The nutrient media was trickled continuously from the top of the reactor at a flowrate of 10 mL/min (flux 0.262 m 3 /m 2 h). It might be possible that there was channeling due to which only a limited area of the packing was getting the nutrient supply. To investigate this limitation flushing trials were conducted, where nutrient media was trickled at a high flowrate of 400 mL/min (flux 10.5 m 3 /m 2 h) for 3 mins. The idea was to disturb the channeling and to enable the nutrient supply to a wider section of the packing. On day 140 the reactor was flushed, as can be seen in Figure this resulted in decreasing the C H 2 from 32% to 19%. However, this improvement in conversion was short-lived and C H 2 increased again. This indicated that channeling might be a factor and the nutrient supply could be improved by routinely flushing the reactor. Hence, from day 150 to 190 the reactor was flushed every second day. During this the fresh media was added on days 150 and 175 with the following Preprint procedure: 100 mL of was removed and 200 mL of the fresh media was added in the sump. As can be seen in Figure , the H 2 conversion improved significantly after media addition on days 150 and 175, the C H 2 reduced to almost 0. However, the C H 2 remained stable for approx. 10 days and afterward it started increasing again. The routine of flushing the reactor every second day was carried out during this period ensured supply over a wider fraction of the packing. Considering this, the decrease in conversion showed that the concentration of nutrients could have decreased over time that resulted in lowering the activity of methanogens. Hence, the concentration levels of the nutrients were measured over time.