Key words--BDOC. DOC. bioassay, drinking water, biodegradability. INTRODI ..... 100 150 200 250 300. Hours. Bovine albumin. ~----o°~ . \. - - ° - ° ~. O--- ~O~. ~.
War. ReJ. Vol. 26, No. 2, pp. 255-258, 1992 Printed in Great Britain. All rights reserved
0043-135492 $5.00 + 0.00 Copyright ~ 1992 Pergamon Press p k
TECHNICAL NOTE A METHOD FOR THE MEASUREMENT OF BIODEGRADABLE ORGANIC CARBON IN WATERS J. FRiAS,I F. RIBAS~and F. LUCENA2 ~Socidad General de Aguas de Barcelona, S.A.. Paseig Sant Joan 39. 08009 Barcelona and :Department of Microbiology, University of Barcelona, Avinguda Diagonal 645. 08028 Barcelona, Spain (First receired March 1991; accepted in revised form July 1991)
Abstract--ln the last few years several methods have been proposed for determining biodegradable dissolved organic carbon (BDOC) in waters. A modification of an original method for measuring BDOC is proposed. This method is suitable for discrete samples and for measuring the biodegradabilityof organic compounds dissolved in water. It consists of a dynamic procedure that measures the decrease in the dissolved organic carbon (DOC) in the sample of water. The sample is rccirculated through a glass column containing a biofilm attached to a novel support medium. The method has been used to study waters at different steps in a water-treatment process and to measure the biodegradability of different dissolved organic substances in water. Key words--BDOC. DOC. bioassay, drinking water, biodegradability
INTRODI IC'I'ION
Determination of biodegradable organic carbon in waters is of particular importance for the water industry. In the last few years different methods have been developed to measure the biodegradable dissolved organic carbon (BDOC) (Joret and Levy, 1986; Ribas et al., 1991; Servais et al., 1987, 1989), that is the fraction of the dissolved organic carbon (IX)C) which can be used by bacteria for their growth. Bacterial regrowth in distribution systems is a consequence of the presence of this biodegradable organic carbon in water (Bourbigot et al., 1984), so, the objective of the BDOC measurement of a water is to predict the potential to support the growth of bacteria. The concentration of biodegradable dissolved organic carbon cannot be assayed by simple chemical methods, because of its complexity and very low concentration. The use of a bioassay procedure is thus required. Several experimental methods have been proposed in order to measure this parameter by means of the assimilable organic carbon by the use of pure strains of standardized bacteria or mixed inocula of indigenous bacteria, where the measured parameter is biomass (as heterotrophic plate count, ATP levels, etc.) formed as a consequence of biodegradable carbon assimilation (Jago and Stanfield, 1985; Kemmy et al., 1989; Van der Kooij et al., 1982). In contrast to these methods, other methods where biodegradable organic carbon is measured by decrease of dissolved organic carbon in samples after a 255
defined period of time, have been proposed (Jorct and Levy. 1986; Ribas et al., 1991; Servais et al.. 1987, 1989). A method useful to the needs of the water treatment industry has been proposed by the authors (Ribas et al., 1991). It was a dynamic procedure that measured the BDOC of circulating water continuously pumped across a biofilm attached to a special support that fills a system of two glass columns. The BDOC value corresponded to the difference in DOC between inlet and outlet water samples. The process was continuous and the analytical results were not significantly different from other bioassays based on the use of indigenous bacteria. The total duration of an analysis was between 2 and 3 h. In this note a modification of the original method is proposed, in order to measure the BDOC in discrete samples in contrast to the continuous sampling proposed in the original method. On the other hand, the same method was also used to measure the biodegradability of different organic compounds dissolved in water. EXPERIMENTAL
The detailed experimental protocol was as follows. The apparatus used in the BDOC determination shown in Fig. I consists of a glass column of 28 mm inner diameter and 620ram between the inlet and outlet of water with glass stoppers on each end. The column was filled with 300 g of an inert support to which the biofilm responsible for D ( ~ removal is attached: S1RAN (Schott Ref. SIKUG 012/051300/A) a sintered porous glass in the form of balls of I-2 mm of diameter, 60-70/zm of pore diameter, 55-60% of pore volume, surface area of 0.15 m2/g and bulk density
Technical Note
256
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F\ Fig. 1. Experimental set-up of the SIRAN column for BDOC determination. Abbreviations: A. inert support (SIRAN); B, porous glass plate; C, peristaltic pump; D. sample of water. of 570 g/I. Across the column, the descent of the support is limited by the presence of a porous glass plate near its base. For the colonization of the support, a continuous circulation, with closed circuit using a water mixture was established. The working flow was 3.5 ml/min. This mixture consists of I/3 river water filtered by 1.2 #m pore diameter membrane filters (Millipore Rawp 04700) to eliminate protozoa which could otherwise develop in the column, and 2/3 of granular active carbon (GAC) filtered water, in order to guarantee the bacterial diversity. In the cases where different products were used as a source of
