DIG-L: my thesis: Fuzzy control and simulation of a biogas plant

["Ernst Murnleitner" <awite2@awite.de>]

Dear readers,

I wish to introduce my thesis work which might be useful for some of you:

Murnleitner, E. (2002) "State Detection and Feedback Control of the
Anaerobic Wastewater Treatment Using Fuzzy Logic". VDI Verlag, Dusseldorf.
ISSN 0178-9589. ISBN 3-18-323715-6.

Abstract:

Anaerobic treatment of wastewater offers the advantage of the elimination of
the main part of pollutants, which saves disposal charges. Compared to the
aerobic technology, less sludge is formed, and energy is produced in the
form of biogas. However, anaerobic treatment has also several drawbacks.
These are the more difficult handling and the extreme long characteristical
times, whereby particularly an overload can lead to a complete break-down of
the plant. A restart takes weeks to months, which has restricted the user's
acceptance compared to conventional aerobic plants. But using intelligent
control systems can circumvent this problem. Up to now comparatively few
control engineering is applied in the wastewater treatment. The controlled
variables are mostly regarded in isolation, e.g. temperature and pH are held
constant and controlled by a local controller. Connecting the particular
measurands and manipulated variables, one can essentially increase the
efficiency of wastewater treatment systems as well as the stability. Even
though such controllers would be possible by using classical control
engineering, the effort would be considerable due to its high complexity.
Therefore, Fuzzy logic (the classical Mamdani-type fuzzy rulebase) was
chosen for state detection and control of the two-stage anaerobic wastewater
treatment. A two-stage anaerobic wastewater treatment reactor system was
modelled and controlled the way the biological state of the reactors could
be predicted. Based upon this, proper control actions were enacted
automatically. Even very strong fluctuations in the loading of both,
concentration and volumetric flow rate, could thereby be handled
successfully. Moreover, effluent concentrations could be kept relatively low
without using TOC, COD or equivalent measurements.
In concrete, the engineering should be developed and tested on a lab scale
plant using wastewater from the potato processing industry. As no existing
plant meeting the requirements was available, particularly in consideration
of the automation, a new lab scale plant was developed and constructed.
For further testing of the control system developed, a dynamic mathematical
simulation model was used. For this, an existing model for an anaerobic
digester was extended in order to be able to simulate the two-stage
anaerobic wastewater treatment reactor system with biofilm. All the relevant
measurands, like pH, hydrogen, methane, as well as the manipulated variables
(flows, pH, temperature) of the controller are covered by the new simulation
model. The model was validated with both sensitivity analysis and with
experimental data. Sensitivity analysis points out the important parameters
of the model. Connected with the fuzzy logic controller software, dynamic
simulations were performed where the command variables were altered by the
output of the fuzzy logic. Data from controlled and uncontrolled experiments
could be reproduced satisfactorily by the use of the dynamic model.
Moreover, effluent quality could be improved by changing several fuzzy sets.
Simulating different overload scenarios, the control system was able to
detect overloads and thus to execute proper control actions.

You can obtain it at VDI Verlag
(http://www.vdi-literatur.de/buchshop/langanzeige.asp?vr_id=5828) or just
send me an email.


Greetings
Ernst Murnleitner


********************************************
Awite Bioenergie
Grepmeier & Murnleitner GbR
Angerstra?e 9
D-85416 Langenbach-Niederhummel
Dr.-Ing. Ernst Murnleitner
http://awite.com
email: mur@awite.de
Tel. +49-8761-334979
Fax. +49-8761-334981
********************************************


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