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2. Waste Audit Methodology

2.1. Introduction

The municipal waste arising from any commercial or industrial sector can be broadly divided into mixed waste and segregated waste as outlined in Figure 2.


Figure 2: 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.

This waste audit 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.

2.2. Methodology

2.2.1. Before the Survey Begins

Before beginning the waste audit survey there are a number of tasks that need to be conducted. These are outlined below:

  1. Meet with the management of the enterprise whose waste is to be audited. It is essential that management commitment is given to the waste audit study so that necessary resources are assigned during the study period.
  2. Schedule the waste audit survey period:
    • Arrange to conduct the waste audit study during typical business activities/operations. Avoid scheduling the survey on or around any special events that would produce wastes not representative of a normal workday/workweek. For example, surveys should not be conducted during bank holidays, Christmas, Easter or public holidays (or special orders in the case of Industry).
    • It is also important to select a survey time period that is sufficiently long to account for fluctuations in waste character and volume that occur in an organisation. For example the volume of waste produced from a hotel may increase at weekends. The recommended duration for the survey is 5 to 7 days. However the longer the survey period, the more accurate and reflective will be the results.
  3. Divide the organisation into areas with similar waste composition (these are referred to as ‘Waste Sources’ for the purpose of this methodology). The number of sources will depend on the complexity of the organisation.
    • For example, waste arising from a small green grocer may be split into two waste areas: office and warehouse/shop-floor. Each of these ‘waste sources’ has a different waste composition – office (mostly waste paper), warehouse/shop floor (mostly organic waste and cardboard).
    • For example, waste arising from hotel bedrooms will be similar in composition. Bedrooms are then chosen as a ‘waste source’ within hotels from which a specific character of waste arises.
  4. Inform relevant staff of their duties and responsibilities during the waste audit survey. They may be required to segregate waste, label waste arisings, etc.
    • Staff should be encouraged to segregate as many waste streams as possible at each ‘waste source’ for the duration of the waste study. Staff should be encouraged to segregate waste streams which may not normally be segregated, for the duration of the waste study.
    • It is especially important to segregate ‘wet’ wastes (high water content, for example food waste) from ‘dry’ wastes. Combining ‘wet’ waste streams with ‘dry’ waste streams, results in moisture transfer and contamination of the waste. Once this occurs it is impossible to accurately determine individual waste material weights and thus characterisation is more difficult.
    • Staff should be discouraged from disposing of non-routine waste during the course of the study, for example, stockpiled electronic waste.
  5. Select a central ‘waste collection area’ where all waste arisings can be collected, sorted weighed and characterised for the duration of the waste audit study. A parking garage, shipping area or other large flat area is preferable. This area should be covered, if possible to provide shelter from adverse weather conditions. Ideally it should also be close to the current waste management facilities to minimise disruption to the daily running of the site.
  6. Gather the necessary equipment to aid in the waste audit survey.
    • Clear waste bags/boxes should be available at each ‘waste source’ to allow wastes to be collected. Pens and labels should also be distributed to each ‘waste source’.
    • The ‘waste collection area’ should contain a weighing scales (with a range from 0 to 20kg, with accuracy to 0.1kgs)), several containers for holding and sorting the waste, shovels, a brush, a first aid kit, clipboard, labels, pens and worksheets. Several copies of the ‘Waste Collection Area Worksheets’ available in Appendix B should be on hand for each day of the survey.
    • Health and safety issues should also be considered. All members of the waste audit team should wear protective clothing (such as rubber gloves, heavy duty shoes, safety glasses and coveralls) and precautions should be taken to ensure that the waste does not come into contact with food or drink.

2.2.2. Conducting the Survey

Once these tasks have been addressed, the waste audit survey may begin. At each ‘waste source’, two categories of waste will be generated:

  • (a) Segregated waste streams – These waste streams will be homogenous and consist of material of a single type, for example cardboard, paper, plastic, food waste etc.
  • (b) Mixed waste streams – These waste streams will be heterogeneous in nature and consist of mixed waste of various types. The characterisation of this waste stream is more difficult.

