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Wednesday, 09 March 2011 17:04

Solid Waste Management and Recycling

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Solid wastes are traditionally described as residual products, which represent a cost when one has to resort to disposal.

Management of waste encompasses a complex set of potential impacts on human health and safety, and the environment. The impacts, although the type of hazards may be similar, should be distinguished for three distinct types of operation:

  • handling and storage at the waste producer
  • collection and transportation
  • sorting, processing and disposal.

 

One should bear in mind that health and safety hazards will arise where the waste is produced in the first place - in the factory or with the consumer. Hence, waste storage at the waste generator - and especially when waste is separated at source - may cause harmful impact on the nearby surroundings. This article will focus on a framework for understanding solid waste management practices and situating the occupational health and safety risks associated with the waste collection, transportation, processing and disposal industries.

Why Solid Waste Management?

Solid waste management becomes necessary and relevant when the structure of the society changes from agricultural with low-density and widespread population to urban, high-density population. Furthermore, industrialization has introduced a large number of products which nature cannot, or can only very slowly, decompose or digest. Hence, certain industrial products contain substances which, due to low degradability or even toxic characteristics, may build up in nature to levels representing a threat to humanity’s future use of the natural resources - that is, drinking water, agricultural soil, air and so on.

The objective of solid waste management is to prevent pollution of the natural environment.

A solid waste management system should be based on technical studies and overall planning procedures including:

  • studies and estimates on waste composition and amounts
  • studies on collection techniques
  • studies on processing and disposal facilities
  • studies on prevention of pollution of the natural environment
  • studies on occupational health and safety standards
  • feasibility studies.

 

The studies must include protection of the natural environment and occupational health and safety aspects, taking the possibilities of sustainable development into consideration. As it seldom is possible to solve all problems at one time, it is important at the planning stage to note that it is helpful to set up a list of priorities. The first step in solving environmental and occupational hazards is to recognize the existence of the hazards.

Principles of Waste Management

Waste management involves a complex and wide range of occupational health and safety relations. Waste management represents a “reverse” production process; the “product” is removal of surplus materials. The original aim was simply to collect the materials, reuse the valuable part of the materials and dispose of what remained at the nearest sites not used for agriculture purposes, buildings and so on. This is still the case in many countries.

Sources of waste can be described by the different functions in a modern society (see table 1).

Table 1. Sources of waste

Activity

Waste description

Industry

Product residues
Default products

Wholesale

Default products

Retail

Transport packaging
Default products
Organics (from food processing)
Food waste

Consumer

Transport packaging
Retail packaging (paper, glass, metal, plastics, etc.)
Kitchen waste (organics)
Hazardous waste (chemicals, oil)
Bulky waste (used furniture) etc.
Garden waste

Construction and demolition

Concrete, bricks, iron, soil, etc.

Infrastructure activities

Park waste
Street cleaning waste
Clinkers, ashes and flue gas from energy production
Sewage sludge
Hospital waste

Waste processing

Rejects from sorting facilities
Clinkers, ashes and flue gas cleaning products from
incineration

 

Each type of waste is characterized by its origin or what type of product it was before it became waste. Hence, basically its health and safety hazards should be laid down upon the restriction of handling the product by the waste producer. In any case, storage of the waste may create new and stronger elements of hazards (chemical and/or biological activity in the storage period).

Solid waste management can be distinguished by the following stages:

  • separation at source into specific waste fraction depending on material characteristics
  • temporary storage at the waste producer in bins, sacks, containers or in bulk
  • collection and transportation by vehicle:
    • manual, horse team, motorized and so on
    • open platform, closed truck body, compacting unit and so on
  • transfer station: compaction and reloading to larger transport units
  • recycling and/or waste processing facilities
  • waste processing:
    • manual or mechanical sorting out into different material fractions for recycling
    • processing of presorted waste fractions to secondary raw materials
    • processing for new (raw) materials
    • incineration for volume reduction and/or energy recovery
    • anaerobic digestion of organics for production of soil conditioner, fertilizer and energy (biogas)
    • composting of organics for production of soil conditioner and fertilizer
  • waste disposal:
    • landfill, which should be designed and located to prevent migration of polluted water (landfill leachate), especially into drinking water resources (groundwater resources, wells and rivers).

Recycling of waste can take place at any stage of the waste system, and at each stage of the waste system, special occupational health and safety hazards may arise.

In low-income societies and non-industrial countries, recycling of solid waste is a basic income for the waste collectors. Typically, no questions are put on the health and safety hazards in these areas.

