- Email: [email protected]
The evaluation of compost quality
310
trends in analytical chemistry, vol. 17, no. 5, 1998
[ 32 ] CEN TC 292 WG2 draft compliance test for monolithic materials ( in preparation ). [ 33 ] H.A. van der Sloot, D. Hoede, Development of a concise test for monolithic materials ( in preparation ). [ 34 ] J.P.G.M. Schreurs, H.A. van der Sloot, Ch.F. Hendriks,
in: Proceedings WASCON 1997 Conference `Putting Theory Into Practice', June 4^6, 1997, Houthem, The Netherlands. [ 35 ] D. Hockley, H.A. van der Sloot, Environ. Sci. Technol. 25 ( 1991 ) 1408^1414.
The evaluation of compost quality A. Gomez*
Deèpartement Agronomique, Institut National de Recherche, 71 avenue Edouard Bourleaux, F-33383 Villenave d'Ornon Cedex, France Composts are considered as organic soil improvement, however, with the introduction of organic substances from industrial or municipal wastes, they should be considered as secondary wastes. The harmonisation and standardization of methods for soils, composts and other wastes is needed for comparable and more comprehensive data for the different countries in the European Union. z1998 Published by Elsevier Science B.V. Keywords: Compost analysis; Extracting processes for compost
Usually, composts are used for land¢ll in agricultural land. It is thus important to evaluate the quality of the ¢nal product, in order to protect the quality of crops and / or the environment. Different analytical methods may be used to determine the composition of composts: i.e. the total or extractable content. These methods are quite similar to those used for soil analysis. An overview of the different processes and the main organic component materials used for compost production is given here. The main extracting processes used to evaluate compost quality and the risk bound with their use are considered.
2. Compost production processes 1. Introduction Traditionally, composts are made with plant material. They are not considered as waste but as organic soil improvement. With the introduction of organic substances such as industrial or municipal wastes, for instance, composts should be considered as secondary wastes. The reasons for the use of wastes in the composting process are multiple: recycling elements with agronomic interest ( e.g. phosphorus, nitrogen, organic matter ), reduction of the initial volume of waste, degradation of toxic organic substances, production of energy ( fermentation followed by the composting process ), and decrease of heavy metals content of a waste by dilution with other organic substances to allow for its agricultural use. Due to the origin of organic component material, composts may contain heavy metals, toxic organic substances, inert components.
Composting is a microbial reaction of mineralisation and partial humi¢cation of organic substances which, under optimum condition, take place within a month. Composting requires that the process be mostly aerobic so that organic matter is partially mineralised and humi¢ed. To make composting suitable for the waste disposal industry requires that three fundamental points are met: brief process with low energy consumption, à aa guarantee the end-product is standard and not à only safe forthat agricultural use but also of satisfactory
à
fertilising value, hygienic safety of plant and end-products [1].
For these reasons composting cannot be spontaneous, but must be controlled in order to obtain a high quality end-product. Several systems are used in view to control the microbial activity.
*Tel.: 346 386 46 15; Fax: 346 386 43 72. 0165-9936/98/$19.00 PII S 0 1 6 5 - 9 9 3 6 ( 9 8 ) 0 0 0 1 3 - 2
ß 1998 Published by Elsevier Science B.V. All rights reserved.
TRAC 2444 1-5-98
311
trends in analytical chemistry, vol. 17, no. 5, 1998
Table 1 Concentration of total trace metals in French sewage sludge (Wg / g of dry matter ) [ 2 ] Element
Cd Cr
Cu
Mean Median
5.3 80 334 4.5 64 286
Hg
Ni
Pb
2.7 2.1
39 133 35 107
Se Zn 7.4 921 3.2 761
2.1. Open systems 2.1.1. Turned pile This classical process is simple but it has some disadvantages. Much space is needed and the control of the level of oxygen is bad. Maturation of composts with this process is not very constant. 2.1.2. Static pile A static composting pile is aerated by forced air. This process allows the control of exact amounts of oxygen and also the control of moisture and temperature of the pile. 2.2. Closed systems 2.2.1. Vertical reactor Vertical reactor can be continuous ^ mass is introduced in one operation ^ or discontinuous ^ masses are introduced at different times. The main disadvantage
is the extreme dif¢culty of controlling the process, mainly the oxygenation of the mass. The lower part is over-ventilated, dried and cooled, the upper part is insuf¢ciently aerated ^ the air is warm, enriched in carbon dioxide, with a low level of oxygen. 2.2.2. Horizontal reactor In this type of equipment, it is possible to control under good conditions oxygenation of the mass, blowing air in from the bottom, humidity and temperature of composting. It is possible to turn the pile inside and to have a very uniform production of compost.
