Q-200. Effect of the Addition of Autoclaved and Non-autoclaved Grass on the Bacterial Diversity in Sulphate Removing Bioreactors.

L. M. Burke1, S. N. Venter2, G. N. van Blerk3, H. A. Greben1;
1CSIR, Pretoria, SOUTH AFRICA, 2Univ. of Pretoria, Pretoria, SOUTH AFRICA, 3ERWAT, Johannesburg, SOUTH AFRICA.

Biological sulphate removal reactors were operated using the degradation products of grass cuttings (GC) as carbon sources and rumen fluid and sulphate reducing bacteria (SRB) as start-up biomass. Volatile fatty acids (VFA) are primarily produced by the rumen associated micro-organisms from the grass cellulose. The produced VFA are then used as carbon and energy sources for SRB, which facilitate biological sulphate removal. The objective of this study was to investigate whether the micro-organisms present on the GC out-competed the rumen fluid associated micro-organisms within the reactor, or assisted in grass fermentation. Autoclaved GC without native microbes and non-autoclaved GC with the native microbes were added to separate reactors and the effect thereof was examined. Degradation of grass cellulose was investigated by means of chemical oxygen demand, VFA, and sulphate reduction analysis. The diversity of the microbial communities in sulphate removing bioreactors was investigated using T-RFLP. At each sampling point in the non-autoclaved reactor the bacterial community structure was dynamic and varied constantly, while that of the autoclaved grass reactor remained more stable. Community composition in both the autoclaved and non-autoclaved reactors comprised of a relatively low diversity of SRB. When sulphate removal efficiency decreased, the microbial diversity also decreased, indicating that microbial diversity is possibly related to optimal ecosystem functionality. In total, over the 151 days of operation, the non-autoclaved grass reactor removed 2% more sulphate than the autoclaved grass reactor, indicating that the native grass micro-organisms added to the non-autoclaved grass reactor did not contribute vastly to GC degradation, but in addition did not hinder the VFA formation by the rumen associated bacteria.