The fate, behaviour and effect of WO3 nanoparticles on the functionality of an aerobic treatment unit

Abstract

Tungsten trioxide is a promising photocatalyst, especially in the degradation of organic pollutants in wastewater treatment. It is thus, crucial to understand the fate and behaviour of the WO3 nanoparticles and its impact on the functionality of the wastewater treatment plant. Such understanding will provide accurate data that can be used for toxicological risk assessment. This was achieved through acclimatization of activated sludge to the simulated wastewater treatment plant operated according to the Organisation for Economic Co-operation and Development 303A guidelines. During acclimatization, chemical oxygen demand (COD), and a five-day biological oxygen demand (BOD5) were monitored. Humic acid impact on the functionality of the domestic waste water treatment plant was investigated as it is a major constituent of wastewaters. The COD removal was above 80% suggesting that humic acid had no impact on the activated sludge activity. The fate of m-WO3 was monitored using X-ray diffraction and scanning electron microscope coupled with electron dispersive X-ray. X-ray diffraction analysis showed presence of m-WO3 in the sludge which was further confirmed with electron dispersive X-ray -mapping which showed presence of tungsten signifying adsorption of the nanoparticles on the sludge. The addition of 15ppm WO3 showed to influence the functionality of the treatment plant as the COD removal dropped to 70% which is below the 80% stipulated guideline signifying adequate removal of the COD. This imply that WO3 nanoparticles possess toxicity effects on the activated sludge. An increase in conductivity was observed in the test effluent suggesting the possibility of dissolution of the nanoparticle. The ICP-OES analyses showed that 80% of W was retained in the sludge while 20–21% m/m run out with the effluent.