Membrane filtration vs conventional clarification - basic principles ('Membrane vs...' series, 3.)

This video is the third in our "Membrane versus.." series, in which membrane processes are compared with the conventional alternatives. This one introduces the different clarification processes and their fundamental characteristics. The classical clarification processes in water treatment can be categorised as gravitation and filtration, where gravitation of the suspended matter can either be by sedimentation or flotation (most often dissolved air flotation or DAF). Gravitation relies on a difference in density between the suspended matter and the surrounding water, and increases with particle size. This will be explained further in a subsequent video (Video 4). Filtration in the municipal water sector conventionally employs sand. This sort of filtration is termed media, or sometimes “depth” filtration, because removal takes place throughout the media bed depth. Membrane filtration can then be defined as surface filtration, because removal takes place predominantly at the interface between the membrane and water. This means that, for membrane filtration, a deposit of the rejected solids - referred to as a filter cake or fouling layer - is formed at the interface. This layer is then responsible for subsequent rejection of the suspended solids in the feedwater. The different mechanisms of particle removal fundamentally affect the purification performance, mode of operation and footprint of each process technology type. A key advantage of a membrane process is that it provides an absolute barrier to any particle larger than the membrane pores - provided the membrane isn't damaged. However, for both the membrane and depth filtration processes the particles deposited onto the surface of the filtering medium have to be periodically removed by cleaning. The gravitation processes, on the other hand, are continuous and simpler in operation. As to how all this impacts on footprint - see Video 4. ----------------------------------- Other videos in our 'Membrane versus..' series: 1. Metrics for assessing water and wastewater treatment technology – Introduction:    • Metrics for assessing water and wastewater...   2. MBRs vs CAS - Membrane bioreactor versus conventional activated sludge technology for wastewater treatment:    • Membrane bioreactor (MBR) v Conventional A...   4. Membranes vs. conventional clarification #2 - Membrane filtration versus media filtration and sedimentation for water treatment – footprint:    • Membrane filtration vs conventional clarif...   5. Membranes vs UV and chemical disinfection for water treatment:    • Membrane filtration vs UV and chemical dis...   6. Reverse osmosis (RO) vs evaporation for desalination:    • Reverse osmosis vs evaporation for desalin...   7. MABRs vs MBBRs - membrane-aerated bioreactor versus moving bed bioreactor technologies for wastewater treatment:    • MABRs vs MBBRs: membrane-aerated bioreacto...