WEF/IWA Biofilm Reactor Technology Conference 2010
Aerobic granulation in sequencing batch reactors fed with both, municipal and synthetic wastewater T. Rocktäschel1, C. Klarmann1, J.C. Ochoa2, S. Deleris,2 , K. Sörensen2, H. Horn1 1
Institute of Water Quality Control, Technische Universität München, Am Coulombwall, 85748 Garching, Germany, (E-mail:
[email protected],
[email protected],
[email protected]) 2 Veolia Environment, Anjou Recherché, Chemin de la Digue – BP 76, 78603 Maison Lafite-cedex (E-mail:
[email protected],
[email protected],
[email protected])
ABSTRACT The aim of this work was to cultivate aerobic granules fed with both synthetic wastewater (R1) and a mixture of municipal and artificial waste water (R2) in laboratory scale sequencing batch (SBR) reactors. In both reactors the organic loading rate (OLR) was kept at a maximum value of 3.3kg/(m³*d) and a completely granulated sludge bed could be achieved within the first two month of operation. However R1 showed much slower biomass growth compared to R2, which can be related to the higher amount of non easy degradable substrate (municipal wastewater). Thus stable granules could be achieved after 200days of operation for R1 compared to R2 where a steady state was not achieved within the entire operation period. Besides granules cultivated in R1 achieved higher removal rates with respect to carbon and nitrogen compared to the granules of R2. Keywords: aerobic granulation, municipal wastewater, sequencing batch reactor, substrate composition
INTRODUCTION The aerobic granulation process can be seen as one of the main innovations for biological wastewater treatment within the last ten years. For this special case of fluidized biofilm without the addition of carrier materials, several main benefits in comparison to the activated sludge process can be pointed out. On the one hand, due to a high biomass concentration, high specific removal utilization rates can be achieved (Belmonte et al. 2009; de Bruin et al. 2004). If this fact is considered with the benefit of significantly higher settling velocities (Qin et al. 2004) the advantage in comparison to the conventional activated sludge process becomes clearer. In addition to that, because of aerobic and anoxic zones within the granule, the enhanced nitrogen removal can be realized simultaneously (Wan and Sperandio 2009). Most of the current studies deal with aerobic granules cultivated with synthetic or industrial wastewater as carbon sources. Besides, commonly activated sludge is used as inoculum for the cultivation of aerobic granules. The present report deals with municipal and artificial wastewater as an influent mix for cultivating aerobic granules.
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WEF/IWA Biofilm Reactor Technology Conference 2010
METHODS Reactor and inoculum Two columns (height of 100 cm and a diameter of 9 cm) with a total operation volume of 5 l were operated as sequencing batch reactors with a total cycle length of 4h. Each cycle consists of 4 phases namely: filling (3 min), aeration (230 min), settling (2 min) and effluent withdrawal (5 min). For implementing a high selection force and in order to wash out filamentous organisms, the settling time was stepwise reduced from 8 to 2 min. The sequence and duration of each cycle were pre-programmed in an electronic process controller. The effluent has been discharged from the middle port of each reactor which results in a volumetric exchange ratio of 50%. Fine air bubbles for aeration were supplied through a dispenser at the reactor bottom with an airflow rate from Q = 300l/h which resulted in a gas velocity between of 1.3cm/s. Both reactors (R1 and R2) were inoculated with activated sludge and otherwise operated similar except to the composition of the influent wastewater. While R2 was operated with sodium acetate as only carbon source the influent composition of R1 consisted of a fifty percent volume mix of pretreated municipal wastewater and synthetic wastewater.
Media In this study, a mixture of pretreated municipal wastewater from a near municipal wastewater treatment plant and a synthetic wastewater with the following composition were used: CH3COONa (2058mg/l)/ C6H12O6 (1.390mg/l), NH4Cl (134-229mg/l), K2HPO4*3H2O (44mg/l), FeSO4*7H2O (8mg/l), MgSO4*7H2O (10mg/l), CaCl2*2H2O (12mg/l). The media was supplemented with the subsequent composition of micronutrients (ml/l): H3BO3 (100mg/l) CoCl2*6H2O (100mg/l) CuSO4*5H2O (30mg/l) FeCl3*6H2O (1000mg/l), MnCl2*2H2O (110mg/l), Na2Mo7O24*2H2O (70mg/l) ZnSO4*7H2O (100mg/l) KI NiCl2 (60mg/l). Due to fluctuating concentrations of the municipal wastewater the influent concentrations for R1 ranged between 800 and 1,100mgCOD/l and 2.4 and 3.3 kgCOD/(m³*d), respectively and was kept constant for R2 at 3.3 kgCOD/(m³*d).
