Envo Material Balance

What defines a Conserved System

• No reactions occur (nonreactive)

• Rxn = 0

What defines a Steady State system?

• Accum = d(CV)/dt = 0

What are the characteristics of a CMBR (Completely Mixed Batch Reactor)?

• No flow in/out

• Complete, instantaneous mixing

• Inherently non-steady state: put something in, let it react, then see how the system changes over time

What are the characteristics of a CSTR (Completely Stirred Tank Reactor / CMFR)?

• Flow in/out

• Complete, instantaneous mixing

What are the characteristics of a PFR (Plug Flow Reactor)?

• No horizontal mixing

• Thin volume “plugs” are transported through the control volume

• Most efficient reactors

Zero-Order Reaction

Reaction rate is constant and does NOT depend on concentration

Zero-Order Graph Identification

A plot of CCC vs ttt is a straight line with negative slope.

Zero-Order Half-Life Behavior

Half-life decreases as concentration decreases.

First-Order Reaction

Reaction rate is proportional to concentration CCC.

First-Order Units of k

k has units of 1/time1/\text{time}1/time.

First-Order Graph Identification

A plot of ln⁡(C)\ln(C)ln(C) vs ttt is a straight line

Second-Order Reaction

Reaction rate is proportional to C²

Second-Order Units of k

k has units of L/(mg·time).

Second-Order Graph Identification

A plot of 1/C1/C1/C vs ttt is a straight line

How to Identify Reaction Order from Words

Rate proportional to concentration” → first order; “rate independent of concentration” → zero order; “rate proportional to concentration squared” → second order

Q

Influent flow

So

Influent substrate concentration

S

Effluent Substrate Conc

X

Mlss conc in aieration tank

Xr

Ras Conc

F/M

food to mico ratio

theta C

solid retention time

mu max

max specifc growth

ks

½ saturation constant

kd

endogenous decay rate

Qw

waste sludge flow rate

Preliminary Treatment

Removes physical debris; protects pumps downstream; example: bar screens, grit chamber.

Coagulation

Destabilizes small particles using metal salts; targets colloids; example: alum addition + rapid mixer.

Flocculation

Gently mixes water to grow larger flocs; targets small suspended solids; example: paddle flocculator.

Sedimentation (Clarification)

Settles large flocs via gravity; removes settleable solids; example: rectangular clarifier.

Filtration

Removes fine particles that remain after settling; reduces turbidity and pathogens; example: rapid sand filter.

Disinfection

Inactivates pathogens; targets bacteria, viruses, protozoa; example: chlorine contact basin or UV system.

Solids Handling

Dewaters and disposes of sludge; targets sludge from settling and filtration; example: belt press or centrifuge.

Primary Treatment

Removes settleable solids and floatable materials by gravity; reduces suspended solids and some BOD; example: primary clarifier / sedimentation tank.

Secondary Treatment

Biologically degrades dissolved and colloidal organic matter; removes BOD and some nutrients; example: activated sludge, trickling filter.

Tertiary Treatment

Polishes water after secondary treatment; removes nutrients, fine solids, pathogens, and dissolved contaminants; example: filtration, nitrification/denitrification, carbon adsorption, membranes.

Disinfection

Inactivates pathogens before distribution or discharge; example: chlorine, UV, ozone.

Solids Handling

Thickens, stabilizes, and dewaters sludge from all treatment stages; example: belt press, centrifuge.