Phosphorus Recovery from Sewage in a Pilot-Scale UASB-DHS System

The operation of a pilot-scale plant for the demonstration of phosphate (P) recovery from actual sewage was investigated for more than 5-years. The pilot plant consisted of a 500 L up flow anaerobic sludge blanket (UASB) and 540 L down flow hanging sponge (F-DHS) reactor as pre-treatment unit, subsequently a 66 L of P-DHS reactor operation was modified to enhance recovery of P. The combined UASB-DHS system could achieve good organic removal efficiencies accounted for 87%, 84% and 90% for BOD, COD, and SS respectively. Under the optimum operational condition, the P-DHS reactor was able to concentrate P up to 120 mg P L-1 in the recovery solution. Nevertheless, high P concentration could not be easily maintained over the years. It started to worsen when the pH in F-DHS effluent dropped until below 6, but then slightly increased when the pH is being controlled in a range of 7-8. Interestingly, a cyclic pattern was observed in the P concentration of the recovery solution in response to the temperature, regardless of whether the pH was controlled or not. High P concentration only achieved temporally in spring (16 < T < 20 degrees C) and further become deteriorated as temperature rise in summer (T > 30 degrees C). Therefore, in order to achieve a high P concentration in the recovery solution the F-DHS effluent temperature should be controlled in a range of 15-20 degrees C.