Geotechnical properties and microstructure of clay contaminated with urban wastewater and remediated with α-Aluminum oxide/α-Iron oxide nanohybrid

Abstract

ABSTRACT Regarding the development of cities and the production of large volumes of urban wastewater and the lack of a suitable wastewater disposal system, leakage from wastewater pipes and wells, in addition to environmental hazards, changes the physical and mechanical parameters of the soil over time. Therefore, as the first phase, negative effects of the wastewater on geotechnical parameters and clay soil microstructure were investigated. Atterberg limits the experiments, triaxial compression, consolidation, XRD and SEM analysis were conducted on samples contaminated with 20%, 60%, and 100% of urban wastewater after 1, 3 and 5 months curing. As the second phase, for soil remediation, the mentioned experiments were performed after adding 0.5–4% N.A(α-Aluminum oxide nanoparticles), N.I(α-Iron oxide nanoparticles), and AI nanohybrid into the contaminated soil. The results show that the wastewater reduces maximum dry density (17.3–15.6 kN/m3), plasticity index (14.8–7.8%), and cohesion (42.3–17.3 kPa), and increases the liquid limit (30.4–35.2%), plastic limit (15.6–27.4%) optimum moisture content (18.7–24.1%), internal friction angle (7.1–9.6°) and compression index (0.139–0.258). Besides, XRD analysis showed a decline in mineral amounts and SEM analysis indicated an increase in pores and flocculated clay structure formation in contaminated soil. Furthermore, by adding the nanoparticles to contaminated soil, soil structure remediation, growth in some minerals amount, and soil-nanoparticles bonding creation were observed in microstructural analysis, resulting in the increase of maximum dry density (15.6–18.5 kN/m3), cohesion (17.3–46.9 kPa), and internal friction angle (9.6–19.1°), and decline in soil optimum moisture content (24.1–17.2%), liquid limit (35.2–22.6%), plastic limit (27.4–17%), plasticity index (7.8–4.4%), and compression index (0.258–0.108). Finally, the mentioned method is recommended to remediate the wastewater-contaminated soils. Finally, utilizing AI nanohybrid as an effective factor to improve wastewater-contaminated soil is recommended, it improves the engineering behavior of contaminated soils and decreases the destructive effects of this type of pollution in the earth’s environment.