(Rubbish Dump at SAB, Austria)

Flashback: Pressing population problem, industry policies, and the toxicity of many industrial by-products, constitute an ever-increasing problem for the disposal of solid waste. Up until recently it was common practice in Europe to deposit residual waste, municipal refuse, and other kind of trash in open or illegal dumps. A substantial criterion is the reduction of the portion of degradable carbon in deposited waste. Current legislative limitations prevent the disposal of rubbish that exceeds a TOC value (total Organic Carbon) of 5% (mass fraction based). On the other hand, bio-mechanically treated waste must not exceed a thermal threshold level of 6.6MJ/kg dry mass. Recycling of paper, glass, metal, and other substances represents a significant contribution in the reduction of the overall amount of waste ending up in landfills. Toxic chemical and hospital waste aiming at landfills have to be incinerated first before gaining access to landfills. Heavy metals (notably mercury, lead, cadmium, etc.) have to be treated/recycled first and are allowed when legal impositions regarding the landfill are met.
Þ For treatment of hazardous substances, refer to the toxic waste-section.
Stricter regulations and harmonisation within the EU has resulted in tough guidelines and recommendations of how and where landfills can be established. Nowadays, modern depots have to be fitted with extra barriers, underground channel system, a sort of roof-top seal and other extras in order to make sure that almost no or minimal risk is present to the neighbouring environment.
Another way to treat municipal waste is often applied with the municipal waste incinerators. Combusting residual waste substantially reduces both volume and TOC but in any case, the ash and the filter cakes have to be deposited into a landfill.
Þ Refer to the residual site.
Considering a landfill as a huge reactor in which anaerobic reaction processes among the constituents regularly is opportune. Therefore, the landfill must be constructed in a way to minimize these secondary reactions. The sanitary landfill is a more sophisticated concept in which waste is spread out in thin and separated layers of tamped earth. The stratification slows down vertical reaction processes that might otherwise occur between layers. Horizontal migration is somewhat slower and less troublesome. Nonetheless, reactions within the pile of waste are unavoidable and take place continuously, and have to be constantly monitored. Analysing both the reaction gases escaping as vapour, and the leakage fluids draining out of the drainage pipes is therefore essential.

Collection: For European standards, the average household is equipped with a 150L garbage can. These cans are emptied twice a week. The trucks dump the collected material into the storage bunker. This is an intermediate storage facility that houses enough material to keep the subsequent fermentation process running even if not enough material is delivered.

Processing: Before exposing the waste material into the revolving rotting drum, it is shredded to pieces in a hammer mill. This intermediate procedure not only reduces the volumetric dimensions of the material, it increases also the over all surface area, facilitating access of microbial activity. Introducing the mechanically treated material for at least 72h into the revolving rotting drums boost microbial activity. Constant aeration, at a preset temperature of 50C not only speeds up the microbial decomposition process, but also kills many pathogenic bacterial strains and protozoic lifeforms. Before driving the pre-processed material into the landfill, it undergoes an indoor post-fermentation process.

Rubbish bunker

Rotting drum

To prolong the mineralization process, the semi-fermented material is stored for 3-4 weeks in the rotting hall. The rotting material is stored and turned over in regular intervals - the microbial metabolism still generates enough heat (about 50-70C) to complete "sterilization" of the rotting matter. To keep fouling smells from escaping into the environment, special floor-bound ventilation slits suck in the gaseous by-products and pass it through charcoal filters. The draining watery reaction liquids are likewise collected and conveyed to the wastewater treatment plant. To maintain the minimum temperature required for this process, heat-exchanger feed back process heat of the exhaust air stream into the rotting hall, thus increasing the overall efficiency. Both drum- and hall-fermentation are steps to further reduce the waste's volume and thus to save landfill space. Fermentation has another advantage as it reduces both the TOC level and the long-term metabolic activity of the material; i.e. fermentation within the rubbish pile while stored at the landfill. One can speak her of semi-mineralised waste, a form of waste which is bio-chemically less reactive than untreated residual waste. These quasi mineralized substances are no longer involved in metabolic processes (ideally, any material discharge into a landfill should be biologically and chemically inert).

By the time the amount of TOC has fallen below 5%, the total volume of the rotting material has decreased drastically. At this stage at least 30% volumetric reduction is achieved (referring to the initial volumetric dimensions), while about 80% of the all over biogenic content has been decomposed. The rotten matter is then loaded onto trucks, weighed, transported, deposited and compressed at the assigned location within the landfill.

Further microbial activity within the dumping site is unavoidable as cross-reactions among the various kinds of ingredients are ongoing as long as the right conditions are there. Stopping this conditions by reducing water and nutrient content of the waste material would be simply too expensive. Therefore a landfill is by far not a pile of dead matter, it remains a living bio-chemical reactor for as long as redox/reactions and metabolic activities are supported by proper humidity levels on the one hand and decomposable matter on the other.

Loading the rotten material for final deposition on the dumping site

Filling up the landfill

Half-full landfill

The landfill itself is structured in several ways to meet the standards of the Austrian environmental protection agency. The landfill is best situated in an area where clay forms a firm and impermeable bottom stratum. To keep off seepage from ever reaching this stratum and ultimately the groundwater layer, the landfill itself is sealed off at the bottom and the flanks with a multi-layer barrier, while the outer edges are likewise diked with a concrete double-chambered sealing strip.
Inside the landfills, at the outer edges, and at the bottom of the landfill, a network of draining pipes are laid to monitor the quality of seepage. Gas pipes incorporated throughout the landfill body, collect the anaerobic fermentation gasses and feed into the main gas tank. Along with the gas products of the biomass fermentation (from other sites of the plant, e.g. composting, garden waste processing, etc.) as well as the sludge fermentation (e.g. from the sewage treatment plant) are gathered as well, they are used to generate heat for the various fermentation steps while electricity, as another by-product, is used to cover part of the electrical demand of the plant.

Once the landfill reached its upper filling capacity it will be covered with an impermeable synthetic layer (to keep rainwater out), followed by a thick stratum of soil or humus obtained from the biodegradable composting process.
Þ Refer to the organic site.
Greening is often done by planting fast growing trees or grass on top of it. To monitor the uptake of toxic substances from the landfill matter below, the humus layer, trees, etc. are regularly cut and analysed within the plants on laboratory facilities. In the case of grass, the goat's milk is used to monitor the accumulation of incorporated toxins (bio-monitoring).

Goats used as biomonitors

References: Abfallsentsorgungs-Konzept der SBGer Abfallbeseitigung (1998); A-5101 Bergheim - AT
Leitbild der SBGer Abfallbeseitigung; Leitbild (1997); A-5101 Bergheim - AT
Abfallwirtschaft der MA48 (1999); Rathaus, A-1082 Wien, II - AT
For additional information visit the SAB web-site, or any of the other sites listed below

Intro / Paper / Glass / Plastic / Metal / Compost / Toxic / Residual / Sewage / Landfill