Pa. J. Engg. & Appl. i. Vol. 5, July 29 (p. 9-4) Kineti Coeffiients for the Biologial Treatment of Tannery Wastewater Using Ativated ludge Proess. Haydar and J.A. Aziz 2 Assoiate Professor, Institute of Environmental Engineering and Researh, University of Engineering and Tehnology, Lahore, Paistan 5489. E-mail: sajj@brain.net.p 2 Professor, Institute of Environmental Engineering and Researh, University of Engineering and Tehnology, Lahore, Paistan 5489. ABTRACT Ativated sludge proess is a highly effetive and ommonly adapted method of aerobi biologial treatment systems and is normally designed on the basis of simplified hydrauli related parameters. Designs of biologial treatment systems based on hydrauli onsiderations are not adequate to ensure effiient operation. This is due to the wide variation in the omposition of wastewater and the omplex nature of the biohemial reations ourring in the treatment proesses. Hene design of biologial treatment systems should be based on the ineti approah rather than hydrauli parameters onsiderations. The present study was aimed at developing ineti oeffiients for the treatment of tannery wastewater by ativated sludge proess. A laboratory sale ompletely mixed ontinuous flow reator was used for the study. The reator was operated ontinuously for 86 days by varying detention times from to 9 days. Influent for the reator was settled tannery wastewater. of the influent and effluent and ML of aeration tan were determined at various detention times to generate data for ineti oeffiients. The ineti oeffiients (maximum substrate utilization rate), K s (half veloity onstant), Y(ell yield oeffiient) and K d (deay oeffiient) were found to be.25 day -, 488 mg/l,.64 and.5 day -, respetively. These oeffiients may be utilized for the design of ativated sludge proess failities for tannery wastewater. Overall removal rate onstant K was found to be.46 day -. Key Words: Kineti oeffiients; tannery wastewater; ativated sludge proess; aerobi treatment; industrial wastewaters.. Introdution Leather industry is the seond highest foreign exhange earning industry of Paistan after the textile setor []. There are over 65 tanneries in Paistan with major lusters loated in Kasur, Karahi, ialot, Multan, Gujranwala and heihupura distrits [2]. The major pollution parameters for tannery wastewater are biohemial oxygen demand (), hemial oxygen demand (COD), suspended solids, nitrogen, sulfides, sulfates and hromium. Most of the times tanning industries in Paistan disharge their untreated effluent in the reeiving water bodies adversely affeting the aquati life and human health. After full-sale implementation of IO 4 in the year 25, the foreign buyers are now muh onerned about the adoption of environmental friendly praties during leather prodution. Due to this onern, tanning industries in Paistan are under tremendous pressure to arry out treatment of their wastewaters to ompete in the global maret. Thus a rapid introdution of treatment failities in tanneries, espeially those whih are export oriented, is envisaged. This trend is already in evidene. Constrution of primary treatment failities has been either ompleted or is under proess in many tanneries []. ome of these tanneries are now heading towards the seondary treatment of their wastewater in order to omply with the National Environmental Quality tandards (NEQ) [4]. Biologial methods, lie ativated sludge proess, are invariably employed for the seondary treatment of a large number of industrial wastewaters. Knowledge of the mirobial inetis and determination of the ineti oeffiients for a partiular wastewater are, therefore, imperative for the rational design of treatment failities [5]. No loal referene is available in the literature for the ineti oeffiients of tannery wastewater. Designers, while designing biologial treatment failities (lie ativated sludge proess) for tannery wastewater use hydrauli approah whih does not result in an effiient treatment system meeting NEQ. In view of the above, the present study was undertaen with the objetive to determine different ineti oeffiients for tannery wastewater so that these may be utilized for the design of treatment failities in tannery setor. 2. Materials and Method Laboratory sale reators are normally used to determine ineti oeffiients. Completely mixed ontinuous flow reator without reyle is usually employed
