Empty bed contact time

EBCT Empty bed contact time SO Strength of the untreated waste... 

The USEPA surveys identified four resin adsorption systems in the pesticide industry [7]. Phenol, pesticide, and diene compounds are all effectively removed by these systems. At least one system realized a significant product recovery via regeneration and distillation. The design surface loading rates vary from 1.0 to 4.0 gpm/ft with empty bed contact times of 7.5 to 30 minutes. 

The chloramine removal efficiency of catalytic carbon is reported to be an order of magnitude greater than that of conventional activated carbons used for dechlorination. Various factors such as empty bed contact time (EBCT), influent chloramine concentration, particle size, and temperature influence treatment efficiency using catalytic carbon (11,12). In a study using water containing 2 mg/L influent chloramine concentration, an increase in EBCT from 10 to 30 s increased the volume of water treated to below 0.1 mg/L chloramine from 250 bed volumes to 11,000 bed volumes. In a different study, reducing the mesh size from 20 x 50 to 30 x 70 increased the bed volumes treated from 11,000 to 28,000 at a 30 s EBCT and 2 mg/L influent chloramine... 

Figure 26.5 shows the RSSCT predictions of atrazine removal compared with the full-scale removal at a water treatment plant in France, at two empty bed contact times [45]. The RSSCT overestimated the removal to a significant extent for the 7 min contact time, also for the 14 min contact time for large-scale... 

Figures 26.9(a) and (b) show how laboratory techniques can assist in the apphcation of GAC for the removal of geosmin and MIB. Figure 26.9(a) shows the results of a mini-column test on GAC removed at various intervals from a GAC pilot plant [17]. The percent removal of MIB was measured in the laboratory by running a mini-column test at the same empty bed contact time as that used in the pilot. Further details can be found in [68]. The results indicate that GAC filters could be tested at regular intervals for the removal of MIB using a simple laboratory trial. Figure 26.9(b) compares the experimental data points obtained during a SBA test with the HSDM fit and predictions [68]. The carbon had been preloaded for 2 years in a pilot plant. The predictions and the...

One criteria for the performance of an adsorbent in a column is the so called adsorbent usage rate . It denotes the amovmt of adsorbent added per volume of water treated. The lower the adsorbent usage rate the more efficient the process. The parameter capacity describes the amount of substance adsorbed per amount of adsorbent added. Both values are subject to many variables such as kinetic conditions in the column, EBCT (empty bed contact time), water composition, etc. 

The empty bed contact time (EBCT) is calculated as follows ... 

Behavior of the strongly basic, macroporous ion-exchange resin Amberlite IRA 958-Cl [11] will be circumstantially explained in the book chapter. Effects of different specific flow rate (SFR) and determination of its optimum value as well as the effects of the empty-bed contact time (EBCT) values on the removal of NOM, arsenic, sulfate, electrical conductivity, bicarbonate, and chlorine from groundwater using strongly basic ion-exchange resin (SBIX) will be examined in this chapter. Determination of the resin s sorption characterishcs is also part of the investigation. A new approach of pseudo equilibrium adsorphon capacity will be presented. 

For a given system, in which the hquid flow rate, impurity concentrations, and sorbent characteristics are fixed, the capital and operating costs are almost entirely dependent on the following two primary variables sorbent exhaustion rate, which is usually expressed as kilograms of adsorbent used per volume of liquid treated, and superficial liquid retention time, empty bed contact time, EBCT, sometimes referred to as empty bed residence time, which is the time that the hquid would take to fill the volume of the sorbent beds sand and is a direct function of hquid flow rate and adsorbent volume. 

Chloramines can be removed from solution using carbon filtration, as noted in Chapter 8.1.4. However, the contact time for removal is can be up to 4 times that of free chlorine. Chloramines can also be removed using sodium thiosulfate or bisulfite, and the reaction is fairly instantaneous. Note that with the carbon filtration removal method, some ammonia is created, which is toxic and should be considered when using an RO with chloramines for food processing and pharmaceutical applications (see Equation 8.3). However, as free chlorine is removed using sodium bisulfite, the chlorine-chloramine equilibrium can shift back to creating more free chlorine. In this case, complete removal of free chlorine cannot be assured. Carbon filters maybe the best method to remove chloramines, but can take anywhere from 5-10 minutes for fresh carbon up to 30 minutes for spent carbon of empty bed contact time for complete reaction with the carbon depending on the age and condition of the carbon. Ultraviolet radiation can also be used to destroy chloramines (see Chapter 8.1.8). 

Due to the fact that free chlorine is in equilibrium with monochloramine, water treated by chloramination should be treated for removal prior to RO membranes. Although most membrane manufacturers allow for a chloramine exposure of about 300,000 ppm-hrs, this exposure is calculated based on PURE chloramine. There are several methods to remove chloramine (e.g., sodium thiosulfate, UV, ascorbic acid) the most common methods are carbon filtration and sodium bisulfite. Empty bed contact time (EBCT) for fresh carbon can be as short as 10 minutes, while used carbon can require up to 30 minutes of EBCT for removal. The reaction for sodium bisulfite is as follows and has rapid kinetics. ... 

The empty bed contact time (EBCT) method is primarily used by the water industry for the design of large-scale adsorbers from pilot-scale data. There is no reason why the method should not be applied, however, to other industrial situations, in particular to liquid phase separations. 

As for the empty bed contact time method, the BDST method is also used extensively by the water industry and can be applied to other industrial situations. The assumption is that the adsorption rate is proportional to both the residual adsorbent capacity and the remaining adsorbate concentration. The relationship between the service time, /, the linear velocity, u, the depth of adsorbent bed, L, the rate constant, k, the adsorptive capacity. No (mass per unit volume), the influent concentration, co, and the concentration at breakthrough, Cb is given by the following equation in which dimensionally consistent units must be used ... 

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