Operation control of anaerobic digesters on the basis of enzyme activity tests.

In our experimental work the pilot plant and full scale anaerobic bioreactors of a communal sewage treatment plant were tested by applying usual control parameters (pH, volatile acid content, alkalinity, gas composition), and enzyme activity (dehydrogenase, protease, lipase) measurements. Influence of temperature change was examined in pilot plant scale, while the effect of alteration in specific organic matter load both in pilot and full scale. Among the control parameters only the change of the volatile acid concentration reflected the occurred influences. During the temperature varying experimental phase the dehydrogenase enzyme activity excellently indicated the influence of the different conditions. The effect of altering substrate load onto the gas production was also well followed by the enzyme activity data (mainly protease, lipase), and more rapidly than by measuring volatile acid concentration. In practice it is expedient to use enzyme activity measurements in those cases, when changes in the substrate composition and load are frequent. Another advantage of these tests is that they can be carried out quickly and at a relative low cost.