Clarifiers hydraulic

In the recycle flow pressurization system (Figure 27.10), a portion (15-50%) of the clarified effluent from the flotation chamber is recycled, pressurized, and semisaturated with air in the air dissolving tube. The recycled flow is mixed with the unpressurized main influent stream just before admission to the flotation chamber, with the result that the air bubbles come out of aqueous phase in contact with suspended particulate matter at the inlet compartment of the flotation chamber. The system is usually employed in applications where preliminary chemical addition and flocculation are necessary and ahead of flotation. It eliminates the problems with shearing the flocculated particles since only the clarified effluent passes through the pressurizing pump and the friction valve. It should be noted, however, that the increased hydraulic flow on the flotation chamber due to the flow recirculation must be taken into account in the flotation chamber design. 

Figure 27.12 shows the improved activated sludge process in which a new secondary flotation is applied in series between the aeration basin and the final sedimentation clarifier for increasing the overall treatment performance and hydraulic capacity of an originally overloaded existing plant. 

Based on the test results, improvements in the hydraulic characteristics of the plant alone are very attractive, with the Krofta Supracell clarifier in a secondary flotation position (see Figure 27.12). 

Rising sludge can also be caused by internal solids overloading and hydraulic overloading to the secondary sedimentation. Poor sedimentation clarifier design and operation in terms of flow-through velocity, weir design, and so on are also possible causes. 

The mechanism for sedimentation (clarification) is based on the density difference between SS and liquid. In addition, SS with larger particle sizes can settle down more easily. Rectangular tanks, circular tanks, combination flocculator-clarifiers, and stacked multilevel clarifiers can be used.14 Oliveira et al.15 reported that flocculation and sedimentation were conducted in the cassava meal industry and reduced the effluent concentration of organics from 14,000 to 2000 mg/L in the bench-scale reactor, with a hydraulic retention time (HRT) of 37 min. 

Attributes are formulated for each objective in order to clarify the degree to which the detailed objectives have been fulfilled. As an example, the following attributes were defined for the objective natural river morphology and hydraulics, [12] coefficient of variation of water depth, and coefficient of variation of flow velocity. 

Shock organic and hydraulic loading created serious operational problems in the system. Bulking sludge and the inability to return solids from the clarifier to the aeration unit further complicated plant operation. 

The second-stage (ammonia removal) effluent contained unacceptable levels of F and P and had to be subjected to third-stage lime treatment. This raises the pH from 8.5 to 11.4 and produces an effluent with concentrations of F and P equal to 25 and 2 mg/L, respectively. The hydraulic design parameters were a 15 min reaction time and a 265 gpd/ft (10.8 m /m /day) clarifier overflow rate. The resulting precipitated solids underflow concentration was 0.6% by wt. In all three stages, an anionic polymer was used to aid coagulation, solids settling, and effluent clarification. 

Because of the large volume of wastewater generated in hydraulic debarking and the problems associated with recycling it, waste treatment and disposal techniques used by the pulp and paper industry are applicable. This involves the employment of heavy-duty clarifiers to remove suspended solids, followed by biological treatment to remove oxygen-demanding substances. 

Fig. 3.13 A transect through wells that display a gradually lower water table, yet the chloride concentration is lower in the well with the lower water table. In this case the explanation is that the wells tap different aquifers and are not hydraulically interconnected. Tritium values further clarify the picture wells I and II tap a confined aquifer, whereas well III taps a phreatic through-flow system.

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... 

---