Thickening and dewatering are bookends of your residuals handling process.  Your operational knowledge/skill here has direct, whole-plant impacts including treatment performance, permit compliance, and operating costs. Thickening and dewatering are separate processes typically used in different locations and in different roles at a WWTP.  The processes have several key similarities and differences:

• Function – both thickening and dewatering aim to increase solids concentration; they do this by removing water from the feed sludge stream
• End Product – it’s all about cake solids
  • For thickening, we get a biosolid with concentration ranging from <1.5% to 8% solids depending on the technology and sludge type. Three percent is most common. 
  • For dewatering, we typically get a biosolid with concentration ranging from 3% to up to 90% solids depending on the technology and sludge type.
• Why – for thickening, the want to reduce the total sludge volume so all our downstream processes can be smaller and less costly. For dewatering, we want to reduce the total weight to minimize hauling and disposal costs.
• Where - Thickening is typically the first step in solids stream. Dewatering is typically the last step in solids stream
• How – There’s a lot of technology out there.
  • Gravity thickeners, DAF, GBT, Centrifuge, RDT, and Screw presses are all commonly used for thickening.
  • Thermal dryers, Drying beds, BFP, P&FP, Screw presses, and Centrifuges are all commonly used for dewatering.

Chemical use (polymer) in thickening/dewatering is a major cost at most WWTPs and from my experience there’s usually a ton of opportunity to improve practices at WWTPs.  While industry knowledge and best practices are well defined this info is often hard for staff to access and apply. That’s why I’ve created a roadmap to help all WWTPs optimize polymer use and reduce the associated operating costs. It gathers all the industry knowledge and presents it in an easy-to-follow format.  Download it for free here.