In this article we will discuss about the various operations involved in water treatment. 1. Sedimentation: Sedimentation is a process of separating from water by gravitational settling the suspended particles that are heavier than water. In water there are mainly two types of suspended solids: (i) Inorganic solids having specific gravity of about 2.65, and (ii) Organic solids having specific [...]
The priliminary treatment of sewage involves the use of only physical unit operations such as screening, comminution, grit removal, skimming, floatation, etc. The physical unit operations involved in preliminary treatment of seawge are accomplished by employing various units or appurtenances which include screens, comminutors, grit chambers or detritus tanks, skimming tanks, floatation units, etc. 1. Screening—Screens: Screening is the first [...]
The various considerations involved in the design of screens and screen channels are as follows: 1. Velocity of Flow: The velocity of flow ahead of and through a screen varies materially and affects its operation. The lower the velocity of flow through the screen, the greater is the amount of screenings that would be removed from sewage. However, the lower [...]
The various considerations involved in the design of grit chambers are as follows: 1. Settling Velocity 2. Surface Overflow Rate (SOR) 3. Detention Period 4. Bottom Scour and Flow through Velocity 5. Velocity Control Devices 6. Number of Units 7. Dimensions of Each Unit 8. Loss of Head. 1. Settling Velocity: Grit chamber may be designed on a rational basis [...]
In this article we will discuss about:- 1. Operations and Units of an Activated Sludge Plant 2. Operational Difficulties in Activated Sludge Plant. Operations and Units of an Activated Sludge Plant: Fig. 13.2 shows a typical flow diagram for an activated sludge plant. The activated sludge process is usually preceded by preliminary and primary treatments of sewage for which screening [...]
Following are the three methods which are employed for the purpose of aeration in activated sludge process: 1. Diffused Air Aeration 2. Mechanical Aeration 3. Combined Diffused Air and Mechanical Aeration. Method # 1. Diffused Air Aeration: In the diffused air aeration method compressed air is introduced into the mixture of sewage and returned activated sludge (or mixed liquor) in [...]
Various systems of mechanical aeration have been developed to achieve the required Agitation, most of which are patented. Some of these systems of mechanical aeration which are commonly used are as indicated below: 1. Hartley System or Birmingham Bio-Flocculation System 2. Haworth System or Sheffield Aeration System 3. Link-Belt System 4. Kessener System 5. Simplex System. 1. Hartley System or [...]
The various types of activated sludge processes are listed below: 1. Conventional Activated Sludge Process 2. Tapered Aeration Process 3. Step Aeration Process 4. Contact Stabilization Process 5. Complete Mix Process 6. Modified Aeration Process 7. Extended Aeration Process. The characteristics and design parameters for these processes are given in Table 13.3. These processes are described in details below: Type [...]
The loading rate of aeration tank is based on the following four parameters: 1. Hydraulic Retention Time (HRT) 2. Volumetric BOD Loading or Volumetric Organic Loading 3. Food to Micro-Organism Ratio (F/M Ratio) 4. Mean Cell Residence Time (MCRT) or Sludge Retention Time (SRT) or Sludge Age. Parameter # 1. Hydraulic Retention Time (HRT): Hydraulic retention time is a loading [...]
The sewage filters that are commonly employed are of the following types: 1. Intermittent Sand Filters 2. Contact Beds 3. Trickling Filters 4. Dunbar Filters 5. Magnetite Filters 6. Rapid Sand Filters Type # 1. Intermittent Sand Filters: The intermittent sand filter is the earliest type of sewage filter used in the biological treatment of sewage. It consists of a [...]