13. Solid waste disposal

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1. Scope

1.1 Definitions
1.2 Problems
1.3 Objectives
1.4 Stages of waste disposal

2. Environmental impacts and protective measures

2.1 Introductory notes
2.2 Typical environmental impacts

2.2.1 Impact of waste collection and waste transport
2.2.2 Impact of waste treatment
2.2.3 Impact of intermediate waste storage
2.2.4 Impact of waste dumping
2.2.5 Impact of waste recycling
2.2.6 Impact of waste incineration

2.3 Avoidance and safety measures

2.3.1 Waste avoidance
2.3.2 Safety measures Safety measures in waste collection and transport Safety measures in waste treatment Safety measures in intermediate waste storage Safety measures in waste dumping Safety measures in waste recycling Safety measures in waste incineration

3. Notes on the analysis and evaluation of environmental impacts

3.1 Introductory remarks
3.2 Waste collection and transport
3.3 Waste treatment
3.4 Intermediate storage
3.5 Waste dumping
3.6 Waste recycling
3.7 Waste incineration

4. Interaction with other sectors

5. Summary assessment of environmental relevance

6. References


1. Scope

1.1 Definitions

Waste is movable objects which the owner wishes to dispose of (subjective definition of waste) or whose controlled disposal is necessary to ensure the well-being of the general public and in particular the protection of the environment (objective definition of waste). Regarding the distinction from hazardous waste, see environmental brief Disposal of Hazardous Waste. Waste disposal comprises the collection, transport, treatment, storage (intermediate storage), dumping and recycling of waste. The avoidance and minimisation of waste does not form part of waste disposal. They are in fact another part of waste management.

Waste management comprises the sum total of all measures for the avoidance and minimisation as well as the controlled and environmentally acceptable disposal of waste of all types, i.e. domestic waste as well as commercial and industrial waste.

The generally accepted rules of the art include those rules which have been tested in practical applications, whereby the majority of the people working in this specialist field regard the processes, plant, facilities or operating methods as correct (3). The technical nature of the rules may vary according to the requirements in individual countries.

The state of the art is the state of development of advanced processes, plant, facilities or operating methods, guaranteeing the practical suitability of one of such technical measures. To determine the state of the art, an assessment must be made in particular of comparable processes, plant, facilities or operating methods which have been successfully tested during operation. The technical nature of the state of the art may vary according to requirements in individual countries (4).

1.2 Problems

The world-wide industrial development of recent decades with its effects on the manufacture of goods and on the consumption patterns of the population, particularly in areas of high population density, has led to an appreciable increase in the volume of waste. In this respect, targeted and target-group-related waste disposal (WD), involving careful analysis and taking into account not only the local conditions and options but also the environmental aspects of the relevant plant, can bring about the necessary improvements. As a rule, these relate to measures not only in the fields of waste management and waste technology, but also in the fields of law, administration, business management and organisation.

The necessary improvements should also aim to achieve reasonable representation for women, as one of the target groups, in the institutions and bodies responsible for waste disposal. This is the best way to guarantee that their legitimate interest in participating in the development and implementation of administrative, business and environmental monitoring will be served.

1.3 Objectives

The controlled disposal of domestic waste and commercial and industrial waste forms a vital part of the infrastructure of human settlements built on the principles of hygiene. It is an essential component of waste management, whose function must be to help

- to protect human health,
- to contribute to the quality of life by improving environmental conditions,
- to maintain the ecological equilibrium of the environment, particularly of the soil and groundwater, and - where it has been disturbed - to restore it,
- to ensure safe disposal of the waste produced by the population as well as by commercial and industrial establishments, depending on the quantity and type of the waste and taking into account the need for avoidance and minimisation, ensuring the long-term sustainability of resources which serve the well-being of the general public and the legitimate needs of individuals.

Figures show that in many countries there is a marked imbalance between waste production and controlled waste disposal. This is because in the countries in question a clear priority has been given to the matter of industrial development, without however paying at least equal attention to the necessary development of waste disposal facilities.

Very often this relates to waste arising from imported industrial goods. There are seldom incentives to avoid waste.

