Importance Of Filtration in Water Treatment For Process Water & Wastewater Reuse

Why is there so much importance on filtration in water treatment for industrial process water treatment and wastewater reuse?

Filtration is very important for many commercial/industrial process water & wastewater reuse applications. In reality, pumping wastewater from somewhere like a refinery, food/beverage, textile or oil produced water application requires pre-filtration due to high amount of suspended solids in these typical applications. In fact, there are typically several filtration and treatment steps in these applications to ensure that the treated water meets the required discharge or reuse standard. In addition, filtration in water treatment ensures reduced operating cost on downstream polishing water treatment systems.

To paint a clear picture of the importance of filtration in water treatment, we will take the oil refining process as an example. One of this processes many end products is gasoline that might fuel your car with. What comes out of the refinery is clean, processed, and separated from anything that would cause excess wear and tear on your engine. You would not put petroleum directly from the ground into a car, diesel truck or an airplane. It is filtered first, so that what actually goes into your car will keep your vehicle operating at maximum efficiency for as long as possible. A well maintained car that gets clean filtered gas and frequent oil filter changes, can last for decades.

Water treatment systems work in a similar way. In this case, the filtration process is the refinery and the downstream treatment units are the cars. This process removes or reduces any contaminants that the downstream systems could not handle effectively. This increases the overall efficiency of the water treatment process and reduces overall operating & maintenance costs.

In addition, the importance of water filtration in water treatment processes such as process water or wastewater discharge or reuse is critical.

Below is a few examples of advanced treatment processes that need prior filtration for successful operation:

• Finer filtration

This includes membrane filters like reverse osmosis filters, ultrafiltration, micro- or nanofiltration as well as any finer media filters or nano cartridge filters. Most filtration systems operate on a gradient. They start out with a rough, course filtration and move along in steps to the finest level necessary.

This process of course to fine filtration is designed to keep the filters going for as long as possible before they need cleaning, back washing or replacement. If you have a mixture of clay, silt, and sand suspended in a solution and immediately try to filter it through a nanofilter, it’s going to clog up quite quickly. However, if you filter this solution through a filter that will catch all the sand first, then one to catch the silt and clay, your fine filter will be able to optimally operate by handling the smaller particles.

Also, pressure is something to consider. Unless a filter works by way of gravity, it likely uses a pressure system to force everything through the filtration medium. These filtration systems are designed to operate under a certain pressure range, but as the filter medium gathers particulates, the system experiences increased head loss, where the pressure difference is so great that the pumps are working less efficiently, and a backwash cycle is initiated to prevent the possibility of particulate break through in the filtered water.

• Disinfection

Disinfection systems involve the treatment of microscopic pathogens by way of oxidation. However, interference due to particulate matter decreases the treatment efficiency of these unit.

For instance, UV disinfection uses ultraviolet radiation to destroy bacteria. The wavelength of the light travels from the light source through the fluid to the targeted contaminants. However, if suspended particles are within the influent, they will physically block the light waves from reaching the pollutants that need to be disinfected appropriately.

• Advanced Oxidation

Similar to disinfection, advanced oxidation operates dissolved compounds. It uses hydroxyl radicals produced through a combination of ozone, hydrogen peroxide, UV light or electro oxidation systems. Unfiltered contaminants prevent the effectiveness of the UV light as described above. However, other contaminants, called hydroxyl scavengers, will also reduce process efficiency if they are present in a high enough concentration. These scavengers have an affinity for the hydroxyl radicals and will sweep in and react with them before the targeted compounds are destroyed. However, proper pre-filtration along (with some other treatments) can keep them out entirely.

• Coagulation

Whether its a chemical or electrochemical coagulation system, a certain level of pre-filtration is key to effective treatment. Coagulation systems are typically used to coagulate and flocculate smaller particles that don’t settle out very quickly or efficiently. The addition of chemical additives or electrical current is what drives the process. However, these processes typically work best at a particular concentration range for the target constituents. Filtering out larger particles prior to these systems, will ensure that these systems work at their maximum efficiency. In addition, higher concentrations of suspended particles would require adding more chemicals or supplying more voltage to the system to operate effectively. To reduce operating costs, the importance of filtration in water treatment is advisable.