The procedures involved in characterising each of these waste streams is presented below:

Segregated Waste

  1. All segregated waste must be sorted and weighed.
  2. Weigh the empty containers that the sorted waste will be placed into. Record these weights on each container.
  3. The waste can then be sorted. Segregated wastes can be sorted easily. All segregated wastes should be sorted into the materials listed in the ‘Waste Collection Area Worksheet – see Appendix B. For example, waste glass must be sorted into ‘glass packaging’ and ‘other glass’.
  4. Each of these fractions must be weighed independently and the total values recorded (excluding the weight of the container) in the ‘Waste Collection Area Worksheet.

Mixed Waste

  1. As the mixed waste is collected at each ‘waste source’, each bag/box of waste should be labelled with the day/date and source of the waste, as follows:
    MIXED WASTE
    Day/Date Fri 29th April 05
    Waste Source Canteen
  2. As the labelled mixed waste arrives at the ‘waste collection area’ all waste bags/boxes should be weighed and the details recorded in the ‘Waste Collection Area Worksheet.
  3. Weigh the empty containers that the sorted waste will be placed into. Record these weights on each container.
  4. Only representative samples of mixed waste must be sorted and weighed.
    • During the survey period randomly take samples of mixed waste (>10kg) from each of the ‘waste sources’.
    • The number of samples, which are sorted and characterised from each ‘waste source’, should be representative of the total volume of waste produced from each ‘waste source’. For example, if ten bags of mixed waste arise from the offices of an organisation per day and only two bags of mixed waste are produced from the canteen then the sampling regime should reflect this ratio.
    • The greater the number of mixed waste samples which are characterised, the more accurate the results will be. Attempt to characterise as many samples as time allows.
  5. The waste samples can then be sorted.
    • Each of these fractions must be weighed independently and the total values recorded (excluding the weight of the container) in the ‘Waste Collection Area.

2.2.3. After the Survey

Following the waste audit survey, the collected data must be compiled into a useful format. The steps involved are different for mixed wastes and segregated waste.

Segregated Waste

  1. From the ‘Waste Collection Area Worksheet’ the daily totals of each material generated should be calculated.
  2. The daily totals of segregated waste for each waste material will be transferred to an electronic spreadsheet which will display the data in graph form.

Mixed Waste

Each ‘waste source’ needs to be calculated separately. These values will be stored into an electronic spreadsheet (Version available from CTC).

  1. Determine total quantity generated from each ‘waste source’ (for example the canteen)
    • From the ‘Waste Collection Area Worksheet’, the total quantity of mixed waste generated each day from each ‘waste source’ must be calculated – for example total daily waste arisings from the canteen of 154 Kg.
    • This figure should be entered into ‘Total Waste Arisings’ (sampled & non-sampled) box for each ‘waste source’ (i.e. canteen) in the electronic spreadsheet.
  2. Determine composition of sorted mixed waste from each ‘waste source’ (for example the canteen):
    • From the ‘Waste Collection Area Worksheet’ the daily totals of each material generated should be calculated.
    • The daily totals of mixed sorted waste for each waste material should be transferred on to the ‘Mixed Waste’ tabs of the electronic spreadsheet (maximum of six ‘waste sources’). For example, mixed waste arising from the offices of an organisation will be input into a different ‘mixed waste’ tab than mixed waste arising from the canteen.
    • The spreadsheets will then automatically calculate the composition of the waste (segregated waste and mixed waste) and the totals are presented in the ‘Summary’ tab of the electronic spreadsheet.

Establish the frequency of non-routine waste and record these details. Non-routine wastes arise as a result of non-routine activities such as stock clearance, maintenance, refurbishment of premises and so on. These waste are not typical of the daily wastes arising on site and may include waste such as construction and demolition waste, obsolete electrical equipment, obsolete furniture and so on. Based on this data, daily estimates of non-routine waste should be estimated and inserted onto the spreadsheet.

Some typical examples of survey results are shown in Appendix A with a number of relevant spreadsheets and information tables given in Appendix B.