Water Treatment Processes Quiz

Pollution

• Pollution is the undesirable change in the physical, chemical, or biological characteristics of air, water, and land.
• This change harms human life, desirable species, industrial processes, living conditions, and cultural assets.
• It also wastes or degrades raw material resources.
• Pollution can be natural or man-made.

Pollutants

• Pollutants are materials or factors that negatively affect the natural quality of any environmental component.
• They are waste products or by-products of used or discarded materials.

Types of Pollution

• Air pollution
• Water pollution
• Soil pollution
• Noise pollution
• Radioactive pollution

Acts & Rules

• Various acts and rules exist to control and prevent pollution.
• Examples are the Water (Prevention and Control of Pollution) Act 1974.
• The Air (Prevention and Control of Pollution) Act 1981
• The Environment (Protection) Act 1986
• Hazardous Waste (Management and Handling) Rules, 1989

How to Save Water

• Leaving taps on while brushing teeth wastes water.
• 5 liters of water is wasted, but only ¼ liter is needed.

Bath or Shower Water

• An average bath uses 80 liters of water.
• An average shower uses only 35 liters of water.

Average Household Water Usage

• The pie chart data shows percentages of water use for various activities in a typical household.

Industrial Water Usage

• Steel production requires 231,620 liters of water for every ton of steel manufactured.
• Manufacturing a new car and four tires requires 144,633 liters of water.
• Oil extraction consumes 2-4.5 barrels of water per barrel of oil, permanently removing 90% of that water from the hydrological cycle.

Water to Drink

• The human body is 66% water.
• Even a 2% dehydration decrease can significantly impact performance.
• Daily water intake should be at least 1.5 liters.

Water Pollution

• Water pollution is the contamination of water by substances or factors that degrade its quality.
• This contamination makes water unfit or unsafe for human use.

Sources of Water Pollution

• Point sources: Pollutants released in regular channels (e.g., a factory discharge).
• Non-point sources: Pollutants released in scattered ways (e.g., agricultural runoff).

Basic Factors Causing Water Body Pollution

• Factors like urbanization, population growth, industrialization, excessive water use, overuse of land, and increased emissions can cause water pollution.

Water Quality

• Water quality is assessed based on factors like:
• Chemical content (Hardness, metals, nutrients, chloride, sodium, organic compounds, etc)
• Physical content (pH, Turbidity, color, odor, etc.)
• Biological content (Faecal coliform, total coliform, etc)

Water Treatment Schematic

• Water treatment involves several stages, from intake to purification.
• Steps include intake, screening, coagulation, sedimentation, filtration, disinfection, and distribution.

Screening

• A preliminary stage in water treatment.
• It removes large non-biodegradable objects to protect the rest of the equipment from damage.

Types of Screens

• Bar screens
• Drum screens
• Disc screens
• Micro screens
• Wedge wire screens
• Vibrating screens (Circular, elliptical, or Vertical)

Types of Screen (size of opening)

• Fine screens
• Coarse screens
• Medium screens
• Coarse often precedes fine

Sedimentation

• Physical process used to settle out suspended solids in water due to gravity.
• Tanks can be rectangular or circular.
• Flocculants are sometimes used to aggregate suspended particles

Sedimentation/Settling

• Water in sedimentation basins should have minimal turbulence to permit settling.
• Impurities settle to the bottom, and the treated water is directed elsewhere for further treatment.

Four Types of Sedimentation

• Dilute, non-flocculent, free-settling: Every particle settles independently.
• Dilute, flocculent: Particles flocculate and settle together.
• Concentrated suspensions (zone settling or hindered): Suspended particles settle in layers in the basins.
• Concentrated suspensions (compression settling): Particles compact to settle more rapidly.

Types of Sedimentation (settle characteristics)

• Discrete settling: individual particles settle independently. This happens when solid concentration is relatively low.
• Flocculant settling: individual particles stick together into clumps (flocs). This happens at higher particle concentrations.
• Hindered settling: Particle concentration is high enough to inhibit water movement.
• Compression settling: particles settle by compressing the lower mass of particles.

