measurement of wastewater treatment efficiency by fluorescence and uv absorbance

M E A S U R E M E N T OF W A S T E W A T E R T R E A T M E N T E F F I C I E N C Y

BY F L U O R E S C E N C E AND UV ABSORBANCE

A B D U L B A R I * and S H A U K A T F A R O O Q * *

University of Petroleum and Minerals Dhahran, Saudi Arabia

(Received 10 April, 1984)

Abstract. The degree of chemical treatment in terms of removal of organic matter from different wastewaters has been investigated by employing potassium ferrate (K2FeO4) and ozone in various combinations. The study was performed in both the batch and the continuous flow systems. The treatment efficiency was determined through three different methods, i.e., chemical oxygen demand (COD), fluorescence and ultraviolet (UV) absorption. Fluorescence and UV absorption techniques were employed due to their specificity in measurement of humic substances, aromatic compounds and heterocyclic systems, whereas COD is a general parameter for the estimation of total organic matter. Fluorescence and UV absorbance values were correlated with respective COD values.

1. Introduction

There has been much concern regarding the presence of organic substances in drinking waters and treated wastewater effluents for reuse. Several treatment schemes have been proposed for their removal. Ozone and iron (VI) (ferrate) have been reported to be effective oxidants of organic matter without the formation of toxic compounds (Rosen, 1973; Waite, 1979). Further, ozone improves water quality by removing colour and turbidity and by increasing the effluent dissolved oxygen (Rosen, 1973; Waite, 1979), whereas ferrate has the capacity to act as a coagulant and nutrient scavenger along with the removal of heavy metals (Murmann and Robinson, 1974). A study was undertaken to investigate the effectiveness of ferrate and ozone in various combinations to remove and oxidize the organic matter from different wastewaters.

The levels of organic matter are usually determined by the standard methods such as chemical oxygen demand (COD), biochemical oxygen demand (BOD), total organic carbon (TOC), etc. These methods are time consuming and/or require expensive instruments. In recent years a number of authors have discussed the correlation between UV absorbance and TOC and dissolved organic matter (DOM), COD and BOD (Mrkva, 1975; Dobbs etaL, 1972; Michail and Idelovitch, 1981). Smart etal. (1976) have studied the correlation between fluorescence and TOC, while Brun and Milburn (1977) have described an automated fluorometric method for the determination ofhumic substances in natural waters. This study has incorporated the use of fluorescence and UV absorbance techniques to measure the wastewater treatment efficiency due to their specificity in the measurement of aromatic compounds, polyaromatic system and their derivatives, heterocyclic systems (Willard et aL, 1974) and humic substances. Chemical

* Department of Chemistry. ** Department of Civil Engineering.

Environmental Monitoring and Assessment 5 (1985) 423-434. 0049-6979/85.15. �9 1985 by D. Reidel Publishing Company.

424 ABDUL BARI AND SHAUKAT FAROOQ

oxygen demand (COD), a general parameter for the estimation of total organic matter, was also measured for comparison purposes.

2. Experimental Methods

Fresh secondary wastewater effluent and raw sewage were brought from the South Aramco activated sludge sewage treatment plant, Dhahran. Preliminary studies were performed in the batch system to determine the optimum dose of ferrate for the removal of organic matter in terms of fluorescence and UV absorbance and COD values. Parallel studies with ferric chloride were also conducted to establish the superiority of ferrate in terms of its use.

The fluorescence was determined at an excitation wavelength of 365 nm and an emission wavelength in the range of 400-600 nm using Turner Fluorometer model 111. The UV spectra were scanned between 240-350 nm using Beckman Spectrophotometer Acta MVII. The absorbance value at 254 nm was used to measure the wastewater treatment efficiency and for correlation with respective COD values. COD measurements were performed according to Standard Methods (1980).

Continuous flow studies were performed on the bench-scale pilot treatment system, details of which are described elsewhere (Farooq et aL, 1982). The filtrate obtained after chemical treatment and filtration was ozonated separately at 50, 60, and 70 V in the ozone contactor. The concentration of ozone in aqueous and gaseous phases were determined using Standard Methods (1980).

The continuous flow treatment studies were performed on three types ofwastewaters, i.e. secondary wastewater effluent, settled raw sewage and lime treated raw sewage. Secondary effluent was brought in the morning prior to the start of the experiment while raw sewage was brought in the evening and allowed to settle overnight (10-12 hr) prior to treatment studies. In case of lime treated sewage the waste was treated with 350 mg 1-1 calcium hydroxide and was allowed to settle 10-12 hr. Lime treatment involved 1 min of rapid mixing followed by one hour of slow mixing.

