3rd lecture Wastewater

mass balances

Provide tools for modeling the production of, transport and fate of pollutants in the environment

Energy balances

Provide tools for modeling the production of, transport and fate of energy in the environment

Mass balances

Or material balance is the mathematical representation of accounting system use to trace enery

Energy balances

The mathematical representation of the accounting system use to trace energy

Reactors

Tank in which physical, chemical and biochemical reactions occur

Control Volume

Region of space which the term Min and Mout are determined

Mass flux

The rate at which mass enters of leave

Mass flux

Flow rate multiplied by cconcentration

Mass balance

Equation to __________ used throughout the environmental engineering and sciences

Mass accumulation rate

The rate of change of mass within the control volume, the total mass within the control volume of the compound where the mass balance is performed

Mass accumulation rate

The control volume is well mixed, the concentration of the control volume and the mass in the control volume is equal to the product of cencentration and volume

steady state

Properties of system do mot change with time

Nonsteady state

The mass in the control volume varied with time

Decay rate

Is the reaction rate that is due to biological degredation

Kinetic reactions

Time dependent reactions are called

Conservative

Form of mass flux that has no chemical formation

Zero order decay rate

Form of mass flux mass where in the rate of loss is constant

First order decay

Form of mass flux mass where in the rate of loss is directly proportional to its concentration

Second order decay rate

dC/dt=-k [C] ^2

Zero order decay rate

dC/dt=-k [C]n thus, dC/dt=-k

First order decay

dC/dt=-k [C] ^n thus, dC/dt=-kC or [C]= [Co] e^-kt

Half life

It has a relationship with the rate constant

Half life

Define as the time required for the concentration of a chemical to decrease by one half

Reactor Analysis

Refer to use of mass balance s to analyze pollutants concentrations in control volume that is either a chemical or natural system modeled as a chemical reactor

Batch Reactor

Type of reactor which is a fully mixed reactor with no flow in or out of the reactor

Plugflow reactor

Or tubular flow. A type of reactor used to model the chemical trasformation as they are transported in pipes

Continous flow stirred tank reactor

Reactor with flow through and is completely mixed

Primary treatment

First process in the wastewater treatment plant to remove organic particulate

Primary treatment

Plays an important function of removing scum that wasnot remove inthe grit chamber

Co^kt

Reaction order zero, Batch

Co^-kV/Q

Reaction order zero, PFR

Co^-kV/Q

Reaction order zero, CFSTR

Co e^-kt

Reaction order first, Batch

Co e^-kV/Q

Reaction order first, PFR

(Co) / (1+kV/Q)

Reaction order first, CFSTR

Co /(1+ktCo)

Reaction order second, Batch

Co/(1+kCo V/Q)

Reaction order second, PFR

-kC^2

Reaction order second, reaction constant

-kC

Reaction order first, reaction constant

-k

Reaction order zero, reaction constant

90-95

Settleable solids primary treatment removal efficiency ME

50-65

Suspended solids primary treatment removal efficiency ME

20-35

BOD primary treatment removal efficiency ME

90-95

Settleable solids primary treatment removal efficiency FS

40-60

Suspended solids primary treatment removal efficiency FS

25-35

BOD primary treatment removal efficiency FS

Sedimentation

Oldest process widely used primary and secondary WW treatment takes place when gravity pulls particle to the bottom of a tank

Its objective is to remove readily available setteable solidsand floating materials and thus reduce the suspended solids content

Clarifier

Settling tanks that recieve raw WW priot to biological and/or chemical treatment

Short circuiting

A hydraulic condition occuring in parts of a tank where the time of travel is less than the flow through time

Septic tank

Cobined settling and skimming tank and as an unheated unmixed anaerobic digester

Septic tank

Provide long settling time 6-8 hrs or more

Two story imhoff tank

Similar to septic tank in removal and and settleable solidsand the anaerobic digestion of solids but consists of setyling compartment where sedimentation is accomplished

Plain settlign tank

Sludge is removed

Rectangular clarifier

Solids which settle to the bottom of a clarifier are usually scraped to one end

Circular tanks

He theoretical flow pattern is radial

Energy dissipating inlets

Used to distribute flow within the feedwell and provide a means of increasing flocculation

Influent control gate

Stops the flow to the clarifier

influent channel or pipe

Transport WW to the clarifier

Influent well

Recieves the flow, reduce the flow velocities and dustributes flow

Influent well

It is a small circular compartment in the top center of the clarifier

Effluent weir

Ensures equal flow

Effluent trough or launder

Collect the settled waste water flowing over the weir and conveys it frlom the clarifier

Scum skimmer arm

Skims the surface of the WW

Scum Trough

Recieves the flowting material scraped

Scum pipe

Allows the collected scum to flow

drive unit

Cause ls the collector to rotate

Vertical drive cage

Transmits power

Sludge collector mechanism

Grags settled solids accrowss clarifier bottom to sump

Blades and scraper squeeges

Scrape sludge from bottom if clarifier to sump

Sump

Collects the sludge before withdrawal

Sludge withdrawal pipe

Remove sthe sludge from the clarifier

1-2

Primary tanks detention time:_____ hrs

Time

Must be long enough to for particles to settle

Volume

Must not exceed tank capacity

Discrete

Particle settle whithout interaction and occurs under low solids concentration

Flocculant

Particle is initially settle independently. The velocity of settling particle are usually increasing

Hindered or zone

The particles tend to remain in fixed position

Compression

Particle concetration is high. The settling velocity reduces

Zeta potential

Hold particles in suspension

Van der Waals

Natural attracting force that we want to enhance

Visual observation

Is the most impprtant process control

Solid loading rate

Flowrate/surface area

Solids loading

Amount of solids that can be removed daily by a clarifier

Detention Time

Period of time that a WW flow is retained in basin, tank or reservoir

Weir Overflow Rate

Amount of water leaving the settling tank

Detention Time

Volume of tank/flow rate

Weir flowrate

Flowrate/weir length

Dissolved air flotation

Injection of air

Dispersed air flotation

Air bubbles are formed

Vacuum air flotation

Saturation with air at atm pressure

Suspended growth bilogical treatment

Activated sludge process

Attached growth biological treatment

Trickling filter, rotating biological contactor

Combined process

High breed

homogeneous reaction

Reactants are distributed uniformely so that the reaction w/in the fluid is same

heterogeneous reaction

a reaction involving reactants in two different phases

batch

Flow is neither entering nor leaving the reactor. Liquid contents are mixed thoroughly

plug flow

Fluid particle pass thought the tank and are discharge in the same sequence in which they enter

Continuous flow stirred tank reactor

The reactants entering the reactor and the products flowing out from the reactor are considered as continuous

Arbitrary Flow Reactor

Partial mixing between plug flow and complete mix