Study On The Preparation Of Concentrated Sludge By Microwave Alkaline Solution And Magnesium Ammonium Phosphate

In today's urban sewage treatment system,almost 90%load of nitrogen and phosphorus in domestic sewage are transferred to the remaining sludge.And the nitrogen and phosphorus elements account for 5%and 10%respectively in the dry weight of the remaining sludge.Therefore,if the remaining sludge is directly treated for sea or landfill without treatment,the nitrogen and phosphorus elements in the excess sludge will cause serious environmental problems such as eutrophication of the water.Considering the pH range of ammonium magnesium phosphate,the microwave-alkali method was used to release total phosphorus,orthophosphate,and ammonia nitrogen in the sludge at first.At the same time,the microwave absorption material was used to increase the heating rate.In addition,the optimum operating parameters of water content,pH,reaction temperature,type and amount of microwave absorbing materials,heating rate,microwave power,and post reaction time were determined by a single-factor experiment.After that,the optimal Mg/P,the best mixing time stirring speed to compound Mg?NH₄?PO₄·6H₂O:During the preparation of the phosphorus-enriched supernatant stage,the optimum moisture content of the concentrated sludge,pH and reaction temperature was determined to be 96%,9.5 and 85°C respectively.Under these conditions,the contents of total phosphorus,orthophosphate,and ammonia nitrogen were 312.6 mg/L,215.8 mg/L,and 125.8 mg/L,respectively.The total phosphorus and ammonia nitrogen production efficiency was 29.66%and 43.17%,respectively.Comparing the performance of heating rate and the release of total phosphorus,orthophosphate,and ammonia nitrogen in SiC,Fe₃O₄,and C powders,Fe₃O₄ was selected as the best absorbing material and its ratio of sludge to microwave absorber is 100:1.The optimum heating rate,microwave power and post reaction time should be controlled at about 7°C/min,170W and 4h respectively.Under these conditions,the contents of total phosphorus,orthophosphate,and ammonia nitrogen were 344.39 mg/L,310.06 mg/L,and142.28 mg/L,respectively.Moreover,the total phosphorus and ammonia nitrogen production efficiency was 32.67%and 48.82%respectively.In the experiment of magnesium ammonium phosphate recovery,the optimum magnesium/nitrogen/phosphorus ratio should be 1.3:1:1.The best stirring time in the six-line mixer should be selected for 30 minutes and the best stirring speed should be controlled at about 200r/min.In this system,the removal rate of PO₄^3-and NH₄⁺-N are 98.03%and 88.84%respectively.