Evaluation of the performance of microbial community induced by NFC-doped TiO2 nanoparticles on aerobic biodegradation of sewage wastewater and its' recoverability

During the recent years, the advanced treatment processes are developed after the determination of pollutants which are resistant to biodegradation in the domestic and industrial wastewater. In this context, heterogeneous photocatalytic advanced oxidation processes are among the most important techniques in which intensive studies have been carried out in recent years. Titanium dioxide (TiO2), which has heterogeneous semiconductor property, is widely used for decomposition of various organic pollutants because of its high active optical properties, chemical stability and non- toxicity. However, due to its ability to absorb 3%-5% of sunlight, it is very common in the literature that TiO2 is doped with the appropriate transition metals or other elements to increase its oxidation power. But, in these studies, it is stated that these doped photocatalysts with nanoparticular structure having specific surface area and high catalytic properties can cause a shock effect on activated sludge systems which are preferred especially as the next treatment stage and problems may be encountered on their biodegradation during operation phase. Therefore, it is very important to understand the behavior of the photocatalysts on the aerobic biological treatment process, and the effect of NFC-doped TiO2, a new generation nanoparticle, on aerobic biodegradation of real domestic wastewater and a peptone mixture synthetic wastewater having similar COD fractions with domestic and most industrial wastewater was determined in this study. For this purpose, the change in oxygen consumption rate of activated and photocatalyst fed activated sludge is determined experimentally for both synthetic and real wastewater (domestic) at acute and chronic levels by using respirometric techniques also species analysis was performed to determine the change after acute and chronic exposure. The aim of this study is determination of the behavior of activated sludge population which is exposed and unexposed to photocatalyst (acclimated to peptone and real domestic wastewater) for synthetic and real wastewater at aerobic condition by respirometric techniques and evaluation of the effect on real domestic wastewater treatment plant efficiency. Thus, the behavior of nanoparticles in conventional activated sludge systems, especially which are widely used in the removal of organic materials that are difficult to biodegradate, such as antibiotic residues in domestic wastewaters, have been evaluated comparatively with the synthetic wastewater. According to the results of the analysis, activated sludge which was fed with real domestic wastewater, was affected more by TiO2 nanoparticle than the activated sludge which was fed with peptone due to the micro-pollutants in the real domestic wastewater. When evaluated in terms of species analysis, the presence of micro-pollutants in the real domestic wastewater caused the presence of filamentous bacteria, which are not preferred, even in the control sample. In both reactors, COD removal efficiency, oxygen consumption rate and beneficial species were inhibited after acute exposure. After 30 days of chronic exposure, filamentous bacteria became dominant in both reactors. The domestic wastewater reactor was more inhibited in terms of COD removal efficiency and oxygen consumption rate than the peptone reactor. The COD removal in the domestic wastewater reactor was virtually eliminated, while it remained around 60% in the peptone reactor. According to the recoverability experiments, the presence of filamentous bacteria in the activated sludge of peptone reactor decreased and an increase was observed in the types of bacteria which are beneficial for the biodegradation. Inhibition of oxygen consumption rate continued in the pepton reactor, but COD removal efficiency recovered by around 19%. In the domestic wastewater reactor, neither COD removal efficiency nor oxygen consumption rate were recovered. According to the species analysis, it was commented that the activated sludge of domestic wastewater reactor could recover itself to a small extent but microorganisms could not reach and consume organic matter due to the fact that filamentous bacteria were still dominant in the environment.