Global Water Supply and Use

Global Water Supply

• The world's water resources are limited and unevenly distributed.
• Oceans constitute 97.5% of the total water.
• Freshwater constitutes 2.5% of the total water.
• Glaciers make up 68.7% of the freshwater.
• Groundwater accounts for 30.1% of the freshwater.
• Permafrost constitutes 0.8% of the freshwater.
• Surface and Atmospheric Water make up 0.4% of the freshwater.
• Freshwater lakes constitute 67.4% of surface and atmospheric water.
• Wetlands make up 8.5% of surface and atmospheric water.
• Soil Moisture accounts for 12.2% of surface and atmospheric water.
• Rivers constitute 1.6% surface and atmospheric water.
• Atmosphere makes up 9.5% of surface and atmospheric water.
• Plants and Animals account for 0.8% of surface and atmospheric water.
• Access to sufficient healthy water resources is crucial for supporting population, agriculture, and industry.

Municipal Water Use

• In 1999, municipal water use was distributed among:
  • Residential: 52%
  • Commercial: 19%
  • Industrial: 16%
  • Leakage: 13%

Canada - Freshwater

• In 2001, the average daily freshwater domestic use per capita in Canada was 335 liters.
• This usage was divided as follows:
  • Bathing: 35%
  • Toilet Flushing: 30%
  • Laundry and Cleaning: 25%
  • Cooking and Drinking: 10%
• Canadian rivers discharge approximately 9% of the world's renewable water supply.
• Canada's population accounts for less than 1% of the world's population.
• Canada has a significant amount of its surface area covered by freshwater.
• Approximately 60% of Canada's freshwater drains to the north.
• 85% of the population resides along the southern border with the United States.
• Municipal water prices in Canada per cubic meter are lower than any other country.

Quality and Quantity Aspects of Water

• Quantity Aspects include:
  • Projected future and present water demand.
  • Design and operation of wastewater treatment plants.
• Quality Aspects:
  • Delivered water must meet certain standards.
  • Wastewater discharged must have limited contaminants.
• There is a need for unit operations in water treatment.
  • Operations include screening, sedimentation, aeration, filtration, coagulation/flocculation, disinfection, and adsorption.
• Physical Characteristics:
  • Color, taste, turbidity, and temperature.
  • Screens and Sedimentation Tanks is used for Solids
  • Filtration is used for Color, Taste and Turbidity
• Chemical Characteristics:
  • pH, salts (ions), and dissolved oxygen (DO).
  • Coagulation and flocculation is used for removing colloidal solids and turbidity.
  • Softening is used for hardness reduction.
• Biological Characteristics include organic matter (OM), bacteria, and viruses.
  • Biological processes are used for treating organic matter (OM).
  • Disinfection is used for eliminating bacteria and viruses.

Historical Water Treatment Trends

• Early 20th century water treatment:
  • Focused on dealing with infectious organisms.
• 1930s-1980s:
  • Engineering cost-effectiveness of water treatment plants improved.
• 1990s to present:
  • Focus on long-term health effects of organic compounds like THMs and VOCs.
  • Re-emergence of microbiological contamination and water-borne diseases.
  • Integrated Management for sustainability, nutrient, and energy recovery.

Material Balance

• French chemist Antoine Lavoisier established the Law of Conservation of Mass in 1789.

• Mass can be neither created nor destroyed and the mass of reactants always equal the mass of products.

• Material Balance:

  • Is an application of the Law of Conservation of Mass.
  • Mass balance analysis that provides a mathematical description of a defined system as a function of time.
  • The general conservation law is described by the equation: Accumulation = Input - Output + Generation - Consumption

• Mass balance problem solving steps:

  • Prepare a simplified schematic of the flow diagram.
  • Draw a system boundary and/or control volume boundary to define the limits.
  • Proper selection of this volume can simplify the material balance computations.
  • A System Boundary identifies liquid and constituent flow.
  • A Volume Boundary identifies the actual volume where change occurs.
  • List all known data and assumptions on the flow diagram.
  • List all rate expressions for chemical and biological reactions.

• Simplifications of material balance:

• Biological degradation in a batch reactor.

  • For a batch reactor with biological degradation and no inflow or outflow
    • Accumulation = -Consumption

• Chemical production in a batch reactor.

• For a batch reactor with chemical production and no inflow or outflow -Accumulation = Generation

• Hydraulics flows of reactors with no chemical or biological production or degradation.

