Waste treatment methods

Disposal methods

Once the waste is collected, it enters the treatment phase. There are various treatment methods that correspond to the nature and origin of the waste materials. Basically, waste can be removed from the economic circuit (disposal) or reintroduced in the circuit (recovery).

Waste disposal must be performed in a way that does not endanger public health and does not entail the use of processes and practices that can be hazardous to the environment.

Disposal operations according to Directive 2006/12/CE [11]

Symbol Type of operation
D1 Deposit into and on land (e.g. landfill, etc.)
D2 Land treatment (e.g. biodegradation of liquid or sludgy discards in soils, etc.)
D3 Deep injection (e.g. injection of pumpable discards into wells, salt domes or natural occurring repositories, etc.)
D4 Surface impoundment (e.g. placement of liquid or sludgy discards into pits, ponds or lagoons, etc.)
D5 Specially engineered landfill (e.g. placement into lined discrete cells which are capped and isolated from one another and the environment, etc.)
D6 Release into a water body, except seas/oceans
D7 Release to seas/oceans, including sea-bed insertion
D8 Biological treatment not specified elsewhere in this Annex which results in final compounds or mixtures which are discarded by means of any of the operations numbered D1-D7 and D9-D12
D9 Physico-chemical treatment not specified elsewhere in this Annex which results in final compounds or mixtures which are discarded by means of any of the operations numbered D1-D8 and D10-D12 (e.g. evaporation, drying, calcination, etc.)
D10 Incineration on land
D11 Incineration at sea
D12 Permanent storage (e.g. emplacement of containers in a mine, etc.)
D13 Blending or mixing prior to submission to any of the operations numbered D1-D12
D14 Repackaging prior to submission to any of the operations numbered D1-D13
D15 Storage pending any of the operations numbered D1-D14 (excluding temporary storage, pending collection, on the site where the waste is produced)

Landfill in Hawaii

Depending on the types of waste they accept, landfills are classified as landfills for hazardous waste (class a), landfills for non-hazardous waste (class b), landfills for inert materials (class c), and landfills for a single type of waste (mono-landfill). They must be equipped with security systems, weighing equipment, laboratories, landfill gas recovery systems and leachate treatment systems, machinery (bulldozers, loaders, compactors, scrapers, excavators) and appropriate maintenance services.

Waste disposal by means of landfill storage without any follow up measure is no longer an accepted practice. Although according to Council Directive 75/442/CEE such landfills were to be closed down by 2007, Romania was unable to meet the deadline. As a result, Romania was granted a transition period until the end of 2009 for hazardous industrial waste, until the end of 2013 for waste generated by the energy, chemical and metallurgical industries, and until 16th July 2017 for municipal waste. The closure scheduling for non-compliant landfills is regulated by Governmental Decision no. 349/2005.

Waste compaction in a landfill

Landfill storage currently entails the eventual closure of the landfill by covering the waste with layers of soil (burial), which is a standard practice in numerous countries. Such landfills are created in quarries that are no longer operational or in abandoned mines. A properly designed and utilized landfill is a relatively inexpensive method of handling waste disposal, which also meets the related ecological standards. The old, non-compliant landfills have negative environmental effects, such as garbage scattering, attracting pests (insects, rodents), and air, water and soil pollution. Air pollution is caused by landfill gases that are produced as a result of fermentation – e.g. carbon dioxide and methane, which are greenhouse gases and contribute to global warming. Water and soil pollution is caused by the leachate (liquid resulting from biochemical processes) that, in the absence of an insulating layer, infiltrates the soil and reaches the groundwater. These types of pollution can be potent enough to prevent plant growth in the vegetation cover. Normally, landfill waste is compacted in order to increase density and stability, and subsequently covered with plastic film and layers of soil.

Organic waste landfills are equipped with gas recovery facilities. The main components of the gas are methane (54%) and carbon dioxide (45%), supplemented by small quantities of hydrogen sulfide, carbon monoxide, mercaptans, aldehydes, esters, and other organic compounds. It can be harnessed by burning. However, if local recovery is not possible, it is recommended that the gas be burnt by using a plant flare, as the greenhouse effect of the carbon dioxide resulting from burning methane is not as strong as that of the initial methane.

In order to prevent the leachate from infiltrating the soil, modern landfills feature insulating layers that can be made of clay or thick plastic (geo-membranes) or textile (geo-textile) film. The thickness of the clay layer must exceed 1 m for inert or non-hazardous waste, and 5 m for hazardous waste.

Due to the issues the operation raises, finding locations for new landfills is difficult, as local residents are against such projects, and the NIMBY (Not In My BackYard) syndrome sets in.

