M.Sc. Urszula GabrielInstitute of Chemical Engineering and Environmental Protection Processes

WATER NETWORKS OPTIMISATION TO MINIMISE WATER USE AND

WASTEWATER GENERATION

Plan of presentation

1. Introduction2. Evolution of water network structures3. Principles of water minimisation4. Review of design procedures for water networks5. Scheme of elaborated algorithm6. Example of algorithm application7. Conclusions

IntroductionBenefits of water network optimisation:

• lower costs of fresh water intake and wastewater disposal

• lower environmental hazard• solving problems of fresh water shortage

One of the main strategies:• maximizing the reuse of water within the plant and seeking opportunities to use the outlet water from one operation to satisfy the water requirement of another or the same operation

Evolution of water network structures

P1DISPOSAL

P3

P2 T1 T2 T3

1) BASIC „INPUT – OUTPUT”STRUCTURE (CENTRAL FEEDING ANDTREATMENT SUBSYSTEM)

WATER

P1 DISPOSAL

P3

P2T1 T2 T3

2) WATER STREAMS ALLOCATION(DECENTRALISED FEEDING,CENTRAL TREATMENT)

WATER

P1

DISPOSALP3

P2

T1

T3

3) REUSE, REGENERATION + REUSE,REGENERATION + RECYCLING(DECENTRALISED BOTH FEEDING ANDTREATMENT SUBSYSTEMS)

WATERT2

P1SOLID

DISCHARGE

P3

P2T1

T3

4) ZERO WATER DISCHARGE(SYSTEM CLOSURE)

FRESHWATER

MAKEUP T2

Principles of water minimisation

• Contamination present in the water doesn’t have to be totally removed but should be reduced to the level enabling reuse of the stream

• water streams of different contamination level, which are supposed to be reused, shouldn’t be merged before sending them to treatment unit

• water slightly contaminated should be directly reused and the most contaminated water streams should be regenerated

Review of main procedures

Method Advantages Disadvantages

Graphical - visual representation - insight into design

- necessity of graph construction

Algorithmic - easy to perform without charts plotting

- rigorous solution

Genetic algorithm

- global optimum guarantee

- necessity of structure encoding

Mathematical programming

- possibility of including additional constraints

- rigorous solution - no global optimum guarantee

Scheme of algorithm

EXPERT SYSTEM

WATER STREAMS ALLOCATION

4) Selection of treatment option

1) direct

2) including mixing

FEEDING SUBSYSTEM TREATMENT SUBSYSTEM

3) including regeneration

Water streams allocation algorithm

The developed method is based on „nearest neighbour algorithm”: to satisfy a particular water demand, the source streams to be chosen are the nearest available neighbours to the demand in terms of contaminant concentration.

If the solution given above requires mixing with fresh water, the most contaminated stream is chosen for regeneration to replace the raw water.

start

ns , nd arrCs(ns, 3)arrCd(nd, 3)

indCs= ns

indCd= nd

CSCD

Y

indCs=indCs-1

N

YCs= CnFSFD

stop

Y

indCs= indCs-1

indCd= nd

N

FS<>0Y N

Nmix./regen.

results_tab

Expert system

The expert system enables selection of the optimal scheme for the treatment of contaminated water according to its characteristic (type of contaminant), required purification level and efficiency of treatment option.

Treatment schemes

• Sedimentation -> D• Chemical treatment (Al) – sand filter ->

C• Chemical treatment (Al) – trickling filter –

activated carbon – ultrafiltration -> B• Chemical treatment (Al) – trickling filter –

activated carbon – ultrafiltration – RO -> A

A, B, C, D – water quality

Efficiency matrix of treatment modulesMethode SS BOD CH3OH Heavy

MetalsBacteria

Sedimentation

55 30 15 - -

Biological treatment

71 88 62 15 -

chemical treatment

70 40 25 84 -

Treackling filter

68 28 16 - -

Activated carbon

60 63 50 60 95

UF 96 - - - 99RO - 10 32 - 99

Example of algorithm application

- Problem statement

Sources Demands

Number CH3OH(ppm)

SS(ppm)

FS

(Mg/h)Number CH3OH

(ppm)SS

(ppm)FD

(Mg/h)S1 0 100 20 P1 10 0 20S2 20 100 100 P2 10 50 100S3 15 800 40 P3 0 50 40S4 0 800 10 P4 0 400 10S5 0 0 170

170

P1

P2

P3

a) 20

10P4

40

T1100170 90

P1

P2

P3

b)20

50

20

90

P4

40T1

40

5010

40

P1

c)P3

P2

T2

P4

T120

20

- Schemes of obtained water networks

- Simulation results

Water network Fresh water intake

[Mg · h-1]

Spare of water [%]

a) “input – output” 170

-

b) direct streams allocation

90

47

c) allocation + regeneration

40

76

As an optimum treatment method the activated carbon is chosen.

methode SS BOD CH3OH Heavy Metals

Bacteria

Sedimentation

55 30 15 - -

Biological treatment

71 88 62 15 -

chemical treatment

70 40 25 84 -

Treackling filter

68 28 16 - -

Activated carbon

60 63 50 60 95

UF 96 - - - 99RO - 10 32 - 99

Conclusions

Applied algorithm:- Indicates water structure for water streams

allocation (giving 45% lower freshwater intake in above case) and for decentralised water regeneration (giving 75% lower freshwater intake)

- proposes an efficient water treatment method.