Effect of Ozone on Secondary Effluents Treatment for Agriculture Reuse

Effect of Ozone on Secondary Effluents Treatment for Agriculture Reuse M. Bataller, E. Véliz, L. A. Fernández, C. Hernández, I. Fernández, C. Alvarez, E. Sánchez. Ozone Research Center P.O. 6414, Havana, Cuba E-mail mayra.bataller@cnic.edu.cu Abstract This paper presents the results of ozonation of secondary effluents from two treatment plants in Havana, Cuba. These facilities have different treatment capacities and the treatment scheme of domestic sewages includes a primary treatment (screening and sedimentation) and a secondary treatment (biological filter followed by sedimentation), finally the effluents are discharged to a river. The samples were collected before the discharge of the effluents at the facilities. The effect of applied ozone doses (up to 4 mg/l) and contact time (5 and 1 min) on several wastewater quality parameters was evaluated. Organic matter content (chemistry oxygen demand and UV absorbance at 254 nm) decreased. The biological oxygen demand reached values below 3 mg/l. Turbidity and total suspended solids decreased. Simultaneously, the ozone effect on the concentration of some nutrients, which are used for fertilizing, was evaluated. The values of ammoniacal nitrogen and the ph remain practically constant. The nitrates values slightly increased. The total phosphorus appeared in very low concentrations and suffers a decrease. Two fundamental parameters, the ozone initial demand and the ozone consumption kinetic constant were determined. Furthemore, biological pollution indicators such as total coliforms and faecal coliforms were determined. Ozone disinfection was very effective, yielding up to 5 log inactivation. Taking into account, the high pathogen microorganism concentrations present in these secondary effluents, values equal or higher than 5 min (hydraulic time of residence) and 2 mg/l (applied ozone dose) guaranteed the disinfection. On the other hand, the quality of ozonated effluents under several experimental conditions fulfilled the WHO Guidelines (1 CFU/1 ml for Faecal Coliforms) for unrestricted wastewater reuse in agriculture and the Guidelines for Water Reuse, U.S. EPA 1

for agriculture reuse (2 CFU/1 ml for Faecal Coliforms) for non-food-crops, pastures for milking animals, fodder, fiber and seed crops. These results indicated that ozonation of secondary effluents is a safe disinfection alternative for wastewaters reuse or disposal. Key Words Ozone, secondary effluents treatment, disinfection. Introduction Some epidemiological studies developed by the World Health Organization (WHO), the Environmental Protection Agency (EPA) and by Latin American countries have demonstrated that reuse of inadequately treated water constitutes a potential vehicle for the transmission of pathogenic agents (Orta et al. 22). This represents a severe risk to the public health. During decades, the chlorination has been the most employed technology for wastewater disinfection. The toxic byproducts formation and insufficient inactivation power of chlorine has allowed the ozone increment use (Janex et al. 2, WEF 1996, IWSA 1997). The elimination of certain pathogen microorganisms is not guaranteed with chlorine treatment the (viruses, Legionella, Pseudomonas aeruginosas, Entamoeba histolytica, cysts of Giardia and Crystosporidium parvum, Mycobacterium, etc) WHO 1996. Ozonation is an attractive disinfection alternative for several reasons: ozone is a strong germicide and simultaneously oxidizes organic matter improving the wastewater quality. The ozone use results in secondary and tertiary treatments are satisfactory (Janex et al. 2). It possible to achieve an effluent quality, which permits its reuse (Larocque et al.1999, Le Pauloue et al. 1999, Kriuthof et al. 1999). Although, it is not established, a dose of 4 and 1 mg/l and a residual ozone concentration between.2 to 1 mg/l is considered enough to guarantee a complete disinfection (EPA). For more stringent criteria though, a higher dose of 1 to 2 mg/l may be necessary (Paraskeva et al. 1998). In Cuba, this ozone application, as a safe alternative to wastewater discharge or reuse, is in progress. Ozone application protects and conserves the environment. It improves microbiological quality of the effluent before its disposal, as well as high chlorine doses are not necessaries. On the other hand, water reuse is becoming more common and gaining acceptance among communities and regulatory agencies. The wastewater disinfection step requires a great security in the execution. This paper presents the evaluation of ozonation effect on the quality of secondary effluents, coming from two sewage treatment plants in Havana, Cuba. Organic matter content, chemical oxygen demand (COD) and UV absorbance at 254 nm, as well as biochemical oxygen demand (BOD 5 ), total suspended solids (TSS), total volatile (TVS), turbidity, ph and disinfection were examined. Simultaneously, the ozone effect on the concentration of some nutrients as ammoniacal nitrogen, nitrates and total phosphorus, which are used for fertilizing, were evaluated. The initial demand and the consumption kinetic constant of ozone of the effluents were 2

