Mechanical Wastewater Treatment Processes
Mechanical processes play an important role in water treatment, especially in the removal of solids. They can separate a wide range of impurities. Mechanical pre-cleaning is particularly important in the treatment of heavily contaminated water,
where different materials can present a particular challenge. By using suitable methods, operators can avoid blockages and damage to the cleaning technology and thus reduce maintenance costs.
Overview of the Mechanical Wastewater Treatment Process
Separation of Solids by Sedimentation
Sedimentation utilises gravity to separate solid particles in sedimentation tanks. A sedimentation tank is a shallow and virtually flow-free tank specially designed for sedimentation processes. The solid particles settle to the bottom.
Sedimentation processes are used in a variety of ways in wastewater treatment: Undissolved substances settle in the primary clarifier. They form the primary sludge, which is then thickened and converted anaerobically in the so-called digestion tower. This produces digested sludge and digester gas, which can be converted into electricity in purified form like biogas to cover energy requirements. Aerobically produced sewage sludge is also fed into the digestion tower after it has been separated from the wastewater by sedimentation in the secondary clarifier. Particles that are heavier than water can also be separated from the liquid using sand traps or sludge collectors.
Coarse and Fine Material Separation
Rakes and sieves are used to remove unwanted solids from the water. This mechanical process is used, for example, to separate nappies and hair, as well as wet wipes and sanitary towels, from the wastewater stream. Before industrial wastewater is cleaned, sieving systems also capture textile fibres, paper labels, plastic residues and production residues such as potato peelings and other peelings.
Depending on the area of application, coarse or fine rakes are used. They clean the water with the help of parallel bars. Screens, on the other hand, have grids, holes and meshes. With different opening sizes from coarse (> 20mm) to micro-screens (<0.05 mm), they separate solids from coarse civilisational waste up to sand and mud particles from the wastewater stream.
Mechanical pre-cleaning is of great importance in the treatment of sanitary wastewater. Fibres contained in the wastewater, especially the extremely tear-resistant textile fibres from wet wipes and fleece, are particularly challenging. They tend to form clumps and can thus cause blockages and enormous damage to pumps and agitators.
DAS Environmental Expert GmbH specialists will work with you to select the appropriate drum sieves or self-cleaning screens to avoid damaging your sewage treatment technology and thus unnecessary maintenance work from the outset and save the costs involved.
Filtration
Filtration is used to separate solids from liquids. To do this, the mixture to be separated passes through a filter, which in the simplest case can be made of paper. For technical applications, filters made of textile fabric or metal are usually used. Sand filters, drum sieves and cloth filters are also frequently used.
Filter systems can be used to remove inorganic and organic suspended matter, sand and dust from water. In sewage treatment, this mechanical separation process is used, among other things, to dewater sludges in filter presses. Filtration is also used in the treatment of drinking and process water from surface water, usually in a multi-stage process.
Sludge Dewatering
Excess sludge is transported with the treated water to a secondary clarifier and separated there by means of gravity before a progressing cavity pump conveys it to the flotate hopper. The separated solids (flotate) from the flotation also arrive there. A flotate sludge pump then conveys the sludge to the downstream sludge dewatering system.
The sludge is then dewatered using a screw press; the remaining residues are transported to a collection point (container) by a screw conveyor.
Your point of contact for the topic of wastewater treatment processes
Dr.-Ing. Anita Haupt
Director Process Design Water Treatment