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WEF/IWA Biofilm Reactor Technology Conference 2010
RESULTS Granule distribution and biomass concentration Figure 1 and Figure 2 present the granule distribution of reactors R1 and R2. In both reactors the first granules appeared within the 2nd week of operation. A granulated sludge bed could be achieved after 55 days (R1) and 49 days (R2), respectively. The granule evolution of R1 shows a steady increase of granular growth throughout the entire experimental phase. After an operation period of approximately 200days the size remains at a stable level (average diameter around 1.8mm) for the remaining operation time. Compared to that the biomass of R2 (see Figure 2) grows in much faster rates and granules with an average diameter of 2.2mm appeared at the end of the operation period. A steady state like for R1 was not achieved. In comparison to R1 the biomass growth was much slower than in R2 (see also the biomass evolution [gTS/l] in Figure 3. The analogous increase of the average diameter and total solid (TS) concentration on the one hand and the decrease of granule number on the other hand is an indicator for higher compactness of the granule during the operation for both reactors. However higher ranges of granule diameters to the total amount of granules by volume in different reactors shows higher biomass concentration within the biofilm. At the end of the operation period (300days) the biomass for an average granule was approximately 0.15 mgTS for granules out of R1 but 1mgTS for those of R2.
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Figure 1: granule distribution R1 (mixed influent composed out of a mix of municipal and artificial wastewater)
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WEF/IWA Biofilm Reactor Technology Conference 2010
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Figure 2: granule distribution R2 (influent of artificial wastewater)
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Figure 3: development of biomass concentration for reactor R1 and R2 Copyright ©2010 Water Environment Federation. All Rights Reserved.
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WEF/IWA Biofilm Reactor Technology Conference 2010
Carbon removal Figure 4 presents the specific COD removal rates per biomass of reactor R1 and R2 for the entire operation period. The variation in the removal rates for reactor R1 is caused by the COD influent fluctuation of municipal wastewater. In summary the COD removal of reactor R1 achieved comparable values to those of reactor two. The removal rates of aerobic granules grown on easy degradable (sodium acetate) substrates are in a range of 0.2 gCOD/(gTS*d) while with a more complex substrate (municipal wastewater) higher rates in a range of 0.4 gCOD/(gTS*d) could be achieved.
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time [days]
Figure 4: carbon removal; rCOD [∆COD/(gTS*d)] of reactor R1 and R2
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Nitrogen removal
The average sludge age for R2 is 22days and nearly twice as high as for R1 (11days). Thereby the granules in R2 are more compact (see Figure 1 and Figure 2). However the higher standard deviation of the sludge age of 6.5days for R2 compared to 2.2days of R1 is an indication for a more inhomogeneous biomass growth in R2. This is also underlined by a variation of the biomass concentration which is shown in Figure 3. It can be assumed that the more homogenous growth in R1 lead to a more stable nitrification which is shown by the higher nitrification rates (see Figure 5) for R1. The nitrogen incorporation into biomass has been considered by assuming 5% nitrogen in the formed heterotrophic biomass. The variation of the nitrogen removal for R1 can again be explained by the fluctuating ammonium influent concentrations of the municipal wastewater. The average ammonium influent concentrations for the reactors were measured with 48mg/l for R1 and 45 mg/l for R2, respectively. It took 81days for R2 and 95 days for R1 to achieve nearly complete nitrification.
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Figure 5: nitrification; rNH4-N [∆NH4-N/(gTS*d)]of reactor R1 and R2
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REFERENCES Belmonte M, Vázquez-Padín JR, Figueroa M, Franco A, Mosquera-Corral A, Campos JL, Méndez R. 2009. Characteristics of nitrifying granules developed in an air pulsing SBR. Process Biochemistry 44(5):602-606. de Bruin LM, de Kreuk MK, van der Roest HF, Uijterlinde C, van Loosdrecht MC. 2004. Aerobic granular sludge technology: an alternative to activated sludge? Water Sci Technol 49(11-12):1-7. Qin L, Tay J-H, Liu Y. 2004. Selection pressure is a driving force of aerobic granulation in sequencing batch reactors. Process Biochemistry 39(5):579-584. Wan J, Sperandio M. 2009. Possible role of denitrification on aerobic granular sludge formation in sequencing batch reactor. Chemosphere.
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