A novel approach for application of white rot fungi in wastewater treatment under non-sterile conditions: immobilization of fungi on sorghum

In this study, we tested a new approach to facilitate the application of white rot fungi (WRF) under non-sterile conditions, by introducing grain sorghum as carrier and sole carbon and nutrient source for WRF. To this end, Trametes versicolor was immobilized on sorghum, and its ability to remove humic acid (HA) from synthetic and real industrial wastewater was studied. HA removal was measured as colour reduction and also analysed via size exclusion chromatography (SEC). Under sterile conditions, 80% colour removal was achieved for both synthetic and real wastewater using immobilized WRF on sorghum, without adding any additional carbon or nutrient sources. Under non-sterile conditions, immobilized fungi could again remove 80% of the colour and reached a maximum of 40 U/L laccase activity. In contrast, non-immobilized fungi cultivated in non-sterile wastewater supplemented with additional nutrients, reached only 10% decolourization and maximum 5 U/L laccase activity. SEC analysis showed that bioremoval of HA by WRF was associated with degradation of HA. Finally, immobilized fungi were used to treat real wastewater, under non-sterile conditions, in a sequential batch order without renewing the immobilized fungi. Four batch feedings were conducted and 80%, 70%, 50% and 40% colour removal was achieved for each batch, respectively, over a total incubation period of 19 days.