PACS system

The addition of powdered-activated carbon (PAC) to the activated sludge process has received considerable attention, particularly with respect to the removal of specific organics. The applicability of activated carbon in removing specific substrates depends on the molecular weight, solubility, polarity, location of functional groups, and overall molecular configuration. Investigations of PAC systems have centered around process enhancement factors. These include ... 

Properties of Activated Carbon Adsorption Isotherm Models Design Consideration of PAC Systems Regeneration... 

Applications and Performance of Physicochemical PAC Systems for Potable Water Treatment... 

About a pound of dry slndge will be generated per pound of carbon added. If regeneration is practiced, carbon slndge is reactivated and reused with only a small portion removed to prevent buildup of inert. PAC physicochemical process systems are reasonably reliable from both a unit and process standpoint. In fact, PAC systems can be used to improve the process reliability of existing systems. Readers are referred to recent reports for additional information (29,30). 

Li, Q., Marinas, B.J., Snoeyink, V.L., and Campos, C. (2003). Three component competitive adsorption model for flow through PAC systems 1 Model development and verification with a PAC/membrane system. Environ. Sci. TechnoL, 37, 2997-3004. 

In 2011, Magrabi analysed 46 adverse events which had been submitted to the US Food and Drug Agency (FDA) [58] and classified them by problem type (Table 1.2). Ninety three percent involved CPOE or PACS systems. 

Chan and Kammer, (2008) and Sim et al., (2011) studied on the immiscible PEO/ENR/LiClO and PEO/PAc/LiClO systems reported that the two Ts of the immiscible blends estimated under constant salt content were observed to be higher than their respective values in the pristine salt-free systems. Figure 24 depicts the variations of T as a function of weight fraction of PEO (IFp ) for the salt-free and salt-added PEO/ENR and PEO/PAc systems. The salt content in the PEO/ENR/LiClO and PEO/PAc/LiClO blends are 12 and 15 wt%, respectively. A close examination of the plots in Figure 24 concludes that the difference in the T value of PEO between the salt-free and salt-added PEO/ENR blends (Ar/ °) is... 

After data acquisition, images are transferred to the hospital s PACS system as well as to a DICOM server, which is not part of the PACS system. Images are stored temporarily on the machine s hard disk. At regular intervals a script checks if there are new data and, if so, the DICOM header information will be sent to a database, the images will be converted to the more common Analyze image format, made anonymous and finally transferred to the medical... 

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

Another interesting, but rather complex system, which couples flow injection analysis, EC and GC has been recently reported (47). This system allows the determination of the total amount of potentially carcinogenic polycyclic aromatic compounds (PACs) in bitumen and bitumen fumes. This system could also be used for the analysis of specific PACs in other residual products. 

As the science of organic chemistry slowly grew in the 19th century, so too did the number of known compounds and the need for a systematic method of naming them. The system of nomenclature we ll use in this book is that devised by the International Union of Pure and Applied Chemistry (IUPAC, usually spoken as eye-you-pac). 

The most limiting factor for enzymatic PAC production is the inactivation of PDC by the toxic substrate benzaldehyde. The rate of PDC deactivation follows a first order dependency on benzaldehyde concentration and reaction time [8]. Various strategies have been developed to minimize PDC exposure to benzaldehyde including fed-batch operation, immobilization of PDC for continuous operation and more recently an enzymatic aqueous/octanol two-phase process [5,9,10] in which benzaldehyde is continuously fed from the octanol to the enzyme in the aqueous phase. The present study aims at optimal feeding of benzaldehyde in an aqueous batch system. 

A model developed by Leksawasdi et al. [11,12] for the enzymatic production of PAC (P) from benzaldehyde (B) and pyruvate (A) in an aqueous phase system is based on equations given in Figure 2. The model also includes the production of by-products acetaldehyde (Q) and acetoin (R). The rate of deactivation of PDC (E) was shown to exhibit a first order dependency on benzaldehyde concentration and exposure time as well as an initial time lag [8]. Following detailed kinetic studies, the model including the equation for enzyme deactivation was shown to provide acceptable fitting of the kinetic data for the ranges 50-150 mM benzaldehyde, 60-180 mM pyruvate and 1.1-3.4 U mf PDC carboligase activity [10]. 

