This peer-reviewed study investigates how environmental conditions, treatment plant processes, and geographical location influence bacterial community composition in activated sludge wastewater treatment plants in South Africa. Nine municipal wastewater treatment plants in the City of Ekurhuleni and City of Cape Town were monitored over a 20-month period using molecular sequencing and multivariate statistical analysis.

The research found that geographical location was the dominant factor influencing bacterial community selection, with site-specific environmental conditions — particularly activated sludge ammonia, total phosphate, and influent chemical oxygen demand — identified as the most significant drivers. Seasonal variation and treatment process configuration showed comparatively minor influence.

The study demonstrates the importance of analysing activated sludge chemistry alongside influent characteristics when evaluating microbial populations and treatment performance. It further confirms that cost-effective screening tools can support advanced microbial analysis for wastewater research.

These findings provide operational value for wastewater treatment management by improving understanding of microbial behaviour, supporting process optimisation, and strengthening environmental monitoring strategies within South African wastewater systems.