3. Main organic component materials In the traditional process to produce compost, agricultural plant material is used. This class of compost has a very low content of trace metals, and when compost is correctly maturated only agronomic analyses are needed to evaluate the fertilising value. Today, composts are produced with other organic sources: from food and agriculture industries. These à Wastes wastes are composed of organic matter, and are not mixed with other impurities. They are free of contamination. Town horticultural wastes from
Table 2 The mean composition in France of household refuse [ 3 ] Component
% D.M.
Cd
Cr
Cu
Hg
Ni
Pb
Zn
Putricible Paper Glazed paper Cardboard Composite Textiles Sanitary textiles Polyester leaf Polyvinyl Ch. Polyethylene P.E. and PP bottles Polystyrene Other plastics Combustible materials Glass Ferrous metals Aluminium Non-combustible materials Battery 8 to 20 mm 6 8 mm
11 11 6 9 2 3 4 6 2 0.6 1 1 1 4 10 4 1 2 0.8 12 8
0.47 0.77 2.8 0.4 2.3 3.7 4.3 1.2 0.77 2.6 36.3 1.9 25.1 7.9 0.49 0.23 12.2 0.88 10.4 0.98 4.28
6 10 14 13 10 6 18 58 128 77 27 28 38 266 8 289 225 47 2 5 30
17 36 52 41 41 115 31 99 56 174 19 95 803 152 6.8 200 265 11 461 33 346
0 0 0.15 0 0 1.04 0.12 0.15 0.12 0 0 0.18 0.12 0 0 0.96 0 0 3064 0 0.12
9.1 6.9 6.1 5.2 19 14 23 76 160 87 27 41 40 40 4.8 227 80 59 72 11 24
170 22 33 22 24 32 198 132 1280 85 37 2890 380 300 120 158 173 31 175 41 380
83 50 59 93 65 158 323 276 85 143 124 136 287 1208 7 135 121 61 198 000 299 674
TRAC 2446 1-5-98
312
trends in analytical chemistry, vol. 17, no. 5, 1998
Table 3 Trace element content of different MSW composts ( elements in Wg / g of dry matter ) [ 4 ] Trace elements
As
Cd
Cr
Cu
Hg
Ni
Pb
Zn
MSW compost without separation MSW compost with mechanical separation MSW compost with selective source separation
7.3 2.9
7.3 2.1 0.74
164 75 19.7
512 290 33
3.3 0.14
112 40 9.5
850 740 83
1640 870 160
à à
park and garden (bushes, leaves of trees, wood ships, grass). These wastes are polluted by lead from the combustion of gasoline and with all the metal produced by town activities (e.g. zinc and cadmium from the wear of tires). These wastes are evaluated at 600 000 t/year in France. Tree bark, sawdust, wood chip. Because of the high C/N ratio, these materials need the addition of a nitrogen-rich material, in some cases manure or pig slurry, but more often sewage sludge. Input of pig slurry or sewage sludge strongly enhances the level of heavy metals in the end-product. Sewage sludge. This is frequently composted with wood wastes. It is a way to dilute heavy metal in the mass to obtain levels of trace metals suf¢ciently low to be used in agriculture. The production of sewage sludge in France is about 1 Mt (see Table 1).
Table 4 Composition and properties of GFT compost ( elements in Wg / g of dry matter ) Parameter
Average ( n = 82 )
Standard deviation
Density kg / m3 Dry matter content Percent water Percent organic matter Cd mg / kg D.M. Cr Cu Hg Ni Pb Zn As N-tot g / kg D.M. P K Mg Cl
650 70 35 38 0.5 14 25 0.12 7 45 160 4 17 2.7 7.5 2.5 3.4
90 8 6 5 0.1 7 6 0.05 3 15 30 1 2 0.57 1.5 0.7 1.2
à Household more than
refuse. In France the production is 21 Mt. The process of composting household refuse is well known and the quality of the product is dependent on the quality of the primary material. The mean composition in France of this waste is given in Table 2 (elements in Wg/g of dry matter).
