What are the main methods of thickening sludge

     Concentration is a more economical and effective way to reduce the volume of sludge. The main dehydration object of sludge concentration is interstitial water. Sludge concentration includes gravity concentration, air flotation concentration, centrifugal concentration and other forms. Among them, the natural gravity is used to separate the sewage. The gravity concentration of mud is a more widely used and simpler concentration method.
(1) Gravity concentration
The gravity thickening tank is usually used to concentrate the sludge by gravity. The reasonable design and operation of the thickening tank depend on the correct grasp of the sludge settlement characteristics. The concentration tank can be divided into two types: batch type and continuous type. The former is mainly used in sewage treatment plants of small-scale industrial enterprises. The latter is used in large and medium-sized sewage treatment plants. Generally, centrifugal pumps can be used to feed mud in gravity concentration tanks, and mud pumps with higher pressure heads such as piston diaphragm pumps and plunger pumps are required for mud discharge. The gravity concentration method is easy to operate, low maintenance management and power costs, but it covers a large area.

(2) Air flotation concentration
It is a method to make the tiny air bubbles adsorb on the suspended sludge particles, so that the particles float together with the small bubbles and separate from the water. It is suitable for hydrophobic sludge where the particles are easy to float, or the suspension is difficult to settle and easy to agglomerate. Happening. According to the different ways of generating microbubbles, air flotation concentration can be divided into electrolytic air flotation, diffuse air flotation and dissolved air flotation. The air flotation and concentration of sludge mainly adopts dissolved air flotation, which can be divided into pressurized air flotation and vacuum air flotation. At present, there are many researches and applications on the former. Activated sludge, aerobic digestion sludge, contact stable sludge, delayed aeration sludge without initial precipitation, and some industrial waste grease and oil are suitable for air flotation and concentration. The primary sedimentation sludge, humic sludge and anaerobic digestion sludge, etc., due to their higher density and better settling performance, the use of gravity concentration is more effective than air flotation concentration.

(3) Centrifugal concentration
The sludge is separated by the difference in the density and inertia of the solid and liquid in the sludge, and the difference in the centrifugal force received in the centrifugal force field. The centrifugal concentration method occupies a small area and has a low cost, but the operating cost and mechanical maintenance cost are higher, so it is less used for sludge concentration. Especially for sludge that can be effectively concentrated by air flotation or gravity sedimentation without adding chemicals, from an economic point of view, centrifugal concentration is not suitable.
(4) Concentration by microporous filter
The filter screen of the microporous filter can be made of wire 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 to separate the molecules of particulate matter within a certain size range.
(6) Biological flotation concentration
After stopping the aeration of activated sludge, after a certain period of time, the sludge will be denitrified, releasing N2 and CO2, and floating and thickening the sludge. For the first sedimentation of sludge, if the water temperature is maintained at about 35°C and parked for more than 5 days, it will have the same effect.
(7) Vibration concentration
The inertial moment of vibration is used to make the various combined moisture between the sludge molecules destabilize and accumulate for concentration. It is mainly used in some special occasions, such as small production scale or test needs.
There are many thickening methods, which should be selected and applied according to the nature of the sludge and different conditions.

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