The Activated Sludge Process

David Jenkins University of California at Berkeley

Operation and Control of Activated Sludge Processes using Microbiological Analysis

Ljubljana, Slovenia

June 5-7, 2019

Traditional purposes of secondary treatment

• Remove organics (BOD, TSS) to higher levels than primary treatment

• Remove bacteria to higher levels than primary treatment

• Remove materials of “sewage origin”

Additional purposes of secondary treatment

• Remove ammonia, nitrogen, phosphorus (nutrients)

• Remove individual organics

• Remove metals

• Prepare wastewater for tertiary treatment

• Recover valuable resources

Define activated sludge (AS) AS is a biological wastewater treatment

process carried out by an enrichment culture of microorganisms.

Enrichment cultures

Cultures in which population is determined by the substrate type and the growth conditions.

What does this mean to you ?

…The designer and the operator deserve what they get!!

Basic activated sludge process configurations

• Continuous flow without gravity clarifier

• Continuous flow with gravity clarifier

• Continuous flow with membrane (MBR)

• Sequencing batch reactor (SBR)

Continuous flow without gravity clarifier (aerated lagoon)

Aerated Lagoon Influent

Secondary Effluent

Continuous flow with gravity clarifier

Aeration Basin

Secondary Clarifier

Influent Secondary Effluent

Waste Activated Sludge,

WAS Return Activated

Sludge, RAS

Mixed Liquor

Continuous flow with membrane (MBR)

AB

Membrane

Inf Eff

(permeate)

WAS RAS

Sequencing batch reactor

Fill React (anoxic)

diffusers

React (aerobic)

Settle Idle

Inf

Draw

Made by enrichment

culture

Biological wastewater treatment processes as enrichment cultures

hv

CH4

Raw wastewater

To Berkeley

Minworth (1950) - trickling filters as far as the eye can see

“Filter” Flies...All Flies have Larval Stages

Anisopus fenestralis

Psycoda alternata

Lumbricillus spp…No Fly Stage…this is the Adult

Effect of “Periodicity of Dosing” on Populations and Biofilm

Biofilm density

Anisopus

Psycoda

Lumbricillus

1-5 min. 30-55 min. B

iofil

m d

ensi

ty,

mg/

m3

Org

anis

m d

ensi

ty, 1

03/m

3

1952 1953 1954 1955 Jan Jan Jan

1952 1953 1954 1955 Jan Jan Jan

Completely mixed activated sludge (CMAS)

AB SC

Inf Eff

WAS RAS

“Plug flow”

Important note

• True plug flow only exists when there are an infinite number of physical obstructions to flow through a basin. • Single long “passes” are not plug flow

NOT PLUG FLOW

AB SC Inf Eff

WAS RAS

(approaching) “PLUG FLOW”

AB SC Inf Eff

WAS RAS

Step-feed activated sludge (Is this “plug flow”?)

SC

Inf

Eff

WAS RAS

AB

Inf

Contact stabilization (Is this “plug flow”?)

Inf

SC Eff

WAS RAS

AB

High purity oxygen (HPO) activated sludge

(Is this “plug flow”?)

O2 in

Inf SC

Eff

AB

WAS RAS

O2 out

Oxidation ditch (Is this “plug flow”?)

AB SC Inf Eff

WAS RAS

Selector activated sludge (Is this “plug flow”?)

Inf AB SC

Eff

WAS RAS Selector

Nitrification/denitrification (N/DN)

Inf Anox SC

Eff

WAS RAS

Aer

IMLR

Enhanced biological phosphorus removal (EBPR)

SC Eff

WAS RAS

Anox Aer

IMLR

Anaer

Coupled processes, TF/AS, TF/SC

AB SC

Inf

Eff

WAS RAS

TF

Roughing Biofilter/AS

Biofilter/Solids Contact

Coupled processes, AS/TF (typically for nitrification)

AB SC

Inf

Eff

WAS RAS TF

Coupled processes, anaerobic digestion/activated sludge

• Used for strong, often nutrient deficient, organic wastewaters…Why?

Integrated fixed film/activated sludge systems

• Both activated sludge and fixed film biomass in aeration basin

• Fixed film support media can be either static (fixed) or suspended (moving)

• Two process types: 1.Moving bed bioreactor (MBBR) –

incorporates RAS 2.Integrated fixed film reactor (IFAS) – no

RAS

IFAS

Screen

MBBR

Screen

Activated sludge with chemical addition

• Phosphate precipitation with either iron (ferric) or aluminum salts. e.g. ferric chloride, alum.

• Organics removal by powdered activation carbon addition (e.g. PACT process)

• Nutrient (N, P) addition for N, P deficient wastewaters)

Simultaneous precipitation

AB SC Inf Eff

WAS RAS

Chemical Addition

Completely mixed activated sludge (CMAS)

AB SC

Inf Eff

WAS RAS

“Plug flow”

Important note

• True plug flow only exists when there are an infinite number of physical obstructions to flow through a basin. • Single long “passes” are not plug flow

NOT PLUG FLOW

AB SC Inf Eff

WAS RAS

(approaching) “PLUG FLOW”

AB SC Inf Eff

WAS RAS

Step-feed activated sludge (Is this “plug flow”?)

SC

Inf

Eff

WAS RAS

AB

Inf

Contact stabilization (Is this “plug flow”?)

Inf

SC Eff

WAS RAS

AB

High purity oxygen (HPO) activated sludge

(Is this “plug flow”?)

O2 in

Inf SC

Eff

AB

WAS RAS

O2 out

Oxidation ditch (Is this “plug flow”?)

AB SC Inf Eff

WAS RAS

Selector activated sludge (Is this “plug flow”?)

Inf AB SC

Eff

WAS RAS Selector

Nitrification/denitrification (N/DN)

Inf Anox SC

Eff

WAS RAS

Aer

IMLR

Enhanced biological phosphorus removal (EBPR)

SC Eff

WAS RAS

Anox Aer

IMLR

Anaer

Coupled processes, TF/AS, TF/SC

AB SC

Inf

Eff

WAS RAS

TF

Roughing Biofilter/AS

Biofilter/Solids Contact

Coupled processes, AS/TF (typically for nitrification)

AB SC

Inf

Eff

WAS RAS TF

Coupled processes, anaerobic digestion/activated sludge

• Used for strong, often nutrient deficient, organic wastewaters…Why?

Integrated fixed film/activated sludge systems

• Both activated sludge and fixed film biomass in aeration basin

• Fixed film support media can be either static (fixed) or suspended (moving)

• Two process types: 1.Moving bed bioreactor (MBBR) –

incorporates RAS 2.Integrated fixed film reactor (IFAS) – no

RAS

IFAS

Screen

MBBR

Screen

Activated sludge with chemical addition

• Phosphate precipitation with either iron (ferric) or aluminum salts. e.g. ferric chloride, alum.

• Organics removal by powdered activation carbon addition (e.g. PACT process)

• Nutrient (N, P) addition for N, P deficient wastewaters)

Simultaneous precipitation

AB SC Inf Eff

WAS RAS

Chemical Addition

Granular activated sludge