MODELING THE EFFECT OF VARIOUS PARAMETERS ON SEWAGE TREATMENT

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1 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt MODELING THE EFFECT OF VARIOUS PARAMETERS ON SEWAGE TREATMENT Abdullah A. Elamari and Manohar Singh Saini Department of Chemical Engineering, Al-Tahadi University, P.O. Box 633, Sirte, Libya s: ; ABSTRACT A study on wastewater treatment in sewage treatment plant in Sirte, Libya was carried out. The sewage chemical analysis for various parameters for raw wastewater and after biological treatment was closely monitored. Regression analysis has shown good correlations between biochemical oxygen demand (BOD) inlet i.e. of incoming raw wastewater and BOD outlet i.e. after biological treatment, suspended solids (SS) outlet and chemical oxygen demand (COD) inlet values with correlation coefficients of.81,.78 and.792 respectively. These correlations could be applied to predict the respective characteristics of the raw wastewater and the treated effluent. All other tested parameters of treated wastewater were in good agreement with expectations based upon the standard and accepted characteristics of sewage for disposal. BOD, COD and SS treatment efficiency had been, on an average of 87, 84 and 89 % respectively. Keywords: BOD, COD, SS, Sewage treatment, Regression analysis. INTRODUCTION The technological advancement has emerged as a boon to the man kind, which in turn has boomed the industrial sector. Industrialization has drifted the rural mass to increased urbanization which has resulted in an enormous increase in the volume of wastewater all around the world. The safe disposal of these wastewaters (Metcalf and Eddy, 23) has created serious concern to the environmentalists (Asana and Cotruvo, 24) on one hand, and the raising water scarcity as a challenge on the other hand. Sewage treatment (Moore and Moore, 1976; Binnie et al., 22) has attracted the world over the safe discharge of wastewater and also the recycle of part of this wastewater in the agricultural sector and for flushing toilets. Sewage is created by residences (toilets, baths, showers, kitchens etc.), markets (vegetable remaining, packing materials, containers etc.), hospitals (disposable syringes, toilets, medicinal wastes etc.), agriculture, institutions, commercial and industrial establishments (effluents etc.). Earlier municipal wastes were disposed using

2 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt the techniques of land disposal (Michael et al., 1994), incineration (Niessen, 1995), ocean dumping, compositing etc. Due to the land limitations and awareness of environmental hazards and regulations (Sunggyu and James, 1999), it has been world over decided to go for sewage treatment under strict parameter controls before disposal or reuse of treated effluents. So, wastewater from different sources/places can be collected or transported via a network of pipes and pump stations to a sewage treatment plant. BACKGROUND There are various methods of sewage treatment, and depending on the factors such as sewage types, sewage load, available land, the use of reclaimed water with required degree of treatment (Bouwer, 1996; Asano and Levine, 1996), a suitable method is employed. Conventional sewage treatment methods work on the following steps: Preliminary sewage treatment: It is employed for the removal of sewage constituents that may cause maintenance or operational problems with the treatment steps. This includes screening and comminuting (grinding) for the removal of debris and rags, grit removal by sedimentation and floatation (Puget et al., 2) for the removal of excess oil and grease. Primary sewage treatment: This treatment involves physicochemical techniques (Gokcay and Dilek, 1994) such as screening, degritting, coagulation, flocculation and sedimentation which remove mostly suspended materials. Since much of the suspended materials are readily oxidizable, so BOD is reduced as well. The effluent from primary treatment may contain high amounts of organic matter. Secondary sewage treatment: Secondary treatment is a biochemical process in which air oxidation mediated by microorganisms removes BOD remaining after primary treatment. Concurrently, additional solids are removed by filtration or sedimentation. Disinfection may be included in secondary sewage treatment. Tertiary sewage treatment: Recently, it has become evident that primary and secondary sewage treatments (Petala et al., 26) are inadequate where water is reused extensively. This treatment includes the removal of nutrients, toxic substances and further removal of suspended solid and organics. In our studies, we have limited treatment up to secondary treatment as the reuse of thus treated water is suitable for irrigation purpose. MATERIALS AND METHODS Wastewater treatment plant: Our study is based on the wastewater treatment plant at Sirte, Libya. The plant receives about 4 m 3 of sewage daily from 5 inhabitants, markets, hospitals and institutions. The station carries out preliminary, primary and secondary sewage treatment under precisely controlled conditions.

