Benefits and Costs of Fire Protection from Reclaimed

WaterFrancis A. DiGiano, Christopher Weaver

Daniel A. OkunDept. of Environmental Sciences and

EngineeringUniversity of North Carolina

Paper Accepted for Publication in JAWWA

The late Prof. Emeritus, Dr. Daniel A. Okun

Advancing Dual Water System Design• Shift fire protection to reclaimed

water- Reduce pipe sizes- Reduce water residence times

• Explore alternative pipe materials- Stainless steel- Prevents leaks- Less water quality deterioration

• Illustrate concepts- Master Planned community - Technical & economic aspects

The Undoing of Water Treatment Technology Investments

• Microbial & chemical rxsat water-pipe wall

• Rxs in storage tanks• Corrosion• Pipe breaks-water

intrusion• Long residence times (2 d

typical; >20 d observed)• Aging infrastructure

Stainless Steel Pipe

• Less susceptible to corrosion– Forms chromium oxide

layer when in contact with water

• Lower potential for biofilmattachment

• Potential installation cost savings

• Easier, faster, more secure connections

Fire Demand Currently ControlsPipe Size

• State code determines fire flow requirements

• Fire demands outweigh indoor + outdoor home demands

• min. of 6-in. diam. req’d

Revised 2008

Water Treatment Plant

Wastewater Reclamation Plant

Lakes, Rivers & Wells

ResidentialCommercial &

Industrial

Fire Demand

Dual Distribution Systems for New Community

Briar Chapel,Chatham County, N.C.

Briar Chapel Phase 1

Phase 1WWTP

Development Overview

• 2,400 homes at build-out over 10 yrs– 300 homes per year in three phases

• Developer: Newland Communities Corp.• Site Engineering: J.R. McAdams, Inc. • Planned Water Infrastructure

– North Chatham County water supply– On-site WWTP with land disposal

WWTP Design

• 3 Phases (250,000 gpd capacity each)• Activated sludge with nutrient removal• Chlorination-dechlorination• Tertiary filtration (anthracite)• UV inactivation• 5 MG upset storage• 80 MG seasonal storage• Spray irrigation on 450 acres

One of Two, 40 MG Storage Ponds

Dual Water System Design:Assumptions for Water Usage

95Indoor + Outdoor34Outdoor (Irrigation)15Toilet Flushing Only61Total Indoor

Water Usage RateGallons per Capita per Day (gpcd)Category

Data Provided by Metcalf & Eddy (2005) and DeOreo et al. (1998)

Dual Water System DesignsOption A: Fire Flow, IrrigationOption B: Add Toilet Flushing

QNR = 90,000 gpdQA = 60,000 gpdQB = 44,000 gpd

Water from North Chatham County WTP

Spray Irrigation

A) 28% reduction in land

B) 53% reduction in land

Reclaimed Water Line

MBR

Typical Membrane Bioreactor (MBR) Effluent Quality Compared to Standards for Reclaimed Water in N.C.

NA3 to 10 Total Nitrogen-N (mg/L)NA< 0.1 Total Phosphorus (mg/L)14 < 10 Total Coliform (CFU/100 mL)10 < 1 Turbidity (NTU)*4 < 1 Ammonia-N (mg/L)5 < 2 TSS (mg/L)

10 < 2 BOD5 (mg/L)

NC MonthlyTreatment

PerformanceLevels

TypicalMBR

EffluentQuality

Parameter

5 MGD MBR Plant in Cauley Creek, Duluth, Ga.

EPANET2 :Potable Distribution Network

Option BRemoval of FireDemand

Existing Plan

Dual Water System Pipe Diameters

82.844,000B3.4

4.4

8.6

Potable WaterLength

Weighted Avg. Diam.

(in.)

860,000A

890,000Removal of FireDemand

none90,000None

Reclaimed Water

Uniform Pipe Diam. (in.)

Water Demand

(gpd)Reuse Option

Smaller Pipe Diameters Reduce Water Age

18.23.82.8B12.64.43.4A175.84.4

Removal of FireDemand

72+16.58.6None

Max.Water

Age,hrs

Avg.Water

Age,hrs

Pipe Diam.(in.)

ReuseOption

EPANET2: Water Reclamation System

WWTP

Elevated storage tank

123

45

WWTP12

3

45

200,000 gal

100 ft. Elevated Storage Tank

Locations of fire event simulations1,500 gpm for 2 hrs (residential)2,500 gpm for 2 hrs (commercial)

Change in Pressure During Simulated Commercial Fire Events in Reuse Network for Option B

0

20

40

60

80

100

120

0 20 40 60 80

Pressure (psi)

Fire 1 at FH-16Fire 2 at FH-78Fire 3 at FH-401Fire 4 at FH-104Fire 5 at FH-303Prior to Fire Event

No.

nod

es w

P<

stat

ed

Average and Maximum Water Age in Water Reclamation Distribution System

• Higher level of reuse results in lower water age• Implications for carrying disinfectant residual

14030B

16869A

Max Age (hrs)Avg Age (hrs)Reuse Option

Costs of Pipe Materials

21.7015.6721.5879.7912

10.208.3613.0038.728

7.804.809.7528.616

4.102.55--14.964

1.60*0.59*--6.062

$/ft$/ft$/ft$/ftDiameter (in.)

