PPFAC Computer Controlled Activated Sludge Process Unit



General Description

The Computer Controlled Activated Sludge Process Unit, "PPFAC", has been designed to simulate theoperation of a wastewater treatment plant, breaking down water organic components with aerobicmicroorganism cultures (activated sludge).

The unit is mounted on a metal frame and consists of two modules connected by a set of hoses (included).

The first module consists of a supply tank with raw water and dissolved organic matter. A computercontrolled stirrer keeps the mixture under constant stirring.

The second module includes the water treatment tank where the activated sludge microorganisms arelocated, a clarifier and other elements required to carry out the wastewater treatment.

The raw water is impelled by a computer controlled pump from the supply tank to the water treatmenttank, where it is mixed with the activated sludge that contains the microorganisms.

Air is supplied to the water treatment tank by a computer controlled compressor.

The tank is divided in two zones separated by a wall: one zone for the nitrification process (ammonium isoxidized to nitrate in the presence of oxygen) and the other zone is for the denitrification process (nitrateis reduced to molecular nitrogen without air). Raw water is mixed with the activated sludge by threecomputer controlled stirrers: two in the nitrification zone and one in the denitrification zone. There are twosensors in the tank that measure the oxygen concentration in the two zones, a pH sensor at the inlet of thetank and a temperature sensor in the nitrification zone.

The oxygen concentration, the pH and the temperature can be modified by computer:

  • The raw water pH value can be modified by adding acid and base with two variable speed peristaltic pumps. Thus, the pH value inactivated sludge processes can be studied.
  • The value of the oxygen concentration in the nitrification zone of the tank can be modified by controlling the air flow supplied by thecompressor at the tank inlet.The temperature can be varied with a heat exchange circuit.
  • A heating element heats water in a tank (with level switch and drain valve)and it is impelled by a pump through a circuit, which transfers its heat to the nitrification zone.

After leaving the tank, the mixture passes to the clarifier, where the activated sludge settles by sedimentation and is separated from thetreated water. Part of that activated sludge returns to the water treatment tank driven by a computer controlled pump. In this clarifier, acoagulant (to reduce repulsive forces between particles) and a flocculant (to form larger flocs) can be added with two computer controlledperistaltic pumps with adjustable speed.

This Computer Controlled Unit is supplied with the EDIBON Computer Control System (SCADA), and includes: The unit itself + a Control Interface Box + a Data Acquisition Board + Computer Control, Data Acquisition and Data Management Software Packages, for controlling the process and all parameters involved in the process.

Exercises and guided practices


  1. Study of wastewater treatment with activated sludge.
  2. Study of the nitrification and denitrification processes.
  3. Study of the influence of the return sludge.
  4. Operation of the unit for steady working conditions.
  5. Study of the sludge age and its influence on the process.
  6. Study of results with a variation of the activated sludge mass flow.
  7. Study of results with a variation of the raw water volumetric load.
  8. Study of the internal recirculation return sludge rate influence onthe pre-denitrification.
  9. Calculation of the pre-denitrification efficiency.
  10. Study of the pH value influence on the biological degradation.
  11. Study of the temperature value influence on the biologicaldegradation.
  12. Study of the oxygen concentration value influence on thebiological degradation.
  13. Sensors calibration


  1. Many students view results simultaneously.To view all results in real time in the classroom by means of aprojector or an electronic whiteboard.
  2. Open Control, Multicontrol and Real Time Control.This unit allows intrinsically and/or extrinsically to change thespan, gains, proportional, integral, derivative parameters, etc, inreal time.
  3. The Computer Control System with SCADA and PID Controlallow a real industrial simulation.
  4. This unit is totally safe as uses mechanical, electrical/electronic,and software safety devices.
  5. This unit can be used for doing applied research.
  6. This unit can be used for giving training courses to Industrieseven to other Technical Education Institutions.
  7. Control of the PPFAC unit process through the control interfacebox without the computer.
  8. Visualization of all the sensors values used in the PPFAC unitprocess.
  9. By using PLC-PI additional 19 more exercises can be done.
  10. Several other exercises can be done and designed by the user.



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