Water Treatment PDF

Pollution  Pollution Pollution is defined as the undesirable change in the physical, chemical or biological characteristics of our air, water & land that may or will harmfully, affect human life, the lives of the desirable species, our industrial processes, living condi...

Pollution  Pollution Pollution is defined as the undesirable change in the physical, chemical or biological characteristics of our air, water & land that may or will harmfully, affect human life, the lives of the desirable species, our industrial processes, living conditions & cultural assets, or that may or will waste or deteriorate our raw material resources Natural and man-made pollution  Pollutants Pollutants are the materials or factors, which cause adverse effect on the natural quality of any component of the environment They are the waste products or by-products of the materials we make use or throw away  Types of Pollution Air pollution Water pollution Soil pollution Noise pollution Radioactive pollution etc  Acts & Rules The Water (Prevention And Control Of Pollution) Act 1974 The Water (Prevention And Control Of Pollution) Cess Act, 1977 The Air (Prevention And Control Of Pollution) Act 1981 The Environment (Protection) Act 1986 Hazardous Waste (Management And Handling) Rules, 1989 Public Liability Insurance Act, 1991 The National Environment Tribunal Act, 1995 Bio-medical Waste ( Management And Handling) Rules, 1998 Recycled Plastic Manufacture And Usage Rules, 1999 Coastal Zone Regulation Notification etc Do you leave the tap on when you clean your teeth? You waste 5 litres of water.You only need ¼ litre! An average bath uses 80 litres of water. An average shower only uses 35 litres.  80% of water use = industrial sector The production of 1 tonne of steel requires 231, 620 litres of water The production of 1 new car + 4 tires require 144, 633 litres of water 2 - 4.5 barrels of water are required to extract 1 barrel of oil, and 90 % of that water is permanently removed from the hydrological cycle. 66% of the human body is made up of water. At just 2% dehydration your performance decreases by around 20%. We should drink at least 1½ litres of water a day.  Water Pollution It is defined as the addition of some substance or factor, which degrade the quality of water so that it either becomes health hazard or unfit for use  Sources of water pollution According to the way in which the pollutants are introduced in water Flow of pollutants through regular channels – point sources Passage of scattered pollutants- diffuse or non-point  Point and Nonpoint Sources NONPOINT SOURCES Rural homes Urban streets Cropland Animal feedlot Suburban POINT developme SOURCES nt Factory Wastewater treatment plant Basic factors causing water body pollution  Water Quality Water quality is defined by analyzing in terms of its: Chemical Content: Hardness , Metals, nutrients, chloride, sodium, organic compounds etc Physical Content: pH, Turbidity, colour, odour etc. Biological Content: Faecal coliform, total coliform etc Water Treatment Schematic  Screening Important preliminary stage Removes the bulk non biodegradable matter, such as plastics, woven materials, pieces of wood and metallic items from the sewage stream The materials may increase BOD of the water and possibly damage downstream equipment  Types of screens Bar screens Drum screens Disc screens Micro screens Wedge wire screen Vibrating screen (Circular, elliptical or Vertical)  Types of screen (size of opening) Fine Coarse Medium Usually coarse screen is placed in front of the fine screen  SEDIMENTATION Sedimentation is a physical water treatment process used to settle out suspended solids in water under the influence of gravity Sedimentation Tanks can be of different shapes, often rectangular or circular There may be primary and secondary settling tanks Flocculants/Coagulants may be added before settling.  Sedimentation/Settling Water with suspended impurities with or without added coagulants is made to flow into settling basins Water is nearly quiescent – low flow with little turbulence Water resides for at least 3 hours and the flocs settle out and collect at the bottom.  