Chapter 10 of CPHEEO Manual
The object of sewage treatment is to stabilise decomposable organic matter present in sewage and the effluent and sludge which can be disposed of in the environment without causing health hazards or nuisance.
Design Period: (Para 10.2 of CPHEEO Manual) Design period of 30 years after its completion.
Sewerage Flow: The quantity of sewerage and its characteristic show a marked range of hourly variation and hence peak, average and minimum flows are important consideration. In the absence of any data average flow of 150 lpcd may be adopted.
The hydraulic design load varies from component to component of the treatment plant with all appurtenance conduits, channel, etc. being designed for the maximum flow which may vary from 2.0 to 3.5 times the average flow. Sedimentation tanks are designed on the basis of average flow while consideration of both maximum and minimum flow is important in the design of screen and grit chamber.
Unit operations/processes, their functions and devices used for domestic wastewater treatment (Table 10-1 of CPHEEO Manual)
| S. No | Unit operations and process | Functions | Treatment Devices |
| 1 | SCREENING | Removal of large floating, suspended and settleable solids | Bar racks and screens of various description |
| 2 | GRIT REMOVAL | Removal of inorganic suspended solids | Grit chamber |
| 3 | PRIMARY SEDIMENTATION | Removal of organic and inorganic settable solids | Primary sedimentation tank |
| 4 a | AEROBIC BIOGICAL SUSPENDED GROWTH PROCESS | Conversion of colloidal, dissolved and residual suspended organic matter into settable biofloc and stable inorganics | Activated sludge process units and its modifications, waste stabilisation Ponds, Aerated Lagoons |
| 4b | AEROBIC BIOGICAL ATTACHED GROWTH PROCESS | Same as above | Trickling Filter, Rotating Biological Contactor |
| 5 | ANAEROBIC BIOLOGICAL GROWTH PROCESSES | Conversion of organic matter into CH4 & CO2 and organic relatively stable organic residue | Anaerobic Filter, Bed Submerged Media Anaerobic Reactor, Upflow Anaerobic Sludge Blanket Reactor; Anaerobic Rotating Biological Contactor |
| 6 | ANAEROBIC STABILISATION OF ORGANIC SLUDGES | Same as above | Anaerobic Digester |
Sewage treatment of processes (Para 10-10 of CPHEEO Manual )
Sewage treatment processes may be generally classified as •Primary Treatment •Secondary Treatment •Tertiary Treatment
The general yardstick of evaluating the performance of sewage treatment plants is the degree of reduction of •Biochemical Oxygen Demand (BOD), •Suspended Solids (SS) •Total Coliforms.
Types of Sewage treatment processes
• Activated Sludge Process (ASP)
• Sequencing Batch Reactor (SBR)
• Moving Bed Bio Reactor (MBBR) / Fluidized Aerobic Bioreactor (FAB)
• Membrane Bio Reactor (MBR)
• BIOFOR – Biological Filtration and Oxygenated Reactor (BIOFOR)
• High Rate Activated Sludge BIOFOR-F Technology
• Submerged Aeration Fixed Film (SAFF) Technology
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