Hriday Kamal Tarafderand

Dr. P. K. Mani

Sewage: Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community.*

Sludge: A mixture of solids and water produced during the treatment of waste water or sewage.*

*Central Pollution Control Board(1993)

Sewage-sludge

Disposal

Sludge in agriculture

Heavy metal accumulation

Food chain transfer

Last link of pollutants

Heavy metals: Specific gravity >5.0

Atomic no. >20

Essential heavy metal Non essential heavy metal

Fe, Zn, Cu, Mn, Mo, Ni Pb, Hg, Cd, As, Cr, Se

Member State

Year Sludge production (t DS)

Agriculturet (DS) % of total

Germany 2007 2056486 592552 70Spain 2006 1064972 687037 65

Sweden 2006 210000 30000 14UK 2006 1544919 1050526 68

Austria 2006 252800 38400 16Italy 2006 1070080 189554 18

In India production of sewage sludge is estimated to be around 1200 tonnes/day

There exists a potential to produce 4000 tonnes of sludge per day

Juwarkar et al., 1991

Metal contents (mg/kg-1) in sewage sludge from different cities in India

Location Zn Cu Cd Pb Ni Cr

Ahmedabad

2147 535 3.5 76.8 32.3 60.4

Delhi 1610 440 5.5 34.5 815 53.5

Nagpur 832 272 1.5 24.3 14.8 49.2

Chennai 935 210 8.3 16.6 60.5 38.5

Jaipur 1720 265 7.3 66.9 37.5 176

Kolkata 1513 188 3.25 157 266 1467

Source : Maity et al (1992).

Sample Standards Cd Cu Pb Zn Mn Ni Cr

Soil (µg g-1)

Indian Standard(Awashthi, 2000) 3-6 135-

270 250-500 300-600 - 75-

150 -

European UnionStandards (EU

2002)3 140 300 300 - 75 150

Plant (µg g-1)

Indian Standard(Awashthi, 2000) 1.5 30 2.5 50 - 1.5 20

WHO/FAO (2007) 0.2 40 5 60 - - -

CommissionRegulation (EU,

2006)0.2 - 0.3 - - - -

Guidelines for safe limits of some heavy metals in soils & plants

Heavy metal Heavy metal availability in sewage availability in sewage sludge amended soilssludge amended soils

• ‘Available’ heavy metals - fraction of the total concentration of heavy metals in the soil, which is present in the soil solution or easily exchangeable from the soil matric surfaces.

Total heavy metal (M)

M in soil solution

Exchangeable

M bound to carbonates

M bound to Fe & Al oxides

M bound to organic matter

Residual fraction

Readily available

=

+

+

+

+

+

Naoum et al. (2001)

Factors affecting heavy metal Factors affecting heavy metal availability to availability to plantsplants

A)Soil properties

B)Plant factors

C)Soil-plant transfer coefficient

A) Effect of soil propertiesA) Effect of soil propertiesa)pH• Availability of cationic heavy metals decreases

with increase in pH (Alloway and Jackson, 1991).

pH

• Whereas, availability of Mo and elements with anionic species increases with increasing soil pH (Smith, 1996).

pH

b) Organic matter-Organo-metallic interactions can be

divided into two groups:

1) Ionic interactions (cation exchange)- includes alkali metals (K, Na, Li) and Group II elements (Be, Mg, Ca).

2) Non ionic bonds- includes elements like heavy metals; they tend to interact especially with groups containing trivalent elements, like N and P.

Livens (1991)

Environmental Protection Capacity (EPC) factor = DxH2K

Dx - thickness of the soil layer in cm, H - soil humus content K - constant depending on the humus quality.

Sludge Soil humus

EPC Heavy metal availability

Hargitai (1989)

Contd.

c) Clays and hydrous oxides-

2) Specific adsorption to surface hydroxyl groups (Miller et al., 1987)

3) Co-precipitation (Martinez and McBride, 1998)

4) Precipitation as the discrete metal oxide or hydroxide (Martinez and McBride, 1998).

Increase in clay and hydrous oxide contents in soils provides more sites for adsorption of metals and reduces the directly bio-available metal (Qiao and Ho, 1996).

1) Non-specific adsorption (exchange) (Basta and Tabatabai, 1992)

d) Redox potential- Heavy metals expected to precipitate as sulphides include- Ni2+, Zn2+, Cd2+, Hg2+ ,Fe3+

Flooded condition- SO4

2- → SO3 - → S2-

S2- + M2+ → MS

Aerobic condition- M2+ + SO4

2- ↔ MSO4

Reducing conditions may cause the dissolution of Mn and Fe oxides (Alloway, 1995).