1.4 Stages of waste disposal

The area of waste disposal (WD) comprises the following disposal stages:

- waste collection and transport (separate collection where applicable)
- waste treatment
- intermediate waste storage
- waste dumping (landfill) and
- waste recycling.

The disposal stages or steps apply to both domestic and commercial and industrial waste. It is not always absolutely necessary, or even advisable, to follow all of these stages; rather, combinations of certain of these steps may be technically the best solution.

Waste transport (in collection vehicles) mostly involves the movement of empty, part-full and full vehicles, but also includes processes for emptying vehicles in transfer stations and treatment plants as well as at landfill sites. The object of waste transport (in special vehicles) is to transport waste between transfer stations and the relevant disposal plants. One must always consider whether the distance between the collection area and disposal plant (e.g. landfill site) has become uneconomic and, if so, provide transfer stations. Within this environmental brief, the transfer of waste is also considered as waste transport.

Within waste treatment the following processes in particular may be used:

biological processes

a) aerobic processes:

- in liquid phase (aeration)
- in solid phase (composting)

b) anaerobic processes (fermentation/biogas extraction):

- single-phase systems (mixing reactor; solid-bed reactor)
- two-phase systems (hydrolysis with complete mixing; solid-bed hydrolysis)

chemical processes: precipitation/flocculation, neutralisation, oxidation, reduction etc.

physical processes: sorting; decanting, dewatering, drying; reverse osmosis, ultrafiltration, emulsion separation etc.

Intermediate waste storage may be important if waste must be temporarily stored in fixed installations, because for economic or process technology reasons it cannot be transported directly for recycling, treatment or landfill.

Waste dumping is a method of controlled final disposal at landfill sites which must be done using state-of-the-art methods (base sealing, treatment of percolation water, landfill gas disposal/utilisation etc.). Waste dumping to some extent represents the final stage of any disposal sequence, regardless of the detailed technical structure of the sequence. The only exception is where waste substances or residues are fully recycled (e.g. agricultural use of sewage sludge, used glass recycling etc.).

Waste recycling includes all processes (methods) for recovering or utilising valuable materials in waste. The principal waste recycling processes are:

- material recycling (e.g. of used glass, used oil, waste paper, plastics, metals etc.)
- liquid phase aeration, composting, biogas extraction (these processes also represent processes of biological waste treatment; see above)
- incineration (utilisation of waste heat, incineration residues)
- agricultural sewage sludge utilisation.

The environmental impacts of the above-mentioned types of waste disposal should first be considered in isolation in order to assess their importance. An integrated assessment should then be carried out for the project, also taking into account any significant interactions.


2. Environmental impacts and protective measures

2.1 Introductory notes

In spite of the basically environment-oriented objective of waste disposal, various problem factors may arise which may be impossible or difficult to overcome:

a) technically/economically unavoidable emissions (residual emissions), from the waste disposal installations which have an overall impact on air, soil and water, on people and on ecosystems

b) adverse consequences of unsuitable use of composting and other forms of recycling on the ecological infrastructure of the region in question

c) unforeseen increase in volume of waste from private households

d) unforeseen increase in volume of waste from commercial and industrial establishments

From the start, reasonable allowance should be made for the above-mentioned problem factors in all project management activities, in order to minimise from the outset any conceivable effects, using suitable measures of an organisational, structural, operational and charge-related nature, and in certain circumstances also with recourse to emergency measures. Considering each relevant sub-sector of waste disposal in turn, the potential typical environmental impacts are as follows (5), (6).

2.2 Typical environmental impacts

2.2.1 Impact of waste collection and waste transport

The collection of domestic waste from individual homes is often not expedient as it is too expensive and the standard of road and housing construction does not permit this. So frequently collection systems with central collection points (interchangeable containers, stationary intermediate storage) must be used. The following must be considered here:

- the consequences of climatically induced, rapid decomposition of waste (insect infestation, odour nuisance, spontaneous ignition, etc.)
- the scattering of waste by animals (dogs, cats, rats).

In the case of large transfer stations, noise and odour nuisance may occur if

- the distance from adjacent buildings is too small or
- soundproofing, aeration, ventilation and deodorisation measures are inadequate or non-existent.

