Phosphorus Control

at GLWA’s High Purity

Oxygen WRRFMajid Khan, PhD., Director-Wastewater Operations

Wendy Barrott, Manager-Research & Innovation

Luther Blackburn, Manager-Wastewater Operations

Contents of Presentation

Overview of the GLWA WRRF

Phosphorus impact on environment

Phosphorus control

Current control at WRRF

Challenges

Search for optimization

Serves 35% of Michigan’s population

• ~3.5 million people in 77 communities

• over a 946 sq. miles of service area

Only one GLWA WRRF in system• Treatment Capacity: 1700 MGD primary

• 930 MGD secondary treatment

• 658 MGD average flow

Solids Disposal Requirements• Average day - 450 dry tons

• Peak day – 850 dry tons

GLWA WATER RESOURCE RECOVERY FACILITY

TO RIVER

TO RIVER

TO RIVER

During dry weather, all wastewater flows to the WRRF for complete treatment. As wet weather flows increase beyond the WRRF’s capacity, retention basins capture the 1st flush. If the capacity of these Combined Sewer Overflow (CSO) Retention Basins is exceeded, primary treated and disinfected CSO flow is sent to the river. During wet weather, when treatment or hydraulic capacity is exceeded, some untreated CSO flows are diverted to the river.

Annually, the WRRF treats enough wastewater to fill 375,000Olympic swimming pools and removes enough solids from the wastewater to fill all the box cars on a train over 30 miles long.

TO ROUGE RIVER

Treated CSO

9 Facilities

Untreated CSO

59 CSO Outfalls

1,698.5 MG

Yearly WRRF Totals

250,390 MG (treated)

165,000 Tons (solids removed)

COLLECTION SYSTEM

The GLWA collection system is a combined system. Sanitary Sewage (from homes, businesses and industries) and Storm runoff (from catch basins) flow through the same sewers.

WATER RESOURCE RECOVERY FACILITY OVERVIEW

FeCl3

SO2

FeCl3

SODIUM BI SULFITE

SODIUM HYPO CHLORITE

PRIMARY CLARIFIERS

AERATION TANKS

SECONDARY CLARIFIERSPUMP

STA 1

PUMP STA 2

BIOSOLIDS DRYER

FACILITY

1° SLUDGE PROCESSING

2° SLUDGE PROCESSING

DEWATERING PRESSES

DEWATERING CENTRIFUGES SLUDGE

INCINERATION

SLUDGE OFFLOADING

JUNCTION CHAMBERPROCESS

WATER

DRO

SLUDGE STORAGE

CHLORINE

Phosphorus

Impact on the Environment

Increasing population requires better phosphorus

management

“The phosphorus content of our land, following

generations of cultivation, has greatly diminished.

It needs replenishing. I cannot over-emphasize the

importance of phosphorus not only to agriculture

and soil conservation, but also the physical health

and economic security of the people of the nation.

Many of our soil deposits are deficient in

phosphorus, thus causing low yield and poor

quality of crops and pastures…."

- President Franklin D. Roosevelt, 1938

2012 Great Lakes Water Quality Agreement

Can we close the phosphorus cycle?

Critical for plant growth

Mined and shipped

Finite resource

Necessary for agricultural

Not evenly distributed globally

Geopolitical issue

A Valuable Resource

Excess phosphorus in waterways causes harmful algae blooms

– Runoff from agricultural fields

– Runoff from CAFOs

– Effluent WWTP.

– Failing septic systems

An Environmental Pollutant

Phosphorus can be captured and reused

Manage manure spreading

Increase capture in WWTP

Manage biosolids spreading

Recovery of phosphorus fertilizers from WWTP side streams and/or biosolids

Phosphorus Conservation

Sustaining Michigan’s Water Heritage

Vision Statement

Ecosystems Approach

A Sampling of the Goals

Protect and restore aquatic ecosystems

Ensure clean and safe waters

Invest in water infrastructure

Personal take away: Achieve a 40% reduction in the phosphorus loads to Western Lake Erie Basin by 2025

A Strategy for the Next Generation

October 2016

Phosphorus Control

At wastewater treatment facilities

Phosphorus Species

Objective: Convert Soluble P to Particulate P

Phosphorus Control in WWTP Effluents

Chemical precipitation is used to remove the inorganic forms of phosphate by the addition of a coagulant to wastewater

Calcium

Aluminum

Iron

Chemical phosphorus removal Biological phosphorus removal

Soluble and particulate phosphorus

Sewage treatment configuration applied to activated sludge systems for removal of phosphate

BPR is achievedBy growing PAOsIn anaerobic to aerobic conditions.

