Goals
The main objectives of waste management are the environmentally sound recovery and disposal of waste. Different waste treatment processes are used for this purpose. These include processes of material or energy recovery. Waste materials can, for example, be sorted, processed and treated with the aim of reusing the recovered materials. Or they can be thermally treated in waste incineration plants with the aim of recovering energy and material slags. For non-recyclable waste, landfills serve to store waste, usually indefinitely. They are divided into landfill classes according to the type of waste that may be landfilled.
Waste hierarchy
The waste hierarchy must be observed in all waste management measures. Appropriate measures must be taken at the respective levels of the hierarchy. For waste treatment, this means that disposal technology must be provided for the following hierarchy levels:
– Prevention (level before waste treatment)
– Preparation for re-use
– Recycling (material recovery)
– Energy recovery
– Disposal
Waste treatment
Waste treatment in Germany is generally carried out at a high technological level. The basic waste treatment processes up to landfill technology are briefly explained below.
Bio-waste utilisation
Bio-waste accounts for 30 to 40 percent of the municipal waste produced in Germany. After separate collection, it can be fermented in biogas plants and the biogas obtained can be used for electricity generation, for heat utilisation or as fuel. Or they can be composted. The composts can be used as fertiliser or for soil improvement, thus substituting peat and mineral fertilisers.
Mechanical-biological treatment
Mechanical-biological treatment (MBT) is one option for treating municipal waste. Two process variants have emerged that differ in the treatment process and in terms of the material flows generated
– Process with biological residue treatment
The aim of these processes is to separate recyclable materials and to produce a residue that can be deposited.
– Mechanical-biological and mechanical-physical stabilisation processes
The aim of these processes is to dry (stabilise) the waste and largely retain the biogenic components in the
high-calorific stabilised material, as well as to recover other recyclable fractions.
Waste incineration
Waste incineration is one of the mainstays of waste disposal in Germany. It was first used on an industrial scale in Germany from 1893 onwards for the thermal destruction of pathogens and the sanitation of waste due to the cholera and typhoid epidemics that were prevalent at the time. From this, waste incineration technology developed further, from the initially simple, manually operated, discontinuous incineration on rigid grates to fully automatic and computer-controlled waste incineration with appropriate flue gas cleaning.
Waste incineration has to fulfil the following disposal tasks:
– destroy, transform, separate, concentrate or immobilise harmful or hazardous contents in the residual waste,
– to reduce the volume and quantity of residual waste as far as possible,
– to convert remaining incineration residues into recoverable materials or to convert them into a form suitable for
disposal; and
– to use the resulting thermal energy as far as possible.
After treatment (separation of metals and impurities, maturation), the slags remaining after incineration can be largely recycled, for example as road construction material, in accordance with the relevant codes of practice for road construction and the LAGA bulletin “Requirements for the material recycling of mineral residues/wastes – Technical rules” (M 20). Non-recyclable slags can be deposited in landfills, provided they comply with the allocation values of the Landfill Ordinance.
Grate furnaces are mainly used for the thermal treatment of municipal waste. However, fluidised bed furnaces are also used. For the thermal treatment of hazardous waste (special waste), which is often a mixture of solid, pasty and liquid waste, the rotary kiln has proven to be a universally applicable incineration facility.
The permit notice for waste incineration plants specifies which wastes (waste code numbers according to the List of Wastes Ordinance) may be incinerated. Hazardous waste may only be incinerated in plants specifically licensed for the respective waste types or in suitable industrial plants.
All thermal waste treatment plants must be designed, equipped and operated in such a way that the emission limit values specified in the Ordinance on the Incineration and Co-incineration of Waste (17th BImSchV) are not exceeded. In order to comply with the requirements, waste incineration plants are equipped with waste gas purification systems. Waste gas purification takes place in a multi-stage system consisting of, among other things, dedusting, dry, quasi-dry or multi-stage wet scrubbing, denitrification and adsorptive post-separation, whereby additives (e.g. H2O, Ca(OH)2, NaOH, activated coke/carbon, NH3) are added to the waste gases.
Waste landfilling
Despite considerable progress in landfill technology with now elaborate measures for sealing, leachate collection and landfill gas utilisation, the landfilling of waste is still unsatisfactory in the long term and can be seen as a possible legacy for the future. For landfills, therefore, one must not rely only on the effectiveness of one protective barrier, but for reasons of safety, a concept with many barriers must be implemented.
Based on these considerations, the multi-barrier concept was developed, which states that several barriers must be effective independently of each other [STIEF 1986]. The most effective, durable and thus most important of the intended barriers against the input of pollutants into the environment is the waste to be deposited – the landfill body – itself.
