Denitrification in Anoxic Tank

Denitrification is a key process in water treatment. It consists of the conversion of nitrates (NO3) to inert nitrogen gas (N2), treating water to reduce its nitrate-nitrogen contents to potable levels.

Vertical agitators can be successfully used in denitrification. In an anoxic basin, a good mixing is fundamental to ensure a proper contact between bacteria and media, and to provide off-bottom solids suspension, preventing sedimentation. This results in an increase of oxygen uptake, a decrease in retention time, and an overall improvement of the denitrification process.

In this particular case, PRO-DO-MIX have been asked to design a mixing solution for a biological treatment plant composed of an anoxic tank, 31.6 m length, 7.3 m width, 7 m height, 6 m liquid level. The sewage sludge to be treated has a maximum concentration of 5 g/l. The Sludge Volume Index (SVI) is ≥ 80 l/kg.

PRO-DO-MIX is an expert in the implementation of anoxic mixing systems to effectively fulfil denitrification. We offered two agitators, model GEL.75262.Q.500.

The mixers’ drive unit is composed of a 7.5 kW motor and an industrial planetary gearbox, able to support the thrusts of the impeller, that is 5 m distant from the mounting flange.

The use of seamless pipes to manufacture the shaft of the mixer allows PRO-DO-MIX to reach a considerable shaft length (5 metres) in one piece, and to limit the mixer’s weight.

The impeller is a 3-blade 3PM-0030 “Evolution”, 2600 mm diameter. This high-efficiency hydrofoil impeller can guarantee an optimal mixing with very low absorbed power (in this case, the power density is only 4 w/m3). That feature helps avoiding air intake, and thus swirl or vortex, making “Evolution” perfect for denitrification. Its profile is specially designed to prevent sedimentations and ensure an excellent homogenisation. It can be positioned very close to the bottom of the tank, even in case of a large impeller diameter.

All wetted parts are made of SS 304.

INDUSTRY: Industrial Waste Water
APPLICATION: Denitrification in Anoxic Tank
LOCATION: Northern Italy
YEAR: 2011
VOLUME: 1400 m3
IMPELLER: 3PM-0030 Evolution