (where μ signifies the viscosity coefficient). If the force of agitation is too excessive, the coagulating floc is broken up by the shear force working in its surroundings and re-disperse. The optimum condition of agitation is unique to respective coagulating reaction systems. Such conditions are currently identified empirically (experimentally) as means of theoretically calculating the condition is yet to be developed . 85 Coagulation

86. ④ Sedimenting separation / concentration / sludge removal The flocs cultured in the coagulation process are then removed from the tank after separation by sedimentation and condensation to an appropriate level of concentration. 86 Coagulation

87. 3.2.3 (4) Coagulating sedimentation system All coagulating sedimentation systems are composed of the four factors described in section (3) above. 87 Coagulation

88. ① Horizontal flow type Agitation of 30 minutes to 1 hour, though the duration needs to be extended when the particle concentration and the temperature is low . 88 Coagulation

89. Horizontal flow type System consists of a flush mixer, a series of flocurator , and a sedimentation basis for the separation of the enlarged flocs . The rapid agitation time is about 1 to 5 minutes, with flow speed in the vicinity of the agitation blades empirically set to 1.5 m/sec ( waterworks utility standard).   The flocurator The particles are attributed with coagulative properties by the flocculating agent. Each flocurator stage is designed to gradually reduce the strength of agitation 89 Coagulation

90. An example of the flush mixer and flocurator (figure 3.2.3-2) Coagulating sedimentation systems incorporating horizontal flow are utilized in water purification plants maintained by waterworks authorities . 90 Figure 3.2.3-2 Example of gradual agitation system and coagulation basin Electric motor Each stage is designed to gradually reduce the strength of agitation according to the floc growth to prevent the formed flocs ’ breakdown Coagulation

91. ② Contact coagulating sedimentation systems The coagulating reaction can be accelerated by suspending large flocs (referred to as “mother flocs ”) in the medium while floc is being produced through the collision of particles . Various contact coagulating sedimentation systems enable a significant reduction in floc formation time and they can settle the suspended solids very swiftly . The system is designed in numerous configurations, roughly categorized into three types depending on the method of solid contact facilitation and the mechanism of solid-liquid separation (a) slurry circulation; ( b) slurry blanket; and (c) mixed/compound types, further sub-divided by agitation method into mechanical agitation, hydraulic (utilizing water jets or pulsation flow) and pneumatic/air agitation. 91 Coagulation

92. The following formula is proposed as a means of calculating the coagulation speed under influence of large existing flocs : 92 where: n : Number of minute flocs (also referred to as micro- flocs ) generated by the introduction of flocculating agent per unit volume (number ・ cm -3 ) N : Number of existing flocs per unit volume (number ・ cm -3 ) D : Diameter of existing flocs (cm) ε : Agitation energy consumed per specific duration within an unit volume of the medium (erg ・ cm -3 ・ s -1 ) μ : Viscosity coefficient of water (g ・ cm -1 ・ s -1 ) Based on this formula, it is evident that the influence from the D 3 N of the existing flocs is significantly large. Coagulation

93. 93 Circulating slurry accelerates coagulation (SS particles’ contact action) and enlarged flocs can settle for short time An example of slurry circulation-based system (High speed coagulating sedimentation system) NIPPON RENSUI CO. http:// www.rensui.co.jp/en/index.html as of June 2012 Primary agitation chamber Secondary agitation chamber Raw water Outflow Coagulant Sludge removal drainage Coagulation

94. An example of slurry circulation-based system 94 Figure 3.2.3-3 Slurry circulation coagulating sedimentation system Coagulation

95. The raw water is introduced to the primary agitation chamber to be combined with existing flocs and flocculating agents. The slurry is then agitated by agitation blades, concurrently pumped into the secondary agitation chamber by the movement of the blade, flowing out into the slurry pool through the draft tube. The solids ( floc ) are separated from the water within the slurry pool, with the slurry flowing down and circulating back into the primary chamber. As particles inducted from the raw water are caught in the floc , the particle concentration within the slurry increases with the passage of time. 95 Coagulation

96. On the context of solid-liquid separation, it is undesirable to increase the density of particle concentration excessively. Accordingly , the floc is condensed by sedimentation within a concentrator located within the slurry pool and eliminated as necessary to maintain a certain level of concentration. 96 Coagulation

