HEAVY METALBIOAVAILABILITY IN THE BIOFERTILIZER

DERIVED FROM SEWAGE SLUDGE

Prof. dr. Valdas Paulauskas, Valdas.Paulauskas@asu.lt

*Assoc. prof. dr. Nomeda Sabiene, Nomeda.Sabiene@asu.lt

Dr. Ernestas Zaleckas, Ernestas.Zaleckas@asu.lt

Aleksandras Stulginskis University,Institute of the Environment and Ecology,

LITHUANIAhwww.asu.lt/me/en/15320

October 17-20, Bari

Rationale

• Sewage sludge composting can form an important part of acomprehensive, integrated waste management system thatemphases resource conservation through source reduction, recyclingand reuse.

• There is no universally accepted and used sewage sludge treatmenttechnology still:– sewage sludge can be treated using aerobic composting,

anaerobic digestion or both methods can be used sequently.• Composting provides a simple but cost effective alternative

treatment method for waste disposal by decomposing organicmatter, producing a pathogen free, stabilised and nutrient richproduct:– quality of the final product (biofertilizer) can be improved by

adding nutrient additives and stabilizing heavy metals.

The aim and objectives

• To find an optimal solution for the sewagesludge composting by producing a high qualityand environmentally friendly product –compost or bio-fertilizer:

– to create suitable technologies for aerobic and anaerobiccomposting of sewage sludge what concern high nutritionalvalue and low heavy metal bioavailability;

– to evaluate heavy metal bioavailability in the compostedproducts by chemical analyses and vegetative pot experiments.

Methods of sewage sludge quality evaluation

• CEN/TC 308 standards on characterization of sewage sludge where used:

– EN 12832:1999. Utilisation and disposal of sludges –vocabulary.

– EN ISO 5667-13:2011. Sampling of sludges.

– EN 12176:2000. Determination of pH-value.

– EN 12879:2000. Determination of the loss of ignition of dry mass.

– EN 12880:2000. Determination of dry residue and water content.

– EN 13342:2000. Determination of Kjeldahl nitrogen.

– EN 3346:2000. Determination of trace elements and phosphorous.

Aqua regia extraction methods.

• Sequential extraction of heavy metals (Emmerich at al., 1982; Lin et al., 1999)

Methods of compost quality evaluation

• CEN/TC 223 standards on characterization of composts:

– EN 12579:2000. Sampling.

– EN 13040: 2007. Sample preparation for chemical and physical tests,

determination of dry matter content, moisture content and laboratory

compacted bulk density.

– EN 12580: 2000. Determination of a quantity.

– EN 13039:2011. Determination of organic matter content and ash.

– EN 13037: 2011. Determination of pH.

– EN 13654-1:2002. Determination of nitrogen - Part 1: Modified Kjeldahl

method.

– EN 13650:2001. Extraction of aqua regia soluble elements.

– EN 13652:2001. Extraction of water soluble nutrients and elements.

• Sequential extraction of heavy metals (Emmerich at al., 1982; Lin et al., 1999)

Object of the research (1)

• Sewage sludge from the Min-Shen municipal sewagetreatment plant (MSTP), Taiwan, R.O.C.

0

1

2

3

4

N P K

3.70

2.01

0.15

%

175

64 46 25 <2 <0.020

200

400

Zn Cu Pb Mn Ni Cr Cd

mg kg-1

907

LT, LAND 20:2005

300 75 140 - 50 140 1.5

EU, EC, 2001

200 100 100 - 50 100 0.7N:P:K – 1:1:1

Object of the research (2)

• Sewage sludge from the Kaunas and Šiauliai municipalsewage treatment plant (MSTP), Lithuania.

N:P:K – 1:1:1LT, LAND 20:2005

300 75 140 140 50 1.5 1.0

EU, EC, 2001

200 100 100 100 50 0.7 0.5

0

2

4

6

N P K

3.202.21

0.56

5.16

2.74

0.54

%Sewage sludge(Kaunas)Sewage sludge(Šiauliai)

257,98108,7594,96

35,85 21,65 1,77115,8 68,4 28,80

15,40 2,9 0,050

200

400

600

800

1000

Zn Cu Pb Cr Ni Cd Hg

Sewage sludge(Kaunas)Sewage sludge(Šiauliai)

14221158

COMPOSTING PROCEDURES1. AEROBIC COMPOSTING

Methodology of the aerobic composting

• The composting was carried out in 13 m-3

aerated piles in the pilot-scale compostingplant at the Pa-Li MSTP in Taipei, Taiwan,R.O.C.