Pa. J. Engg. & Appl. i. Vol. 5, July 29 for its easy operational ontrol. In suh a reator, detention time ( ) is equals to mean ell residene time ( ). The proedure is to operate the unit over a range of effluent substrate onentrat-ions. Hene, several different (at least five) are seleted for operation ranging from to days. Using the data olleted at steady state onditions, mean values are determined for influent ( o ), effluent (), and mixed liquor suspended solids (ML) of the aeration tan (denoted by X) to find out the ineti oeffiients [6]. The laboratory sale reator used in this study has been shown in Fig.. The reator was made of perspex glass of 5 mm thiness. The wastewater to the reator was fed using a 2-litre glass bottle. Peristalti pump was used to regulate flow for a partiular. The apaity of the aeration tan was 6 liters. Diffuser stones were used to supply air and were plaed at the bottom of the aeration tan along the wall. Filtered air was supplied to the diffusers stones from an air pump. A final larifier followed the aeration tan with 4.2 liters apaity. Wastewater samples for laboratory sale reator were olleted from a loal tannery named addiq Leather Wors. The tannery was equipped with a primary treatment plant omprising of equalization tan, primary sedimentation tan (PT), deanter and sludge drying beds (Fig. 2). The detention times in equalization tan and PT at maximum wastewater flow of 7 m/day were 6.4 hours and.9 hours, respetively. In tanneries, all the proesses are arried out as bath operations and wastes originating thereof vary onsiderably in omposition. Hene the wastewater samples were olleted at the outlet point of PT to get reasonably homogenous samples (Fig.2). N u ll a h B h a i d Waste tream (tanning,dying) Vol = 227 m Equalization Tan - ize = 9 x 7.5 x 4.7 m To Ravi Primary edimentation Tan Vol = 282 m Dia = m Effluent Depth =.5 m ampling Point ludge Deanter Vol = 55.6 m ludge 2 4 5 6 ludge Drying Beds 2 (ize 8m x 5m = 4 m ) Waste tream (soaing,liming,deliming,bating) Vol = 227 m Equalization Tan - 2 ize = 9 x 7.5 x 4.7 m Fig. 2: Line seth of primary treatment plant at addiq Leather Wors Fig. : Line seth of laboratory sale ompletely mixed ontinuous flow reator. 4
Kineti Coeffiients for the Biologial Treatment of Tannery Wastewater Using Ativated ludge Proess Total Kjeldahl Nitrogen (TKN) and Phosphorous (P) tests were arried out on the settled wastewater olleted to he the level of these nutrients for satisfatory biologial treatment. The : N : P for the wastewater was found to be :2:.9 as against a reommended value of :5: [7]. The phosphorous was thus defiient and this defiieny ould hamper a satisfatory biologial treatment. Therefore, the defiieny was met by adding alulated amount of Potassium Dihydrogen Phosphate (KH 2 PO 4 ) in the wastewater. Benh sale reator was started on 7.6.2. After seeding with domesti sewage, it was run as a bath system up to 9.6.2 to develop biomass. Thereafter, it was run on a ontinuous basis till 6.9.2. Complete operational shedule of the reator is given in Table. Table : Operational shedule of laboratory sale reator From Date To No. of Days Flow Rate (L/day) (Days) 9.6.2 4.7.2 26 2 5.7.2 8.7.2 4 9 4 9.7.2.8.2 4 7.2 5 2.8.2 5.8.2 4 5.4 7 6.8.2 6.9.2 8 4 9 Total 86 amples from the influent to the reator and effluent from the final larifier were simultaneously olleted to arry out tests. amples from the reator were olleted to find out ML, dissolved oxygen (DO), ph and temperature. Mean values of o, and X at various were used to find out ineti oeffiients while DO, ph and temperature tests were arried out to ensure favorable environmental onditions in the reator for biologial treatment. All the tests were arried out as per proedures laid down in the tandard Methods [8].. Results and Disussion Kineti oeffiients of interest for the design of ativated