POST-TREATMENT

REVERSE OSMOSIS (RO) FILTERS

A Reverse Osmosis (RO) filter is a membrane-based treatment process that uses semi-permeable membranes and high pressure to remove dissolved salts, organic compounds, microorganisms, and other contaminants from water. A Reverse Osmosis filter is usually applied after conventional and secondary treatment have already removed most solids and organic matter.

During the process, the treated wastewater is pressurized and forced across RO membranes. Pure water, known as permeate, passes through the membrane, while the remaining cancentrated stream, known as brine or reject, carries away dissolved impurities.

The main purpose of RO filters is to produce very high-quality effluent that can be reused for industrial processes, irrigation, boiler feed water, or, in advanced systems, even for potable reuse. The key advantage of RO is its ability to remove up to 99 percent of dissolved salts, heavy metals, pathogens, and other substances that are not removed by conventional treatment, making it one of the most effective polishing steps for water reuse.

ULTRAFILTRATION (UF)

Ultrafiltration is a membrane-based filtration process that removes very fine suspended solids, colloids, bacteria, and some viruses from wastewater. In a WWTP, the process involves pumping wastewater through UF membrane modules (hollow fiber, flat sheet, or spiral wound) under moderate pressure. The membranes act as a physical barrier, allowing water and low-molecular-weight solutes to pass through while retaining larger particles and micro-organisms. Periodic backwashing and chemical cleaning prevent fouling and maintain efficiency.

MULTIMEDIA FILTERS

A Multimedia Filter (MMF) is a pressure filter that relies on several layers of media to physically remove suspended solids and turbidity from water. Typically, the fitter contains anthracite at the top, sand in the middle, and garnet at the bottom, sometimes supported by gravel. As wastewater passes downward through the filter, larger particles are trapped in the coarse upper layers, while finer particles are captured in the lower, denser media. Over time, the filter accumulates solids and is cleaned through backwashing to restore performance.

The MMF is often used as a pretreatment step before sensitive downstream processes such as reverse osmosis, ultraviolet disinfection, or advanced oxidation. Its main role is to protect equipment and improve the clarity of water by removing suspended solids and reducing turbidity. Compared to single-media filters, multimedia filters are more efficient because their graded media structure allows for better solids retention and longer filter runs.