Reuse of dewatered aluminium-coagulated water treatment residual to immobilize phosphorus: Batch and column trials using a condensed phosphate

The aluminium content in dewatered aluminium-coagulated water treatment residual (DAC-WTR) can lead to a high phosphorus (P) removal capacity. Therefore, DAC-WTR has been used as adsorbent/soil amendment to remove P in several studies, focusing mostly on orthophosphates (ortho-P). This study is concerned with extending such reuse of DAC-WTR to remove P using a condensed phosphate as the model P source. Using a 48 h equilibration time and a 1.18mm (mean particle size): (1) P removal was found to increase with increasing DAC-WTR dosage, but specific uptake of P per mass of DAC-WTR was decreased. (2) A maximum adsorption capacity of 4.52 mg-P/g of DAC-WTR was obtained at a pH of 4.0. In the continuous flow test, P removal efficiency decreased from 90 to 30% when loading was increased from 3.9 to 16.5 g-P/m2 day. An average 45% removal efficiency was obtained after an intentional P loading surge. At the end of the continuous flow test, an operating removal capacity of 2.66 mg-P/g of DAC-WTR was determined which was 83.3% of the adsorption maxima obtained in the batch tests. There was no excessive loss of solids during the continuous flow test and aluminium content in the effluent remained below 0.1 mg-Al3+/l. These results have demonstrated that dewatered DAC-WTR can further be used as a low-cost adsorbent media for condensed phosphate removal.