3 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt Analysis: The following different tests give the analytical results being carried at the plant: Physicochemical analysis: Wastewater before any treatment and after biological treatment inclusive of disinfection was analyzed for acid/alkaline ph, nitrogen (N), P 2 O 5, suspended solids (SS), solid residues (SR), chlorides, sulphates, detergents, oil and fats and chemical oxygen demand (COD) using standard methods (Standard Methods, 1995). Biological test: Biological oxygen demand (BOD 5 ) and bacteria coliform (using membrane filtration procedure) tests were conducted for the untreated i.e. raw wastewater and after primary secondary sewage treatments using the standard methods (Standard Methods, 1995). RESULTS The standard and accepted characteristics of treated wastewater under different categories of treatments are given in Table 1. All the parameters shown in Table 1 are regularly analyzed in the plant for the satisfactory treatment of wastewater before disposal. The results of the analysis of selected characteristics under present studies before (raw wastewater) and after biological treatment are shown in Table 2. Table 1: Standard Analytical Characteristics of Treated Sewage Sl. No. Characteristic Unit After Biological Treatment After Final Treatment 1. ph BOD 5 < 15 < 1 3. COD < 3 < 2 4. Suspended Solids < 2 < 1 5. Solid Residues < 14 < 1 6. Chlorides < 4 < 4 7. Sulphates < 4 < 4 8. Nitrogen < 5. < P 2 O 5 < 25 < Detergents <.5 < Oils & Fats < 5 < Bacteria Coliform Index < 1 < 1

4 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt Table 2: Selected Analytical Characteristics of Wastewater Sl. No. BOD Before Treatment ( ) COD SS N BOD After Biological Treatment ( ) COD SS N Figure 1 shows the variation of BOD(O), i.e. BOD values after biological treatment of sludge with that of BOD(I), i.e. BOD values of raw wastewater (before treatment). On linear regression, this has given the following relation (with correlation coefficient =.81): BOD(O) =.25 BOD(I) (1) Figure 2 shows variation of COD(I), i.e. COD values of raw wastewater (before treatment) and BOD(I) with the following relation (with correlation coefficient =.792): COD(I) =.4851 BOD(I) (2)

5 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt The COD(O), i.e. COD values after biological treatment of sludge are in the accepted limits of its characteristics and are almost independent of the BOD(I) values. Similarly, Figure 3 shows the variation of SS(O), i.e. SS values after biological treatment of sludge with that of BOD(I) with the following relation (with correlation coefficient =.78): SS(O) =.82 BOD(I) (3) The other parameter N(O), i.e. Nitrogen values after biological treatment of sludge are in the accepted limits of its characteristics and are almost independent of the BOD(I) values. The comparison of observed and calculated values of BOD(O), COD(I) and SS(O) are shown in Figures 4, 5 and 6 respectively. Table 3 shows the comparison of the values of slope, intercept and correlation coefficient for each of the above figures respectively with that of ideal one (Sastri et al., 1994; Singh Manohar et al., 1998). Table 3: Comparison of Regression Analysis Values Figure No. Slope Values of Intercept Corr. Coeff Ideal One DISCUSSION Figure 1 shows correlation of BOD(O) with BOD(I). Although all the values of BOD(O) are within the permitted limits but it is observed from Table 2 that for the values of BOD(I) 68, the values of BOD(O) are approximately nearing the permitted limit. Further increase in BOD(I) values may require slightly variation in treatment conditions. In Figure 2, it is observed that COD(O) values are independent of BOD(I), indicating that the treatment is quite satisfactory for it.

6 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt 16 BOD [O], BOD [I], Figure 1 : Variation of the values of BOD [O] with BOD[I] Figure 1: Variation of the values of BOD(O) with BOD(I) COD[I] COD[O] COD, BOD [I], Figure 2: Effect of BOD[I] on COD[I] and COD[O] values Figure 2: Effect of BOD(I) and COD(O) values Figure 3 gives the variation of SS(O) with BOD(I). From Table 2 it is observed that the value of SS(O) at Sl. No. 1 and 5 is slightly higher (2 to 5%) than the permitted one. This may be due to analytical error. The other parameter N(O) is independent of BOD(I) values here. Slightly higher values at Sl. No. 3, 4 and 7 in Table 2 for this are almost in permitted limits.

7 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt 25 2 SS[O] N[O] SS[O],N[O], BOD [I], Figure Figure 3: Effect 3: Effect of BOD[I] of on BOD(I) SS[O] and on N[O] SS(O) values and N(O) values Comparison of calculated values of BOD(O) and SS(O) with the observed values of BOD(O) and SS(O) are in good agreement as shown in Figures 4 and 6 respectively. Similarly, Figure 5 shows the good agreement of calculated values of COD(I) with those of observed values of COD(I). 14 BOD [O] Calc., BOD [O] Obsd., Figure 4: Comparison of BOD of BOD(O) [Calc.] with Calc. BOD with [O] Obsd. BOD(O) Values Obsd. values

