Clarifier operations

The net percentage of soflds in the clarifier underflows increases in going from the first to the second to the third clarifier. Typical values are 11, 15, and 21% soflds, respectively. Clarifier operations have been investigated by computer simulation studies (17). 

Control philosophies for clarifiers are based on the idea that the overflow is the most important performance criterion. Underflow density or suspended sohds content is a consideration, as is optimal use of flocculation and pH control reagents. Automated controls are of three basic types (I) control loops that optimize coagulant, flocculant, and pH control reagent additions (2) those that regulate underflow removal and (3) rake drive controls. Equahzation of the feed is provided in some installations, but the clarifier feed is usually not a controlled variable with respect to the clarifier operation. 

Possible causes of sludge bulking include (a) absence of certain necessary trace elements in wastewater (b) wide fluctuations in wastewater pH (c) limited DO in the aeration tank (d) inadequate FIM ratio (e) inadequate mean cell residence time Tc (f) inadequate return sludge pumping rate (g) internal plant overloading and (h) poor sedimentation clarifier operation. 

Rise Rate Rise rate of water is the flow rate (total hydraulic load) divided by the surface area of the clarifier. Most clarifiers operate between 0.75 gpm/ft2 and 1.25 gpm/ft2, with the exceptions of inclined-plate... 

Fortunately, many ideas needed in electron microscopy can be taken over from optical microscopy theory. This applies both to wave optics and geometrical optics. Wave optics is particularly helpful in clarifying operation at high resolution, where phase-contrast effects predominate. Geometrical optics is important for understanding the action of the lenses in the column. 

Brine from the top of the clarifier overflows by gravity to the clarifier pump tank. A turbidity meter in this line can monitor the solids content and provide an alarm in case of an upset in the clarifier operation. Again, operation and control are similar to those discussed in connection with brine saturation. The top of the tank should be at least as high as the top of the clarifier overflow system. This provides more brine storage capacity as well as time to correct a pump failure or other simple operating problems. The normal level in the pump tank is about 50%. Level control options are as in Fig. 11.3 ... 

A classic example of a clarification process used in Brazil is that of ethanol production by yeast Saccharomyces cerevisiae. The viability of ethanol production is based on the efficiency of the clarifying operation, which depends on the recycling of yeast to the fermentation reactor and, consequently, the maintenance of high cell concentrations in the culture medium. " Another relevant aspect for the appropriate process performance is the selectivity afforded by centrifugation, keeping bacteria in suspension while yeasts and other larger solids can sediment. The separation occurs due to the density difference between bacteria and yeast, the latter being removed from the supernatant due to their lower density. The partial removal of bacteria, the main contaminant, is a fundamental factor for an effective fermentation. ... 

Rise Rate Rise rate of water is the flow rate (total hydraulic load) divided by the surface area of the clarifier. Most clarifiers operate between 0.75 gpm/ft and 1.25 gpm/ft, with the exceptions of inclined-plate settlers, which operate at higher rise rates, as high as 2.0 gpm/ft and the Actiflo recirculation clarifier which operates at a rise rate of at least 16 gpm/ft (Actiflo is a registered trademark of Veolia Water North America, Chicago, IL). 

---