Four types of Sedimentation Dilute, non-flocculent, free-settling (Every particle settles independently) Dilute, flocculent (Particles can flocculate as they settle) Concentrated Suspensions, Zone Settling or Hindered (Sludge Thickening) Concentrated Suspensions, Compression (Sludge Thickening)  TYPES OF SEDIMENTATION In discrete settling individual In flocculant settling, particles settle independently individual particles stick together into clumps called It occurs when there is flocs a relatively low solid This occur when there is a concentration greater solids concentration & chemical or biological reactions alter the particle surfaces to enhance attachment  In hindered settling the Compression settling particle concentration is occurs when particle great enough to inhibit settle by compressing the water movement mass below Water must move in spaces between particles Settling in Treatment Train  Types of sedimentation Fill and draw type Continuous flow type Rectangular a)Horizontal Circular b)Vertical  Fill and Draw type Fill the water and after the detention period draw the water from the tank  Circular In circular sedimentation tanks the clarifier mechanism has sludge scrapers attached to a rotating arm scraping the sludge towards a central hopper. Peripheral drive type, fixed bridge or fixed half bridge (cage drive) Low maintenance, faster sludge removal & higher removal efficiencies  Rectangular settling tanks In rectangular clarifiers scrapers are carried along the tank bottom collecting the sludge into a trough or hopper at the influent end of the tank. In rectangular clarification tanks the mechanism may be of the chain and flight type or have scrapers and scum removal equipment suspended from a traveling bridge. Rectangular tanks are predominantly used in very large treatment plants or in confined spaces, making maximum use of the area available.  Coagulation Goal: To alter the surface charge of the particles that contribute to color and turbidity so that the particles adhere to one another and are capable of settling by gravity  Measurements of turbidity The most widely used measurement unit for turbidity is the FTU (Formazin Turbidity Unit). ISO refers to its units as FNU (Formazin Nephelometric Units). Jackson Candle Method: (Jackson Turbidity Unit or JTU) is essentially the inverse measure of the length of a column of water needed to completely obscure a candle flame viewed through it. The more water needed (the longer the water column), the clearer the water. Nephlometer: Nephelometric Turbidity Units (NTU). It has a detector setup to the side of the light beam to detect scattered light. More light reaching the detector means more scattering and more turbidity Turbidity in lakes, reservoirs, and the ocean can be measured using a black and white disk (Secchi disk) that is lowered into the water until it can no longer be seen. The depth recorded is inversely related to turbidity.  Colloids Small particles (0.001 to 1 m) Usually negatively charged Particles repel so suspension is considered stable  Coagulation and Flocculation Coagulation (process) + + + + + + + + + ++ ++ + ++ + + + + + + + + ++ + + ++ + + Colloidal particles + + (0.001 - 1 m) floc (1 - 100 m)  Coagulant Non-toxic and relatively inexpensive Insoluble in neutral pH range - do not want high concentrations of metals left in treated water. Alum: Al2(SO4)3 14H2O Ferric chloride: FeCl3 Ferric sulfate: FeSO4 Polyelectrolytes etc.,  Factors Influencing Coagulation Water pH: coagulants work better under alkaline pH Temperature: High T Low viscosity better settling Type and concentration of suspended matter: better removal when more concentrated Type of Coagulant: Fe flocs are heavier than Alum flocs. Heaver flocs are removed faster. Coagulant Dose: need optimum dose Mixing time and method: violent agitation is better  Aeration A fluid-holding tank with provisions to aerate its contents by bubbling air or another gas through the liquid or by spraying the liquid into the air. By using cascade By using trickling beds By air diffusion By using spray nozzles  Filtration The final step in removing particles is filtration. Removal of those particles that are too small to be effectively removed during sedimentation Multiple removal mechanisms depending on design Sedimentation effluent: 1 - 10 TU Desired effluent level: 11 required for Mg removal) Sodium hydroxide addition for surface water – coagulant chemicals reduce pH – increase pH to reduce corrosivity  Additional Processes Fluoride addition – Added either as NaF, Na2SiF6, H2SiF6 – React in water to yield fluoride ion (F-) Well documented that fluoride levels of ~ 1 ppm reduce incidence of dental caries (cavities) Some controversy remains  Additional Processes Polyphosphate addition – Added for corrosion control as it forms a protective film on pipes – Also helps to control lead levels in tap water as it complexes with lead  Advanced Treatment Processes Advanced Oxidation Processes – improved disinfection – oxidize synthetic organic chemicals – taste and odor control Activated carbon adsorption – remove recalcitrant synthetic organic chemicals, THMs, taste and odor compounds – concern with bacterial growth problems Membrane process – discriminate on both size and chemistry – selective removal including desalinzation  Residuals Management Sludge from clarifiers Finished water  Residuals Management – Dewatering Lagoons Sand-drying beds Freeze treatment Centrifugation Vacuum filtration Continuous belt filter press Plate Pressure filters Residuals Management – Ultimate Disposal On-site storage Landfilling Land application – soil amendment Reclamation/recycling – new products 80% of all illness in developing countries is caused by water related diseases. 