Settling in Treatment Train

• Diagram shows flocculation basin, settling basin, and dual media filter.

Types of Sedimentation (types of flow)

• Fill and draw type: Fill tanks, store, and then draw treated water.
• Continuous flow type: Water passes continuously through the tank, which can be rectangular or circular.

Circular Sedimentation Tanks

• Sludge scrapers are attached to a rotating arm within circular tanks to scrape sludge toward a central hopper.
• Scrapers are often of peripheral drive, fixed bridge, or fixed half-bridge (cage drive) type.
• Such tanks use a low-maintenance design and a fast and highly effective sludge removal process.

Rectangular Settling Tanks

• Rectangular clarifiers use scrapers to collect sludge at the influent end.
• Mechanisms may include chain-and-flight types or scrapers and scum removal equipment suspended from a traveling bridge.
• These tanks are commonly used in major water treatment centers to utilize space effectively.

Coagulation

• The goal is to alter the surface charge of turbidity-causing particles, promoting their adhesion and settling under gravity.

Purpose of Coagulation/Flocculation

• The primary goal is to remove turbidity from the water.
• High turbidity hinders disinfection, so a maximum allowable level of 0.5 NTU is recommended, while 0.1 NTU is ideal.
• Coagulation also helps remove suspended bacteria and color.

Measurements of Turbidity

• FTU (Formazin turbidity unit) and FNU (Formazin nephelometric units) are common measurement units.
• The Jackson Candle method measures turbidity; a longer column of water needed to obscure the flame indicates lower turbidity.
• Nephelometry measures light scattered by particles to estimate turbidity.
• Secchi disks measure turbidity by lowering them into the water until they can no longer be seen; the depth shows turbidity inversely.

Process Steps of Coagulation/Flocculation

• The process typically involves three steps: flash mixing, coagulation, and flocculation.
• In practice, only flash mixing and flocculation are used at treatment plants.
• Coagulants are added to the water in the flash mixing process to evenly distribute them and create violent agitation for better mixing.
• During coagulation, the chemicals neutralize the electric charges of fine particles, encouraging them to clump.
• The subsequent flocculation step involves gentle mixing of the particles to form larger flocks to be easily settled.

Overview of the Process

• The desired product of the coagulation/flocculation process is water with most turbidity removed, in the form of settled flocs.
• Optimal floc size is between 0.1–3 mm.

Colloids

• Small particles (0.001 to 1 μm) that are usually negatively charged.
• These particles repel each other, maintaining a stable suspension.

Coagulation and Flocculation

• Coagulation alters the surface charge of colloidal particles to make them clump together. In contrast, flocculation involves gentle mixing to join the clumps into larger flocks.

Coagulants

• Common non-toxic and inexpensive coagulants include alum (aluminum sulfate), ferric chloride, ferric sulfate, and polyelectrolytes.
• They're insoluble in neutral pH ranges, so they don't leave behind metal contaminants.

Preliminary Water Treatment

• Series of steps that purify water before other treatment stages.
• Steps include intake, protective bar screens, travelling water screens, low-lift pump well, chemical coagulants Chlorination.

Factors Influencing Coagulation

• Water pH: Coagulation works better in alkaline conditions.
• Temperature: Higher temperature results in lower viscosity and improved settling.
• Type of suspended matter: More concentrated matters lead to higher removal rates.
• Coagulant type: Heavier coagulants (e.g., ferric salts) settle faster.
• Coagulant dose: An optimal dose is needed for maximum efficiency.
• Mixing time and method: Violent agitation results in better mixing

Aeration

• A process where air is introduced into water to oxygenate, or another gas is bubbled through.
• Processes include using cascades, trickling beds, air diffusion, and spray nozzles.

