1. 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
2. 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).
3. 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)
4. 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
5. RESULTS
• Physico-chemical properties of soil used in the experiment
a Meers et al., 2007
Physico-chemical properties
pH-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±9
4.8±0.4
6.2±0.7
88
8
4
0.0±0.3
12±1
727±80
6. RESULTS
Biomass production of beans grown on soil with the different amendments
0
5
10
15
20
25
30
35
40
45
50
Totalfreshweight(g)
Amendments
FRESH BIOMASS
Total fresh biomass in (g)
7. 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
8. 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
9. RESULTS
Concentration 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
10. 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.
11. DISCUSSION
Biomass 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).
12. 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.
13. 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.
