Basic Research On Phosphorus Removal By Coupling Phosphorus Removal Agent With Steel Slag

With the national requirements for phosphorus discharge from sewage plants,most sewage plants use increased phosphorus removal agent dosage to reduce the phosphorus concentration in the effluent using precipitation with the ionic effect,which inevitably results in the waste of phosphorus removal agent and increased costs of phosphorus removal.Steel slag is the waste generated by steel making,the amount of steel slag piled up in China is only increasing.How to solve the problem of high use of phosphorus removal agent and the comprehensive utilization of steel slag is worth studying.In this study,the phosphorus removal performance of steel slag and the phosphorus removal performance of iron salts were firstly investigated,and then the iron salts were coupled with steel slag to explore its phosphorus removal effect,in order to reduce the use of phosphorus removal agents through the use of steel slag.The maximum adsorption capacity of steel slag is temperature dependent,and the higher the temperature the greater the equilibrium adsorption capacity.The experimental results of phosphorus adsorption by steel slag are suitable to be characterized by Langmuir’s formula,and the mechanism of phosphorus removal by steel slag is more inclined to single-molecule adsorption.2 g of steel slag was treated with 20 mg/L phosphorus-containing wastewater in a water bath shaker at 25°C and160 r/min,and the phosphorus concentration in the effluent could reach 0.2 mg/L after3 hours of reaction.The iron salt dosing amount,initial phosphorus concentration,and p H are all factors that affect the performance of iron salt phosphorus removal.The minimum ratio of n（Fe）:n（P）for phosphorus in the effluent with initial phosphorus concentration of2mg/L is 2.5;the minimum ratio of n（Fe）:n（P）for phosphorus in the effluent with initial phosphorus concentration of 4,6,8mg/L is 2.2;the minimum ratio of n（Fe）:n（P）for phosphorus in the effluent with initial phosphorus concentration of 12,16mg/L is 2.2;the minimum ratio of n（Fe）:n（P）for phosphorus in the effluent with initial phosphorus concentration of 12,16mg/L is 2.2.The minimum ratio of n（Fe）:n（P）to achieve the standard is 2.This is the minimum iron salt dosing ratio to achieve the standard for phosphorus in the effluent under the conditions of each initial phosphorus concentration.According to the above concentration of the minimum iron salt dosing,adjust the p H of raw water to 6～8,settling 30min phosphorus concentration in the effluent can reach0.2 mg/L,too alkaline and acid phosphorus concentration in the effluent will increase.The settling performance of the floc in the effluent has a relatively large impact on the phosphorus concentration of the effluent,the formation of iron salt phosphorus removal floc is small,settling performance is also poor,by adding PAM and modified Fe PO₄ sludge to improve the settling performance of iron salt phosphorus removal floc.The phosphorus concentration in the effluent is 0.15～0.3mg/L lower than that in the non-injected PAM,which improves the settling performance of the floc.Modified Fe PO₄ slag was effective in removing phosphorus from wastewater with only iron salt dosing,but not effective in removing phosphorus from wastewater with iron salt+PAM dosing.In the experiment of combined steel slag and FeCl₃,when n（Fe）:n（P）=1.5,the phosphorus concentration of effluent decreased by 3～5mg/L when combined steel slag and FeCl₃ were added simultaneously than FeCl₃ alone;2g of combined steel slag and FeCl₃ were added simultaneously,and the phosphorus concentration of effluent was around 0.5mg/L;3g of combined steel slag and FeCl₃ were added simultaneously,and the phosphorus concentration of effluent was around 0.2mg/L or so.