Usually, the quality of composts is related to inert content: domestic refuse compost ( inert 6 6% of D.M. ), good quality town refuse compost ( inert 6 15^20% of D.M. ), mean quality town refuse compost ( inert 6 25^30% of D.M. ). Regarding Table 2, it can be seen that inert components are strongly involved in enrichment of compost with metals. It is possible to produce composts with a mixture of different wastes, and in this case the pollution of the end-product is increased because it is the sum of the contamination of the whole material. During the composting process some organic contaminants disappear, the product is sanitised during the pasteurisation period, but trace metals remain in the end-product, and this constitutes a very important problem from an agricultural and environmental point of view. Considering that the composting process leads to a loss of about 50% of the initial mass, the level of metals increases by a factor two [ 3 ]. Table 5 Trace metals, organic carbon and nitrogen extracted with water or potassium pyrophosphate in fresh or mature composts [ 5 ]
Reference: Quality control GFT compost. Source: Vereniging van Afvalverwerkers-VVAV.
Cd Wg / g D.M. Cu Wg / g D.M. Pb Wg / g D.M. C.O.T. mg / l N mg / l
TRAC 2446 1-5-98
Fresh compost
Mature compost
H2 O
K4 P2 O7 0.1 M
H2 O
K4 P2 O 7 0.1 M
0.9 3.7 2.1 270 5.6
0.3 8.8 110 1200 2.8
0.2 8 1 330 8.4
0.7 7.4 130 2000 8.4
313
trends in analytical chemistry, vol. 17, no. 5, 1998
Table 6 Organic and mineral composition of humic acids extracted from soil and compost [ 6 ]
Ashes % C% N% C /N S% P2 O5 Wg / g Ca Wg / g Fe Wg / g Zn Wg / g Pb Wg / g C.E.C. pH 6
Soil
MSW compost ( 4 month maturation )
24.8 48.7 2.15 18.6 0.51 4134 116 23969 48 31 332
10.1 48.2 5.41 8.9 1.07 5348 109 2026 207 152 160
contents are higher for composts, with a resulting strong capacity to bind trace elements. The infra red spectra show the presence of N-H stretching associated to the O-H stretching by H bounds, clearly indicating the presence of protein groups in the humic acids, and con¢rming the ability to bind with metals [ 6 ]. A study of biological stability with a respirometric technique shows that humic compounds from composts are easily biodegradable [ 6 ].
5. Relevant parameters for extraction / leaching processes
4. Quality of composts 4.1. Effect of organic starting material
Depending on the origin of organic components, the composition of composts may change signi¢cantly. In Table 3, the metal composition of different composts is given. In Table 4, the composition and properties of composts derived from source separated municipal putricible and garden waste are given. 4.2. Maturation effect
Maturation of compost has a great in£uence on the solubility / extraction of metal, organic carbon and nitrogen. As far as there is a relationship between solubility, transportation of trace elements by organic soluble carbon and bioavailability, maturation can be considered an important factor in heavy metal plant uptake from composts. Table 5 shows the evolution of solubility of metals at two steps of maturation. 4.3. Comparison of humic substances from soil and compost
Comparing the chemical composition of humic substances extracted from soil ( sandy podzolic soil ) and compost (MSW ), important differences can be seen (Table 6 ). Ash content is lower for compost, and the humic acids are weakly bound with the mineral content of the waste, as can be veri¢ed by infra red spectra at 1000 and 1100 cm31 [ 6 ]. Nitrogen and sulphur
Clearly organic matter content is one of the most relevant parameters in extraction / leaching processes. It facilitates metal transportation by means of soluble metal complexes ^ pH is of great importance in this case. Mn and Fe oxides may reduce the mobility by sorption processes and for this reason are also an important factor ^ in this case redox conditions are important. Soluble salts may always be present in composts. Percolation therefore mainly dominates the release of metals in the case of composts.
