Parikshit Verma

EIA and Sustainability Assessment – Asian EIA and Effective Tool Development

Seol, Korea,

June 5, 2007

Modeling Phytoremediation of Heavy Metal Contaminated Mine Spoil Dumps

National Environmental Engineering Research Institute (NEERI), Nagpur

Barren Manganese Mine Spoil Dump

After 10 years - Revegetated Manganese Mine Spoil Dump

Definitions / Terminology

It is applied at sites with contamination of

− Organic Chemicals – BTEX, TNT, RDX, PCBs − Nutrient – Ammonia, Phosphate, Nitrate− Metal pollutants – Lead, Cadmium, Zinc, Arsenic, Chromium

Phytoremediation

Use of plants / vegetation for in situ treatment of wastewater, contaminated soils or sediments.

Some plants shows the capability to withstand relatively high concentration of chemicals without toxic effects (Hyperaccumulators).

Chemical uptake and translocation in the plant body

Unsaturated / Vadose zone

Processes that takes place in the root zone

Soil Water Partitioning

sdw MkM

Metal Uptake by Plant Root

wm

wp

MK

MIS

max

Michaelis and Menton Type of Reaction

Plant Root Growth

maxmax

12

,Z

Zh

Z

tTtzS rp

47.103.315.0 max DTM

DAPSinZZ r

Saturated and Unsaturated Zone

–Soil

–Water

–Soil

–Air

–Thin film of Water around soil particle

Saturated and Unsaturated Zone

sr

– Residual Moisture – Saturation Moisture

Moisture Retention Characteristics Curve

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.450

0.5

1

1.5

2

2.5

3

3.5S

uctio

n he

ad,

log(

h) (

cm)

Moisture content

mn

rs

r

h

h

1

1

Moisture flux in Unsaturated Zone

Relationship between Soil Moisture and Suction Head is called Soil Moisture Retention Characteristics (MRC)

1)(z

hhkq

1)()(z

hhk

zt

hhc

1

1

1

1

mn

rsnn

h

hn

hhc

Mathematical models used in the Metal Uptake model

• Richards Equation• Water uptake by plant root• Metal uptake by plant root• Root growth with time• Plant root properties• Moisture Retention Characteristics (MRC)• Soil properties – Bulk Density, Clay content, Carbon content etc.• Pedotransfer Function• Soil Water Partition of pollutants• Hydrodynamic Dispersion• Moisture flux joining groundwater• Chemical species flux joining groundwater

pww

ws SqMz

MD

zM

tM

t

)()()(

Expensive and time consuming

mn

rs

r

h

h

1

1

Pedotransfer Functions

• Bulk density• Clay content• Carbon content• Particle size distribution

fMRC Parameters

θs, θr, n, m, α

Space – Time Domain of One Dimensional Transient Metal Uptake Model

Computational Scheme

Richard’s Equation descritized using Implicit scheme

12

)(11

111

1

2

11

1111

1

z

hh

z

kk

z

hhhk

t

hhhc

ti

ti

ti

ti

ti

ti

tit

i

ti

ti

1)()(z

hhk

zt

hhc

011

111

itii

tii

tii DhChBhA

2

11

z

kA

ti

i

2

11

2

1

z

k

z

k

t

hcB

ti

ti

i

2

1

z

kC

ti

i

z

kk

t

hhcD

ti

ti

ti

i

11

1

Calculate c(h)

Ih-h'I<Calculate

k(h)

Calculate Z(r)

Calculate S(z,t)

Calculate Ai

Calculate Bi

Calculate Ci

Calculate Di

Input n,a,ksInput

n,a,s,r

Input Zmax, DAP,

DTM

Input Tp(t), (h)

Input Initial condition,

Boundary condition

Input Assume

(h')

Solution matrix Calculate (h)

Replace h' with calculated value of h

Yes

Output Suction Head

(h)

No

Water flux

Plant root uptake function

Techniques of Phytoremediation

– Phyto-transformation

– Rhizosphere Bioremediation– Phyto-stabilization– Phyto-extraction– Rhizo-filtration

Limitations – Limited regulatory acceptance

– Long duration of time for cleanup– Potential contamination of fodder crop and food chain

– Other treatments are not cost effective– Very large sites– Low concentration of contaminants– Only polishing treatment is required– Where vegetation is used as final cap / site closure

Applicability

Why Phytoremediation Model Software ?

• Design of experiments to determine the parameters of sub-surface phenomenon.

• Preparation of irrigation schedule for plantation on mine spoil dump.

• Decision on harvesting time of plants.

• Estimation of amount of heavy metal present in the plant.

NEERI PHYTOREM Model Software Demonstration