Liquid filtration industrial wastewater treatment

The application of FO in recent years has expanded, not only in terms of installed capacity but also in the diversity of industries where the technology has been installed. Applications such as power generation, desalination, wastewater treatment (osmotic membrane bioreactor) and liquid food concentration are reported in the literature [4]. Commercial FO products are available for a variety of applications including personal water filtration and desalination, oil gas drilling water reclamation and landfill leachate treatment. 

Pressure filtration differs fi-om vacuum filtration in that the liquid is forced through the filter medium by a positive pressure instead of a vacuum. Among the most widely used in Che chemical process industry (and widely used in Europe for wastewater treatment) is Che filter press. As shown in Figure 3, Che filter press operates by pumping the sludge between plates that are covered with a filter cloth. The liquid seeps throu Che filter cloth leaving the solids bdiind between the plates. Whoi the spaces between the plates are filled, the treatment plant operator separates the plates and removes the solids. 

Water is the most commonly used liquid in industry and in all human activities. Thus most liquid-solids separation equipment is specifically designed for treating aqueous systems. In water suspensions, the sizes of solid partieles are usually very small (in the micron and submicron size range) and surface-active forces often play an important role. Representative examples are the mineral slurries, lyophilie eolloids, slimes, and wastewater mixtures. The treatment of aqueous systems involves four stages floeeulation (elarification), sedimentation (settling), consolidation (compression or compaction), and phase separation (filtration or centrifugation). 

Flocculation and sedimentation arc two processes used to separate waste streams that contain both a liquid and a solid phase. Both are well-developed, highly competitive processes, which arc oflcii used in the complete treatment of waste streams. They may also be used instead of, or in addition to, filtration. Some applications include the removal of suspended solid particles and soluble heavy metals from aqueous streams. Many industries use both processes in the rcmowal of pollutants from their wastewaters. These processes work best when the waste stream contains a low concentration of the contaminating solids. Although they are applicable to a wide variety of aqueous waste streams, these processes arc not generally used to treat nonaqueous or semisolid waste streams such as sludges and slurries. 

Radioactive metal wastes from the nuclear industry are of increasing concern as the amount of waste to be disposed of increases. Current treatment of nuclear wastewater involves the addition of lime, which is effective in precipitating most metals out of solution with the exception of radium (Tsezos Keller, 1983). Barium chloride (BaCl2) is used to precipitate radium from sulfur-rich effluents as barium-radium sulfate. Other treatment methods include incineration for some solid wastes, and filtration, adsorption and crystallization for liquid wastes (Godbee Kibbey, 1981). 

There are two other types of technologies—reverse osmosis (RO) and electrodeionization (EDI)—that remove dissolved solids from a liquid stream. Both are widely used in the water purification industry and have potential for use in the treatment of CMP wastewater. RO is a method by which water is forced through a semipermeable membrane that does not allow ions to cross. EDI removes ions from a liquid stream by means of an applied voltage. Both the EDI or RO are very effective in removing anions and cations, but the tradeoff is that the feed to the EDI or RO must be preconditioned to prevent damage to the equipment. In particular, the feedwater to an RO should not have a silt density index (SDI) greater than 3.0, which may require additional filtration to ensure all the solids are removed from the liquid stream. Some EDI manufacturers recommend that the feedwater to the EDI be RO permeate or of better quality. 

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