Toxicity of solid residues resulting from wastewater treatment with nanomaterials

•The use of NMs in effluent treatment will result in the formation of solid residues.•The ecotoxicity of the solid residues was studied.•These solid residues can negatively affect C. riparius.•The effect depends on the type of effluent as well as on the compounds attached to the NMs.

Nanomaterials (NMs) are widely recommended for wastewater treatments due to their unique properties. Several studies report the different advantages of nanotechnology in the remediation of wastewaters, but limited research has been directed toward the fate and potential impacts of the solid residues (SRs) produced after the application of such technologies. The present work aimed at investigating the ecotoxicity of SRs resulting from the treatment of three effluents (OOMW, kraft pulp mill, and mining drainage) with two NMs (TiO2 and Fe2O3). The invertebrate Chironomus riparius was selected as test organism and exposed to the residues. The effect on percentage of survival and growth was assessed. Results showed that the SRs from the treatments nano-TiO2(1.0 g L−1)/H2O2(0.5 M) and nano-Fe2O3(1.0 g L−1)/H2O2(1.0 M) from OOMW and nano-Fe2O3(0.75 g L−1)/H2O2(0.01 M) from kraft pulp mill effluent exhibited lethal toxicity to C. riparius. Only the exposure to SRs resulting from the treatment with nano-Fe2O3(0.75 g L−1)/H2O2(0.01 M) applied to the kraft pulp mill effluent significantly affected the growth rate based on the head capsule width. In terms of growth rate, based on the body length, it decreased significantly after exposure to the SRs from the treatments nano-TiO2 (1.0 g L−1) and nano-Fe2O3(0.75 g L−1)/H2O2(0.01 M) of kraft paper mill effluent and nano-Fe2O3(1.0 g L−1)/H2O2(1.0 M) of OOMW. According to our study the SRs can promote negative effects on C. riparius. However, the effects are dependent on the type of effluent treated as well as on the organic and inorganic compounds attached to the NMs.