The embodiments herein disclose a method and apparatus for mixing sludge retained in a digester. A jet nozzle assembly for mixing contents of a vessel is used. The jet nozzle assembly having a central outlet pipe terminating at a jet nozzle, a low pressure nozzle assembly disposed concentrically about the central outlet pipe, the low pressure low pressure nozzle having a plurality of openings disposed circumferentially about the low pressure nozzle assembly. The plurality of openings are an axial distance from the outlet jet nozzle.

The embodiments herein disclose a method and apparatus for mixing sludge retained in a digester. A jet nozzle assembly for mixing contents of a vessel is used. The jet nozzle assembly having a central outlet pipe terminating at a jet nozzle, a low pressure nozzle assembly disposed concentrically about the central outlet pipe, the low pressure low pressure nozzle having a plurality of openings disposed circumferentially about the low pressure nozzle assembly. The plurality of openings are an axial distance from the outlet jet nozzle.

The present disclosure discloses a slightly heavy particle system for wastewater treatment, comprising a contactor. Said contactor includes a gas-liquid-solid three-phase region, and said gas-liquid-solid three-phase region includes gas phase, liquid phase, and solid phase. Said liquid phase is the continuous phase and said solid phase is slightly heavy particles. Said slightly heavy particles are able to carry some microorganisms on their surfaces at least, and the density of said slightly heavy particles is higher than the density of said liquid. The slightly heavy particle system of the present disclosure applied in wastewater treatment can increase the concentration of microorganisms significantly, improve the ability to bear impact load, produce less sludge, and without sludge expansion. Meanwhile, the means to suspend slightly heavy particles with the combined effect of gas and liquid is able to reduce energy consumption to a larger extent. Therefore, this system features with high efficiency and low energy consumption.

A water treatment system including: a biological treatment stage for treating an organic wastewater by an action of a microorganism; an ozone gas producing stage for generating ozone gas; a sludge transferring stage for withdrawing and transferring a part of the microorganism-mixed liquid in the biological treatment stage; an ozone treatment stage for bringing ozone into contact with the part of the microorganism-mixed liquid transferred; and a treated liquid returning stage for returning the treated liquid after the ozone treatment from the ozone treatment stage to the biological treatment stage. Undecomposed aggregated microorganisms after the ozone treatment are separated and concentrated, and an ozone treatment is selectively applied to the aggregated undecomposed microorganisms thus separated and concentrated.

A slightly heavy particle system for wastewater treatment includes a contactor. The contactor includes a gas-liquid-solid three-phase region, and the gas-liquid-solid three-phase region includes gas phase, liquid phase, and solid phase. The liquid phase is the continuous phase and the solid phase is slightly heavy particles. The slightly heavy particles are able to carry some microorganisms on their surfaces at least, and the density of the slightly heavy particles is higher than the density of the liquid. The slightly heavy particle system applied in wastewater treatment can increase the concentration of microorganisms significantly, improve the ability to bear impact load, produce less sludge, and without sludge expansion. Meanwhile, suspending slightly heavy particles with the combined effect of gas and liquid is able to reduce energy consumption to a larger extent. Therefore, this system features with high efficiency and low energy consumption.