Application of aquatic fungi in bioreactors for the treatment of textile dye model effluents

Textile dyes are designed to resist fading upon exposure to sweat, light, water, oxidizing agents, and microbial attack. Therefore they are hardly removed from effluents by conventional wastewater treatment. Dye-containing effluents can be treated by a number of physico-chemical processes. Nevertheless, some of these methods do not degrade xenobiotics resulting in a pollution transfer, whereas other methods are of limited use due to different constraints related to e.g. costs or general applicability. The development of suitable bioremediation processes may provide a viable alternative. Terrestrial white-rot fungi (WRF) are able to decolorize dyes through the use of relatively nonspecific extracellular oxidative enzymes. However, unfavourable conditions often found in process effluents such as high contents of inorganic ions and extreme pH values limit the practical applicability of WRF. To overcome this problem with concomitantly keeping the advantages of fungi compared to other microorganisms, our work focuses on fungi isolated from aquatic environments. Aquatic ecosystems represent an as yet only scarcely explored source of new fungi that are possibly more suitable than other organisms for the treatment of certain wastewaters since the living conditions and hence possible organismic adaptions found there may better fit to unfavourable characteristics of process effluents. Here we present the application of immobilized mycelium of three strains of aquatic fungi for the treatment of textile dye model effluents. These strains, Phoma sp. UHH5-1-03, Coniothyrium sp. Kl-S5 and Alternaria sp. Tt-S1, were isolated from different aquatic habitats, partly with high salinity. Prior to their use in bioreactors, a simple and scalable immobilization procedure was developed. Cookerhood filters, a cheap and biodegradable material, were used as a support. Model effluents of different dye application classes (reactive, direct and acid) were treated in internal loop airlift and bubble column reactors (repeated batch mode) under sterile and nonsterile conditions. Depending on the applied model wastewater, fungal strain and bioreactor setup, a decolorization above 90 % could be achieved in three consecutive cycles and a total operation time of 16 days. The process was successfully upscaled to a 10 L reactor. The most promising strain, Phoma sp., decolorized a model wastewater for acid dyes by 61 % after 15 days of operation. Chemical oxygen demand of the wastewater was reduced by 36 %. The presented results underline the potential of aquatic fungi for the development of a whole-cell treatment process of textile dyeing effluents