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Online course

12. Final Settling

Final settling is the most common way of solid-liquid separation in conventional activated sludge systems. The first part of this course deals with functions of secondary settling tanks (clarification, thickening and storage), different settling tank configurations in practice including most common operational problems, and measurements of sludge settleability. You will also get familiar with the flux theory for estimation of settling tank capacity and other methods for design and operation of secondary settling tanks such as empirical design, WRC design, ATV design and STOWA design. At the end of the course you will be able to compare settlers designed using different methods. Modelling approaches to secondary settlers are also included as well as examples and exercise to test and broaden your knowledge. Case studies and standard experimental methods for the evaluation of sludge settling properties are also part of this informative curriculum.

Welcome by Ferenc Házi

Course information

  • Learning Objectives

    After completion of the course you should be able to:

    • Understand the purpose of final settling and identify the key points for a clarifier design;
    • Pinpoint operational problems and address a solution;
    • Measure sludge settleability parameters;
    • Apply the flux theory and compare different settler design approaches:
    • Differentiate mathematical modeling levels and select the proper one for your purposes.
  • Syllabus

    This course covers the following topics:

    • Settling Tanks in Practice;
    • Measures of Sludge Settleability;
    • Flux Theory;
    • Design and Operation;
    • Modeling of Secondary Settlers.
  • Organization

    Courses in this series consist of video lectures, presentation slides, reading materials, exercises, and assignments with solutions. In principle, each video presentation has its complementary presentation slides. All videos are available for viewing in the section “Video-recorded presentations”. The materials are packaged in three (.zip) files, namely, the “Videos”, the “Presentations”, and the “Documents”. Files may be of considerable size, so you need to ensure that your computer has sufficient bandwidth and capacity for downloading. This course is based on the chapter in the book “Biological Wastewater Treatment: Principles, Modeling, and Design” 2nd edition (Chen et al., 2020). To check and expand your knowledge on the subject, it is recommended to study the corresponding chapter in the complementary book  “Biological Wastewater Treatment: Examples and Exercises” (Lopez-Vazquez et al., 2023). The two chapters are open access and available in the section “Documents (.zip) on this webpage. For those interested in related experimental methods, it is advised to consult relevant methods in the book “Experimental Methods in Wastewater Treatment” (Van Loosdrecht et al., 2016). The complete book and video-recorded experimentation are available on this website as a separate course (

  • Delivery Method

    This course is currently designed for a SELF-STUDY mode. It is FREE and does not include guidance, support, exams, assessment, and certification. It is possible that shortly, the series (or its parts) will be adopted by institutions who may deliver the guided version, including certification. As soon as this is the case, it will be advertised on this website.

  • Open Access

    The content is available for free unlimited access and use, consistent with Global Sanitation Graduate School’s commitment to ensuring open access to information and knowledge. Please note that the video materials fall under the Attribution 4.0 International (CC BY 4.0) license (, presentations under the Attribution 4.0 International (CC BY 4.0) license  (, readers (OA books of IWA Publishing) under the Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) license (, and other readers under the license specified by the publisher. Although care has been taken to ensure the integrity and quality of these materials and information, no responsibility is assumed by the author(s), Global Sanitation Graduate School, or IHE Delft Institute for Water Education for any damage to property or persons as a result of the use of these materials and/or the information contained herein.

Video-recorded presentations

Here you can watch all video-recorded lectures of this course.

12.1 Introduction

Ferenc Házi



1 of 6

12.2 Settling Tanks in Practice

Ferenc Házi


2 of 6

12.3 Measures of Sludge Settleability

Ferenc Házi


3 of 6

12.4 Flux Theory

Ferenc Házi


4 of 6

12.5 Design and Operation

Ferenc Házi


5 of 6

12.6 Modeling of Secondary Settlers

Ferenc Házi


6 of 6

Download course materials

In this section, you can download all presentations, and other documents that make up this course.


Prof, Damir Brdjanovic, PhD

Course resource person | IHE Delft Institute for Water Education