Microbiological Quality Evaluation and Multivariate Analysis of Wastewater Treatment Efficiency in a Semi-Arid Urban Setting: The Case of Al-Muameera WWTP, Iraq

Abstract

Microbial contamination continues to be a general challenge in discharged and reused wastewater, especially in semi-arid regions where treated effluent has become an alternative water sources. This work assesses the microbiological quality of sewage influent and effluent at Al-Muameera Wastewater Treatment Plant (WWTP), Hilla City, central Iraq as well as investigates the correlation between microbial indicators/parameters in raw and treated wastewater via multivariate statistics.Wastewater samples (influent/effluent) were taken in a six-month sampling campaign (November 2024–April 2025). Total coliform bacteria (TCB) and fecal coliform bacteria (FCB) were counted as indicators for microbial contamination, and the log₁₀ transformation of bacterial counts was performed to normalize their frequency distribution. Multivariate statistical analyses (PCA, HCA and heatmap visualizations based on Pearson correlation of the integrated physicochemical and microbiological data) were conducted.The findings demonstrated an enormous amount of bacterial count in the influent wastewater, which was originated from raw domestic sewage. After treatment, bacterial numbers decreased significantly, although high concentrations of both TCB and FCB remained in the treated effluent. Results of Boxplot analysis clearly distinguished influent and effluent bacterial concentration, whereas PCA and cluster analysis successfully categorized samples according to treatment stage and showed strong correlations among bacterial indicators, organic matter, and suspended solids. Heatmap also indicated distinct correlations of the microbial parameters with specific physicochemical variables, particularly BOD₅, COD and TSS.Such results suggest that, although the conventional treatment in the Al-Muameera WWTP operation may represent a partial human microbial risk reduction, bacteria removal is not sufficient to warrant safe effluent disposal or unrestricted reuse. The combined use of microbiological indicators and multivariate statistical approach, developing a computer based method (software package) thus provides an effective tool to assess treatment efficacy and public health risks in semi-arid urban areas.