6. Extracting / leaching tests All the extracting reagents for soils are frequently used for composts: e.g. neutral salts such as ammonium acetate, EDTA, acid solutions, oxidising / acid reagents. But because of the relatively high level of trace elements, it is possible to work with water ( soluble part ) or with a weak extraction procedure ( CaCl2 , MgCl2 , NaNO3 , T ). These extraction procedures give a good idea of nutrient availability for crops and indications of the risk of release of harmful substances. If one needs to predict, in the medium term, the mobility or the availability of trace elements, it is useful to work with alkaline reagents. Dissolving a greater quantity of organic matter gives a good indication of the risk for crops and ground waters. Many reagents may be used for this purpose, and some data are available for potassium pyrophosphate [ 5 ].
7. Conclusion Composts are not considered as waste but as organic soil improvement, so they can be incorporated in soils.
TRAC 2446 1-5-98
314
trends in analytical chemistry, vol. 17, no. 5, 1998
All the processes of characterisation, sampling, pretreatment, extraction and leaching tests, analysis, etc. have to be considered on this basis. They must be studied and standardised similarly as for soils. In addition, some speci¢c tests, taking into account the high content of organic matter and trace elements, e.g. alkaline extraction, need further studies to be done. The harmonisation and standardisation of methods for soils, composts and other wastes is needed, with the aim of having comparable and more comprehensive data for the different countries of the European Union.
References [ 1 ] M. de Bertoldi, G. Vallini and A. Pera, in J.K.R. Gasser ( Editor ), Composting of Agricultural and Other Wastes, Elsevier Amsterdam, 1984, pp. 27^34. [ 2 ] J. Wiart and M. Verdier, Rapport AGHTM et FNDAE, 1994, 60 pp. [ 3 ] B. Morvan, J. Carre, TSM 2 ( 1995 ) 138^140. [ 4 ] W. de Feyter, in Symposium International sur le Traitement des Deèchets, Pollutec 94, 18^20 October 1994, Lyon, 1994, pp. 199^211. [ 5 ] P. Prudent, Theése Universiteè de Marseille, France, 1993. [ 6 ] A. Gomez and C. Lejeune, in M. de Bertoldi, M.P. Ferranti, P. L'Hermite and F. Zucconi ( Editors ), Compost: Production, Quality and Use, 1986.
Conclusions of the workshop: standards, measurements and testing for solid waste management Ph. Quevauviller*
European Commission, Standards Measurements and Testing Programme, DG XII (M075 3 / 09 ), Rue de la Loi 200, B-1049 Brussels, Belgium The quality of waste treatment processes and of ¢nal ( recycled ) products relies upon the availability of standards and testing methods. There is a clear need to develop ( and validate ) methods, e.g. for the control of treatment processes or for the characterisation of the end-products in view of their use in land¢ll, concrete, construction materials, etc. In this respect, the collaboration between industry and research organisations should be strengthened. In order to stimulate partnership between industry and research for the identi¢cation of possible actions to be undertaken in the ¢eld of standards, measurements and testing for solid waste management, the SMp pT programme of the European Commission organised a workshop. This paper summarises the round-table discussions and expert recommendations, as well as an outline of the programme of the workshop
*Corresponding author.
which was held in Pau ( France ), 5^7 May 1997. z1998 Elsevier Science B.V. Keywords: Solid waste; Waste treatment processes; SMpT Programme
1. Aim and organisation of the workshop The new regulations relating to industrial waste management have the ambitious objective to stop the direct release of wastes by 2002, by stipulating that wastes of different origin should be recycled where possible. The effects of different waste treatment processes should be accurately determined to ensure correct waste management and the industry is aware that signi¢cant efforts are required to optimise these treatments for obvious economic reasons. The quality of treatment processes and of ¢nal ( recycled ) products relies upon the availability of standards ( such as those prepared by CEN or ISO ) and testing methods ( e.g. chemical analysis for the assessment of environmental risks or land¢ll use ). There is a clear need to develop
0165-9936/98/$19.00 PII S 0 1 6 5 - 9 9 3 6 ( 9 7 ) 0 0 1 0 9 - X
ß 1998 Elsevier Science B.V. All rights reserved.