The aim of the above-ground disposal strategy is therefore to reduce the pollutant potential of the waste even before it is deposited to such an extent that the environment cannot be negatively affected by emissions in either the short or long term. The pollutants contained in the waste must therefore be converted into compounds that largely approximate geochemical bonding forms. In this ideal case, the technical barrier of such a landfill has only a control function, and the site characteristics serve as a safety barrier against the remaining residual risk.
In Germany, all wastes and waste mixtures with an organic content specified according to the landfill class must be treated before being deposited. The allocation of waste to differently equipped landfill types is carried out according to the requirements of the Landfill Ordinance. This defines landfill classes (DK), which result in different requirements for the operation and especially for the closure and aftercare of the landfill.
Overview of landfill classes
Depending on the permissible pollutant content of the waste that may be deposited, the Landfill Ordinance provides for five landfill classes (DK):
– DK 0 – Above-ground landfill for inert waste (low-polluting mineral waste)
– DK I – Above-ground landfill for non-hazardous waste (with very low organic content)
– DK II – Aboveground landfill for non-hazardous waste (with low organic content)
– DK III – Aboveground landfill for non-hazardous waste and hazardous waste
– DK IV – Underground landfill
In an annex to the Landfill Ordinance, the respective permissible pollutant contents (admissibility and classification criteria) for above-ground landfills are laid down. Different requirements are placed on the landfill classes with regard to the technical safety systems (base and surface seals, re-cultivation, drainage, landfill gas and leachate collection). Requirements to be met in this respect are set out in detail in annexes to the Landfill Ordinance. In the following, the essential requirements for the landfill classes are presented in simplified form.
Above-ground landfill for inert waste (DK 0)
Landfills in landfill class 0 can be used, for example, to dispose of uncontaminated building rubble and uncontaminated soils. These landfills must have a geological barrier at least one metre thick and a mineral drainage layer 0.3 metres thick.
Class I above-ground landfills
Moderately contaminated (non-hazardous) waste can be deposited in Class I landfills. As a rule, this is moderately contaminated excavated earth and building rubble and comparable commercial mineral wastes. Class I landfills must have a sealing component made of mineral components with a minimum thickness of 50 centimetres.
Class II above-ground landfills
Class II landfill may be used for the disposal of contaminated but non-hazardous waste, in particular pre-treated (incinerated or rotted) municipal waste containing a very low organic content and where a very small amount of pollutant may be released by leaching. In addition to the deposit of pre-treated municipal waste, comparable mineral commercial waste can also be deposited.
The seals at the base and the surface of the landfill must consist of two sealing components. At the base of the landfill, the second sealing component shall be a convection barrier (plastic geomembrane or asphalt liner).
Above-ground landfill for hazardous waste (DK III)
Hazardous wastes (special wastes) requiring special monitoring may be deposited in landfills of landfill class III. The geological barrier must be at least five metres thick. In addition, a sealing control system is required.
Underground landfill (DK IV)
In underground landfills, certain hazardous wastes are deposited either
– in a mine with a separate disposal area designed or intended to be separate from a mineral extraction operation,
or
– in a cavern completely enclosed in the rock.
Special regulations apply to underground disposal sites to ensure that the waste is deposited in a manner that is safe over the long term for the site and that there is no risk of harm to the biosphere.
Physical-chemical treatment
In physical-chemical treatment plants, mainly liquid and pasty hazardous wastes (special wastes) are treated. The waste is treated with the aim of converting or separating pollutants in such a way that the separated substances can be sent for suitable recycling or disposal. Chemical processes for substance conversion (e.g. neutralisation, oxidation, reduction) or physical processes for substance separation (e.g. filtration, sedimentation, distillation, ion exchange) are used to concentrate the hazardous constituents.
The treatment of inorganically contaminated waste includes, among other things, the treatment of acids, alkalis, solutions containing heavy metals or sludges. The organically contaminated wastes to be treated are mainly aqueous liquids or sludges contaminated with oils or greases. These include, for example, waste water containing oil, residues from oil and petrol separators or from tank cleaning.
Physical-chemical treatment plants usually have an individual treatment concept that is tailored to the waste to be treated. The state of the art of selected types of plants is described in the BAT reference document “Waste Treatment Plants” (EU Official Journal C 275/15 of 25.10.2006).
Sources:
STIEF, K.(1986): “Das Multibarrierenkonzept als Grundlage für Planung, Bau, Betrieb und Nachsorge von Deponien”, Müll und Abfall 1/86, p. 15/20