Full-scale trial in the Greater Copenhagen area
Summary and conclusions
Background information
The full-scale trial
Technical solutions
The collection systems
Separation criteria and
information
Quantities collected
Collection and treatment
Financial issues
Organisational aspects
Recommendations and
further development
Background information
In December 1999, the City of Copenhagen, the two incineration plants of I/S Amagerforbrænding and I/S Vestforbrænding, the Waste Disposal Company of 1898 (R98) and the Greater Copenhagen Waste Society were granted financial support from the Danish Environmental Protection Agency for conducting a full-scale trial involving collection and anaerobic digestion of organic domestic waste from Greater Copenhagen.
The overall purpose of the trial was to demonstrate and document anaerobic digestion as a valid treatment form for source-separated organic domestic waste (hereinafter referred to as biowaste).
Also technical and organisational aspects relating to collection and anaerobic digestion of biowaste were investigated.
The full-scale trial
The trial comprised collection of biowaste from 16,366 households situated in the municipalities of Brøndby, Frederiksberg, Gladsaxe, Herlev, Hvidovre and the City of Copenhagen.
Collection equipment was acquired, separation criteria were set up and an information strategy was prepared. Subsequently, information material was prepared. During the trial, data on the amount of biowaste collected were registered, and quality of separation as well as potential of biowaste was investigated. In order to clarify experience and attitudes of participating householders, a participant survey was conducted.
Technical solutions
The collection systems
An easily recognisable and logical collection system was chosen in order to secure a biowaste fraction of a quality that could enter the anaerobic digestion plant without pretreatment.
For the collection of biowaste in the kitchens, either paper bags for use with a wire basket or a brown waste bin was used. For the outdoor collection system either a ventilated brown plastic container or a paper sack was used.
Waste was collected, reloaded and transported for pre-treatment and anaerobic digestion in a co-digestion plant (organic waste and manure). At the point of collection, visual control was made in order to secure a clean biowaste product.
Biowaste was delivered to the EGJ (EnergiGruppen Jylland A/S) co-digestion plant in Herning, as there was no pre-treatment capacity available at plants on Zealand or Funen.
Separation criteria and information
For the full-scale trial, criteria were set up for separation of biowaste, and they were generally understood and followed by participants. Large parts of biowaste, however, were not segregated, mainly because the paper bags seemingly were too small. Biowaste still wrapped was also discharged as residual waste.
Prior to trial start and during the entire period of investigation, information was given to participants. This was done both in the form of printed information and information published on the project website. The trial showed that participants found the printed information sufficient.
The participant survey showed that only 4% of the participants in the full-scale trial visited the project website despite the fact that the site contained information on environmental advantages of anaerobic digestion and the anaerobic digestion process, information that was said to lack in the printed information.
Quantities collected
The rate of purity of collected biowaste was 96%, indicating that the collection system worked well and that criteria for separation of waste were understood and followed.
However, the trial showed that some of the collection equipment chosen for the trial gave rise to problems. Liquid leaked from the paper bags for collection of biowaste in the kitchens, resulting in problems for the users. During warm periods biowaste gave rise to maggots in the plastic containers, which especially the ventilated plastic containers did not reduce sufficiently.
As part of the trial the amount of biowaste collected from each of the participating areas was registered, and the quality of waste separation was investigated. On average between 0.5 and 2.3 kg/household/week were collected depending on the trial area.
Figure 0.1:
Waste flow from household (potential), amount of biowaste segregated and
amount of biowaste led to the anaerobic digestion plant (in kg/household/week)
The survey of separation quality showed an average of 4.4 kg biowaste per household per week (the potential) out of a total amount of domestic waste of about 10 kg. On average 1.4 kg biowaste were collected per household per week (33% of the potential).
Upon pre-treatment of the biowaste around 1/3 was removed - some of which was suitable for anaerobic digestion. On average 1 kg biowaste per household per week was led to the anaerobic digestion plant.
No difference in the amount of biowaste collected from the outdoor plastic containers and the paper sacks respectively was registered.
Quantities collected were largest in areas with households having individual collection equipment and lowest in areas with households using communal collection equipment (especially multi-storey housing). This pattern is confirmed in the survey of separation quality. The participant survey showed that one of the reasons was the lower rate of participation in multi-storey housing areas.
