Ultrafiltration labor

Ultimately, the usefulness of tracer methods will partially depend upon how readily they can be incorporated into a field study. Methods that can be applied to filtered water samples are less labor intensive than those requiring some type of fractionation, such as the use of small-volume XAD-8 columns or ultrafiltration. However, column or ultrafiltration fractionation can be streamlined to make them practical for field studies, and the better resolution of DOM chemistry may make the extra effort worthwhile. If fulvic acid or high molecular weight fractions are isolated in a study, these can be saved for potential subsequent analysis of trace moieties as motivated by initial results. Finally, the overall question being addressed in a particular experimental or field study will determine which tracer methods, if any, are included. 

In recent years, developing technology has led to the use of ultrafiltration and microfiltration membranes for juice clarification (1,4-13). The use of membranes has several advantages. Lower labor costs may be possible due to automation possibilities of membrane filtration (8). Filter aids such as diatomaceous earth (DE) aren t needed (9) so that product that would have been discarded with DE is saved, and DE acquisition and disposal costs are eliminated. Enzymes may be rejected by ultrafiltration membranes (4,12) causing the ultrafiltration equipment to act as an enzyme reactor (12), although some odor-active volatiles may be retained, resulting in some loss or change in flavor (8). 

Because of the time and labor involved in algal assays, FRP (0.45 or 0.2 pm) has often been used as a surrogate for readily BAP, and TP (which includes the particulate, condensed, and organic phosphorus components) as a measure of potentially BAP. However, a number of studies have shown that neither FRP nor TP correlate well with algal assay-measured BAP. This may be because FRP tends to overestimate the true orthophosphate due to hydrolysis of labile organic and condensed species. Use of ultrafiltration through a low molecular mass filter prior to measurement of reactive phosphorus has been proposed as better estimator of BAP than other available chemical methods. 

The other bottleneck for lactic acid production is the operating cost. For example, sterilization is necessary for fermentative production. Hence, microorganisms have an optimal fermentation temperature between 30 2°C (John et al., 2007). Therefore it is difficult to avoid contamination if the medium is not sterilized. Qin et al. (2009) have reported the use of a newly isolated thermophilic strain. Bacillus sp. strain 2 to 6, for the unsterilized fermentative production of L-lactic acid. A high yield (97.3%), productivity (4.37g/L/h), and optical purity of L-lactic acid (99.4%) were obtained in batch and fed-batch open fermentations (Qin et al., 2009). This will help to reduce energy consumption and lower labor costs. Moreover, because of the inhibitory effects of a low pH on cell growth and lactic acid production, CaCOs must be added to maintain a constant pH as a consequence, the regeneration of precipitated calcium lactate is observed (Datta and Henry, 2006). To solve this problem, a sodium lactate-tolerant strain. Bacillus sp. Na-2, was obtained by ion-beam implantation and applied during an L-lactic acid production process (Qin et al., 2010). On the other hand, new processes can be applied to prevent the production of calcium lactate, for example, reverse osmosis, ultrafiltration, electrodialysis, and solvent extraction (Datta and Henry, 2006). 

Unlike RO, or EDI, ultrafiltration does not remove ions but removes colloids, macromolecules, or fine suspended matter. Ultrafilters reject solutes ranging in size from 0.003 to 10 p,m. UF resembles RO in that the energy requirement is supplied as pumping power. UF plants are usually well automated and require httle labor. 

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