Activated Sludge -Three Things You Need To Know To Improve Process Efficiency YSI WATER RESOURCE RECOVERY WEBINAR

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Activated Sludge Process Control

Influent

Return Activated Sludge (RAS)

Mixed liquor Effluent

Final settling tank

AIR

Aeration tank

Waste Activated Sludge (WAS)

Internal Mixed Liquor Recycle (IMLR)

Great Inventions of the 20th Century

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Ardern and Lockett Published 1914

The culmination of years of research and discovery

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Aeration

Growth of humus

Activation

Activated Sludge

(micro-) biological

Aerated

Suspended growth

Hydraulic retention time Solids retention time Requires specially trained personnel

What all configurations have in common

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Aeration

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Aeration and the (Bio-Chemical) Environment

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0

+

Nitrification

Denitrification

Fermentation

P release

ORP, mV

Oxic Anaerobic Anoxic

-

BOD removal

P uptake

Effect of DO Concentration on Biological Treatment Basis for maintaining DO at or below 2 mg/L setpoint

D.O. Reaction

0.75

D.O. : Reaction

Control of nitrification also ensures BOD removal

cBOD removal

Nitrification

0.5 1.0 2.0 1.5 2.5 3.0 O2 (mg/l)

1/2 vmax

vmax

Rea

ctio

n ra

te

0.3

Dissolved Oxygen and Performance

Balancing nitrification - denitrification

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% o

f max

pro

cess

rate

Dissolved oxygen

Source: Gustaf Olsson, Lund University, Sweden

Dissolved Oxygen and Energy

10 Source: Blum, D., High Efficiency Aeration, Clarifier, Illinois WEA, Summer 2013

D.O.

1.5 x

> 4 x

Optical DO Measurement

ASTM D888-09 Test Method C

Very stable calibration Less maintenance No sulfide interference Accuracy: +/- 1% No stirring No warm-up

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Continuous Spot sampling

ORP

Ion selective electrode (ISE)

Continuous

Spot sampling

Reference electrode

Membrane

Junction

ISE (mV)

Sludge Wasting

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Sludge Wasting Controls How Much Biomass Approaches to sludge wasting Settleability

Constant MLSS Centrifuge/spin F/M Solids Retention Time

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Sludge Age, MCRT, SRT, CRT

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Qe, Xe

V, MLSS

Qr, Xr Qw, Xr

Qi, Xi

Biomass in the system Biomass entering / leaving the system

Target SRT

COD removal COD removal +nitrification

COD removal +nitrification +denitrification

COD removal +nitrfication +

denitrification + Premoval

SRT

What are treatment requirements?

16 function

0.0

4.0

8.0

12.0

16.0

5 10 15 20 25

Nit

rifi

cati

on

SR

T, d

Nitrification Design

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Design SRT; SF=1.5

Operating Range

Min. SRT

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SRT and Energy

SRT and Performance

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Efflu

ent T

SS

1 year Source: Wahlberg, E. What makes secondary clarifiers work, WEFTEC 2013

Solids Measurement - Optical

Reflectance or absorbance

Fast

Simple Factory calibrated Low maintenance

Continuous

Spot sampling

Sludge Recirculation (RAS and IMLR)

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Constant flow set RAS flow rate manually (open loop) Constant percentage set RAS flow proportional to ww flow (feed forward)

Sludge Recirculation for Control of Biomass Distribution RAS is critical to clarifier performance

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RAS Flow Rate Control

Sludge blanket depth approach

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WW flow

RAS flow

MLSS

Thickening Failure

Q + Qras

Qras

Q MLSS

Flux

RAS Flow Rate Control

Sludge blanket depth approach

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WW flow

RAS flow

MLSS

MLSS

Thickening Failure

Q + Qras

Qras

Q MLSS

Flux

RAS Flow Rate Control

Sludge blanket depth approach

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WW flow

RAS flow

MLSS

MLSS

Thickening Failure

Solids washout

Q + Qras

Qras

Q MLSS

Flux

RAS Flow Rate Control

Sludge blanket depth approach

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WW flow

RAS flow

MLSS

Thickening Failure

Q + Qras

Qras

Q MLSS

Flux

RAS Flow Rate Control

Sludge blanket depth approach

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WW flow

RAS flow

Increase RAS

MLSS

MLSS

Thickening Failure

Q + Qras

Qras

Q MLSS

Flux

Sludge Blanket Depth Measurement

28 Visual Acoustic (sludge level detector)

Sludge Recirculation for Control of Denitrification Nitrate is the critical measurement 1) Meet nitrogen limits

2) Maximize use of wastewater COD

3) Minimize external carbon

29 Source: Ingildsen, P, Wendelboe, H., Improved nutrient removal results using in situ continuous on-line sensors with reduced response time, WEFTEC 2003

ISE Ammonium and Nitrate

Potentiometric (like pH/ORP)

Measuring electrodes: NH4+, NO3-,

Compensation electrodes: K+, Cl-

Reagentless Stable calibration Replaceable electrodes Large measuring range

Continuous

ISE Ammonium and Nitrate

Potentiometric (like pH/ORP)

Measuring electrodes: NH4+, NO3-,

Compensation electrodes: K+, Cl-

Reagentless Stable calibration Replaceable electrodes Large measuring range

Continuous

Spot sampling

Optical Nitrate

Spectral or single-wavelength

No electrodes Factory calibrated (spectral)

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Summary and Future Webinar Topics

Process control it is easier than you think

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Aeration to control the environment

Sludge wasting to control the total biomass

Sludge recirculation to control biomass distribution

Activated Sludge -Three Things You Need To Know To Improve Process EfficiencyActivated Sludge Process ControlGreat Inventions of the 20th CenturyArdern and Lockett Published 1914Activated SludgeAerationAeration and the (Bio-Chemical) EnvironmentEffect of DO Concentration on Biological TreatmentDissolved Oxygen and PerformanceDissolved Oxygen and EnergyOptical DO MeasurementORPSludge WastingSludge Wasting Controls How Much BiomassSludge Age, MCRT, SRT, CRTTarget SRTNitrification DesignSRT and EnergySRT and PerformanceSolids Measurement - OpticalSludge Recirculation (RAS and IMLR)Sludge Recirculation for Control of Biomass DistributionRAS Flow Rate ControlRAS Flow Rate ControlRAS Flow Rate ControlRAS Flow Rate ControlRAS Flow Rate ControlSludge Blanket Depth MeasurementSludge Recirculation for Control of DenitrificationISE Ammonium and NitrateISE Ammonium and NitrateOptical NitrateSummary and Future Webinar Topics