Retention efficiency

Verification of the microbial retention efficiency of the membrane filters may be undertaken using either Hquid or aerosol challenge tests. A Hquid challenge test is more stringent. Furthermore, this test can provide retention information for process conditions such as extreme moisture after sterilization or air entrained with water drops. A Hquid challenge is performed using a protocol similar to that described for Hquid filtration. 

The retention efficiency of membranes is dependent on particle size and concentration, pore size and length, porosity, and flow rate. Large particles that are smaller than the pore size have sufficient inertial mass to be captured by inertial impaction. In liquids the same mechanisms are at work. Increased velocity, however, diminishes the effects of inertial impaction and diffusion. With interception being the primary retention mechanism, conditions are more favorable for fractionating particles in liquid suspension. 

For most free amino acids and small peptides, a mixture of alcohol with water is a typical mobile phase composition in the reversed-phase mode for glycopeptide CSPs. For some bifunctional amino acids and most other compounds, however, aqueous buffer is usually necessary to enhance resolution. The types of buffers dictate the retention, efficiency and - to a lesser effect - selectivity of analytes. Tri-ethylammonium acetate and ammonium nitrate are the most effective buffer systems, while sodium citrate is also effective for the separation of profens on vancomycin CSP, and ammonium acetate is the most appropriate for LC/MS applications. 

Fig. 1 Scheme illustrating the influence of water discharge (y axis) and solute concentration (metals and nutrients on the x axis) on in-stream retention efficiency measured on the basis of the nutrient spiraling concept. The most remarkable Metal (M) effects on biofihns are indicated in the... 

Table 2 Fate and effects of metals in a stream receiving a point-source of metals (upper part of the table) or diffuse input via urban runoff (lower part of the table). Summary of the expected influence of four different hydrological situations base-flow in a rainy period a flood after a rainy period low-flow after a long period of low rainfall (water scarcity) and a flood produced after this drought. Metal concentration (M) metal retention efficiency (measured on the basis of the nutrient spiraling concept) exposure (dose and duration) bioaccumulation (in fluvial biofilms) and metal sensitivity (of biofihns)...

Marti E, Aumatell J, Gode L, Poch M, Sabater F (2004) Nutrient retention efficiency in streams receiving inputs from wastewater treatment plants. J Environ Qual 33 285... 

Efficiency testing of high-efficiency partieulate air (HEPA) filters used for the supply of sterile air to aseptie workplaces (Chapter 22) is normally achieved by the generation upstream of dioetylphthalate (DOP) or sodium ehloride particles of known dimension, followed by deteetion in downstream filtered air. Retention efficiency is reeorded as the percentage of partieles removed under defined test conditions. Microbiological tests are not normally performed. 

AE is essentially a ratio of the element of interest retained in the organism compared with the original uptake. In demisponges, where digestion is largely by amoebocytes, it is sometimes referred to as retention efficiency when applied to the food particles, such as bacteria, diatoms or detritus ... 

The same shipment of raw, cooked and roasted glandless whole kernel cottonseed flours used in the FDA study was used to determine the protein efficiency ratio (PER) of each flour (8). The adjusted PER (Table II) of cooked (2.10) cottonseed was significantly higher than roasted (1.77) cottonseed. Protein retention efficiency (PRE) for roasted cottonseed (58.08) was lower than values for raw (60.54) and cooked (62.95) cottonseed. Relative protein values (RPV) indicated a utilization of 91, 91 and 96% of the protein in raw, roasted and cooked cottonseed, respectively. The multiplication of the (RPV) percentage utilization and the protein content of the cottonseed (Table I) results in the relative utilizable protein values (Table II). 

Two studies (44,63) had shown that growth performance and nitrogen retention efficiency of chicks were severely reduced by the inclusion of raw full fat winged bean seeds at rates of up to 400g/kg in semi-purified diets. Heat treatment of winged beans prior to dietary incorporation results 1n reversal of the growth depression and increases the efficiency of food utilization. 

