In the industrial and manufacturing plant, the generation of wastewaters is an unavoidable process, and in most cases, a process of reducing the organic load and other contaminants must be carried out before discharging water into the environment.
Recently, we have witnessed the widespread adoption of the membrane-based technologies for the treatment of wastewater. Among all of these, the nanofiltration wastewater management technique has resulted in a highly effective method for the removal of a wide variety of organic compounds from wastewater. NF processes investigated for the removal of color contents and reductions of the COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon). These two parameters are highly important for reusing the water as well as for drainage, also because pollution boards don’t allow to drain the water with high COD.
In this article, we will delve into the functioning of Nanofiltration and understand how it is an effective method for TOC & COD removal.
Nanofiltration is a membrane treatment process that is primarily used to separate dissolved solutes from wastewater. Nanofiltration refers to the process of movement of solvent through a semipermeable membrane from the solution to the pure solvent by applying excess pressure on the solution side.
It is highly used for the drinking water purification, particularly with regard to the removal of salt and other effluent materials from water molecules. However, now, it is not just limited to drinking water purification.
Today, this technique is used worldwide for the purification of industrial, residential, commercial, and scientific purposes.
The membranes of Nanofiltration aren’t a complete barrier to the dissolved salts in the wastewater. As per the type of salt and membrane, the permeability of salt may be low or high. In the case of low salt permeability, the difference of osmotic pressure between the two compartments may become almost as high in reverse osmosis. However, due to the membrane’s high salt permeability, the salt concentrations in the two compartments would not remain significantly different. As a result, if the salt permeability is great, osmotic pressure is less important.
In the nanofiltration process, there are nanometer-sized pores through which particles smaller than 10 nanometers pass through the membrane. This pore size is smaller than that used in microfiltration and ultrafiltration, but a little bigger than reverse osmosis membranes.
Note: The dimensions of pores are influenced by pH, temperature, and time during development, with pore densities ranging from 1 to 106 pores per square cm.
There are four major mechanisms to remove Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) from wastewater through nanofiltration. Let’s understand each of the mechanisms in brief:
This is the most used mechanism for COD and TOC removal. The size of the pores in nanofiltration membranes lies between 0.1 and 1nm. These pores can effectively remove organic molecules and contaminants larger than their molecular weight cutoff (MWCO), which is generally 200-1000 Da.
The molecules that are larger in size and contribute to COD and TOC get physically rejected by the membrane.
The membranes in nanofiltration have a negative charge. Thus, they repel negatively charged organic pollutants present in wastewater. It includes humic acids, phenols, and other dissolved organic matter contributing to COD/TOC.
It enhances the removal of organic contaminants and reduces the overall pollutant load.
Because of hydrophobic interactions or electrostatic attraction, certain organic molecules—even those that are smaller than the membrane pores—are adsorbed onto the membrane surface, further lowering COD and TOC.
The nanofiltration membranes reject monovalent salts with less efficiency (typically 20-80%). However, they show high efficiency (80-99%) in removing divalent and larger organic compounds (>300 Da).
Permeate flux and salt rejection are the key performance parameters of the nanofiltration process. Under specific reference conditions, flux and rejection are intrinsic properties of membrane performance. They get influenced by various parameters, including:
· Feed Water Salt Concentration: If the feed water salt concentration increases and all other parameters remain constant, both permeate flux and the salt rejection will decrease.
Nanofiltration offers a wide range of benefits in diverse industries due to its versatile nature. Here are the major advantages or applications of nanofiltration:
As we mentioned earlier, nanofiltration has played an important role in purifying drinking water. It can remove contaminants like pesticides, heavy metals, and organic compounds. The water quality has improved, and it is safe for consumption.
In the wastewater treatment plants, nanofiltration treats the industrial wastewater and removes COD and TOC. It can remove dissolved impurities and color from industrial effluents.
During the drug-making process, the pharmaceutical industry uses nanofiltration to remove undesirable contaminants and separate and concentrate active pharmaceutical ingredients (APIs).
Nanofiltration can remove calcium and magnesium present in hard water, eventually softening it. It prevents the formation of limescale and enhances the lifespan of household appliances.
In various industrial processes, nanofiltration enables the recovery and purification of valuable compounds, reducing waste generation and improving overall process efficiency.
In this article, we have understood the transformative role of nanofiltration in removing TOC and COD from industrial wastewater. With the advancements in manufacturing technology, the future of nanofiltration in wastewater treatment seems promising.
At WiproWater, we provide highly advanced wastewater treatment systems based on nanofiltration techniques. WiproWater and its nano-filtration membrane technology represent the future of wastewater treatment. By choosing our cutting-edge technology, industrial plants can achieve sustainability and compliance, optimize costs, and contribute to a greener planet.