BIOMASS REDUCTION AND MINERALIZATION INCREASE DUE TO THE CILIATE TETRAHYMENA-PYRIFORMIS GRAZING ON THE BACTERIUM PSEUDOMONAS-FLUORESCENS

The currently high sludge production and increasing processing costs c all for waste-water treatment plants with high purification efficiency and low biomass production. We studied the latter issue through two-s tage chemostat cascades to assess the overall biomass reduction due to ciliate grazing. The bacteria were cultured in the first chemostat wh ereas the ciliates, grazing on the bacteria from the first chemostat, were cultured in the second chemostat. Mathematical modelling was used to describe the bacteria/ciliate dynamics and some of the growth para meters were fitted. In the second chemostat 22-44% of the carbon origi nating from the first chemostat was mineralized to CO2. An extra bioma ss reduction of 12-43% was possible due to grazing by the ciliates. At lower growth rates of the ciliates the extra biomass reduction was hi gher than at high growth rates. This finding is auspicious, suggesting that predator organisms indeed can reduce sludge production.