For two years lab-scale experiments were done to find the conditions to enhance the start-up of anaerobic fixed film reactors. Five reactors were operated in parallel with a sythetic wastewater containing acetic, propionic and butyric acid in a weight relation of 2:1:1 resulting in a COD of 20,000 mg/l. Using polypropylene curlers (NOR-PAC R 92/1) as support medium (substratum) and mostly digested sludge of a municipal wastewater treatment plant as inoculum, we found that the activity of the starter culture, effluent recirculation, calcium dosage and the mode of increasing the organic loading rate had a significant influence on start-up behaviour. Depending on the way to run the start-up space loading rates of 10 to 30 g COD/(l·d) could be reached within 58 days. In contrast to these “manual” start-ups it is shown that the most efficient way is to run a start-up pH-statically with an automatic substrate feeding regulated by the pH measured in the top of the reactor. Within 36 days a space loading rate of 60 g COD/(l·d) with a COD removal efficiency of 70 % could be reached.

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