For each of the trial areas, a calculation was made of total amount of domestic waste divided into the fractions of paper, cardboard, glass, biowaste and waste suitable for incineration. Results are shown in table 0.1 below. Data are compared with average national data from Danish households registered under the Danish Information system for waste and recycling - the ISAG - for year 2000. Also the results from Environmental Project no. 264, 1994, Danish Environmental Protection Agency, "Domestic waste from private households" are shown, representing results from investigations of the composition of domestic waste, The data included in table 0.1 list the potential of the different fractions contained in domestic waste.
Table 0.1:
Estimated amounts of domestic waste in each area of the trials calculated per
fraction and per household for the year of 2001
Collection and treatment
Collection and transportation, including reloading of biowaste, worked as intended during the trial. The visual control of the biowaste that was done by the refuse collector, contributed to a high quality of the collected biowaste.
The trial showed, among other things, that it is important to have a caretaker responsible for proper use of the waste collection system in blocks of flats. In small, old blocks of flats in Copenhagen there is often no such caretaker, and this may be one of the reasons for the low rate of participation in these areas.
Investigations of the generation of gas showed that each tonne of organic waste (biowaste from the trial mixed with organic industrial waste and manure) resulted in a gas generation of between 50 and 60 Nm3. The anaerobic digestion potential is further investigated in a separate project. Analyses of the residual product show that limit values are complied with, and the product can therefore be used for agricultural purposes.
Total amounts of digested biowaste after pre-treatment made up 0.4 - 5.2% of the total amount of biomass entering the anaerobic digestion plant during the trial. Of the digested organic waste, 97% was used for agricultural purposes and 3% was led to incineration.
Financial issues
Fixed asset investments during the trial are estimated as representative for the costs of introducing separate collection of biowaste. By contrast, costs connected to operation in the trial are not representative for a scheme established at the entire municipality level, as the trial areas, among other things, were located far from each other, and as some of the areas were small.
In order to evaluate the costs of separate collection of biowaste, a calculation of expected costs for collection in the Cities of Copenhagen and Frederiksberg have been made. For the other trial areas the actual costs have been stated.
The calculation for the Cities of Copenhagen and Frederiksberg shows that total operating costs per household per year in blocks of flats amount to DKK 175. Costs for the other trial areas were DKK 281 per household per year. The corresponding costs for households having individual collection equipment were DKK 650 and 576 respectively. These costs cover collection, administration, information, transportation and treatment (including pre-treatment).
The trial showed that it was most expensive to establish collection from households with individual collection equipment primarily due to the fact that the capacity (volume) of collection equipment is not fully used.
Organisational aspects
Overall, the trial showed that there is no significant difference between agreements to be made concerning collection equipment and waste collection during the full-scale trial and agreements to be made by local authorities for establishment of collection of residual waste.
By contrast, the trial showed that there is a significant difference between agreements with traditional waste treatment plants and agreements made with an anaerobic digestion plant. The most important difference is that the primary obligation of an anaerobic digestion plant is to treat manure from contracting farmers. The planning of daily operation of the plant therefore is set from this primary obligation, resulting in the plant not being able to give the guarantee for treatment that local authorities normally would demand from any other waste treatment facilities. The anaerobic digestion plant used in the full-scale trial thus was only capable of treating the biowaste in 80% of the trial period.
Recommendations and further development
The trial showed that it is possible to collect biowaste with a high rate of purity. It seems possible to ensure separation of biowaste that is currently not separated. From the results of the full-scale trial, however, the project group cannot point to exact solutions securing a higher degree of waste separation.
The trial showed that according to the participant survey the information strategy was sufficient in relation to user requests. At the same time, only a small part of the potential of biowaste was separated. It is therefore not possible to state whether there is a connection between information efforts and results of the trial. There may be a need for a supplementary investigation of the connection between the information strategy and the effects of it.
Pre-treatment of biowaste, as it has been conducted during this trial, resulted in about 1/3 of the biowaste being removed and therefore not digested. It would therefore be desirable if better pre-treatment methods were developed so that less biowaste is removed before reaching the anaerobic digestion plant.
Costs of paper bags for collection in the kitchens together with the distribution of these bags in the blocks of flats of the Cities of Copenhagen and Frederiksberg, accounted for almost 45 % of total operating costs. Therefore it is necessary to find alternative methods in this respect, in order to reduce costs.