97. 3.2.3(5 ) Applicable scope In coagulating sedimentation, the particle diameter distribution of the source suspended solid is (relatively) irrelevant for the most part, with the sedimentation speed of the floc derived from the coagulation process deciding the efficiency of separation. Accordingly , coagulation method is applied to colloidal interfusion ( mixing, adding ) which can not be settled by a natural sedimentation method. Additionally , the coagulation/sedimentation method effectively separates COD, chromaticity, trace amounts of oil (emulsion) and heavy metal as long as the contaminants are distributed in colloidal form . 97 Coagulation

98. Phosphoric salt Coagulation also corresponds to the removal of phosphoric salt by utilizing calcium hydroxide or aluminum sulphate (or ferric salt) as the flocculating agent. 消石灰法＆硫酸ばん 土 In calcium hydroxide method, the pH of the water is increased to 9.5 or higher to precipitate the calcium phosphate by chemical reaction prior to coagulation and sedimentation. In this case, organic polymers or ferric salts are used as the flocculating agent. In aluminum sulphate method, it is assumed that the aluminum or ferric salts introduced into the water chemically reacts to the phosphorus to form insoluble salts and the coagulation is induces by excess aluminum salts. Normally , organic polymers or calcium oxide is added to promote the coagulation. Flocculating agents often added to the aeration tank of the active sludge treatment system to remove the phosphorus contained in organic effluent . 98 Coagulation

99. 3.2.4 Flotation Separation ‘Dissolved air flotation’ introduces very fine air bubbles into the waste water. The bubbles, which attach to or become entrapped within particles, float to the water surface to form a solids layer that can be skimmed off. Flotation 99

100. Schematic figures of Pressurized-air Flotation 100 Scum (floating sludge) Air bubbles Water in scum (sludge ) 　 is relatively smaller than one of sedimentation sludge Flotation

101. Flotation Separation If the suspended solid within the water has a density smaller than water, the solids naturally float to the surface, allowing for their separation. Although floatation is an inversion to sedimentation, floatation/sedimentation methods are both associated with gravity, and are therefore collectively referred to as gravitational separation method. In the context of effluent treatment, oil is one of the primary contaminant with density less than that of water . Flotation 101

102. Flotation Separation If both coagulating sedimentation and floatation methods are applicable to the treatment of a certain type of effluent, the treatment method should be determined upon adequate evaluation on the laboratory or pilot plant, thus comparing the construction and operation costs. Relative merits of the two methods can be summarized as: Flotation 102

103. Rate of floatation is higher than the rate of sedimentation. Power consumption is greater in pressurized floatation treatment. Turbidity of the treated water is lower in coagulating sedimentation. Water content of the resulting sludge is lower in pressurized floatation. Pressurized floatation method tends to be more stable to fluctuations in the temperature of the raw water. 103 Floatation treatment is often applied to oil-containing effluents from petroleum processing, automobile and mechanical processing, as well as effluent containing carbon particles and effluents from paper production plants. Flotation

104. In one example of sewage sludge concentration using pressurized floatation method, the original sludge with a concentration of 0.5 % to 1.5% is infused with air-saturated water pressurized to 300 kPa (gauge) on quantities of twice to three times the amount of the raw water. The contaminant is floatation concentrated in the process to yield a concentrated sludge with concentration ranging from 3.5 % to 6%. 104 Flotation

105. Flotation Separation Process for separating suspended materials continuously from the waste water by floating up SS: its specific gravity is smaller than water; ex. oil SS slightly larger density or same will be attached very small air bubbles to the surface of the particles and reducing its apparent specific gravity -> floating up The Stokes’ law V = g （ ρ － ρ ） d 2 18μ g is the gravitational acceleration, acceleration of gravity (cm/s 2 ) ρ is the mass density of the particles, density of particle (g/m3) ρ is the mass density of the fluid, density of water (g/cm3) (vertically downwards if ρ  >  ρ , upwards if ρ  <  ρ  ) Flotation 105

106. Pressurized-air Flotation Oil separator under atmospheric 　 　 pressure 　 (ex. API, PPI, and CPI will be applied based on oil particle diameter >150, >100, >60 μm ) Air, dissolved in water under pressure (200 -500 kPa ), is released to the atmospheric pressure in the form of numerous minute (small) bubbles, which are attached to the surfaces of the particles suspended in waste water, thus floating them up to the water surface. Flotation of the particles attaching air bubbles is the reverse phenomenon of sedimentation and the floating velocity is given by Stokers’ equation. Flotation 106

