Assessment of the effects of greywater reuse on gross solids

movement in sewer system

Roni Penn 1 Eran Friedler 1 , Manfred Schütze 2

1

1. Environmental, Water & Agricultural Eng.Faculty of Civil & Environmental Eng.

Technion – Israel Institute of TechnologyHaifa, Israel

2. ifak- Institut fuer Automation und KommunikationMagdeburg, Germany

IntroductionShortage of fresh water is a serious worldwide

problem

Domestic consumption

70%

Greywater (GW)60-70%

DarkKitchen sink Dishwasher

Washing machine?

Urban consumption (Israel) Over 700*106 m3/year- The sector consuming the largest amount of

freshwater

LightBath

Shower Washbasi

n

2

Blackwater30-40%

Toilets

Potential reduction of GWRToilet ~ 30%Toilet +garden irrigation ~ 40%

IntroductionGWR research focused, on a single-house scale, on recycling systems and possible sanitary and environmental affects.

overlooked

Questions to be asked:

• What could be the effects of GWR on urban WW collection systems and on WWTPs?

• Are these effects positive or negative?

• How will they change with increasing penetration of on-site GWR? 3

Effects on domestic WW quantity and quality, on urban wastewater collection systems and on urban wastewater treatment plants (WWTP)

GW can contain non negligible concentrations of organic and microbial contamination. Treatment of GW before reuse

• Prevent sanitary and environmental hazards• Prevent aesthetic disturbance

Within the urban environment, GW "demand" < GW "production" Treat and reuse the less polluted GW streams (SH, BT and WB) The more polluted discharge to the urban sewer system

4

Introduction

“GWR” home “Conventional” home

GW SourceGW SourceGW Source

GW SourceToilet

flushingGW Source

Selected for reuse Not reused

On-site

treatment

SludgeScumetc

Blackwater

Garden irrig.

Overflow

Sewer

WWTP

GW SourceGW SourceGW Source

GW SourceGW SourceGW Source

GW SourceToilet

flushingGW Source

Selected for reuse Not reused

On-site

treatment

SludgeScumetc

Blackwater

Garden irrig.

Overflow

Sewer

WWTP

GW SourceGW SourceGW Source Toiletflushing

Raw GW

Not reused

Sewer

WWTP

Blackwater

GW SourceGW Source

GW SourceGW SourceGW Source Toiletflushing

Raw GW

Not reused

Sewer

WWTP

Blackwater

GW SourceGW Source

A B

5

Types of homes contributing WW

6

Effect of GWR- quantity and quality effectsQuantity effectsWastewater flows released to the sewer reducedwastewater flows in the sewer network reducedwastewater flows to the WWTP reduced

Quality effectsTreatment changes the quality of the wastewater discharged to the urban sewerReduced flows (less dilution?)

7

7

Flat densely populated coastal area neighborhoods sewer pipes ~

6 km Separate sewer

15,000 residents

SIMBA

6

The chosen neighborhood

Scenarios examined

 

Currentsituation

Extreme situation

To be expected

1 2 3 4 5

GWR type& penetration proportion

(1) NR 100% 0% 0% 70% 70%

(2)RWC 0% 100% 0% 30% 15%

(3)RWC+IR 0% 0% 100% 0% 15%

Separate sewer systems, Sludge released at 8:00, Toilet flush volume: (1) 9L full, 6L half

(2) 6L full, 3L half

Effects of GWR on:

sewer blockages?

• Flow characteristics• Gross solids movement

Diurnal patternLINK 36 LINK 97 LINK 71 LINK 154

FRO

UD

E [-]

FLO

W

[m3 /m

in]

VELO

CIT

Y [m

/s]

PRO

POR

TIO

NA

L D

EPTH

(d/D

) [-]

00.5

1

54.5

43.5

32.5

21.5

10.5

0

0.08

0.07

0.06

0.05

0.04

0.03

0.02

0.01

0

54.5

43.5

32.5

21.5

10.5

0

54.5

43.5

32.5

21.5

10.5

0

1.4

1.2

1

0.8

0.6

0.4

0.2

0

1.4

1.2

1

0.8

0.6

0.4

0.2

0

1.4

1.2

1

0.8

0.6

0.4

0.2

0

1.4

1.2

1

0.8

0.6

0.4

0.2

00.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

1.4

1.2

1

0.8

0.6

0.4

0.2

0

1.4

1.2

1

0.8

0.6

0.4

0.2

0

1.4

1.2

1

0.8

0.6

0.4

0.2

0

1.4

1.2

1

0.8

0.6

0.4

0.2

0 0 4 8 12 16 20 24T [h]

0 4 8 12 16 20 24T [h]

0 4 8 12 16 20 24T [h]

0 4 8 12 16 20 24T [h] 9

Gross solid transportGWR domestic WW - reduces flows with in the sewer system – reduced higher rate of blockages?

Upstream: based on model by Walslki et al., 2011. Downstream: based on model based on tractive force

(TF) (Walski et al., 2004.)

Upstream DownstreamFlow Intermittent More steady

Solids Larger,un-submerged

Smaller, submerged

different approaches for each part of the sewer:

10

11

SG specific gravity S slope of pipe Q flow (L/s) V volume of pulse (L)a 0.45: full - partial movement a 18: full - partial movement

0.25: no movement - partial movement 10: no movement - partial movement

𝑸= 𝒂𝑺𝑮/𝑺𝟎.𝟐

Pulse to move solid with attenuation, short duration

 

Flow to move solid no attenuation, long duration

 

𝑽=𝒂𝑺𝑮 /𝑺𝟎 .𝟐

Gross solid transport – upstream (Walslki et al., 2011)

36

48

57

97

107

71

85

154

85

Outlet pipe

𝟑 .𝟓×𝟑×

Gross solid transport - upstream

0.020.220.76

0.280.390.33

00.060.94

0.110.380.51

00.140.86

0.180.360.46

0.270.380.35

0.020.210.77

0.750.030.21

0.820.050.13

0.660.10.24

0.780.040.17

0.850.050.1

0.780.030.19

Critical Tractive Force TF (Walski et al., 2004)

Average boundary tractive stress

𝝉=𝝆 𝒈𝑹( 𝑺𝟏𝟎𝟎 ) 𝝉𝒄=𝒌𝒅𝟎 .𝟐𝟕𝟕

K 0.867 (N/m2) d diameter (mm) for a discrete design sand particle

of 2.7 specific gravity

• For: discrete grit particle• Transported often enough

tractive stress (Pa), density of liquid (kg/m3) R hydraulic radius (m)

13

Gross solid transport - downstream

d=6mm =1000 𝝆

Modeling gross solid transportGenerator

module

SIMBA

Velocity

Conclusions

Gross solid transport:

Upstream linksSmall amounts of WW discharged

no GWR 67% of the day full / partial

movement

GWR 76% of the day no movement

Middle linksadditional houses

discharge WW

Higher proportions of the day for full

movement

Downstream links

full movement in all scenarios

GWR: toilet flushing: saves ~25% of the water consumption

GWR: toilet flushing & irrigation: saves ~40%

Higher GWR:

• d/D decrease connect additional homes to existing sewers

construct smaller systems

Highest reduction – peak usage hours

•Instantaneous: Q, V, (d/D) decrease

THANKS FOR LISTENING!

16

QUESTIONS?