Effect of Ca2+ in compound coagulant on the coagulation effect of high dissolved phosphorus in pit water
Ca2+ modified AlCl3 and PACl were used as coagulants to carry out coagulation experiments.The mechanism of action of modified coagulants was analyzed through turbidity of effluent,residual aluminum,total phosphorus,floc particle size and organic composition,etc.,and the mechanism of the effect of Ca2+ in coagulants on the coagulation effect of high phosphorus pond water was discussed.In terms of turbidity removal,Ca2+ can significantly reduce effluent turbidity at low dosages.When the dosage was 0.10 mmol/L,the turbidity of PACl effluent decreased by 33.52 NTU,AlCl3,and 28.72 NTU.In terms of residual aluminum removal,when AlCl3 is used as a coagulant,Ca2+ can reduce the concentration of residual aluminum in the effluent by increasing the charge neutralization ability of the coagulant.In the aspect of dissolved phosphorus removal,Ca2+ reacts with phosphate or increases the removal rate of dissolved phosphorus by compressing an electric double layer and adsorption charge neutralization.When the dosage is 0.20 mmol/L,the removal rate of dissolved phosphorus is 16.1%higher than that before modification when the concentration of Ca2+ is 0.9 mmol/L,PACl.In terms of floc size,Ca2+ can promote unstable condensation between particles,increase floc size and fractal dimension,and increase floc size by 79 μm when AlCl3 dosage is 0.20 mmol/L.The addition of Ca2+ makes the shearing resistance of the flocs formed by AlCl3 stronger,but it is more difficult to recover after the flocs are destroyed,which makes the strength factor and recovery factor of PACl flocs become larger.In terms of organic matter removal,Ca2+ can improve the removal rate of organic matter.For the dosage of 0.20 mmol/L and 0.06 mmol/L of Ca2+,the fluorescence response value of the coagulant modified by AlCl3 decreased from 1 100 to 800.
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