determinated. The most favorable operation conditions to guarantee a safe disinfection and to diminish the environmental impact were determined. The results were compared with the WHO Standard 1989 (1 CFU/1 ml for Faecal Coliforms), for unrestricted wastewater reuse in agriculture and the Standard for Water Reuse, US. EPA 1992 (2 CFU/1 ml for Faecal Coliforms), for agriculture reuse: non-food-crops, pastures for milking animals, fodder, fiber and seed crops. On the other hand, Cuban Standard NC- 27: 1999 was also taken into account. Materials and Methods Experimental Secondary effluents samples from the Quibu and Ma. del Carmen plants in Havana were evaluated. The samples were collected before the discharge of the effluents to water bodies. These facilities have different treatment capacities and the domestic sewages receive the same treatment scheme. A general treatment scheme is showed in figure 1. Ozonations were carried out using two bubble columns, which have a glass porous diffuser, a sample port, entrance and exit of gas. Ozone generator model AQOZO/CIOZONO (Cuba) was used to supply the ozone/oxygen gas mixture. The experiments were operated in continuous and counter current mode. The range of ozone doses employed varied from high to very high, with respect to reported values for disinfection. For different ozonation conditions, inlet gas ozone concentration and hydraulic residence time, same ozone doses were applied in order to evaluate the effect on quality of the effluents. Experimental conditions are presented in Table 1. Domestic Sewages Screening Primary Sedimentation Activated sludge (Anaerobic digester) Sludge treatment Secondary Sedimentation Discharged to a river Biological Filter Ozonation Figure 1. General treatment scheme of domestic sewages in Quibu and Ma. del Carmen facilities. 3

Table 1. Experimental conditions Parameter Group I Group II Volume reactor (L).6 4 Liquid flow rate (L/h) 7,2 24 Hydraulic residence time (τ ) (min) 5 1 Gas ozone concentration 1, 15, 3 5, 1, 2 Gas flow rate (L/h) 1 5 Gas superficial rate (m/h) 7.6 The gas ozone concentration and the absorbance at 254 nm were determined using a spectrophotometer model Ultrospec III, Pharmacia. The dissolved ozone concentration was determined by the indigo method (Bader and Hoigné 1981). Physico-chemical parameters values, concentrations of Faecal and Total Coliforms were evaluated before and after the ozonation. Analyses carried out according to Standard Methods (APHA, 1995). Determination of ozone initial demand and consumption kinetic constant The initial demand (ID) and consumption kinetic constant (k) due to overall ozone consumption by moderate or slow reactions (considered as pseudo first order reaction) were determinated according to the method proposed by Roustan (1998). It establishes a mass balance respect to ozone, which is readjusted to obtain the equation [1]. Both parameters were determinated from the plot of liquid ozone concentration (C O3L ) versus transferred ozone dose (TOD). The concentration increases with the increment of TOD, the slope (1/(1+kt)) is a function of k and of τ (hydraulic residence time: ratio of the liquid flow and liquid volume). The slope allows to calculate the k value and the intercept the ID value. Then, these parameters can be calculated according to: [1] CO 3L = TOD / (1+kτ) - ID / (1+kτ) Results and Discussion The values of the ozone initial demand and consumption kinetic constant due to overall ozone consumption change with the water quality and can vary during the different seasons for the same water source. Table 2 presents the results for each of tested effluents before the ozonation. Experiments were carried out in different weeks. It can observe that the values generally are in the same order. Hence, the effluent quality remained enough stable during the study period, aspect that facilitates the evaluation. k values are smaller than.5 min -1 which indicates that there is not a very strong consumption of ozone (Roustan et al. 1998). A case only, corresponding to Ma. del Carmen plant indicated a value of.9 min -1. 4