2.2.2 Impact of waste treatment Introductory remarks

The qualitative and quantitative criteria for proper waste treatment are derived primarily from its environmental impact and from emission and immission standards, which in turn are derived from the relevant waste management requirements and from the legislation, regulations etc. in force. In many countries the latter rarely exist or where they do exist are inadequate. Direct application of, say, German, EC or American laws and regulations rarely provides an appropriate solution.

Rather, it is necessary to develop measures suited to the prevailing general constraints and to implement them with the involvement of the population. Biological treatment

a) Composting

The organic components of domestic waste are converted during the composting process into humus-forming substances. Both the raw and finished compost can be used in agriculture, horticulture and landscaping to improve the soil. If local (digested) sewage sludge is rotted down with it, this improves the fertilising value of the compost.

On the whole the technologically simplest composting processes have proved the best, even if the labour costs are higher. Static rotting processes, particular stack composting, are ideal. The following discussion therefore focuses primarily on this type of process.

Compost has a beneficial and relatively long-lasting effect as a soil improver, but can also have very adverse environmental effects. The compost raw materials, namely domestic waste and possibly sewage sludge, may contain substances which in high concentrations have a harmful effect on soil, plants and hence also, via the food chain, on consumers (animals, people). Heavy metals are a particular hazard. The only research carried out so far into the importance of organic toxic compounds has produced conflicting findings. It is vital to reduce the pollutant content to harmless levels through appropriate selection and pre-sorting of relevant raw materials. See also 3.3 and (7).

The groundwater and surface waters may also be at risk from leaching and percolation of pollutants.

An assessment of the environmental impact of composting plants must start by considering the following problem factors:

- occupation of land (by construction works, machinery, areas for compost stacks and residue landfill etc.)
- noise emissions from the composting works (due to raw material deliveries, removal of compost and residues) and from the residue landfill process
- odour emissions from the composting works (should be minimal with careful operation and favourable general conditions).

b) Fermentation (biogas extraction)

Although composting and biogas extraction are fundamentally different processes, they do not differ substantially in their environmental impact. See also a).

Other forms of energy can be saved by the use of biogas, though the operation of biogas plants carries technical risks (see environmental brief Renewable Sources of Energy). Physical, chemical treatment

Plants for physical and/or chemical treatment may differ very considerably as regards the processes used (see also 1.4). It would therefore be going beyond the scope of this brief to describe in detail these plants’ effects on the environment. Depending on the individual case, some or all of the following problem factors may be involved:

- occupation of land (by construction works, machinery, areas for storage of materials/waste materials and for residue landfill sites etc.)
- noise emissions (due to delivery and removal of waste materials, valuable materials and residual materials)
- odour emissions
- pollution of surface waters (after treatment of liquid residues)
- pollution of groundwater (due to leaking and insufficiently drained storage areas for materials/waste materials, etc.)
- air contamination by pollutants (immissions)

2.2.3 Impact of intermediate waste storage

What is said in applies here too, provided the holding time is not too long.

2.2.4 Impact of waste dumping

Waste dumping is the final stage of almost every disposal sequence (see 1.4). However the type and quantity of the waste to be dumped depends on the socio-economic circumstances of the disposal area and on the waste technology structure of the disposal sequence. To a very large extent, this also applies to the field of commercial and industrial waste disposal.

If the landfill is located on a geologically and hydrogeologically suitable site and has an effective base seal and drainage system, as well as proper percolation water and landfill gas disposal and an optimised system for incorporating the waste, one can assume that

- percolation water, gas, odour and noise emissions,
- nuisance from insects, rats and birds and
- dust and paper drift

will be limited to a degree controllable by modern methods.

The scarcely avoidable adverse environmental impacts of a landfill site can be outlined as follows:

- Because of the relatively large area occupied, establishing a landfill site involves considerable interference with nature and the landscape. This can, however, be very largely offset by appropriate recultivation measures.
- In the body of a landfill site for domestic waste, the decomposition processes which take place are largely biological and predominantly anaerobic. However, there is a potential long-term risk for the environment - arising from the waste which cannot be rendered inert - which should not be underestimated. This applies especially to commercial and industrial waste which is not or only poorly degradable (5).
- Recultivated landfill sites can only be used for a few purposes. Generally it is not possible to build on them. Every landfill produces landfill percolation water and landfill gases (including methane), which must be properly treated or disposed of, or utilised in the case of landfill gas. The only problem is that percolation water continues to be produced even when the landfill has ceased to operate, although in diminishing quantities.

