Preliminary study of Shortcut Nitrification and Denitrification Using Immobilized of Mixed Activated Sludge and Denitrifying Sludge

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1 Available online at Procedia Environmental Sciences 11 (2011) Preliminary study of Shortcut Nitrification and Denitrification Using Immobilized of Mixed Activated Sludge and Denitrifying Sludge Yan Chen, Yingjun Wang *, Minghao Fan, Hangbiao Jin College of Resources and Environment Sichuan Agricultural University Ya an, China * Corresponding author: wwyyjj1972@163.com Abstract Biological removal of nitrogen in artificial domestic water was investigated using immobilized microbes, which were activated sludge and denitrifying sludge directly entrapped in polyvinylalcohol (PVA) gel beads in a suspended bead reactor (SBR). Immobilization was transformed into bioaugmented processes to enhance the removal ef ciency to pollutants. Optimal environment should be provided for the bioaugmented bacteria during systems start-up. In the present research, proper dissolved oxygen (DO) concentration, ph, and temperature were controled as a crucial environmental factor on the performances of the immobilized systems. Results showed that the system was efficient in CODCr removal with TN removal efficiency over 85%. This was the rst attempt to evaluate the characters of immobilized sludge system in which shortcut nitrification and denitrification occurred Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Intelligent Information 2011 Published Technology by Elsevier Application Ltd. Selection Research and/or Association. peer-review under responsibility of [name organizer] Open access under CC BY-NC-ND license. Keywords: Immobilization; Shortcut nitrification and denitrification; Polyvinylalcohol 1. Introduction The traditional nitrogen removal process normally needs two reactors have to be constructed separately for aerobic nitri cation catalyzed by autotrophs and anaerobic denitri cation by heterotrophs. Compared with it, shortcut nitrification and denitrification could occurred in one reactor, which saves the oxygen required for nitrite oxidation (25% of the total oxygen demand), 40% of the carbon demand, sludge volumes, reaction time and so on [1,2]. Immobilization of microorganism offers a promising way for the improvement of the efficiency of bioprocesss in the field of wastewater treatment. Because of simple, reliable, and stable characteristics [3], more and more research around immobilization of microbes have appeared such as desorbing and recovering Cr(VI) [4], immobilization catalyzed by ultraviolet [5], sodium sulfate being a new inducer [6] and et al. This study describes laboratory methods used to co-immobilize activated sludge and denitrifying sludge Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Intelligent Information Technology Application Research Association. Open access under CC BY-NC-ND license. doi: /j.proenv

2 1172 Yan Chen et al. / Procedia Environmental Sciences 11 (2011) in small beads and to show the performance of arti cial bioaugmented biological system. 2. Materials and methods 2.1 Activated sludge and denitrifying sludge Activated sludge was taken from the Cyclic Activated Sludge System (CASS), which was one unit of the wastewater treatment station that served the scientific research base of Sichuan agricultural university. Denitrifying sludge was cultivated using a modified method of Lichao AN in the laboratory [7]. 2.2 Immobilization method Activated sludge and denitrifying sludge were both centrifuged at 3000 r/min for 10 min, then, removed the supernatants, the rest of it was concentrated sludge (concentrated sludge was rinsed with deionized water and then centrifuged several times). Mixed two concentrated sludge according to weight ratio 1:1. Follow these steps for forming gel beads as described prevously by Lisheng ZHANG [8]. 2.3 The composition of synthetic wastewater and the determination of indicators Synthetic wastewaters used for batch experiments contained (per liter): NH4Cl, 0.20g; NaHCO3, 0.40g; Na2HPO4 12H2O, 0.04g; NaCl, 0.02g; KCl, 0.01g; MgSO4 7H2O, 0.03g and CaCl2 2H2O, 0.01g. Whereasthe concentration of glucose in the wastewater was varied greatly according the desired efficiency. Dissolved oxygen (DO), ammonium nitrogen (NH 4 + -N), nitratenitrogen (NO 3 - -N), nitrite-nitrogen (NO 2 - -N) and Chemical Oxygen Demand (COD Cr ) were determined according to the protocols in the Standard methods for the examination of water and wastewater (National Environmental Protection Agency, 2002). 2.4 Lab-scale equipment and operation mode The lab-scale device system used in the experiment was shown in Figure 1. Figure 1 Schematic diagram of the experimental setup and control(1. DO meter, 2. ph meter, 3. air pump, 4. rotameter, 5. sampling spot, 6. water bath, 7. base frame) It was made of Polyethylene terephthalate and had a total liquid volume of 2 L. The gel beads were

