BIOLOGICAL EFFECTS OF SOIL AMMENDMENTS TO IMMOBILIZE HEAVY METAL CONTAMINATION

By Nelson Ambueh Pangsi

Promoter(s) :Prof. Dr. ir. Filip Tack

Prof. Dr. ir. Erik Meers

Tutor:Stijn Van Slycken

INTRODUCTION

• The campine region have been diffusely contaminated by heavy metals (Zn, Cd and Pb) which results from pyro-metallurgical processes.

• The use of conventional methods are unrealistic because of their deleterious impact on the soil and cost of implementation.

• In situ immobilization ( the use of immobilizing agents) has been proposed as a solution to this situation.

• The objective of this study is to evaluate the effectiveness of in situ immobilization by using beans (Phaseolus vulgaris L).

MATERIALS AND METHODS

• The Study Area (Campine region) and experimental site is Lommel (51°12’41’’N; 5°14’32’’E).

Position of the Campine region with an overview of the Cd concentration (mg kg-1) measured in the soil in the region of interest (OVAM, 2008)

MATERIALS AND METHODS• Soil samples for the experiment was collected from the top soil layer (25 -30 cm).

• The soil physico-chemical properties; pH, electrical conductivity and organic matter contents were measured.

• The amendments mixed with soil includes; biochar (5 %), compost (5 %), phosphate sludge (5 %), digestate (5 %), bioterra (5 %), calcium carbonate (1 %) and slovakite

(5 %).

• Plant cultivation.

• Plants harvesting.

• Growth and Biomass measurement

• Determination of elemental content

RESULTS

• Physico-chemical properties of soil used in the experiment

a Meers et al., 2007

Physico-chemical propertiespH-KCl (Control)EC (µS/cm-1)OM(%)CEC (cmol(+)kg-1

aSand (%)aSilt (%)aClay (%)aCaCO3 (%)Cd (mg kg-1)Zn (mg kg-1)

6.4±0.1 63±94.8±0.46.2±0.788840.0±0.3 12±1727±80

RESULTSBiomass production of beans grown on soil with the different amendments

Biochar

Compost

Bioterra

Slovak

eit

Digesta

te

CaCO3

Phosphate

sludge

Blank+water

Blank+fe

rtilize

r0

5

10

15

20

25

30

35

40

45FRESH BIOMASS

Total fresh biomass in (g)

Amendments

Tot

al fr

esh

weig

ht (

g)

Bean plants in untreated soil (control) after 4weeks Bean plants in blank soil and fertilizer after 4weeks (reference)

Bean plants in soil amended with phosphate sludge after 4weeks Bean plants in bioterra amended soil after 4weeks

Bean plants in biochar amended soil after 4weeks Bean plants in compost amended soil after 4weeks

Bean plants in digestate amended soil after 4weeks Bean plants in blank soil and fertilizer after 4weeks (reference)

Bean plants in calcium carbonates amended soil after 4weeks Bean plants in slovakite amended soil after 4weeks

RESULTSConcentration of Cd and Zn (mg kg-1) in plant materials mean±standard deviation, n=4

Amendment Cd(mg kg-1)

Zn(mg kg-1)

Control+water 3.65±0.07d 666±70e

Blank+Fertilizer 3.84 ±2.09d 649±335e

Carbonate 1.22 ±0.17bc 152±12b

Bioterra 0.24±0.04a 46±5a

Slovakite 0.48±0.04a 65±8a

Biochar 2.68±0.53c 416±780d

Compost 2.68±0.53c 297±29c

Digestate 0.9±0.1b 116±31b

PHS 6.66±0.79e 808±151f

Different letters represents significance level of concentration at α= 0.05 PHS : Phosphate sludge

DISCUSSION Biomass production on phosphatic amended soil (bioterra, phosphate sludge and fertilizer)• Phosphatic amendments immobilizes Cd and Zn through phosphate -induce precipitation.

• Bioterra produce a high biomass and contain the least amount of Cd and Zn within its plant materials.

• This is attributed to the fact that, bioterra increases soil pH, fine particle size increases its surface area for sorption.

Biomass production on organic amended soils (biochar, compost and digestate)

• Organic amendments immobilizes Cd and Zn through the formation of organo-metallic complexes.

• The biomass of digestate is also high and the concentration Cd and Zn in its plant materials are also low.

• This is attributed to the fact that digestate consist of lipids, lignin, cellulose and dead bacteria from within the digester which are biologically stable.

DISCUSSIONBiomass production on carbonate amended soil (slovakite containing dolomite

and calcium carbonate)

• Carbonates are acid neutralizing and immobilizing metals. They immobilizes Cd and Zn through precipitation as metal-carbonates.

• The biomass of slovakite is also high, the concentration of Cd and Zn in its plant materials are also low. This is attributed to the fact that, slovakite is capable of increasing soil pH and the formation of OH- through hydrolysis reactions.

• slovakite contain smectites (clay) with a high CEC (110 cmol(+)kg-1).

CONCLUSION

• The study has focused on plant performance (biomass production) upon addition of immobilizing agents on metal polluted soil from the Campine region.

• The best amendments to reduce Cd and Zn mobility in this sandy, slightly acidic soil are bioterra and slovakite. This is based on their high biomass production of beans (Phaseolus vulgaris L.), increased soil pH and very low concentration of Cd and Zn in their plant materials.

FUTURE SUGGESTIONS

• The experiment should be done in the field .

• Changes in soil physico-chemical properties after a long period of applying amendments.

• Eutrophication as a result of phosphatic amendments.

THANKS FOR YOUR KIND ATTENTION