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The water trickles through the trays, keeping the filter wool wet but not completely submerged, allowing aerobic bacteria to grow and aiding biological filtration. The water returns to the aquarium like rain. [14] Alternatively, the wet/dry filter may be placed below the tank. In this design, water is fed by gravity to the filter below the ...
Gravity plays a part by forcing the flow of water to pass through the D.E. cake which filters out any unwanted particles. As the flow of water continues, water that has been clarified at the base of the filtration tank exits through the water outlet to any designated vessel. [20]
The ponds or basins may range in depth from 1.5 to 5.0 meters. [6] In a surface-aerated system, the aerators provide two functions: they transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes).
The other advantages of this system include its low power costs, since the pumps utilised in depth filters require minimal power input due to the small pressure within the system. Depth filtration is also flexible in terms of being able to scale up or down the system while outputting a high rate of yield (>95%). [8]
The creatures burrow and overturn the top two to three inches of sand in search of food, which causes water to circulate deeper in the sand than it would if the creatures were not present. Deep sand beds may be made of a variety of materials, but typically fine or "superfine" sand is used, with a grain size between 1 mm and 0.05 mm.
Since the surface area of the tank is WL, and v s = Q/WL, v h = Q/WH, where Q is the flow rate and W, L, H is the width, length, depth of the tank. According to Eq. 1, this also is a basic factor that can control the sedimentation tank performance which called overflow rate. [13]
Economy favors using small tanks; but if flow rate through the tank is too high, most particles will not have sufficient time to settle, and will be carried with the treated water. Considerable attention is focused on reducing water inlet and outlet velocities to minimize turbulence and promote effective settling throughout available tank volume.
Spent backwash water is either discharged without treatment to a sanitary sewer system or is treated and recycled within the plant. [4]: 22.37–22.40 Historically, backwash water was discharged directly to surface water supplies; however, direct discharge is now highly regulated through NPDES discharge permits and is often discouraged.