(710g) Preparation Characterization and Application of an Affinity Flat Sheet Membrane

Arsenic is one of the main toxic heavy metals which are listed in US EPA’s 129 priority pollutants. On one hand, arsenic in the groundwater is of natural origin and being released from the sediment into the groundwater due to the anoxic conditions of the subsurface. It is unmanageable and an issue of major concern. On the other hand, industrial waste discharge of arsenic exacerbates the problem. The Arsenic pollution of ground water is found in many countries throughout the world. The more strict regulations also bring a big challenge to conventional treatment technologies, such as ion exchange chemical precipitation, adsorption and membrane. Thus, to overcome the disadvantages of the current treatment technologies, a combined technology of adsorption and membrane filtration is proposed. The objectives of this study were to obtain a highly performed affinity membrane and to understand the working mechanism.

PSF/zirconium based nanoparticle blend flat sheet membranes with different amount of nanoparticle loaded were synthesized. The morphology and structure of membranes were analyzed by scanning electron microscope (SEM) and atomic force microscope (AFM). The performance of membranes was evaluated in terms of pure water flux (PWF), porosity, contact angle, tensile strength and elongation at break respectively. The adsorption capacity of the membrane also was tested by adsorption isotherm experiment.

Results showed that the addition of zirconium based nanoparticle additive increased the ratio of large pore in the skin layer and weakened the tensile strength. PWF and porosity of membranes increased with the increase of zirconium based nanoparticle dosage. The tensile strength attained its maximum before the nanoparticle was added. The nanoparticle had high stability in the nanoparticle blend membranes. The adsorption isotherm experiments showed the maximum adsorption capacity of the affinity membrane was as high as 120 mg-As/g-membrane. 

It was observed that there is a certain buffering effect from the membrane. The optimal pH for arsenic adsorption on to the affinity membrane is wider than the zirconium based nanoparticle. The kinetics study shows that the adsorption of oregano-arsenic onto the membrane is much slower than that of inorganic arsenate. The adsorption kinetics can be well described by pseudo second order rate model. The Langmuir model can be well used to describe the adsorption isotherms of arsenic onto the membrane. The presences of humic acid dose not significantly influence the adsorption of arsenic on the membrane. The existence of fluoride, silicate or bicarbonate slightly hinders the adsorption of arsenic onto the membrane. However, the presence of phosphate does not significantly affect the adsorption of arsenic onto the membrane. The adsorption of arsenic is less sensitive to the ion strength, which indicates the inner-sphere adsorption mechanism is involved in the adsorption of arsenic onto the membrane. The continuous filtration experiments shows the As(V) concentration in the permeate remains at a level of less than the maximum contaminant level (MCL = 10ppb) at the treated volume less than 10 L. The adsorption capacity before breakthrough (when the effluent concentration is above 10 ppb) is 12 mg/g. XPS spectroscopic analyses demonstrate that the arsenic was uptake onto the membrane.