It is relevant also to compare the results in Fig.5 with previously published data for PAC production under similar environmental conditions, where with higher concentrations of initial benzaldehyde (600 mM), pyruvate (400 mM) and PDC activity (8.4 U ml ) a similar maximum concentration of PAC of 330 mM was produced [6]. PDC stability was similar in both processes with half life values of approximately 27h. However, PAC production was much faster in the benzaldehyde emulsion system, presumably due to higher initial enzyme concentration. 

The conclusion ifom this comparison is that the optimal feeding program with its lower benzaldehyde concentrations did not result in any increase in PDC stability or final PAC concentration. This suggests that a component(s) other than benzaldehyde (with its limited solubility of 90-100 mM in this system containing 2.5 M MOPS buffer) is more critical in achieving increased PAC concentrations and productivities. 

It is possible that product inhibition by PAC or by-product inhibition by acetoin or acetaldehyde may play a more important role than benzaldehyde in influencing PAC production in this aqueous phase system. 

The Dionex system uses a Garbo Pac PA-1 anion exchange column and a CarboPac PA-1 Guard. The column was loaded with 25 pi of the RG solution and eluted with a linear gradient of 0 - 0.5 M NaOAc in 0.1 N NaOH during 50 minutes. The flow rate was 1.0 ml/min and the process was monitored using a PE detector. 

Monkiedje et al. [10] investigated the fate of niclosamide in aquatic system both under laboratory and field conditions. The octanol/watcr partition coefficient (Kaw) of niclosamide was 5.880 x 10 4. Adsorption isotherm studies indicated that the Freundlich parameters (K, n) for niclosamide were 0.02 and 4.93, respectively, for powder activated carbon (PAC), and 9.85 x 10 5 and 2.81, respectively, for silt loam soil. The adsorption coefficient (Aoc) for the drug was 0.02 for PAC, and 4.34 x 10-3 for the same soil. Hydrolysis of niclosamide occurred in distilled water buffer at pH above 7. No photolysis of the drug was observed in water after exposure to long-wave UV light for 4 h. Similarly, neither chemically volatilized from water following 5 h of sample aeration. Under field conditions, niclosamide persisted in ponds for over 14 days. The half-life of niclosamide was 3.40 days. 

Consequently, if the reaction enthalpy is unknown for a given process, the quantum yield must be determined from other measurements. Conversely, if the reaction enthalpy is known, then the quantum yield for the photochemical reaction can be measured. PAC has been used to obtain quantum yields for excited state processes, such as fluorescence, triplet state formation, and ion pair formation and separation. In systems in which competitive reactions occur, care must be taken to accurately account for the partitioning. For example, if a reactive intermediate yields two products, then the measured heat of reaction is the sum of the two individual heats of reaction multiplied by their respective yields. Consequently, there are three unknowns, the partitioning and the individual heats of reaction. Two of them must be known to properly evaluate the third. 

The accuracy of the thermochemical data obtained by this technique has been examined in numerous systems. In general, the data compares well, 1 kcal/mol, with that obtained by other spectroscopic and calorimetric methods. The accuracy and reproducibility of the data is dependent on the magnitude and time scale of the heat deposition detected by PAC that is associated with a given chemical process. Highly exothermic reactions are easy to detect, whereas ones that are not are difficult to detect. A thermoneutral reaction is invisible to PAC. Reactions that occur significantly slower than the response time of the transducer are not detected. Reactions that occur either slightly slower or faster than the response time are difficult to resolve accurately. Clearly, the proper choice of the transducer is extremely important in order to resolve accurately a given chemical event. 

---