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The decline in membrane performance due to both biofouling and particulate fouling is a major issue for membranes in the water treatment industry. In spiral wound modules, commonly used in reverse osmosis and nanofiltration, the presence of feed spacers results in an increased potential of fouling. We describe a novel cleaning method to be used in the restoration of membrane module performance. The method described here involves the use of water saturated with dissolved CO 2 at higher pressures and rinsing of the fouled membrane/ spacer channel at a lower pressure. Due to depressurization, bubbles nucleate at spacer filaments and improve the cleaning efficacy significantly. The study compared the cleaning efficacy of three methods in the removal of fouling from a membrane/spacer channel; water rinsing, water/N 2 sparging, and water/CO 2 (dissolved) nucleation. Using water rinsing, 40% of the fouling on the spacer-filled channel could be removed; a water/ N 2 mixture removed 85% of the fouling. With the dissolved water/CO 2 , there was complete removal of the fouling (all measured as restoration of the hydraulic resistance of the clean channels). Such an efficient tool to recover the performance of severely fouled desalination membrane modules could replace or reduce today's expensive, sensitive, and chemically intensive cleaning processes.

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Worldwide limestone filtration is used in many treatment plants for the conditioning and (re)mineralization of drinking water to increase concentrations of Ca^ ' and HCO3 , pH and saturation index, thereby improving the quality of the water regarding corrosion control, buffering and taste.Typical applications include (very) soft groundwater with (very) low alkalinity and desalinated water.In Norway, some plants use a product made of ground natural limestone, called micronized CaC03 slurry (MCCS), which is dosed as slurry of fine particles (1-2 nm) into the raw water. In this study the potential of MCCS as an alternative to limestone filtration was investigated. Experiments were performed to determine the dissolution kinetics of MCCS and other CaCO3-products, including natural limestone grains and two precipitated CaC03 powders. As expected from theory, the dissolution kinetics are strongly influenced by the particle size of the CaC03 and the driving force towards the chemical equilibrium. However, all CaCO3-products needed substantial detention times (30 min and more) to dissolve completely. It is concluded that MCCS is generally not a feasible alternative for limestone filtration as a stand-alone option for the conditioning and (re)minerallzation of drinking water. Applications of MCCS are limited and should either be found in combinations with coaguiation/filtration or with other conditioning and (re)mineraiization methods.