Treatment: Physico-Chemical Approach Conventional Approach and - - PowerPoint PPT Presentation
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
Strategies for Wastewater Treatment: Physico-Chemical Approach Introduction What does Wastewater Contain ?? > 98% water (by weight)
Wastewater Treatment involves removing the contaminants from water Cost of removal of contaminants: from Rs. 10/kL to
Secondary Treatment of Domestic Sewage before disposal into rivers Tertiary Treatment of Industrial Effluent for Recycling Origin of Wastewater: Domestic/Commercial
Industrial
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? UO-1 UO-2 UO-3 UO-4 UO-n Raw Wastewater Treated Wastewater Chemical Addition Mixing + Bacterial Action Heating / Pressure Catalyst Aeration By Designing a Wastewater Treatment Process Train 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
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’ 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
recycling.
Strategies for Wastewater Treatment: Physico-Chemical Approach Introduction
Grit Chamber Proportional Weir Grit Collection Sewer Rectangular Open Channel Bar Rack / Screens Front View Top View 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 Large floating materials are caught in the screen and removed Three screens with progressively smaller openings are provided in series to remove all floating material > 1 mm size
Sewer Rectangular Open Channel Bar Rack / Screens Front View Top View 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 Placed immediately after bar rack / screen The channel is suddenly widened, so that horizontal flow velocity is reduced in grit chamber. Particles settle in the chamber and are removed. Proportional Weir Grit Chamber Proportional Weir Grit Collection Front View Top View
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) Variable Flow (from Grit Chamber) Equalization Tank Constant Flow In- Line Equalization Equalization Tank Variable Flow Constant Flow Inflow Outflow Off - Line Equalization Placed immediately after Grit Chamber Inflow into Equilization tank is variable, but the outflow is constant. Equilization tank is required for efficient
the downstream unit operations. Two types of Equilization tanks are possible, off-line and on-line equilization.
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations
SC-1 SC-2 SC-3
GC EQ To Primary Treatment From Sewer The wastewater after preliminary treatment has, 1) No floating matter 2) No inorganic particles of size > 0.2 mm 3) Equalized Flow The First Unit Process: Preliminary Treatment
Rapid Mix Tank: Vertical Shaft Impeller Plan Elevation Inflow
Coagulant Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Rapid Mix Tank Type: Physical Process Unit Process: Primary Treatment Purpose: Dispersal of Coagulant Coagulant addition is mostly required for industrial wastewater treatment. This unit is generally not required for domestic wastewater treatment. The objective of the rapid mix tank is to quickly disperse the added coagulant into the bulk wastewater
Flocculation Tank: Horizontal Shaft Paddle Plan Elevation Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Flocculation Tank Type: Physical Process Unit Process: Primary Treatment 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. The objective of the flocculation tank is to facilitate the agglomeration
particles destabilized by coagulant addition. The larger particles thus formed are removed in the settling tank provided immediate downstream
the flocculation tank.
Sludge
Scum Remover Effluent Launder Inlet Channel
Elevation of Sedimentation Tank
Baffle
Settling Zone L D Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Primary Sedimentation Tank Type: Physical Process Unit Process: Primary Treatment Purpose: Sedimentation of organic particles up to 60 mm size Organic particles up to 60 mm size are removed in the sedimentation tank
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations FT PST To Secondary Treatment From Preliminary Treatment The wastewater after Primary treatment has, 1) No floating matter 2) No inorganic particles of size > 0.2 mm 3) Equalized Flow 1) All organic and inorganic particles up to 60 mm size removed The Second Unit Process: Primary Treatment RMT Coagulant Optional Preliminary Treatment Primary Treatment After Primary Treatment wastewater mainly has colloidal and dissolved organic and inorganic matter
Strategies for Wastewater Treatment: Physico-Chemical Approach Conventional Unit Operations Name of UO: Biological Treatment - Secondary Sedimentation Type: Biological – Physical Process Unit Process: Secondary Treatment Purpose: Removal of colloidal organic and inorganic and dissolved organic matter SST To Tertiary Treatment or Disposal From Primary Treatment The wastewater after Secondary treatment may have, 1) Non-Biodegradable organic matter (may impart color) 2) Small concentrations of colloidal organic matter (mostly biomass) 3) Dissolved inorganic matter (cations and anions) Domestic wastewater after secondary treatment looks clean The Third Unit Process: Secondary Treatment Bioreactor Dissolved
matter (assuming biodegradable) is almost completely removed. Colloidal
matter is partially removed. Colloidal organic and inorganic matter, along with biomass effluent from the bioreactor is removed. Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends
SC-1 SC-2 SC-3
GC EQ To Primary Treatment From Sewer The First Unit Process: Preliminary Treatment FT PST To Secondary Treatment From Preliminary Treatment RMT Coagulant Optional The Second Unit Process: Primary Treatment SST To Tertiary Treatment or Disposal From Primary Treatment The Third Unit Process: Secondary Treatment Bioreactor
Biological Process Large floating organic matter and inorganic particle up to 0.2 mm size is removed Flow is equalized. Inorganic and organic particle up to 60 mm size is removed. Dissolved organic matter and colloidal organic and inorganic matter is removed.
Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends Recent Trends: Conversion of Non-Biodegradable organic matter to a more biodegradable form during primary treatment using physico-chemical methods. This helps more efficient organic matter removal during secondary treatment. This is mostly applicable for industrial effluents with large non-biodegradable organic content. Physico-Chemical Tertiary Treatment Processes:
metals, etc.) followed by removal of residual particulate matter and precipitates by sand and membrane filtration (micro-, nano-filtration).
a) activated carbon adsorption, b) nanofiltration, and c) post-ozonation.