Thus, soil with a fluctuating water table will often have a lower adsorptive capacity for metals such as Cd and As which are strongly sorbed by hydrous oxides of Fe and Mn (Ghorbani, 2008).

Cont.Cont.

e)Effects of other elements-

i) Antagonistic effect-With high P contents, at neutral to alkaline pH, a precipitation of Cd3(PO4)2 takes place (Jing and Logan, 1992).

ii) Synergistic effect-High concentrations of Cl - may increase the availability of Cd to plants ( Sommers and McLaughlin, 1996).

f) CaCO3 content-

At high pH and high pCO2 (partial pressure of CO2) values, calcite (CaCO3) sorbs Cd, as CdCO3, and diminishes its availability (Evans, 1989).

Other metals likely to precipitate as carbonates at high pCO2 and pH values include: Fe2+, Zn2+ and Pb2+

(Evans, 1989).

Soil moisture

Soil temperature

Soil aeration

g) Other factors-

Metal High accumulations Low accumulations

Cd Lettuce, Spinach, Celery, Cabbage

Potato, Maize, French bean, Peas

Pb Kale, Rye grass, Celery Some barley cultivars, Potato, Maize

Cu Sugar beet, Certain barley cultivars,

Leek, Cabbage, Onion

Ni Sugar beet, Rye grass, Mangold, Turnip

Maize, Leek, Barley, onion

Zn Sugar beet, Mangold, Spinach, Beetroot

Potato, Leek, Tomato, Onion

a) Plant species-

B) Plant factors-B) Plant factors-

Alloway (1990)

Other plant factors:

b)Cultivars

c)Genotype

E) E) Soil-Plant Transfer CoefficientSoil-Plant Transfer Coefficient

Transfer Coefficient (TC)= ----------------[M]plant

[M]soil

[M]plant- concentration of an element in the test plant tissues

[M]soil- total concentration of the same element in the soil where this plant is grown

Transfer coefficients of Cd, Ni, Pb and Zn Transfer coefficients of Cd, Ni, Pb and Zn in clay loam soilin clay loam soil

Cd Ni Pb Zn

0.40 0.04 0.004 0.13

0.65 0.04 0.005 0.24

1.00 0.20 0.010 0.42

Warm Cool

Control

ss@10 t ha-1

ss@50 t ha-1

Cd Ni Pb Zn

0.45 0.04 0.005 0.15

1.16 0.08 0.010 0.45

1.72 0.21 0.010 0.68

Antoniadis (1998)

Heavy metal Heavy metal accumulationaccumulation

in soils and plantsin soils and plants

Effect of untreated sewage sludge on heavy Effect of untreated sewage sludge on heavy metal accumulation in soilmetal accumulation in soil

Treatments AB-DTPA extractable 0.1 N HCl extractable Zn (mg kg-1) Cu (mg kg-1) Pb (mg kg-1) Cd (mg kg-1)

T0 (NPK: 120:60;60 kg ha-1) 1.76e 1.66d 0.25 0.042T1 (ss @ 10 t ha-1) 2.95d 1.70d 0.31 0.048T2 (ss @ 20 t ha-1) 4.76c 2.13c 0.36 0.049T3 (ss @ 40 t ha-1) 5.87b 2.76b 0.40 0.056T4 (ss @ 80 t ha-1) 6.75a 3.01a 0.42 0.060

LSD 0.057 0.057 NS NS

Khan et al. (2007)

Effect of Municipal sewage sludge (MSS) and Effect of Municipal sewage sludge (MSS) and mixture ofmixture of

MSS & Yard waste (YS) on heavy metal MSS & Yard waste (YS) on heavy metal accumulationaccumulation

MSS MSS+ YS Native soil

Heavy metals in soil and soil mixAntonious et al. (2010)

Squa

sh y

ield

(lbs

/acr

em

g kg

-1 d

ry s

oil

Heavy metal concentration of squash fruitsHeavy metal concentration of squash fruits grown on MSS amended soilgrown on MSS amended soil

Conc

entr

ation

in(m

g kg

-1)d

ry fr

uit

Heavy metals in squash fruits

Conc

entr

ation

in(m

g kg

-1)d

ry fr

uit

Squash harvest

Heavy metal Maximum permissible limit in vegetables & fruits (mg kg-1dw)*

Cd 0.2Cu 20Ni 10Pb 9Zn 100Cr 0.5

* State Environmental Protection Administration, China Antonious et al. (2010)

