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The Phosphorus Problem: Treatment Options and Process Monitoring Solutions YSI WATER RESOURCE RECOVERY WEBINAR

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What is Phosphorus?

• Essential to life – all living organisms require it • No substitutes • Major component of fertilizer • Creates nuisance conditions in excess • Limiting nutrient in fresh water • High quality reserves are depleting

It’s more than just the letter ‘P’

2

‘P’ Promotes Growth of Algae

• Human health • Environmental • Economic

Excessive algal growth has many undesirable effects

3

How Does ‘P’ Get Into Surface Water?

4

Diffuse sources Point sources

Regulating ‘P’ in Point Source Discharges

• Technology-based limits (TBL) • Typically 1.0 mg/L TP monthly average

• Total Maximum Daily Load (TMDL) • Mass-based limit – as treated water flow ↑ concentration must ↓

• Water quality based emission limits (WQBEL) • Numeric concentration limit to not cause adverse effects

3 types

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Status Of Numeric Nutrient Criteria (WQBEL)

Current

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Status Of Numeric Nutrient Criteria (WQBEL)

2016

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The Wisconsin Example

Adverse effects threshold depends on surface water type

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What Are You Going To Do?

Options for complying with ‘P’ limits

• Variance based on economic feasibility • Water quality trading

• Trade with your neighbor • Adaptive management

• Watershed based • Operational changes / add chemical

• Improve treatment process • Significant upgrades likely if WQBEL

is < 0.6 mg/L • Compliance schedule will extend 5+

years (not more than 9 years)

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Phosphorus Removal Treatment Options

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Terminology

• ‘P’ = phosphorus • TP = total phosphorus = particulate + dissolved phosphorus • Orthophosphate = dissolved phosphorus = PO4

3-

• (E)BPR = (Enhanced) Biological Phosphorus Removal • Oxic = aerobic = DO • Anoxic = DO; NO3 • Anaerobic = DO; NO3

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How is ‘P’ Removed?

2 ways

1. Biological 2. Chemical

Basic concept: ‘P’ dissolved ‘P’ Particulate

‘P’

How is ‘P’ Removed?

2 ways

1. Biological 2. Chemical

Basic concept: ‘P’ dissolved ‘P’ Particulate

‘P’

Effluent TP

Most WRRFs Are Not Designed to Remove ‘P’ Some ‘P’ removal occurs normally

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Soluble - P (Ortho-P)

Particulate P

Influent

Soluble - P

Particulate P

Secondary Effluent

TP

Biological Transformation

WAS

Bio or Chem P Removal

Most WRRFs Are Not Designed to Remove ‘P’ Some ‘P’ removal occurs normally

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Particulate P

Treated Effluent

Effluent TP

WAS

Soluble - P

Chemical Removal – How It Works

Addition of ferric or alum to water triggers a complex chain reaction

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Takacs, et al (2011), “Chemical P removal – from lab tests through model understanding to full-scale Demonstration“, Influents, Water Environment Association of Ontario.

‘baby’ ferric hydroxide floc

Fe:P ratio (moles)

Dis

solv

ed P

targ

et, m

g/L Model Prediction

Plant Data

Surface complexation + Co-Precipitation + Other competing reactions Increased sludge production & alkalinity consumption

Relationship Between Dosage and Ortho P

Surface complexation

Lower sludge production & alkalinity consumption

Chemical P Removal

Control strategies • Pre-precipitation

Fe/ Al

‘P’

Chemical P Removal

Control strategies • Simultaneous

precipitation Fe / Al Fe / Al

‘P’

Chemical P Removal

Control strategies

• Post precipitation

‘P’

Fe / Al

Chemical P Removal

Control strategies

• Multiple dosing points

Why EBPR works? Energy Released by PHB oxidation is 24-36 times energy required for PHB storage

