Fuzzy estimator is developed for determining the concentration of plas
mid-bearing microorganism (x(+)) in a continuous bioreactor. Membershi
p functions, fuzzy ranges for the inputs and outputs are defined. A fu
zzy rule base is constructed relating the inputs to the output based o
n operators experience. A defuzzification method is selected and the n
on-fuzzy value of x(+) is obtained. The results are compared with the
actual values of x(+) which are obtained by numerically solving the mo
del equations of the system. The estimator is also tested for the othe
r operating conditions. The estimator performs well for other operatin
g conditions also.