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ARTICLE IN PRESS Water Research 38 (2004) 3340-3348 Integrated real-time control strategy for nitrogen removal in swine wastewater treatment using sequencing batch reactors Ju-Hyun Kima,*, Meixue Chenb, Naohiro Kishidac, Ryuichi Sudoa a Center for Environmental Science in Saitama, 914, Kamitanadare, Kisai, Saitama 347-0115, Japan b State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P.O. Box 2871, China c Department of Environmental Resources Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 1698555, Japan Received 7 May 2003; received in revised form 29 March 2004; accepted 11 May 2004 Abstract A new integrated real-time control system was designed and operated with fluctuating influent loads for swine wastewater treatment. The system was operated with automatic addition control of an external carbon source, using real-time control technology, which utilized the oxidation-reduction potential (ORP) and the pH as parameters to control the anoxic phase and oxic phase, respectively. The fluctuations in swine wastewater concentration are extreme; an influent with a low C=N ratio is deficient in organic carbon, and a low carbon source level can limit the overall biological denitrification process. Consequently, a sufficient organic source must be provided for proper denitrification. The feasibility of using swine waste as an external carbon source for enhanced biological nitrogen removal was investigated. The real-time control made it possible to optimize the quantity of swine waste added as the load fluctuated from cycle to cycle. The average removal efficiencies achieved for TOC and nitrogen were over 94% and 96%, respectively, using the integrated real-time control strategy. r 2004 Elsevier Ltd. All rights reserved. Keywords: Denitrification; External carbon source; ORP Real-time control; SBR; Swine wastewater1. IntroductionSwine wastewater has previously been considered as one of the major sources of nitrogen pollution dis-charged into the environment. Traditional biological removal of nitrogen was achieved by a sequence of nitrification and denitrification processes. Since the fluctuations in swine wastewater concentration are extreme due to the varying practices of manure manage-ment, in recent years, the real-time control process using oxidation-reduction potential (ORP) and/or pH as parameters (Lo et al., 1994; Plisson-Saune et al., 1996;*Corresponding author. Tel.: +81-480-73-8369; fax: +81-480-70-2031.E-mail address: a1098356pref.saitama.jp (J.-H. Kim).Chapentier et al., 1998; Fuerhacker et al., 2000) to control the oxic and anoxic cycles of a system has received much attention for swine wastewater treatment (Ra et al., 1998, 1999; Tilche et al., 2001) in sequencing batch reactors (SBRs). Compared to the traditional process, real-time control strategy for a batch treatment process using ORP and/or pH was self-adjusted to various treatment conditions such as influent strength and treatment status. This resulted in flexible hydraulic retention time (HRT) from cycle to cycle (Ra et al., 2000). The high and stable removal rate of nitrogen was also achieved (Ra et al., 1998; Cheng et al., 2000).Although real-time control strategy based on ORP and/or pH has been applied to many swine wastewater treatment systems, until now, the success of the systems has not been convincing because much effort in the 0043-1354/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2004.05.006 ARTICLE IN PRESS J.-H. Kim et al. / Water Research 38 (2004) 3340-33483341studies has dealt primary with the typical ORP and/or pH profiles of a complete nitrification and denitrification cycle and focused on aeration control (Ra et al., 1998; Cheng et al., 2000). In fact, the control set-points on the ORP or pH profiles would not have appeared in the acclimated nitrate sludge (Kim and Hao, 2001; Kishida et al., 2003).Biological denitrification is known to occur by the action of heterotrophic bacteria using available carbon sources (John and Robert, 1985; Lee et al., 1995, 1997). Because the influent with a low C=N ratio is deficient in organic carbon and the low carbon source level can limit the overall biological denitrification process, sufficient organic source must be provided for proper denitrifica-tion. Using the fermented swine waste (Lee et al., 1997) or activated sludge (Ra et al., 2000) as an electron donor for denitrification in SBRs has been suggested by several authors, and such external carbon sources are viable choices for enhancing SBR performance. However, any excess external carbon added over the amount required for the process appears in the effluent, and results in increased cost of operation. Therefore, the addition of the external carbon source should be optimized with the fluctuation of wastewater.The specific objective of this study was to establish an integrated swine wastewater treatment system and operating strategies suitable for the fluctuations of influent loads. Particularly, under low C=N load cycles, the system can optimize the addition of the external carbon source to enhance nitrogen removal, as well as toRelay box (On/ Off)efficiently remove the pollutants from wastewater. For this purpose, swine waste as external carbon source for denitrification of nitrate was examined, and a pulsed pattern of addition was determined. In addition, ORP and pH as practical real-time control parameters were evaluated. The SBR with an integrated strategy of real-time control and a pulsed input control of swine waste were designed and continuously operated for swine wastewater treatment.2. Methods2.1. Sequencing batch reactor and operating strategiesThe SBR was operated as shown in Fig. 