Table 2. Values of the initial demand (ID) and consumption kinetic constant (k) of secondary effluents ID k (min -1 ) Quibu Plant 4.29.12 1.94.8 1.28.5 Ma. del Carmen Plant.76.6.96.2 1.45.3 1.62.3 9.94.9 Heavily polluted effluents increase the initial demand and the consumption of ozone, and reduce the disinfection potential of ozone. It also may be desirable for ease of operation that the plant has only small fluctuations in flow and quality of wastewater (Paraskeva et al. 1998). Measurable dissolved ozone appears after the satisfaction of initial ozone demand of the effluent, hence the monitoring of dissolved ozone concentration is very important. Results from a number of experimental runs of Ma del Carmen plant effluents are presented in Figure 2. The run 4 (Exp. 7a, 8a and 9a) achieved the lowest dissolved ozone concentration in the effluent, which had the highest values of k and ID (.9 min -1 and 9.94 mg/l respectively). Dissolved ozone concentration 3.5 3 2.5 2 1.5 1.5, 8 16 Ozone transferred dose 21 Exp. 7a, 8a, 9a Exp. 4a, 5a, 6a Exp.1a, 2a, 3a Figure 2. Dissolved ozone concentration vs transferred ozone dose for several runs of Ma del Carmen Plant effluents The physico-chemical characterization of secondary effluents and treated effluents under different ozone applied doses is showed in Table 3. The ph stays practically constant, between 7 and 8. Turbidity and total suspended solids decreased. The TSS/TVS ratios were about 1, indicating the organic nature of TSS presented in the secondary effluents. The effect of ozone on COD depends on the composition of the effluent matrix and on the initial COD values. In all experiments COD values were reduced systematically with increasing ozone dose. The highest reduction 5

percents were up to 65 % (Figure 3). This behavior was also observed in run 4 that achieved a 41.4 % reduction of COD at the highest value of gas ozone concentration. Table 3. Average physico-chemical results of secondary effluents and treated effluents under different ozone applied doses. Quibu Plant (7/26) Group I Parameter DBO 5 DQO Abs. 254 (cm -1 ) Turbidity (UT) N-NH 4 N-NO 3 P total Secondary - 67..22 25.3 14..42 1.93 effluent 14-45.7.145 14.26 13.5.42 1.13 21-43.3.121 12.37 13.5.43 1.6 42-36.1.74 6.18 13..46.96 Ma. del Carmen Plant (9/26) Group I Secondary - < 3.14 12.73 13..53 1.79 effluent 14 - -.11 7.33 12..54.57 21 - -.76 5.19 11.5.61 <.5 42 - -.66 4.6 11..66 <.5 Ma. del Carmen Plant (2/27) Group II Secondary 47.5 76.4.19 5.1 17..44 2.7 effluent 1 22.6 44.9.68 1.26 16.1.46 1.45 21 15.4 33.5.59.47 16.3.49.85 42 9.8 23..45.32 14.9.5 <. Gas ozone concentrations % DQO reduction 1. 8. 6. 4. 2.. 1 2 3 4 5 Experimental runs performed under three values of CO3 gas at different dates Figure 3. % COD reduction from several experimental runs The nitrates values are slightly increased in ozonated effluents. However, the values of ammoniacal nitrogen remain practically constant. Two aspects can explain this fact. The high reactivity of ozone on the aminoacids and amines present in microorganism cells, resulting in ammonification (Doré, 1989) and the nitrates formation from ammoniacal nitrogen. The total phosphorus appears in very low concentrations and decreases. Results from a number of experimental runs of Ma del Carmen Plant effluents are showed in Figure 4. 6

