Bar screen

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Rakes or sieves are an important purification step in wastewater treatment plants. The wastewater then flows through a rake or sieve with those rough ingredients are retained. The separated substances are called screenings or screenings. Process technology, there is a separation of solids from a liquid ( a branch of mechanical engineering, to which also belongs filtration ). Screens are usually the first cleaning stage in sewage treatment plants. Rare Screens are used at the end of the sand trap or in the return sludge stream.

Types of computing

Rake are classified according to different criteria. The most common finding is the distinction according to the size and shape of the aperture geometry.

A classification of the separating surface is also possible according to the type of the species. As computing devices are referred to as parallel bars. Grid, holes or mesh featuring a sieve. Historically, the most common are bar screens, but also a stage screen. With higher demands on the Rechengutrückhalt sieves are used. However, it must be noted that a higher hydraulic loss occurs at seven.

A further distinction is made according to the nature of the cleaning of the separating surface. There are surfaces to be cleaned by hand and automatic cleaning systems. The automatic cleaning is done via gripper chain rakes or Exzentersysteme. Screens often have movable separation surfaces, the brushes are cleaned and Spülleisten me.

Coarse screen

Coarse screen having an opening size of 10 mm to 50 mm are used to protect the mechanical parts of the system and to prevent clogging.

Fine Screen

Fine screen with an aperture size of 2 mm to 10 mm are used to reduce the solids accumulation in the mud. With the use of fine screens the aim is, as far as possible to remove solids.

Fine screen

Must be particularly trouble-prone machines and components of the treatment plant as membrane plants are protected, fine sieves are used with an opening size of less than 2 mm. The separation surface is fully occupied usually after a short time with screenings. Therefore, it is more of filtration, also in the particles that are smaller than the opening geometry, are retained.

Screenings

Screenings has a water content of about 50%. The solids composed mainly of organic substances such as toilet tissue, feces, and food residues. Mineral elements such as sand and clay have a share of 4-9 %. With the use of fine screens and fine screens sand is increasingly included. Screenings can produce all kinds of civilization contain garbage. This includes packaging, dentures, squares and car tires. Problematic are contained fibers (textile fibers, hair, paper and plastics) in the wastewater. Due to their structure, they tend to tressing and may result in pumps and agitators damage.

From domestic wastewater between 5-15 liters per inhabitant per year Rohrechengut be found in Western Europe. Due to the leaching of easily soluble organic components and the compression of the screenings, the quantity to be disposed of is reduced to an average of 2.2 kg per inhabitant and year screenings. Depending on the habits, the amount vary greatly in other countries. Screenings is a hygienically problematic waste, which must not be disposed of in Germany. Therefore, the disposal is carried out most often by burning.