Use of control reactors in biological wastewater treatment studies

Stimulation and inhibition studies are often conducted to study the effect of nutrients, heavy
metals, organic substances, etc. on anaerobic bacteria. The approach followed generally involves using one
biological reactor as a control reactor and then comparing the performances of other reactors with it. Biological
identities such as micro organisms, however, can behave differently even if their operating conditions may
appear to be the same. In this experiment, two batch-fed anaerobic reactors were operated under similar conditions
with respect to sludge source, feed type, organic loading, solids retention time, temperature, etc., yet their performance was found to be significantly different. This study also shows that the decision for increasing the organic loading rate on anaerobic biological reactors should not be governed by the COD removal efficiency alone. Rather it should be based on the methanogenic activity of the biomass.