TRAC 2446 1-5-98
trends in analytical chemistry, vol. 17, no. 5, 1998
[ 32 ] CEN TC 292 WG2 draft compliance test for monolithic materials ( in preparation ). [ 33 ] H.A. van der Sloot, D. Hoede, Development of a concise test for monolithic materials ( in preparation ). [ 34 ] J.P.G.M. Schreurs, H.A. van der Sloot, Ch.F. Hendriks,
in: Proceedings WASCON 1997 Conference `Putting Theory Into Practice', June 4^6, 1997, Houthem, The Netherlands. [ 35 ] D. Hockley, H.A. van der Sloot, Environ. Sci. Technol. 25 ( 1991 ) 1408^1414.
The evaluation of compost quality A. Gomez*
Deèpartement Agronomique, Institut National de Recherche, 71 avenue Edouard Bourleaux, F-33383 Villenave d'Ornon Cedex, France Composts are considered as organic soil improvement, however, with the introduction of organic substances from industrial or municipal wastes, they should be considered as secondary wastes. The harmonisation and standardization of methods for soils, composts and other wastes is needed for comparable and more comprehensive data for the different countries in the European Union. z1998 Published by Elsevier Science B.V. Keywords: Compost analysis; Extracting processes for compost
Usually, composts are used for land¢ll in agricultural land. It is thus important to evaluate the quality of the ¢nal product, in order to protect the quality of crops and / or the environment. Different analytical methods may be used to determine the composition of composts: i.e. the total or extractable content. These methods are quite similar to those used for soil analysis. An overview of the different processes and the main organic component materials used for compost production is given here. The main extracting processes used to evaluate compost quality and the risk bound with their use are considered.
2. Compost production processes 1. Introduction Traditionally, composts are made with plant material. They are not considered as waste but as organic soil improvement. With the introduction of organic substances such as industrial or municipal wastes, for instance, composts should be considered as secondary wastes. The reasons for the use of wastes in the composting process are multiple: recycling elements with agronomic interest ( e.g. phosphorus, nitrogen, organic matter ), reduction of the initial volume of waste, degradation of toxic organic substances, production of energy ( fermentation followed by the composting process ), and decrease of heavy metals content of a waste by dilution with other organic substances to allow for its agricultural use. Due to the origin of organic component material, composts may contain heavy metals, toxic organic substances, inert components.
Composting is a microbial reaction of mineralisation and partial humi¢cation of organic substances which, under optimum condition, take place within a month. Composting requires that the process be mostly aerobic so that organic matter is partially mineralised and humi¢ed. To make composting suitable for the waste disposal industry requires that three fundamental points are met: brief process with low energy consumption, à aa guarantee the end-product is standard and not à only safe forthat agricultural use but also of satisfactory
à
fertilising value, hygienic safety of plant and end-products [1].
For these reasons composting cannot be spontaneous, but must be controlled in order to obtain a high quality end-product. Several systems are used in view to control the microbial activity.
*Tel.: 346 386 46 15; Fax: 346 386 43 72. 0165-9936/98/$19.00 PII S 0 1 6 5 - 9 9 3 6 ( 9 8 ) 0 0 0 1 3 - 2
ß 1998 Published by Elsevier Science B.V. All rights reserved.
TRAC 2444 1-5-98
311
trends in analytical chemistry, vol. 17, no. 5, 1998
Table 1 Concentration of total trace metals in French sewage sludge (Wg / g of dry matter ) [ 2 ] Element
Cd Cr
Cu
Mean Median
5.3 80 334 4.5 64 286
Hg
Ni
Pb
2.7 2.1
39 133 35 107
Se Zn 7.4 921 3.2 761
2.1. Open systems 2.1.1. Turned pile This classical process is simple but it has some disadvantages. Much space is needed and the control of the level of oxygen is bad. Maturation of composts with this process is not very constant. 2.1.2. Static pile A static composting pile is aerated by forced air. This process allows the control of exact amounts of oxygen and also the control of moisture and temperature of the pile. 2.2. Closed systems 2.2.1. Vertical reactor Vertical reactor can be continuous ^ mass is introduced in one operation ^ or discontinuous ^ masses are introduced at different times. The main disadvantage
is the extreme dif¢culty of controlling the process, mainly the oxygenation of the mass. The lower part is over-ventilated, dried and cooled, the upper part is insuf¢ciently aerated ^ the air is warm, enriched in carbon dioxide, with a low level of oxygen. 2.2.2. Horizontal reactor In this type of equipment, it is possible to control under good conditions oxygenation of the mass, blowing air in from the bottom, humidity and temperature of composting. It is possible to turn the pile inside and to have a very uniform production of compost.
