Physical Cleaning Methods

Physical cleaning methods depend on mechanical forces to dislodge and remove foulants from the membrane surface. Physical methods used include forward flushing, reverse flushing, hackwashing, vibrations, air sparge, and CO2 back permeation. 

MF and UF used in pretreatment to RO are more frequently cleaned by physical cleaning and less frequently by chemical cleaning. Cleaning frequencies reported in ht-erahire varied widely. Physical cleaning frequency is approximately every 40 min with a chemical clean scheduled every 6 mo (98). An air backwash frequency of 15-20 min is sufficient for hollow-fiber MF membranes (77). In a UF evaluation study, backwashing was able to achieve an average flux recovery of 86.5% (99). It was observed in the same study that flux restoration could be achieved even when backwash was reduced from 10 to 1 min. 

There has not been adequate investigation into physical and physicochemical cleaning methods for RO membranes (70). It was commented that there is httle published information on membrane cleaning and regeneration. Most cleaning studies reported are based on trial and error (4,87). A more systematic approach is required to study the 

In conclusion, the use of membrane technology in water and wastewater treatment has begun to emerge as the most significant advancement in water treatment in the past 20 yr, and its presence is expected to become widely spread in the future. 

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Nitrogen, unlike pyritic sulfur, is mosdy chemically bound in organic molecules in the coal and therefore not removable by physical cleaning methods. The nitrogen content in most U.S. coals ranges from 0.5—2.0 wt %. 

Based on literature data, physical cleaning methods generally seem to be less effective at trace element removal then chemical methods. 

This classification is useful in that the removal of minerals from coal in preparation plants is strongly influenced by the mineral s physical mode of occurrence. Fine-grained quartz, clay, and pyrite disseminated within macerals are least susceptible to removal by physical cleaning methods whereas rock fragments and minerals in layered, nodular, and fissure modes break free and are more easily removed. 

Physical cleaning methods can remove inorganic sulfates (gypsum) and most of the coarse pyrite the finely disseminated microcrystalline pyrite and organic sulfm are usually not separable by such processes. This means that in the case of coal containing 70% of sulfm in pyritic form and 30% as organic sulfm, the physical cleaning can rednce the sulfur content by about 50%. 

Processes approved for sodium treatment are water chemical methods. Alcohol is forbidden by the CEA since an accident occurred during the decommissioning of the RAPSODIE reactor in 1994 [7, 8], Physical cleaning methods (e.g. scraping, evaporation) are more limited at an industrial scale due to their relatively tedious nature. 

Generally, precombustion coal cleaning is achieved by the use of physical techniques, some of which have been used for more than a century. Physical cleaning methods typically separate undesirable matter from coal by relying on differences in densities or variations in surface properties. 

Physical cleaning can remove only matter that is physically distinct from the coal, such as small dirt particles, rocks, and pyrite. Physical cleaning methods cannot remove sulfur that is chemically combined with the coal (organic sulfur), nor can they remove nitrogen from the coal. Currently, physical cleaning can remove 30%-50% of the pyritic sulfur and about 60% of the ash-forming minerals in coal. 

Cleaning method The physical principle used to dislodge and remove the coliccred dust from the fabric,... 

Physical methods can effectively remove some trace constituents from coal, especially if deep cleaning methods are employed (7 ). However, such methods do not adequately remove finely disseminated minerals or organically bound elements, thereby necessitating chemical treatments for removing such components. 

Lin, Y. A. (Ed.), Physical Cleaning of Coal—Present and Developing Methods, Marcel Dekker, New York, 1982. 

Fine colloidal or soluble inorganic contaminants are removed from water by physical-chemical methods of waste water cleaning. The main methods used are coagulation, oxidation, sorption, extraction and electrolysis methods. 

Hair-cleaning methods may be classihed according to the following categories chemical and physical properties, microscopic methods, and subjective or sensory evaluation procedures. Chemical or physical methods may involve either direct analysis of the hair itself [13, 20] or analysis of hair extracts [17,18]. For direct analysis of hair, chemical methods such as... 

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