Needs and gaps of internal process modelling of

Tidal Flow Engineered Wetlands.

Beautiful wetlands: Hall of Green Wilderness, Yuan Yao 1770

Lordwin Jeyakumar

PhD Student

Centre for Water Resources Research

Civil Engineering department

Newstead Building

UCD Belfield, D4

Supervisor

Dr.Yaqian Zhao

First ICAERE

Constructed Wetlands

“… a designed and man made complex of saturated substrate,

emergent and submergent vegetation, animal life and water

that simulates natural wetlands for human use and benefits.”

(Hammer,1989)

Free Water Surface

Horizontal Sub-Surface FlowVertical Flow

Reed beds

Tidal Flow

CW site

144

Constructed wetlands emulate nature by……

Mechanical filtering

Chemical transforming and

Biologically consuming

…….potential pollutants in the waste water streams

China’s Yangtze River 1998 Flood

Economic losses were estimated in 32,000 million dollars and 230

million persons were affected.

Causes

The increase of settlements construction on flood prone areas.

The increase destruction of wetlands near lakes and rivers to

accommodate more farming.

The increase of river basin deforestation

Solutions

Wetland Restoration

Stopping deforestation

Functions of Wetlands

Treatment of livestock and municipal wastewater.

Treatment of highway runoff and urban storm waste water.

Hydrological and hydraulic modifications.

Water Quality improvement.

Shoreline stabilization and erosion control.

Life supporting wildlife and plant habitats.

Open wilderness and aesthetics.

Benefits of Constructed Wetlands

Cost effective treatment of non point source pollution.

Reduction of operation and maintenance costs relative to

conventional water treatment plants.

Reduction of flood hazards and erosion.

Opportunities for enhancement of wildlife habitats biodiversity

revitalization, academic research, public education and community

recreation amenities.

Models Strength Weakness

Rules of thumb Fastest Uncertainty

Roughest Design Methods

First-Order Widely used for CW design ‘Blackbox’ based on only

I/O data.

Monod type equations Follows first order and

possible cal. for BC.

Over simplification of

parameters

ASM 1,2,2D,3 Widespread application in

WWT.

Some components are not

possible to add

CW2D Explains transport and

reaction of main

constituents

Fails to explain clogging

phenomenon

FITOVERT Explains clogging ad

degradation of OM & N

More work is still required

Model Review

P1 P2

P2

Ground alum

sludge cakes

Gravel support

Raw wastewater Reed bed

feed tankEffluent

Schematic view of tidal flow reed bed treatment system

First-order model

ecctk

inout

cc

out

in

tk ln

1

Cin is influent concentration, mg/l,

Cout is effluent concentration, mg/l,

k is reaction rate constant, d-1, and

t is time, d-1

Cout= 0.1071Cin + 0.3464

R2 = 0.8203

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0

Cin (mg/l)

Cout (

mg

/l)

Relationship between Cin and Cout of RP throughout the experimental period

Cout = 0.8936Cin + 0.2837

R2 = 0.8203

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

0.0 2.0 4.0 6.0 8.0 10.0

Cout (mg/l), Experimental

Cout (

mg

/l),

Pre

dic

ted

Relationship between Cout (experimental) and Cout (predicted) of RP throughout

the experimental period

Water quality parameters Mean Cin (mg/l) Mean

Cout (mg/l)

Experimental

Mean

Cout (mg/l)

Predicted

k (d-1)

Reactive Phosphorus

(RP)

28.3 3.4 3.30 17.1

Soluble Reactive

Phosphorus (SRP)

17 1.5 1.42 19.8

Chemical Oxygen

Demand (COD)

197.2 45.5 39.2 12.9

Biological Oxygen

Demand (BOD)

106.6 19.5 20.2 13.9

Suspended solids 71.9 9.6 5.5 20.4

Results of first order model calculation for various water quality

parameters

Major Pathways

2.0m 0.75m 0.75m 0.75m 2.0m

1 2 3 4

AB

Connection

for inlet pipe

Connection

for exit pipe

System 1

Mesh cage for

submersible pump

0.30m (L), 0.30m

(W) and 1.35m (H)

Tanks A and B are 10,000L capacity circular tanks each with individual dimension of 2500mm (diameter), 2810mm (height) and

a lid opening at the top measuring 480mm.