• Composition of the mixture:

– sewage sludge 62% (5490 kg),

– bulking agent (sawdust) 24% (2122 kg),

– recycled compost (obtained from previous studies

and used as inoculants) 14% (1265 kg).

• Air flow rate was controlled by a computer-regulated solenoid valve and was measured bya flow meter. The average air flow rate was13.85 m-3h-1

• The composted mixture was turned once aweek during the first month of the compostingcycle and twice a week during the secondmonth.

• The composted mixture was sampled weeklyduring the 2-month period.

Roller door

Compost bin A

Roller door

Compost bin D

Compost bin B

Compost bin E

Compost bin C

Compost bin F

Deo-doringVessel

Pretreatment operational area

Roller door

14 m

8m

7

m

4 m 4 m

Changes in characteristics of composted mixture during composting

0

20

40

60

80

0 7 14 21 28 35 42 49 56

days

Temperature, oC

5055606570

0 7 14 21 28 35 42 49 56

Moisture, %

8688909294

0 7 14 21 28 35 42 49 56

days

Organic matter, %

Material Ash, % C/N N, % P, % K, % pH

Sewage sludge 25.40 7.4 3.70 2.01 0.15 7.70Sawdust 0.38 420.0 0.14 n.d. n.d. 5.60Recycledcompost 15.50 19.4 2.46 n.d. n.d. 5.80

Raw composted mixture 7.80 30.5 1.74 n.d. n.d. 7.20

Final compost 11.20 19.4 2.64 1.57 0.33 6.20Changes +3.40 -11.1 +0.90 -1.00

Changes in chemical composition of mixture during composting

COMPOSTING PROCEDURES2. ANAEROBIC COMPOSTING

Methodology of the anaerobic composting

• Biofertilizer was produced by anaerobic treatment of sewage sludgefrom Kaunas and Raseiniai MSTP (200 g) and meat-bone mass mixture(100 g). Nutrients ratio N:P:K was adjusted to 1:1:1 (total amountreaching to about 6 %):– P content was increased before anaerobic digestion by acidic (45 % H3PO4)

meat-bone mass treatment ( ratio 1:5),

– K amount was increased after anaerobic digestion by adding to digestate30% of cement kiln dust and K2SO4 mixture.

• For biological activation of digestion process pig manure (5 % fromtotal mixture mass) was added.

• Anaerobic digestion was performed in the laboratory anaerobic reactor(volume 18 l) under mesophilic conditions (at temperature 38.5-39.5oC)for 8 days until gas emission stopped.

1

2 3

4 5

Fee

dsto

ck

Bio

gas

Effluent

Scheme: 1 – level of liquid, 2 – electricaldriver, 3 – mixer, 4 – insulation, 5 –heating coil

View of the laboratory anaerobicdigester (biogas reactor) with ameasurement/control panel

Equipment of the anaerobic composting

• Sterilization of organic waste mixture(killing of pathogenic microorganisms andparasite eggs) was carried out in 3 stages:

– initial chemical sterilization by acidicwaste treatment with phosphoric acid;

– sterilization during anaerobicdigestion process in a biogas reactor;

– thermal pasteurization during bio-fertilizer drying process.

• Already after second stage (anaerobictreatment) bio-product met sanitaryrequirements for sewage sludge appliedon agricultural land as fertilizer (LAND20:2005).

17,900,000

184,222 324,500

Before treatment

12,127,777 (decrease

32.2%)

117,555 ( decrease

36.2%)

236,777 (decrease

27.0%)

After treatment

Total bacteriaamount,CFU g-1

Faecalstreptococci,CFU g-1

Enterobacter,CFU g-1

Changes in microbiological composition of composted mixture during composting

• amount and calorific value of the received biogas could nearly satisfy the energy needs forthe mesophilic anaerobic digestion and drying processes.

• Life Cycle Analysis showed that simultaneous biogas-bio-fertilizer production and directusage of bio-energy make this waste utilization process more energetically effective andenvironment friendly.

