A supervisory expert system based on fuzzy logic rules was developed for diagnosis and control
of a lab- scale plant comprising anaerobic/anoxic/aerobic modules for combined high rate biological N and C
removal. The design and implementation of a computational environment in LabVIEW for data acquisition,
plant operation and distributed equipment control is described. The Fuzzy Logic toolbox for MATLAB was
also used for the development of the fuzzy logic rule based system. The fuzzy rules were generated from
quantitative and qualitative information, to identify the status of the plant operation and to decide the best
commands to be sent to the final control elements to recover the stable operation in case of disturbances of
the processes. A step increase in ammonia concentration from 20 to 60 mg N/L was applied during a trial
period of 73 hours. Recycle flow rate from the aerobic to the anoxic module and by-pass flow rate from the
influent directly to the anoxic reactor were the output of the fuzzy system that were automatically changed
(from 34 to 111 L/day and from 8 to 13 L/day, respectively), when new plant conditions were recognized by
the expert system. Denitrification efficiency higher than 85% was achieved 30 hours after the disturbance and
15 hours after the system response at an HRT as low as 1.5 hours. Nitrification efficiency gradually increased
from 12 to 50% at an HRT of 3 hours. The system proved to properly react in order to set adequate operating
conditions that timely led to recover efficient N and C removal rates.Fundação para a Ciência e a Tecnologia (FCT) - doctoral research grant BD/1299/2000.União Europeia (UE) - Fundo Social Europeu (FSE) - doctoral research grant BD/13317/2003
