Solid Waste Technology and Management

2
Waste Generation and Characterization

2.1
Waste Characterization: Approaches and Methods

Anders Lagerkvist and Holger Ecke

Luleå Technical University, Sweden

Thomas H. Christensen

Technical University of Denmark, Denmark

Characterization of solid waste is usually a difficult task because of the heterogeneity of the waste and its spatial as well as temporal variations. This makes waste characterization costly if good and reliable data with reasonable uncertainty is to be obtained. Therefore, a waste characterization is often narrowly defined to meet specific needs for information. This may however limit the general usefulness of the information gained, for example, if the specific purpose limited the characterization to a subset of variables. In general, data available in the solid waste area are limited and often with limited representation.

This chapter describes common approaches and methods in waste characterization including common terms, sampling, characterization methods and data evaluation. The focus is on the characterization of waste as it is generated or collected, while specific issues on characterization related to individual treatment processes and waste products are dealt with in the following chapters: Characteristic data on residential waste (Chapter 2.2), commercial and institutional waste (Chapter 2.3), industrial waste (Chapter 2.4) and construction and demolition waste (Chapter 2.5).

If information about waste is required, it is always advisable to check the literature and the internet to see if relevant data is available already. However, in all cases the relevance of the data with respect to cultural, climatic and economical basis as well as the quality and age of the data available must be carefully assessed.

2.1.1 Waste Characterization: Concepts

The characterization of waste has the purpose of providing information for addressing a problem or issue. A clear perception of the problem or issue to be addressed is important in order to specify the purpose of the characterization and to identify the appropriate approach and methods to be used.

The problems or issues requiring information in terms of data can be many different, for example, national policy setting, regional planning of waste management, legal aspects, administration, cost accounting, design and operation of facilities and environmental assessment.

The purpose of a characterization can be, for example:

• To provide data on waste quantities and composition for use in regional or national waste statistics as a basis for policy setting on recycling.
• To classify waste as hazardous or non-hazardous waste according to national regulation, which will determine the legal framework for the handling of the waste.
• To document adherence to specified quality criteria for recycled materials, for example, according to metal scrap categories set by the metal scrap industry.
• To determine the efficiency of an introduced recycling scheme by quantifying recovered and non-recovered material.
• To determine waste generation rates for residential waste for the forecasting of waste quantities according to population growth.
• To characterize waste quantity and composition for the design of a waste incinerator.

The purpose of a waste characterization must be clearly identified in collaboration with those professionals who will use the data afterwards in order to generate the information needed for solving the problem or addressing the issue. In this context, it is important to address or at least be aware of the representative nature of the waste characterization, which is often compromised because of limited resources available for the characterization. Representative characterization includes:

• Spatial variation: Define the area for which the information from the characterization will be used. Evaluate whether significant spatial variations are expected and if these variations should be characterized or just represented in the average characterization.
• Temporal variation: Define which period the information from the characterization should represent and if temporal variations within this time period should be characterized or just represented in the average characterization. In particular, seasonal variations may be of concern if the actual sampling period represents only a short period of the year. Weekly variations may be significant if the characterization is performed in connection with the existing waste collection scheme.
• Uncertainty or fundamental variation: Although spatial and temporal representations may be properly addressed, the heterogeneity of waste is still significant and any characterization will be associated with substantial uncertainty. This heterogeneity is a function of the properties of the waste and can be described by Gy’s formula (Gy, 1998). Only by correct sampling and sufficient sample mass, as described later, can the heterogeneity of the waste be covered by the characterization. This uncertainty should be estimated and must be compatible with the use of the data.

The following terms are useful in waste characterization:

• Waste categories: Broad classes of waste coming from sources with common characteristics. Residential waste, commercial and institutional waste, industrial waste, construction and demolition waste are the main categories.
• Waste types: Subclasses of waste categories and have common characteristics with respect to source and composition. For example, residential waste includes these waste types: household waste, garden waste, bulky waste, household hazardous waste. Industrial waste holds several types according to industrial branch.
• Waste quantities: Often reported as wet weight, since this is easily measured. Occasionally quantities are given as volume based on the size of the bins that were used for collecting the waste.
• Unit generation rates: Quantities of waste per defined time frame and per generating characteristic unit. For residential waste, the unit generation rate is often kg/year/person or kg/week/household. For commercial waste, the unit generation rate could be kg/year/employee or kg/year/m2 of store or kg/1000 Euros of sales. The definition of the unit generation rate should reflect the main factor determining the waste generation; a factor that at the same time is accessible in statistics or important in physical planning. The use of waste generation rates makes it more easy to evaluate and generalize measured waste quantities. However, identifying the basis for the quantities, e.g. number of inhabitants corresponding to the waste quantity is often less trivial than it sounds, because the waste quantification is often performed after collection and not directly at the source.
• Material fractions: Visually identifiable fraction in the waste with common features: paper, plastic, glass, organic kitchen waste, etc. Each material fraction may be divided into sub fractions as for example in the case of paper: newspaper, advertisements, magazines, paper towels, etc.
• Items: Individual objects of different natures present in a material fraction and therefore with common properties.
• Substances: Individual chemical substances in the waste, which typically require analytical techniques to identify. This could be water, protein, ash content, nitrogen, cadmium, etc.

2.1.2 Waste Characterization: Sampling

A critical step of a waste characterization is the sampling and the sample preparation. As mentioned, the spatial and temporal variations, on a large as well as small scale, must be taken into account often leading to large waste samples. In addition, the heterogeneity, as reflected in the waste often being a mix of various particle sizes of different composition, is a challenge since many chemical analytical methods require only of few grams of sample. Thus it is important that several tonnes of waste in a sample are correctly represented in the subsample actually analyzed in the laboratory.

The representative nature and the uncertainty cannot be addressed without some a priori information about the waste. The literature and the internet may provide some useful information, but it may also be useful to look at information related to the waste generating process, for example how a production process works, or how people’s income is distributed over a geographical area. Anecdotal information from waste collectors may also provide some insight. If too little relevant data is available, it may be necessary to perform a preliminary waste characterization, which then can provide data for the final design of the waste characterization.

The representative of the waste characterization is greatly influenced by the sampling strategy, the sample size, the number of samples and the subsampling needed to prepare the material for characterization. For residential waste, tonnes of waste are likely required to provide a reasonable representation (Pohlmann, 1994; Maystre and Viret, 1995), while for more homogenous waste, for example waste from process industries, representative characterization can be reached with smaller samples.

2.1.2.1 Sampling Strategy

There are basically three different strategies that can be used in sampling solid waste (Nordtest, 1995):

• Random sampling: When random sampling is used, all parts of the waste have an equal chance to be sampled. This sampling method is used if the...