Lecture 1 - Waste Characterization (Ch. 2.1) Flashcards
What is waste characterizations used for?
For national policy setting, regional planning of waste management, legal aspects, administration, cost accounting, design and operation of facilities and environmental assessment.
In more detail this could be:
- 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.
Explain the following terms used in waste characterization:
1) waste categories
2) waste types
3) waste quantities (commonly used unit)
4) unit generation rates
5) Material fractions
6) Items
7) Substances
1) 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.
2) 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.
3) 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.
4) 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.
5) 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.
6) Items: Individual objects of different natures present in a material fraction and therefore with common properties.
7) Substances: Individual chemical substances in the waste, which typically require analytical techniques to identify.
This could be water, protein, ash content, nitrogen, cadmium, etc.
Explain the three types of sampling strategies:
1) Random sampling,
2) Stratified random sampling,
3) Systematic random sampling
1) 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 waste is regarded as homogenous. An example is the investigation of the waste
generated in an area with only multi-family housing.
2) Stratified random sampling: Stratified random sampling is used if the waste is regarded as inhomogeneous. By
stratifying the waste in different parts, where each part is homogenous, random sampling could then be performed
for each part. This sampling procedure is very useful when the composition of the waste is to be determined in
a municipality, which is divided in homogenous areas. How detailed the division should be depends on the need
of accuracy of the investigation. The easiest stratification in characterization of residential waste is to divide the
residential areas in areas with multi-family housing (apartments) and single-family housing. Waste from these types
of housing often shows a significant difference in generation rates and to some extent also in composition.
3) Systematic random sampling: Systematic random sampling is a less used method in waste sampling. It is not a totally
randomized sampling method. In this method, the first sample is taken randomly but the following samples are taken
in a pre-defined system. For example, every tenth waste bag is collected in an area or bags from every house with an
even house number are selected. With this kind of sampling strategy there is always a risk to make sampling errors if
there are systematic variations in the population.
How do you choose the sample size?
think about homogenous waste vs. inhomogenous waste
The sample size is smaller in the case of homogenous waste and the opposite for inhomogenous waste.
The characterization of waste in terms of analysis and test can be divided into three distinct analysis. Which ones?
- Physical analyses.
- Chemical analyses.
- Performance testing.
Mention types of physical analysis and explain them
- Picking analysis/quantifying material fractions as identifiable items. –> Performed to obtain information of the material composition of the waste often with the purpose of evaluating the success of existing recycling schemes or to introduce new schemes.
for example, plastics can be divided into PVC, polyethylenes, polyethenes + propylene and ‘other plastics’, or according to their origin, such as food packaging, beverage and water containers, foils, bags, utensils and others. - Particle size distribution. –> used to assess the suitability of the waste for mechanical sorting and certain treatment methods as well as for assessing compressibility and other mechanical properties.
When using dry or wet sieving, the sample is passed through a series of standard sieves having successively smaller mesh sizes. - Moisture content. –> The moisture content is determined by weighting the waste before and after drying. Drying takes often place at 77 ◦C or 105 ◦C until constant weight. At 105 ◦C, in addition to water, also volatile fatty acids, specific organic components and mercury may volatilize. The moisture content usually is expressed as a percentage of the wet weight.
- Densities. –> The density is used for the layout and design of waste collection, treatment facilities and landfills. There are two kinds of densities: bulk density (ρb) and material density (ρm). The bulk density is the wet weight of the waste packed in a known volume and hence depends highly on the pressure exerted. The material density or the specific density is the density without any void space.
Mention types of chemical analysis and explain them.
- pH and alkalinity.
- Organic matter.
- -> The organic matter content can be determined by several approaches. Volatile solids (VS) is determined as the loss of dry matter (weight) upon ignition of the sample, which is assumed primarily to be organic matter. A usual procedure is to dry the sample at 105 ◦C and to keep it in a muffle oven for 2 h at 550 ◦C in the presence of air. The remaining part after ignition is called the ash content.
- -> Total organic carbon (TOC) is determined by measuring the amount of CO2 generated by thermal destruction of the sample.
- Inorganics. –> The inorganic content represents a wide variety of substance. Nutrients, salts and heavy metals are the most important ones. Almost all analytical methods with acceptable accuracy require that the substance to be analyzed is extracted or released upon destruction of the solid phase into an appropriate medium, typically a gas phase or liquid/aquatic phase.
- -> The nutrients of importance are nitrogen compounds (Kjeldahl-N, ammonium-N, nitrate-N), phosphate (P), potassium (K) and sulfur (S). The salt ions are typically chloride, sulfate, bromide, sodium, calcium and magnesium. The heavy metals (Cd, Cr, Cu, Hg, Ni, Pb, Zn) and the lithophilic elements aluminum (Al), silicon (Si) and iron (Fe) are in particular sensitive to the extraction step preceding the analytical determination.
- Heating value/calorific value. –> The heating value, also called heat value and calorific value, is usually determined in the laboratory by means of a bomb calorimeter. A known amount of waste is combusted in oxygen and the energy released is determined from the temperature increase in the well-insulated calorimeter caused by the combustion. The unit is MJ/kg. During combustion all water in the sample evaporates, as does the water formed by oxidizing the hydrogen in the waste materials. However, this vapor is condensed in the bomb calorimeter, contributing to the energy output and therefore included in the measured heating value. This measured value is called the higher heating value, or gross calorific value, in contrast to the lower heating value, which is the higher heating value minus the energy needed to evaporate all water.
Mention types of performance tests and explain them
- Compressibility tests –> performed to gain knowledge about waste densities as a function of the pressure or forces
compressing the waste. Such information is used to evaluate compaction of waste in the context of collection, storage
and also landfilling of waste. Compressibility can be measured in different ways, but often an oedometer is used. - Leaching tests –> performed to gain knowledge about aqueous leachability of substances from the waste. Such
information is related to landfilling of waste and to reuse of waste materials in construction. A key issue is to describe
leaching over time, in some cases several hundred years. - Respiration tests –> measure how degradable the waste is by quantifying how much oxygen it requires during a defined
period, typically 4–21 days. Such information is used in characterizing compost, mechanically/biologically treated
waste intended for landfilling and maybe old waste in landfills that need remediation. - Biochemical methane potentials –> measured to gain knowledge about the amount of methane that can be generated
from organic waste under optimal conditions at mesophilic or thermophilic temperature. Such information is related
to anaerobic digestion and landfilling of organic waste.