107. Henry’s Law Henry's law S tating that the amount of a gas that dissolves in a liquid is proportional to the partial pressure of the gas over the liquid at a constant temperature, provided no chemical reaction takes place between the liquid and the gas. It is named after William Henry (1774–1836), the English chemist who first reported the relationship. Fig. the University of Texas at Austin Flotation 107

108. Applicability of floatation and points to consider The optimum gas-solid ratio and solid-removal characteristics (based on the nature of SS) The gas-solid ratio is determined from the pressure of air tank and the mixing ratio of pressurized water (flow rate and pressure) The gas-solid ratio, usually 0.02 or more, is the ratio of the mass of the generated bubble and the mass of the separable solid (Henry’s Law) Considering factors Air/water flow rate, exhaust air, 　 　 bubble condition, temperature, 　 　　 exhaust air and sludge (>A/S), scum (floating sludge) control Followings are some types of pressurized-air 　　　　　　　　　　　　　　　　　 flotation tanks, vertical and horizontal etc. Flotation 108

109. Flotation 109

110. Flotation 110

111. Mainly hydrogen gas (w: small portion of oxygen) generated by water electrolysis is utilized to float up SS in waste water Flotation 111

112. Flotation(F) vs. Sedimentation(S) Floating velocity is higher than sedimentation in general, for example F takes 15 – 30 minutes for processing S takes 60 – 120 minutes for processing Turbidity: F < S Electric energy: F > S Water in Scum (sludge): F < S ex. 95% vs. 99% Flotation Note: Flotation: In case of refineries or petrochemical plants, they use dissolved nitrogen flotation to minimize the potential for explosion 112

113. 3.2.5 Clarifying filtration 113

114. 3.2.5 Clarifying filtration Trace amounts of suspended solids remaining after treatment by gravitational separation method (floatation/sedimentation) is further removed through clarifying filtration method. As sand is typically used as the filtration medium, the method is also referred to as sand filtration. Anthracite and garnet may also be used as the filtration medium, and the method is sometimes called granular bed or deep bed filtration . Gradual sand filtration and rapid sand filtration are basically conducted in waterworks purification to eliminate the turbidity of the water. In sewage treatment, rapid sand filtration (hereafter referred to as “sand filtration”) is used as the finishing process. 114

115. In sand filtration, the suspended solids are captured and detained in the gap existing among the medium within the filtration bed. However, the captured particles are extremely small on comparison with the gap (pore) among the medium. It is therefore assumed that the suspended particles adhere to the filtration medium through flocculation in addition to the mechanical sieving effect of the medium. ふるい分け 115 Clarifying filtration

116. Accordingly sand filtration is not effective against colloidal particles which are unresponsive to coagulation. Additionally , the filtration resistance increases with the passage of time, and the process must be terminated to cleanse the filtration bed once the filtration resistance or the turbidity of the treated water reaches a specified limit. Sand filtration systems should be designed to increase the filtration yield per processing cycle, while reducing the water requirement during the cleansing process ( backwash). 116 Clarifying filtration

117. 117 An example of gravitational sand filtration system configuration

118. 3.2.5 (1) Configuration of sand filtration systems In the depicted system, the difference in the water level between the filtration pool and the post-filtration basin is utilized as the driving force of the system (Fig. 3.2.5-1 ） . The upper section of the post-filtration catchment is exposed, enabling the condition of the catchment to be visually confirmed and facilitating maintenance/management activities. This configuration is often adopted in waterworks purification facilities 118 Clarifying filtration

119. Figure 3.2.5-2 Configuration of pressurized sand filtration systems 119 http://www.kotobukikk.com/yousui.html Higher filtration ratio ・ Anthracite and sand, 2 layers For drinking water, secondary treatment, and pre- treatmen ｔ of recycling water 　 Source: Kotobuki KK Clarifying filtration

