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Bioavailabilty and crop uptake of heavy metals from Sewage sludge

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How Sewage and sludge amendment leads to heavy metal contamination.

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Bioavailabilty and crop uptake of heavy metals from Sewage sludge

  1. 1. Hriday Kamal Tarafder and Dr. P. K. Mani
  2. 2. 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)
  3. 3. Sewage-sludge Disposal
  4. 4. Sludge in agriculture Heavy metal accumulatio n Food chain transfer Last link of pollutants
  5. 5. Heavy metals: Specific gravity >5.0 Atomic no. >20
  6. 6. Essential heavy metal Non essential heavy metal Fe, Zn, Cu, Mn, Mo, Ni Pb, Hg, Cd, As, Cr, Se
  7. 7. Member State Year Sludge production (t DS) Agriculture t (DS) % of total Germany 2007 2056486 592552 70 Spain 2006 1064972 687037 65 Sweden 2006 210000 30000 14 UK 2006 1544919 1050526 68 Austria 2006 252800 38400 16 Italy 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
  8. 8. 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).
  9. 9. 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 Union Standards (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 - - - Commission Regulation (EU, 2006) 0.2 - 0.3 - - - - Guidelines for safe limits of some heavy metals in soils & plants Guidelines for safe limits of some heavy metals in soils & plants
  10. 10. Heavy metal availabilityHeavy metal availability in sewage sludgein sewage sludge amended soilsamended soils
  11. 11. • ‘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)
  12. 12. Factors affecting heavy metal availability toFactors affecting heavy metal availability to plantsplants A)Soil properties B)Plant factors C)Soil-plant transfer coefficient
  13. 13. A) Effect of soil propertiesA) Effect of soil properties a) 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
  14. 14. 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)
  15. 15. Environmental Protection Capacity (EPC) factor = DxH2 K 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.
  16. 16. 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)
  17. 17. 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
  18. 18. 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.
  19. 19. 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).
  20. 20. 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).
  21. 21. Soil moisture Soil temperature Soil aeration g) Other factors-
  22. 22. 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)
  23. 23. Other plant factors: b)Cultivars c)Genotype
  24. 24. 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
  25. 25. Transfer coefficients of Cd, Ni, Pb and Zn inTransfer coefficients of Cd, Ni, Pb and Zn in clay loam soilclay 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)
  26. 26. Heavy metal accumulationHeavy metal accumulation in soils and plantsin soils and plants
  27. 27. Effect of untreated sewage sludge on heavyEffect 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 0.042 T1 (ss @ 10 t ha-1 ) 2.95d 1.70d 0.31 0.048 T2 (ss @ 20 t ha-1 ) 4.76c 2.13c 0.36 0.049 T3 (ss @ 40 t ha-1 ) 5.87b 2.76b 0.40 0.056 T4 (ss @ 80 t ha-1 ) 6.75a 3.01a 0.42 0.060 LSD 0.057 0.057 NS NS Khan et al. (2007)
  28. 28. Effect of Municipal sewage sludge (MSS) and mixtureEffect of Municipal sewage sludge (MSS) and mixture ofof MSS & Yard waste (YS) on heavy metal accumulationMSS & Yard waste (YS) on heavy metal accumulation MSS MSS+ YS Native soil Heavy metals in soil and soil mix Antonious et al. (2010) Squashyield(lbs/acremgkg-1 drysoil
  29. 29. Heavy metal concentration of squash fruitsHeavy metal concentration of squash fruits grown on MSS amended soilgrown on MSS amended soil Concentrationin (mgkg-1 )dryfruit Heavy metals in squash fruits Concentrationin (mgkg-1 )dryfruit Squash harvest Heavy metal Maximum permissible limit in vegetables & fruits (mg kg-1 dw)* Cd 0.2 Cu 20 Ni 10 Pb 9 Zn 100 Cr 0.5 * State Environmental Protection Administration, China Antonious et al. (2010)
  30. 30. Heavy metal accumulation in ChineseHeavy metal accumulation in Chinese cabbagecabbage grown in sewage sludge amended soilgrown in sewage sludge amended soil Heavy metals Sewage sludge Limits for sewage sludge usage a Soil SEPA limits for soils b As (mg kg-1 ) 322.76±31.77 75 30.12±2.33 30 Cd (mg kg-1 ) 5.06±0.65 20 0.57±0.22 0.6 Cr (mg kg-1 ) 48.85±5.22 1200 29.07±2.23 250 Pb (mg kg-1 ) 41.19±4.78 1000 12.85±1.11 350 Ni (mg kg-1 ) 25.32±1.28 200 21.88±1.72 60 Cu (mg kg-1 ) 105.08±4.57 1500 18.96±1.22 100 Zn (mg kg-1 ) 1872.23±22.7 1 3000 113.44±5.43 300 Total heavy metal concentrations in sewage sludge & soil a Permissible limits of sewage sludge usage in agriculture in China b State Environmental Protection Administration (SEPA) in China Wang et al. (2008)
  31. 31. 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±0.0 7 0.25±0.02 0.25±0.0 7 0.41±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±0.0 2 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 soil b 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)
  32. 32. 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 content inEffect of sewage sludge on nutrient and heavy metal content in soilsoil Singh & Agrawal (2010)
  33. 33. Treatment Cu Mn Zn Cr Cd Ni Pb Untreated soil 0.48 1.43 11.58 0.32 0.23 0.43 0.42 6 kg m-2 SSA 0.77 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 SSA 2.22 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 0.40 9 kg m-2 SSA 180.78 0.41 12 kg m-2 SSA 164.50 0.42 Heavy metal uptake by green mung from sewageHeavy metal uptake by green mung from sewage sludge amended soilsludge amended soil Singh & Agrawal (2010)
  34. 34. Way outsWay outs A) Prevention of heavy metal contamination B) Management of contaminated soil
  35. 35. A) Prevention of heavy metal contaminationA) Prevention of heavy metal contamination i) Reducing heavy metal content of sewage sludge- Acid hydrolysis Alkaline hydrolysis Fenton’s peroxidation treatment
  36. 36. Acid and alkaline hydrolysisAcid and alkaline hydrolysis Conditions Acid hydrolysis Alkaline hydrolysis pH 3 10 Temperat ure 120o C 100o C Time 1 hour 1 hour Heavy metals Untreat ed Acid thermal hydroly sis Alkaline thermal hydroly sis Cd 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)
  37. 37. 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 peroxidation Cd 1.44 0.6 Cr 90 74 Cu 284 130 Pb 219 191 Ni 46 20 Zn 859 189 Concentration (mg kg-1 dry solid) of heavy metals in the sludge cake after dewatering for untreated sludge and sludge subjected to Fenton’s peroxidation Dewil et al. (2006))
  38. 38. 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 41 Cd 39 85 1.9 39 Cr 1200 3000 150 3000 Cu 1500 4300 75 1500 Pb 300 840 15 300 Hg 17 57 0.85 17 Mo 18 75 0.90 18 Ni 420 420 21 420 Se 36 100 5 100 Zn 2800 7500 140 2800 US EPA (1993)
  39. 39. 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’
  40. 40. 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
  41. 41. ConclusionConclusion ss  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.
  42. 42. 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

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