What Is a Liquid-Solid Separator?
Liquid-solid separator devices are used to separate and remove solids from liquids. They are primarily employed in the field of sewage treatment.
Sewage treatment involves two stages: the separation of solids from sewage and the treatment of pollutants dissolved in the water. The former is accomplished through the use of liquid-solid separators, which are a more cost-effective solution. The latter is challenging to address with liquid-solid separators, and biological treatments such as activated sludge are generally employed. If pollutants persist in the liquid, the accumulation of excess sludge after biological treatment can increase, leading to a deterioration in treatment efficiency.
Uses of Liquid-Solid Separators
Liquid-solid separators find applications in the pretreatment of sewage and in the dehydration and concentration of sludge. The choice of equipment varies based on the dewatering method employed and whether a coagulant is added.
Equipment that removes solids through screens, among other methods, is utilized for sewage treatment. Examples include screw presses, roller presses, and belt screens. Equipment used for sewage treatment can operate without the addition of flocculants.
For sludge treatment, vacuum dehydrators, pressure dehydrators, belt presses, screw presses, and centrifugal dehydrators are commonly used. These sludge treatment devices primarily rely on the use of flocculants.
Principles of Liquid-Solid Separators
Liquid-solid separators are mainly employed for dewatering through filtration or centrifugal force. Since the moisture content of the cake after treatment differs between these two types of methods, the choice depends on the nature of the sludge being treated.
Typical examples of filtration-type dewatering equipment include pressure dehydrators and belt presses. In a pressure dehydrator, a pressurizing pump forces the sludge into a filter chamber for dewatering. Although there are some drawbacks, such as the need for cake discharging and assembly after each dewatering cycle, the advantage is the ability to apply a significant amount of filtration pressure.
In the case of the belt press, sludge is coagulated using a polymer coagulant and then dewatered using a belt-shaped filter cloth. Liquid sludge is pre-concentrated by gravity and then pressed using rolls because it seeps from between the belts. Pressurized dehydrators have traditionally been the primary choice for filtration systems, but belt presses are gradually gaining popularity.
Centrifugal dehydrators dewater the sludge by utilizing centrifugal force. Centrifugal dehydrators harness the centrifugal force generated by high-speed rotation and can be classified into cylindrical and conical types based on the shape of the rotating body. The cylindrical type is suitable when maintaining the clarity of the liquid is crucial, whereas the conical type is preferred when reducing the moisture content of the cake is the primary objective.