3. Results and Discussion

Batch studies were performed in standard Phipps-Bird Jar test apparatus. This involved 1 min of rapid mixing followed by slow mixing for 30 min after addition of chemical in the wastewater sample. The chemically treated effluent was allowed to settle for 90 min prior to decanting supernatant for various analysis. The results for secondary wastewater treatment with ferrate and ferric chloride are given in Figure 1. It can be seen from the figure that concentrations of COD decrease with increase in ferrate and ferric chloride doses. Similar trend has been observed with UV and fluorescence measurements for both the chemicals. However, reduction in fluorescence is much higher in ferrate treated effluent as compared to ferric chloride treatment. This indicates change in structure of some organic compounds due to ferrate oxidation, resulting in the decrease of fluorescence value, although removal of organic compound appears to be

M E A S U R E M E N T O F W A S T E W A T E R T R E A T M E N T E F F I C I E N C Y 425

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same for both the chemicals as indicated by COD observations. UV absorbances show little difference in reaction mechanism of two chemicals due to similar values.

A second set of experiments was repeated with a mixture of 75 ~o secondary effluent and 25 ~o raw sewage in order to observe the effects of increased turbidity and organic matter in terms of treatment efficiency for both ferrate and ferric chloride. Similar trends were observed, Figure 2, when compared to the previous observations, except that initial COD values were much higher (210 mg 1- ~ versus 39.4 mg 1 - 1). COD removal was better for ferrate when compared to ferric chloride at lower doses. This trend was reversed at higher chemical doses.

The data from the last two experiments were also used to determine any relation between fluorescence and UV absorbance against their respective COD values. All three characteristics indicate concentration of organic matter in the sample. UV and


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fluorescence techniques measure UV light absorbing and fluorescence exhibiting organic compounds whereas COD measures the total chemical oxygen demand of the organic compounds through chemical (dichromate) oxidation. Fluorescence and UV absorbance measurements were used because they have been reported to measure specific groups of organic compounds such as aromatic, polyaromatic and heterocyclic (Michail and Idelovitch, 1981; Willard et al. , 1974) as compared to general oxidation of organic compounds by COD test. The results of UV and fluorescence values are plotted against COD values in Figures 3 and 4 respectively, where the lines of best fit, as determined by the linear regression analysis (y = a x + b), are shown. Four experimental observations were employed in calculating the correlation coefficient, r, for each line, as shown in the Figure 3 and 4. The correlation coefficient was found within the range of 0.72 to 0.99 for fluorescence-COD and 0.68 to 0.92 for UV-COD. This indicates with less than 90 ~ to 99 ~ certainty that the decrease in COD is proportional to the decrease

MEASUREMENT OF WASTEWATER TREATMENT EFFICIENCY 427

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in fluorescence and UV absorbance. In Figure 3 the results obtained from ferrate treatment on secondary effluent and mixture of secondary effluent and raw sewage are plotted. It can be seen that for a given type of wastewater sample the fluorescence value decreases with corresponding decrease in COD. Similar trends were observed for UV and C O D values. Results from ferric chloride treatment were plotted in Figure 4. It was observed that the UV and fluorescence values decrease with corresponding decrease in COD. In case of ferrate treatment for sewage and effluent mixture, fluorescence intensity decreases from 32 to 30 units for corresponding decrease in C O D from 200 to 194 m g l - 1 (Figure 3). Whereas in ferric chloride treatment for same decrease in fluorescence intensity (32 to 30)the C O D decreases from 190 to 142 mg 1- 1. This shows a sharp decrease in fluorescence in the case of ferrate treatment as compared to ferric chloride. The same was true for secondary effluent. Similar trends were observed for UV and C O D data. Based on these observations it can be concluded that ferrate is more effective in removal and oxidation of most of fluorescence exhibiting- and UV fight absorbing-organic compounds.

In order to confirm the above correlation between U V - C O D and fluorescence-COD, a set o f batch experiments were performed for ferrate treatment using samples of varying


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COD values (secondary effluent, raw sewage, and their mixtures). Twenty three experimental observations were used to find the lines of best fit using linear regression analysis as shown in Figure 5 and 6. The values of correlation coefficient were 0.87 for fluorescence-COD and 0.95 for UV-COD. This indicates with over 9 9 . 9 ~ certainty that the correlation exists between fluorescence-COD and UV-COD.

Results of continuous flow study at various stages of treatment of secondary effluent are given in Figure 7. The effluent was treated with 15 mg 1-1 of ferrate and ferric chloride separately prior to ozonation at various voltages. The fluorescence at various stages of treatment with ferrate and ferric chloride are given in Figure 7a and their respective COD values for both chemicals are given in Figure 7b. The trends in decrease of fluorescence and COD values in the continuous flow system were similar to the observations of the batch system, hence confirming the earlier interpretations obtained from Figure 1 and 2. Further increased ozonation results in corresponding decrease in COD and fluorescence values. It should be noted from Figure 7a that reduction in fluorescence after ozonation was more pronounced in ferric chloride treated sample as compared to the one treated with ferrate. This is because ferrate application has already oxidized part of the fluorescence exhibiting organic matter whereas ferric chloride was


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Figure 8a and 8b give the treatment efficiency at various stages of continuous flow system in terms of decrease in fluorescence and COD values of raw settled sewage and lime treated raw sewage respectively. Results were similar to the secondary effluent study (Figure 7a and 7b) except that initial COD and fluorescence values were much higher. In this study lime treated raw sewage was also directly ozonized after by-passing the routine treatment of ferrate and filtration at 60 and 70 V respectively. The results are given in Figure 8b. It can be seen that direct ozonation was quite effective after lime treatment but lacks the efficiency due to addition of ferrate and the filtration process. In general there was sharp reduction in fluorescence values after ozonation in all three cases of treatment schemes, indicating the removal and oxidation of fluorescence exhibiting compounds.

