Clarification pretreatment process

Because no research data is available on the disinfection potency of hydroxyl radical, it is not a recognized disinfectant. Thus, any disinfection must be achieved with the companion oxidant, such as ozone, prior to the formation of the hydroxyl radical. The hydroxyl radical is used primarily for removal of volatile organic chemicals, pesticides, and taste and odor compoxmds that are not effectively removed by conventional clarification/ filtration processes rather than for disinfection. Therefore, AOPs are generally not used for disinfection of RO pretreatment systems. 

The process of pretreating hard water with lime and sometimes soda as well, based on standard precipitation methods, to reduce the hardness either to a minimum level or more usually to a preset level of, say, 85 ppm, thereby lowering the total treatment costs. Usually carried out in specially designed tanks and followed by clarification and filtration. Calcium bicarbonate is always removed, requiring one equivalent... 

Pretreatment involving filtration and clarification for removal of suspended solids and turbidity may improve treatment efficiency. To reduce the interference of inorganic and organic compounds, other treatment processes may have to be combined with UV/H202 systems for effective treatment. In some situations, pH control may be required to prevent precipitation of metal salts during the oxidation process and to avoid a loss in efficiency due to the precipitates. Generally, metal hydroxide precipitation can be avoided for pH less than 6. Alkaline pH can adversely affect the reaction rate, possibly due to the base-catalyzed decomposition of H202. 

Wastewater treatment systems can be classified, in addition to pretreatment, as preliminary, primary, secondary, and tertiary (advanced) treatments. Pretreatment of industrial wastewater is required to prevent adverse effects on the municipal wastewater treatment plants. Preliminary treatment is considered as any physical or chemical process that precedes primary treatment. The preliminary treatment processes may consist of influent screening and grit removal. Its function is mainly to protect subsequent treatment units and to minimize operational problems. Primary treatment is defined as the physical or chemical treatment for the removal of settleable and floatable materials. The screened, degritted raw wastewater from preliminary treatment flows to the primary clarification tanks, which are part of the primary treatment facilities. Secondary wastewater treatment is the process that uses biological and chemical treatment to accomplish substantial removal of dissolved organics and colloidal materials. The secondary treatment facilities may be comprised of biological reactor and secondary clarification basins. Tertiary (advanced) wastewater treatment is used to achieve pollutant reductions by methods other than those used in primary and secondary treatments. The objective of tertiary wastewater treatment is to improve the overall removal of suspended solids, organic matter, dissolved solids, toxic substances, and nutrients. 

Wastewater reclamation was pioneered using advanced conventional treatment processes to upgrade the water quality of wastewater to reusable standards. When RO was first introduced to produce water closer to drinking water quality from wastewater, a conventional treatment process was employed as pretreatment to the RO. A typical conventional pretreatment configuration would include flocculation, lime or alum clarification, recarbonation, settling, filtration, and activated-carbon adsorption. Biological activity is controlled by chlorination. 

Sedimentation Portable water clarification municipal treatment storage pond for toxic waste and mineral processing waste and pretreatment step for feed to filters and centrifuges. 

UF is a pressure driven moleeular sieving process. Due to the size of the pores, the particles that are too large to pass through are physically blocked out, while the dissolved salts and essential minerals pass through the membrane (Fig. 4.7). This process is useful for clarification and disinfection of water but cannot remove dissolved contaminants like fluoride. UF can however be employed for pretreatment to RO process to reduce turbidity and microbial load on the membrane. 

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