5 4 Total phophorous 3 2 1 14 21 42 Applied ozone dosis S1 S2 S3 Experimental runs (different dates) Figure 4. Effect of applied ozone dose on the total phosphorus The transferred ozone dose is an important factor in ozone treatment. An increased ozone concentration in the feed gas at a given hydraulic residence time (5 min) reached a marked increase of the ozone transferred dose (Figure 5). However, to raise the hydraulic residence time at a given gas ozone concentration (1 mg/l) do not achieved an important effect on transferred ozone dose (Figure 6). Similar results were obtained for other experimental conditions. Hence, gas ozone concentration is the parameter, which exerts the major influence on the amount of transferred. Transferred ozone dose 3 25 2 15 1 5 1 2 3 Exp. 2,5,8 Exp. 3,6,9,Exp. 4,7,1 Gas ozone concentration Figure 5. Transferred ozone dose vs gas ozone concentration (t: 5 min) 7

16 Transferred ozone dose 14 12 1 8 6 4 2 5 5 1 Exp. 2, 11, 2a Exp. 5, 14, 2a Exp. 8, 16*, 8a Hydraulic residence time (min) Figure 6. Transferred ozone dose vs hydraulic residence time (gas ozone concentration: 1 mg/l) Disinfection Effectiveness Microbiological quality is the most contentious issue linked to wastewater reuse for irrigation. Today, the WHO standards represent the minimum level to assure the public health. On the other hand, the California criteria stipulate conventional biological wastewater treatment followed by tertiary treatment, filtration and chlorine disinfection to produce effluents that are suitable for irrigation use. Asano et al, 1996 reported two important epidemiological studies, which demonstrated that irrigated food crops with municipal wastewater reclaimed according to the California guidelines can be consumed without adverse health effects. However, the nutrients removed by tertiary treatment are not available for fertilizing. EPA has adopted more comprehensive and strict wastewater reuse criteria, respect to California and WHO guidelines. Considering these aspects, the results were evaluated according to EPA and WHO guidelines. The microbiological results indicated that the disinfection was guaranteed for the effluents of Quibu Plant and Ma. del Carmen plants. An applied ozone dose of 14 mg/l to Quibu effluents during 5 min was enough to fulfill the WHO Standard (1 CFU/1 ml) when initial concentration was about 1 4 CFU/1 ml. However, when the initial concentration was closed to 1 6 CFU/1 ml an ozone dose of 21 mg/l was required According to EPA criteria (Faecal Coliforms: 2 CFU/1 ml) ozone dose of 21 mg/l was very effective. Figure 7 shows log inactivation values as a function of ozone applied dose at a given hydraulic residence time (5 min). 8

- log (N/No) 5 4.5 4 3.5 3 2.5 2 1.5 1.5 1 2 3 4 5 Applied ozone dose Exp.1,2,3 Exp. 4,5,6 Exp. 7,8,9 Figure 7. Inactivation of Faecal Coliforms as a function of applied ozone dose for Quibu effluents (t: 5 min). Table 4 presents microbiological results of Ma. del Carmen Plant effluents. Under a hydraulic residence time of 5 min and an ozone applied dose of 21 mg/l the Faecal Coliforms values did not exceed the permitted limit by WHO Standard, but an ozone dose higher should be applied to macth EPA requirements. Whereas, 1 min and an ozone dose of 1 mg/l permitted to fulfill EPA Standard (Faecal Coliforms: 2 CFU/1 ml). Hence, as safely, dose of 2 mg/l should be applied during 1 min. The effect of dissolved ozone concentration on the disinfection can be observed during run 4 (with the lowest values of this parameter) Table 4. Microbiological results of secondary effluents and treated effluents under different ozone applied doses. Faecal Coliforms Ozone applied dose (CFU/1mL) Secondary effluent 1 21 42 τ : 1 min 2.4 x 1 6 1.7 x 1 5 7.9 x 1 5 * 1.7 x 1 2 1.4 x 1 2 1.6 x 1 4 * 7 1 4.9 x 1 2 * 4 5 14* τ : 5 min 7. x 1 4 1.6 x 1 6 3.5 x 1 6 1.6 x 1 3 2.5 x 1 4 1.2 x 1 4 9.2 x 1 2.8 x 1 3 5.2 x 1 2 Note: The number of Faecal Coliforms should not be exceed 8/1 ml in any sample * Values corresponding to run 4 5 75 5 The Cuban standard NC 27: 1999 regulates the wastewater discharges according to the qualitative classification of the receptor bodies. Table 5 reports the specifications for rivers and reservoirs. In this case the reservoir corresponds to specification A and B, according to the sanitary authority classification, which corresponds to the use, conservation necessity and possible risk for the health of the water body. The results indicate that the quality of treated effluents under several experimental conditions fulfills the established Cuban standard. 9

