Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Approach and Recent Trends Purnendu Bose Department of Civil Engineering IIT Kanpur
Strategies for Wastewater Treatment: Physico-Chemical Approach Introduction Origin of Wastewater: Domestic/Commercial or Industrial What does Wastewater Contain ?? approx. 1 – 2 % Contaminants > 98% water (by weight) Wastewater Treatment involves removing the contaminants from water Cost of removal of contaminants: from Rs. 10/kL to Rs. 400/ kL Secondary Treatment of Domestic Tertiary Treatment of Industrial Sewage before disposal into rivers Effluent for Recycling
Strategies for Wastewater Treatment: Physico-Chemical Approach Introduction Types of Contaminants in Wastewater Inorganic: 1) Particulate; 2) Colloidal; 3) Dissolved Organic: 1) Large Floating Material; 2) Particulate; 3) Colloidal ; 4) Dissolved; Biodegradable Non-Biodegradable Biological Treatment Physico-Chemical Treatment
Strategies for Wastewater Treatment: Physico-Chemical Approach Introduction Objective of Wastewater Treatment: Removal of Organic and Inorganic Contaminants How is it Done? By Designing a Wastewater Treatment Process Train Catalyst Chemical Addition Raw UO-1 UO-2 UO-3 UO-4 UO-n Wastewater Heating / Pressure Aeration Mixing Treated + Wastewater Bacterial Action UO – Unit Operation
Strategies for Wastewater Treatment: Physico-Chemical Approach Introduction ‘Unit Processes’ in Wastewater Treatment: Say, a wastewater treatment train consists of ‘n’ unit operations, UO(1) – UO(n) The first ‘ i ’ unit operations, i.e., UO(1) – UO(i) constitute an ‘unit process’ called, ‘Preliminary Treatment’ The unit operations from ‘ i + 1 ’ to j, i.e., UO(i+1) – UO(j) constitute an ‘unit process’ called ‘Primary Treatment’ . The unit operations from ‘j + 1 ’ to ‘k’, i.e., UO(j+1) - UO(k) constitute an ‘unit process’ called Secondary Treatment’ . The unit operations from ‘k + 1 ’ to ‘n’, i.e., UO(k+1) – UO(n) constitute an ‘unit process’ called ‘Tertiary Treatment’ . Each ‘Unit Process’ performs a particular function in wastewater treatment
Strategies for Wastewater Treatment: Physico-Chemical Approach Introduction Functions of ‘Unit Processes’ in Wastewater Treatment: Preliminary Treatment: Physical Processes Unit Operations in Preliminary Treatment removes, 1) large organic floating material and 2) inorganic particulate and matter from wastewater Primary Treatment: Physical/Chemical Processes Unit Operations in Primary Treatment removes, 1) organic particulate matter and inorganic colloidal matter from wastewater and 2) also help (if required) in transforming non-biodegradable dissolved organic matter in wastewater to a more biodegradable form Secondary Treatment: Biological/Physical Processes Unit operations in Secondary Treatment remove colloidal and dissolved organic matter from wastewater Tertiary Treatment: Biological/Chemical Physical Processes Unit operations in Tertiary Treatment remove, 1) residual dissolved organic matter from wastewater, 2) residual organic/inorganic particulate matter from wastewater, 3) dissolved inorganic matter from wastewater Treated wastewater may be disposed, reused or recycled
Strategies for Wastewater Treatment: Physico-Chemical Approach Introduction Disposal, Reuse and Recycling Treated wastewater may be discharged to natural water bodies provided the relevant discharge standards are attained through wastewater treatment. This is known as wastewater disposal. Alternatively, the treated wastewater may be used for certain other beneficial purpose, provided adequate treatment is given to the wastewater to meet the water quality standards for that beneficial use. This procedure of using water for multiple beneficial uses is known as reuse. Alternatively, the treated wastewater may be used for the same beneficial purpose as before, provided adequate treatment is given to the wastewater such that it meets the standards for the original beneficial use. This procedure for using water for the same beneficial use is known as recycling. Domestic sewage after ‘Secondary Treatment’ is generally suitable for disposal into natural surface water bodies Industrial effluent may require some ‘Tertiary Treatment’ before being suitable for disposal into natural water bodies. Both domestic sewage and industrial effluent can generally be reused for various beneficial purposes after adequate ‘Tertiary Treatment’ . Industrial effluent can be recycled, generally after adequate ‘Tertiary Treatment’