carbon, the substance at the same concentration used during the experiment was added to the colonization mixture. The water mixture was changed daily in all cases. The period of colonization was 5 days. After this period of colonization, the biofilm was adapted to the sample of water by continuous circulation with a closed circuit of different successive samples of the same kind of water to be tested that had been changed daily. The adaptation period was between 5 and 8 days depending on the kind of water. Once this period had passed, the column was ready to perform BDOC determinations. For the biodegradable organic carbon determination, the water was continuously pumped across the column with a peristaltic pump connected with the samples and the column by silicone rubber tubing, with closed circuit (Fig. I). The inlet of the column is situated at its lower end, and the outlet at the upper end. The sample is pumped with a working flow of 3.5 ml/min. All the experiments were performed at a temperature of 21 + 2"C. For the determination of BDOC, the evolution of DOC during a period of 5 days was followed, except when different products were used as a source of carbon. In this case the period was more large, until a constant DOC level was reached. The samples for DOC analyses were taken daily, and the biodegradable dissolved organic carbon (BDOC) was calculated as the difference between the initial DOC and the minimum value obtained in the period of analysis. For DOC determination the samples were filtered through 0.22~m pore-size membranes (Millipore GVPWP 02500) carefully rinsed first with 150 ml of distilled water. DOC measurements were performed with a Model 700 TOC Analyzer O.I. Corporation, College Station, Tex. Every sample was determined in duplicate considering the mean value of the two measures. Six kinds of water samples from different steps in the treatment process were used in the experiments performed at different times: Llobregat river water (Barcelona, Spain), water prechlorinated and with flocculants added, water at the outlet of clarificrs, water filtered by granulated active carbon, finished plant treatment water and tap water, In the chlorinated water, thiosulphate was added in order to guarantee the total neutralization of chlorine. On the other hand, a standard mineral solution (Geller. 1983) supplied with different substances as a source of carbon with different biodegradability, was tested at high and low concentration. The tested substances were: glucose, glutamic acid, citric acid, ammonium benzoate, urea. bovine albumin, n-dodecylsulphate sodium salt and a surfactant (Marlon-TP) derivated from the sodium n-dodecylsulphate. In all cases a volume of 3 I. was collected in an Erlenmeyer flask (Pyrex glass) heated to 550°C for 3 h. One liter was used to rinse the column before the measurement of biodegradable organic matter in the water samples; and 2 I. for the BDOC determination. RESULTS AND DISCUSSION The biodegradable dissolved organic carbon ( B D O C ) is the p o r t i o n o f dissolved organic carbon ( D O C ) that can be used as a source o f g r o w t h by
Table I. BDOC determination in waters of different steps in the water-treatment process Tap water Finished water Filtered water Outlet decanters Prechloriw,ted water River water
n
Initial DOC
8 12 12 12 12 12
3.13±1.39 3.38 ± 0.89 5.62 ± 1.55 8.58 ± 0.89 7.22 ± 1.00 5.45 ± 1.06
BDOC 1.24-1-0.33 1.59 ± 0.73 1.70 ± 1.04 1.44 ± 1.06 1.62 ± 0.92 2.00 ± 0.96
%BDOC/initial DOC 25.14±9.21 28.94 ± 1I..54 29.25 ± 12.42 15.70 ± 10.87 22.06 ± 11.84 36.07 ± 14.35
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Fig. 2. Evolution o f D O C decrease with the different substances assayed.
heterotrophic microorganisms. The modification of an original method for the measurement of B D O C proposed by the authors has been used in the study
of the different steps o f a water-treatment process. Table I shows the results obtained. The results are expressed as the mean of the series of experiments.
258
Technical Note
The ratio %BIX)C/initial DOC is similar in tap water and finished treatment water, and higher in fiver water. These percentages are similar to those found using other methods in BDOC determination that show a higher BDOC in river waters than in the other kinds of waters. The lowest percentage was observed at the outlet of clarifiers, the rest of the percentages being similar in the other types of water. In order to measure the percentage of the biodegradable fraction from different organic substances a standard mineral solution (Geller, 1983) supplied with different substances at different concentrations was used as a model to determine their biodegradability using the proposed method in BDOC determination. The period of BDOC determination depends on the nature of the product assayed, ranging from hours to days, until DOC determination becomes stable. Figure 2 shows the results obtained for all the substances assayed. In all cases the period until minimum DOC was reached is a short period of time (a few days in the substance with less biodegradability). The greatest level of biodegradability was obtained for the simplest molecules, both at low concentration and at high concentration.
CONCLUSIONS
It has been shown that the mcthod proposcd in this note for the measurement of BDOC, offers the possibility of working with a discrete volume of sample as a modification of the original method proposed as a control method in water treatment. The results obtained arc similar to those obtained using other
methods proposed for the measurement of BEK~. However, the time of analysis is shorter in the procedure proposed here. Moreover, it can be used in the measurement of potential biodegradability of different substances dissolved in waters. REFERENCES
Bourbigot M. M., Dodin A. and Lherithier R. (19M) La flare bact6rienne darts un r~seau de distribution. ;Vat. Res. 18, 585-591. Geller A. (1983) Growth of bacteria in inorganic medium at different levels of airborne organic substances. Appl. envir. Microbial. 46, 1258-1262. Jago P. H. and Stanfield G. (1985) Development and application of a method for determining the assimilable organic carbon content of drinking water. Water Research Centre, Medmenhan, Bucks., England. Internal Report 1038-H. Joret J. C. and Levy Y. (1986) M6thode rapide d'evaluation du carbone eliminable des eaux par vole biologique. Trib. Ceb. 39, 3-9. Kemmy F. A., Fry J. C. and Breach R. A. (1989) Development and operational implementation of a modified and simplified method for determination of assimilable organic carbon (AOC) in drinking water. War. Sci. Technol. 21, 155-159. Ribas F., Frias J. and Lucena F. (1991) A new dynamic method for the rapid determination of the biodegradable dissolved organic carbon (BDOC) in drinking water. J. appl. Bact. 71, 378-387. Servais P., Anzil A. and Ventresque C. (1989) Simple method for determination of biodegradable dissolved organic carbon in water. Appl. era,it. Microbial. 55, 2732-2734. Servais P., Billen G. and Hascoet M. C. (1987) Determination of the biodegradable fraction of dissolved organic matter in waters. War. Res. 21,445-450. Van der Kooij D., Visser A. and Hijnen W. A. H. (I 982) Determining the concentration of easily assimilable organic carbon in drinking water. J. Am. War. Wks Ass. 74, 540-545.