120. As indicated in figure 3.2.5-2, the pressurized sand filtration system is closed off, with filtration implemented by pump pressurization. As gravitational filtration systems depend on the difference of level to provide the pressure for filtration, the structure inevitably requires height. In the case of pressurized filtration, the necessary pressure can be achieved simply by increasing the pump output. Drawbacks of the system are the requirement for the use of steel plates and other high tensile strength materials, and the fact that the configuration is limited to cylinders to withstand the applied internal pressure. Other than the method of pressurization, operation principle of the two filtration system is exactly the same. 120 Clarifying filtration

121. During treatment, the accumulation of the captured suspended solids gradually blocks the gaps (pore) present among the filtration layer, thus increasing the filtration resistance. To resolve this situation, pressurized water is regularly injected into the chamber from below the filtration layer to cleanse the medium. This procedure is called back washing, and may be combined with the spraying of pressurized water to the surface of the filtration layer for enhanced cleansing effect. Air wash (elutriation) is also effective in case of turbidity types with strong adhesive properties . 121 Clarifying filtration

122. Garnet http ://www.kk-rinkai.co.jp/products/other/index.html 122 Anthracite Silica sand http://www.kubota.co.jp/amenity/japanese/private_business/yohaisuisyori/sunaroka_kasseitansyori.html Clarifying filtration

123. Filtration medium Filtration medium – generally sand -- is the most important aspect of filtration systems. Water work authorities believe sand with effective diameter of 0.5 to 0.7 millimeters with uniformity coefficient of less than *1.7 to be best suited as filtration medium. 　有効径＆均等係数 *The measure of variation in particle sizes of filter and ion exchange media. The coefficient is defined as the the ratio of the sieve size that will permit passage of 60% of the media by weight to the sieve sieve size that will permit passage of 10% of the media material by weight . Uniformity Coefficient= 60% of the media/10 % of the media ( Effective diameter ) 123 Clarifying filtration

124. Filtration medium The effective diameter signifies grains complying to the condition that, when sieved, 10% of the medium passes through a screen mesh of the specified size – in this case, 0.5 to 0.7 millimeters. Meanwhile , the uniformity coefficient signifies the ratio of effective diameter to the mesh size which allows 60% of the overall mass to pass through. Uniformity coefficient increases corresponding to the irregularity of grain size, and materials indicating a high uniformity coefficient is considered unsuitable for use in filtration treatment . If all gain size is same the uniformity coefficient will be 1. 124 Clarifying filtration

125. The layer of filtration medium is generally between 500 to 700 millimeters. To prevent the sand to flush out of the lower catchment section, a layer of supporting gravel is laid between the lower catchment section and the filtration layer. The supporting layer is typically configured with fine grained sand on top with layers of coarse grained sand laid underneath. 125 http://www.setubikyo.or.jp/main 水処理工学ノート ４ 砂ろ過処理 U ； ろ過速度（ 透水速度） Q ； ろ過 流量　 A ； ろ 層面積 L ； ろ 層 厚さ　　 y ； 損失水頭 http:// www.civil.chuo-u.ac.jp/lab/eisei/jugyou/mizushoriNO4.1.pdf#search=' Clarifying filtration

126. 3.2.5(2) Filtration resistance The water head difference created as the water permeates through the filtration layer is termed filtration loss of water head or filtration resistance, and gradually increases with extended filtering . Accordingly, the process is terminated when the filtration resistance reaches a pre-designated value (typically 15 to 20 kPa ), initiating the cleansing of the filtration medium . The filtration resistance without any detainment of suspended solids is termed initial loss of head, and forms the basis of filtration system design. The filtration resistance for water flowing through a granular bed ( layer) is generally represented by the Kozeny -Carman's equation indicated below : 126 Clarifying filtration

127. 127 Kozeny -Carman's equation where : ho: Filtration resistance of a clean filtration layer (Pa) k: Coefficient (--) u: Filtration speed (m/s) L: Filtration layer thickness (m) μ: Viscosity coefficient of water (kg ・ m -1 ・ s -1 ) d: Filtration medium particle diameter (m) ε: Void fraction of filtration layer (--) Clarifying filtration

128. In ordinary sand, the void fraction is usually within the range of 0.40 to 0.50. As indicated in figure 3.2.5-3, the void fraction function value calculated as ( 1 – ε) 2 ／ ε 3 tends to increase abruptly as the value ε decreases. More specifically, suspended solids detained ( captured) within the filtration layer reduces the void fraction ε with the passage of time, increasing the filtration resistance. Even when the total quantity of the detained particles is equal, large concentrations of the detained suspended solid in the surface portion of the filtration layer will rapidly increase the resistance for downward flows . 128 Figure 3.2.5-3 Function of void fraction Clarifying filtration