sludge proess are: = Maximum rate of substrate utilization per unit mass of miroorganisms, time K d = Endogenous deay oeffiient, time - K s = Half veloity onstant, substrate onentration at one-half of the maximum growth rate, mass/unit volume Y = Cell yield oeffiient, mg/mg (defined as the ratio of the mass of ells formed to the mass of substrate onsumed. value is employed to find out the volume of biologial reators. Greater is the value of, smaller will be the size of reator [9]. K s has no diret appliation in proess design. It only gives an idea about the hange in the speifi growth rate of bateria with a hange in the onentration of the growth limiting substrate. Y is used to estimate the total amount of sludge produed as a result of wastewater treatment. K d is used to find out the net amount of sludge to be handled and hene the size and ost of the sludge handling failities an be found out from this information [9]. Data to determine above oeffiients were generated by operating the benh sale reator at different. Mean values of o, and X orresponding to eah are presented in Table 2. The following linearized equation was used to find and K s [6]. X o K s By using the above equation, a graph was plotted with / on the x-axis and X /( o -) along y-axis (Fig. ). A linear regression line was fitted to the plotted data. Interept on the y-axis and the slope of this line were used to find and K s. The equation of the fitted line is also shown on the graph. 7 6 5 X 4 o (days) 2 () y = 56.44x +.2 R 2 =.985...2. / Fig. : Determination of and K s Table 2: Mean values of data for ineti oeffiients n o (mg/l) (mg/l) X (mg ML/L) Range Mean 2 Range Mean 2 Range Mean 2 6 45-62 55+ 64 69-5 9 + 24 25-297 + 4 6 45-59 54 + 54 65-84 + 6 27-278 26 + 8 5 6 46-529 48 + 4 5-8 67 + 7-26 27 + 4 7 6 442-6 525 + 7 29-5 9 + 252-2 279 + 26 9 6 4-544 497 + 44 2-9 29+ 8 268-9 8 + 24 Number of samples 2 Mean + tandard Deviation 4
Pa. J. Engg. & Appl. i. Vol. 5, July 29 The following linearized equation was used to find Y and K d. [6]. o Y X A graph was plotted with / along y-axis and ( o -)/X along x-axis (Fig. 4). A linear regression line was fitted to the plotted data. Interept on y-axis and the slope of the line was used to find K d and Y. The equation of the fitted line is also shown on the graph..5..25.2.5..5 K d (2) y =.646x -.5 R 2 =.988..2..4.5 o X Fig. 4: Determination of K d and Y The values obtained for, K s, Y and K d (from Fig. and Fig. 4) are presented in Table. Table : Kineti oeffiients for tannery wastewater. Kineti oeffiient Value Units.25 day - K s 488 mg/l Y.64 unitless K d.5 day - At a mean reator temperature of.2 ºC No referene for the ineti oeffiients of tannery wastewater ould be found in the literature for the purpose of omparison with other similar wors. However, the results obtained were within the range noted for the ineti oeffiients of other industrial wastewaters as shown in Table 4. A omparison of ineti oeffiients for tannery wastewater with other industrial wastewaters would be interesting. ubstrate utilization rate for tanneries (.25 day - ) is less as ompared to others and thus larger volume of biologial reator would be needed to treat tannery wastewater. This less value of may be due to speifi nature of tannery waste. Deay oeffiient Kd is quite low for tannery wastewater when ompared with other industrial wastewaters, whih indiates larger net sludge volumes resulting from biologial treatment. Cell yield oeffiient (Y) is omparable with other industrial wastewaters. Half veloity oeffiient (Ks) is also omparable with the reported values exept that for shrimp proessing. Table 4: Kineti oeffiients for some industrial wastewaters Wastewater Type Pulp and Paper mill [] Pulp and Paper mill [] hrimp Proessing [2] Unit Typial Value day - 5. K s mg/l 5 Y mg/mg.47 K d day -.9 day - 6.4 K s mg/l 59 Y mg/mg.4 K d day -.6 day - 6.9 K s mg/l 85.5 Y mg/mg.5 K d day -.6 Coeffiients Coeffiients Basis Overall removal rate onstant K was also determined from the available data. K an be employed for the design of other aerobi biologial treatment systems suh as aerated lagoon