The effect of co-occurring inorganic solutes on the removal of arsenic(V)from water using cationic surfactant micelles and an ultrafiltration membrane

摘要

The effect of co-occurring inorganic solutes existence in feed water on the removal of arsenic(V)and permeate flux was investigated for the treatment process using a cationic surfactant cetylpyridinium chloride(CPC)and a 5 kilo-Dalton(kDa)polyethersulfone(PES)membrane.Simulated water and well water(Washoe County STMGID #9 operational well,Nevada)were used for this study.The concentrations of arsenic([As]_F=0-105 mug/L)and inorganic solutes([HCO_3~-]=0-4.1 mg/L,[HPO_4~(2-)]=0-0.3 mg/L,[H_4SiO_4]=0-90 mg/L,and [SO_4~(2-)]=0-400 mg/L)in simulated feed water were varied.The pH level ot'simulated feed water was adjusted to 8 since the well water pH was around 8.The arsenic concentration in the well water was 73 mug/L.The concentrations of carbonate,phosphate,silicate,and sulfate in the well water were 1 mg/L,0.17 mg/L,69 mg/L,and 8.2 mg/L,respectively.PES membrane without surfactant micelles was found to be ineffective for arsenic removal.The highest arsenic removal in the presence of inorganic solutes is 25%,corresponding to a permeate water arsenic concentration of 30 mug/L which is well above the new maximum contaminant level(MCL)of 10 ug/L.With the addition of 10 mM CPC to the feed water,the arsenic removal efficiency is significantly increased ranging between 78.1% and 100%.The arsenic removal efficiency was found to be dependent on the feed water arsenic and co-occurring inorganic solute concentrations.Except for one UF experiment performed with the simulated feed water containing 105 mug/L arsenic and 400 mg/L SO_4~(2-)(23 mug/L arsenic in permeate water),all the other UF experiments produced permeate water with arsenic below the new MCL.The presence of HCO_3~-,HPO_4 ug/L ,and H_4SiO_4 species in feed water does not affect the arsenic removal efficiency(100%)except in one case(99% removal efficiency for the feed water containing 105 mug/L arsenic and 90 mg/L H_4SiO_4).The experiments performed with well water result in almost 100% arsenic removal(arsenic level in permeate water is below the detection limit of ICP-MS,1 ug/L).Furthermore,absolute permeate flux was also found to be dependent on the feed water arsenic and co-occuring inorganic solute concentrations.An increase in feed water arsenic concentration results in a decrease in the permeate flux.For the experiments performed with simulated water containing CPC and arsenic,the permeate water flux is 56.5 +-2.5% of ultra clean water flux.The permeate flux reduces further as the co-occuring inorganic solute concentration or the total dissolved solid in feed water increases.It is 43.5 +-3.5%,45.5 +-7.5%,43.5 +-6.5%,and 37.5 +-5.5% of the ultra clean water flux for the simulated water containing HCO_3~-,HPO_4~(2-),H_4SiO_4 and SO_4~(2-)species,respectively.With the well water,permeate flux was found to be 33% of the ultra clean water flux.Only 1.52 +-0.33% of the surfactant molecules used were detected in permeate water.Surfactants in permeate water can be further separated and reused in the feed stream.