The Right Technology for the Job

Core Treatment Technologies

Reverse Osmosis (RO)

Reverse Osmosis (RO) is a water purification technology that uses a semi-permeable membrane under hydraulic pressure to remove dissolved salts and impurities from a feed stream.

RO membranes are highly effective at removal of the most challenging constituents including the smallest monovalent ions like sodium and chloride. In drinking water treatment they are commonly used for removal of nitrate, heavy metals and trace amounts of synthetic organic compounds. RO is also one of the technologies available for removal of per- and polyfluoroalkyl substances (PFAS). Other monovalent ions, such as Fluoride can be readily removed by RO.

RO systems operate continuously, utilizing spiral-wound membranes housed within pressure vessels. A high-pressure pump propels feed water into these vessels, overcoming the natural osmotic pressure. This produces two distinct streams: permeate, which is the purified water, and concentrate, which contains the removed solutes. The percentage of water captured as purified water is known as Volumetric Recovery, which typically ranges from 65% to 85% for drinking water applications. Maintaining adequate cross-flow velocity on the feed side of the membrane is a key factor in proper operation, as the turbulence helps prevent fouling.

Ultrafiltration (UF)

Ultrafiltration (UF) is a pressure-driven separation process that uses a membrane for physical separation. It is highly effective at removing suspended solids, colloids, bacteria, protozoa, and some viruses through size exclusion.

With membrane pore sizes typically ranging from 0.01 to 0.1 micrometers, UF provides an absolute barrier to fine particulate matter. UF membranes often employ a similar pressurized, hollow-fiber configuration to Microfiltration (MF), the key distinction is UF's smaller pore size, which allows for removal of smaller contaminants.

Nanofiltration (NF)

Nanofiltration works much like Reverse Osmosis, but its rejection of contaminants is focused on larger di- or trivalent ions and dissolved organics. This allows it to operate at lower pressures, making it more energy-efficient for certain tasks.

NF systems use the same pressure vessels and system configurations as RO but employ different membranes. A key use of NF in drinking water applications is for the removal of dissolved organic molecules that can create harmful disinfection by-products when combined with chlorine. Removing these organics using NF prevents the formation of disinfection byproducts, a significant advantage for municipal water treatment.

Multimedia Filtration (MMF)

Multimedia filtration uses a media mix of engineered sand, anthracite and larger structural media to provide filtration for removal of impurities from water. This technology, also referred to as rapid sand filtration, is simple and reliable and allows removal of suspended solids, pathogenic organisms and some organic macromolecules.

MMF uses a reverse-graded, dual-media bed. A top layer of larger, less dense anthracite sits above a lower layer of smaller, denser sand. As water flows downward, the largest particles are captured in the coarse top layer, while progressively smaller particles are removed by the finer sand layer below. This design utilizes the entire depth of the filter bed for solids storage.

Greensand Filtration (GSF)

Greensand Filtration is a catalytic oxidation and filtration process that uses manganese greensand for removal of iron and manganese. This technology has been used for decades to reliably remove troublesome iron and manganese that can cause aesthetic and health problems in drinking water applications. The process functions like a multi-media filtration system but with this specialized media.

The core of the process is the media, manganese greensand, which is coated with manganese dioxide. This coating acts as a catalyst to accelerate the oxidation of dissolved iron and manganese. The process requires the continuous injection of an oxidant, such as sodium hypochlorite (bleach), which converts soluble iron and manganese into solid, filterable particles. These newly formed particles are then immediately filtered out by the media bed.

GSF is vital for treating groundwaters where the absence of oxygen has allowed iron and manganese to remain dissolved. Its most critical industrial application is as pre-treatment for Reverse Osmosis, as dissolved iron and manganese will precipitate on RO membranes and cause severe fouling, permanently reducing performance and requiring costly replacement.

Granular Activated Carbon (GAC)

Granular Activated Carbon (GAC) is an adsorption technology, not a filtration technology. Its job isn't to physically strain out particles, but to remove dissolved chemical contaminants using a surface adsorption mechanism.

The effectiveness of GAC comes from its large internal surface area. One pound of carbon has more than 35 acres of surface area, or the equivalent of almost 100 football fields. This surface is mostly non-polar, which gives it a strong affinity for other non-polar molecules, like dissolved organic compounds. As contaminated water flows through the GAC bed, weak intermolecular forces attract these organic contaminant molecules, causing them to stick to the carbon's surface and leave the water.

GAC is a consumable medium. As its active sites become filled with contaminants, the carbon becomes "spent" or "exhausted." The point at which it can no longer effectively remove the target contaminant is known as "breakthrough." At this point, the spent GAC must be removed and replaced with fresh carbon.