Two anaerobic continuous stirred tank reactors (CSTR), with a
working volume of 1 l each, were operated at organic loading
rates of 1 and 2 g CODl1 d1. One reactor was fed with a
suspension (colloidal sodium oleate) and the other with a
solution (sodium acetate) to study the changes in protozoa
population with respect to feed composition. Each substrate
was supplemented with Vanderbilt mineral media (Nuri et al.,
2001). An HRT variation of 5–10 days in 1 l was obtained with a
peristaltic pump (Autoclude VT, UK) with a 2mm i.d. tube,
cyclic mode operation, 15 s on and 10min off. All other
conditions were identical for both reactors. The pH was
controlled by adding 1N NaOH or 1N HCl. Reactors were
seeded with sludge collected from an anaerobic dairy wastewater
treatment plant. Biogas generated in the reactors was
measured by liquid displacement. Protozoa-inhibited CSTR
was obtained by adding cycloheximide (200mgl1) to feed.อ