Application of membranes to treat wastewater for its recycling and reuse: new considerations to reduce fouling and increase recovery up to 99 percent

Abstract

A B S T R AC TThe RO process is very attractive for providing high product quality through the removal of a number of contaminants like oil, detergents, organics, nitrates, ammonia, phosphates etc. However the main disadvantages of the modern RO techniques are connected with membrane fouling, concentrate fl ow and pretreatment that increase operational costs, complicate design and create problems of brine utilization. Often pretreatment costs even exceed reverse osmosis facilities costs. Now a number of successful attempts were undertaken to modify spiral wound membrane channels to limit fouling and scaling potential. As presented in a number of publications, elimination of the spacer mesh from the feed channels eliminates dead regions that provide scaling and fouling conditions whilst also reducing the risk of particle "trapping" and associated dramatic pressure increase. Introduction of a new "open channel" confi guration offers a new perspectives to escape fouling and development of novel techniques to treat water with high fouling potential (high suspended matter, organics and supersaturated solutions). This novel concept of spiral wound module with an "open channel" design is developed, fi eld-tested and introduced into practice. Fouling control is achieved due to the elimination of spacer and the implementation of an optimum hydraulic mode providing suffi cient cross fl ow velocities, fl ushings and cleanings. The main principles of high recoveries, low maintenance and zero discharge are ensured by concentration of brine through re-circulation by 50−100 times by volume. Several examples of water treatment fl ow diagrams are presented to demonstrate of zero concentrate fl ow discharge. Coagulated suspended matter after membrane fl ushes is collected, sedimented and fi nally dewatered. The concentrated solution containing salts and impurities together with the wet sludge constitutes no more than 1 percent of initial water in part due to high supersaturation values due to the strong stability of calcium carbonate solutions.

A review of polymeric membranes and processes for potable water reuse

“…Hence, increasing fouling resistance remains the biggest challenge for spiral wound membranes. Ongoing research, through the last decade, focused on the optimization or complete removal of the feed spacer mesh from the spiral wound feed channels [144,145]. Spacers in the feed can create dead regions that promote scaling, fouling, and particulate deposition.…”

Research for waste water treatment technology with low production of excessive active sludge

“…Table 1 show positive results of the application of immobilized activated sludge that allows increasing the dose of sludge in the aeration facility, which accordingly improves their oxidative capacity and creates favorable conditions for development and retention of specific slow-growing strains of microorganisms able to destruct various hardly oxidized contaminants [25][26][27]. Table 1.…”

The influence of hydrodynamic factors, membrane surface properties and channel geometries on membrane performance and fouling mechanisms

“…The main disadvantages of spiral wound modules are attributed to the presence of separation spacer mesh in the feed channel as it traps fouling particles and increase a crossflow channel resistance [4,20]. The places (spots) where mesh contacts the membrane surface provide "dead" areas without cross-flow, resulting in high concentration increase at the membrane surface that initiates formation of colloids and crystals of sparingly soluble salts.…”