Page 24 - March 2020 - WT Site

Fig-2 (a) Disc diffuser (b) Tube diffusers

b. Jet Aeration System: To provide the oxygen source for the the decanting rate is not controlled. Generally used in small
biological reaction, a jet aeration manifold with multiple jet installations. Mechanical problems related to valve and actuators
nozzle assemblies is connected to a pump and a blower. Each require regular maintenance. This is of low cost. These are used
jet has a primary mixing nozzle and an outer secondary nozzle. in small installations. It is represented in Fig-3 [8].
Jet aeration provides high oxygen transfer and complete mixing
to provide both anoxic and aerobic conditions as required to b. Floating decanters: The decanter floats on water due to
promote biological nutrient removal. Jets, with their large solids buoyancy and the treated water leaves the tank through a flexible
handling capability and robust design, are ideal for the constant rubber hose. The outlet quality is poor and inconsistent as the
on/off operation common with SBRs [7]. decanting rate is not controlled. Buoyancy problems lead to
decanter sinking. These are used in small and medium installations.
2.2.2. Decanter Systems: They are higher cost than valve arrangement. It is represented in
Decanters are used for removal of clean water from the top of Fig-4[8].
the SBR tank after settle phase of operation. There are 3 types
of decanting systems available.1.Valve arrangement 2.Floating
decanters 3.mechanically operated decanters

a. Valve Arrangement: Valves are positioned at different
levels in the tank’s side, and these are opened sequentially from
top to bottom. The outlet quality is poor and inconsistent as

Fig-4: Floating decanters

c. Mechanically operated Decanters: The decanter is pushed
down by a top-mounted motor-driven gearbox in a precise manner
by PLC. Outlet quality is very good and consistent as the decanter
descent rate is controlled. It is used in small and large installations.
Fig-3: Valve arrangement decanter

26 Water Today - The Magazine March 2020