8 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt COD [I] Calc Figure 5: Comparison of COD [I] Calc. with COD [I] Obsd. values COD [I] Obsd., COD [I] Obsd. Figure 5: Comparison of COD(I) Calc. with COD(I) Obsd. values 25 SS[O] Calc., SS[O] O bsd., Figure 6: Comparison of SS [O] Calc. with SS [O] Obsd. values Figure 6: Comparison of SS(O) Calc. with SS(O) Obsd. values In Table 3 the values of slope, intercept and correlation coefficient of the regression analysis of these calculated parameters BOD(O), COD(I) and SS(O) with those of corresponding observed ones are compared with the respective ideal values. Whereas these values for BOD(O) and SS(O) are in good agreements but higher value of intercept for Figure 5 suggests that the correlation between COD(I) calculated and observed one holds good at higher initial values of observed values. This may be because of correlation developed at corresponding higher values of COD(I) with BOD(I) already shown in Figure 2 earlier. Further studies on effect of different month cycles and analyzing the effluent for final treatment are in progress.

9 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt CONCLUSIONS The present studies could be summarized for the following suggestions: (i) The effluent treatment plant at Sirte, Libya handles the wastewater from different sources with efficient treatment before its disposal. (ii) The raw wastewater coming to the effluent plant is almost of the similar composition during this part of studies. (iii) The correlations between BOD values of raw wastewater and treated sludge values for BOD, COD, SS and N could be established under the prevailing similar conditions of raw wastewater and the applied treatment methodology. (iv) The regression analysis has resulted good correlations between BOD(I), and BOD(O), SS(O) and COD(I) with correlation coefficients of.81,.78 and.792, respectively. (v) The calculated values of BOD(O), COD(I) and SS(O) are in good agreement with the corresponding observed ones within ± 1% error. ACKNOWLEDGMENTS The authors are thankful to M/S ODEC, Sirte, Libya to provide the analytical and logical support, from time to time, to accomplish these studies. REFERENCES Asana, T. and Cotruvo, J. (24) Groundwater recharge with reclaimed municipal wastewater, Health and Regulatory Considerations. Water Res. 38, Asano, T. and Levine, A.D., (1996) Wat. Sci. Technol., 3(1-11), Binnie Chris, Kimber Martin and Smethurst George, (22) Waterworks waste and sludges, , Thomas Telford Publishing, London. Bouwer, H., (1996) Wat. Sci. Technol., 33(1-11), Gokcay, C.F. and Dilek, F.B., (1994) Water Sci. Technol., Metcalf and Eddy, (23), Wastewater Engineering: Treatment, Disposal, Reuse. 4 th ed., McGraw-Hill, New York. Michael, D. LaGrega, Phillip L. Buckingham and Jeffrey C. Evans, (1994) Hazardous Waste Management, , McGraw-Hill International Editions, Singapore. Moore John W. and Moore Elizabeth A., (1976) Environment Chemistry, , Academic Press, INC., NY. Niessen, W., (1995) Applications in Environmental Engineering, 2 nd edition, Marcel Dekker Inc.

10 Twelfth International Water Technology Conference, IWTC12 28, Alexandria, Egypt Petala, M., Tsirdis, V., Samaras, P., Zouboulis, A. and Sakellaropoulos, G.P. (26) Wastewater reclamation by advanced treatment of secondary effluents. Desalination 195, Puget, F.P., Melo, M.V. and Massarani, G. (2) Wastewater Treatment by Floatation. Braz. J. Chem. Eng. 17 (4-7). Sastri, K.S., Rao, M.R. and Singh Manohar (1994) Modelling the Effect of Functionality Distribution on the Crosslinking Characteristics of Hydroxyl Terminated PolyButadiene Liquid Prepolymers. Polymer 35, Singh Manohar, Kanungo, B.K., Bansal, T.K. and Rao, M.R., (1998) Modelling of Polyurethanes Based on Hydroxy Terminated PolyButadiene Prepolymer: Prediction of Mechanical Properties of Solid Propellants. Defense Science Journal 48(2), Standard Methods for the Examination of Water and Wastewater (1995), 19th ed., American Public Health Association / American Water Works Association / Water Environment Federation, Washington, DC. Sunggyu Lee and James, G. Speight, (1999) Environmental Technology Handbook, , Taylor and Francis Publishers, New York. Nomenclature BOD Biochemical oxygen demand, COD Chemical oxygen demand, SS Suspended solids, SR Solid residues, N Nitrogen, BOD(I) BOD values of raw wastewater (before treatment), COD(I) COD values of raw wastewater (before treatment), BOD(O) BOD values after biological treatment, COD(O) COD values after biological treatment, SS(O) SS values after biological treatment, N(O) N values after biological treatment, COD(I)Obsd. Observed values of COD(I), COD(I)Calc. Calculated values of COD(I), BOD(O)Obsd. Observed values of BOD(O), BOD(O)Calc. Calculated values of BOD(O), SS(O)Obsd. Observed values of SS(O), SS(O)Calc. Calculated values of SS(O),