Reverse Osmosis Fouling Research Articles

Fouling reduction using centrifugal membrane separation

The effect of membrane orientation in a centrifugal membrane system (CMS) on the alleviation of fouling of reverse osmosis (RO) and nanofiltration (NF) membranes by colloidal foulants was examined. Colloidal silica fouling of RO membranes is dramatically reduced relative to a conventional reference system for all membrane orientations except (0, 180, 0) in which the centrifugal force is directed towards the active face of the membrane. The fouling of RO membranes by humic acid is not alleviated to the same extent as the silica case except for the (90, 90, 0) orientation that combines a favorable alignment of the centrifugal force along the membrane face, and a Coriolis force also along the membrane face. The influence of these two factors is also seen in protein fouling of a NF membrane. The critical flux in NF is significantly enhanced by CMS even though a substantial protein-fouling layer is present on the membrane. Some membrane orientations in the CMS environment can inhibit the onset of a fouling layer and, once formed, enhance the permeability of that layer.

A novel inhibitor for scale control in water desalination

Premature membrane failure and membrane fouling in reverse osmosis and efficiency loss in distillation processes during water desalination are generally the result of mineral scale deposition in critical parts of these processes. The efficiency of multi-stage flash evaporators is compromised by operating at lower temperature than an ideal temperature to reduce scaling problem. A novel compound, polyamino polyether methylenephosphonate (PAPEMP) is an ideal additive for desalination operations because it simultaneously, controls calcium carbonate and calcium sulfate scale formation and deposition. It can reduce or eliminate acid feed, thus limiting the hazards associated with it and lessening equipment corrosion. In acid feed systems, PAPEMP chemistry is very forgiving in the event of over or underfeed of acid. Unlike most other phosphonates, PAPEMP's high tolerance for calcium ions completely avoids membrane fouling with calcium phosphonate salts. The inhibitor is also very effective for controlling silica/silicate deposits and stabilizing hydroxides of iron, demonstrating that PAPEMP is able to overcome all the shortfalls of the current technology used for scale/deposit control in water desalination.

Desalting and ground water management in the San Joaquin Valley, California

Desalting brackish ground water can be combined with ground water management in the San Joaquin Valley to partially alleviate environmental and economic problems caused by agricultural drainage water. Desalting subsurface drainage water produced from on—farm shallow drainage systems is costly due to high salinity and the potential for scaling and fouling of reverse osmosis (RO) membranes. When subsurface drainage water is transported in open canals, algal growth and accompanying organic transformations present pretreatment problems that have yet to be solved. Similar problems have been experienced at desalting facilities outside the San Joaquin Valley using comparable feed waters. The proposed pumping of usable ground water from the semiconfined aquifer on the Valley's west side to lower the shallow water table and thus eliminate waterlogging of crop root zones may result in degradation and mining of usable ground water and contamination of the confined aquifer below the Corcoran clay, the principal confining layer in the Valley. A combination of brackish ground water desalting and ground water management by pumping unusable shallow ground water from an interval between the crop root zones and the usable water body at the bottom of the semiconfined aquifer would result in (1) a lower salinity feed water that will reduce the cost of desalting, (2) a feed water that requires little, if any, filtration to protect RO membranes, and (3) the removal of the body of water containing high levels of salt and selenium that endanger usable water in both aquifers. The combination of brackish ground water desalting and ground water management would result in the production of usable quantities of fresh water for California's ever-increasing population and a reduction in the cost of reclaiming and managing drainage water by desalination.

Pretreatment of seawater by flocculation and settling for particulates removal

Seawater flocculation was studied in this investigation as an aid in preventing fouling of reverse osmosis (RO) membranes by particulates. The behavior of clays in seawater and their possible use in the pretreatment process was also investigated. Mediterranean seawater samples were found to have a salinity of about 36‰, pH of 7.9–8.2 and turbidity of 1.0–17.5 NTU (Nephelometric Turbidity Units). After 1–3h of quiescent setting, 30–50% of the turbidity remained and then stabilized, pointing to a possible advantage of lagooning prior to further treatment. Tests carried out with artificial seawater, as well as natural seawater, were carried out to study particle removal in general, and algae and clay in particular. Different conventional and polyelectrolytic flocculants were used in the experiments. The best clarification was found using alum and an anionic polymer in combination, resulting in 20–100 particles per ml and a turbidity of less than 1 NTU. It was also found that particle size distribution measurements may provide a better picture of the quality and mechanism of treatment.

Effects of acceleration on particulate fouling in reverse osmosis

Experimental data show that acceleration, as in a centrifuge, is effective in reducing the amount of particulate fouling in reverse osmosis. The effects of acceleration on particulate fouling were determined by testing hollow-fiber elements under accelerations of up to 500 G. The fouling agent was 40 ppm of iron hydroxide suspended in a solution of 0.5 percent sodium chloride. The data indicate that steady-state operating conditions of a fouled membrane are approached asymptotically. 500 G of acceleration allows a fouled membrane, in a steady-state, to realize over 90 percent of its unfouled capacity; the same membrane in a nonaccelerated state produced as little as 62 percent of its unfouled desalinate flow.