Typical Chemical Treatment Opportunities

Ferric Reaction with Phosphorus

The following illustrates a “stoichiometric reaction” of Fe+++ with P

FeCl3 + H3PO4 = FePO4 + 3HCl

1 mole of Fe reacts with 1 mole P

→5.2 mg ferric chloride per 1 mg P

→0.92 mg alkalinity per mg of ferric chloride

But the precipitation is not linear

Biological Phosphorus Removal

Uses Phosphorus Accumulating Organisms (PAOs) in an anaerobic – aerobic system

Under anaerobic conditions

Proliferation of PAOs occurs

PAOs assimilate fermentation products (acetate) into storage products (polyhydroxybutyrate – PHB) and concomitantly release stored polyphosphate as ortho phosphate

In the aerobic tank

PHB is oxidized and concomitantly phosphate is stored within the cell – luxury phosphorus uptake

Stoichiometrically about 10 grams of bCOD is needed for the removal of one gram of phosphate

Enhanced biological phosphorus removal (EBPR)

Anaerobic Aerobic

PO4

PO4

O2

Volatile Fatty Acids

Poly P Poly P

PHBPHB

From wastewater

Typical Biological Phosphorus Removal

Secondary

clarifier

Aerobic tankAnaerobic/

Fermentative tank

Primary

effluent

Return activated sludge (RAS)

Disinfection

In Real Life: Phosphorus Removal Factors

– Dose

– pH

– Phosphorus profile

– Mixing

– Contact time

– Aging

– Alkalinity

– Separation process

Chemical

‒ Anaerobic zone integrity

‒ Substrate availability

‒ Phosphorus vs. substrate limited

– Adequate Cations

‒ Aerobic zone

‒ Secondary phosphorus release

‒ Solids separation

Biological

Current Phosphorus Control

Phosphorus Permit Requirements

• Permit requirements for Total Phosphorus (TP)

• Secondary effluent is 0.7 mg/l with a seasonal limit of 0.6 mg/l from April – September

• Primary effluent - wet weather –1.5 mg/l

23

GLWA-WRRF Phosphorous Control Protocol

Maintain soluble phosphorous entering into aeration basins: 0.5 – 1.0 mg/l

Maintain D.O. in last stage of aeration basins: 2.0 - 4.0 mg/l

Maintain secondary clarifier’s hydraulic loading: 37 - 40 MGD

Maintain sludge blanket depth in secondary clarifiers: 2 – 3 ft

Maintain Sludge Retention Time (SRT) in gravity thickeners: <24 hrs

Keep sludge aerated in storage tanks before it is sent for dewatering

Dose Ferric Chloride: During dry weather @1.5 mg/l, wet weather 2.0 mg/l only if soluble phosphorous is above 1.0 mg/l entering into aeration basins

Outcomes: Phosphorus compliant, nutrient sufficient to prevent filamentous growth, prevent anaerobic activity in clarifiers for low effluent SS

Historical Phosphorus 1990-2017 YTD

0

0.2

0.4

0.6

0.8

1

1.2

mg/

l

Wastewater Treatment Plant Secondary Effluent Total Phosphorous Concentration

Pre-2015 NPDES Permit Limit 1.0 mg/l

January 2015 NPDES Permit Limit 0.7 mg/l

NPDES Permit Seasonal Limit 0.6 mg/l

Generally works well

However at Seasonal Low Flows

0

0.5

1

1.5

2

2.5

3

3.5

Sep-16 Oct-16 Nov-16 Dec-16 Jan-17 Feb-17 Mar-17 Apr-17 May-17 Jun-17 Jul-17 Aug-17 Sep-17

mg/

l

Wastewater Treatment Plant Total Phosphorus Concentration

Influent Effluent Permit monthly limit 0.7 mg/l Permit seasonal 6-month average limit 0.6 mg/l

Effluent TP bumps against seasonal limit

Continuing Challenge to Improve

Drivers for improvement

• Control chemical costs – always present!FerricPure Oxygen

• Multiple opinions that ferric was being overfed and multiple suggested changes to control scheme

• Desire to continue good phosphorus removal at low flows

• Desire to push for lower phosphorus effluent levels

However: Questions Needed to be Answered

Data suggested biological phosphorus removal was present

• Plant wasn’t designed for it and our control scheme did not account for it

• What conditions in bioreactors promoted Bio-P?

