Activated Sludge Acclimation –Operator Guideline

Objective: Establish initial biomass and begin controlled aeration

Steps:

Start influent → fill oxidation ditch to ~1/3 depth

Start underwater propeller

Add seed (inoculum) sludge

Start aeration system

Blower: start immediately

Brush/disc: start at full water level

Continue filling to design operating level

Gradually increase aeration to maximum capacity

Secondary Sedimentation Tank:

Begin filling simultaneously

After 2 hours:

Start scraper

Start return sludge pump

Control Parameter:

Sludge Return Ratio: 50% – 100%

Objective: Promote floc formation and microbial growth

Actions:

Observe sludge condition:

Look for initial floc formation

Adjust influent:

Increase gradually once floc appears

Perform water replacement (~25%) to add nutrients

Repeat fill–replace cycle as needed

Trigger Point:

When sedimentation tank overflows → start downstream processes (e.g., disinfection)

Objective: Maintain conditions for microbial activity

DO Requirements:

Outlet DO ≥ 1.0 mg/L

Adjust aeration based on:

Low DO in influent/return sludge → increase aeration

Anoxic influent → rapid oxygen supply

High nutrient load → higher oxygen demand

Common Issue:

Foam formation (early stage)

Control by water spraying

Objective: Improve settling and biomass quality

Key Parameters:

SV₃₀ (30-min settling ratio):

Target: ~20%

Sludge Appearance:

Early: similar to influent

Later: larger flocs, dark brown color

Nutrient Control:

Maintain BOD:N:P ≈ 100:5:1

Add nutrients if deficient

Objective: Achieve stable system performance

Indicators of Completion:

Stable MLSS (sludge concentration)

Good settling performance

Effluent SS meets standard

Action:

Begin controlled excess sludge wasting

Objective: Establish baseline for normal operation

Record the following:

SV₃₀

DO levels

Sludge return ratio

Sludge wasting rate

Microscopic observations

Adjust Return Ratio Based On:

Low influent / poor growth → increase return

Sludge bulking → decrease return

Risks of Low Return Ratio:

Insufficient biomass → poor treatment

Sludge stays too long in clarifier:

Anaerobic conditions

Sludge floating & odor

High sludge blanket → high effluent SS

Nitrification → denitrification in clarifier:

Sludge rising / volume increase

System is considered fully acclimated when:

All parameters are within design range

Sludge is stable and well-settling

Effluent quality meets standards consistently