Characteristic

Raw stuff for compostingSewagesludge

(Kaunas) (200g)

Sewagesludge

(Šiauliai) (200g)

Sewage sludge(Kaunas)+ Meat-

bone mass(200+100g)

Sewage sludge(Šiauliai)+ Meat-

bone mass(200+100g)

Biogas output, l 7.2 7.5 34.7 36.85

Relative biogasgeneration rate, l kg-1 DM 217.0 150.8 443.2 384.3

Content of biogas, %

− CH4

−CO2

−O2

61.830.72.0

51.321.92.8

68.525.71.40

64.225.21.60

Changes in gas emissions during composting

Effect of cement kiln dust (30%) onsewage sludge properties

0,0

0,5

1,0

1,5

2,0

2,5

3,0

N 0,02 2,72 1

P 0,039 2,47 0,99

K 2,38 0,99 1,52

CKD (30%) SSCKD(30%)

+SS

7

9

11

13

0 10 20 30 40 50

pH

CKD + SS

0

20

40

60

80

0 10 20 30 40 50

Moisture, %

Composition, %

CKD+SS

%

1:1:1.5

0% 20% 40% 60% 80% 100%

CKD

SS

CKD(30%)+SS

CKD

SS

CKD(30%)+SS

CKD

SS

CKD(30%)+SS

CKD

SS

CKD(30%)+SS

7.7

1.7

4.6

55.4

5.7

32.5

26.1

48.3

33.3

48.2

956.6

508.8

0.7

1.2

0.6

2.9

9.7

6.6

2.5

67.5

29.2

0.5

201.438.4

Immobile HM, mg/kg Mobile (EDTA extractable) HM, mg/kg

Zn

Cu

Cd

Ni

Effect of cement kiln dust on heavy metal mobility in sewage sludge

Changes in chemical composition of mixture during composting

Material N, % P, % K, % pH

Sewage sludge (Kaunas), 200 g

3.20 2.21 0.56 7.66

Sewage sludge (Šiauliai), 200 g

5.16 2.74 0.54 7.20

Meat-bone mass, 100 g5.26 10.60 - 4.65

Cement kiln dust + K2SO4, 30%

0.02 0.04 2.38+2.57

13.60

Raw composted mixture 8.52 7.50 6.05 8.25

Final product 5.92 6.25 6.02 7.45

Changes -2.60 -1.25 -0.03 -0.80

EVALUATION OF THEHEAVY METAL BIOAVAILABILITY

1. Aerobically processed compost

Heavy metals in the aerobically processed compost

MaterialCu Mn Ni Pb Zn Cd Cr Hg As

Sewage sludge 175 46 25 64 907 <0.02 <2.0 - -

Recycled compost

88 102 23 50 509 <0.02 <2.0 - -

Sawdust 5 13 8 13 50 <0.02 <2.0 - -

Raw composted mixture

71 76 21 47 315 <0.02 <2.0 - -

Final compost 85 78 23 39 403 <0.02 <2.0 1.5 1.3

EU EC, 2001 100 - 50 100 200 0.70 100 0.5 -

EC No. 889/2008 70 - 25 45 200 0.70 70 0.4 -*Exceed MPC

Sequential extraction of heavy metals

Exchangeable Fraction F1

Bound to Carbonates FractionF2

Bound to Fe-Mn Oxides FractionF3

Sample, 1g

1M CH3COONa (pH 5), 6h, 20oC

1M MgCl2(pH7), 1h, 20oC

0,04M NH2OH·HCl, 5h, 96oC

0,02M HNO3+30% H2O2, 3h,85oC

30% H2O2, 2h, 85oC

3,2M CH3COONH4, 0,5h, 20oC

HNO3+HF+HCl, microwave digestion

Bound to Organic Matters/ Sulphides Fraction F4

Residual Fraction F5

Lin,J.G.,Chen,C.Y.,Chen,S.Y.,1999. Effects of pH on metals specification in a contaminated sediment. Journal ofthe Chinese Institute of Environmental Engineering 9,49–56.

Heavy metal chemical speciation

0%

20%

40%

60%

80%

100%

Zn Pb Mn Cu

Heavy metals in sewage sludge

0%

20%

40%

60%

80%

100%

Zn Pb Mn Cu

Heavy metals in compost

F5

F4

F3

F2

F1

Mn (38-37%) F1 exchangeable > Zn (45-40%) F3 Fe-Mn oxides >Cu (90-99%) F4 organic compounds > Pb (70-19%) F5 sulphides, minerals

