Dear Rafik,

Nanofiltration

The membranes constitute a physical treatment, so they have physical limitations. Water containing suspended particles or organic materials can clog the membranes. Some water, particularly surface water, may require pre-treatment. These devices produce small volumes of highly concentrated solution, which must be rejected.

Membranes are classified according to the size of molecules that can stop it is the nominal cutoff threshold of molecular weight or NMWC. The nanofilters have NMWC about 1000 Daltons or less. The process needs to exercise great pressure on water to force through extremely small pores (0.001 micrometers or one nanometer, hence the name) and remove contaminants.

Source water should always be treated prior to nanofiltration, for that the suspended particles do not clog the membrane and do not reduce its effectiveness. Waters rich in iron, chlorine and manganese will probably also be pre-treated. Even under ideal conditions, nanofiltration devices, such as reverse osmosis must be regularly cleaned and replaced.

The membranes are made of different materials, each with its advantages and disadvantages. Managers of water distribution networks must choose wisely the membrane depending on conditions.

Salt of the retaining standard rates are between 80 and 85%. On this occasion, the polyvalent ions (e.g. Ca, Mg) are more blocked than monovalent ions (e.g. Na, K) so that nanofiltration systems are also often used as an alternative to a conventional softening. Nanofiltration membranes have a moderate retention for monovalent salts.

Advantage of nanofiltration: low investment costs and, above all, less energy costs!

Photocatalysis

It is effective at low pollutant concentrations. It requires low power consumption. It is a destructive and non-selective technology. It operates at ambient temperature and pressure. Catalyst used nontoxic, active in various physical forms, cheap. In general, this method can be described as clean decontamination process.

With my best regards

Prof. Bachir ACHOUR

as dear professor Achour said, the photodegradation of organic pollutants is a green route to degrade toxic pollutants to a non-toxic or less toxic materials.this route in comparison with filtration is cheaper,has easy work up and more effective,and more importantly it is more green.

good luck

Dear Rafik,

It is entirely dependent on nature of pollutant, One can not predict the supremacy of one technology over other e.g. if pollutant is of inorganic in nature, Nano or membrane would perform better, but pollutant of organic in nature might pass thru the membrane by diffusing (as in the case of MEE distillate from distillery), thus Photocatalytic system would perform better.

Thus selection technology should be based on merits, cost, & applicability with respect to nature of pollutant.

thanks & regards

Dinkar

The methods are not directly comparable. Many inorganic substances cannot be treated with photooxidation. Membrane treatment creates a concentrate waste that needs further treatment.

Efficiency is about removal relative to cost of treatment. Both processes require a lot of energy, but I think for the most of the types of pollutants there both methods can be applied, membrane would require the lowest energy per volume of treated water.

The water treatment marked seems to agree with me, as there are far more treatment systems that use membrane treatment for water purification than photocatalysis. 

It all depends on your pollutant character and concentration. Both are different technologies and difficult to compare on energy grounds. System efficiency relates to your removal goal. 

Dear peers,

Many thanks for your valuable answers. However, careful reading of the answers reveals that there is no consensus among the peers on the best method i to be used.

As you might know that pollutants such as pharmaceuticals  are found in the range of micro- to nano-grams/liter. The question is: are both methods have the ability to completely remove simultaneously a mixture of pollutants consisting of 10-100 compounds in the concentration range indicated and which method is more efficient and less costly? Is there any publication comparing the cost and efficiency for removing a certain pharmaceutical in a known concentration by both methods? If yes please provide me with the publication/s.

Again thank you,

Rafik

i think it depends on your goal.Photocatalysis can degrade pollutants eg. dye,pigments etc. or it can kill bacteria. but after photocatalysis may be it is needed to separate dead bacteria.and if dye and pigments get degrade they can form other products.

plz hv alook

Article Indian Edible Chuna (Calcium Oxide/Hydroxide) as a Green Photocatalyst

Article Simultaneous Waste Water Purification via Photocatalysis and...

This greatly depends on the pollutant material to be removed and also the volume of polluted resource to be treated. Also, photo-catalytic degradation needs sufficient sunlight to be economical. 

However, Nanofiltration entails pre-treatment processes to obtain a polluted fluid flow with certain concentration before being sent into the Nanofiltration membrane unit.