From an economic point of view, perfusion cultures of animal cells should be operated at high perfusion rates [17]. However, the high cell concentrations achieved in such cases result in several technical constraints, such as oxygen transfer, CO2 removal, medium formulation, and, especially, cell retention efficiency. 

The main streams of a separator are usually three the feed stream containing the cells to be separated, the underflow containing the separated cells, and the overflow containing the cells that the separator could not capture. The cell separation efficiency (or retention efficiency) E is defined by Eq. (3), and gives the fraction of cells recovered in the underflow. 

Besides fouling, cell retention efficiency is another important factor regarding spin-filter performance. A poor retention capacity of a spin-filter leads to a low apparent growth rate of the cell culture due to cell leakage (Eq. 10). 

As a consequence, the perfusion bioreactor can only be operated up to a cell concentration supported by the perfusion rate In this way, spin-filter retention efficiency determines the maximum attainable cell concentration in a given perfusion process. 

Yabannavar et al. [81] used Eqs. (19) and (20) for scale-up purposes. Based on successful operation conditions determined for an existing 12-L bioreactor, they calculated the spin-filter dimensions and operation conditions for an existing 175-L bioreactor. Experiments with the spin-filter designed for the large-scale bioreactor resulted in an absence of filter clogging with cell retention efficiency similar to the 12-L bioreactor. This was considered as an evidence that the suggested scale-up strategy is adequate. 

Following preliminary hypochlorite treatments, a coherent process path was identified and implemented. Corn starch was oxidized with 6.4% (w/w) hypochlorite for two hours and given a combined base-heat gelatinization process (Method A). This base material exhibited excellent physical characteristics (i.e., stable emulsion with 20% db lemon oil incorporation into an aqueous dispersion, low lemon oil vapor phase flux (low headspace content), lack of inherent flavor and aroma) and when finally tested for spray dried lemon oil (20% db) retention efficiency in a lab-scale mini-dryer, the viability of this polymer was ascertained. Nearly 70% of the added lemon oil was retained following the drying of this DE 1.45 starch, a measure of functionality matched only by gum arabic (34). 

Other Interferent Studies with Nylon Filters. Retention of HONO on Gelman Nylasorb (nylon 6) filters was tested 0.3 to 1 xg/m3 HONO was sampled in air (—50% RH) at 20 L/min with 47-mm filters for 16-23 h. At saturation, the filters contained 1.8 xg/cm2 N02 this result indicates less than 50% efficiency for HONO retention (19). Sampling 440 xg/m3 HONO at 20 L/min with 47-mm Gelman Nylasorb filters (nylon type unstated), Sickles and Hodson reported about 25% retention efficiency, with a similar saturation value, and noted that such retention was reversible. Substantial oxidation of HONO to N03 on the filter surface by 03 was demonstrated in laboratory and atmospheric trials (21). Perrino et al. (20) observed with 47-mm Gelman Nylasorb (nylon type unstated) filters an efficiency for HONO that increased from about 25 to about 90% as the flow rate decreased from 12 to 2 L/min, with saturation at —50 xg/filter. Nitrite to nitrate conversion on the nylon filter surface increased from 13% at 45 ppb 03 to 93% at 200 ppb 03. 

The sorbents most frequently used for collection of vapor-phase PAH compounds include Tenax GC (74-76), PUF (70, 77), and XAD-2 (77, 78). Comparisons of retention efficiencies and breakthrough volumes indicate that Tenax GC and XAD-2 are more efficient than PUF for more volatile PAH compounds (e.g., anthracene). Lee et al. (73) noted XAD-2 resin to be preferable to Tenax GC because of its higher capacity, especially for lower boiling compounds. 

In the past, several terms have been coined to describe the retention efficiency of the filter system beta value, microbiological safety index, reduction ratio, and titer reduction ratio [64,68,72], The log reduction value (LRV) is a filter retention efficiency term that is the logarithm to the base of 10 of the ratio of the number of organisms in the challenge suspension to the number of organisms in the filtrate. 

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