INFLUENCE OF REMINERALIZATION ON THE EVOL UTION OF THE BIODEGRADABILITY OF NATURAL ORGANIC-MATTER DURING OZONATION

Tests were carried out in order to show the effects of recarbonation o n the evolution of the biodegradability of natural organic matter duri ng ozonation. To achieve this objective, four series of tests were con ducted on the effluents of one of the sand-anthracite filters at the S te-Rose plant (City of Laval, Canada). Table 1 presents the chemical c haracteristics of these effluents. In performing these four series of tests, each sample was divided into four portions. The first portion w as not modified: this was the filter effluent water with an alkalinity of 25 mg/l CaCO3. The alkalinity of the other three portions were adj usted to 100, 175 and 250 mg/l CaCO3, respectively, by adding increasi ng quantities of sodium bicarbonate. Then, each portion was ozonated a t the same ozone dose using the apparatus shown in Fig. 1. After ozona tion, the UV absorbance, the alkalinity and the ozone, oxalate and BDO C concentrations were measured. Standard methods as described in APHA et al. (1992) [APHA, AWWA and WEF (1992) Standard Methods for the Exam ination of Water and Wastewater. Washington, D.C.] were used for alkal inity and ozone measurements. BDOC measurements were based on a modifi ed version of the Joret and Levi method [Joret, J. C. and Li vi, Y. (1 986) Methode rapide d'evaluation du carbone eliminable des eaux par vo ie biologique. Trib. Cebedeau 39, 3-9; Joret, J. C., Levi, Y., Dupin, T. and Gilbert, M. (1988) Rapid method for estimating bioeliminable or ganic carbon in water. AWWA 1988 Annual Conference, pp. 1715-1725. Orl ando, Florida.] and on the Servais Billen method [Servais, P., Anzil, A., Ventresque, C., (1989) Simple method for determination of biodegra ble dissolved organic carbon in water. Appl. Environ. Microbiol. 55(10 ), 2732-2734.]. These tests were performed four times at one-month int ervals 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 r espectively. Table 2 indicates the average ozonation conditions. These tests gave the following principal results. in one series (fixed ozon e dose and an alkalinity ranging between 25 and 250 mg/l CaCO3), the r eduction in UV absorbance increased with alkalinity. For the first ser ies of tests, this reduction measured 40% in water whose alkalinity wa s 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 ozo ne dose also increased from series to series. Thus, for the last serie s of tests, when the ozone dose was 1.0 mg O-3/mg DOG, the reduction i n UV absorbance varied between 60 and 70%. Recarbonation also affects the production of oxalate and of biodegradable dissolved organic carbo n (BDOC) as shown in Figs. 4 and 5. Thus, in one series of tests, oxal ate production and BDOC production increased as a function of alkalini ty. When the results obtained for a sample whose alkalinity was unajus ted (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% fo r the oxalate and the BDOC, respectively (third series of tests) were observed. It is expected that results for these two parameters would p arallel one another since oxalate is easily biodegradable. Analysis of all the results has shown (Fig. 7) that there is a linear relationshi p between oxalate production and BDOC production. Specific UV absorban ce (SUVA), which was defined by Edzwald and van Benschoten (1990) [Edz wald, J. K. and van Benschoten, J. E. (1990) Chemical Water and wastew ater Treatment. Springer-Verlag, Berlin.] as UV absorbance/DOC is corr elated with BDOC/DOC on figure 6. A similar relationship was observed by Gilbert (1987) and Gilbert (1988) [Gilbert, E. (1987) Biodegradabil ity of ozonation products as a function of COD and DOC elimination by example of substituted aromatic substances. Wat. Res. 21, 1273-1278; G ilbert, E., (1988) Biodegradability of ozonation products as a functio n of COD and DOC elimination by the example of humic acids. Wat. RES. 22, 123-126.] while they were working with water containing more aroma tic compounds and humic acids. (C) 1998 Elsevier Science Ltd. All righ ts reserved.