3. Main organic component materials In the traditional process to produce compost, agricultural plant material is used. This class of compost has a very low content of trace metals, and when compost is correctly maturated only agronomic analyses are needed to evaluate the fertilising value. Today, composts are produced with other organic sources: from food and agriculture industries. These à Wastes wastes are composed of organic matter, and are not mixed with other impurities. They are free of contamination. Town horticultural wastes from
Table 2 The mean composition in France of household refuse [ 3 ] Component
% D.M.
Cd
Cr
Cu
Hg
Ni
Pb
Zn
Putricible Paper Glazed paper Cardboard Composite Textiles Sanitary textiles Polyester leaf Polyvinyl Ch. Polyethylene P.E. and PP bottles Polystyrene Other plastics Combustible materials Glass Ferrous metals Aluminium Non-combustible materials Battery 8 to 20 mm 6 8 mm
11 11 6 9 2 3 4 6 2 0.6 1 1 1 4 10 4 1 2 0.8 12 8
0.47 0.77 2.8 0.4 2.3 3.7 4.3 1.2 0.77 2.6 36.3 1.9 25.1 7.9 0.49 0.23 12.2 0.88 10.4 0.98 4.28
6 10 14 13 10 6 18 58 128 77 27 28 38 266 8 289 225 47 2 5 30
17 36 52 41 41 115 31 99 56 174 19 95 803 152 6.8 200 265 11 461 33 346
0 0 0.15 0 0 1.04 0.12 0.15 0.12 0 0 0.18 0.12 0 0 0.96 0 0 3064 0 0.12
9.1 6.9 6.1 5.2 19 14 23 76 160 87 27 41 40 40 4.8 227 80 59 72 11 24
170 22 33 22 24 32 198 132 1280 85 37 2890 380 300 120 158 173 31 175 41 380
83 50 59 93 65 158 323 276 85 143 124 136 287 1208 7 135 121 61 198 000 299 674
TRAC 2446 1-5-98
312
trends in analytical chemistry, vol. 17, no. 5, 1998
Table 3 Trace element content of different MSW composts ( elements in Wg / g of dry matter ) [ 4 ] Trace elements
As
Cd
Cr
Cu
Hg
Ni
Pb
Zn
MSW compost without separation MSW compost with mechanical separation MSW compost with selective source separation
7.3 2.9
7.3 2.1 0.74
164 75 19.7
512 290 33
3.3 0.14
112 40 9.5
850 740 83
1640 870 160
à à
park and garden (bushes, leaves of trees, wood ships, grass). These wastes are polluted by lead from the combustion of gasoline and with all the metal produced by town activities (e.g. zinc and cadmium from the wear of tires). These wastes are evaluated at 600 000 t/year in France. Tree bark, sawdust, wood chip. Because of the high C/N ratio, these materials need the addition of a nitrogen-rich material, in some cases manure or pig slurry, but more often sewage sludge. Input of pig slurry or sewage sludge strongly enhances the level of heavy metals in the end-product. Sewage sludge. This is frequently composted with wood wastes. It is a way to dilute heavy metal in the mass to obtain levels of trace metals suf¢ciently low to be used in agriculture. The production of sewage sludge in France is about 1 Mt (see Table 1).
Table 4 Composition and properties of GFT compost ( elements in Wg / g of dry matter ) Parameter
Average ( n = 82 )
Standard deviation
Density kg / m3 Dry matter content Percent water Percent organic matter Cd mg / kg D.M. Cr Cu Hg Ni Pb Zn As N-tot g / kg D.M. P K Mg Cl
650 70 35 38 0.5 14 25 0.12 7 45 160 4 17 2.7 7.5 2.5 3.4
90 8 6 5 0.1 7 6 0.05 3 15 30 1 2 0.57 1.5 0.7 1.2
à Household more than
refuse. In France the production is 21 Mt. The process of composting household refuse is well known and the quality of the product is dependent on the quality of the primary material. The mean composition in France of this waste is given in Table 2 (elements in Wg/g of dry matter).
