Detention

Standard Pest Methodfor Determining Bacterial detention of Membrane Filters IJtili dforPiquid Filtrations ASTM F838-83, American Society for Testing and Materials, Philadelphia, Pa., 1983 reapproved 1988. 

K. Mobeig, TAPP11989 detention and Drainage Short Course Notes, TAPPI Press, Adanta, Ga., 1989, pp. 65—86. 

Typical methane yields and volatile soHds reductions observed under standard high rate conditions are shown in Table 12. Longer detention times will increase the values of these parameters, eg, a methane yield of 0.284 m at normal conditions /kg VS added (4.79 SCF /lb VS added) and volatile soHds reduction of 53.9% for giant brown kelp at a detention time of 18 days instead of the corresponding values of 0.229 and 43.7 at 12 days under standard high rate conditions. However, improvements might be desirable in the reverse direction, ie, at shorter detention times. 

When the overflow clarity is independent of overflow rate and depends only on detention time, as in the case for high soHds removal from a flocculating suspension, the required time is deterrnined by simple laboratory testing of residual soHd concentrations in the supernatant versus detention time under the conditions of mild shear. This deterrnination is sometimes called the second-order test procedure because the flocculation process foUows a second-order reaction rate. 

The most important design dimensions of a thickener are pool area and depth. The pool area is chosen to be the largest of the three layer requirements. In most cases, only the zone-settling and compression layer requirements need to be considered. However, if the clarity of the overflow is critical, the clarification zone may need the largest area. As to the pool depth, only the compression layer has a depth requirement because the concentration of the soHds in the underflow is largely deterrnined by the time detention and sometimes by the static pressure. Thickness of the other two layers is governed only by practical considerations. 

Because of large equipment and land requirements, capital costs for wastewater-treatment plants are high. A collection system that conveys both sanitary and storm flows must be designed to deal with high peak flows at the treatment plant detention basins are usually provided in order to smooth the flow into the plant and reduce the sudden peak flow. In the absence of such precautions, it may be necessary to by-pass a portion of the flow. 

Sludge is destroyed by microorganisms and the kinetics of their life processes is temperature dependent. Short anaerobic digestion detention times are obtained at 35°C. Even shorter detention times are possible at 52—54°C, but detention in this range is costly. An increase in detention time occurs at 35—43°C and then a progressive decrease takes place until 52—54°C. This variation is caused by a change in character of the dominant process organisms. 

Stabilization Ponds. Stabilization ponds have a water depth of 1—2 m and oxygen is suppHed by surface entrainment or by algae. The BOD loading must be low and the detention time is 5—25 days (218). 

Aerated Lagoons. Aerated lagoons are 2—5 mhquid depth depending on the aeration system and detention times are 2—10 days. They are mainly used because of their efficiency in removing BOD from textile effluents (2). 

W. B. Williamson, H. S. Gandhi, and E. E. Weaver, ffects ofFuelA.dditiveMMT on Contaminent detention and Catalyst Performance, SAE 821193,... 

Areal efficiencies for properly designed clarifiers in which detention time is not a significant factor range from 65 to 80 percent, and the surface area should be increased accordingly to reduce the overflow rate for scale-up. 

Shoiild the particles have a tendency to cohere slightly during sedimentation, each sampling time, representing a different nominal detention time in the clarifier, will produce different suspended-sohds concentrations at similar rates. These data can be plotted as sets of cui ves of concentration versus settling rate for each detention time by the means just described. Scale-up will be similar, except that detention time will be a factor, and both depth and area of the clarifier will influence the results. In most cases, more than one combination of diameter and depth will be capable of producing the same clarification result. 

These data may be evaluated by selecting different nominal overflow rates (equivalent to settling rates) for each of the detention-time values, and then plotting the suspended-solids concentrations for each nominal overflow rate (as a parameter) against the detention time. For a specified suspended-sohds concentration in the effluent, a cui ve of overflow rate versus detention time can be prepared from this plot and used for optimizing the design of the equipment. 

Detention Test This test utihzes a 1- to 4-L beaker or similar vessel. The sample is placed in the container, flocculated by suitable means if required, and allowed to settle. Smah samples for suspended-sohds analysis are withdrawn from a point approximately midway between liquid surface and settled solids interface, taken with sufficient care that settled solids are not resuspended. Samphng times may be at consecutively longer intei vals, such as 5, 10, 20, 40, and 80 min. 

The suspended-solids concentration can be plotted on log-log paper as a function of the sampling (detention) time. A straight line usually wih resiilt, and the required static detention time t to achieve a certain suspended-sohds concentration C in the overflow of an ideal basin can be taken directly from the graph. If the plot is a straight hne, the data are described by the equation... 

Detention efficiency. Conversion from the ideal basin sized by detention-time procedures to an actual clarifier requires the inclusion of an efficiency factor to account for the effects of turbulence and nonuniform flow. Efficiencies vaiy greatly, being dependent not only on the relative dimensions of the clarifier and the means of feeding but also on the characteristics of the particles. The cui ve shown in Fig. 18-83 can be used to scale up laboratoiy data in sizing circular clarifiers. The static detention time determined from a test to produce a specific effluent sohds concentration is divided by the efficiency (expressed as a fraction) to determine the nominal detention time, which represents the volume of the clarifier above the settled pulp interface divided by the overflow rate. Different diameter-depth combinations are considered by using the corresponding efficiency factor. In most cases, area may be determined by factors other than the bulksettling rate, such as practical tank-depth limitations. 

FIG. 18 83 Efficiency curve for scale-up of barch clarification data to determine nominal detention time in a continuous clarifier,... 

If a solids-contact clarifier is required, the surface-area requirement must exclude the area taken up by the reaction chamber. The reaction chamber itself is normally sized for a detention time of 15 to 45 min, depending on the type of treatment and the design of the unit. 

III) East LC-APCI-MS/MS analysis using a short luonolitliie separation eoluiun eoupled to a triple-quadiupole luass speetroiueter operating in luultiple reaetion luonitoring (MRM) detention luode. 

A prerequisite of a eleaning program is some kind of fouling detention system. Naturally, this system must eover the prime reason for eleaning. If the maehine is a gas turbine, the prime reason may be horsepower eapability, or it may be effieieney. On a eentrifugal eompressor, the prime reason for... 

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