The relationships between fluorescence and their respective COD values at different treatment stages of secondary effluent and settled raw sewage from continuous flow

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systems are plotted in Figure 9. It was observed that for each wastewater, the value of C O D decreases as the fluorescence decreases, hence confirming the relationship between C O D and fluorescence as found in the batch studies. However, the change in absorbance per unit change in C O D was different for different treatments. These stages are clearly visible in case of raw sewage due to large quantity of organic matter as compared to secondary treated effluent. Further, there was large change in fluorescence of secondary effluent for small reduction in C O D values.

UV scans were also performed on the samples obtained from different treatment stages of lime treated sewage. All the samples were scanned from 240 nm to 350 nm to compare the changes in UV absorbances. The UV scanned curves are plotted in Figure 10. Curves 1 and 6 represent different treatment stages, i.e., raw sewage, lime treatment, ferrate, filtrations, and ozonation at 60 to 70 V respectively. While curves 7 and 8 represent the direct ozonat ion of lime treated sewage at 60 to 70 V respectively. It can be seen that the values of UV absorbance in general and also at 254 nm (used to correlate UV and COD) decrease after each treatment. Further a comparison of curves 5 and 7 shows similar spectra, indicating an equal change in properties of certain


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groups of compounds: however the COD reduction was different in both cases (Figure 8b). Same is true for curves 6 and 8. This extra information determined by fluorescence and UV absorbance will be worthwhile in studying the changes in the properties of organic matter during various stages of treatment, which cannot be obtained from COD test.

4. Conclusion

On the basis of this study the following conclusions may be drawn. (1) Ferrate is a better chemical than ferric chloride for treatment and oxidation of

organic matter from wastewaters.

M E A S U R E M E N T O F W A S T E W A T E R T R E A T M E N T E F F I C I E N C Y 433

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(2) Ferrate and ozone in combination are excellent agents for removing and oxidizing organic matter from different types of wastewaters.

(3) There is good correlation between COD and fluorescence, and COD and UV absorbance for the given types of wastewater studied. Therefore, UV and fluorescence measurements could be used as a general parameter for the estimation and changes in specific classes of organic matter such as aromatic compounds, polyaromatic systems and their derivatives, heterocyclic systems, and humic substances.

The main advantages of fluorescence and UV absorbance is that the measurement are very simple and fast and they do not need sophisticated equipment.


Acknowledgement

The Authors gratefully acknowledge the support of the Civil Engineering Department, University of Petroleum And Minerals, Dhahran, and Saudi Arabian National Center for Science and Technology to conduct this research.

References

Bran, G. L. and Milburn, D. L. D.: 1977, 'Automated Fluorometric Determination of Humic Substances in Natural Water', Analytical Letters 10, 1209-1219.

Dobbs, R. A., Wise, R. H., and Dean, R. B.: 1972, 'The Use of Ultra Violet Absorbance for Monitoring the Total Organic Carbon Content of Water and Wastewater', Water Research 6, 1173-1180.

Farooq, S., Bari, A., Siddiqui, R. H., Khararjian, H., Ali, I., and Abdulappa: 1982, 'Chemical Treatment of Secondary Effluent with Ferrate and Ozone for Reuse', Technical Proceedings, WSIA 10th Annual Conference and Trade Fair, Hawaii, Volume III.

Michail, M. and Idelovitch, E.: 1981, 'Gross Organic Measurements for Monitoring of Wastewater Treatment and Reuse', Chemistry in Water Reuse, Vol.I, William J. Cooper, Ann Arbor Science, Ch. 3, 35-64.

Mrkva, M.: 1975, 'Automatic UV-Control System for Relative Evaluation of Organic Water Pollution', Water Research 9, 587-589.

Murmann, R. K. and Robinson, R. R.: 1974, 'Experiments Utilizing FeO42- for Purifying Water', Water Research 8, 543-547.

Rosen, H. M.: 1973, 'Use of Ozone and Oxygen in Advanced Wastewater Treatment', Journal Water Pollution Control Federation 45, 2521-2536.

Smart, P. L., Finlaysoh, B. L., Rylands, W. D., and Ball, C.M.: 1976, 'The Relation of fluorescence to Dissolved Organic Carbon in Surface Water', Water Research 10, 805-811.

Standard Methods for the Examination of Water and Wastewater, 1980; APHA, AWWA-WPCF. Waite, T. D.: 1979, 'Feasibility of Wastewater Treatment with Ferrate', Journal of Environmental Engineering

Division, ASCE 105, 1023-1034. Willard, H. H., Merritt, L. L., and Dean, J. A.: 1974, InstrumentalMethods of Analysis, D. Von Nostrand Co.

measurement of wastewater treatment efficiency by fluorescence and uv absorbance

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