Filtration

• The process of removing particles not removed by coagulation, sedimentation or other methods.
• Multiple filtration mechanisms exist, depending on the system design.
• Sedimentation effluent will be in the range of 1–10 TU, and the final effluent will be less than 0.3 TU.

Slow Sand Filtration

• Uses only sand as the filter media
• Gradual, lower flow rates
• Typically used in smaller plants without the need for covers.

Sedimentation Effects of Filtration

• Filters can remove particles smaller than the pores through void spaces effectively.
• Settling is assisted by entrapment in a gelatinous biofilm.

Biological Effects

• The slimy layer (biofilm, Schmutzdecke) on filter surfaces contains microorganisms (algae, bacteria, etc.) and trapped debris.
• This layer enhances trapping efficiency and metabolizes organic impurities into harmless products.
• The top inch of the sand layer requires periodic skimming to mitigate clogging.

Electrolytic Effects

• Sand grains and impurity particles have opposite charges.
• Neutralization of charges causes aggregation and trapping of impurities.

Slow Sand Filters: Pros and Cons

• Pros: Affordable, effective for smaller plants in warm areas, can remove solids efficiently and a high percentage of coliforms.
• Cons: Slow rate, large area required for implementation.

Rapid Sand Filters

• Larger, graded particles are used as filter media.
• Faster throughput than slow sand filters.
• Requires backwashing (to remove trapped particles and alleviate filter clogs) once daily, typically for 10-15 min.
• Can be fluidized or non-fluidizing.
• The backwash process may utilize water troughs.
• Design often involves one filter out of service at a time to handle flows and ensure consistent service.

Filtration

• Final stage of water treatment to eliminate small particles that cannot be removed by other stages.

Rapid Sand Filter Process (Schematic, image)

• Shows the general setup, with tanks, channels, and connected piping for water movement.

Backwashing Rapid Sand Filtration

• Force water or air upwards from the clearwell to clean the filter.
• The particles are suspended, allowing trapped particles to be removed.
• Backwash water is treated or disposed of.

Pressure Filter

• Direct application of pressure across the filter medium (300–700 KN/m²).
• Cleaning typically utilizes backwash (or compressed air).
• Requires frequent cleaning.
• Smaller footprint and suitable for industrial use.

Disinfection

• Water is disinfected after filtration.
• Chlorine gas is often the disinfectant used.
• Key goals are to effectively eliminate pathogenic organisms and assure residual disinfection during subsequent distribution.

Breakpoint Chlorination

• As chlorine is added, it's consumed by chemical reactions influencing a rise in chlorine concentration.
• The rate will depend on the addition rate and reaction process.
• Usually, reaction rates speed up rapidly until most reactions are complete, after which addition of additional chlorine results in a residual for extended protection before distribution (approx. 30 mins).
• The point where chlorine concentration starts to increase again is termed the breakpoint.

Residual Chlorine

• A residual of 0.2–0.3 mg/L is often desired to assure continuous protection from recontamination before distribution.
• Breakpoint may not be evident for certain water types because different organic components react at different rates.

Pre, Post and Double Chlorination

• Chlorination steps can come before or after other water treatment processes.
• Chlorination before filtration or sedimentation is termed pre-chlorination, whereas chlorination after the processes is post-chlorination.
• In many systems, both are used, termed double chlorination. If more chlorine is needed during any of the stages more chlorine may be used.

Superchlorination-Dechlorination

• When water quality is uncertain or contains resistant microorganisms, substantial amounts of chlorine are added and dechlorination with sulfur dioxide is afterward implemented to remove excess chlorine.

Other Disinfectants

• Hypochlorite salts (NaOCl and Ca(OCl)2): More expensive but easier to handle and frequently used in small supply operations.
• Chloramines (NH₂CI, NHCI2, NCI₃): Require longer contact times when used as a primary disinfectant; often used for combined disinfectants.
• Chlorine dioxide (ClO₂): Very effective but requires on-site production.

