Mechanical separation of solid substances by filtration
Filtration separates solid substances from liquids. To do this, the mixture to be separated passes through a filter; in the simplest case, it can be made of paper. For technical applications, filters made of textile or metal fabric are mostly used. Sand filters, rotary sieves and cloth filters are also frequently used.
With the aid of filter systems, suspended organic and inorganic substances, sand and dust can be removed from the water. In wastewater technology, this mechanical separation process is used, among other things, for the dewatering of sludge in filter presses. In the treatment of water for industrial use and drinking water from surface waters, filtration is also applied; generally in a multi-stage process.
Membrane filtration is also a mechanical separation process. In this case, a membrane serves as the filter medium. This method is typically used to separate very small components.
Cleaning wastewater with membrane technology
With membrane filtration, dissolved and undissolved substances can be separated from waste water and concentrated. Thus, the separation is carried out under pressure; the membrane, with a given pore width, retains particles (eg molecules) from a certain size. The different processes are used for water treatment, for the cleaning of waste water, for the recycling of process water and for the concentration of recyclable materials for their recovery.
The micro filtration is used to separate particles, bacteria and yeast. It is used, among other things, for cold sterilization and the separation of oil and water emulsions.
The ultra filtration is an important process for treating drinking water and wastewater. It is used to separate particles, microorganisms, proteins and turbidity from water, among others, in the membrane bioreactor (MBR).
Ultrafiltration is used for example for cleaning recirculating water in swimming pools. Since the formation of clogging layers adhering to the membrane can be avoided quite well, existing sewage treatment facilities are increasingly being supplemented with an ultrafiltration called “polishing step”. In retrofitting older classic treatment plants, ultrafiltration can be inserted directly into or after the bioventilation tank to replace subsequent treatment steps or to increase the performance of biological wastewater treatment.
The nano filtration can separate viruses, heavy metal ions, large molecules and very small particles. This process is used in the softening of water and in the treatment of drinking water.
The osmosis inversa is an important step process the concentration of landfill leachate, in the treatment of drinking water in rural regions that are not connected to the mains, in seawater desalination or descaling water boilers in power plants. To do this, the concentration of dissolved substances in liquids is increased through a semi-permeable membrane, reversing the osmosis process with pressure: if the pressure is higher than the respective osmotic pressure, the solvent molecules diffuse on the side of the membrane on which the dissolved and less concentrated substances are found. This process is also used to obtain ultrapure water.
Wastewater treatment by flotation
In flotation, substances dispersed or suspended in liquids are transported to the surface with the help of small gas bubbles, where they are removed with a removal device. Flotation processes are used in wastewater treatment to separate suspended oils, fats and fine solids.
The smaller the microbubbles, the better the particles or droplets settle. For this reason, dissolved air flotation (DAF) is frequently used in wastewater treatment technology. This has been noted for its proven efficiency and cost effectiveness. Flotation processes can be further enhanced by employing auxiliary means, such as manifolds, skimmers, regulators or pressure devices.
Separation of solid substances by sedimentation
Sedimentation uses the force of gravity in sedimentation tanks to separate solid particles. A sedimentation tank is a flat tank with almost no current flow, especially for sedimentation processes. Solid particles settle to the bottom.
Sedimentation processes are used in multiple ways in wastewater treatment: undissolved substances are deposited in the primary settling tank. These form the primary sludge, which then thickens and becomes anaerobic in the digester. This generates digested sludge and digestion gas, which in its already clean form as biogas can be used to produce electricity and meet energy demand. Aerobically generated sewage sludge can also be introduced into the digester, after it has been separated by sedimentation from the residual water in the settling tank. Particles that are heavier than water can be separated from the liquid with the help of grit traps or sludge collectors.