129. 3.2.5 (3 ) Cleansing of the filtration medium The filtration medium needs to be cleansed when the filtration resistance value reaches a predestinated level. Backwashing (flow back cleansing) is generally used in conjunction with surface cleansing and air elutriation. Insufficient cleansing of the filtration layer may result in the formation of mud balls (agglomeration of turbidity substances attached to alien substances) over time. The mud balls are nodules comprised of a mixture of filtration medium particles, suspended solids and adhesive substances in a spherical form, particularly occurring in the filtration treatment of raw water containing large quantities of algae and other microorganisms. 129 Clarifying filtration

130. The effectiveness of backwash (flow back cleansing) is maximized while the filtration layer is fluidized and the maximum number of particle collisions are in progress. The following equation is proposed for the calculation of the optimal flow back speed : 130 where : u B : Optimal flow back speed (m/s) v t : Sedimentation speed of individual filtration medium particle (m/s) Clarifying filtration

131. 3.2.5 (4 ) Multilayer filtration and upflow filtration Various improvements and innovations are made to achieve economic filtration . In sand filtration, the water generally flows from above to below. Because the grains contained in the sand layer is not uniform, repeated implementation of backwash stratifies the filter bed, creating layers of finer grains in the upper section. 131 水処理工学ノート ４ 砂ろ過処理 As the water is applied from above to below, a significant portion of the suspended solids is detained in the fine-grained top layer, concentrating most of the filtration resistance in the top section of the bed. This situation is uneconomic in that the intermediate and bottom layers of the sand have not functioned sufficiently in detaining the turbidity before the head loss achieves the predestinated cleansing value. http:// www.civil.chuo-u.ac.jp/lab/eisei/jugyou/mizushori Clarifying filtration

132. This situation can be avoided by using filtration grains of uniform diameter, but a uniformity coefficient value of 1 is impossible to attain as long as natural sand is used as the filtration medium. The ideal configuration of the filtration layer would be to constantly maintain a layer of coarse grains on top, with the granular diameter decreasing in the lower sections of the bed, with the sequence never being disrupted by backwash (flow back). To this end, filtration medium of alternate density are combined . Natural filtration medium currently in use include anthracite, sand and garnet, with the dual-layered combination of anthracite and sand being most common. 132 Clarifying filtration

133. Although the typical combination is as indicated in table 3.2.5-1, the optimal combination of grain size and layer thickness depends on the condition of the water quality . 133 Clarifying filtration

134. One method of suppressing the fluidization is to install a steel latticework referred to as the “grid” at a depth of about 10 cm below the top of the sand layer. This configuration is illustrated in figure 3.2.5-4. The depth of the filtration bed is 2 meters, with the lower layer consisting of 1.4 meters of coarse sand with diameter of 2.0 to 3.0 mm, the upper layer filled by fine-grained sand of 0.6 to 0.8 mm to the depth of 0.6 meters. In this configuration, the cleansing is conducted by terminating the water flow and supplying air from below to disrupt the bridging effect of the grid, then washing away the detained floc with water. 134 Clarifying filtration

135. 135 Filtered water Clarifying filtration

136. Up-down flow filtration systems apply the advantages of both dual layer and upward flow filtration technologies. The configuration of this system is as indicated in figure 3.2.5-5. In this system, the raw water enters the filtration layer from above and below, with the outflow passing through the collecting pipe located in the middle section of the filtration layer. The downward flow passes through the anthracite layer into the upper section of the sand layer, while the upward flow enters from the bottom of the sand layer, with both flows passing through the sand in the sequence of coarse grain to fine grain . In this system, the fluidization of the sand due to the upward flow is suppressed by the downward flow, eliminating the need for grids. The suspended solids deeply penetrate the filtration layer before detainment in these systems, making it necessary to devise methods to cleanse the entire filtration layer swiftly . 136 Clarifying filtration

