WEFTEC.06. *Corresponding author Department of Civil and Environmental Engineering, The University of Western Ontario

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1 Performance of Aerobic MBR Treating High Strength Oily Wastewater at Mesophilic Thermophilic Transitional Temperatures R. Kurian, G. Nakhla* Earth Tech Canada Inc., Thornhill, L3T 7Y6 Ontario *Corresponding author Department of Civil and Environmental Engineering, The University of Western Ontario Abstract The performance of an aerobic membrane-coupled bioreactor (MBR) operating at mesophilic- thermophilic transitional temperatures (40 C) treating oily rendering wastewater has been evaluated in terms of COD, BOD 5, oil and grease, solids and ammonia removal at 5 and 10-day HRT. The COD removal efficiency increased from 78% to 96%, BOD 5 removal from 87 to 99% and oil and grease removal from 92 to 95% with the increase in hydraulic retention time (HRT) from 5 to 10 days. The operation at atypically high temperatures showed promise as a treatment solution due to the low sludge yields of 0.03 g VSS/g COD. Keywords Membrane-coupled bioreactor, oily wastewater, transitional temperature Introduction The growth of industries producing high-strength and complex wastewaters makes it imperative to develop suitable treatment systems for these wastewaters. Aerobic biological processes operated at high temperatures are highly advantageous in treating high temperature, high strength industrial wastewaters due to its ability to combine the advantages of conventional aerobic and anaerobic processes that include rapid biodegradation kinetics and low biological solids production respectively (Rozich and Bordacs, 2002). High treatment temperatures are considered to be advantageous for wastewaters with high oil and grease content, owing to the enhanced solubility of this contaminant at higher temperatures. Despite this advantage in thermophilic treatment, Çetin & Sürücü (1990), Barr et al. (1996), Tripathi & Allen (1999), Lapara and Alleman (1999) have documented the deterioration of sludge settleability with increasing temperature. The inability to separate sludge from liquid combined with low sludge yields will result in washout of biomass and low quality. Membrane technology was successfully employed in this experiment to overcome this problem. Though thermophilic reactor coupled with membrane is not a new concept and has been experimented by Lopetegui and Sancho (2003) and Klatt and Lapara (2003), the use of an immersed membrane at high temperatures is quite uncommon. 3249

2 Experimental Setup The laboratory scale continuous aerobic MBR (Figure 1), consisted of a 4 L storage tank followed by a 4.5 L clear Plexiglas reactor. Sludge obtained from a laboratory-scale thermophilic MBR operating at 45 C for 160 days on the same high-strength rendering wastewater was used to seed the reactor. The reactor temperature was maintained at 40±3 C using a Corning hotplate stirrer. The reactor was aerated continuously with compressed air through the immersed membrane to maintain DO >1 mg/l. A membrane module ZW-1, Zenon Environmental, Oakville, Ontario, of pore size 0.04 μm and of surface area m 2 was employed to retain solids in the reactor. A peristaltic pump with twin heads (Minipuls3, Gilson Inc., Canada) was used to draw permeate through the immersed membrane unit and pump influent into the reactor. The system operation continued over 87 days at a 5-day HRT and for 48 days at the 10-day HRT and sludge retention time (SRT) of 45 days for both HRTs. The SRT was calculated based on sampling volumes since no deliberate sludge wastage was deemed necessary. Figure 1. Experimental set-up for continuous MBR Analytical Methods Parameters analyzed included total suspended solids (TSS), volatile suspended solids (VSS), COD, BOD 5, TKN, ammonia-n, nitrate-n, nitrite-n, oil & grease and phosphorous. Influent, reactor mixed liquor and final samples were analyzed for TSS, VSS and BOD 5 using Standard Methods (APHA 2003). TSS and VSS were measured using 1.2 μm filter paper. The total and soluble COD for these samples were determined employing the HACH Odyssey Analyzer and the heating reactor with standard HACH testing kits. Ammonia, nitrate, nitrite and phosphate were determined using a high performance liquid chromatogram (HPLC, Dionex Canada Ltd., Oakville, Ontario). TKN was measured digesting, distilling and titrating samples according to standard procedures. Soluble samples were extracted by filtering through 0.45 μm filter paper (Wheaton). Dissolved oxygen (DO) was measured with a portable YSI Dissolved Oxygen Meter Model 50. All instruments were calibrated with blanks and standards prior to each analysis. 3250

3 Results COD and BOD removal The MBR operated at a lab scale dealt with challengingly high strength wastewater as can be seen in Table 1. The plant underwent an efficient oil recovery system prior to being channeled to the DAF unit. The DAF treated wastewater was used in these studies. Table 1 clearly illustrates the variability of contaminants constituting this wastewater pre and post DAF treatment. Table 1. Raw and DAF Characteristics Parameters Raw wastewater DAF Effluent Range Average Range Average TSS (mg/l) VSS (mg/l) TCOD (mg/l) SCOD (mg/l) Ammonia- N (mg/l) O & G (mg/l) The influent and characteristics measured at both HRT conditions and the contaminant removal efficiencies are shown in Table 2. It is evident from this table that the MBR performance exhibited extreme sensitivity to changes in the HRT or loading rates. The VSS in the reactor remained steady at approximately 10,000 mg/l during both runs. Lowering the HRT from 10 to 5 days drastically affected the COD removal efficiency, reducing it from 97% to 78%. A similar trend was observed in the BOD removal efficiency, with BOD concentrations deteriorating substantially: from 95 mg/l to 1497 mg/l. However, the system attained a pseudo-steady state at both HRTs despite the high variations in influent characteristics as depicted in Figure 2. It is interesting to note that volatile fatty acids (VFA) which are typically considered to be readily biodegradable under aerobic conditions persisted in the (Table 2), despite the extended HRTs. The breakthrough of VFAs at the 5-day HRT emphatically corroborates the kinetic limitations for this wastewater. 3251

