What is sludge dewatering? Moisture content of dewatered sludge and types of dewatering machines [Basic Knowledge]
When the moisture content decreases by 1 point, how much does the amount of dewatered sludge change? This will explain the calculation method, the type of dewatering machine, and what happens to the dewatered sludge afterward.
Dewatering of sludge refers to the process of further separating water from sludge that has already had some water removed through concentration, using machinery to produce solid dewatered sludge. Dewatered sludge is also referred to as dewatering cake. According to the Sewerage Act, public sewer managers are required to strive to reduce generated sludge through methods such as dewatering and incineration. ■ Moisture content is the ratio to the total weight Moisture content is a value that indicates what percentage of the total weight of the sludge is made up of water. The remainder is the proportion of solids; for example, if the moisture content is 78%, then the solids make up 22%. For instance, if we estimate the solid concentration of concentrated sludge to be 3.5% and the moisture content of directly dewatered sludge to be 78%, then if the amount of solids is the same, the weight after dewatering would be 3.5 divided by 22, which is about one-sixth of the concentrated sludge. ■ Does a 1-point difference matter?! When the moisture content of dewatered sludge decreases from 80% to 79%, the proportion of solids increases from 20% to 21%. Since the amount of solids does not decrease, the weight calculation is 20 divided by 21, resulting in about 95%, which means a reduction of approximately 5%. The higher the moisture content, the more significant the impact of the same 1-point difference on the quantity. Please feel free to consult with us first.
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■Can dewatering machines be categorized by how they separate water? The main types used in wastewater treatment in food factories are as follows: 1. Squeezing with filter cloths or screens: Filter press, screw press, belt press 2. Separating by centrifugal force: Centrifuge 3. Suction and filtration: Vacuum dewatering machine ■There is no machine that excels in all aspects When comparing machines, both the screw press and filter press excel in dewatering rates, but both have disadvantages in terms of equipment costs. Conversely, in terms of SS recovery rates, the vacuum dewatering machine excels, putting the screw press at a disadvantage, thus changing the order of evaluation. No single machine excels in all categories, and the suitable machine varies depending on the characteristics of the sludge and installation conditions. This is why many types are commercially available. ■Does moisture content change during operation? The screw press can adjust the moisture content by regulating the opening and closing of the scraper at the outlet of the dewatering cake. Additionally, adding coagulants to create strong flocs is also done to reduce moisture content. Not only the type of machine but also the chemicals and operating conditions influence the final results.
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■What happens to dewatered sludge afterwards? Sludge from food factories is often dewatered and transported off-site for disposal, and there are also treatment facilities that further dry it for use as fertilizer or incinerate it. In drying, there is a method that uses a rotary dryer to produce dried sludge with a moisture content of 10% or less for discharge. In any case, the starting point is how much water can be reduced through dewatering. ■Too much water for composting! The initial moisture content of sludge suitable for composting is 40-60%. Sludge containing 80-90% moisture exceeds the suitable range, so adjustments are made to the moisture content, such as returning some of the produced compost. ■Moisture content is key even in incineration! For sewage sludge, there is technology that eliminates the need for auxiliary fuel in incinerators by reducing moisture content. There are also technologies that dry dewatered sludge into granular fuel with a moisture content of around 6-10%. The lower the moisture content, the less water needs to be evaporated during incineration or drying. ■Selection of coagulants and updating of dewatering machines Our company offers consultations on the selection of coagulants used for sludge dewatering and the updating of dewatering machines, including wastewater treatment facilities. Please feel free to contact us first.
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