PVC C900 Reuse§

PVC C900DIPSS 5#

#SS5 = Schedule5 stainless steel*PVC C900 not available in 2-in diameter; S40 is substituted§PVC C900 Reuse for reclaimed water line only- higher cost due to production change to purple color

Cost Estimates (in thousands of dollars) for Existing Plan & Reuse Options A and B

1,074767 1,160 794 820482Total Costs*

718 718 718 718 718--Reclaimed Water§

356 49 443 76 102482Potable Water

All SS 5

All PVC*

All SS 5

All PVC

DI/PVC# DI

Reuse Option BReuse Option AExisting Plan

DistributionSystem

#Cement-lined DI for pipe diameters>6 in. and PVC for pipe diameters<6 in.§ Includes $400,000 for elevated 200,000-gal, reclaimed water storage tank*All pipes are less than 6-in diameter and thus, no DI/PVC option is provided

Costs for WWTP

0.20

0.25

Cap. (mgd)

2,203,000Existing design (BNR, chlorination-dechlorination, anthracite filters, UV)1

1,772,800MBR, UV, sludge handling2

CostTreatment Features

1Newland Communities, 20072Black & Veatch, 2007

Spray Irrigation Land SavingsAssume equalization by storage of wastewater generated

during non-landscape irrigation season (6 mos)

Toilet flushing (year around)With irrigation reuse (6 mos)Equalization of QLD,NR and QLD,I

With irrigation reuse (6 mos)Equalization of QLD,NR and QLD,I

No reuse

Condition

15(61-15)- 34 = 12[(61-15)+12]/2 = 29

Option BQTF

QLD,I

QLD,E

(61 – 34) = 27(61 + 27)/2 = 44

Option AQLD,I

QLD,E

61Existing PlanQLD,NR

gpcdDaily per capita flow rate

Estimated Land Savings and Storage Rqmts

• % land area saved in Option A ( 1- QLD,E /QLD,NR) ×100 = 28% (9 acres)

• % land area saved in Option B [1-QLD,E/ QLD,NR] ×100 = 53% (17 acres)

• Storage requirement (at build-out)(QLD,NR - QLD,E) ×180 days × 6,000 pop. = 18 MG

Savings in Spray Irrigation Land Area

18 (80 available)53Option B18 (80 available)28Option A

Storage Volume During Non Irrigation Season (MG)

at Build-out

Land AreaSavings (%)

ReuseOption

$372,000Original Design

$197,000Savings for Reuse Option B

$104,000Savings for Reuse Option A

Savings in Spray Irrigation Equipment Costs

Cost Offsets to Dual Water System Piping Costs (in $1,000)

Cost OffsetsAdded DS Costs

-53%(17 acres)

- $ 197 +$ 285 to 592 B (irrig. + toilet flushing)

- $ 104

Spray Irrig. Equipment

+ $ 314 to 678 -28%(9 acres)

A (irrig.)

Spray Irrig. Land Area

Reuse Option

Includes $400,000 for elevated storage tank

Impact of Dual Water System on Water Treatment Costs

• WTP is not currently necessary for Briar Chapel Project but if so

• Reduction of potable water demand during peak summer translate to capital cost savings of– 35 % in Option A – 51% in Option B

• Savings could be applied to install more advanced water trmt

Conclusions• Length-averaged pipe diam. decreased

– from 8.6 to 4.6 in. by removing fire demand – to 3.8 in. for irrigation reuse– to 2.8 in. for irrigation + toilet flushing reuse.

• Avg. water age decreased – From 17 to less than 5 hrs

• 50-100% higher pipe costs for dual water system– cost of 200,000 gal storage tank substantial – SS doubles cost but may be advantages

Conclusions (continued)

• Piping cost increase offset by:– Savings in spray irrigation equipment– 9 to 17 acres of land become available for

development (for pop. of 1,100 out of 6,000)• Equalization storage required but volume

available• Other potential benefits

– Savings in capital costs of WTP– Savings in water supply development

Recommendations

• Address safety of reclaimed water for fire fighting and toilet flushing in private residences

• Predict chlorine residuals in reclaimed water line• Use more detailed cost analysis

– EPA’s Asset Management model– Total Life Cycle Costing

• Quantify deferred costs of expanding water supplies and other infrastructure by implementation of water reuse

Acknowledgments

• Ed Timoney, Newland Communities Corp.• Chris Sandt, J.R. McAdams, Inc.• Weidong Zhang, Hazen & Sawyer• John Greene, OWASA• Steve Lamb, Nickel Institute• Sean Farley, U.S. Pipe and Foundry Co.• Brandon Smith, HD Supply Waterworks