Aluminium-based water treatment sludge was used as a coagulant for removing/recovering phosphate from the effluent of upflow anaerobic sludge blanket (UASB) reactor treating municipal wastewater. The effect of three variables, namely sludge dose, initial pH andfresh coagulant (poly-aluminium chloride, PACl) dose was studied using response surface methodology. About 87% phosphate removal could be obtained at the optimum conditionsof sludge dose 13.8 g/L, initial pH 6, and fresh PACl dose 5.8 mg Al/L. In order to achieve a sim-ilar phosphate removal, a dose in the range of 30–40 mg Al/L of fresh PACl was required. Theresults suggest that water treatment sludge can be reused as a coagulant for post-treatmentof UASB reactor effluent treating municipal wastewater and can be considered as a promis-ing alternative for removing phosphate which can substantially reduce the consumption of fresh PACl. The sludge generated during this process could potentially be used in land application which results in recycling of phosphate.