Usually, the quality of composts is related to inert content: domestic refuse compost ( inert 6 6% of D.M. ), good quality town refuse compost ( inert 6 15^20% of D.M. ), mean quality town refuse compost ( inert 6 25^30% of D.M. ). Regarding Table 2, it can be seen that inert components are strongly involved in enrichment of compost with metals. It is possible to produce composts with a mixture of different wastes, and in this case the pollution of the end-product is increased because it is the sum of the contamination of the whole material. During the composting process some organic contaminants disappear, the product is sanitised during the pasteurisation period, but trace metals remain in the end-product, and this constitutes a very important problem from an agricultural and environmental point of view. Considering that the composting process leads to a loss of about 50% of the initial mass, the level of metals increases by a factor two [ 3 ]. Table 5 Trace metals, organic carbon and nitrogen extracted with water or potassium pyrophosphate in fresh or mature composts [ 5 ]
Reference: Quality control GFT compost. Source: Vereniging van Afvalverwerkers-VVAV.
Cd Wg / g D.M. Cu Wg / g D.M. Pb Wg / g D.M. C.O.T. mg / l N mg / l
TRAC 2446 1-5-98
Fresh compost
Mature compost
H2 O
K4 P2 O7 0.1 M
H2 O
K4 P2 O 7 0.1 M
0.9 3.7 2.1 270 5.6
0.3 8.8 110 1200 2.8
0.2 8 1 330 8.4
0.7 7.4 130 2000 8.4
313
trends in analytical chemistry, vol. 17, no. 5, 1998
Table 6 Organic and mineral composition of humic acids extracted from soil and compost [ 6 ]
Ashes % C% N% C /N S% P2 O5 Wg / g Ca Wg / g Fe Wg / g Zn Wg / g Pb Wg / g C.E.C. pH 6
Soil
MSW compost ( 4 month maturation )
24.8 48.7 2.15 18.6 0.51 4134 116 23969 48 31 332
10.1 48.2 5.41 8.9 1.07 5348 109 2026 207 152 160
contents are higher for composts, with a resulting strong capacity to bind trace elements. The infra red spectra show the presence of N-H stretching associated to the O-H stretching by H bounds, clearly indicating the presence of protein groups in the humic acids, and con¢rming the ability to bind with metals [ 6 ]. A study of biological stability with a respirometric technique shows that humic compounds from composts are easily biodegradable [ 6 ].
5. Relevant parameters for extraction / leaching processes
4. Quality of composts 4.1. Effect of organic starting material
Depending on the origin of organic components, the composition of composts may change signi¢cantly. In Table 3, the metal composition of different composts is given. In Table 4, the composition and properties of composts derived from source separated municipal putricible and garden waste are given. 4.2. Maturation effect
Maturation of compost has a great in£uence on the solubility / extraction of metal, organic carbon and nitrogen. As far as there is a relationship between solubility, transportation of trace elements by organic soluble carbon and bioavailability, maturation can be considered an important factor in heavy metal plant uptake from composts. Table 5 shows the evolution of solubility of metals at two steps of maturation. 4.3. Comparison of humic substances from soil and compost
Comparing the chemical composition of humic substances extracted from soil ( sandy podzolic soil ) and compost (MSW ), important differences can be seen (Table 6 ). Ash content is lower for compost, and the humic acids are weakly bound with the mineral content of the waste, as can be veri¢ed by infra red spectra at 1000 and 1100 cm31 [ 6 ]. Nitrogen and sulphur
Clearly organic matter content is one of the most relevant parameters in extraction / leaching processes. It facilitates metal transportation by means of soluble metal complexes ^ pH is of great importance in this case. Mn and Fe oxides may reduce the mobility by sorption processes and for this reason are also an important factor ^ in this case redox conditions are important. Soluble salts may always be present in composts. Percolation therefore mainly dominates the release of metals in the case of composts.