Other Disinfectants (Ozone, UV radiation)

• Ozone (O₃): Powerful oxidant, effective at killing cysts; no taste or odor issues; more expensive and needs on-site production.
• Ultraviolet radiation: Effective bactericide; water needs to be free of turbidity or slime. No residual protection.

Disinfection By-products (DBPs)

• Trihalomethanes (THMs): Results of reactions between chlorine and organic matter; have links to gastrointestinal tract cancers.
• Haloacetic acids: New rules require limits for five compounds.
• Bromate and Chlorite: Also are regulated.

Water Softening

• Temporary hardness: Caused by calcium or magnesium carbonates and bicarbonates; removed via boiling or adding lime.
• Permanent hardness: Caused by calcium and magnesium sulfates, chlorides, or nitrates; removed via lime soda process, zeolite process, or demineralization.

Additional Processes - pH Adjustment

• Recarbonation: Used to adjust the pH of softened water, returning it to an optimal level for further treatment.
• Sodium hydroxide: Used to raise pH for corrosion prevention, especially in surface water.

Additional Processes - Fluoridation

• Fluoride (F⁻) is added to water either as NaF, Na₂SiF₆, or H₂SiF₆.
• It is used to prevent dental cavities.
• Levels of approximately 1 ppm have been shown to be beneficial.

Additional Processes - Corrosion Control

• Polyphosphates are added to prevent pipe corrosion by forming a protective film on pipes and reducing lead levels.

Advanced Treatment Processes

• Advanced Oxidation Processes: Used for disinfection enhancement and oxidation of synthetic organic chemicals and taste/odor control in water.
• Activated carbon adsorption: Used to remove recalcitrant synthetic organic chemicals (THMs), taste and odor compounds. Treatment concerns with bacterial growth exist.
• Membrane process: Discriminates both on size and chemistry, and includes selective removal (e.g., desalination).

Residuals Management

• Stages focusing on managing or disposing of residuals from water treatment, including processing, storage, or final disposal techniques.

Residuals Management - Dewatering

• Different methods that concentrate and dewater sludge, including lagoons, sand-drying beds, freeze treatment, centrifugation, vacuum filtration, continuous belt filter press, and plate pressure filters.

Residuals Management - Ultimate Disposal

• Options for ultimate sludge disposal include on-site storage, landfilling, soil amendment, reclamation/recycling, or other disposal methods.

Water-Related Diseases

• A significant portion (80%) of illnesses in developing countries are water-related.
• Large amounts (90%) of untreated wastewater are discharged directly into water sources in developing countries.

Effects of Water Pollution

• Effects on aquatic ecosystem: Biological magnification and eutrophication are prominent.
• Effects on human health: Hazards of groundwater pollution.

Eutrophication

• A process where water bodies receive excessive nutrients leading to excessive plant growth.
• This results in several reductions in water quality, such as algal blossoms that cause light depletion and reduce oxygen for bottom-dwelling organisms.

Eutrophication (continued)

• Algal blooms cause drastic fluctuations in dissolved oxygen (DO).
• Under extreme conditions, anaerobic conditions, and the growth of bacteria like Clostridium botulinum can ensue, resulting in fish mortalities.
• Phosphorous is a major culprit in eutrophication.

Sources of high nutrient run-off

• Waste water, run-off and leachate (from waste disposal, animal feedlots, and mines), run-off from agriculture, irrigation, and septic tanks, and overflows from combined storms increase nutrients.

Ecological Effects of Water Pollution

• Ecological effects of pollution include increased phyto-plankton biomass, toxic or inedible species, gelatinous zooplankton blooms, reduced water transparency, taste/odor issues in water and treatment challenges, DO depletion, fish kills, loss of desirable fish, and shellfish, and decreased resource values (i.e., decreased tourism).

Domestic Effluent Treatment

• The treatment of raw sewage for safe discharge.