Overall it can be said that landfill - in spite of its ecological disadvantages - at present is an indispensable component of a central waste disposal system.

2.2.5 Impact of waste recycling Preliminary remarks

The recovery or utilisation of valuable materials in waste should always take precedence over other forms of disposal. This is true for the following reasons:

a) By extracting and recycling secondary raw materials from waste, raw materials and energy are saved and at the same time pollution of the environment is reduced.

b) By saving raw materials the countries in question can reduce their dependency on imports.

c) Recycling of domestic waste or its conversion into compost, if possible also using population-equivalent quantities of domestic sewage sludge, should lead to a corresponding reduction in the importation or production of mineral fertiliser. Mineral fertiliser is less energy-efficient to produce and less ecologically favourable to use.

d) When using compost made from waste and waste/sewage sludge, one must ensure that concentrations of heavy metals and organic substances which are not readily degradable do not exceed certain figures (cf. 3.3) (7), (8). If only limited chemical analyses are possible, corresponding estimates must be made using plausibility assessments of the origin of the compost raw materials. The same applies to thermal recycling (incineration) of waste and the recycling of the residual materials produced (slag, ash). Impact of material recycling

The separation of valuable materials from domestic waste greatly facilitates its proper disposal. If relevant waste items are already collected at source (i.e. pre-sorted), this can greatly facilitate the collection and transport of the remaining waste, likewise if generally accessible banks are used for the valuable materials, and these materials are taken away in accordance with market-economy principles. On the whole one should note that:

- The landfill sites have to take less waste, and so their operating life is extended and this then reduces the occupation of new land and soil.
- In the case of refuse incinerators, less ash and slag are produced, as the glass and metal intake is reduced (9). On the other hand, since the waste contains less paper, plastics and textiles, the calorific value of the waste is also reduced. This is however partly compensated for by the simultaneous reduction in the inert content. Moreover, by reducing the plastic content, particularly PVC, the pollutant content of the flue gases is reduced.
- Separation of valuable materials from domestic waste also has certain advantages in the case of composting: the treatment of the compost raw material and of the finished compost is facilitated by the separation of glass, metal and plastic components.
- The separated materials can, depending on their category, be reused in the manufacture of paper, glass, metals, building materials, etc. When undertaking projects of this kind, one should on no account fail to take an overall view, balancing out the possible environmental impacts (see also (10) - (16)).

If raw material recovery from waste is carried out on a commercial scale, thus if for example domestic waste is extensively sorted and treated under the split-bin collection system (dry fraction/wet fraction) with reference to the total dry fraction produced, and then returned to production on the relevant recycling lines, the operation of the relevant plants can have adverse effects on the environment. In this regard, section also applies here (physical, chemical treatment). Impact of composting

Biological waste treatment processes are normally used for composting. For this reason, see also a) concerning the effects of composting.

2.2.6 Impact of waste incineration

The incineration of domestic waste largely has the following waste management benefits (5), (12):

- substantial reduction in the waste quantities to be dumped:

Volume reduction without slag recycling between 80 and 90 %, with slag recycling as high as 97 %; weight reduction (without slag recycling) is around 60 - 70 %

- production of heat energy and recyclable by-products (slag for road-building). Calorific value of domestic waste is 6,000 to 10,000 KJ/kg (5), (9), (10)
- safe sterilisation and disinfection of waste
- as a result of the small quantities of residues, finding new landfill sites is far easier than in the case of waste-only landfill.

Disadvantages of waste incineration are:

- relatively high investment and operating costs, for flue gas cleaning among other things.
- proper servicing and maintenance require well-trained staff and sufficient operating revenues. If a waste incinerator is not operated correctly, considerable pollution of the environment may occur, in particular through:

flue gas emissions (dioxins)

wastewater (with wet flue gas cleaning and cooling of slag with water)

- there will be unavoidable production (even with correct operation) of:

flue dust from flue gas dedusting

solid residues from flue gas cleaning

dioxins and other environmental toxins.

