Flocculation pretreatment process

Under alkaline BW conditions, if magnesium bicarbonate is not removed by softening or other pretreatment processes, it forms brucite, an insoluble flocculant sludge of magnesium hydroxide [Mg(OH)2],... 

Combining flocculation and coagulation in a pretreatment process has also been smdied. In a key paper by Lopez-Ramirez et al. [64], the secondary effluent from an activated sludge unit was pretreated, before RO, with three levels intense (coagulation-flocculation with ferric chloride and polyelectrolite and high pH sedimentation), moderate (coagulation-flocculation with ferric chloride and polyelectrohte and sedimentation), and minimum (only sedimentation). The optimum for membrane protection, in terms of calcium, conductivity, and bicarbonates reduction, was the intense treatment. Membrane performance varied with pretreatment but not reclaimed water quahty. The study recommended intense pretreatment to protect the membrane. 

A more flexible option from an operational viewpoint is the implementation of process-oriented enhancements that intensify particle separation. This can be achieved by two different methods. In the first method, the suspension to be separated is pretreated to obtain a cake with minimal resistance. This involves the addition of filter aids, flocculants or electrolytes to the suspension. In the second method, the period during which suspensions are formed provides the opportunity to alter suspension properties or conditions that are more favorable to... 

Chemical pretreatment is often used to improve the performance of contaminant removal. The use of chemical flocculants is based on system efficiency, the specific DAF application and cost. Commonly used chemicals include trivalent metallic salts of iron, such as FeClj or FeSO or aluminum, such as AISO. Organic and inorganic polymers (cationic or anionic) are generally used to enhance the DAF process. 

Studies on orthokinetic flocculation (shear flow dominating over Brownian motion) show a more ambiguous picture. Both rate increases (9,10) and decreases (11,12) compared with orthokinetic coagulation have been observed. Gregory (12) treated polymer adsorption as a collision process and used Smoluchowski theory to predict that the adsorption step may become rate limiting in orthokinetic flocculation. Qualitative evidence to this effect was found for flocculation of polystyrene latex, particle diameter 1.68 pm, in laminar tube flow. Furthermore, pretreatment of half of the latex with polymer resulted in collision efficiencies that were more than twice as high as for coagulation. 

A major aspect of an SLS process may be conditioning of the slurry to improve its filterability. Table 11.4 summarizes common pretreatment techniques, and Table 11.5 lists a number of flocculants and their applications. Some discussion of pretreatment is in Section 11.3. 

Depending on the nature of the product, pretreatment of the feed material may be desirable to improve the separation characteristics. Possible techniques are based on chemical or physical treatment and include thickening, flocculation, and coagulation. A simple heat treatment process where the temperature of the broth is elevated and held for a period of time can reduce... 

Extracellular Products. In order to prevent cell lysis, removal of cells from a fermentation broth is usually started within hours after harvest. After cell separation, the clarified fermentation broth is more stable and can be stored refrigerated for days. Upon harvest, most primary recovery steps involve some pretreatment of the fermentation broth, which can range from simple cooling and dilution for fungal broths to pH adjustments, addition of salts, stabilizers, or flocculation agents in order to minimize degradation of the desired product and facilitate further processing. For labile compounds, such as protease enzymes,... 

A modular pilot size plant involving coagulation/flocculation, centrifugation, ultrafiltration, and sorption processes was designed and constmeted by Benito et al. [13] for the treatment of oily wastewaters. Empirical equations developed by Shaalan [65] predict the impact of water contaminants on flux decline. These formulae enable decision-making concerning a suitable water pretreatment scheme and also selection of the most appropriate cleaning cycle. 

As illustrated, many surface water schemes employ ozonation as a pre- and/or post-treatment to GAC adsorption (in some instances, the ozonation process is supplanted by chlorination). Ozonation as a pretreatment to carbon adsorption achieves two basic objectives 1) ozone applied in first stage ozonation, as in the Mulheim and Choisy-le-Roi cases described in Table 2, serves as a disinfectant, a dissolved oxygen (D.O.) input to raw waters of low D.O., and as an aid to more efficient flocculation, which means greater removals in the sedimentation step and 2) ozonation has been shown to convert a rmmber of organic compounds which are otherwise resistant to treatment into forms which can be effectively removed in GAC beds, either by direct adsorption or by bio-oxklation [10 ]. A number of other pretreatments have been found to lengthen carbon... 

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. 

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