Summary and conclusions, Miljøstyrelsen

Organisationsmodeller for udnyttelse af organisk dagrenovation i biogasanlæg

Summary and conclusions

According to Waste 21, organic domestic waste constitutes a resource that is not sufficiently utilized today for composting or biogas treatment. The short-term target (year 2004) is recycling of organic waste corresponding to 7% of the total quantity of domestic waste, or corresponding to 150,000 tons/year. Of this quantity, approx. 100,000 tons/year should be recycled by biogas treatment. The long-term target is recycling of organic domestic waste corresponding to 20-25% of the total quantity of domestic waste.

Waste 21 mentions as one of the major barriers to achieving the targets mentioned above, the lack of introduction - for organisational and technological reasons - of compulsory separated collection of organic domestic waste and residual waste for composting and biogas treatment.

In this project, a number of models concerning organisation of source separation, collection and pre-treatment of the organic part of the domestic waste have been made and evaluated so that subsequent treatment and spreading of the organic material (organic manure and compost) on agricultural land can take place.

The aim of the organisation models is to

make better utilisation of the waste as resource in biogas plants and joint biogas plants possible;

define the responsibilities and obligations of municipalities, public waste companies, treatment plants as well as of other parties involved;

ensure that the parties involved have the necessary capacity in terms of resources and financing;

ensure that the environmental, energy and resource conditions can be managed effectively.

The preparation of models and descriptions of responsibilities and obligations includes considerations as regards the organisational conditions, ownership and available resources in the biogas and waste sector.

The project illustrates the organisation and responsibility aspects of the models. The project is based on the following two primary ownership models as they are at present considered the most realistic alternatives, as regards biogas plants, to treatment of organic domestic waste:

joint biogas plants owned by farmers;

biogas plants owned by the municipalities/companies.

As an introduction to the problem analysis carried out, the legislation in the form of the two central orders (on sludge and supervision) is described, and a general system description of the route of the organic domestic waste "from kitchen to agricultural land" has been made. In this system description, the consequences of the choice of solutions are described in relation to subsequent pre-treatment, treatment and marketing of organic manure and compost.

The problem analysis itself is largely based on the result of a workshop held, the structure of which was in accordance with the so-called LFA concept (Logical Framework Approach). The participants represented a number of relevant organisations, municipalities, public waste companies and treatment plants.

On the basis of the workshop, it was possible to formulate some requirements and wishes to be met in order to obtain sufficient future recycling of organic domestic waste by means of biogas treatment.

The requirements and wishes formulated can be characterised by the following headings:

There is a demand for central initiatives;

Quality requirements and environmental effect;

Municipal initiatives - financial considerations;

Common platform for dialogue and cooperation;

Pre-treatment - the natural interface.

The subsequent analysis of the formulated requirements and wishes both showed some general needs to be considered and some needs of a more functional character directly related to the ways in which recycling systems for organic domestic waste can be organised in practice. The organisation models described in the project are primarily based on a wish for ensuring that the last-mentioned types of needs are met.

Some technical preconditions and limitations in connection with collection of source-separated organic domestic waste, subsequent pre-treatment and final treatment in biogas plants and marketing of organic manure and compost have been reviewed and evaluated. The review especially focused on consequences as to quality and effectiveness in the treatment, and on monitoring aspects and responsibilities in this connection.

Based on the experience from the relatively few existing plants and pilot plants tested during recent years for pre-treatment of source-separated organic domestic waste, the conclusion is that pre-separation of source-separated organic domestic waste will typically have as a result that 20-50% of the waste will be sorted out before the material is sent to the biogas plant.

In case a collection concept is chosen in which the use of plastic bags requires establishment of pre-separation, experience shows that it should be considered carefully which type of pre-separation is chosen to minimise the loss of organic material during the pre-treatment. Alternatively, the choice could be a collection concept based on paper bags. This does not require establishment of pre-treatment in the form of pre-separation. However, this type of concept requires a targeted effort towards the households participating to ensure a sufficiently high quality of the source-separated organic domestic waste.

In order to make it possible to monitor the source-separated waste delivered, the pre-treatment - whether this includes actual pre-separation or just shredding and mixing of the waste - should be arranged in a separate physical unit combined with a buffer storage for short-time storage of the pre-treated waste until analyses show that it can be delivered to the biogas plant.

In connection with the biogas treatment, it is discussed whether the use of the anaerobic technology in the long term may result in active reduction in the content of environmentally hazardous substances in the waste, i.e. LAS, NPE, DEHP and PAHs. Ongoing studies indicate that at least the content of LAS in the waste can be reduced under anaerobic conditions. If so, continuous mass flow calculations should be made, corresponding to the conditions for treatment of sludge by composting, so that it can be established that decomposition of the substances actually takes place, and that it is not just dilution of the substances by mixing with other biomasses, e.g. in a joint biogas plant.

Evaluations of the possibilities of marketing organic manure and compost following biogas treatment show that, basically, there are no obstacles to placing biogas treated organic domestic waste and liquid domestic animal manure treated correspondingly on the same footing. However, the marketing possibilities depend to a high degree on the availability of the procurement arrangements for slurry manure established by agriculture.

In this connection, it is important to be aware of local differences in requirements and wishes for handling of the organic manure and compost (whether liquid or solid) and the marketing price.

In connection with the organisation models, an introductory description and evaluation have been made of the parties who might play a practical role in the utilisation of the organic domestic waste for biogas treatment, i.e. municipalities, public waste companies, municipal works and private enterprises in the form of joint biogas plants, recycling enterprises, haulage contractors and tractor stations.

The parties mentioned have been evaluated on the basis of:

Organisational strength;

Financial strength;

Technical strength;

Experience of corresponding tasks;

Knowledge of domestic solid waste handling;

Knowledge of the agricultural sector/marketing of organic manure and compost.

A strong organisation should be composed of members who together score high on all the parameters mentioned. Based on the result of the evaluation of the possible members, the following examples of, theoretically, strong organisations can be mentioned.

If organic domestic waste is to be delivered to the private joint biogas plants, an organisation with the participation of these plants and the waste companies, possibly in cooperation with private reuse and recycling enterprises, could match the demand for relevant strength and interests.

If organic domestic waste is to be delivered to biogas plants owned by municipalities and organised under the municipal works, it would be practical more actively to involve the municipality, alternatively the public waste company in the organisation and possibly to establish strategic cooperation with relevant tractor stations in the surrounding area.

Three concrete organisation models have been made focusing on the pre-treatment (whether it includes pre-separation or not) as the natural interface:

Pre-treatment within the framework of the public waste companies with participation of private joint biogas plants;

Pre-treatment within the framework of a municipal biogas plant with participation of a public waste company;

Pre-treatment handled by an independent organisational unit with participation of a public waste company and private joint biogas plants.

The three organisation models have been described in terms of investments, operation and maintenance, operations control and responsibility and have subsequently been evaluated in relation to the following criteria:

Provision and retention of technical and financial resources;

Utilisation of the waste as a resource and effective management of energy and environmental conditions;

Precise definition of responsibilities and obligations considering both general public interests and the participants;

Handling of risks in the form of existing and possibly more rigorous environmental and hygiene requirements, stop-down, load and capacity variations etc;

Possibilities of marketing organic manure and compost, including handling of changes of the buyers’ attitude.

The evaluation carried out of the organisation models does not unambiguously point out one of the models as being better than the others. The choice of organisation model will depend on the concrete preconditions and on the location in the country of the organisation. The organisation models and the evaluations can be used for balancing advantages against disadvantages of a concrete decision on choice of treatment concept for the organic domestic waste based on biogas treatment.