Influence of C : N ratio on the start-up of upflow anaerobic filter reactors

The long duration of the start-up period is a major drawback of the anaerob ic wastewater treatment systems. A better understanding of the factors affe cting biomass aggregation and adhesion, the two main mechanisms of biomass retention, could make the start-up more efficient and rapid. The objective of the present work is to determine the effect of the carbon:nitrogen ratio on the efficiency of biomass retention in upflow anaerobic filters. For th is purpose, two substrates of two different C:N ratios (nitrogen limited, N L, and nitrogen balanced, NE) were considered. In fed-batch operation it wa s shown that a nitrogen limitation in the very first phase of reactor start -up seems to enhance appreciably biomass adhesion. A feeding strategy to up flow anaerobic filters, consisting on maintaining a N limitation during the first two weeks resulted in a moro efficient biomass retention, with a hig her specific methanogenic activity. By using this policy, the total methano genic capacity attained after 4 weeks exceeded that obtained in the system fed with the balanced substrate from the beginning of the operation by 20%. (C) 2000 Elsevier Science Ltd. Ali rights reserved.