3 Yan Chen et al. / Procedia Environmental Sciences 11 (2011) Author name / Procedia Environmental Sciences 00 (2011) added by 8% of the effective volume of the reactor.water temperature in the reactor was routinely kept at 30± 1 with a thermostatic water bath. A cycled operating period: instant fill, 12 h aeration and rapid draw. All the wastewater in the study was sampled before the effluent of the system was stable for over 10 days continuously Results and discussion 3.1 Nitrogen removal under different DO concentration The influent profiles of NH4+-N and COD Cr concentrations were about 55mg/L and 280mg/L, separately. After 20 days of acclimation, the reactor started vigorous biodegration. DO concentration in the reactor was setted at 2.0, 4.0 and 5.5mg/L via an aeration gas rotameter. Each DO setting sustained for 7days. NH 4 + -N, NO 2 - -N and NO 3 - -N concentrations were presented in Fig. 1 for one period under different DO. Table 1 Removal rate under different dissolved oxygen DO Removal rate % Effluent mg/l mg/l TN NH + 4 -N NO - 3 -N NO - 2 -N (A) Concentration( mg / L) ammonia nitrogen nitrate nitrogen nitrite nitrogen Time(h) (B)

4 1174 Yan Chen et al. / Procedia Environmental Sciences 11 (2011) Concentration( mg/l) ammonia nitrogen (C) nitrate nitrogen nitrite nitrogen Time(h) Figure 2 Changes of NH4+-N, NO2--N and NO3--N under 2 (A), 4 (B), 5.5 (C) mg/l DO Although reports on the threshold DO concentration are not the only certainty [ 9-10 ], nitrite accumulation is to the key parameters achieved by nitrifying oganism, which are the absolute aerobic autotrophic bacteria. Compared with conventional activated sludge, the greater transfer resistance of oxygen became from gel beads, the more difficult DO penetrated into beads. When DO concentration was 2.0mg/L, only 1/4-1/3 of beads were fluidized in the reactor as well as TN and NH + 4 -N removal efficiency decreased 59.18% and 59.98% compared with beads chanced to be completely fluidized (4.0 mg/l DO). At this time accumulation of NO - 2 -N and NO - 3 -N didn t show up (Fig. 1A) because ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) propagated very slowly when DO was at a low level [9,11]. And mass transfer properties between liquid and beads were low. The optimum removal efficiency of NH + 4 -N and TN achieved 97.48% and 87.96% with 4 mg/l DO. The concentrations of NH + 4 -N obviously dropped during the whole cycle. However, NO - 2 -N and NO - 3 -N accumulated little 3 hours ago in Fig. 1B. It demonstrated nitrification and denitrification occurred concurrently in the same reactor, this process has been termed simultaneous nitrification and denitrification (SND) [12]. In the initial reaction time, the substrates were adsorbed by the surface layer of beads, where NH + 4 -N was transformed into NO - 2 -N and NO - 3 -N by the aerobic bacteria. Then, by the mass transfer, NO - 2 -N and NO - 3 -N diffused into the inner layer of beads, where denitrifying bacteria converted NO - 2 -N and NO - 3 -N into nitrogen and nitrous oxide etc rapidly. At 7 th hour the peak concentration of NO - 2 -N 14.64mg/L achieved but NO - 3 -N was detected little. Ammonia oxidation rate exceeded the rate of nitrite oxidation so that inhibited the activity and growth of nitrobacteria in nitrification. Then short nitrification and denitrification occurred. NO - 2 -N accumulation and denitrification directly from NO - 2 -N took place. When DO concentration was enhanced to 5.5 mg/l, gel beads were in drastic fluidized condition and NH + 4 -N and TN removal rate didn t increased but declined. It just may be that excess aeration promoted DO to penetrate into the inner layer and shrinked anoxic micro-environment of beads, inhibiting denitrification. Even at the end of cycled period, NO - 2 -N and NO - 3 -N concentration surpassed NH + 4 -N. 3.2 Effect of CODCr on nitrification and denitrification

