Acidogenic digestion of effluents of the cheese industry in packed bed biofilm reactors

Dissertation for the Master degree in BiotechnologyThe main goal of the present work was to study the production of volatile fatty acids (VFAs) from cheese whey powder (CWP) by employing a packed bed bioreactor (PPBR) for the anaerobic acidogenesis. First experiments were performed in 100-mL Pyrex bottles to study the acidogenesis trends, namely: lactose consumption, VFAs and biogas production and composition. These tests were done with freely suspended-cells (control experiment) and with immobilized cells using granular activated carbon (AC) and ceramic cube Vukopor S10 supports. The utilized inoculum – an acidogenic mix consortium- belongs to an analogous CWP digestion process in which a different culture system is being studied. Therefore, the incubations conditions were the same as for that culture system: 20 g/L of CWP (corresponding to 15 g/L lactose), 37ºC and pH 6. The observed trend consisted on lactose consumption, lactic acid formation (as an intermediate product) and from this VFAs production. The best yield was obtained when Vukopor was used (87% against 30% for AC); after 9 days the VFAs was (g/L): acetic (1.6), propionic (2.4); butyric (6.6) acids. The mentioned preliminary studies allowed selecting the operational hydraulic retention time(HRT) for the bioreactors. Two recirculate 1-liter PBBR one filled with Vukopor and other with AC were developed. CWP concentration, pH and temperature were the same as in the microcosm experiment. Both were operated in batch and continuous. In first batch performed in PBBR-Vuko it was achieved 6 g/L of propionic. However a loss of capability of producing it was observed during continuous operation. It was ascribed to a wash-out of related strains. With PBBR-Vuko were tested two different hydraulic retention times (HRT), 9 and 6 days, instead for PBBR-AC only HRT of 9 days. The yields for PBBRVuko were the same as at the microcosms scale, 80% for both HRT. On the other hand, the yield for PBBR-AC was 20%, this is a confirmation that AC was not the proper support even at a 1-L scale. Additionally to immobilization study, it was also set up a bioreactor with freely suspended cells. In this last mentioned bioreactor when a HRT of 6 days was set up it was observed a decrease in the VFAs yield to 44%. From this, it was concluded that the immobilization is an advantage for the VFAs production