Definitions

• Sullage: Wastewater from domestic sources (bathrooms, kitchens, etc).
• Sewage: Liquid waste (sullage, latrines, industrial waste, etc.) from communities.
• Domestic Sewage: Liquid waste largely from residential sources.
• Industrial Sewage: Liquid waste primarily generated from industrial facilities.
• Stormwater: Rainwater entering the sewer system.
• Subsoil water: Groundwater seeping into the sewer system.
• Nightsoil: Human and animal excreta.
• Sewer: Conduit carrying sewage to disposal sites.

Methods of Domestic Sanitation

• Conservancy system: Human excreta is processed by human agency, while garbage is collected in bins for transport.
• Water carriage system: Sewer system is used with water to carry human wastes.
  • Separate sewage and stormwater systems.
  • Combined systems.
  • Partially combined systems.

Sewage Physical Characteristics

• pH: Measures acidity or alkalinity of the sewage.
• Color: Dark color often indicate DO-depletion.
• Odor: Often unpleasant, particularly indicative of poor waste management.
• Temperature: Can affect treatment processes and organism growth.
• Solids: Measured as Total, suspended, and settleable solids.

Dissolved Oxygen

• At least 4 ppm DO is necessary before sewage discharge.
• Biologically active organic matter degrades in varying stages (carbonaceous - first 20 days of process, nitrogenous - second stage or longer).
• Biologically inactive matter.

BOD (Biochemical Oxygen Demand)

• The amount of dissolved oxygen consumed by a sample in a given time period (3, 5, or 10 days) at a standard temperature.
• Total BOD = carbonaceous oxygen demand + nitrogenous oxygen demand.
• For 5-day BOD, nitrogenous oxygen demand is often assumed to be limited during the period considered.

Stages of BOD Satisfaction

• BOD will increase during stages of breakdown (i.e., consumption of oxygen in the water during decomposition).
• Stages exist for carbonaceous and nitrogenous matter.

COD (Chemical Oxygen Demand)

• The amount of oxygen needed to oxidize all organic matter present (biologically active and inactive) through chemical oxidation using potassium dichromate or potassium permanganate.
• COD is usually measured within 3 hours.
• Usually, COD > BOD.

THOD (Theoretical Oxygen Demand)

• Theoretical oxygen demand can be calculated if all wastewater constituents and their concentrations are known.

Decomposition of Sewage

• Aerobic Decomposition: Oxygen present; occurs quickly through bacterial action with complete decomposition and stable by-products such as CO₂ and H₂O.
• Anaerobic Decomposition: No Oxygen present; a slow process with incomplete decomposition requiring further treatment with unstable and offensive products such as CO₂,CH₄, H₂, NH₂, etc.

Treatment of Sewage

• Primary Treatment: Removing large solids (e.g. grit and organic matter).
• Secondary Treatment: Further removing smaller solids using microorganisms to degrade organic matter to a lesser level requiring further treatment (e.g. lagoons, trickling filters, rotating biological contactors (RBCs), or activated sludge).
• Tertiary Treatment: Additional treatment processes to further remove impurities.

Sewage Treatment Schematic

• Diagram illustrating the stages of sewage treatment (using activated sludge for secondary treatment), including primary treatment, screens, comminutor, primary clarifier, grit chamber, grit disposal, secondary treatment (including aeration tank, secondary clarifier, and disinfectant), effluent discharge to surface water, and sludge treatment and disposal to complete the sewage processing cycle.

Package Plant for Aeration and Sedimentation

• Diagram of the basic physical structure of a plant for aeration and sedimentation.

Oxidation Ponds

• Open ponds used to aerate and treat sewage, using sunlight penetration and air-mixing due to winds and algal growth to facilitate oxygen enhancement and effective aerobic bacterial activity to degrade organic matter in sewage.

