What are the main methods of sludge concentration

      Concentration is an economical and effective method to reduce the volume of sludge. The main dewatering object of sludge concentration is interstitial water.

Sludge thickening includes gravity thickening, air flotation thickening, centrifugal thickening and so on. Among them, gravity thickening, which uses natural gravity to separate sludge-liquid, is a widely used and relatively simple thickening method.

(1) Gravity concentration

The gravity thickening tank is usually used for gravity thickening of sludge.The reasonable design and operation of thickening tank depends on the correct control of sludge settling characteristics.Concentrator can be divided into two types: intermittent and continuous.The former is mainly used in sewage treatment plants of small treatment plant type industrial enterprises.The latter is used in large and medium-sized sewage treatment plants.Usually, gravity concentrator mud can be used centrifugal pump, mud needs to use piston diaphragm pump, plunger pump and other high pressure head mud pump.Gravity concentration method is easy to operate, low maintenance management and power costs, but occupies a large area.

(2) flotation concentration

It is a method to adsorb tiny air bubbles on suspended turbidity sludge particles, so that particles float up with small bubbles and separate from water. It is suitable for hydrophobic sludge with particles floating up easily, or suspension is difficult to settle and easy to aggregate.According to the different ways of generating microbubbles, the flotation concentration can be divided into three types: electrolysis flotation, scattered flotation and dissolved flotation.The main method of sludge floatation is dissolved air floatation, which can be divided into pressurized air floatation and true air floatation.Activated sludge, aerobic digested sludge, contact stabilized sludge, delayed aerated sludge without primary precipitation and some industrial waste oil and oil are suitable for floatation concentration.Due to the high density and good settling performance of primary sedimentation sludge, humus sludge and anaerobic digestion sludge, gravity concentration is more efficient than air flotation concentration.

(3) Centrifugal concentration

Using the density and inertia difference of the solid and liquid in the sludge, it is separated by the different centrifugal force in the centrifugal force place.Centrifugal concentration is less used for sludge concentration because of its small footprint, low cost, high cost of operation and mechanical maintenance.Especially for the sludge which can be effectively concentrated by air flotation or gravity sedimentation without adding agents, it is not suitable to use centrifugal concentration from the economic point of view.

(4) Concentration by microporous filter

The mesh of the microporous filter can be made of metal mesh, polyester fabric or polyester fiber.The sludge is concentrated by filtration.

(5) diaphragm concentration

Including ultrafiltration concentration method and reverse osmosis concentration method, using semi-permeable membrane filtration effect to make particulate matter molecules in a certain size range separate.

(6) Biological flotation concentration

After the aeration of activated sludge is stopped, after a certain period of time, the sludge will produce denitrification, release N2 and CO2, and the sludge will be floating and concentrated.For primary sedimentation sludge, if the water temperature is kept at about 35℃ and parked for more than 5d, it will also have the same effect.

(7) Vibration concentration

The inertia moment of vibration is used to make the various bound moisture between the sludge molecules lose stability and gather together, so as to concentrate.Mainly used in some special occasions, such as small production scale or test needs.There are many methods of thickening which should be selected and applied according to the nature of sludge and different conditions.

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