137. pH control 137 3.2.6 pH adjustment

138. 3.2.6 pH adjustment In all bodies of water, pH is one of the fundamental water quality-related properties subject to regulation. pH adjustment is an important pre-processing procedure to effectively implement biological and coagulating sedimentation treatments . Neutralization signifies the addition of acid/alkali to restore the pH of the water to neutral . 138 pH adjustment

139. 3.2.6 (1) 　 pH Portions of the water molecule dissociate into hydrogen ion and hydroxide ion in the following manner : The mole concentration of hydrogen ions [H + ] and hydroxide ions [OH - ] in water is established according to the following formula (Kw): At the temperature of 25 degrees Celsius, K w = 10 -14 mol 3 /L 2 is established, and the logarithm for formula (Kw ) is calculated as: When water is neutral, the above formula is calculated as logK w = log[H + ] = log[OH - ] = -7. Value - log[H + ] is indicated as the pH, to be called hydrogen ion concentration index. At ambient temperature (25 degC ), pH < 7.0 is acidic while pH > 7.0 is alkali. 139 pH adjustment

140. pH r elationship between [ Ｈ ＋ ] [ＯＨ － ] 140 logK w = log[H + ] = log[OH - ] = -7 multiplicative inverse The mole concentration of hydrogen ions [H + ] the negative logarithm hydrogen exponent Mole; 6.02×10 23

141. 141 http://www.epa.gov/acidrain/education/site_students/phscale.html http://cannabisseedsnow.com/growing-marijuana-guide/marijuana-ph-and-fertilizers/ pH adjustment

142. 142 ‘Sensing pH, controlling pH’, By Brian LaBelle ( 1 May 2005)

143. 3.2.6 (2) Neutralization curve In the chart, the quantity of acid/alkali added is indicated along the abscissa axis, while the pH value of the sample specimen is plotted along the ordinate with the resulting curve designated as the neutralization curve. 143 An example of the curve is indicated in figure 3.2.6-1. The neutralization curve for hydrochloric acid rises abruptly in the vicinity of pH 3 to 11, and the application of small amounts of the neutralization agent (sodium hydroxide solution) causes the pH to react significantly. On the other hand, the neutralization curve for acetic acid rises in the range of pH 3 to 6, with the fluctuation occurring more gradually. This is due to the buffering property of the acetic acid solution. ( 酢酸 sakusan ) pH adjustment

144. ｐ H Neutralization curve: Reaction between an acid and a base which produces a neutral solution (pH = 7 ) 144 The amount of an alkali required to neutralize solutions of the same pH is not always same. A solution containing heavy metal ions, for example, requires more alkali for the hydroxide precipitation CH3COO, acetic acid (acetate ions) with buffering capacity and HCl requiring small amt. of NaOH , each curve is shown in the left figure 　 Acetic acid is a weak acid because its molecules dissociate very little, producing few hydrogen ions in the solution Hydrochloric acid ( HCl ) Acetic acid CH3COO Figure 3.2.6-1 　 Neutralization curve for 20 mL of 0.10 mol /L hydrochroric acid and acetic acid Volume of solution for 0.10 mol /L- NaOH (milliliter) pH adjustment

145. 3.2.6 (3) Neutralization agent In selecting the neutralization agent, such characteristics as the response speed, neutralization curve, and sedimentation/dehydration of the resulting product material should be taken into consideration, selecting the most economical of the candidates. Characteristics of neutralization agents commonly used are indicated in table 3.2.6-1 . 145 pH adjustment

146. 146 CaO , calcium oxide or quicklime/ unslaked lime, is also utilized (powdered form) pH adjustment

147. 3.2.6 (4) Processing of effluents containing metallic ions Effluents containing metallic ions are generally acidic. When increasing the pH value by adding alkali, the metal ion responds to hydroxide ions and produces hydroxide sedimentation. This is due to the fact that the concentration of hydroxide ions increases with the rise of the pH, reducing the solubility of the metal ion. This relationship can be calculated based on the solubility product constant values. 147 pH adjustment

148. When n number (valence) of metallic ion is represented as M n + , the following equation is obtained. 溶解度積 Ksp The solubility product constant is constant depending on the type of hydroxide ( refer to table 4.1.3-2 in section 4.1.3 ) . Meanwhile, the equation is established, resulting in the following equation for the solubility of the metallic ion Mn +: 　 148 Accordingly, a linear relationship is established between the pH and Log[ Mn +], and can be plotted as indicated in figure 3.2.6-2. pH adjustment

