Engineered systems for wastewater treatment and disposal

하수 : 생활에서 발생되는 배수의 총칭으로, 오수와 우수로 구성 오수 : 가정에서 발생되는 생활하수, 공장이나 사업장에서의 배수, 지하수 등이 집합된 것이며 우수란 빗물이 도로 등의 배수로를 통하여 모 여진 물이다. 하수의 특징 : 질적으로 매우 복잡하고, 지역에 따라 다르며 오수와 우수를 함께 집수하 는 합류식인가, 별도로 하는 분류식인가에 따라 그 특성 이 변화, 처리구역의 지역적 특 성, 규모, 인간의 생활양식, 공장의 조업방식과 시간대별, 요일 별, 계절에 따라 양적, 질 적으로 변화. 하수의 발생원 집 : 화장실, 씽크대, 욕조, 등 도로 : 빗물, 지하수 등의 길거리의 배수 학교 : 배수로, 화장실, 하수구 공장 : 공장폐수 하수처리의 주요 기능 고형물 제거 : 하수중의 모래, 넝마, 막대기, 요구르트병 등 제거. 오염물질과 유기물 감소 : 호기성 미생물에 의하여 유기물 등 오염물질을 분해, 제거 산소 회복 : 호수, 하천, 바다로 보내지는 처리 수에 산소를 회복. 시설의 중요성 각종 질병을 유발하는 세균으로부터 공공위생을 보호. 맑은 하천, 해안, 맑은 물을 위한 수질을 보호.

Activate Sludge Plant for a Municipal Wastewater

Tertiary Treatment of a Secondary Effluent by Physical-Chemical Methods

Physical-Chemical Treatment of Raw Municipal Wastewater

Completely Mixed Activated Sludge Plant for an Industrial Wastewater

Dispersed Plug-Flow Activated Sludge Plant for an Industrial Wastewater. Aerated Lagoon System for an Industrial Wastewater

1. Primary treatment : Pre-treatment OperationsApplications ScreeningRemoval of coarse and settleable solids by interception CommunitionGrinding of coarse solids to a more or less uniform size Flow equalizationEqualization of flow and mass loadings of BOD and SS MixingMixing of chemicals and gases with wastewater, and maintaining solids in suspension Flocculation Promotes the aggregation of small particles into larger particles to enhance their removal by gravity sedimentation SedimentationRemoval of settleable solids and thickening of sludge Flotation Removal of finely divided SS and particles with densities close to that of water. Also thickens biological sludges FiltrationRemoval of fine residual SS remaining after biological or chemical treatment MicroscreeningSame as filtration. Also removal of algae from stabilization-pond effluents

1) Screening : To remove coarse solids ☞ To protect pumps and other mechanical equipment To prevent clogging of valves and other appurtenances ※ Municipal wastewater : BOD, SS 20 ～ 35% 제거 Definition sketch for types of screens used in wastewater treatment.

 Bar rack Coarse : 38 mm 이상 Fine : 12 ～ 25 mm * The slope : 30 degree(in general) For mechanical cleaning : 70 degree

Head loss : Kirschmer

Bar typeβ Sharp-edged rectangular2.42 Rectangular with semi-circular upstream face1.83 Circular1.79 Rectangular with semi-circular upstream and down stream faces1.67 Table Kirschmenr's values of β  Design of Coarse Screen Installations (1)location (2) approach velocity (3) clear openings between bars or mesh size (4) headloss through the screens (5) screenings handling, processing, and disposal (6) controls

 Fine Screens Typical fine screens: (a)static wedgewire, (b)drum, and (c) step. Instep screens, screenings are moved up the screen by means of movable and fixed vertical plates.

 Design of Fine-Screen Installations

 Microscreens

2) Flow Equalization ◈ Principal applications are for the equalization of * Dry-weather flows * Wet-weather flows from separate sanitary sewers * Combined storm water and sanitary wastewater flows ◈ The principal benefits * Wastewater treatability is reportedly enhanced after equalization * Biological treatment is enhanced, because shock loadings are eliminated and can be minimized, inhibiting substances can be diluted * The effluent quality and thickening performance of secondary sedimentation tanks following biological treatment is improved through constant solids loading * Effluent filtration surface area requirements are reduced, filter performance is improved and more uniform filter back-wash cycles are possible * In chemical treatment, damping of mass loading improves chemical feed control and process reliability.  Design Considerations The design of flow equalization facilities is concerned with the following questions: 1. Where in the treatment process flowsheet should the equalization facilities be located? 2. What type of equalization flowsheet should be used, in-line or off-line? 3. What is the required basin volume? 4. What are the features that should be incorporated into design? 5. How can the deposition of solids and potential odors be controlled?

3. MIXING AND FLOCCULATION Mixing (1) mixing of one substance completely with another (2) blending of miscible liquids (3) flocculation of wastewater particles (4) continuous mixing of liquid suspensions (5) heat transfer  Continuous Rapid Mixing in Wastewater Treatment (1)the blending of chemicals with wastewater (e.g.,the addition of alum or iron salts prior to flocculation and settling or for dispersing chlorine and hypochlorite into wastewater for disinfection) (2) the blending of miscible liquids (3) the addition of chemicals to sludge and biosolids to improve their dewatering characteristics  Flocculation in Wastewater Treatment (1) Increasing removal of suspended solids and BOD in primary settling facilities (2) Conditioning wastewater containing certain industrial wastes (3) improving performance of secondary settling tanks following the activated-sludge process (4) as a pretreatment step for the filtration of secondary effluent

Typical mixing times and applications for different mixing and flocculation devices used in wastewater treatment facilities

for microflocculation(Kolmogoroff (1941) to describe the size of eddies formed as result of power input to a fluid) Static Mixers In-line Mixers High-Speed Induction Mixer Pressurized Water Jets Turbine and Propeller Mixers

Static Mixers

Turbine and Propeller Mixers (1) radial-flow impellers and (2) axial-flow impellers

Power for mixing Pumping capacity

Typical design criteria for turbine and propeller mixers  Design considerations (1) the velocity gradient G, subject to the caveats (2) the rotational speed (3) the ratio of the impeller diameter to the equivalent tank diameter

Types of Mixers Used for Flocculation in Wastewater Treatment (1) static mixers (2) paddle mixers (3) turbine and propeller mixers Over and under baffled reactor

Paddle mixed in a baffled tank

4. GRAVITY SEPARATION THEORY  Particle Settling Theory

For nonspherical particles (Gregory et al.) factor is 1.0 for spheres, 2.0 for sand grains greater than 20 for fractal floc.

Settling in the Laminar Region : less than about 1.0 Settling in the Transition Region Settling in the Turbulent Region

Discrete Particle Settling

Definition sketch for the idealized settling of discrete particles in three different types of settling basins: (a) rectangular, (b)circular, and (c) upflow. (Crites and Tchobanoglous, 1998.)

For discrete particles within a given settling velocity range

Flocculent Particle Settling