The authors have been engaged in the research and development concerning the recovery of MAP (Magnesium Ammonium Phosphate) using a fluidized-bed crystallized phosphorus removal system. In the reactor of the fluidized-bed crystallized phosphorus removal system, seed crystals (of MAP) are fluidized previously and new MAP crystals are produced on the seed crystal surfaces. Conventionally, the reactor consisted of one reaction tank only, but this practice had the problem that as the crystallization progresses, the seed crystal is grown excessively and as a result, the effective reaction surface areas are decreased and the fluidization effect is degraded, causing the recovery ratio to be decreased. Recently, the authors have devised a two-tank type reactor by adding a sub reaction tank to the reactor (now the main reaction tank) so that the MAP particle size in the main reaction tank may be kept constant making the recovery ratio stable. They conducted a demonstration test with a pilot experimental system of the 2-tank type reactor. For raw water T-P 111 to 507 mg/L, the main reaction tank treated water T-P 14.0 to 79.5 mg/L and phosphorus recovery ratios 84 to 92% were obtained. Because the mean MAP particle size in the main reaction tank could be kept constant, the phosphorus recovery ratio could always be above 80%, realizing stable treatment.
A research was made on phosphorus recovery conditions using a MAP (Magnesium Ammonium Phosphate) method and anaerobically digested desorption liquor (containing ammonia and phosphorus). A fluidized-bed phosphorus removal system was used as the reactor. The main objective of the research was to study the treatment performance, influent phosphorus load and MAP microcrystallization, and phosphorus recovery. One typical result of treatment performance was a treated water T-P of 26.6 mg/L and a phosphorus recovery of 81%, versus a raw water T-P of 142 mg/L. It was found that MAP microcrystallization increased and phosphorus recovery declined along higher influent phosphorus loads. In a case where the mean MAP particle size was 1.5 mm, the recovery was about 80% under an influent phosphorus load of 25 kg-P/m 3 /d, 60% under 40 kg-P/m 3 /d, and reaching a constant recovery rate of about 70 kg-P/m 3 /d at loads exceeding 100 kg-P/m 3 /d. The constant recovery rate was assumed as due to the limit in the growth rate of MAP particles. Study results indicated that effective phosphorus recovery using the fluidized-bed system could be achieved by maintaining the MAP particles in the reactor to be small (1 -2 mm) so that they could be easily handled.
Removal and recovery of phosphorus from sewage in form of MAP (magnesium ammonium phosphate) have attracted attention from the viewpoint of eutrophication prevention and phosphorus resource recovery as well as scaling prevention inside digestion tanks. In this work, phosphorus recovery demonstration tests were conducted in a 50 m3/d facility having a complete mixing type reactor and a liquid cyclone. Digested sludge, having 690 mg/L T-P and 268 mg/L PO4-P, was used as test material. The T-P and PO4-P of treated sludge were 464 mg/L and 20 mg/L achieving a T-P recovery efficiency of 33% and a PO4-P crystallization ratio of 93%. The reacted phosphorus did not become fine crystals and the recovered MAP particles were found to be valuable as a fertilizer. A case study in applying this phosphorus recovery process for treatment of sludge from an anaerobic-aerobic process of a 21,000 m3/d sewage system, showed that 30% of phosphorus concentration can be reduced in the final effluent, recovering 315 kg/d as MAP.
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