149. Solubility of metals 149 Figure 3.2.6-2 Relationship between the solubility of metallic ions and pH pH adjustment

150. When acid pickled effluents (acid cleaning) from ironworks or metal-surface treatment facilities containing iron ions are being treated, the neutralization precipitates ferric hydroxides. As illustrated in figure 3.2.6-2, Fe 2+ ions cannot be sufficiently removed without increasing the pH to 9 or 10. However, the transformation of the ion to trivalent by injecting air during the neutralization process allows for an almost complete removal of the ferric ion with the acidity in the vicinity of pH 4. 150 pH adjustment

151. Amphoteric metals It is known that, the settleability ( sedimentation ability ) and thickenability of the sludge could be significantly improved by circulating portion of the hydroxide sludge sedimentation to the neutralization chamber during this phase . It should be noted that the hydroxides of metals including aluminum, lead, zinc, and chrome are amphoteric in nature, responding to excessive hydroxide ions within a high pH environment. The reaction will cause the metal to redissolve into the water as metal complex ions. 151 pH adjustment

152. 152 pH adjustment

153. Amphoteric metals In other words, the solubility of metal complex ions are represented as a straight diagonally right up plot on the double logarithm axis in relation to the pH (see Fig. 3.2.6-2). The value of the equilibrium constant K takes on a unique value for respective metals (refer to table 4.1.3-3 in section 4.1.3). The solubility of metals forming amphoteric hydroxides indicates the minimum value for the specific pH values, and should be taken into consideration in the sedimentation removal of these metals . 153 pH adjustment

154. 3.2.6 (5) pH adjustment system The agitation chamber is the core portion of the neutralization system. Dimensions of the neutralization chamber vary depending on the types of effluent treated and the types of agents used. When using calcium hydrate, sodium hydrate or sodium carbonate as the neutralization agent, a retention time of 5 to 30 minutes will suffice . The simplest configuration capable of automatically adjusting the pH as depicted in figure 3.2.6-3 . 154 pH adjustment

155. 3.2.6 (6) Improvement of thickenability for metal hydroxides Metal hydroxides created by neutralizing acidic effluents containing metallic ions by conventional methods of treatment indicate; low rate of sedimentation and sludge dewatering. The water content for the sludge consisting of such hydroxides remains above 97% after sedimentation/concentration treatment by thickeners. Even if the sludge was to be retained within storage reservoirs for extended durations, the resulting final water content will not decrease to less than 75 to 85%. Furthermore, dehydration by filter press will only result in sludge-cakes with water content in the range of about 55 to 80 %. 155 pH adjustment

156. 156 Figure 3.2.6-3 Basic method of pH adjustment This system provides a sufficient level of accuracy in case the effluent to be treated has a high reactivity with a large buffer index and small flow fluctuation. pH adjustment

157. However, it is known that if the sludge separated within a sedimentation facility is circulated back into the neutralization reaction chamber, the sedimentation thickening dehydration characteristics of the sludge will indicate a significant improvement. Within the metal mining industry, this method is known as the “sedimentation repetition neutralization” method, and applied to the treatment of pit effluents. When implementing the method, the process requires approximately 30 to 60 days from the initial operation to achieve steady operation . 157 pH adjustment

158. HDS * method is a similar neutralization process involving the introduction of alkaline agents to the sludge to be recirculated, then interfusing the sludge with the raw effluent for neutralization. *Volume reduction technology of heavy metal sludge It is reported that the procedure reduced the water content to 70 - 80% in thickener processed sludge, with a water content of 40 to 45% for dehydrated sludge cakes after compressing with a filtration press. 158 pH adjustment

159. pH control To remove harmful heavy metals dissolved in acidic water by changing them to un-soluble hydroxides through neutralization Or to adjust pH to optimum levels best suited for coagulants to exhibit highest coagulation efficiency The optimum amount of acid or alkali to be added for pH control of waste water should be determined from the neutralization curve 159 pH summary

160. Heavy metal treatment Hydroxides, insoluble precipitate, are the form of precipitate most commonly utilized Others incl. carbonates or sulfides in some cases Hydroxides of Cr3+, Al+ and Zn2+ etc. dissolve again into water at high pH range by reactions with excess hydroxyl ion. 160 pH summary

