Effects of ciliates and rotifers on fungal degradation of natural tannins in bench tests

Tannery wastewater presents high concentrations of pollutant recalcitrant molecules, such as tannins, characterized by high refractory organic load, which reduce the efficiency of biological treatment processes. Recent studies showed that several fungal strains, including Aspergillus tubingensis MUT 990, thanks to their ability to produce the enzyme tannase, were effective in the degradation of such recalcitrant molecules. However, the growth of A. tubingensis and, consequently, its degradation performance decrease when the bacterial load is high. The aim of the study is to evaluate whether the introduction of bacterivorous organisms, such as protist ciliates and/or rotifers, in bench scale experiments using fungi to remove natural tannins could favor fungal growth and recalcitrant compounds removal. To achieve this goal, rotifers and different functional categories of ciliates were isolated and cultures established. Paramecium calkinsi, Tetrahymena sp., Vorticella sp. and a culture of rotifers were later selected due to their capability to survive and actively grow in Tara medium (tannin extract of Caesalpina spinosa 0.9 g/l). A preliminary batch experiment has been performed to investigate whether the selected organisms could enhance recalcitrant compounds removal of A. tubingensis, immobilized on polyurethane foam cubes, toward Tara tannin medium. The following parameters have been monitored: bacterial concentration, fungal dry weight, soluble chemical oxygen demand, total organic carbon (TOC), and A280 (indicative of phenol concentration). Preliminary results suggest an effect of some treatment (e.g. in the presence of Vorticella sp. or rotifers) on bacterial load reduction, increase in fungal dry weight and a reduction on final TOC. A second wider batch of experiments is presently ongoing and results will be also presented