90% of wastewater in developing countries is discharged directly into rivers and streams without treatment.  Effects of water pollution Effects on aquatic ecosystem Biological magnification Eutrophication Effects on human health Hazards of ground water pollution  EUTROPHICATION Eutrophication is a process whereby water bodies such as lakes estuaries and slow-moving streams receive excess nutrients that stimulate excessive plant growth (algae, periphyton attached algae and nuisance plant weeds) & is likely to cause several reductions in water quality In aquatic systems species such as algae experience a population increase (called an algal bloom) Algal blooms limits the sunlight available to the bottom dwelling organisms and cause wide swings in the amount of dissolved oxygen in water  Under eutrophic conditions DO greatly increases during day time, but is greatly reduced after the dark by the respiring algae and by the microorganisms that feed on the increasing mass of dead algae In extreme cases anaerobic conditions ensue promoting growth of Clostridium botulinum bacteria ,that produces toxins deadly to birds and mammals Phosphorous is often regarded as the main culprit in cases of eutrophication in lakes  SOURCES OF HIGH NUTRIENT RUN OFF Waste water effluent (municipal and industrial) Run-off & leachate from waste disposal systems Run-off & infiltration from animal feedlots Run off from mines, oil feeds & unsewered industrial sites Run-off from agriculture/irrigation Septic tank leachate Overflows of combined storms & sanitary sewers Algal bloom in a lake Overgrowth of floating Aquatic plants Fish mortality due to loss of Oxygen in Indonesian lake  ECOLOGICAL EFFECTS Increased biomass of phytoplankton Toxic or inedible phytoplankton species Increase in blooms of gelatinous zooplankton Decreases in water transparency Taste, odor and water treatment problems DO depletion Increase incidences of fish kills Loss of desirable fish species Reductions in harvestable fish & shellfish Decreases resource values of rivers, lakes and estuaries such that recreation, fishing, hunting and aesthetic enjoyment are hindered Domestic Effluent Treatment  Definitions Sullage: Wastewater from bathrooms, kitchen, washing, etc minimal organic matter, not odorous Sewage: – Sanitary sewage: Liquid waste from community including sullage, latrine discharge, industrial waste etc Domestic sewage Industrial Sewage – Ground and surface water entering the sewers. Stormwater: rainwater admitted into sewers Subsoil water: groundwater seeping into sewers Nightsoil: human and animal excreta Sewer: Underground conduit or drain through which the sewage is carried to discharge or disposal  Methods of Domestic Sanitation Conservancy System: human excreta carried by human agency. Sullage flows in open drains or percolates. Garbage collected in bins and transported by lorries Water carriage system: Water is added to human excreta and carried by sewers – Separate: foul sewage and stormwater – Combined: – Partially combined  Sewage Physical Characteristics pH Color: – Black indicates O2 depleted Odor Temperature Solids: Total, suspended and settleable  Dissolved Oxygen At least 4 ppm DO before discharge Organic Matter – Biologically active Carbonaceous: first state 20 days Nitrogenous: second stage (NH3 oxidation) – Biologically Inactive  BOD Biochemical oxygen demand (BOD) is the amount of dissolved oxygen consumed by a sample in a standard period (3, 5, 10 days) at standard temperature. – 5 day BOD at 20°C The total BOD = carbonaceous oxygen demand + nitrogenous oxygen demand. Traditionally, because of the slow growth rates of those organisms that exert the nitrogenous demand, it has been assumed that no nitrogenous demand is exerted during the 5-day BOD5 test. Stages of BOD Satisfaction BOD ppm (Yt) II: nitrogeneous I: Carbonaceous Time in days (t)  Chemical Oxygen Demand Amount of oxygen required to oxidize all the organic matter (biologically active and inactive) in a wastewater sample using a strong oxidizing agent like potassium dichromate or potassium permanganate Measured within 3 hrs COD>BOD Limiting COD is 250mg/L  ThOD Theoretical Oxygen Demand If all the constituents of the wastewater and their concentrations are known , a theoretical oxygen demand can be calculated.  