Heavy metal accumulation in Chinese Heavy metal accumulation in Chinese cabbagecabbage

grown in sewage sludge amended soilgrown in sewage sludge amended soilHeavy metals Sewage

sludgeLimits for sewage

sludge usage a

Soil SEPA limits for soils b

As (mg kg-1) 322.76±31.77 75 30.12±2.33 30Cd (mg kg-1) 5.06±0.65 20 0.57±0.22 0.6Cr (mg kg-1) 48.85±5.22 1200 29.07±2.23 250Pb (mg kg-1) 41.19±4.78 1000 12.85±1.11 350Ni (mg kg-1) 25.32±1.28 200 21.88±1.72 60Cu (mg kg-1) 105.08±4.57 1500 18.96±1.22 100Zn (mg kg-1) 1872.23±22.7

13000 113.44±5.43 300

Total heavy metal concentrations in sewage sludge & soil

a Permissible limits of sewage sludge usage in agriculture in Chinab State Environmental Protection Administration (SEPA) in China

Wang et al. (2008)

Heavy metal

Control 5% a 10% a 15% a 20% a 25% a Limits b

As 2.1±0.21 5.8±0.88 5.9±0.97 7.4±1.08 10±0.59 7.9±0.97 0.05

Cd 0.14±0.07 0.15±0.07 0.25±0.02 0.25±0.0

70.41±0.0

1 0.24±0.09 0.2

Cr 0.7±0.15 2.4±0.47 3.1±0.25 3.2±0.34 5.5±0.53 5.8±0.79 0.5

Pb 0.08±0.01 0.17±0.4 0.24±0.6 0.27±0.2 0.19±0.02 0.22±0.5 9

Ni 1.2±0.2 0.6±0.2 1.6±0.4 1.6±0.6 2.1±0.3 3.1±0.1 10

Cu 2.6±0.5 4.7±0.7 5.6±1.1 4.2±0.8 3.6±0.9 4.2±1.1 20

Zn 43.4±5.8 63.3±9.3 65.9±6.6 78.9±11.6

72.5±11.1 69.5±10.7 100

Contd.Contd.

a Percentages of sewage sludge in soilb Maximum permissible limits of metal contaminants (SEPA, China)

Concentration of heavy metals (mg kg-1) in leaves of Chinese cabbage grown in soil amended with various content of sewage sludge

Wang et al. (2008)

Parameters Unamended soil 6 kg m-2 SSA 9 kg m-2 SSA 12 kg m-2 SSA

pH (1:5) 8.18 ± 0.02 8.06 ± 0.02 8.09 ± 0.06 7.85 ± 0.03

EC (mScm-1) 0.24 ± 0.01 0.29 ± 0.01 0.32 ± 0.02 0.39 ± 0.01

Organic C (%) 0.77 ± 0.02 1.41 ± 0.01 1.52 ± 0.02 1.74 ± 0.01

Total N (%) 0.18 ± 0.00 0.20 ± 0.00 0.20 ± 0.00 0.21 ± 0.00

P (mg kg-1) 54.43 ± 3.90 111.81 ± 3.54 124.2 ± 2.59 132.8 ± 3.37

Cu (mg kg-1) 3.51 ± 0.24 8.50 ± 0.27 10.81 ± 0.26 11.13 ± 0.42

Mn (mg kg-1) 13.27 ± 0.73 34.36 ± 0.86 41.17 ± 1.13 42.05 ± 1.19

Zn (mg kg-1) 2.11 ± 0.49 11.95 ± 0.46 22.95 ± 1.29 30.91 ± 1.69

Cr (mg kg-1) 0.34 ± 0.03 0.77 ± 0.05 1.50 ± 0.07 1.66 ± 0.05

Cd (mg kg-1) 1.51 ± 0.19 6.39 ± 0.30 6.44 ± 0.34 7.36 ± 0.34

Ni (mg kg-1) 4.95 ± 0.22 9.69 ± 0.13 10.29 ± 0.16 10.75 ± 0.27

Pb (mg kg-1) 2.83 ± 0.18 8.49 ± 0.47 10.04 ± 0.25 11.06± 0.15

Effect of sewage sludge on nutrient and heavy metal Effect of sewage sludge on nutrient and heavy metal content in soil content in soil

Singh & Agrawal (2010)

