Development of a method to enhance granulation in a laboratory batch system
The success and efficiency of the UASB process are dependent on the formation of active granular biomass and since this is a slow process, one of the main problems in the application of the technology remains the long start-up periods. Batch cultures with lactate, glucose or sucrose as substrate, were seeded with anaerobic sludge and incubated in shake waterbaths over a period of 14 d. For all substrates, a drop in pH within the first 2 d was experienced. In the glucose and sucrose units the pH dropped to 6.0 and to below 5.5, respectively within the first 24 h. Thereafter, a continual drop was experienced, eventually resulting in system acidification. With the lactate units, the pH dropped to 6.5 by Day 2, with a subsequent climb unit the pH-stabilised around 6.7 to 6.9. The volatile fatty acid (VFA) profiles of all the units showed an increase of acetic and propionic acids, with the latter at the highest concentration during the first 5 d, corresponding to the decrease in pH. An increase in granulation was observed for the glucose (354%) and lactate (559%) units, but no granulation increase was found for the sucrose units. The increase in granule formation indicated that granulation may be enhanced in batch systems over a shorter period and that the granulation process is facilitated by a rapid drop in pH at the start, resulting from the major increase in propionic and acetic acids, followed by a subsequent increase and stabilisation in pH, and an increase followed by a steady decrease in propionic and acetic acid concentration until the formation stabilised.