  • Accumulation = Input - Output

• Steady-state concentrations exist within the system where concentrations do not change with time:

  • There is no accumulation in the system,
    • Accumulation = 0
    • 0 = Input - Output + Generation - Consumption

Total Mass Balance and Reaction Rates

• Total Mass Balance can be performed for mass entering/leaving a unit, junction, or system.
• It can be described mathematically as:
  • δη/δt = ±km^n
• Reaction rates in environmental engineering applications that is most frequently used:
  • Mass = Concentration x Volume
• Rate equation variation, where:
  • δη/δt=(δC/δt)V=V(δC/δt)
• For a zero-order reaction (n=0):
  • δη/δt=±k
  • δC/δt=±k
  • C = C₀ ± kt
• For a first-order reaction (n=1):
  • Units of k→ 1/time
  • δη/δt = ±kM
  • V (δC/δt) = ±k (CV)
  • δC/δt = ±kC
  • ∫dC/C = ±k ∫dt

Reactor Design

• Reactors are the vessels where reactions take place.
• Treatment efficiency is controlled by reaction kinetics and reactor retention time.
• Batch Process:
  • Feed added to the beginning of the process instantaneously.
  • Products are removed instantaneously at the end of the process.
  • No mass enters or leaves between charge and emptying.
• Semi-Batch (Unsteady Flow) Process:
  • Feed is instantaneous.
  • Removal is continuous or vice versa.
• Continuous (Steady Flow) Process:
  • The influent and effluent are continuous throughout.
  • Rates may vary but may also remain constant.
  • Designed so that reactants have sufficient time to react.
  • Reaction time is the time reactants remain in the system.
• Ideal Hydraulic Flow depends on degree of mixing and differing intrinsic mixing intensities.
  • Maintenance of solids requires high mixing intensity.
  • Sedimentation relies on low mixing intensity.
• Completely Mixed Stir Tank Reactor (CSTR):
  • Referred to as a Completely Mixed (CM) Reactor/Continuous Flow Stirred Tank Reactor (CFSTR).
  • Perfectly mixed from a hydraulic perspective.
  • Influent is instantaneously and evenly dispersed through the entire reactor volume.
  • The concentration within a CSTR basin equals the effluent's concentration at any time.
  • Reactor design incorporates:
    • Vessels with similar dimensions.
    • Significant mixing mechanisms.
    • A liquid recirculation stream.
• Plug Flow Reactor (PFR):
  • Also referred to as Plug Flow Tank Reactor (PFTR) or Tubular Reactor (TR).
  • Has no lateral hydraulic mixing.
  • Influent passes through with no longitudinal mixing.
  • Concentrations are uniform within each cross-section.
  • Each fluid particle remains inside for one detention time.
  • PFR reactors are significantly longer than they are cross-sectional.

Residence Time and Tracer Studies

• Residence Time/Distribution Age:
  • The time a fluid element stays in a reactor.
• Elements of fluid take variable routes in the reactor resulting in variable lengths of time to pass through.
• Hydraulic Retention Time (HRT) / Mean Residence Time:
  • Time that dissolved/suspended reactants stay & are exposed to necessary conditions.
• Residence Time Distribution: method to analyze the hydraulic performance of reactors.
• Residence Time Distribution (RTD) Curves:
  • Record of times each fluid element takes to pass through the system.
  • Assumptions include:
  • Closed system boundaries to back mixing.
  • Constant Fluid Density
  • System is at a steady state.
• Stimulus-Response/Tracer Studies:
  • Used to experimentally determine RTD by introducing tracer material at system inlet & observing the response.
• Tracer injection methods:
  • Pulse Input:
    • Instantaneous injection of some tracer over a short time.
    • Requires less tracer (cost efficient), but the detection limit can prevent final measurements from being recorded, which misses tailing effects miss and underestimates dead zones.
  • Step Input:
    • Continuous injection until the effluent tracer concentration equals the influent.
    • Detection limit of instruments does not matter.
    • More expensive, tracer remains in the system, and bypassing can be missed.
  • Periodic Input
  • Random Input