Facultative Ponds

• Ponds capable of both aerobic and anaerobic reactions, with three layers: lower layer involving anaerobic decomposition and release of by-products (CO2, NH3, CH4 etc.), a middle layer that is photosynthetic and releases oxygen from algae facilitating aerobic bacteria growth. The upper layers involve aerobic bacteria that further utilize oxygen to oxidize organic matter.

Sludge Management

• Processing of sludge, a residual product from treatment of wastewater or sewage, which could be from primary or secondary treatment stages, including various chemical or thermal treatments to safely and effectively dispose of the residual matter.

Sludge Processing (Methods)

• Unstabilized organics: Biological or thermal treatment for stabilization.
• Inert organics/inorganics: Concentrated, dewatered, and deposited into the environment.

Sludge Processing (Chemical Conditioning)

• Methods involving the use of lime, alum, and other ferric salts for increasing sludge mass for easier removal and removing fine particles.

Sludge Processing (Thermal Conditioning)

• Methods utilizing temperatures between 180 and 230°C for 15-60 minutes under pressure between 13-20 atm for effective dewatering of sludge.

Sludge Processing (Methods) – Filters

• Rotary drum vacuum filters, rotary vacuum filters, filter press, and sand beds are used for various filtration and dewatering processes.

Sludge Disposal

• Methods used to dispose of sludge (e.g., incineration, land spreading).

Industrial Solid Waste Management

• Overall processes including management steps: Waste Generation, Storage, Collection, Transfer/Transport (of wastes), Processing/Recovery, and Disposal.

Landfilling

• A method of waste disposal using compacted waste cells.
• Sequential waste dumping with soil cover is a typical method implemented to reduce odor and other possible deleterious effects.

Industrial Waste Water (Classification)

• Domestic wastewater
• Process wastewater
• Cooling wastewater

Wastewater Characteristics

• Organics: Organic compounds in the wastewater.
• Inorganics: Inorganic constituents of the waste, including salts and minerals.
• pH and Alkalinity: Measures acidity and alkalinity for regulation and effect on treatment efficiencies.
• Temperature: Can affect treatment systems and biological organisms.
• Dissolved Oxygen (DO): Concentration of dissolved oxygen in wastewater affects the biological activity throughout the processes involved.

Industrial Wastewater Treatment

• Typical steps involve primary treatment, aerobic treatment, secondary treatment, and sludge processing/disposal.

Pretreatment

• Equalization: Levels out flow and concentration fluctuations affecting treatment.
• Neutralization: Corrects pH imbalances.
• Grease and oil removal: Separates grease and oils from the waste with various methods;
• Toxic substances: Reduces harmful concentrations to safe limits or removes them completely before further treatment stages.
• Grit chambers: Separation of inert particles like sand to protect other machinery and components.

Primary Treatment (Methods)

• Screens: Remove/keep larger solid particles from passing further.
• Grit chambers: Removing the grit/solid and inert material that is heavier or denser than water through settling.
• Gravity sedimentation: Removing particles through settling.
• Chemical precipitation: Adding chemicals to aggregate particles to accelerate the settling process before additional treatment stages.

Secondary Treatment

• Biological treatment: Using microorganisms to breakdown and remove biodegradable substances to reduce the organic content of the waste water to a usable level of discharge.
• Methods include lagoons, trickling filters, rotating biological contactors (RBCs), and activated sludge.
• Aerobic: Oxygen present in water supporting aerobic decomposition (e.g., trickling filters, activated sludge).
• Anaerobic: No oxygen present in water; supporting anaerobic decomposition (e.g., septic tanks, anaerobic lagoons).
• Facultative: Conditions allow for both aerobic and anaerobic reactions (e.g., facultative lagoons).

Tertiary Treatment

• Additional treatments to further refine or enhance the discharge water quality (e.g., advanced oxidation processes, membrane processes).

Test your knowledge on key concepts in water treatment processes. This quiz covers coagulation, sedimentation, aeration, and various treatment methods, including wastewater management and advanced oxidation processes. Challenge yourself to understand the intricacies of maintaining clean water.