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Bar Rack / Screen Type: Physical Process Unit Process: Preliminary Treatment Purpose: Removal of Large Floating Material (up to 1 mm size) from Wastewater Proportional Weir Grit Chamber Bar Rack / Screens Sewer Large floating materials are caught in the screen and removed Rectangular Open Channel Three screens with progressively Top View smaller openings are provided in series to remove all floating material > 1 mm size Front View Grit Collection
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Grit Chamber Type: Physical Process Unit Process: Preliminary Treatment Purpose: Removal of Inorganic Particles (up to 1 mm size) from Wastewater Proportional Weir Placed immediately after bar rack / Grit Chamber screen Bar Rack / Screens The channel is suddenly widened, so that horizontal flow velocity is reduced in grit chamber. Particles settle in the Sewer chamber and are removed. Top View Rectangular Open Channel Top View Front View Front View Proportional Weir Grit Collection
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Equilization Tank Type: Physical Process Unit Process: Preliminary Treatment Purpose: Flow Equilization Equalization Tank (Flow Equalization) Placed immediately after Grit Chamber Equalization Inflow into Equilization tank is Constant Flow Variable Flow Tank variable, but the outflow is (from Grit Chamber) constant. In- Line Equalization Equilization tank is required for Variable Flow Constant Flow efficient operation of the Outflow downstream unit operations. Inflow Two types of Equilization tanks Equalization are possible, off-line and on-line Tank equilization. Off - Line Equalization
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations The First Unit Process: Preliminary Treatment From Sewer GC EQ SC-1 SC-2 SC-3 To Primary Treatment The wastewater after preliminary treatment has, 1) No floating matter 2) No inorganic particles of size > 0.2 mm 3) Equalized Flow
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Rapid Mix Tank Type: Physical Process Unit Process: Primary Treatment Rapid Mix Tank: Vertical Shaft Impeller Purpose: Dispersal of Coagulant Coagulant addition is mostly required for industrial wastewater treatment. Plan This unit is generally not Coagulant Elevation required for domestic wastewater treatment. Inflow The objective of the rapid mix tank is to quickly disperse the added coagulant into the bulk wastewater outflow
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Flocculation Tank Type: Physical Process Flocculation Tank: Unit Process: Primary Treatment Horizontal Shaft Paddle Purpose: Flocculation of destabilized particles Flocculation tank provided immediate downstream of the rapid-mix tank. It is mostly required for industrial wastewater treatment. This unit is generally not required for domestic wastewater treatment. Plan The objective of the flocculation tank is Elevation to facilitate the agglomeration of particles destabilized by coagulant addition. The larger particles thus formed are removed in the settling tank provided immediate downstream of the flocculation tank.
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Primary Sedimentation Tank Type: Physical Process Unit Process: Primary Treatment Sedimentation of organic particles up to 60 m m size Purpose: Inlet Channel Effluent Baffle Scum Remover Launder L D Settling Zone Organic particles up to 60 mm size are Sludge removed in the Elevation of Sedimentation Tank sedimentation tank
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations The Second Unit Process: Primary Treatment Coagulant From Preliminary RMT FT PST To Secondary Treatment Treatment Optional The wastewater after Primary treatment has, 1) No floating matter Preliminary Treatment 2) No inorganic particles of size > 0.2 mm 3) Equalized Flow 1) All organic and inorganic particles up to 60 m m size removed Primary Treatment After Primary Treatment wastewater mainly has colloidal and dissolved organic and inorganic matter
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