Tanks 1, 2, 3 and 4 are plastic tanks with about 1,100L capacity each and approximate dimensions of 1100mm x 1380mm x

1345mm (L x W x H)

Four stage Tidal flow Constructed wetland system

Groups and parameters being measured

Nutrients Organics Met. Real time Phy. Obs.

NH3-N BOD5 Rainfall pH Reeds

NO3--N COD Atm.

Temp

ORP Clogging

NO2--N Sol. COD Sunshine Temp Flow level

Total N Aluminum Gusts Cond.

Total P Sol. Alum. Wind Salinity

Sol.Rea.P SS DO

Turbidity % SAT

Model Development

Mass Balance

RP/SRP Plant RP/SRP PlantRP/SRP Plant

RP/SRP WaterRP/SRP Water RP/SRP Water

RP/SRP Water

RP/SRP Alum-

SludgeRP/SRP Alum-

Sludge

RP/SRP Alum-

Sludge

RP/SRP Alum-

Sludge

RP/SRP Plant

1 2 3 4

1 2 3

4

1 2

3 4

inflow

Uptake

DesorptionAdsorption

Flow 1 2 Flow Flow 3

Desorption

Adsorption

Desorption

Adsorption

Desorption

Adsorption

Uptake Uptake Uptake

Outflow

Conceptual diagram showing the most important processes in phosphorus build into the model. The model is composed of 4

repetitive subsystems (the columns), each modelling the transformations of the particular compartment. The horizontal arrows

represent water flow and the vertical arrows represent process equations

Strong affinity

PAl 3+

|Alum Sludge

Conceptual diagram showing the most important processes in Nitrogen build into the model. The model is composed

of 4 repetitive subsystems (the columns), each modelling the transformations of the particular compartment. The

horizontal arrows represent water flow and the vertical arrows represent process equations

Organic Nitrogen

1 2 3 4

Organic Nitrogen Organic Nitrogen Organic Nitrogen

2 3 4

Ammonia Nitrogen Ammonia Nitrogen Ammonia Nitrogen Ammonia Nitrogen

Nitrate Nitrogen Nitrate Nitrogen Nitrate Nitrogen Nitrate Nitrogen

Nitrite Nitrogen Nitrite Nitrogen Nitrite Nitrogen Nitrite Nitrogen

1 2 3 4

1 2 3 4

1 2 3 4

Organic Nitrogen

Ammonia Nitrogen

Nitrate Nitrogen

Nitrite Nitrogen

Ammonification

Nitrification

Gaseous Nitrogen

Nitrogen Oxide

Gaseous Nitrogen

Nitrogen Oxide

Gaseous Nitrogen Gaseous Nitrogen

Nitrogen Oxide Nitrogen Oxide

Denitrification

)(1

sarb

s

w

L

D

Once the nitrogen reaches the biofilm surfaces, its concentration is

determined by diffusion term and a reaction term (Polpraset et al., 1994)

For Example

Michaelis – Menton Expression

….possible to explore implifications of different rate constants and

different in flux and outflux scenarios on overall system behaviour

Michaelis-Menton Dynamics

Future Outlook

Science has recently provided wetland engineers with biomolecular

probes to decrypt the microbial basis of treatment processes.

More research should be focused on the internal mechanism such as

ammonification, nitrification, denitrification, plant uptake, adsorption,

desorption, sedimentation, mineralization etc.

Recent wetland research and the unfolding revolution in molecular and

environmental microbiology suggest that these techniques will

powerfully inform wetland engineering designs in the future.

Efficient dynamic software like STELLA can be used as a tool for better

understanding the processes happening underneath the wetland

system.

Passive methods will remain important, but as an informed design

choice, not a technology limitation

Conclusion

Constructed Wetlands/Engineered Wetlands are crucial in protection of

Environment

TFEW and Alum sludge plays a pivotal role in the removal of

pollutants from Wastewater.

Moreover, increasing scientific sophistication of treatment wetland

designers is only the beginning of a more profound understanding in the

near future of how these complex reactors function at a molecular level

Thanking You

Beautiful wetlands