Arbejdsrapport fra Miljøstyrelsen, 1/2004 – Madaffald fra storkøkkener

Food Waste from Catering Centres

Summary and conclusions

Pursuant to the new EU Regulation on animal by-products the use of waste food from catering centres for animal feed is no longer allowed. Therefore, appropriate alternatives for disposal of the waste food should be investigated. The project deals with biogas, combustion and composting as possible treatment methods, and various forms of possible collection systems. Not surprisingly, technical matters and matters regarding handling of waste food are examined, and an environmental assessment in the form of LCA screening of the various solutions is carried out. In terms of environmental effects (emissions) the difference between biogas and combustion depends especially on the collecting and pre-treatment system chosen. In any case, biogas will be advantageous within the field of waste and to some extent within the field of resources, too.

Background and Objective

Since the coming into force in 1986 of the Statutory Order on collection of waste food from catering centres, waste food has been collected separately and processed in three plants (in Denmark). Subsequently, it has been used for pig feed. With the EU directive on livestock by-products the use of this waste product for feed is no longer allowed for veterinary reasons, except for mink feed. However, the mink feed trade is not interested in using the waste food. Alternative disposal options of the waste food will, therefore, be biogasification, incineration and possible composting.

In this project the circumstances of these treatment methods, specifically in relation to waste food from catering centres, are discussed, and the possible collection and pre-treatment systems for the waste food related to the treatment method in question are examined. Furthermore, in relation to pre-treatment the directive implies that the waste food should by hygienised by means of biogasification and composting.

The project has two overall objectives. One is to analyse and describe the possible future systems for collection and treatment of the waste food, focussing on the advantages and disadvantages regarding technique and handling. Another objective is to map out and estimate energy, resource, and environmental matters regarding the various systems with a view to comparing the solutions.

The Investigation

The project was carried out by NIRAS, and in the course of the project co-operation partners were Aalborg University, Aalborg Kommunes Renovationsvæsen (Aalborg Community Sanitation Department), Reno Nord I/S and Biocentrum-DTU (The Technical University of Denmark).

Different actors who have knowledge of or are connected with the existing and possible future collecting and treatment systems have performed a number of interviews/telephone interviews.

On the basis of these interviews and in existing relevant literature the possible future systems were analysed, and advantages and disadvantages regarding technique and handling were illustrated.

In LCA screenings the major resource consumption and environmental impact during the whole life cycle is made up. The approach builds on the principles of ISO 14040 and on experience from a Ph.D. project carried out in NIRAS. Furthermore, the UMIP environmental assessment method wasapplied. The calculations were made by means of the PC tool SimaPro.

LCA screenings were performed in the following systems:

Biogas with central collection and pre-treatment (collection in buckets)
Biogas with decentralised collection and pre-treatment, respectively, with and without collection of waste food in plastic bags.
Collection of ordinary refuse with subsequent combustion in the traditional combustion plants
Composting with decentralised collection and pre-treatment

From this method of application of the waste food, energy and/or manure is produced which can replace other products. The LCA screenings, therefore, deduce the resource and environmental impacts related to the production of the products replaced.

Mr. Per Christensen, professor at Aalborg University, has carried out a critical review of the LCA screenings.

Main Conclusions

Neither technical nor handling problems are expected in relation to the treatment of the actual waste food. Biogas, incineration and composting are all suitable methods. To a larger extent attention should be drawn to collection and pre-treatment of the waste food.

The choice of collection systems can result in very different service levels towards catering centres. The major part of the centres is used to receiving a cleaned bucket after emptying, and in many cases it is allowed to take the bucket into the centres, which facilitates the daily routine. To a number of centres it might, therefore, be a comprehensive transition to introduce a system in which the personnel is to wash containers and the collection buckets required for use in the centres.

With the existing system the collection frequency is one or two times per week in the area of Jutland and Funen, and two or three times per week (or more) in Copenhagen and Zealand. According to the collectors the collection frequency primaryly is determined by limited space and odour problems at the restaurants and catering centers.

It is estimated that waste food might be collected and pre-treated without any technical and handling problems, however the handling of large pieces of bones and foreign bodies such as forks and knives should be considered.

The results of the LCA screenings demonstrate, not surprisingly, that composting is a poor solution in terms of both resources and the environment, even for remote catering centres.

Provided that the expected levels for energy production on the basis of waste food and ammonia evaporation from storage and spreading can be maintained, biogas as a “clean” treatment method is better than combustion in respect of environmental effects (emissions), resources and waste. However, systematisation of collection and pre-treatment methods is important too.

The difference between combustion and biogas with centralised collection/pre-treatment is rather marginal in terms of environmental effects and resource consumption, whereas – as far as waste is concerned - the centralised biogas solution is better.

The decentralised biogas solutions (especially solutions without plastic bags) are better than combustion as regards resource consumption and waste. And also better in respect of environmental effects, provided that the previously mentioned levels can be maintained. Assessment of sensitiveness shows that results concerning environmental effects are sensitive towards major fluctuations in energy production and extent of ammonia evaporation, implying that results concerning environmental effects occasionally may turn out in favour of combustion.

In other words: waste is the LCA parameter where the difference between the biogas and the combustion solution is greatest l. The combustion process produces rejects, which must be deposited, whereas the biogas solutions reduce bulky waste from coal mining abroad.

Thus, the final balancing and conclusion depend on the actual importance attached to the saved loads, especially regarding waste but also regarding resources as to biogas solutions seen in relation to situations where environmental effects are in favour of the combustion method.

Project results

The results are divided in:

resource consumption,
waste amounts

Composting proves to be by far the poorest solution - primarily because the composting method replaces no energy; secondarily because composting causes ammonia emissions.

The reason why decentralised biogas solutions outmatch combustion is the fact that the biogas solutions displace more electricity. This influences resource consumption and environmental effects – as to the latter especially regarding greenhouse effect and ecotoxicity, water, chronical and acute. Acidification and nutritive salt load, however, are heavier as regards biogas, which is due to ammonia emissions in connection with storage/disposal and nitrogen leakage.

Similar conditions are valid for the centralised biogas solution. However, as regards environmental effects the centralised biogas solution proves to be poorer than combustion. This is due to additional transport requirements and clean-up procedures for the present-day collection buckets used by the majority of catering centres.

As to waste, the difference between biogas and combustion is remarkable. As mentioned below, combustion causes deposit of rejects, whereas biogas solutions reduce bulky waste from coal mining abroad. Sensitiveness assessments show that results concerning environmental effects are sensitive towards extent of ammonia emission and towards major fluctuations in energy production rate of the involved plants.