WE&T’s Operator Essentials column presents easily accessible and digestible fundamental information. It is intended to share “what every operator should know” about each topic covered. The column is arranged as a grid of knowledge, principles, and practical considerations — each successive column provides more detailed information.

WE&T’s Operator Essentials column presents easily accessible and digestible fundamental information. It is intended to share “what every operator should know” about each topic covered. The column is arranged as a grid of knowledge, principles, and practical considerations — each successive column provides more detailed information.

WE&T’s Operator Essentials column presents easily accessible and digestible fundamental information. It is intended to share “what every operator should know” about each topic covered. The column is arranged as a grid of knowledge, principles, and practical considerations — each successive column provides more detailed information.

WE&T’s Operator Essentials column presents easily accessible and digestible fundamental information. It is intended to share “what every operator should know” about each topic covered. The column is arranged as a grid of knowledge, principles, and practical considerations — each successive column provides more detailed information.

WE&T’s Operator Essentials column presents easily accessible and digestible fundamental information. It is intended to share “what every operator should know” about each topic covered. The column is arranged as a grid of knowledge, principles, and practical considerations — each successive column provides more detailed information.

Historically, dryers have been used to produce biosolids products for land application, fertilizer amendment, volume reduction for landfilling, or fuel sources (cement kiln, lime kiln, etc.). With many facilities considering high-temperature processes (HTPs) because of their potential destruction of per- and polyfluoroalkyl substances (PFAS), greater mass reduction and potentially more valuable end products, dryers will be required to pre-dry biosolids for these processes as well.

This Fact Sheet will provide a high-level overview of dryer requirements and considerations for dried biosolids to be used in HTPs.

Thickening is a valuable step in the wastewater treatment process, designed to increase the solids content of sludge by removing excess liquid. Unlike dewatering, which aims to produce the driest cake possible, thickening enhances sludge consistency for better handling and downstream processing. Proper optimization of thickeners reduces sludge volume, improves process efficiency, and lowers operational costs, supporting consistent and efficient daily operations. This optimization also aids in maintaining compliance with environmental regulations and contributes to environmental sustainability.

Utilities commonly use thickening centrifuges, gravity thickeners, gravity belt thickeners (GBTs), and rotary drum thickeners (RDTs) for sludge thickening (see photos of thickening devices in Figure 1). This Fact Sheet serves as an educational resource for operators, detailing the operating principles and benefits of these devices. By understanding how each type of thickener device functions, operators can maximize solids capture, optimize polymer usage, improve facility performance, and maintain a safe working environment.

For additional technical details, formulas, and case studies addressing typical performance and other pertinent information, please refer to the References and Additional Resources sections at the end of this document.

Utilities use a variety of equipment to dewater solids, but currently, the most common technologies include belt filter presses (BFPs), centrifuges, and screw presses. Each of these technologies is briefly described below, along with suggestions for how each could be adjusted to aid in optimization efforts. As other types of equipment become more widely used, this Fact Sheet will be updated. The optimization suggestions in this fact sheet focus on dewatering equipment-based changes rather than process-oriented impacts. For useful formulas and example problems, technical details on dewatering equipment, polymer, or process impacts on solids dewaterability, please
refer to the References and Additional Resources Sections at the end of this Fact Sheet.

Now that the data has been collected, in accordance with Optimization of Thickening and Dewatering for Operators Series, Fact Sheet #3 – Data Collection and Analysis (WEF, 2024), it is time to utilize that data to create and place into action a logical and effective plan to optimize your thickening or dewatering system, and to make that optimization plan sustainable for the long-term. The main purpose of this “roadmap” operator Fact Sheet is to provide practical information for an operator to:

1) Use analyzed data to decide what actions to take, and in what order (i.e., how to create a “roadmap”).
2) Understand when investing budget into optimization is justifiable.
3) Understand how and when to determine if your optimization efforts have been successful.
4) Understand how to make the optimization results sustainable for the long-term.

The main purpose of this Fact Sheet is to provide practical information for an operator to 1.) Develop a meaningful sampling and data collection program for establishing baseline data as the foundation for achieving your optimization goals and 2.) Organize and analyze the collected baseline data to help identify trends and optimization opportunities. This fact sheet also provides tips and reminders for collecting representative biosolids samples, as well as a high-level list and resources for bench-scale tests that can be beneficial for optimizing thickening and dewatering.

The focus of this fact sheet is on the first three steps that are critical to setting up a successful optimization effort shown in Figure 1, which are to 1) assess the equipment's physical condition, 2) check how it is operating and whether the equipment is still meeting its original design criteria, and 3) identify any gaps or bottlenecks. Proceeding with an optimization effort before completing these three steps would be fruitless.

Operators can and should perform the equipment and operational assessments described within this fact sheet to the level that they are comfortable with. However, if you could use some help, it might be appropriate to engage an internal or external engineer, or some other staff member, to assist with conducting the equipment or operations assessments.

The purpose of the Optimization of Thickening and Dewatering for Operators Series, Fact Sheet #1: Introduction is 1) to provide an introduction to what it means to optimize your thickening or dewatering system and 2) to provide an overview of the more in-depth fact sheets contained within this series.