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EVALUATING ALTERNATIVES FOR DISPOSING OF

WATER PLANT SOLIDS INTO A WASTEWATER PLANT

Matthew Valade, P.E. July 25, 2014

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Presentation Outline

• Project Background • Why Dewater Croton Residuals Offsite? • Pilot Study at Hunts Point WWTP • Final Resolution • Conclusions

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New York Water Supply: Tunnels and Aqueducts

3

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Croton WTP - A Brief History

• 1842 – Croton begins supplying water to NYC • 1997 – Consent Order required Croton filtration • 1999 – Mosholu Golf Course (Bronx) site selected • 2001 – Design stopped due to legal clarification of

use of public park land – this design included residuals dewatering facilities on site

• 2002-04 – Several sites evaluated – MGC again selected but smaller footprint required Design does not include on site residuals dewatering

• 2005 – Construction work for Croton WTP begins • 2014 – Startup is underway

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Coagulant

Backwash Filtration

Solids

Dissolved Air

Flotation Mixer 1 Flocculation

Fluoride

UV

Sulfuric Acid

Mixer 2

Coagulant Polymer

Sodium hypochlorite (intermittent)

Filter Aid Polymer

Sodium hypochlorite

Sodium hydroxide

Corrosion inhibitor

Mixer 3

Sodium hypochlorite

pH Balance Waste Washwater

Treatment Process

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Woodlawn Cemetery

Plant Site

Jerome Avenue

Mosholu Golf Course

Woodlawn Train Station

Jerome Park Reservoir

Photograph taken in 2004 before construction

Overview of the Facility Location

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Croton Water Treatment Plant

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Final Excavation - July 6, 2007

N

Raw Water Tunnel

Treated Water Tunnel

555-ft

683-ft

9.2 Acres

90-ft

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Construction – as of May 2010

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Construction – as of May 2014

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Why Dispose Croton Residuals Offsite?

• Dewatering residuals on-site: Limited space on site No truck access to Operating Level below

grade • Concerns with truck exhaust • Space Constraints

Reduce truck traffic to and from the WTP Considerably higher Cap/Op costs

• Issues with dewatering Croton residuals on-site led DEP to consider dewatering residuals offsite at Hunts Point WWTP

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• Discharging Directly to Sewer was Banned

• Closest WWTP to site • Existing Dewatering Facility • Sufficient space for any

required facilities • Sufficient Dewatering capacity

13 dewatering centrifuges Space for 3 new centrifuges

• 7.5 mile Force Main Required

Why Hunts Point?

Hunts Point WWTP

Croton WTP

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Croton WTP Flow and Residuals

Solids Loads Croton WTP

Flow, MGD

Total Suspended

Solids, lb/day

Average Design Conditions

144 17,300

Maximum Design Conditions

290 44,500

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Characteristics of Croton WTP Residuals

WTP Residuals Dissolved Solids Parameter Concentration

TSS 30 mg/l

Aluminum 1,700 mg/l

Iron 150 mg/l

Manganese 55 mg/l

Heavy Metals Trace Amount

Toxic Or hazardous None

pH ~ 6.2 units

Aluminum Hydroxide 50%

Organic 41%

Other inert (metals, non-organic solids) 9%

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Hunts Point WWTP Background

• Biosolids loads Hunts Point WWTP: 100,000 lb/day Imported Sludge: 214,000 lb/day

• Dewaters thickened, digested biosolids Hunts Point and imported biosolids from

other NYCDEP WWTPs separately • Pelletize dewatered biosolids prior to off

site disposal

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Croton Residuals Dewatering Alternatives at Hunts Point

• Separate Dewatering Dewater water treatment residuals and wastewater

biosolids sludge separately

• Blend Croton residuals with Hunts Point sludge Introduce at primary/secondary settling and

dewater water treatment residuals and wastewater biosolids sludge together

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Separate Dewatering Advantages Disadvantages

• Uses specific conditioning for WTP residuals

• No effect on WWTP biosolids dewatering

• Requires new polymer system and dedicated centrifuges

• May impact cake disposal options

• Pilot testing needed to confirm impacts

• Net decrease likely in % solids in cake

• Requires dedicated storage for alum sludge

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Blended Dewatering Advantages Disadvantages

• Use existing polymer to condition the two sludges

• Use existing centrifuges • Possible to blend the

Croton WTP sludge with Hunts Point sludge prior to dewatering

• Possibility of lower dewatered cake percent being produced with blended sludge

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Effects of Aluminum Hydroxide on Wastewater

• Limited Research/Literature

• Therefore, it was decided to pilot test to study the alternatives

• Full scale using existing Hunts Point WWTP dewatering centrifuges

• BioWin Computer Modeling used to estimate theoretical effects of introducing WTP residuals to Hunts Point WWTP process

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Hunts Point WW Process Concerns

• BNR Consent Order requiring Total Nitrogen (TN) to under 44,200 lb/d at 2017 influent flows and loads

• Biowin Analysis included three Croton Residual addition points Primary Settling Tanks Final Settling Tanks Gravity Thickeners

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Biowin Model Predictions (1 of 2)

• Primary Settling (PS) Tanks Increased sludge settling Increased solids can potentially overload Gravity