6. Extracting / leaching tests All the extracting reagents for soils are frequently used for composts: e.g. neutral salts such as ammonium acetate, EDTA, acid solutions, oxidising / acid reagents. But because of the relatively high level of trace elements, it is possible to work with water ( soluble part ) or with a weak extraction procedure ( CaCl2 , MgCl2 , NaNO3 , T ). These extraction procedures give a good idea of nutrient availability for crops and indications of the risk of release of harmful substances. If one needs to predict, in the medium term, the mobility or the availability of trace elements, it is useful to work with alkaline reagents. Dissolving a greater quantity of organic matter gives a good indication of the risk for crops and ground waters. Many reagents may be used for this purpose, and some data are available for potassium pyrophosphate [ 5 ].
7. Conclusion Composts are not considered as waste but as organic soil improvement, so they can be incorporated in soils.
TRAC 2446 1-5-98
314
trends in analytical chemistry, vol. 17, no. 5, 1998
All the processes of characterisation, sampling, pretreatment, extraction and leaching tests, analysis, etc. have to be considered on this basis. They must be studied and standardised similarly as for soils. In addition, some speci¢c tests, taking into account the high content of organic matter and trace elements, e.g. alkaline extraction, need further studies to be done. The harmonisation and standardisation of methods for soils, composts and other wastes is needed, with the aim of having comparable and more comprehensive data for the different countries of the European Union.
References [ 1 ] M. de Bertoldi, G. Vallini and A. Pera, in J.K.R. Gasser ( Editor ), Composting of Agricultural and Other Wastes, Elsevier Amsterdam, 1984, pp. 27^34. [ 2 ] J. Wiart and M. Verdier, Rapport AGHTM et FNDAE, 1994, 60 pp. [ 3 ] B. Morvan, J. Carre, TSM 2 ( 1995 ) 138^140. [ 4 ] W. de Feyter, in Symposium International sur le Traitement des Deèchets, Pollutec 94, 18^20 October 1994, Lyon, 1994, pp. 199^211. [ 5 ] P. Prudent, Theése Universiteè de Marseille, France, 1993. [ 6 ] A. Gomez and C. Lejeune, in M. de Bertoldi, M.P. Ferranti, P. L'Hermite and F. Zucconi ( Editors ), Compost: Production, Quality and Use, 1986.
Conclusions of the workshop: standards, measurements and testing for solid waste management Ph. Quevauviller*
European Commission, Standards Measurements and Testing Programme, DG XII (M075 3 / 09 ), Rue de la Loi 200, B-1049 Brussels, Belgium The quality of waste treatment processes and of ¢nal ( recycled ) products relies upon the availability of standards and testing methods. There is a clear need to develop ( and validate ) methods, e.g. for the control of treatment processes or for the characterisation of the end-products in view of their use in land¢ll, concrete, construction materials, etc. In this respect, the collaboration between industry and research organisations should be strengthened. In order to stimulate partnership between industry and research for the identi¢cation of possible actions to be undertaken in the ¢eld of standards, measurements and testing for solid waste management, the SMp pT programme of the European Commission organised a workshop. This paper summarises the round-table discussions and expert recommendations, as well as an outline of the programme of the workshop
*Corresponding author.
which was held in Pau ( France ), 5^7 May 1997. z1998 Elsevier Science B.V. Keywords: Solid waste; Waste treatment processes; SMpT Programme
1. Aim and organisation of the workshop The new regulations relating to industrial waste management have the ambitious objective to stop the direct release of wastes by 2002, by stipulating that wastes of different origin should be recycled where possible. The effects of different waste treatment processes should be accurately determined to ensure correct waste management and the industry is aware that signi¢cant efforts are required to optimise these treatments for obvious economic reasons. The quality of treatment processes and of ¢nal ( recycled ) products relies upon the availability of standards ( such as those prepared by CEN or ISO ) and testing methods ( e.g. chemical analysis for the assessment of environmental risks or land¢ll use ). There is a clear need to develop
0165-9936/98/$19.00 PII S 0 1 6 5 - 9 9 3 6 ( 9 7 ) 0 0 1 0 9 - X
ß 1998 Elsevier Science B.V. All rights reserved.
TRAC 2446 1-5-98