Spittelau incineration plant, in Viena

Incineration is a combustion-based method used for waste disposal. This is one of the thermal treatment methods used for waste management. The incineration results in heat, gas, steam and ashes. Incineration can be performed with small individual plants or at industrial scale. Solid waste can be incinerated, as can liquid and gaseous waste. This method is preferred for areas in which no land is available for establishing landfills, as is the case of Japan, as well as for certain hazardous waste – e.g. biological waste generated by medical activities. However, the industrial-scale incineration of such waste is controversial because of the gaseous pollutants it generates, mainly dioxins (polychlorinated dibenzodioxins – PCDD and polychlorinated dibenzofurans – PCDF) resulting from combustion. Incineration plants are furnaces equipped with direct or inverted supply grates, rotary-kiln furnaces, vertical furnaces, fluidized bed combustion, or suspension combustion. They can treat (incinerate) low-calorific waste of only 10 MJ/kg. Lately, there have been talks about waste coincineration, which entails incineration using large energy boiler furnaces or cement kilns, and mixing waste with the plants’ regular fuel. The share of waste in the fuel mixture is of approximately 10%. The term “coincineration” applies to the cases in which using a fuel mixture containing waste does not interfere with the incineration plant’s regular use. If the main activity of such a plant is waste incineration, the process will be referred to as “incineration” instead of “coincineration”, and authorization conditions will be stricter, as they will apply to the former term.

The international symbol for recycling.

Recovery refers to the extraction of resources that can be reused from waste. This can mean recycling, reuse, regeneration or any other extraction process for auxiliary raw materials. Both materials and energy can be recovered. Materials can be reused for the production of new goods, and energy can be converted to electricity. [11] As in the case of disposal, recovery activities must not endanger people’s health and must not make use of processes or practices that can be hazardous to the environment.

Recovery operations according

to Directive 2006/12/EC [11]

Symbol Type of operation
R1 Use principally as a fuel or other means to generate energy
R2 Solvent reclamation/regeneration
R3 Recycling/reclamation of organic substances which are not used as solvents (including composting and other biological transformation processes)
R4 Recycling/reclamation of metals and metal compounds
R5 Recycling/reclamation of other inorganic materials
R6 Regeneration of acids or bases
R7 Recovery of components used for pollution abatement
R8 Recovery of components from catalysts
R9 Oil re-refining or other reuses of oil
R10 Land treatment resulting in benefit to agriculture or ecological improvement
R11 Use of waste obtained from any of the operations numbered R1-R10
R12 Change of waste for submission to any of the operations numbered R1-R11
R13 Storage of wastes pending any of the operations numbered R1 to R 12 (excluding temporary storage, pending collection, on the site where it is produced)

Recovery of materials

Steel waste, sorted and bundled, prepared for recycling at the Central European Waste Management facility in Wels, Austria.

To ensure a successful recycling operation, the waste must be sorted according to the materials’ quality, and this begins with separate collection. Waste can also be sorted at specially-designed waste sorting plants.

Regular materials that can be recovered are beer can aluminium, food packaging and spray steel, high-density polyethylene – HDPE, and polyethylene terephthalate – PET, bottles and jars, newspaper and magazine paper, packaging cardboard. Also recoverable are plastic products such as polyvinyl chloride – PVC, low-density polyethylene – LDPE, polypropylene (PP) and polystyrene (PS), although they are not currently being collected. Products made of such materials are usually homogeneous and consist of a single component, which makes recycling easier. In comparison, recycling electrical and electronic equipment is more difficult, as the process requires technologies that can separate the various constituting materials.

Recovery of materials

Mechanical-biological waste treatment plant in Lübeck, Germany, 2007.

In landfills, recovery begins with the sorting of materials. For mixed waste, the first operation is shredding, performed in mills equipped with hammers, strikers, shredders, and graters. The following operations are sorting according to size using drum sieves, vibrating sieves, cyclone-based densimetric sorting, magnetic sorting of ferrous material, optic sorting (for glass) and, possibly, manual sorting. The outcome is purified by washing. The sorted and purified waste is bundled using presses, and is then ready to be shipped to the beneficiary. If the mixed waste contains biological components, they can be processed biologically, but the other recoverable materials must be separated beforehand as well as possible. In Romania, recovery is ensured by a series of companies specialized in waste treatment for recycling purposes.

Biological processing

Composting plant.

Organic waste, such as plant debris, food residues and paper, can be used by means of composting, which entails an organic matter decomposition process. This results in compost, an excellent agricultural fertilizer. The composting process produces biogas with a high methane content, which can be used as such, for instance for gas stoves, or by power plants for electricity production. In composting plants, the natural organic matter decomposition process is accelerated. Composting can be performed both in small individual household plants and in large industrial plants (e.g. sewage treatment plants). Composting can make use of both aerobic and anaerobic fermentation.

Municipal sewage sludge represents another biogas source that is generated by city or industrial sewage treatment plants. Combustible materials can be obtained by both biological processing, and by high-pressure pyrolysis and gasification processes in an oxygen-deficient atmosphere. Advanced methods (plasma arc gasification) can produce a syngas with a superior composition, made of carbon monoxide and hydrogen.

Energy recovery

Waste that can generate energy recovery includes wood (crop wood waste, wood processing and demolition industry waste), landfill gas and biogas. Wood has a calorific value of 14–17 MJ/kg, and landfill gas and biogas have similar compositions and calorific values of 20–25 MJ/m³N. As a result, they can be used by household appliances, or by boilers for heat production or, with the help of turbines, for electricity production.

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