Characteristics of a Tracer

• For a tracer to be effective, it must:
  • Be inert (no loss via reaction)
  • Have the save same density as the fluid
  • Easily dissolve into the fluid
  • Not adsorb readly onto surfaces
  • Accurately measurable over a wide range of concentrations
  • Have a low detection limit and quantification
  • Have low molecular diffusivity
  • Have zero background concentration and not generated during the experiment
  • Be inexpensive
• C Curve (Concentration vs. Time): referred to as centroid of the distribution
• Experimental Mean Residence Time:
  • For equidistant, discreet time steps for experimental mean residence time, it is valid that:
    • t ≈ ∑(tᵢCᵢΔt) / ∑(CᵢΔt)
• where:
  • t = Mean Experimental Residence Time
  • T = Time
  • M/L^3 = C = Tracer Concentration at the Exist Stream
• The curve measures the spread of distribution, and if a function was measured with equidistant discrete time steps:
  • σ² ≈ ∑(tᵢ-t)²CᵢΔt/ ∑(CᵢΔt)
    • Where
      • T= t = Mean Experimental Residence Time
      • Time= t
      • M/L3 = C=Tracer Concentration at the Exist Stream
      • σ²=Variance of the Residence Distribution

Coagulation and Flocculation

• Water and wastewater contain solid material of varying sizes from large visible objects such as wood and rags, to colloidal material such as bacteria and small in-organic solids.
• Large Visible Objects are removed via screens or a bark rack.
• Settleable Particles that are greater than 50 µm are able to be removed via sedimentation.
• Colloidal Particles are removed via coagulation and flocculation.
• Coagulation and flocculation focuses on the removal of colloidal particles.
• Colloidal particles range approximately from 10-9 m to 10-6 m.
• Colloidal system comprised of finely divided particles (dispersed phase) in continuous dispersion medium.
• Concerns associated with colloidal include:
  • Turbidity/color.
  • Pathogens and Toxics attach to surface.
  • Natural Organic Matter (NOM)
• The stability of a particle, it is caused via accumulation of electrical charges at the surface.
• Colloidal particles, the surface charge causes suspension without aggregation long term.
• Coagulation and flocculation is to turn particles into flocs.
• Settling velocity of a particle is dependent on its diameter.
• Settling velocity equation: Vsettling ∝ d²

Coagulation and Surface Charge

• Coagulation encompasses:
  • Reactions, mechanisms, and results in particle aggregation during water treatment.
  • Chemical Addition (coagulant destabilizes colloids).
  • In-situ Coagulant Formation
  • Chemical Destabilization of Colloidal and Dissolved Particles
  • Physical intra-particle contact resulting in agglomeration into large particles.
• Flocculent is a chemical added to enhance flocculation.
• 1st three steps take place in the rapid mix basin
• Last step takes place in the flocculation or a slow mix basin
• Separation generally takes place via sedimentation, flotation, filtration or sometimes used membrane filtration
• Particles in water carry a negative charge in normal pH ranges due to:
  • Ionization (OH Group in Silica)
  • Adsorption (Human Substances)
  • Isomorphism Replacement (replacement of Si by AI)
  • Structural Imperfection (Broken Bonds on the Edge)
• Colloidal Particle, primary charge attracts the solution ions of opposite charge within the Fixed Layer/Stern Layer.
• Compact layer is surrounded by counter ions called the Diffuse Layer. Electrostatic field created from from concentration difference
• Repulsive forces are caused by the zeta potential by attraction due Van der Waals Forces
• Zeta potential of colloidal particles can decreased by:
  • Boiling
  • Freezing
  • Addition of Electrolytes which counter ions added in fixed layer Adjustment of the pH of the system toward the isoelectric point
• Materials used for coagulation must be nontoxic insoluble and have high charge density
  • Metal salts: Availability and cheap costs.
  • Polymers: Costly

Coagulation cont.

• Schulze-Hardy Rule:

  • Ability of an agent to coagulate colloids in water relates to its charge and synthetic polymer size.
  • Colloid precipitation is dependent on ion charge 3+>2+>1+. Coagulation Mechanisms: -Double Layer Compression: -Decreases energy barrier via counter ions. Destabilization via compression of the diffuse layer surrounding the particle reduces particle aggregation. Adsorption and Charge Neutralization: some hydrolyzed metal salts can adsorb to its the surface, and if the adsorbed species carries the opposite sign then adsorb Enmeshment (Sweep Floc) metal hydroxide precipitate at high metal salt concentrations. Inter-particle Bridging: Polymers adhere and remove

• pH and dose important factors

• Optimum values happen via Jar Test.