or waste stabilization ponds for the treatment of tannery wastewater []. For this purpose a graph was plotted with along x-axis and (o-)/ along y-axis (Fig. 5). A linear regression line passing through the origin was fitted to the plotted data []. The equation of the line is also shown on the graph. lope of this line gave the value of K as.46 day -. The result was in agreement with the findings of Metalf and Eddy (2), who reported that value of K varied from.5 to.5 day -. (o ) 6 4 2 8 6 4 2 y =.46x R 2 =.8224 2 4 6 8 Fig. 5: Determination of K During the ourse of study, the reator temperature flutuated between 29 to C, whih falls within the suitable temperature range for heterotrophs treating wastewater under aerobi onditions [4]. The ph of the reator remained between 6.5 and 8. whih is a suitable range for biologial treatment [9,5]. DO of the reator remained between and 4.5 mg/l whih was above the desirable range of 2 mg/l for biologial treatment [9,6]. 42
Kineti Coeffiients for the Biologial Treatment of Tannery Wastewater Using Ativated ludge Proess 4. Conlusions The ineti oeffiients (maximum substrate utilization rate), Ks (half veloity onstant), Y (ell yield oeffiient) and Kd (deay oeffiient) were found to be.25 day -, 488 mg/l,.64 and.5 day -, respetively. The determination of these oeffiients may be helpful in () understanding the inetis of substrate utilization (2) sludge prodution and () design of biologial treatment failities based on ativated sludge proess for settled tannery wastewater. Thus these oeffiients have both aademi value and pratial signifiane. The value of overall removal rate onstant K was found to be.46 day - and this value may be employed for the design of aerobi biologial treatment failities based on aerated lagoon or waste stabilization ponds. Anowledgements This study was funded by head grant 22 of University of Engineering and Tehnology, Lahore, Paistan. The assistane of Mr. Muhammad Hashmat in setting up laboratory sale reator is anowledged. REFERENCE [] Export Promotion Bureau of Paistan (EPB), http://www.epb.gov.p/v/statistis/apr/summery_prod ut_wise.xls PHPEID=768862b489b698b79ad97f5765 (aessed Aug. 5, 27) [2].. Tahir, and R. Naseem; eparation and purifiation Tehnology, 5(27), 2-2. [] M. Iqbal, I. Haque. and J. A.. Berns; Draft Environmental Report on the Leather etor in Paistan, Environmental Tehnology Program for Industries. Federation of Paistan, Chamber of Commere and Industries, Federation House, Karahi, Paistan, (998)-5 [4] Government of Paistan (GOP), 2. National environmental quality standards for muniipal and liquid industrial effluents. http://www.elaw.org/assets/pdf/revisedneq.pdf (aessed 2 ep., 27) [5] Edgardo, et. al.; Water A, 27(2),69-76 [6] Metalf and Eddy, In.; Wastewater Engineering. Treatment, Disposal, Reuse, rd Edition, MGraw-Hill, New Yor. (99) 275-279 [7] Metalf and Eddy, In.; Wastewater Engineering, Treatment and Reuse, 4 th Edition, MGraw-Hill, New Yor, (2) 545-644 [8] tandard Methods for the Examination of Water and Wastewater APHA, AWWA, WEF, Washington DC, U, (998) [9] L. D. Benefield and C. W. Randall; Biologial Proess Design for Wastewater Treatment., Prentie-Hall, In., Englewood Cliffs, N.J., (98) 2-27 [] R. A. Kormani;, Jour. of Water Pollution Control Fed., 44(972) 45-458. [] A. Rashid;Treatment of Effluent from Pulp and Paper Industry.", M. Thesis, Institute of Environmental Engineering and Researh, University of Engineering and Tehnology, Lahore, Paistan, (995) -67 [2] C. R. Horn and F. G. Pohland; Proeedings of the 28 th Industrial Waste Conf., Purdue University, West Lafayette, Indiana, (97) 89-8. [] W. W. Eenfelder and D. L. Ford; Water Pollution Control, Experimental Proedures for Proess Design., Pemberton Press, Jenins Publishing Company, Austin, New Yor, (97) 5-77 [4] R. N. Doetsh and T. M. Coo;. Introdution to Bateria and their Eobiology, University Par Press, Baltimore, Md. (97) [5] J. F. Wilison; Introdution to Mirobiology, Halsted Press, A Division of John Wiley & ons, In., New Yor, (975) [6] D.. Parer and M.. Merrill; Jour. Water Pollution Control Fed., 48(976) 25-252. 4