Heavy metals in compost and soil mixturesSample Clay,

%OM, %

pH Cu,

mg kg-1

Pb,mg kg-1

Mn, mg kg-1

Zn mg kg-1

Compost - 82.2 5.80 88.00 49.82 101.86 509.32

Sandy soil 4.5 2.01 6.51 8.99 14.11 173.01 33.10

Sandy soil-compost (20:1) 0.45 5.57 6.25 11.09 16.10 194.41 55.34

Sandy soil -compost (5:1) 0.23 15.89 6.02 13.08 17.18 191.17 101.06

Clay soil 32.5 2.14 6.12 10.78 20.36 318.18 42.67

Clay soil - compost (20:1) 6.5 9.14 6.07 11.13 21.46 327.34 62.33

Clay soil -compost (5:1) 1.6 17.95 5.92 16.33 22.75 361.20 108.56

MPC (HN 60:2004) - - - 100 100 1500 300

MPC (86/278/EEC) - - - 50-140 50-300 - 150-300

Heavy metal mobile/stabile fractions incompost and soil mixtures

0%

20%

40%

60%

80%

100%Zn

0%

20%

40%

60%

80%

100%Pb

F4-F5

F1-F3

0%

20%

40%

60%

80%

100%Mn

0%

20%

40%

60%

80%

100% Cu

SampleRatio (F1-F3)/F4-F5

Pb Cu Zn Mn

Sewage sludge 0.22 0.03 1.83 2.02Compost 0.24 0.07 2.84 7.22Sandy soil 0.42 0.39 1.54 1.43Sandy soil-compost (20:1) 0.71 0.12 2.17 2.10Sandy soil-compost (5:1) 0.65 0.12 2.31 1.81Clay soil 0.37 0.21 0.22 0.37Clay soil-compost (20:1) 0.50 0.12 0.56 0.50

Clay soil-compost (5:1) 0.43 0.08 0.93 0.58

Potential heavy metal biovailability

Compost Mn >>Zn> Pb>> Cu Mixture:Sandy soil Zn> Mn>>Pb > Cu Zn>Mn >Pb > CuClay soil Mn = Pb > Zn ≈ Cu Zn>Mn >Pb>>Cu

EVALUATION OF THEHEAVY METAL BIOAVAILABILITY

2. Anaerobically processed bio-fertilizer

MaterialCu Ni Pb Zn Cd Cr Hg

Sewage sludge (Kaunas), 200 g 258.0 35.9 108.8 1422.0 21.70 95.0 1.77

Sewage sludge (Šiauliai), 200 g 115.8 15.4 68.4 1158.0 2.90 28.8 0.05

Meat-bone mass, 100 g - - - - - - -

Cement kiln dust+ K2SO4, 30% 24.3 - 184.1 54.4 9.50 - -

Final product 137.2 23.4 61.3 990.4 2.72 37.9 0.10

EU EC , 2001 100 50 100 200 0.50 100 0.50

EC No. 889/2008 70 25 45 200 0.70 70 0.40

Heavy metals in the anaerobically processed compost

*Exceed MPC

Sequential extraction of heavy metals

(F1) – exchangeable fraction

(F2) – adsorbed fraction

(F3) – oxidizable fraction (bound to organic matter)

(F4) – acid soluble fraction (bound to carbonates)

(F5) – residual fraction (bound to silicates and detritus materials

Emmerich,W. E., Lund, J. L., Page, A. L. and Chang, A. C. (1982). Solid phase form of heavy metal in sewage sludge in sewage sludge treated soils. Journal of Environmental Quality. 11, pp. 178–181

0

20

40

60

80

100

Cr Cd Ni Pb Cu Zn

Che

mic

al f

ract

ion,

%

.

F1 F2 F3 F4 F5

0

20

40

60

80

100

Cr Cd Ni Pb Cu Zn

Che

mic

al f

ract

ion,

% .

F1 F2 F3 F4 F5

before anaerobic treatment after anaerobic treatment

Heavy metal speciation

F1-F2 (0.3-18.6%) : Ni ≥ Zn > Cu ≥ Cd >Pb >Cr; Ni ≥ Zn ≥ Cu > Cd ≥Pb ≥Cr F3-F5 (81.4-99.7%): Cr>>Pb>Ni > Cd ≥ Cu ≥ Zn; Cr>>Pb≥Ni > Cd > Zn ≥ CuF5 (15-75%): Cr>> Pb >Ni>Cd ≥Cu ≥Zn; Cr>> Ni≈ Pb> Cd> Zn ≥ Cu

PbCu

Zn

F1-F3

F4-F50

1020304050607080

90100

Perc

enta

ge, %

.

a

CrCd

Ni

F1-F3

F4-F50

1020304050607080

90

100

Perc

enta

ge, %

.