Table 5. Indicators of maximum acceptable faecal contamination values in the receptor body. (Rivers and Reservoirs) Total Coliforms NMP/1mL Faecal Coliforms NMP/1mL A 1 2 B 5 1 C * * Note: * Limit is fixed by the sanitary authorities. Conclusion In the systems under study gas ozone concentration is the parameter, which exerts the major influence on the amount of transferred. For the secondary effluents from both treatment plants an applied ozone dose of 21 mg/l during 1 min should be applied to fulfill EPA Standards for agriculture reuse. References 1. Asano, T. and Levine A.D. 1996. Wastewater reclamation, recycling and reuse: past, prsente and future. Wat. Sci. Tecnolog., 33, 1-11: 14-21. 2. APHA. AWWA. WPCE. 1995. Standard Methods for the Examination of Water and Wastewater, 19 th Ed. Washintong D.C. 3. APHA, AWWA, and WEF, 1995. Standard Methods for the Examination of Water and Wastewater, 19 th Ed. Washington D.C. 4. Bader, H. y Hoigné, J. 1981. Determination of ozone in water by the indigo method. Water Research, 15: 419. 5. Beltrán, F. 24. Ozone reaction kinetics for water and wastewater systems. Lewis Publishers ed. Washington D.C. 6. EPA 1992: Guidelines for Water Reuse, 625/R-92/4. 7. IWSA. 1997. The practice of chlorination: application, efficacy, problems and alternatives. International Water Supply Association Blue Pages. 8. Janex, M., Savoye, P., Roustan, M., Do-Quang, Z., Lazarova, V. 2. Wastewater Disinfection by ozone: influence of water quality and kinetic modeling. Ozone Science & Engineering, 22, 2: 113-12. 9. Kriuthof, J. y Masschelein, W. 1999. State of the art of the application of ozonation in BENELUX Drinking Water Treatment. Ozone Science & Engineering, 21, 2: 13. 1. Larocque, R. 1999. Ozone applications in Canada: A state of the art review. Ozone Science & Engineering, 21, 2: 119. 1

11. Le Pauloue, J. y Langlais, B. 1999. State of the art of ozonation in France. Ozone Science & Engineering, 21, 2: 153. 12. Norma Cubana NC 27: 1999. Vertimiento de aguas residuales terrestres y al alcantarillado. Especificaciones. 13. Paraskeva, P., Lambert, S.D., Graham, N.J.D. 1998. Influence of ozonation conditions on treatability of secondary effluents. Ozone Science & Engineering, 2, 2: 133. 14. Roustan, M., Debellefontaine, H., Do-Quang, Z., Duguet, J.P. 1998. Development of a method of ozone demand of a water. Ozone Science & Engineering, 2, 6: 513. 15. WEF. 1996. Disinfecting Wastewater for Discharge and Reuse. Proc. of Water Environment Federation Specialty Conference, Portland, Oregon. 16. WHO 1989: Health guidelines for the use of wastewater in agriculture and aquaculture. 17. WHO 1996: Guidelines for drinking-water quality. 2 nd Ed. 11