161. Sulfide , insoluble precipitate Heavy metal sulfides More insoluble than their hydroxides Mercury, cadmium, lead, and copper Precipitated as sulfides by adding hydrogen sulfide gas or sodium sulfide solution Mercury: impossible to precipitate as hydroxide but as sulfide 161 pH summary

162. Oxidation The chemical combination with oxygen It also includes loss of hydrogen and an increase in valence of a metal 　原子価増加 A reaction in which the atoms in an element lose electrons and the valence of the element is correspondingly increased . Reduction is the reverse process of oxidation 162

163. The most popular oxidizing agent used in the field of waste water treatment is chlorine Effective pasteurizer and essential to the decomposition of organic compounds, hydrogen sulfide and cyanides in water Chlorine is present in water in the form of Cl2, HClO and ClO - (depend on pH) Chlorine or ozone is principally used for the oxidative decomposition of cyanide (CN) Note that some types of heavy metals coexisting in the waste water retards oxidation ( cyano -complexes of iron, nickel, cobalt, etc.) 163

164. Sludge disposal Sludge containing heavy metals such as Hg, Cd, Pb , Cu and Zn ions Toxic if freed to the surrounding environment To be sealed in a concrete block and disposed after a strict solubility test (leaching test) - 164

165. Arsenic ( As) converting all of the arsenic to a valence of +5 (some will be +3) which is easier to remove The technologies for As removal include adsorption on alumina, reverse osmosis membrane separation, ion exchange, chelate resin, or lime softening. Alumina may have a problem with progressive loss of capacity R emoval by activated alumina may be utilized for drinking water treatment (strong adsorption) As 165

166. Arsenic ( As) converting all of the arsenic to a valence of +5 (some will be +3) which is easier to remove The technologies for As removal include adsorption on alumina, reverse osmosis membrane separation, ion exchange, chelate resin, or lime softening. Alumina may have a problem with progressive loss of capacity R emoval by activated alumina may be utilized for drinking water treatment (strong adsorption) As 166

167. Semiconductor plant waste water aluminum salt Iron salts Iron salts raw water As 167

168. Standard treatments oxidize any trivalent arsenic with peroxide, permanganate, 過マンガン 酸塩 、 ultraviolet light, or other oxidizer followed by precipitation, filtration, etc. as above. UV light and titanium oxide have improved oxidization efficiencies for other compounds but I haven't seen any data on arsenic yet . Each source (your water) should be analyzed and specific treatments tested before you invest in a system. As 168

169. Co-Precipitation Arsenic Removal There are several Best Available Technologies (BAT) for arsenic removal from water , and after careful consideration of the advantages and disadvantages of each, many Michigan water utilities have chosen Oxidation/Filtration, specifically in the form of Iron Co-Precipitation Filtration. Recently , Tonka has provided systems for Michigan communities that treat over 50 million gallons of water per day . February 15, 2012 by Rick Mann   Tonka Equipment Company Arsenic Removal in Holly, MI As 169

170. Effective, Efficient Treatment for Arsenic Removal Iron co-precipitation filtration is a simple and very cost-effective method for treating arsenic, and the technology also removes iron and manganese. There are four steps : Oxidation - Soluble iron, Fe(II), and arsenic, As(III), are oxidized, typically with chlorine . This step forms iron hydroxide solids and As(V) arsenate. 　 ヒ 酸塩 ; ヒ酸 Co-Precipitation or adsorption – As(V) arsenate adsorbs or coprecipitates with the iron hydroxide solids. Additional iron may be added as Fe( Cl )3. Filtration – Particles/precipitants (ferric arsenate) are filtered from the water. Particles / precipitants are backwashed to waste February 15, 2012 by Rick Mann   Tonka Equipment Company As 170

171. The oxidation step creates a form of arsenic As(V) arsenate which is preferred for iron co-precipitation because it is less toxic and less soluble. Arsenate is a charged anion, which makes it easier to remove with Iron Co-Precipitation . Arsenic removal efficiency is directly related to iron concentration. Tonka has had excellent removal at all of our plants in Michigan using naturally occurring iron. In the rare occasion (in MI) that the natural iron to arsenic ratio is not sufficient, additional iron can be added to achieve optimized arsenic removal. February 15, 2012 by Rick Mann   Tonka Equipment Company As 171