• Could Bio-P be maximized to reduce ferric feed?

Plant struggled to remove phosphorus during low flows < 500 MGD

• Why?

• Permit compliance becomes challenging in late summer

University-Utility Partnership

• Characterize the mechanisms of phosphorus removal, chemical and biological, with the goal optimizing performance and reducing costs for chemical additions

• Verify presence of bio-P organisms

• Characterize the profile of the phosphorus (total, colloidal, soluble) over time

• Measure kinetics in bioreactors

• Measure oxygen profile in all bio-reactors

• Update the process model to support further optimization efforts

Results to date

Preliminary

Grit

Landfill

Scum - Landfill

Primary Bio P

Rivers

To Sludge Thickening

To Sludge Thickening

Cl2 SO2

Landfill

Land application

Ash -Landfill

Conclusion: Plant definitely has Bio-P

Excellent Solids

Removal

Chemical- Ferric Chloride

Verified Plant is operating like this

WRRF Constituent Mass Loadings Generally

Independent of Influent Flow: Phosphorus

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

400 500 600 700 800 900 1000

Ph

osp

ho

rus

(lb

-P/d

ay)

Flow (mgd)

Relationship Between Plant Influent Flow and Phosphorus Loading

TP SP

Data 2013 - 2016

Flow, Mass Loading Relationship Leads to Correlation

of Flow and Concentration

0.0

0.5

1.0

1.5

2.0

2.5

400 600 800 1000 1200 1400 1600 1800

TSP

(m

g-P

/L)

Flow (mgd)

Influent TSP PEAS TSP

Jan – Mid-Sept, 2017

TSP Removal (mg-P/L) Varies with Flow Rate

Across Primaries

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

400 600 800 1000 1200 1400 1600 1800

Del

ta T

SP (

mg-

P/L

)

Flow (mgd)

Jan – Mid-Sept, 2017

Begin to loose SP removal @ ~ 550 MGD

And, Chemical Use Efficiency Varies with Flow

Rate Across Primary

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

400 600 800 1000 1200 1400 1600 1800

Del

ta T

SP/F

e (m

g-P

/mg-

Fe

Flow (mgd)

Jan – Mid-Sept, 2017

Decreasing Chemical efficiency

In general mixing is poor, but improves slightly between 650 and 500 MGD

Mixing Improvement Needed

TSP Removal by Biological Process Increases as Flow

Decreases Because More TSP Available

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

400 500 600 700 800 900 1000

TSP

(m

g-P

/L)

Flow (MGD)

SE PE

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

400 500 600 700 800 900 1000

Bio

logi

cal T

SP R

emo

val (

mg-

P/L

)Flow (MGD)

Bio-P Maximum Removal ~ 1.0

Data 2013 - 2016

New hypothesis for control

• Primary SP removal decreases with decreasing flow, and Bio-P increases –maxes capability out

• At much lower flow primary SP removal becomes very bad and Bio-P cannot remove more; phosphorus is higher in secondary effluent

• To address poor SP removal at very low flow – now adding ferric at the end of aeration decks (post aeration)

Installed FeCl3 Addition for Polishing

Plan to further lock in improvements

• Continue to refine control protocol for continued good phosphorus removal at low flow ---

• Add increased mixing to ferric addition points in PS 1 and PS2- need engineering

• Investigate two step ferric dosing as way to reduce ferric use after mixing upgrade

• Evaluate addition of ferric to side-streams

• Evaluate methods to increase Bio-P removal and reduce ferric addition

• Increase sensor and automated control for Ferric Chloride addition

QUESTIONS