Particle Removal Processes

All surface waters contain particles of different origin, sizes and materials, which must be removed efficiently before water distribution. There is a renewed interest in improved particle separation due to the hygienic problems with infectious cysts and oocysts of parasites (Gia-rdia, Cryptosporidium), which are particles in the size range of 3-12 (am. Depending on the raw water quality, particle separation may be accomplished typically by  

In recent years, membrane processes such as micro- and ultrafiltration have been studied and introduced for near-to-complete particle removal. 

It has been observed for more than 30 years that preozonation ahead of particle removal units can improve the efficiency significantly, can induce a lower coagulant demand or allow higher flow rates, e. g. in deep-bed filtration. Ozone gas is added either before or together with the coagulant (ferric or aluminum salts or cationic polymers) at rather low dosages of 0.5-2 mg L l. The terms microflocculation or ozone-induced particle destabilization are used in practice (Jekel, 1998). 

The mechanisms involved appear to be rather complex and several mechanistic models have been described (for a recent review see Jekel, 1998). Results from the references therein as well as from additional pilot and full-scale applications indicate that an optimal ozone dosage exists, typically in the lower range of 0.5-2 mg L l or, related to the DOC, 0.1-1 mg mg-1. The optimal point must be determined by tests in the combined treatment. 

The relative improvements (reference is particle removal without ozone) are quite variable, but were reported to be about 20-90 % lower turbidities and/or lower particle counts in the filtered water. The presence of dissolved organic matter is frequently essential and DOC should be at least 1 mg L The preozonation effects depend strongly on the presence of alkaline earth cations, especially calcium. 

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The major purpose of ambient particulate sampling is to obtain mass concentration and chemical composition data, preferably as a function of particle diameter. This information is valuable for a variety of problems effects on human health, identification of particulate matter sources, understanding of atmospheric haze, and particle removal processes. 

In the case of the scrubberless approach, the damaged layer is in practice generally removed during the underetch particle removal process (ammonia... 

In contrast, laser irradiation has been shown to provide a potential solution to this problem. Laser-induced removal of the contaminants can be effected either via direct absorption of the laser light by the particles and/or the substrate ( dry laser cleaning ) or via the prior application of a liquid film ( steam laser cleaning ) [3]. The particle removal process can be evaluated either directly, by post-treatment optical or scanning electron microscopic examination of the sample, or indirectly via the scattering by the par-... 

Filtration Suspended, precipitated, and oversize particle removal process water, wash water, waste oil, boiler feed water cleanup mineral dewatering and recovery of valuable products. 

In order to improve the efficiency with which the adhering particles are removed, one must either raise the air-flow velocity or intensify some auxiliary particle-removing process. For ex-... 

Inorganic chemicals may also be used. Beatonite may be used as a flocculant ia combination with polymer treatmeat. Alum, oace a common coagulant, is less used because its concentration can build up ia recycle water. Alum oftea biads ink to fibers and iacreases the difficulty of deinking. Removal of the very small flexographic ink particles ia process water is difficult. Ultrafiltratioa (qv) has beea proposed for removing these very small dispersed ink particles (53). 

The concentration of indoor pollutants is a function of removal processes such as dilution, filtration, and destruction. Dilution is a function of the air exchange rate and the ambient air quality. Gases and particulate matter may also be removed from indoor air by deposition on surfaces. Filtration systems are part of many ventilahon systems. As air is circulated by the air-conditioning system it passes through a filter which can remove some of the particulate matter. The removal efficiency depends on particle size. In addition, some reactive gases like NOj and SOj are readily adsorbed on interior surfaces of a building or home. 

Gas Filtration Vendors are the primary source for sizing baghouses, however the process engineer should at the very least make an estimate of the pressure drop requirements for an intended system. The pressure drop will, of course, provide information needed on the approximate size of the fan needed, and the energy requirements needed to operate a system. In fact, pressure drop is the primary parameter in establishing particle removal efficiency for a fabric filtration unit, and hence, is usually the starting place for discussions with the equipment supplier. 

Cyclone collectors are popularly used both for particle removal and for particle sampling (Fig. 13.1). The separation process of a cyclone relies on the centrifugal accelerations that are produced when particle-laden fluid experi-... 

Particles are present in outdoor air and are also generated indoors from a large number of sources including tobacco smoking and other combustion processes. Particle size, generally expressed in microns (10-6 m) is important because it influences the location where particles deposit in the respiratory system (U.S. Environmental Protection Agency 1995), the efficiency of particle removal by air filters, and the rate of particle removal from indoor air by deposition on surfaces. 

As a starting point we can view the ocean as one large reservoir to which materials are continuously added and removed (Fig. 10-17). The major sources of material include rivers and winds, which carry dissolved and particulate materials from the continents to the sea. The major removal process is the formation of marine sediments both by settling of particles through the water column as well as by precipitation of insoluble solid phases. For many ele-... 

Particle Natter Remove by prefiltering or centrifugation. Addition of concentrated HCl is effective in dissolving inorganic particles when processing water samples. 

Flotation is a solids removal process that introduces a gas, usually air, into the wastewater stream. The gas adheres to the suspended solids, reducing their density and causing them to rise to the surface of the water, where they are skimmed off. The advantage of flotation clarification over sedimentation is that lighter particles that require very long retention times to settle are removed more quickly. 

Fu et al. (2002) report the optimization of a fabrication procedure for microspheres based on the poly( anhydride-co-ether) P(SA-EG). The microspheres are fabricated by solvent removal process that produces a porous structure with densities in the range of 0.344 and 0.077 g cm-3 and sizes that are optimized for delivery to the deep lung by inhalation (Fu et al., 2002). An appropriate in vitro cell culture model for characterization of the particle-epithelia system was also developed (Fiegel et al., 2003). 

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