The above-mentioned residues require disposal in special waste landfill sites or in special areas of domestic waste landfill sites.

In addition one can expect noise emissions from the waste incinerator (due to delivery of waste and the removal of ash/slag and other residual materials), as well as (to a lesser degree) odour emissions.

On the whole, waste incinerators are particularly suitable where waste has to be disposed in densely populated areas which are highly sensitive in terms of groundwater conservation, i.e. where there is a lack of suitable landfill sites, and where waste avoidance is poor.

2.3 Avoidance and safety measures

2.3.1 Waste avoidance

Waste which has not been produced does not need disposal! In other words: the use of appropriate procedures and measures to reduce or avoid the production of waste takes pressure off the capacities of waste disposal systems and thus off the environment.

In the domestic sphere waste can largely only be avoided if the general public adopts a waste-saving attitude (avoidance of superfluous packaging, non-returnable containers, disposable articles etc.) and if industry is motivated to economise on packaging (less packaging material, reusable containers etc.). There are opportunities here for state intervention via prohibitions, taxes etc.

To avoid waste in the commercial and industrial sphere it is always best to avoid or at least reduce the production of commercial and industrial waste (special waste) at source, in particular by adopting new recycling-oriented production processes. Appropriate avoidance strategies are however not always easy to implement, particularly in view of the technical and economic conditions prevailing in factories and the legal and practical difficulties of enforcement.

It is easier to adopt recycling strategies for commercial and industrial waste. First it is necessary to identify relevant establishments with the quantities and types of waste produced (creating a waste register).

There are relatively good opportunities for recycling commercial and industrial waste/residues in many countries, e.g. in the sectors of chemical cleaning and metal surface treatment (electroplating), as the process materials and raw materials are relatively expensive and thus recycling is profitable in these establishments. Information on the general options and processes is given in (17), (18), (19).

2.3.2 Safety measures Introductory notes

In this section, the term "safety measures" is used to denote all those measures which serve to minimise and compensate for the environmental impact and, where applicable, to make up for disturbances of the natural order, ensuring or safeguarding the environmental effectiveness of waste disposal measures.

Waste disposal plants are to be built and operated with observance of the conditions of use and stipulations laid down by the authorities in accordance with the applicable rules of the art (27). By applying this principle and carefully identifying at an early stage, i.e. during the planning of the waste disposal project, the effects on man and the relevant ecological conditions, e.g. in the area of flora and fauna, as well as the hydrological and geological conditions, and if allowance is made for their conservation in the project, one can expect minimal adverse effect on the natural balance.

Moreover, safe waste disposal demands not only detailed knowledge of the waste constituents but also compliance with stringent requirements in respect of the technologies, installations and building structures to be used (17). Safety measures in waste collection and transport

In the design, construction and operation of plants and facilities for the collection and transport (removal) of waste, in the interests of reducing the environmental impact the objectives should be as follows:

- introduction of a collection system for separate collection of recyclable materials (e.g. split-bin system: wet/dry fraction). Where appropriate in the individual case, banks (for glass, paper etc.) should be provided. If this is not possible due to cost or other constraints, other ways of separating valuable materials should be sought, e.g. in the course of delivery of waste to transfer stations, landfills, etc.; use of scavengers (waste sorters)
- optimisation of collection frequency, to avoid noise and odour emissions etc.
- creation of organisational and physical conditions for reliable disposal and a flexible collection system
- assurance of sanitary conditions to prevent the spread of disease
- creation of facilities for proper collection, removal and disposal of commercial and industrial waste
- in the case of transfer stations:

against noise: enclosure of noise-producing machinery, motors etc.

against odours and other emissions into the air: enclosure of relevant areas, containment and filtration of waste air etc.

where necessary: landscaping to soften the visual impact.