4 Influent COD & BOD 5-day HRT 10-day HRT time (days) Effluent COD &BOD5 2000influent COD 0 influent BOD COD BOD Figure 2. Variation in COD and BOD corresponding to influent variations. Table2. Steady-state characteristics from lab-scale continuous flow MBR. Parameter Influent 5-d HRT Effluent 5-d HRT (Av. ±Std. Dev.) Percentage removal Influent 10-d HRT Effluent 10-d HRT Percentage removal TCOD ± ± k=0.8 k=-0.4 TBOD ± ± k=0.8 k=-0.4 Oil & Grease ± ±4 95 k=-0.8 k=-0.3 TKN 1848 k= ± k= ± Ammonia-N ± ±66 79 k=-0.3 k=0.1 VFA 17752± ±625 N/A 17752± ±101 N/A (mg COD/ L) The value of k* represents the skewness 3252

5 COD removal across the membrane The membrane itself contributed to the physical removal of soluble COD in the reactor owing to filtration as depicted in Figure 3. Based on average conditions the soluble COD (scod) removed by filtration through the membrane was 1538 mg/l (75% of 2051 mg scod/l in the reactor) during the 10-day HRT and 1383 mg/l (22% of 6286 mg scod/l in the reactor) during the 5-day HRT. Effluent COD y = x R 2 = y = x R 2 = scod in reactor 5 day 10-day Figure 3. scod removal across membrane. Oil and Grease removal The increased HRT marginally increased the removal efficiency of oil and grease from 92% to 95% corresponding to concentrations of 51 mg/l and 33 mg/l at 10 and 5 day HRT respectively (Table 2). TKN removal The ammonia-n removal efficiencies across the reactor was 69% and 79% at 5-day and 10-day HRT, corresponding to concentrations of 411 and 329 mg/l respectively. The absence of nitrifying activity was established by batch experiments on reactor sludge. Considering the high temperature of C and operational ph of 8.2, ammonia stripping contributed to a considerable portion of ammonia removal. The TKN removal across the MBR can be broken down as shown in the pie diagrams (Figure 4 (a) and (b)). Observed Yield The observed yield was calculated based on the plot of cumulative VSS production versus the cumulative COD destruction as shown in Figure 5. It can be seen that an impressively low yield of 0.03 g VSS/ g COD was observed which is only 15% of what was observed in a conventional MBR treating similar wastewater (Acharya et al., 2004). 3253

6 5-day HRT sludge wastage ammonia stripping 4(a) 10-day HRT sludge wastage ammonia stripping 4(b) Figure 4. Balance of TKN (a) at 5- day HRT (b) at 10- day HRT 4000 y = x R 2 = cumulative dvss cumulative dcod Figure 5. Yield calculation the continuous flow MBR. 3254

7 Major Findings The low observed yield of 0.03 g VSS/g COD reveals that this aerobic MBR is a potential solution to difficulties related to high sludge generation in conventional systems treating high strength wastewaters. The increase in HRT from 5-day to 10-days increased the COD and BOD 5 removal efficiency from 78% and 87% to 97% and 99% respectively. The 5-day HRT proved insufficient contact time for complete biodegradation as evident from the presence of readily biodegradable VFA in the. Despite the high removal efficiencies of contaminants ammonia stripping should not be overlooked. Acknowledgments The authors express their heartfelt gratitude to Dr. A. Bassi, CRESTech and Finnie Distributors (1997) Inc., St. Mary s, Ontario, for all co-operation and financial support. Reference: Acharya C.; Nakhla G.; Bassi A.; Kurian R.(2004) Treatment of high strength pet food wastewater using two stages membrane bioreactors. Accepted for publication in Water Environ. Res. Apr, APHA AWWA WPCF (1998) Standard Method for Examination of Water and wastewater. 20 th -ed, American Public Health Association, Washington, D.C, USA. Barr, T.A.; Taylor, J.M.; Duff, S.J.B. (1996) Effect of HRT, SRT and temperature on the performance of activated sludge reactors treating bleached kraft mill. Water Res. 30(4), Çetin, F.D.; Sürücü, G. (1990) Effects of temperature and ph on the settlability of activated sludge flocs. Water Sci. Technol. 22(9), Klatt, C. G.; Lapara, T.M. (2003) Aerobic biological treatment of synthetic municipal wastewater in membrane-coupled bioreactors. Biotechnol. Bioengineering 82(3), Lapara T.M; Alleman J. E. (1999) Thermophilic aerobic wastewater treatment. Water Res. 33(4), Lopetegui, J.; Sancho, L. (2003) Aerated thermophilic biological treatment with membrane ultrafilteration: alternative to conventional technologies treating paper mill s. Water Sci. Technol.: Water Supply 3(5-6), Rozich, A. F.; Bordacs, K. (2002) Use of thermophilic biological aerobic technology for industrial waste treatment. Water Sci. Technol. 46(4-5, 2nd World Water Congress: Wastewater Treatment and Sludge Management, 2001), Tripathi, Chandra S.; Grant Allen, D. (1999). Comparison of mesophilic and thermophilic aerobic biological treatment in sequencing batch reactors treating bleached kraft pulp mill. Water Res. 33(3),