Household waste products that can be utilized for reclamation

Household waste products that can be utilized for reclamation

If we speak about household waste and its recycling, most of us have paper, glass and plastics in mind, some of us metals and bio-waste too. According to the statistical data of Eurostat, each citizen of the EU27 produces annually 500 kg of solid waste in average.


Nevertheless, we often forget about waste that every household and company produce too, and what’s more, in considerable volumes. It is residues which are flushed down the drainpipes, whether in the kitchen, bathroom or toilet. Fats, detergents, leftovers or excreta from human organisms, all this goes through the pipes, together with rainwater, pollens, sand, technical liquids and other pollutants from the roads, to sewage plants. Sewage plants are designed for the treatment of sewage and rainwater. Water from industrial production may be treated in sewage plants too.

How does a sewage plant work?

Waste water is conducted to a sewage plant through the main sewer from the sewerage system. At the end of the main sewer there is a gravel catcher, which catches coarse undissolved elements (next to gravel also paving blocks, bricks, etc.). The next stage is a screen, which removes coarse floating dirt. Beyond the screen there is a sand catcher, which is frequently combined with a fat catcher. Its task is to separate mineral suspensions (sand) from organic undissolved substances; it is advantageous to leave organic substances in waste water. The separation process is based on different densities of both materials. The removal of sand eliminates its setting at undesirable places and reduces the abrasion of possible subsequent plants.

p1080477The last plant for mechanical treatment is a sedimentation tank. In this tank fine undissolved substances deposit and floating dirt is skimmed off the tank surface. This is how a primary sludge is formed, which then enters a biological process. Biological treatment is done in a biological reactor. In this reactor the pollutants from waste water are removed by means of micro-organisms, which are called activated sludge. Activated sludge is capable of removing a large amount of organic pollutants and nitrogen and phosphorus compounds from waste water.

The mixture of water and activated sludge then flows to a secondary clarifier, where purified water is separated from activated sludge due to its sedimentation. Part of the activated sludge goes back to the biological reactor, while the other part is separated as an excessive sludge and conducted for further treatment to a sludge management company.

What is sludge management?

Sludge from sewage plants in the North Moravian Region (Czech Republic) is almost exclusively treated by OBSED Company, which has been a member of the .A.S.A. Group since 2007. From sludge supplied by sewage plants from Jablunkov in the east of the region to Bruntál in the west and Frenštát pod Radhoštěm in the south it makes its own products – reclamation substratum and industrial compost.

backhus%20finalThe sludge from sewage plants is loaded on trucks and transported to a reclamation site, where it is converted into reclamation substratum. Depending on admixtures, such reclamation substratum may be either covering substratum (with an admixture of soil) or subjacent substratum (with an admixture of light ash). On reclamation areas, sludge with admixtures is aligned in long rows using loading machines, forming thus gobs. A special Backhus machine then homogenizes the gobs, by which final substratum is created. It is subsequently conditioned for a period of 90 days on the delimited area. Then samples of the substratum are taken. If the laboratory samples, which are examined by accredited laboratories, comply with the company standards, the substratum is used in the terrain. OBSED Company (www.obsed.cz)  is the only one in the Czech Republic to own a Backhus machine of the necessary capacity – its output ranges from 300 to 3,000 tons per hour. The substratum usually matures 90 days. Samples taken in regular intervals are sent to a laboratory, which confirms their compliance with the relevant standard and the substratum is thus fit for being used in the terrain.

Annually, OBSED Company treats roughly 40 – 50,000 tons of sludge. The result is the volume of final substratum approximately three times larger. The substratum produced is further utilized in reclamation building projects as a filling material, possibly as the top layer rich in nutrients: this layer is a guarantee of the quality growth of grass, bushes or trees, which are used for the biological reclamation of a territory. To a limited extent, sewage plant sludge is added into farmland, in a controlled way, to act as a fertilizer for plants.

This is another instance of a process, which exemplifies the philosophy of “circular economy”. Its substance is a conviction that consumption, throwing out of a product or pouring of something into the drainpipes does not necessarily have to mean the end of the lifecycle of a specific product. Products can be used again, somewhere else, entering thus a new cycle. In this particular case, waste is used to renew a territory affected by industrial activities. This is only possible based on a duly applied resource management, which is the pillar of the effective functioning of the .A.S.A. Group in eight countries of Central and Southeast Europe.

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