Membrane Life-Time Limitation

The overall lifespan of a membrane is governed by the membrane chemical resistance and its antifouling property. Common membrane-cleaning processes employ acidic and alkaline solutions for removing salt precipitates and organic foulants, respectively, to recover the membrane permeability and other performances, which are important to minimize the energy consumption and operating costs (Li and 

Drawbacks of NF Membranes and Methods Employed to Improve Their Performances 

Hydrophobic membrane surface that encourages organic fouling 

Develop membranes with lower surface roughness to reduce the accumulation of foulants onto the membrane surface Hydrophilic NF membranes can be developed through grafting process using hydrophilic materials Biofilm formation or biofouling can be avoided through membrane modification using nanoparticles 

Elimelech 2004 Religa et al. 2013 Simon et al. 2013). However, the deterioration of membrane structures due to the acidic or alkaline solution can greatly shorten the membrane lifespan. The ability of the polymeric membrane to withstand an extreme pH condition will definitely determine the life expectancy of the membrane in certain applications. In addition, fouling control of polymeric membranes, through either operating condition adjustment or membrane material selection, is important in order for the wider employment of NF processes to become feasible. 

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For small volumes, 13 or 25 mm diameter, filtration membranes may be fitted into plastic or stainless steel holders (e.g. the Swinnex filter holder made by the Millipore Corp. Appendix 3) which, after autoclaving, are fitted onto a syringe containing the liquid to be sterilised. Care must be taken in the assembling of the membrane in the holder as incorrect assembly leads to the escape of the membrane from its retaining gaskets with subsequent failure of the filtration process. The plastic holders have a limited life time as they distort on autoclaving. 

Although plasticized PVC membranes with ion selective receptor molecules as sensing membranes give already quite satisfactory results for a limited life time, the adhesion of the membrane to the surface is not stable and plasticizer and ionophore leach out the... 

In summary, various modes of physical and chemical degradation exist, which limit life times of operating DEFCs. In particular, membrane moisture variation or chemical impurities can rapidly degrade performance and must be controlled. 

Exposure to tantalum metal dust may cause eye injury and mucous-membrane irritation. The threshold limit value (TLV) in air is 5 mg/m, LD q is <400 mg/kg and the Occupational Safety and Health Administration (OSHA) time weighted average (TWA) exposure limit is 5 mg/m (47). The immediate dangerous to life or health (IDLH) concentration is 2500 mg/m (48). Whereas some skin injuries from tantalum have been reported, systemic industrial poisoning is apparently unknown (47). 

Cycle time usually limited by life of membrane. 

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