EBPR (Enhanced Biological Phosphorus Removal) Mechanism

Aerobic Anaerobic

Waste Sludge Loaded with P

BOD (VFA) uptake & C (PHB) Storage P release

Feed condition Battery charging

Ortho- P

• PHB Oxidized

• Excess P Uptake

Starved condition Battery discharging

Anaerobic/Oxic (A/O) Process Configuration

RAS

Anaerobic Aerobic

Net P Removal

Ortho-P ≥3 x Infl. Ortho-P

BOD PHB Storage

BOD Oxidized

Concentrations in Bioreactor

Location in Bioreactor

Biological Phosphorus Removal

1. Excess phosphorus 2. Readily degradable carbon 3. Cyclic anaerobic/oxic conditions

3 requirements

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Phosphorus Removal Monitoring Solutions

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Orthophosphate Cabinet Analyzers

Chemical or biological removal

• Wet chemistry • 4 main components:

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• Electronics • Photometer & tubing • Sample transport • Reagent & solutions

Features of an Online Analyzer

• Low reagent consumption • Suitable for outdoors • Automatic calibration • Integrated permeate pump • Filter module

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Monitoring for Chemical P Removal

• Effluent monitoring

P 700 IQ


• Feedback control • Pre-precipitation

P 700 IQ


• Feedback control

• Simultaneous precipitation

P 700 IQ

P 700 IQ


• Feedback control

• Post precipitation

P 700 IQ


• Feed forward control

P 700 IQ

Watertown, WI Simultaneous precipitation

Chemical Cost Reduction

Analyzer installed in 2012

$0

$20,000

$40,000

$60,000

$80,000

$100,000

2011 2012 2013 2014 todate

Ferric chloride costs

Annual expense

• 3.0 mgd • Limit = 1.0 mg TP /L

(for now) • Paid for itself in 1 year

+ other benefits • Decreased sludge

production

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EBPR Monitoring

• COD/BOD • DO • Nitrate • TSS • ORP • Blanket depth

Everything is important!

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Biological ‘P’ Removal

Orthophosphate release and uptake • ‘P’ - release / anaerobic

• Adjust mixing • Activate swing

zone

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P 700 IQ


Orthophosphate release and uptake

• ‘P’ – uptake / oxic

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P 700 IQ

0.0

2.0

4.0

6.0

8.0

10.0

0.0% 20.0% 40.0% 60.0% 80.0% 100.0%

Aeration Volume (% of Total Aeration Vol.)

Ort

ho-P

, mg/

L

10-Sep-07

11-Sep-07

12-Sep-07

Courtesy City of Xenia

Dissolved Oxygen

‘P’ uptake is rapid when conditions are right

‘P’ Uptake in Oxic Zone

Too low DO concentration limits performance

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Anaerobic Aerobic

‘P’ Release

Infl. TP

Ortho-P

Location Along Bioreactor

‘P’ Uptake in Oxic Zone

Too low DO concentration limits performance

40

Anaerobic Aerobic

‘P’ Release

Infl. TP

Ortho-P

Location Along Bioreactor

~55%

~30%

EBPR Monitoring

ORP

Reproduced G Olsson, M Nielsen, Z Yuan, A Lynggaard-Jensen, J-P Steyer (2005) Science & Technical Report No. 15, Instrumentation, Control, and Automation in Wastewater Systems, with permission from the copyright holders, IWA Publishing

ORP Control of Intermittent Aeration

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• Too low – not enough time for PAO’s • Too high

• Secondary release • Competition • Settleability

The role of SRT

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‘P’ Removal and Sludge Settleability

Don’t let the ‘P’ get away!

10% P

6% P

8% P

4% P

2% P

Effluent TP = Dissolved P + Particulate P

Process Control Strategy for Achieving the Lowest Effluent TSS SRT control and sludge blanket control

45 Wahlberg, E. “What makes secondary clarifiers work”, WEFTEC 2013

Further reading

• Neethling, et al, Factors influencing the reliability of enhanced biological phosphorus removal, WERF report 01-CTS-3ASP, 2005.

• Jeyanayagam, S. and Husband, J., Chain Reaction: How chemical phosphorus removal really works, Water Environment & Technology, 2009.

• USEPA, Phosphorus Removal Design Manual (purple book), EPA/625/1-87/001, 1987.

• Narayanan, B. et al, Critical role of aerobic uptake in biological phosphorus removal, WEFTEC proceedings, 2006.

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