Generally speaking, waste is categorized partly according to source, partly according to means of disposal, and partly according to characteristics. Municipal refuse, for example, contains several categories which are collected and treated in the same way, whereas hazardous waste characteristically has especially dangerous properties irrespective of source. Municipal waste is commonly categorized as follows:

• Domestic garbage: food scraps, packaging etc. from daily housekeeping.

• Bulky domestic waste: refrigerators, furnitures etc.

• Street rubbish: from street sweeping.

• Garden and park waste.

• Building and demolition rubbish.

• Metal scrap: from cars, other vehicles etc.

• Latrine and septic waste.

• Waste from institutions: hospitals and health stations etc. which often contains infectious refuse.

• Waste from commercial activity: offices, hotels, restaurants, shops, markets etc.

• Industrial waste, which can be subdivided into:

  - organic waste from fisheries, aquaculture farms, agriculture, foodstuff industries,

  - mining waste,

  - various branch-specific residuals,

  - general garbage resulting from most industrial undertakings: from cantines,

  workshops, warehouses etc.

• Sludge from wastewater treatment plants.

  Waste may contain different amounts of several components. The composition will vary between countries and cultures, as well as seasonally. Typical components in municipal waste are:

• easily decomposable organic matter: food scraps, waste from fruit and vegetable markets, dead animals, septic excrements etc.

• combustible organic matter: cardboard, paper, textiles, bone etc.

• plastics,

• metals,

• glass,

• ashes,

• sand and gravel.

• Hazardous waste, which can be subdivided into:

  - organic waste: waste oil, solvents, paint, lacquer, glue, distillation residue, pesticides, pathogenes etc.

  - inorganic waste: various toxic metals and heavy metals, cyanides, acids, bases, asbestos etc.

Hazardous waste is characterized by a high potential for direct damage to health and welfare, or by causing serious pollution and environmental harm. It can be:

a) highly inflammable (e.g. solvents, oil products),

b) etching (e.g. acids, bases),

c) reactive, i.e. react spontaneously in contact with other materials and lead to generation of toxic gases, explosion, fire or heat generation (e.g. cyanides, acids, bases, alkaline matter),

d) toxic (e.g. pesticides, heavy metals),

e) infectious (matter containing pathogenes),

f) carcinogenic, or

g) ecotoxic, i.e. substances that accumulate in the ecosystems and/or poison these directly.

A complete survey of dangerous components and types og hazardous waste is provided in tables 1, 2 and 3 at the end of this booklet.

Hazardous waste can occur as residuals of a series of activities, e.g.: Agriculture, animal husbandry, forestry and industries related to these primary activities, e.g. dairies, breweries, textile and leather industries, wood, chemical-pulp and paper industries; Energy production based on oil or coal and related activities, e.g. mining and oil drilling; Metallurgical industries and production of electronic equipment, glass, ceramics/porcelain, asbestos and cement; Chemical industry and processing. Households and service industries are also sources of hazardous waste, e.g. Iead-containing batteries, paint and solvents, chemicals from photo laboratories, research laboratories, cleaning plants, hospitals etc. (cf. booklets for initial environmental assessment of Agriculture, Animal Husbandry, Forestry, Industry and Mining). Some types of hazardous waste can be potentially dangerous over time, whereas some become dangerous only in combination with other residual products, naturally occurring substances, or when exposed to special conditions, e.g. heat. Occasionally, waste which is not originally hazardous can nevertheless become very dangerous if sufficient amounts of it are generated.

• Nuclear waste: Handling requires extraordinary solutions, being generally regulated by special directives. Accordingly, they will not be described in any detail in this initial assessment booklet.

The amounts of municipal waste are usually smaller in developing countries because of lower production and consumption, and extensive sorting and recycling of a series of waste components among poor population groups (cf. chapter 2). These conditions lead to a higher waste density because of the absence of paper, plastics, glass, packaging etc. In return, the share of easily decayable organic matter is greater.

Prior to the planning of waste management measures, the composition of the municipal waste should be thoroughly examined. This is of great importance with regard to choice of technology and system of waste management.