• Ferric salts work the best at 4.5-5.5 pH, . while aluminum salts are most affective 5.5-6.3. Turbidity reduction occurs at rapid mixing for 1 minute, while the slow mixing slow mixing is for 15-20minutes and settlement is for 15-20 minutes.

• Flocculation: Process in which colloidal particles with are brought into contact -Agitation of water containing the flocs and particles

• For particles less than 0.1 µm: Flocculation is caused by diffusion, or Perikinetic

• For particles greater than 0.1 microns: Flocculation is caused by Orthokinetic or Mixing

Mixing Considerations

• Thorough mixing is essential for efficient Coagulation and Flocculation via Rapid Mixing

1. Mixing Time
2. Velocity Gradient, (G) G is relative velocity of two particles and a high G value means more violent mixing.

• Proportional to the power used energy dissipation -G gradient velocity= (sec-1)

• power power input (watts(N*m/second) V volume(m3)

• µ viscosity(N*seconds/m^2)

• high Rapid mixing gradients occur when seconds is required

• Mechanical Mixing, In line static Mixing, mechanical mixing is most common in CSTR

• Low velocity gradients: such that line particles will not break up. Requires longer minutes Pipe flocculators, horizontal flow battles, turbine mixers needed.

Mixing Practice

• Given the Design Flow Rate (Qa) and Detention time (t)

• From the temperature using the water determine the Viscosity (u)

• Divide the flow into at least 2 flucation to help half

• Basing flocciation should always be divided into more than 3 compartments to ensure that the volume of flucation is optimized

• Velocity will be higher at lower temperatures to ensure that the G flow values can easily be decreased.

  • The initial stage is best served by the higher vales

    • The latter stages are easily broken by smaller values

• The number of floculaiton basins should be determined to help easily achieve the proper equation

  • V=Qat

• Volume can be calculated as

  • V₁=V2=V3=V/3

• Select the wheel diameter

• Select clearace between 0.5 meter and 1500 feet

• Select a clearace

• Select the department by ensuring that you use diament to determine the appropriate clear channel

• Select the appropriate number to find the equation:

  Equation depth= diament + (clearane X2) assuming each partment is equal to length one you have to solve the problem, with equation

• W=U/DI

  • Select spacing between Wheels to help determine shaft

• Select Number of Wheels

15. Determine the paddlpe boards Lp= width to width = Clearneence Awa to wheel shaft

Equipment needs equation: Pp= width to wheel for shafts

Eq. 11. determine ration CD for department

Determine power requirements for each

P1= U1VG2

Rotational Speed determine CD with P1CAP2 v1=2nrkn PI= (V(P Determine the parameters

Each sector has radial parameters such as radial and rotational CDA +2 p kr^3 32/m2

Sedimentation

• The removal of particles through the use of gravity. In water. Sediment basins -The pans may be rectangle triangle and other shapes
• The involved is dependent on the characteristics

To sign the involved required it

• type 1 discrete settings are particles dont interact
• discrete particles contain constant size
• the other may include fluculenate setliing
• type two flucolent settling

Sedimentation: Type 1 - 4

• 3rd Zone= concentration -mass setting suspension can s4etteis from water between

• type 4- compression settlement-

  • settle achievement

• the setting rate

rate is a constant rate

The setting independent of particle over time before concgulation, linearr ,overflow iticla

Settling Velocity

• In order to determine the required particles for a long amount of time must have

Equation for for laminar flow

• REYNOLD given R= VCD Eq. 27

• • • for laminar flow < 1 and 22
  • eq 29

• For transition CD = 24

• For laMInar settings

• Assumes the lamatar flow to help determine settling if Reynold

Number will

If it is the result is validated- otherwise it must be the flucalulated Use co efficienct to help reach the requirements RECALCULATING IN REPEAT to determine new converage by setlling

Sedimentation Basin

-Continuous flow, steady and no dead space or short circuiting.

• inlet there is the

Plug flow there is no settling

particles flow horizontally 100 Settling is steady doesn's shift Removed to reenter system don't reenter Flow coverages to top- Steady is

Dimensions. Settling rate cont

-rate ALL PARTICLES ARE DEPENDENT

Long comumn Settin g Tests

musthave THE SAME

Calculatre removal for samperla C =O.

Select design depth and measure

Plot time graph to REMOVAL is STARTING

DESIGN OVERflow

Tank will e qual Flow = area 1 design overflow rates to

• flow rates to