BioProject

Two 10L continuous stirred tank reactor (6L working volume) were used in this experiment: One reactor served as control reactor (CR; without hydrogen addition) while hydrogen was supplied to the other reactor, hereby referred to as the upgrading reactor, or UR. More...

Two 10L continuous stirred tank reactor (6L working volume) were used in this experiment: One reactor served as control reactor (CR; without hydrogen addition) while hydrogen was supplied to the other reactor, hereby referred to as the upgrading reactor, or UR. The inoculum came from two 10L laboratory reactor digesting cow manure at thermophilic temperature (55oC) with hydraulic retention time of 20 days. Both reactors were fed with the mixture of cow manure and cheese waste. The cow manure was collected from the cow farm in Ås, while the cheese waste was obtained from the Food pilot plant at Norwegian University of Life Sciences (NMBU). Both the cheese waste and cow manure were collected and was stored at 4oC until further usage.The temperature of both reactors was maintained at thermophilic condition (55oC), with a hydraulic retention time of 20 days. Three-blade Elephant Ear impeller operated in the down-pumping mode was used for mixing at 80 rpm. Approximately 300 g of substrate (90% CM: 10% CW) were fed into the reactors every 24 hours after the same amount of effluent had been discharged. Initially, the organic loading rate was kept at 0.83 gVS L-1 d-1. Starting day 64, H2 was injected into UR, which was mounted at the bottom of the reactor. The sparger measured 12 cm in length and had a 12 mm outer diameter. The flow rate of H2 was initially set to 3 mL min-1 (H2:CO2 ratio = 2:1). To increase the contact time between anaerobic microbes and H2, gas recirculation was introduced from day 64. A peristaltic pump was used to recirculate the output gas at gas recirculation rates of 7.63 mL min-1.The experiment was running for 172 days and divided into 6 different phases (I – VI).Stirring speed (80 vs 120 rpm), CM:CW ratio (90%:10% vs. 80%:20%), feeding frequency (24h vs. 48h), and H2:CO2 ratio (2:1 vs. 4:1) were varied from day 79 to 172 to examine how these factors influenced the process performance of the two reactors. The effluent samples for microbial analysis were collected for each phase, both from control and H2-supplemented reactors and stored at -80oC until DNA analysis. 16 samples were sent for microbial analysis, 2 were inoculum (INO) and feeding substrate (FEED) and 14 samples came from the effluent of the reactors. DNA extraction and sequencing were performed by DNASense (Aalborg, Denmark). Less...