The invention relates to a method of economically recycling
phosphor from excess
sludge. The method comprises the following steps: (1), pre-treating the excess
sludge; (2), carrying out
alkaline hydrolysis on the excess
sludge, wherein the
alkaline hydrolysis is carried out by a single-stage
alkaline hydrolysis method or a two-stage alkaline
hydrolysis method; measuring concentration of orthophosphate and
ammonia nitrogen in liquid supernatant; and (3), adding
magnesium salt aqueous liquor with a Mg / P
molar ratio of 0.8-2, stirring and reacting for 10 minutes-120 minutes, gravitationally or centrifugally separating precipitates, naturally
drying the precipitates to obtain a
magnesium ammonium phosphate crude product. Organic substances remained in the liquid supernatant can be used for producing
methane by anaerobic
fermentation or supplementing a
carbon source by a
reflux wastewater treatment system, also can be used for supplementing
alkalinity needed for an anaerobic unit, so that comprehensive utilization of excess sludge is facilitated. The method disclosed by the invention has the advantages that
nutrient elements in the sludge are comprehensively utilized, process is simple, and
phosphor can be recycled by only adding the
magnesium salt; and meanwhile,
ammonia nitrogen can be partly recycled without regulating pH, and the obtained
magnesium ammonium phosphate crude product can be used for producing fertilizers.