Treatment Cu Mn Zn Cr Cd Ni PbUntreated soil

0.48 1.43 11.58 0.32 0.23 0.43 0.42

6 kg m-2

SSA0.77 1.92 20.58 0.83 0.80 1.47 1.88

9 kg m-2

SSA 1.65 2.18 20.62 1.18 1.35 2.85 2.62

12 kg m-2

SSA2.22 2.82 22.07 1.47 1.62 5.67 3.47

Treatment Yield (g m-2) Harvest index (g g-1)Unamended soil 102.88 0.34

6 kg m-2 SSA 143.34 0.409 kg m-2 SSA 180.78 0.4112 kg m-2 SSA 164.50 0.42

Heavy metal uptake by green mung from sewage Heavy metal uptake by green mung from sewage sludge amended soilsludge amended soil

Singh & Agrawal (2010)

Way outsWay outs

A) Prevention of heavy metal

contamination

B) Management of contaminated

soil

A) Prevention of heavy metal A) Prevention of heavy metal contaminationcontamination

i) Reducing heavy metal content of sewage sludge-

Acid hydrolysis

Alkaline hydrolysis

Fenton’s peroxidation treatment

Acid and alkaline hydrolysisAcid and alkaline hydrolysis

Conditions

Acid hydrolysis

Alkaline hydrolysis

pH 3 10

Temperature

120oC 100oC

Time 1 hour 1 hour

Heavy metals

Untreated

Acid thermal hydroly

sis

Alkaline thermal hydroly

sisCd 2.05 0.83 2.17

Cr 25.5 15.4 14.7

Cu 183 189 45

Pb 158 148 57

Ni 12.7 2.1 13.2

Zn 2144 370 1712

Operating conditions of acid and alkaline hydrolysis

Concentration (mg kg-1 dry solid) of heavy metals in the sludge cake after dewatering for untreated sludge and sludge subjected to hydrolysis

Dewil et al. (2006)

Fenton’s peroxidation treatmentFenton’s peroxidation treatment

Adjusting pH to 3 using H2SO4 + Fe2+

Addition of Ca(OH)2

Addition of polyelectrolyte

Addition of H2O2 (reaction time ≈ 1 hour)

Treatment procedure

Heavy metal

Untreated sludge

Fenton’s peroxidatio

nCd 1.44 0.6Cr 90 74Cu 284 130Pb 219 191Ni 46 20Zn 859 189

Concentration (mg kg-1 dry solid) of heavy metals inthe sludge cake after dewatering for untreated sludge

and sludge subjected to Fenton’s peroxidation

Dewil et al. (2006))

ii) Regulating the rate of application-Pollutant Pollutant

concentration in EQ sludge

(mg kg-1)

Ceiling concentration in sludge applied to

land (mg kg-1)

Annual pollutant

loading rates (kg ha-1 yr-1)

Cumulative pollutant

loading rates (kg ha-1)

As 41 75 2 41Cd 39 85 1.9 39Cr 1200 3000 150 3000Cu 1500 4300 75 1500Pb 300 840 15 300Hg 17 57 0.85 17Mo 18 75 0.90 18Ni 420 420 21 420Se 36 100 5 100Zn 2800 7500 140 2800

US EPA (1993)

iii) No application-iii) No application-

The land is already high in heavy metal concentrations

Soil pH < 5.0 or clay content < 10%

Concentration of any of the heavy metals in the sludge is beyond ‘ceiling limit’

B) Management of contaminated soilB) Management of contaminated soil

Increasing the soil pH to 6.5 or higher

Draining wet soils

Applying phosphate

Careful selection of plants

Application of organic matter

Application of Biochar

ConclusionConclusionss

Heavy metal content of both sewage sludge and soil should be considered during making decisions regarding sewage sludge use in agriculture.

Risks of heavy metal contamination of crops grown in sewage sludge amended soils can be minimized to some extent by altering various physico-chemical properties of the soil.

Use of sewage sludge should be avoided in crops that accumulate heavy metals in levels toxic to humans without themselves showing any toxicity symptoms.

For safe agricultural use of sewage sludge, regular monitoring of soil and crop edible parts for heavy metal accumulation is necessary.

Future research should be carried out to have a better understanding of long-term implications of heavy metal availability to plants grown in sewage sludge amended soils.

Efforts in developing feasible techniques, to reduce heavy metal content of sewage sludge for agricultural use, should be made.

Development of standard limit of metals in sewage sludge under Indian context is needed.

Research Needs