Abstract
The imminent arrival of nanoparticles (NPs) to the wastewater treatment plants (WWTP) brings concern about their effects, which can be related to the wastewater composition. In this work, the effects of titanium dioxide (TiO2) NPs in the removal of carbon, nitrogen, and phosphorus by activated sludge bioreactors during the treatment of synthetic, raw, and filtered wastewaters were evaluated. Floc size, compaction of sludge, and morphological interactions between sludge and NPs were also determined. The main effect of TiO2 NPs was the inhibition of up to 22% in the removal of ammonia nitrogen for all types of wastewaters. This effect is strong dependent on combined factors of TiO2 NPs concentration and content of organic matter and ammonia in wastewater. The removal of dissolved organic carbon was affected by TiO2 NPs in lower level (up to 6%) than nitrogen removal for all types of wastewaters. Conversely to adverse effects, the removals of orthophosphate in the presence of TiO2 NPs were improved by 34%, 16%, and 55% for synthetic, raw, and filtered wastewater, respectively. Compaction of the sludge was also enhanced as the concentrations of NPs increased without alterations in the floc size for all types of wastewaters. Based on TEM and STEM imaging, the main interaction between TiO2 NPs and the activated sludge flocs was the adsorption of NPs on cell membrane. This means that NPs can be attached to cell membrane during aerobic wastewater treatment, and potentially disrupt this membrane. The effects of TiO2 NPs on macronutrient removal clearly depended on wastewater characteristics; hence, the use of realistic media is highly encouraged for ecotoxicological experiments involving NPs.
Highlights
TiO2 nanoparticles (TiO2 NPs) are present in multiple everyday products such as food, toothpaste, sunscreens, among others (Weir et al 2012)
Activated sludge treating Synthetic wastewater (SWW) was not affected in the presence of all TiO2 NPs concentrations, in terms of soluble COD (sCOD) removal, which were statistically similar to its control group
Since experimental conditions were similar for all three wastewaters, the negative effect of TiO2 NPs over sCOD removal can be attributed to the type of wastewater and concentration of NPs
Summary
TiO2 nanoparticles (TiO2 NPs) are present in multiple everyday products such as food, toothpaste, sunscreens, among others (Weir et al 2012). According to life cycle assessment studies ( Keller and Lazareva, 2013; Adam et al, 2018;), the unintentional release of TiO2 NPs to the environment during or after the use of such products is expected. Water streams have been identified as the main transport media of NPS in the environment due to the connection between treated effluents and water bodies (Brar et al 2010; Kunhikrishnan et al 2015). Some studies have reported the presence of TiO2 NPs in wastewater streams (Kiser et al 2009; Tuoriniemi et al 2012), even in the sludge of the bioreactors applied for wastewater treatment (Polesel et al 2018; Huang et al 2020; Cervantes-Avilés and Keller 2021). The interaction between these NPs and microorganisms may damage the performance of the wastewater treatment process
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