Solid-liquid separation
Separating solids from the liquid phase is crucial for reliably meeting required effluent standards.
Typical solids include, for example, suspended matter present in the water, oils and fats, as well as residual activated sludge from biological treatment processes.
Depending on the composition of the wastewater, various separation methods are employed; the performance of these methods can be further enhanced through the addition of flocculants.
Circular Scrapers:
These systems utilize gravity to separate settleable solids within a circular sedimentation tank. Particles collect on the tank floor and are removed by a rotating scraper mechanism, while the clarified water is discharged in a controlled manner. This process requires minimal maintenance and is suitable for large volumes of wastewater.
Chain Scrapers:
Chain scrapers operate based on the principle of sedimentation. Solids that have settled on the tank floor are transported into a sludge hopper by means of chain-driven scrapers and are then removed. The clarified water is drawn off from the surface.
Dissolved Air Flotation (DAF):
In dissolved air flotation, gas (usually air) that has been dissolved under pressure is released due to a sudden drop in pressure. The resulting micro-bubbles attach themselves to solid particles and fat globules, carrying them to the water's surface. From there, they are removed as floating sludge.
This process is particularly well-suited for wastewater containing fats or high levels of emulsions, such as that generated by the dairy and food industries.
Inclined Plate Clarifier (Lamella Clarifier):
Inclined plate clarifiers accelerate sedimentation through the use of slanted plates (lamellae). This increases the effective settling area while significantly reducing the space required compared to conventional sedimentation tanks. The process is especially effective for separating out settleable solids.
Rake Mechanism (Thickener Mechanism):
Rake mechanisms are used, among other things, for the pre-thickening of excess sludge from biological wastewater treatment. Similar to a circular scraper, they collect and remove settled solids. Additional stirring arms loosen the sludge, while floating matter (scum) can be removed separately from the surface. Pre-thickening reduces the volume of the sludge, which facilitates subsequent dewatering.
Hydrocyclone:
A hydrocyclone separates solids using centrifugal forces. As the wastewater stream rotates, heavier particles are pushed outward and separated, while the liquid is discharged from the center.
Gravel and Sand Filters:
In this type of filtration, pre-treated wastewater is passed through a filter bed that retains any remaining solids. Depending on the design of the filter, the flow can be directed from top to bottom or from bottom to top. Gravel and sand filters are suitable for large volumes of wastewater and require relatively little space. Regular backwashing is required to maintain filtration performance.
Activated carbon filters:
Activated carbon filters utilize the large surface area of activated carbon to remove dissolved substances from water through adsorption. In addition to retaining specific particles, this process is particularly effective at reducing organic compounds as well as substances that cause odors or discoloration. To ensure consistently high purification performance, the filter capacity must be monitored, and the activated carbon must be replaced or reactivated in a timely manner.
