Comparative evaluation of halloysite nanotubes and zirconium oxide nanoparticles for agricultural drainage wastewater treatment

Abstract Agricultural drainage wastewater contains complex mixtures of dissolved salts, nutrients, organic pollutants, heavy metals, and microbial genetic material, posing significant challenges for water quality management and agricultural reuse. Unlike most previous studies that investigated synthetic wastewater or single-contaminant systems, this study presents a laboratory-scale comparative evaluation of halloysite nanotubes (HNTs) and zirconium oxide nanoparticles (ZrO₂-NPs) for the treatment of real agricultural drainage wastewater collected from Mansoura University, Egypt. Wastewater quality was evaluated using physicochemical analyses, heavy metal determination, quantitative PCR (qPCR)-based microbial genetic marker analysis, hydrochemical assessment, and multivariate statistical analyses, including Pearson correlation, principal component analysis (PCA), and hierarchical cluster analysis (HCA). Both nanoadsorbents improved wastewater quality under the investigated experimental conditions, although distinct treatment behaviors were observed. HNT₃ produced the greatest reductions in most physicochemical parameters and heavy metal concentrations, whereas ZrO₂-NPs generally resulted in greater reductions in detectable bacterial, protozoan, and viral genetic markers measured by qPCR. Multivariate statistical analyses consistently differentiated treated samples from untreated wastewater and supported the observed treatment patterns. Hydrochemical assessment further demonstrated reductions in salinity- and sodicity-related hazards relative to internationally recognized irrigation water quality criteria, although some irrigation risk indicators remained within categories requiring appropriate management depending on crop type, soil characteristics, and local irrigation conditions. The integrated assessment demonstrates that the complementary performance of HNTs and ZrO₂-NPs extends beyond heavy metal removal to include improvements in physicochemical water quality, reductions in detectable microbial genetic markers, and hydrochemical characteristics relevant to irrigation. These findings provide laboratory-scale evidence supporting the potential application of nanoadsorbents for agricultural drainage wastewater treatment under controlled conditions. However, because adsorption kinetics, adsorbent regeneration, microbial viability, viral infectivity, nanoparticle residuals, environmental risk, and field-scale performance were not evaluated, further investigations are required before practical agricultural wastewater reuse can be recommended.