Continuous wastewater treatment by t. Versicolor immobilized on lignocellulosic supports

Abstract

Over the last century, the water pollution has become a major problem which affects a large part of population and the environment. It is originated principally due to the discharges of untreated or inadequately treated wastewater in water bodies. Conventional wastewater treatment plants (WTTPs) typically remove organic compounds, but they are not designed to remove other pollutants such as micropollutants, so they can be discharged into the environment together with the effluents from the WTTPs. Among the possible treatments, white-rot fungi (WRF) have become a promising alternative for the wastewater treatment because it can remove a wide range of micropollutants due to their nonspecific ligninolytic enzymatic system. WRF have been studied for the removal of a wide range of micropollutants in real wastewater, but the bacteria overgrowth usually produced a decline in removal efficiencies and consequently short-term operations are obtained. The present thesis proposes the application of a bioreactor system using the WRF Tramentes versicolor immobilized on a lignocellulosic support, to solve this problem and to allow the continuous long-term wastewater treatment. First of all, a substrate screening was performed in order to select the best lignocellulosic material for fungal growth. The pallet wood was selected for the following experiments. Immobilization studies were performed in a fluidized bed bioreactor. Good results were obtained with complex wood pellets, but the process results not scalable, hence new systems were proposed. A trickle-bed bioreactor and a packed-bed bioreactor were developed and operated in a continuous long-term treatment with T. versicolor immobilized on pallet wood. Both reactors were employed for the treatment of wastewater from different sources: hospital wastewater with pharmaceutical active compounds, food-processing industrial wastewater with humic acids and rural area wastewater with pesticides. The optimization of operational conditions is a key issue to improve the reactor performance. In the trickle-bed bioreactor, the recycling ration and the total volume were optimized. Meanwhile, in the packed-bed bioreactor preliminary studies of pH, fungal biomass, wood sorption and aeration were carried out. In conclusion, both bioreactors systems with T. versicolor immobilized on pallet wood are a good alternative for the continuous long-term treatment of different wastewaters. The trickle-bed bioreactor achieved 61% of PhACs removal from hospital wastewater during 85 days; 50% humic acid removal from industrial wastewater for 26 days; and 84% diuron removal from synthetic tap water during 18 days. In the packed-bed bioreactor treating real wastewater, more than 90% removal of diuron was obtained during 50 days.