DIFFERENT TYPES OF SLUDGE GRANULES IN UASB REACTORS TREATING ACIDIFIED WASTEWATERS

The influence of a high energy substrate, i.e. sucrose, on the granula r sludge yield and the development of different types of granular slud ge was investigated by using Upflow Anaerobic Sludge Bed (UASB) reacto rs fed with synthetic wastewater. The feed COD was a mixture of volati le fatty acids (VFA) i.e., 20, 40, and 40% of the COD as C-2-, C-3-, a nd C-4-VFA, respectively. Furthermore, experiments were carried out in which 10 and 30% of the VFA COD was substituted with sucrose. The fol lowing distinctly different types of granules were observed in each te strun: in the reactor fed with solely VFA, black (B) and white (W) gra nules developed; in the reactor fed with a mixture of 90% VFA and 10% sucrose, three types of granules i.e., B, W, and grey (G) granules cou ld be seen; in the reactor fed with 70% VFA and 30% sucrose, only W an d G granules were found. The granular sludge yield increased proportio nal to the amount of sucrose GOD. At steady-state performance of the r eactors, specific acidogenic (SAA) and methanogenic (SMA) activity tes ts on these granules revealed that B granules had the highest SMA with low SAA. The W granules had very high SMA with low SAA. G granules ga ve the highest SAA with a considerable SMA. Measurement of coenzyme F- 420 revealed that B granules consist mainly of acetoclastic methanogen s. The fore-mentioned tests were supplemented with analyses of the was h-out cells present in the reactor effluent and the results suggested that acidogens, if present, prevail at the granule surface. The B gran ules were particularly rich in Ca, Mn, and Zn minerals. The size distr ibution analysis showed that the granule diameter increased in the fol lowing order: B < W < G granules. The biogas bubbles tended to adhere to the B and W granules but not so strongly to the G granules.