In-plant wastewater treatment strategies to deal with bypass wastewater in excess of plant capacity are critical in securing sustainable wastewater management. To address this issue, potassium ferrate (VI), which is a dual disinfectant and coagulant, is assessed in this study as the sole chemical applied to enhance the primary treatment of bypass wastewater. The effect of rapid mixing speed is investigated for the first time along with potassium ferrate (VI) dosage by means of central composite design and response surface methodology. Escherichia coli (E. Coli), Faecal Coliform (FC), Total Suspended Solids (TSS), and Orthophosphates (P O 4 3−) were considered as the process responses. All responses other than P O 4 3− showed good agreement between the observed and modelled values. While there was no point of maximum or minimum response for both E. Coli and FC, whose removals were found to increase with the increase of both the mixing intensity and potassium ferrate (VI) dosages, TSS removal exhibited optimal responses. The effluent quality achieved by potassium ferrate (VI), as an independent treatment, can be sufficient for certain types of unrestricted and restricted irrigation reuse purposes suggested by World Health Organisation (WHO) reuse guidelines.