Summary and conclusions, Miljøstyrelsen

DEHP i husholdningsaffald

Summary and conclusions

Background and objectives

A number of recent studies in Denmark on contaminants in biologically treated waste has revealed problems with regard to compliance with current threshold limits for the plasticizer DEHP in organic fertilisers produced from the organic fraction of domestic waste. This can limit the possibilities of recycling for this waste category.

Therefore, the Danish Environmental Protection Agency has financed this study, which has two main objectives:

to develop methods and procedures for sampling and analysis of domestic waste for use as organic fertiliser;

to investigate the possible relation between waste collection schemes and contents of DEHP in the waste, and to outline possible future collection and pre-treatment strategies.

Activities

The study comprised three main categories of activities:

Identification of possibilities and strategies for representative sampling of waste at facilities for biological treatment of domestic waste, and practical testing of sampling equipment and methods. For that purpose, a review and description of the existing Danish treatment plants was made.
Development and documentation of a laboratory method for homogenisation and work-up of samples of organic domestic waste, primarily with the aim of determining the content of DEHP.
Analysis and assessment of the possible relation between the quality (purity) of the organic waste fraction and the content of DEHP through an investigation at selected Danish plants for biological treatment of domestic waste. Proposal of a strategy to reduce the content of DEHP in this waste category to an acceptable level.

1. Strategies and methods for sampling of domestic waste

There are two main types of processes used in Denmark for biological treatment of domestic waste (composting and anaerobic digestion for production of biogas) and about 20 facilities carrying out such treatments. Despite this modest number of facilities, there are so many specific differences in design and operation procedures that it has been necessary to define seven treatment scenarios to cover the spectrum of situations that could become relevant in an environmental control context.

Basically, the purpose of the environmental quality control of the biowaste or the derived organic fertiliser is to ensure that the environmental loads of various contaminants are kept at an acceptably low level. The sampling procedure should therefore focus on the fraction of the waste that is actually being treated biologically and subsequently is used for soil improvement purposes in agriculture and elsewhere. At the same time the current rules for quality control must be taken into account.

The main issue to tackle in that context is linked to the regulatory requirement that the quality standards must be observed for each waste fraction i.e. before any mixing of different types of waste (e.g. household waste with garden waste) takes place. This requirement will cause considerable practical problems at the treatment plants since the samples taken must also be representative of the waste received at the plant. Therefore, it is important that the rules are interpreted and administered in a way so as to comply with the overall purpose of measuring contaminant levels in the waste while at the same time not becoming an obstacle to the desired extension of biological treatment of biowaste in Denmark.

In particular, a reasonable interpretation is important for the following:

The term "producer of waste" must be interpreted in an operational manner. This means that organic domestic waste delivered to a treatment plant from different places, but according to identical prescriptions of waste sorting and collection, should be perceived as waste from only one producer. If not, it would be necessary to control every truck load separately which, obviously, would hardly be possible in practice. Neither is it considered necessary due to the homogeneity of the Danish households with regard to food consumption, use of everyday products etc.

Sampling should be allowed after the addition of materials for structural improvement of the waste matrix during the biological treatment process such as garden/park waste, straw or newspapers. Fixed standard contents of various contaminants in such materials could be determined after which simple back-calculations could be made of the contents in the household waste itself. Hereby practical sampling difficulties could be reduced considerably and, in many cases, a higher degree of representativity of samples obtained.

A number of practical methods and equipment for sampling and partial homogenisation of household waste have been tested and suitable equipment has been identified that can produce samples which can be handled by analytical laboratories in a routine manner.

2. Homogenisation and work-up of household waste samples in the laboratory

The study has included experimental work to develop a laboratory method for final homogenisation of household waste samples (with contents of plastic and other impurities). The method uses an initial strong freezing of the sample material by means of liquid nitrogen followed by division into finer particles in a professional mincing machine.

In addition to this, a number of extraction methods for DEHP from the homogenised sample were tested. However, no justification was found for the replacement of the method currently in use, the method of the Danish EPA for sewage sludge analysis. The combined method (homogenisation, extraction and analysis) was documented using waste from three different treatment plants and a precision of ± 30% was achieved. This is considered acceptable for a sample matrix as complex as household waste.

3. Relation between waste quality and content of DEHP

To examine the possible relation between waste separation efficiency and content of DEHP in source separated household waste, a programme of sampling and analyses at six selected biological treatment plants was conducted in the autumn of 2000. Three biogas plants and three composting plants were selected for the programme which beforehand were believed to be grouped in pairs in three categories ("good", "average" and "poor") with regard to the degree of source separation. The results showed that 10 out of 11 samples from "good" and "average" plants had contents of DEHP well below the maximum allowable concentration (MAC). The last sample had a visual appearance that was atypical for the plant in question. At the "poor" plants five out of six samples exceeded the MAC for DEHP.

The conclusion is that in general the existing guidelines to the households for source separation of household waste are sufficiently precise and restrictive to ensure an acceptable waste quality as far as DEHP is concerned.

With regard to packaging of household waste it is recommended that dedicated paper bags for kitchen waste are used by the households or, at least, that only special types of plastic waste bags are accepted. Probably, the best result will be achieved if the waste collection companies also deliver the waste bags directly to the households.

Actually, the most important thing for the municipalities, the treatment plants and the waste collection companies is to ensure that the households comply with the guideline requirements when separating their waste. This can be achieved by a combination of frequent information campaigns to the citizens and specific measures against repeated violations of the guideline requirements by single households e.g. that the waste is simply not being collected or the collection fee is raised.

It is recommended that the treatment plants install pre-treatment equipment that can separate the most significant impurities from the organic fraction before the biological treatment is commenced. Hereby, the transfer of DEHP and other contaminants in the impurities will be minimised.

Materials for improvement of waste structure

Finally, the study included an investigation of the contents of heavy metals and organic pollutants in four typical types of materials used for structural improvement of waste in connection with biological treatment processes. The four materials were garden/park biowaste, straw, newspapers and coloured printed matters (e.g. advertising brochures from supermarkets etc.). Generally, the contaminant levels were below 25% of the MAC values. The exceptions were PAHs in garden/park biowaste, arsenic in coloured printed matters and cadmium in 1 out of 4 garden/park waste samples and in 1 out of 2 straw samples.

It is proposed to determine standard contents of heavy metals and organic pollutants for these materials at the average value of the values determined in this study plus the standard deviation of this value.