WHY PRE-TREATMENT IS NECESSARY?
Reverse Osmosis (RO) has been used for desalination, softening and contaminant removal. As the available "clean", fresh and groundwater sources are being depleted worldwide, RO technologyis applied to surface water, wastewater, and groundwater. These types of water contain significantly more particles, organics and other solids that may not be compatible with RO Membrane processes. Therefore, the correct pre-treatment plays a critical role in the performance, life and total cost of the ownership of these systems as incorrect usage causes fouling of the membrane.This requires some of the parameters such as TOC, TSS, temperature, pH, etc., historical data to determine the minimum, average and expected values ??to correctly plan and design the system.
The primary objective of the pre-treatment is to make the RO feedwater compatible with the membrane. The pre-treatment is necessary to increase the efficiency and life of the membrane elements by minimizing fouling and degradation of the membrane.
The fouling refers to the inclusion of particles such as sludge, clay, suspended solids, biological sludge, algae, silica, iron flakes and other materials on the surface or, worse still, in the pores of the membrane. Typically fouling initially occurs in first stage conduit elements and then affects itself through the following elements. Scale formation refers to the precipitation and deposition of poorly soluble salts such as calcium sulphate, barium sulphate, calcium carbonate, silicon dioxide, calcium fluoride, and any other super-saturated salts in the immediate surface of the membrane. Typically, the scaling begins at the last stage tail elements (on the reject side) as theses treat the water with the highest ion concentrations. Once a scale crystal is formed within membrane element, it acts as a nucleation site for additional scale formation, and the rate of scale formation increases exponentially.
Inadequate pre-treatmentoften requires frequent cleaning to restore product flow and salt repellence. This results in excessive costs of dry cleaning, increases the downtime of the system and in severe cases results in permanent loss of performance, degradation of the membrane and therefore, a shorter life of the membrane.
Proper pre-treatment of raw water makes it compatible as feed water for RO.Therefore, the correct pre-treatment plays a critical role in the performance, life and total cost of ownership of these systems. Although the salt repellent properties of RO membranes have been known in the industry since the years of the 1980s, the feedwater compatibility has particles, fouling rates, effects on the membrane life.The pre-treatment is generally considered sufficient when the cleaning of the membrane is limited to 3-4 times a year or less.