a

CrCd

Ni

F1-F3

F4-F50

1020304050607080

90100

Perc

enta

ge, %

.

b

PbCu

Zn

F1-F3

F4-F50

1020304050607080

90100

Perc

enta

ge, %

.

b

before anaerobic treatment before anaerobic treatment

after anaerobic treatment after anaerobic treatment

Heavy metal mobile/stabile fractions

SampleRatio (F1-F3)/F4-F5

Cr Cd Ni Pb Cu Zn

Before treatment

0.09 0.43 0.51 0.14 0.80 0.50

After treatment

0.14 0.47 0.53 0.11 2.50 0.40

Change ratio +1.6 +1.1 1.0 -1.3 +3.1 -1.3

Potential heavy metal biovailability

Cu>>Ni≈Zn>Cd>>Pb≈Cr

Vegetative pot experiment

NutrientsK

Commercial compost

I Compost-perlite

1:1

II Compost-perlite

1:2

III Compost-perlite

1:3

N, % 0.48 2.91 1.89 1.41

P, % 0.22 3.08 2.01 1.48

K, % 0.54 2.97 1.96 1.45

Heavy metal, mg/kg DM

Growth medium

EU E

C, 2

001 Leaves of salad

Lim

it

**

Con-trol I II III Con-

trol I II III

Chromium (Cr) 6.2 24.3 16.2 12.2 100 1.30 2.50 2.81 2.25 5

Cadmium (Cd) 0.2 0.7 0.5 0.4 0.7 0.04 0.11 0.08 0.10 0.2*

Lead (Pb) 4.3 14.3 9.5 7.2 100 0.01 0.07 0.06 0.04 0.3*

Nickel (Ni) 3.9 14.1 9.4 7.1 50 1.60 3.75 3.31 3.50 10

Copper (Cu) 29 156 104 78 100 5.30 12.6 10.0 10.5 20

Zinc (Zn) 57 254 169 127 200 35 85 59 74 100

Heavy metals in growth mediumand salad leaves

* MPC, Lithuanian legislative document HN 54:2003. ** Kabata Pendias A., Pendias H. 1992. Trace elements in soils and plants, CRC Press.

Heavy metal bioaccumulation factor and potential bioavailability

Mixture/Element

Control

(Commercial

compost)

I Compost-

perlite

1:1

II Compost-

perlite

1:2

III Compost-

perlite

1:3

Potential

bioavai-

lability

Cr 0.21 0.10 0.17 0.18 0.14

Cd 0.20 0.16 0.16 0.25 0.47

Pb 0.002 0.005 0.006 0.006 0.11

Ni 0.41 0.27 0.35 0.49 0.53

Cu 0.18 0.08 0.10 0.13 2.50

Zn 0.61 0.33 0.35 0.58 0.40

Conclusions (1)

It is important to take into account amounts ofnutrients and contaminants when producingcomposts and bio-fertilizers from sewage sludge.

It is recommended:

– to optimize nutrient amounts and ratios(N:P:K 1:1:1) using amendments of otherwastes;

– to reduce HM bioavailability immobilizingthem when increasing pH, content ofcarbonates and organic matter.

Conclusions (2)

• During aerobic composting total HM amounts as well as theirpotential availability increased (Pb 0.22-0.24; Cu 0.03-0.07; Zn 1.83-2.84; Mn 2.02-7.22) due to their transfer to more mobile fractions (F1-F3 - exchangeable, carbonates and Fe-Mn oxides bound fractionsexcepting Cu which was generally bound to the organics fraction F4).

• During anaerobic sewage sludge treatment only Cu potentialavailability increased markedly (0.8-2.5) due to its’ affinity to theorganic matter while insignificant increase of Cd (0.43-0.47) and Ni(0.51-0.53) as well as decrease of Pb (0.14-0.11) and Zn (0.5-0.4) wasobserved.

• Obtained differences are due to different methods of sequentialextraction and interpretation of mobile-stable fractions as well ascould be due to different methods of sewage sludge composting.

Conclusions (3)

• Amendment of the aerobically processed compostincreased HM potential availability excepting Cu due toits’ affinity to the organic matter and behavior in thesoils due to changes in speciation:

• In the soil-compost mixtures potential heavy metal availabilityranked in the order Zn > Mn > Pb > Cu while in

• compost Mn>>Zn>Pb>> Cu,

• sandy soil Zn >Mn>>Pb > Cu,

• clay soil Mn = Pb > Zn ≈ Cu.