Concentration of Natural Organic Matter

The concentration of NOM from Moonej Mooney Dam in the Brisbane Water National Park (NSW, Australia) using microfiltration (MF), reverse osmosis (ROJ and freev e drying is described. Characterisation of the product is shown in Chapter 4. 

The recovery of the RO process was 99.7 %, and a concentration factor of 250 was achieved. No chemical modifications of the samples were carried out and no precipitation occurred during operation of the RO. A total volume of 5000T of surface water was concentrated and dried to produce 230g of powder with a carbon content of approximately 12%. 

The performance of the two membrane processes in terms of rejection and flux was monitored throughout operation and the results are shown in this Appendix. This concentration experiment has lead to the further understanding of membrane performance and initiated some of the more fundamental studies carried out in the course of this PhD. 

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Le-Clech, P., E.-K. Lee, and V. Chen. 2006. Hybrid photocatalysis/membrane treatment for surface waters containing low concentrations of natural organic matters. Water Res. 40 323-330. 

Figure 7.2 Effect of the concentration of natural organic matter (mg C L ) from two water sources on pseudo-first-order rate constants for the reduction of 3-chloronitrobenzene in 5-mM hydrogen sulfide and at 25°C. Hyde County water, pH 7.50 elm extract, pH 7.00. [Reproduced with permission from F. M. Dunnivant, R. P. Schwarzenbach, and D. L. Macalady, Environ. Sci. Technol. 26, 2133 (1992). Copyright 1992, American Chemical Society.]...

A great diversity in the concentration of dissolved organic matter also occurs in natural water. Commonly, the concentration ranges from 0.5 to 50 mg/liter. Fresh water and seawater typically have values of 0.5-1.5 mg/liter (18). 

Let us now turn to some kinetic considerations of NAC reduction. As an example, consider the time courses of nitrobenzene (NB) concentration in 5 mM aqueous hydrogen sulfide (H2S) solution in the absence and presence of natural organic matter (Fig. 14.7). As is evident, although reduction of NB by H2S to nitrosobenzene and further to aniline (Eq. 14-31) is very favorable from a thermodynamic point of view (see Fig. 14.4), it seems to be an extremely slow process. However, when DOM is added to the solution, reduction occurs at an appreciable rate (Fig. 14.7). In order to understand these findings, some general kinetic aspects of redox reactions involving NACs should be recognized. 

Historically, attention on soil organic matter (SOM) has focused on the central role that it plays in ecosystem fertility and soil properties, but in the past two decades the role of soil organic carbon in moderating atmospheric C02 concentrations has emerged as a critical research area.This chapter will focus on the storage and turnover of natural organic matter in soil (SOM), in the context of the global carbon cycle. 

One practical use of Fenton and photo-Fenton processes is the removal of natural organic matter (NOM) from organic rich waters before the chlorine disinfection of drinking water. It was observed that, under optimal conditions, both processes achieved more than 90% TOC removal, leading to the potential formation of trihalomethanes at concentrations below 10 ig IT1, well under UK and US standards [78]. 

Sea water contains a much lower concentration of dissolved organic matter than river water. More than half of this dissolved organic load is of a humic nature. These dissolved organic acids tend to flocculate as the salinity increases (10). Hair and Bassett (11) have observed an increase in the particulate humic acid load of an estuary as one approaches the sea. Although no studies of the distribution of humic materials throughout an estuarine system have been performed, it would appear that estuaries and their sediments in particular, act as a major sink for the dissolved and particulate humic materials. Nissenbaum and Kaplan (12) have observed that terrestrial humic materials are not deposited at great distances from shore in the marine system. A study of the flux of particulate carbon through the Chesapeake Bay comes to a similar conclusion (13). 

Trichloroacetate rapidly reacts with the solvated electrons produced by laser flash photolysis of natural organic matter isolated from the Suwannee River, and thus quenches the absorption of the electrons at 720 nm. The ibsorption is also quenched by the addition of other good electron acceptors, including oxygen, protons, or nitrous oxide. In natural waters, halocarbon concentrations are typically very low, and the dominant scavenger of solvated electrons is oxygen. 

Cook, D. and Newcombe, G. (2002). Effect of natural organic matter concentration and character on the adsorption of microcystin analogues onto PAC. Proceedings of the American Water Works Association Water Quality Technology Conference, November 11-13, 2002, Seatde, USA. CD ROM. 

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