Thickeners & Digesters, and decrease sludge quality from Gravity Thickeners

Increases CBOD removal (source of carbon for denitrification process in BNR treatment)

78% increase in PS load, reduces HRT and VSS destruction in digesters, increased methanol demand

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Biowin Model Predictions (2 of 2)

• Final Settling Tanks (FSTs) Addition prior to FST’s increased solids loading to

clarifiers, lower effective SRT (30% drop) 38% higher solids to digesters, reduced HRT and

VSS destruction • Gravity Thickeners

Potentially higher removal of solids (+37%) No significant drop in PE VSS/TSS ratio, no SRT

effects, no increased methanol demand Solids Loading Rates matched WEF MOP Best Alternative of 3 Locations

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Previous Bench Scale Tests

• Results Separate Dewatering Results:

• WWTP ~ 22 to 27%

• WTP ~ 18 to 20%

Combined Dewatering Results • Indicated that dewatered solids from combining

sludges ranged between 8 – 22%

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Pilot Study Scope

• Dewatered alum residuals from Warner WTP at Hunts Point WWTP Warner WTP: similar raw water quality & treatment

process to Croton WTP 6,000 gallon truck for residuals 2.5-3% solids

• Study polymer types and dosage rates that produce high solids cake Polymer for Alum Sludge: Flopam NE1619 Polymer for Wastewater Sludge: Flopam NE1516

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WTP Residuals vs. WWTP Biosolids

• Critical difference that dictates sludge conditioning is Difference in the cationic demand between alum

residuals and anaerobically digested biosolids WTP (alum) residuals has a low cationic charge Anaerobically digested biosolids has a high cationic

charge Therefore need to study both single (WTP residuals

alone) and dual conditioning (combined WTP residuals with WWTP biosolids)

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Single & Dual Charge Conditioning

• Single Conditioning 80% Charge Existing WWTP Polymer, a

High Charge Cationic Polymer

• Dual Conditioning 10% Cationic Charge Polymer 80% Cationic Charge Existing WWTP

Polymer

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Preliminary Jar Testing

• Results: Existing Polymer was effective for dewatering the blended sludge

• Recommended using both types of charged polymers to maximize cake solids

• Pilot Test: 10% charge polymer into alum feed

80% charge Polymer into WWTP biosolid feed.

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Figure 1: Pilot Test Design

Existing Polymer

Polymer Feed Pump

Existing Tank

Existing Metering

Pump

Polymer Tote

Polymer Make Down

System

Alum Sludge Aquarium WTP

Alum Feed Pump

M

Imported Sludge

Hunt’s Point

Sludge Feed

Centrifuge

Drain

Dewatering

Centrate

Dewatered Cake

Figure 1: Pilot Test Design

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Figure 2: Pilot Arrangement

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Figure 3: Polymer System

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Single Conditioning Results (Not Optimized)

• As alum residuals:biosolids INCREASED Cake solids DECREASED (polymer constant).

• The lowest cake solids was 22.6% at 4:1 alum to wastewater sludge ratio

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Dual Conditioning Results

Results at 16-38% alum to wastewater sludge ratios 6:1 blended sludge ratio produced a high cake solids

(29%) with 60 lb/DT (neat) Existing Polymer and 45 lb/DT (neat) 10% charge polymer.

4:1 blended sludge ratio, the same cake solids were produced but required 20-30% more polymer

2.5:1 blended sludge ratio, increase in the polymer dosage did not increase the cake solids.

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Figure 4: Recommended Operations

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Conclusions

• Dual conditioning produced better cake Maximum Flexibility

Allows the flexibility to treat the solids mixture with a proper combination of low and high charge polymers.

• And…..confirmation of existing Hunts Point dewatering equipment will work on Croton WTP residuals, BUT…

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Direct Sewer Discharge Part Deux

• NYC DEP Operating Bureau allows Croton Sludge to be pumped to sewer

• Existing infrastructure has been utilized • Sludge monitoring via industrial

discharge permit: routine sampling req'd • Monitoring of BNR process at WI WWTP

shows no impact to treatment • Pumping strategy during Wet Weather

to mitigate CSO events

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Overview of the Facility Location

Ward’s Island WWTP

Hunt’s Point WWTP

Croton WTP

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Questions?

Thank you!

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Alum Sludge Addition Impacts

• On Gravity Thickening Need higher GT underflow to digesters Solids Loading Rate does not exceed WEF

MOP values (7.1 to 9.5 lb/ft^2/d)

• On Digestion 5,000-10,000 lb/day additional must be landfilled

due to: • Under 15-day HRT requirement reducing %VSS destruction • Hunt’s Point won’t meet PSRP compliance for Class B sludge with

current online infrastructure May reduce digester performance with

decrease in total gas production, Methane production, COD reduction, and organic N decomposition

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Alum Sludge Addition Impacts

• On Dewatering Increase digested sludge load 60-70% Evaluation whether centrifuge capacity exists for

additional sludge load necessary Combined sludge produces cake solids of 24%

• On Biological Nitrogen Removal (BNR) Potential decrease in ammonia production

• Beneficial reduction of influent N load to secondary treatment

• May inhibit nitrification which would require supplemental Sodium Hydroxide