![]() ![]() The other two groups of models additionally take into account the properties of the membrane and are divided into: solution-diffusion and pore-flow models. The first group of models is derived from irreversible thermodynamics and considers the membrane as a black box. In the mathematical modelling of NF, three groups of models describing transport across a membrane can be distinguished. Therefore, the authors of this study postulate using mathematical modelling to determine the total volume membrane charge density and correlate the pH of separated solutions, which would help in the assessment of membrane performance. As a result, zeta-potential values are obtained, while such measurement methods require a sample in a flat, powder or even fibre form, which requires the destruction of a membrane. Nowadays, the only possible way is to use streaming potential techniques. However, there is no experimental technique which would enable the quantification of the membrane charge value in direct way, especially during separation. Therefore, a modelling-based approach has been published. A strong charge present at the membrane surface has a crucial effect on the ion retention of the membrane unfortunately, the experimental determination of the membrane charge, which could explain ion transport through a NF membrane, is challenging. Another important parameter in the transport and interpretation of retention is the membrane charge present along the surface of a membrane and also through the pores. For a charged compound, both steric hindrance and electrostatic interactions are responsible for rejection. In general, transport during NF depends on diffusion, convection and electrostatic interactions. Nanofiltration (NF) is a process with low power demand in comparison to reverse osmosis or distillation, which works in the pressure range of 0.4–3 MPa, and also it does not introduce any additional ingredients that may pose problems with their removal, or affect the purity of the product. The continuous development of new polymeric and inorganic membranes with high efficiency and selectivity as well as the improved knowledge regarding separation mechanisms allowed for the replacement of conventional techniques using membrane processes. In the last 20 years, membrane processes have gained significant attention in the field of separation processes. However, wide industrial applications are limited by the relatively high operational costs. When high contaminant removal is a goal, nanofiltration is generally found to be cost-effective. ![]() Newer processes, such as adsorption on novel adsorbents (natural materials), photocatalytic processes, electrodialysis or membrane processes, appear to be more effective than traditional treatment methods. ![]() These processes have significant disadvantages, which include: incomplete removal, high-energy requirements, and the production of toxic sludge. The removal of heavy metals from inorganic effluents can be achieved by conventional treatment processes, such as chemical precipitation, flotation, ion exchange and electrochemical deposition. Current knowledge indicates that it is better to prevent than combat the effects therefore, recent research has been directed towards methods of preventing the migration of heavy metals from industrial wastewaters to the environment at the source, rather than through their treatment later on. ![]()
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