Tertiary treatment makes the treated wastewater more suitable for recycle/reuse. Degree
Aliphatic Compounds are easily biodegradable Compounds with Aromatic rings and Cross linkages are difficult to Degrade Biodegradability Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends
Strong Oxidizing Agents: Advanced Oxidation Processes (AOPs) Only Ozone (O3): Ozone (O3) is a strong oxidizing agent. In aqueous solutions O3 often directly reacts with the target contaminant. O3 may combine with OH- in water and through a series of reactions form hydroxyl
O3/UV: H2O2/UV: H2O2/O3: Fe2+/H2O2 (Fenton’s Reaction): Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends 2 h 2 3
h 2 2 2 2 3 2 3 2 2 2 2
] OH [
3 2 2 2
Mechanism of AOP: Strong oxidizing agents attack electron-rich sites in complex organic molecules, i.e., aromatic rings and double bonds. This breaks up the molecules into more aliphatic components, which are more amenable to subsequent biodegradation. Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends Name of UO: Pre-Oxidation (AOP) Type: Chemical Process Unit Process: Primary Treatment Purpose: Enhancing Biodegradability of Non-Biodegradable Organic Matter FT PST To Secondary Treatment From Preliminary Treatment RMT Coagulant Optional PO Optional Pre-Oxidation (PO) will enhance the biodegradability of non-biodegradable
matter
found in industrial effluents. This is beneficial for the subsequent biological treatment The Second Unit Process: Primary Treatment
Removal of Specific Inorganic Cations/Anions: Chemical Precipitation Addition of chemicals to promote precipitation of specific cations/anions in secondary treated effluent. Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends Name of UO: Chemical Precipitation Type: Chemical Process Unit Process: Tertiary Treatment Purpose: Removal of specific dissolved inorganic cations/anions FT From Secondary Treatment RMT Chemical Used mainly for removal of phosphate from domestic effluent or in the treatment of industrial effluent. Chemical Precipitation will precipitate specific dissolved inorganic cations/anions present in secondary treated effluent.
Backwash Tank Backwash Tank Pump Backwash Rapid Sand Filter Schematic Plan Front Sectional View Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends Filtration: Removal of Residual Particulates and Precipitates Filtration can be done either using sand filters, i.e., rapid sand filters or pressure filters, followed by membrane filters, i.e., micro- or ultra-filtration. Name of UO: Filtration Type: Physical Process Unit Process: Tertiary Treatment Purpose: Removal of residual particulates and precipitates
Pressure Filtration
Operating principle is the same as in a rapid sand filter Due to higher pressure application, throughput in pressure filters are higher Compact systems, which can be purchased off the shelf and installed quickly
Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends
Membrane Filtration
Water is passed through membranes of various pore sizes. Depending on the pore-size
Inlet Outlet Reject Hollow Fiber Membranes Outlet Membrane Reactor Schematic
Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends FT From Secondary Treatment RMT Chemical After filtration, the treated effluent will have no particulate or dissolved solids. Hence the turbidity of the effluent should be below 1 NTU. However, the effluent may still contain residual non-biodegradable organic matter and salts. RSF/PF M/U Filt Chemical Precipitation Residual Solids Removal
Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends Name of UO: Adsorption Type: Chemical Process Unit Process: Tertiary Treatment Purpose: Removal of residual dissolved organic matter Activated Carbon Adsorption Treated effluent is passed through columns containing activated carbon. Dissolved
molecules are attached to the activated carbon surface and thus removed from the effluent
Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends Name of UO: Post-Ozonation Type: Physical Process Unit Process: Tertiary Treatment Purpose: Removal of residual dissolved organic matter (Color, odor) Name of UO: Nano-filtration Type: Physical Process Unit Process: Tertiary Treatment Purpose: Removal of residual dissolved organic matter NF Filtered Effluent AC Post Ozonation Removal of Residual Organic Matter Removal of Residual Organic
Sparkling Water.
Strategies for Wastewater Treatment: Physico-Chemical Approach Recent Trends Name of UO: Ion Exchange Type: Chemical Process Unit Process: Tertiary Treatment Purpose: Removal of residual dissolved inorganic matter Name of UO: Reverse Osmosis Type: Physical Process Unit Process: Tertiary Treatment Purpose: Removal of residual dissolved inorganic matter Filtered Effluent IE/RO Removal of Residual Inorganic Ions Recyclable Effluent
SC-1 SC-2 SC-3
GC EQ To Primary Treatment From Sewer The First Unit Process: Preliminary Treatment FT PST To Secondary Treatment From Preliminary Treatment RMT Coagulant Optional PO Optional The Second Unit Process: Primary Treatment SST To Tertiary Treatment or Disposal From Primary Treatment The Third Unit Process: Secondary Treatment Bioreactor
Biological Process Large floating organic matter and inorganic particle up to 0.2 mm size is removed Flow is equalized. Inorganic and organic particle up to 60 mm size is removed. Non-biodegradable organic matter is made biodegradable Dissolved organic matter and colloidal organic and inorganic matter is removed.
FT From Secondary Treatment RMT Chemical NF/DF Biological Process Ammonia/Nitrate Removal RSF/PF M/U Filt NF Filtered Effluent AC Post Ozonation IE/RO Phosphate, heavy metals precipitation and residual colloidal matter and precipitate removal Residual dissolved non-biodegradable organic matter, organic micro-pollutants, color, odor removal Residual Inorganic cations and anions, i.e., salt removal