Detailed On -Site Methodology

The municipal waste arising from any commercial or industrial sector can be broadly divided into mixed waste and segregated waste as outlined in Figure A.1

Figure A.1 Flow diagram of waste characterisation methodology steps.

Although the volume of mixed waste is usually known from waste disposal records the composition of this waste stream is often difficult to determine. Mixed waste consists of a wide number of waste materials and will vary in composition depending on the nature of the enterprise and its activities. For example the mixed waste stream arising from a hotel will contain a higher percentage of food waste than that from a public office. Mixed wastes also vary in character within an enterprise. For example, the waste from the kitchen of a hotel will vary considerably in composition to the waste arising from the bedrooms of the same hotel.

Wastes streams which are easily segregated include waste paper, cardboard, glass and metal. These segregated waste streams are often collected and sent for recycling. For the purposes of this study, the segregated waste is further sub-divided and characterised (e.g. cardboard).

This methodology requires that a waste characterisation survey of all the major waste sources within an organisation be conducted. The number of sources in an organisation will depend on the complexity of the activities and the associated waste. For example, municipal waste from an industrial site might be grouped into waste arising from the kitchen/canteen area, offices, grounds and general working areas.

Separation at source is the key to the methodology as this ensures that cross contamination is kept to a minimum. Cross contamination occurs when different fractions are mixed in a general bin (e.g. food and paper). This mixing has the tendency to yield somewhat ambiguous figures (in the case of food and paper, the paper weight may be recoded as heavier than the actual paper weight due to absorption of water) and is combated through separation of the individual streams, where possible, at source. Cross contamination is recognised as one of the main areas of error within municipal waste characterisations and should not be confused with inherent contamination (e.g. residual liquid in a PET bottle).

Qualitative and quantitative data on the character of the waste arising from the main sources can thus be gathered to determine the character of the total waste stream.