An investigation of the fate and behaviour of a mixture of WO 3 and TiO 2 nanoparticles in a wastewater treatment plant.

The fate and behaviour of WO3 and TiO2 mixture were investigated following the Organisation for Economic Co-operation and Development 303A guidelines. The nanoparticles were found not to influence the chemical oxygen demand removal efficiency which was maintained >80% hence the activated sludge process was on affected. The nanoparticles were eliminated from the wastewater with a greater percentage of 99.8% for TiO2 and 95.5% for WO3 found in the sludge. The activated sludge process also had no effect of the polymorphs of the nanoparticles as X-ray diffraction revealed presence of monoclinic WO3 and anatase TiO2 which were spiked into the influent. The nanoparticles were mainly removed by bio-adsorption on the activated sludge surface. The total plate count revealed that the bacterial colonies present in the control and the test units were comparable during the gradual introduction of nanoparticles in the chambers. The biomass was >0.75 MLVSS/MLSS (mixed liquor volatile suspended solids/mixed liquor suspended solids) in both the aeration vessels thus a greater proportion of the sludge were the microorganisms. A greater percentage of the Ti and W found in the effluent was mainly due to the nanoparticles adsorbed on the suspended solids with only 3.6% Ti and 28.6% W due to dissolution of nanoparticles.