Tests were carried out in order to show the effects of recarbonation on the evolution of the biodegradability of natural organic matter during ozonation. To achieve this objective, four series of tests were conducted on the effluents of one of the sand-anthracite filters at the Ste-Rose plant (City of Laval, Canada). Table 1 presents the chemical characteristics of these effluents. In performing these four series of tests, each sample was divided into four portions. The first portion was not modified: this was the filter effluent water with an alkalinity of 25 mg/l CaCO3. The alkalinity of the other three portions were adjusted to 100, 175 and 250 mg/l CaCO3, respectively, by adding increasing quantities of sodium bicarbonate. Then, each portion was ozonated at the same ozone dose using the apparatus shown in Fig. 1. After ozonation, the UV absorbance, the alkalinity and the ozone, oxalate and BDOC concentrations were measured. Standard methods as described in APHA et al. (1992) [APHA, AWWA and WEF (1992) Standard Methods for the Examination of Water and Wastewater. Washington, D.C.] were used for alkalinity and ozone measurements. BDOC measurements were based on a modified version of the Joret and Levi method [Joret, J. C. and Li vi, Y. (1986) Methode rapide d'evaluation du carbone eliminable des eaux par voie biologique. Trib. Cebedeau 39, 3-9; Joret, J. C., Levi, Y., Dupin, T. and Gilbert, M. (1988) Rapid method for estimating bioeliminable organic carbon in water. AWWA 1988 Annual Conference, pp. 1715-1725. Orlando, Florida.] and on the Servais Billen method [Servais, P., Anzil, A., Ventresque, C., (1989) Simple method for determination of biodegrable dissolved organic carbon in water. Appl. Environ. Microbiol. 55(10), 2732-2734.]. These tests were performed four times at one-month intervals using filter effluent from the same filter each time. An ozone dose of 0.2 mg O-3/mg DOC was used for the first series of tests. The ozone doses for the other series were 0.5, 0.8 and 1.0 mg O-3/mg DOC respectively. Table 2 indicates the average ozonation conditions. These tests gave the following principal results. in one series (fixed ozone dose and an alkalinity ranging between 25 and 250 mg/l CaCO3), the reduction in UV absorbance increased with alkalinity. For the first series of tests, this reduction measured 40% in water whose alkalinity was 25 mg/l CaCO3 and increased to 50% in water whose alkalinity was 250 mg/l CaCO3. In addition, it was observed that the reduction increased from series to series (Fig. 3). This is to be expected, since the ozone dose also increased from series to series. Thus, for the last series of tests, when the ozone dose was 1.0 mg O-3/mg DOG, the reduction in UV absorbance varied between 60 and 70%. Recarbonation also affects the production of oxalate and of biodegradable dissolved organic carbon (BDOC) as shown in Figs. 4 and 5. Thus, in one series of tests, oxalate production and BDOC production increased as a function of alkalinity. When the results obtained for a sample whose alkalinity was unajusted (25 mg/l CaCO3) are compared with those obtained for a water whose alkalinity was modified to 250 mg/l CaCO3, increases of 56 and 46% for the oxalate and the BDOC, respectively (third series of tests) were observed. It is expected that results for these two parameters would parallel one another since oxalate is easily biodegradable. Analysis of all the results has shown (Fig. 7) that there is a linear relationship between oxalate production and BDOC production. Specific UV absorbance (SUVA), which was defined by Edzwald and van Benschoten (1990) [Edzwald, J. K. and van Benschoten, J. E. (1990) Chemical Water and wastewater Treatment. Springer-Verlag, Berlin.] as UV absorbance/DOC is correlated with BDOC/DOC on figure 6. A similar relationship was observed by Gilbert (1987) and Gilbert (1988) [Gilbert, E. (1987) Biodegradability of ozonation products as a function of COD and DOC elimination by example of substituted aromatic substances. Wat. Res. 21, 1273-1278; Gilbert, E., (1988) Biodegradability of ozonation products as a function of COD and DOC elimination by the example of humic acids. Wat. RES. 22, 123-126.] while they were working with water containing more aromatic compounds and humic acids. (C) 1998 Elsevier Science Ltd. All rights reserved.