Information on the principles and environment-friendly methods of waste collection and transportation in developing countries, and also on waste management in general, is given in (20). See also (5). Safety measures in waste treatment

In terms of conserving resources in developing countries, biological waste treatment systems, namely

- composting plants
- biogas extraction plants

are particularly relevant (21), (26). In addition, depending on the circumstances, the following should be considered:

- plants for physical treatment (sorting plants, material recovery plants, sludge dewatering plants etc.) as well as
- plants for chemical treatment (fermentation/flocculation and neutralisation plants etc.) (5), (17).

Safety measures include:

- those against noise emissions: enclosure of noise-producing equipment, motors, blowers and other machinery etc.
- those against odours and (other) emissions into the air: enclosure of relevant areas, containment and cleaning or filtration of waste air etc.
- those against harmful pollution of surface waters by relevant process materials, stored materials and residues: building and operation of (wastewater) treatment plants (where necessary), (further) proper disposal of the relevant emissions (e.g. discharge into public sewerage system)
- fencing of open landfill sites
- those against harmful pollution of underground waters: creation of impermeable and properly drained storage areas, work areas etc. and appropriate supervision
- those to soften the visual impact: planting, building of aesthetically appropriate buildings, provision of compensation areas etc.
- specification and monitoring of adherence to regulations for industrial and operational safety of biogas plants. Safety measures in intermediate waste storage

See also Safety measures in waste dumping

In the case of landfill sites, bearing in mind what is said in 2.2.4, in principle the following measures are necessary:

- where no geological barrier is present as a substratum (clay, marl), production of a permanently effective base seal (as a rule a combination seal with a mineral component (clay) and a layer of carefully jointed, high-grade plastic sealing strips) covered by a likewise permanently effective drainage layer
- construction and operation of a plant to treat the landfill percolation water produced
- construction and operation of degassing facilities
- reliable control of incoming waste (entry control)
- application of the prescribed methods for incorporation of waste
- daily covering of the operating areas (for reduction of odour emissions, paper drift, insect infestation; to avoid fire danger and unaesthetic appearance)
- against dust and noise: moistening of landfill surfaces and landfill roads, regular cleaning of the landfill and access roads, construction of tyre cleaning plants, planting of peripheral areas; installation of acoustic barriers, protective planting
- checking of groundwater using observation wells
- stage-by-stage recultivation
- follow-up measures after closure of the landfill site (percolation water treatment, monitoring of observation wells etc.).

It is expressly pointed out that the above-mentioned requirements concerning the planning, construction and operation of landfill sites may vary (i.e. become more or less stringent) depending on the potential risk posed by the waste sent to the landfill site, e.g. in the case of soil landfills, building waste landfills or special waste landfills with particularly hazardous wastes. Safety measures in waste recycling

See also

See (14), (15), (5), (17) for information on appropriate and environment-friendly management of material recycling and waste utilisation. Safety measures in waste incineration

In the case of waste incineration plants, bearing in mind what is said in 2.2.6, the following measures are necessary:

- dedusting of (cooled) waste gases with electrostatic precipitators or fabric filters, followed by
- removal of anorganic toxic gases (dioxin risk) in a flue gas scrubber, using one of the established sorption processes:

wet sorption process
dry sorption process
half-dry sorption process.

- proper recycling or disposal of the solid residues produced, namely grate slag/ash, filter dusts and the reaction products from waste gas cleaning:

grate slag/ash:

Dumping in landfills, but recycling in road-building and dam construction where possible (particularly if evenly and thoroughly burnt)

filter dust:

In view of the high pollutant concentration, disposal on special waste landfills, compacting where applicable

reaction products of flue gas cleaning:

Depending on the neutralisation products, common salt, Glauber’s salt, calcium chloride or gypsum are produced. Dumping on suitable special waste landfills; evaporation, then recycling. Recycling processes are still being developed.

- Proper disposal of liquid residues, which are produced as wastewater:

washing water from flue gas cleaning
cooling and washing water from the wet slag remover
sealing, rinsing and spray water.

The above-mentioned wastewater is highly polluted; it must be cleaned and discharged into the public sewerage system, or evaporated.

Moreover, steps must be taken to prevent noise emissions and, to a lesser degree, odour emissions, also measures to compensate for the land occupied. In addition see also and (5) 7610 ff.

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