Analysis Of Impact Factors On Sub-Step Recovery Of Phosphorus From Sludge And Its Optimization By Response Surface Methodology

Most phosphorus existed in sludge is discharged in living sewage treatment plant,and phosphorus content can be as high as 6.9%of the dry weight in sludge.The recovery of phosphorus can avoid not only the secondary pollution caused by the sludge,can also achieve the recycling of resources.In this paper,the first step is to recover the phosphorus from sludge.The second step is to explore the influence factors on phosphorus recovery under the condition of eliminating organic.Coupling between heating and acid-adding digested sludge to release its phosphous.The MgO as the magnesium source in the first step recovered phosphorus from sludge supernatant.The CaO or dolomite as the calcium source or both the calcium and magnesium source in the second step recovered phosphorus from the supernatant in the first step,respectively.Finally,the response surface method was investigated to optimize the influence factors.To digest sludge to release its phosphorus,the results show that the sludge concentration 9 g/L was higher efficiency than sludge concentration of 7 g/L or 11 g/L for phosphorus release using the ultrasonic to digest sludge.The heating temperature 90℃ was slightly higher efficiency by heating method to its release;combined heating with acid-added method to digest sludge obtained a result that its release was higher efficiency by using 2%HCI.The MgO as the magnesium source in the first step recovered phosphorus from sludge supernatant,the results show that phosphorus recovery rates up to 97%,which several influential factors were involved that including pH 9,reaction time 15min,stirring speed 120 r/min,MgO dosage 250 mg/L and reaction temperature 25 ℃ in the experiment.Next,the CaO as the calcium source in the second step recovered phosphorus from the supernatant in the first step,the results show that the optimal experimental condicions was involved such as pH 10.5,reaction time 20min,stirring speed 200 r/min,CaO dosage 200 mg/L and reaction temperature 50 ℃.The dolomite as both the calcium and magnesium source in the second step recovered phosphorus from the supernatant in the first step,the experimental results show that the optimal experimental conditions was involved such as pH 9.5,reaction time 60min,stirring speed 150 r/min,dolomite dosage 200 mg/L and reaction temperature 25 ℃.The response surface optimization model was applied for the MgO as the magnesium source in the first step.The results showed that the model of the multiple correlation coefficients R2 of 0.9187,and operable experimental conditions were ensured,such as pH 9,MgO dosage 245 mg/L and stirring speed 130 r/min.The CaO as the calcium source or dolomite as both the calcium and magnesium source in the second step recovered phosphorus from the supernatant in the first step by the response surface optimization model,respectively.The results showed that the both model of the multiple correlation coefficients R2 of 0.9825 and 0.9840,respectively.Those operable experimental conditions were ensured for the CaO as the calcium source,such as pH 10.2,CaO dosage 155 mg/L and reaction temperature 55℃.Those operable experimental conditions were ensured for the dolomite as both the calcium and magnesium source,such as pH 9.4,dolomite dosage 190 mg/L and reaction temperature 26℃.