Quality Control

A good image for compost can be built up with assured quality and a quality label. Germany, Denmark, the Netherland, and Belgium have developed a composting system which is very important for the quality assurance. Elements of the quality assurance system are quality assurance of European composting and digestion plants (in: ECN 2008):

• Intake control

• Limits for harmful substances

• Quality criteria for the valuable constituents in the compost

• Composting production

• External control (product and/or production)

• In-house monitoring

• Quality label for the product

• Certificate for the plant and/or for the product

• Declaration of the properties of the compost

• Recommendations for use and application

• Training and qualification of the operator

• Management and operation of plants (plant assessment)

• Annual certificates

Table 12.4 shows the status of quality assurance of European composting and digestion plants. This is very important for the classification of compost and digestion quality (Table 12.5).

Table 12.4 Status of quality assurance of European composting and digestion plants (stand: Dec. 2001) (in: ECN 2008)

Country

Plants with quality assurance

Plants with quality sign or certificate

Austria

10

2

Belgium

22

10

Luxemburg

3

3

The Netherlands

22

4

Germany

429 Composting, 16 digestion

400 Composting, 10 digestion

Sweden

2 Composting, 8 digestion

-

Denmark

Draft of quality assurance system

-

Norway

Quality assurance system exists

-

United Kingdom

Quality assurance system in introduction

Table 12.5 Classification of compost and digestion quality in Europe (in: ECN 2008) Country Type of compost/quality class

Austria Quality Class A + (organic farming), Class A (high quality) and Class B

(minimum quality/noon food production areas) Belgium Yard and Vegetable, Fruit and Garden VFG Compost

Denmark Organic household waste compost with no classification up to now. No quality criteria for green/yard waste compost necessary. Germany Fresh and matured compost, mulch and potting soil compost solid and liquid digestion residues The Netherlands Compost and very good compost

Sweden Very fresh, fresh and matured compost, digestion residues

Table 12.6 Potentially toxic element limits and allowed in the EU (mg kg 1 DM) (in: ECN 2008)

Country

Cd

Cr

Cu

Hg

Ni

Pb

Zn

Austria

1

70

150

0.7

60

120

500

Belgium

1.5

70

90

1

20

120

300

Denmark

0.4

-

1,000

0.8

30

120

400

Germany

1.5

100

100

1

50

150

400

Ireland

1.5

100

100

1

50

150

350

Luxemburg

1.5

100

100

1

50

150

400

The Netherlands

1

50

60

0.3

20

100

200

Eastland

2

100

100

1

60

150

400

Sweden

1

100

100

1

50

100

300

United Kingdom

1.5

100

200

1

50

150

400

The quality criteria for the classification are the following (in: ECN 2008):

• Potentially toxic element content (Table 12.6)

• Organic pollutants

• Hygienic requirements

The level of the potentially toxic elements in compost materials used in a research by Manungufala et al. (2007) was found in the following order: Fe > Mn > Cr > Ni > Zn > Cu > Co > Cd.

Although a united compost quality system of the European Union does not exist, the European Compost Network (ECN), as an initiative of the ORBIT Association developed a Quality Assurance System providing the necessary background information and documentation to build up a European Quality Assurance System (ECN-QAS). Product definitions and characterizations of this system are shown in Table 12.7.

Silva et al. (2007) characterized a municipal solid waste compost (MSWC) based on standardized European Methods (ECN) for soil improvers and growing media and found that MSWC presents a lower C/N ratio (15) than peat and composted pine bark.

The German Federal Compost Association (BGK) has defined general quality standards comparing the following elements (Siebert 2008):

Table 12.7 Product definitions and characterizations (in: ECN 2006)

Area of

Characterization Purpose of use application

Remarks

Fresh Compost

Mature Compost

Compost as mixing component for growing media

Sanitized decomposed material (from aerobic treatment), Rate of degradation: low Sanitized decomposed material (from aerobic treatment), Rate of degradation: high Sanitized decomposed material (from aerobic treatment), Rate of degradation: very high

Soil improvement, Fertilization

Soil improvement, Fertilization

Agriculture, Recultivation

As constituent for growing media production

Agriculture, Landscaping, Horticulture, Hobby gardening

Horticulture, Growing media production

Declaration: no application on soils with new sowing or growing crops

• External monitoring: continuous and independent control of product quality

• Internal monitoring: control and documentation of the decomposition respiratory digestion process by the plants

• Quality criteria: standardization of the product quality

• Quality label: characterization of the product quality

• Compulsory declaration: description of the essential product characteristics and constituents

• Application guidelines: information on correct application

• Furnishing proof and the documents required by the plants to show treatment according to the Biowaste and Fertilizer Ordinance to the regional competent authorities

The British Composting Association has established very recently a set of guidelines for compost, called the BSI (British Standard Institute) PAS (Publicly Available Specification) 100. There are a variety of such voluntary industry standards in Europe and worldwide, such as the German Compost Association (BGK) RAL-standard for compost developed 10 years prior to the British standard, and updated recently to include separate standards for fermented by-products (from biogas reactors) and sludge. In the USA, Procter & Gamble Company sponsored the USCC in the early 1990s to develop compost process and product standards called TMECC, still in a draft state. These standardization programs are intended to provide structure in the composting community for handling the entire composting process from raw materials and production methods, through quality control and lab testing.

Validation of treatment plants should be done with the exposition of representative test organisms, followed by the determination of the inactivating rate after the exposition time, so that the technical parameters that must be kept during the constant process control cab be defined (HACCP-concept). The validation with representative test organisms defines the technical parameters, which must be kept and help to measure the residual risk during the application of the treated material in the right areas. The monitoring of the end products can be meaningful, if for technical reasons validation is not possible by exposition of test organisms and if the organisms (e.g., E. coli or enterocci) can be found in a large number in the raw material. The monitoring of the final products on natural test organisms is easily feasible and also cheap because it is not necessary to accomplish additional installations (Philipp 2008).

Sharma et al. (2005) developed robust calibrations for some of the key parameters from the spectra or fresh phase I and II composts and found by the laboratory measurement that for phase I samples were greater than those of the phase II samples except for ash, due to a higher degree of heterogeneity in the substrate.

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