In the intensely industrialized countries, there is a clear trend for putting increased focus on recycling of the huge amounts of waste produced. Important reasons go beyond the direct market value of the waste, and include the lack of proper disposal facilities and the growing public awareness of the imbalance between consumption and protection of the natural environment. Thus, waste collection and scavenging have been renamed recycling to upgrade the activity in the mind of the public, resulting in a steeply growing awareness of the working conditions in the waste business.

Today, the occupational health and safety authorities in the industrialized countries are focusing on working conditions which, a few years ago, passed off unnoticed with unspoken acceptance, such as:

  • improper heavy lifting and excessive amount of materials handled per working day
  • inappropriate exposure to dust of unknown composition
  • unnoticed impact by micro-organisms (bacteria, fungi) and endotoxins
  • unnoticed exposure to toxic chemicals.

 

Recycling

Recycling or salvaging is the word covering both reuse (use for the same purpose) and reclamation/recovery of materials or energy.

The reasons for implementing recycling may change depending on national and local conditions, and the key ideas in the arguments for recycling may be:

  • detoxification of hazardous waste when high environmental standards are set by the authorities
  • resource recovery in low income areas
  • reduction of volume in areas where landfilling is predominant
  • energy recovery in areas where conversion of waste to energy can replace fossil fuel (coal, natural gas, crude oil and so on) for energy production.

 

As previously mentioned, recycling can occur at any stage in the waste system, but recycling can be designed to prevent waste from being “born”. That is the case when products are designed for recycling and a system for repurchasing after end-use, for instance by putting a deposit on beverage containers (glass bottles and so on).

Hence, recycling may go further than mere implementation of reclamation or recovery of materials from the waste stream.

Recycling of materials implies, in most situations, separation or sorting of the waste materials into fractions with a minimum degree of fineness as a prerequisite to the use of the waste as a substitute for virgin or primary raw materials.

The sorting may be performed by waste producers (source separation), or after collection, meaning separation at a central sorting plant.

Source Separation

Source separation will, by today’s technology, result in fractions of waste which are “designed” for processing. A certain degree of source separation is inevitable, as some mixtures of waste fractions can be separated into usable material fractions again only by great (economic) effort. The design of source separation must always take the final type of recycling into consideration.

The goal of the source sorting system should be to avoid a mixing or pollution of the different waste fractions, which could be an obstacle to easy recycling.

The collection of source-sorted waste fractions will often result in more distinct occupational health and safety hazards than does collection in bulk. This is due to concentration of specific waste fractions - for instance, toxic substances. Sorting out of easily degradable organics may result in producing high levels of exposure to hazardous fungi, bacteria, endotoxins and so on, when the materials are handled or reloaded.

Central Sorting

Central sorting may be done by mechanical or manual methods.

It is the general opinion that mechanical sorting without prior source separation by today’s known technology should be used only for production of refuse derived fuel (RDF). Prerequisites for acceptable working conditions are total casing of the mechanical equipment and use of personal “space suits” when service and maintenance have to be carried out.

Mechanical central sorting with prior source separation has, with today’s technology, not been successful due to difficulties in reaching proper sorting efficiency. When the characteristics of the sorted out waste fractions become more clearly defined, and when these characteristics become valid on a national or international basis, then it can be expected that new proper and efficient techniques will be developed. The success of these new techniques will be closely linked to prudent consideration to obtaining acceptable working conditions.

Manual central sorting should imply prior source separation to avoid occupational health and safety hazards (dust, bacteria, toxic substances and so on). The manual sorting should be limited to only a limited number of waste fraction “qualities” to avoid foreseeable sorting mistakes at the source, and to facilitate easy control facilities at the plant’s reception area. As the waste fractions become more clearly defined, it will be possible to develop more and more devices for automatic sorting procedures to minimize direct human exposure to noxious substances.

Why Recycling?

It is important to note that recycling is not a waste processing method that should be seen independently of other waste management practices. In order to supplement recycling, it is necessary to have access to a properly managed landfill and perhaps to more traditional waste processing facilities such as incineration plants and composting facilities.

Recycling should be evaluated in connection with

  • local supply of raw materials and energy
  • what is substituted - renewable (i.e., paper/tree) resources or non-renewable (i.e., oil) resources.

 

As long as oil and coal are used as energy resources, for example, incineration of waste and refuse-derived fuel with energy recovery will constitute a viable waste management option based on energy recovery. Minimization of waste quantities by this method, however, must end in final deposits subject to extremely strict environmental standards, which may be very expensive.

 

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