Decomposition of Sewage Aerobic Anaerobic O2 present; fast (hours) No O2; slow (days or weeks) Aerobic and facultative bacteria Anerobic bacteria Complete decomposition. Incomplete decomposition. End Products inoffensive, stable: End Products unstable, offensive and CO2 + H2O. require further treatment: CO2, CH4, H2S, NH3 etc. Measured from DO utilization Measured from gas yield May require aeration No aeration Bulk of energy from waste ends up Significant fraction of energy remains in in bacterial biomass and heat end products and can be utilized. Less sensitive Highly sensitive Trickling filter, activated sludge Septic tank, anerobic lagoon, fermenter, digester, oxidation pond etc. biogas plant  Treatment of sewage Primary treatment Secondary treatment Teritary treatment  Sewage Treatment Schematic With Activated Sludge Secondary Treatment Package plant for Aeration and Sedimentation  Oxidation Ponds Air-mixing due to wind Sunlight penetration Algal growth provides photosynthetic O2 Promotes growth of aerobic bacteria Bacteria oxidize the organic matter in the sewage  Facultative ponds 3-5 m deep; 3 strata: – Lower layer—Benthal deposits and lower layers of water. anaerobic bacteria decompose wastes & release decomposition products CO2, NH3, CH4, and other nutrients. – Middle layer—photosynthetic algae, use nutrients to grow and release O2, which facilitates growth of aerobic bacteria – Upper layer aerobic bacteria oxidize organic wastes using O2 from air and algae. Residuals Management Sludge from clarifiers INDUSTRIAL POLLUTION CONTROL  Industrial Waste Water Domestic Process Cooling Waste Water Waste Water Waste Water  Wastewater Characteristics Organics Inorganics pH and Alkalinity Temperature Dissolved Oxygen  Industrial Wastewater Treatment Raw Treated water Sewage Primary Aerobic Secondary treatment Treatment treatment sludge sludge Sludge Sludge processing disposal  Pretreatment Equalization – level out hydraulic loads on treatment units and concentration variations Neutralisation – for acidic or basic waste water. Mix acidic and basic wastes. Sodium hydroxide & lime for acidic wastes. Sulphuric acid, hydrochloric acid & CO2 for basic wastes.  Pretreatment Grease and oil removal- Done near the point of their mixing with water. Gravity and simple skimming, adding chemicals to break emulsions, grease traps. Toxic substances – Reduce heavy metals below toxic levels and prevent discharge of toxic complex organics.  Primary Treatment Screens - remove moderate size particles Grit chambers – rapid separation of inert particles like sand or hard inert particles.  Primary Treatment Gravity Sedimentation – removes slowly settling particles. - designed on the basis of retention time, surface overflow rate, and minimum depth - removal efficiency affected by hydraulic flow pattern though the tank. Sedimentation tank  Primary Treatment Chemical precipitation - agglomerates tiny particles into large particles that settle rapidly in normal sedimentation tanks. Coagulants – aluminium sulphate, ferric chloride, ferrous sulphate, lime and polyelectrolytes. Choice of coagulant depend on - particles being removed - pH of waste waters - cost & availability of precipitants  Secondary Treatment Removes colloidal and soluble organics through microbial metabolism Biological treatment systems uses bacteria that convert biodegradable organics in solution into suspended organics which flocculate and are removed by gravity sedimentation Colloidal solids tend to be absorbed onto microbial flocs  Secondary Treatment Biological Waste Water Treatment Aerobic Anaerobic Excess DO Without DO Organics Organics CO2, water Acids, ketones, aldehydes, alcohol Methane, CO2  Secondary Treatment Lagoons - Facultative Lagoons use both aerobic & anaerobic reaction - Aerated Lagoons additional oxygen supplied by mechanical surface aerators and diffused aerators - Anaerobic Lagoons first stage in treatment of strong organic wastes Cross section of a facultative Lagoon Aerated Lagoon Anaerobic Lagoon Secondary Treatment Secondary Treatment Secondary Treatment Activated Sludge Process  Physical Chemical Treatment For wastewaters that are either toxic to or difficult to treat with biological treatment First Step – use of chemical precipitants to remove suspended solids by flocculation and gravity sedimentation Second Steps – Activated carbon bed, ion- exchange columns, sand media or multimedia filters, reverse osmosis  Sludge Processing Unstabilised organics – biological or heat treatment for stabilization Inert organics and inorganics – concentrated, dewatered and returned to the environment  Sludge Processing Chemical conditioning Uses lime, alum and various ferric salts Increases mass of sludge Removes fine particle Thermal conditioning Dewaters sludge Temperatue at 180 to 230°C for 15 to 60 minutes a pressure of 13 to 20 atm.  Sludge Processing Filter Press Rotary Vacuum Filter Sand Beds  Sludge Disposal Incineration Land Spreading  Management of Industrial Solid Wastes Waste Generation Storage Collection Transfer/transport Processing/Recovery Disposal Land Filling  T h a n k Y o u CONSERVE WATER