5 Yan Chen et al. / Procedia Environmental Sciences 11 (2011) Nitrite concentration( mg /L) mg/L 300mg/L 450mg/L 600mg/L 750mg/L Time(h) Figure 3 Effect of influent CODCr on the variation of NO2--N Fig.3 showed that NO 2 - -N changed during one cycled period under 6 kinds of influent COD Cr concentration. Effluent NO 2 - -N content increased from 14.85mg / L down to 1.32mg / L along with 150 to 750mg/L COD Cr. When the influent COD Cr is 150mg/L, accumulation of NO 2 - -N reached peak value 21.78mg/L at 5 th hour, which looked like a steeple. The maximum value of other curves rised aroud 7 th hour, which were congruent with the above observations under different DO(Fig. 2). It was probable that when influent COD Cr became 700mg/L, the curve is smooth and NO 2 - -N didn t accumulatied during the cycled period. With the decrease of C/N ratio, concentration of free ammonia was relatively higher and effect growth of AOB and NOB, while NOB were more vulnerable [13]. With the increase of influent COD Cr, the removal efficiency of TN increased from 73.66% to 91.03%, but the removal rate enhanced only 5.76% along with increase of influent COD Cr from 300 to 750mg/L. In this study COD Cr concentration threshold was about 300 mg/l, which didn t only ensure carbon source enough but also accumulated NO 2 - -N in favor of short nitrification and denitrification. 3.3 Effect on removal rate by temperature The operational parameters were same except temperature that was set at 30, 25 and 20.Results were showed in Table 2. Table 2 Removal rate under different dissolved oxygen temperature Removal rate % Effluent mg/l TN NH + 4 -N NO - 3 -N NO - 2 -N The bioaumgent system fulfilled the shortcut nitrification and denitrification when temperature was 25 and 30. Effluent NO - 3 -N did not significantly increase along with increment of NO - 2 -N, which accouted more than 90% of the total of NO - 2 -N and NO - 3 -N. When 20 was a low temperature, the TN and NH + 4 -N removal rate decreased by 18.34% and 43.02%. In generally, the optimum growth temperature of AOB and NOB are different. And shortcut nitrification and denitrification need higher appropriate temperature (30-35 ), which restrain NOB but AOB, to occurred [14]. On the other aspect higher ph also repress NOB as well as temperature [11],

6 1176 Yan Chen et al. / Procedia Environmental Sciences 11 (2011) which was a probable reason to promote shortcut nitrification and denitrification at Conclusions The new bioaugment immobilized systems had the function of both aerobic and anoxic system and had potential in new approaches to biologically remove nitrogen from wastewat. It could be inferred that SND and shortcut nitrification and denitrification in artificial beads were responsible for the nitrogen removal. 5. Acknowledgements This study was supported by the Key Project of Education Department in Sichuan Province (10ZA059) and State-level Plan for Innovation of Students of Sichuan Agricultural University ( ). References [1] P. Zheng, X. Xu, B. Hu, New theory and technology of biological nitrogen removal, Beijing: Science Press, pp , [2] G. Zhu, Z. Peng, H. Guo, Biological nitrogen removal with nitrification and denitrification via nitrite pathway, Journal of Harbin Institute of Technology, vol. 40, pp [3] J. Rungrod, K. Konstantinos, K. Eakalak, Immobilized cell augmented activated sludge process for enhanced nitrogen removal from wastewater, Water Environment Research, vol. 79,pp ,2007. [4] H.Li, T. Liu, Z. Li, et al, Low-cost supports used to immobilize fungi and reliable technique for removal hexavalent chromium in wastewater, Bioresource Technology, vol. 99, pp , [5] Z. Qiao, Z. Liu, Z. Liu, et al, Immobilization of activated sludge in poly(ethylene glycol) by UV technology and its application in micro-polluted wastewater, Biochemical Engineering Journal, vol. 50,pp , [6] T. Takei, K. Ikeda, H. Ijima, et al, Fabrication of poly(vinyl alcohol) hydrogel beads crosslinked using sodium sulfate for microorganism immobilization, Process Biochemistry, In Press. [7] L. C. An, J. Sun, T. Xue, et al, Study on single-stage biological nitrogen removal technique by co-immbolized microorganisms, Pollution Control Technology, vol. 16, pp. 5-7, [8] L. Zhang, W. Wu, J. Wang, Immobilization of activated sludge using improved polyvinyl alcohol (PVA) gel, Journal of Environmental Sciences, vol. 19, pp , [9] K. Hanaki, Nitrification at low levels of dissolved oxygen with and without organic loading in a suspended growth reactor, Water Res, vol. 24, pp , [10] G. Ruiz, D. Jeison, R. Chamy, Nitrification with high nitrite accumulation for the treatment of wastewater with high ammonia concentration, Water Res, vol. 37, pp , [11] H. J. Laanbroek, S. Gerards, Competition for limiting amounts of oxygen between nitrosomanas europaea and nitrobacteria winogradskyi grown in mixed continuous cultures, Arch Microbiology, vol.159, pp , [12] K. Pochana, J. Keller, P. Lant, Model development for simultaneous nitrification and denitrification, Water Sci. Tech, vol. 39, pp , [13] P. Sun, Y. Zhang, X. Quan, Process control of simultaneous shortcut nitrification and denitrification in a sequencing batch moving bed biofilm reactor (SBMBBR), Acta Scientiae Circumstantiae, vol. 28, pp , [14] K. A. Third, B. Gibbs, M. Newland, Long-term aeration management for improved N-removal via SND in a sequencig batch reactor, Water Res, vol. 31, pp.3523, 2005.