1. The water temperature was maintained at 2372 C. The reactor was constructed using Plexiglas and had a working volume of 9 L. A mechanical agitator was installed in it for complete mixing. Air (2.4 L/min) for the reactor was provided by an aerator through an air stone placed at the bottom of the reactor. The reactor had five sequences: influent feeding, anoxic phase, oxic phase, sludge settling, and effluent transfer. The anoxic and oxic times were automatically controlled by the compu-ter depending on the variable process, while the times of influent feeding, sludge settling and effluent decanting were fixed at 5, 55 and 5 min, respectively. For every cycle, 0.3 L of the influent wastewater was fed into the reactor.PCI/O PC CardMonitoring the time variations of ORP and pHEffluent InfluentSwine waste ORP probe pH probe DO probeAirSBREffluent bucketAeratorAir stoneFig. 1. Schematic diagram of a single batch sequencing reactor with real-time control strategy. ARTICLE IN PRESS 3342J.-H. Kim et al. / Water Research 38 (2004) 3340-3348The ORP, pH and DO probes were inserted into the SBR. The output signal was directed to a computer. The influent pump, effluent pump, aerator, agitator and swine waste pump were controlled by a relay box connected by electrical cable.Our experiment was started with high C=N ratio load (TOC/TN1.5) influent, which was collected after screening treatment. After one week of operation, the fluctuating influent was continuously used for 8 months in our experiment. Swine waste as an external carbon source was added into the SBR for complete denitrifica-tion after a time determined by our experiment if there was insufficient carbon source in the influent.For the purpose of easy automatic control, a pulsed input pattern of swine waste was used to compensate for the external carbon source. During low C=N load influent cycles, the diluted swine waste was pumped into the SBR by a pulse-metering pump with a pulse of 1 g/ cycle, and the time interval between additions was designed to be 10 min. If the quantity of swine waste added was deficient for complete denitrification, the next addition cycle was started, and when the nitrate knee point, which indicates the end of denitrification, appeared on the ORP profile, the addition of swine waste was stopped. Therefore, the quantity of swine waste added adapted to fluctuations in the wastewater, and the optimization was easily achieved by the pulsed input pattern.2.2. Influent swine wastewater, waste and seed sludgeThe swine wastewater used in this study was obtained from a local farm in Saitama, Japan. The practical swine wastewater with high C=N ratio (TOC/TN ratio: more than 1.2) and low C=N ratio (TOC/TN ratio: less than0.8), which was obtained before and after coagulation treatment, respectively, was used alternately in the experiment. The C=N ratio of the raw wastewater was markedly changed by the separation of feces and urine. The TOC/TN ratio in the wastewater was varied in the range of 0.45-1.53. The swine wastewater was stored at4 Cuntil required.The swine waste was obtained from the same farm. Prior to use, the waste was screened using a sieve with0.5 mm mesh openings to remove large solids, diluted with tap water, and then used as an external carbon source in low C=N ratio load periods for complete denitrification. The characteristics of the diluted swine waste are listed in Table 1.The average concentration of mixed liquor suspended solids (MLSS) in the system was maintained at approximately 7000 mg L 1. When the concentration of MLSS in the reactor was more than 8000 mg L 1, sludge was drawn out. During the experiment period, the average SRT was 32 days.Table 1Characteristics of the diluted swine wasteParametersMeanMin-maxStd. dev.mg L 1(n 15)TOC26,16711,410-55,64017,010BOD590,28046,370-172,20031,850TN45292418-68821741TP26001500-3810821TSS917240-395043,7202.3. Sampling and analytical methodsParameters routinely assayed included TOC, BOD5, total nitrogen (TN), NH4-N, NO3-N, NO2-N, total phosphorous (TP), PO4-P, MLSS, mixed liquor volatile suspended solids (MLVSS), and total suspended solids (TSS). Track analysis that covered the entire cycle was carried out at high and low C=N ratio load. Mixed-liquor samples were taken during track analysis. Analysis for NH4-N, NO3-N and NO2-N was carried out for each track study. Analysis for BOD5, TSS, MLSS and MLVSS was performed in accordance with the standard method (APHA, 1995). The NH4-N, NO3-N, NO2-N and PO4-P were analyzed with an ion chromatograph (Yokogawa IC 7000). The TOC was analyzed with a Shimadzu total organic carbon analyzer (TOC 5000). TN and TP were analyzed with a total nitrogen/phosphorous analyzer (TN-30, TP-30, Mitsu-bishi Chemical Corp.)3. Results and discussion3.1. Real-time control point in high C/N ratio load cyclesIn high C=N ratio load cycles, with real-time control technology using ORP and pH as anoxic and oxic control parameters, a treatment process can be operated effectively without the addition of an external carbon source to enhance the denitrification. During the initial period with the high C=N ratio load influent relative constant final effluents were obtained along with high nutrient removal. The typical control set-points are shown in Fig. 2. Point A is the feeding point, and after5 min the anoxic phase was started. From the nutrient profile, it can be seen that NO3-N is completely denitrified to nitrogen gas through NO2-N within75 min, using the influent organic materials as a carbon source. Point B is known as the nitrate knee in the ORP curve, which represents the complete removal of nitrate. Reportedly, sulfate reduction that produces sulfides starts just after denitrification is complete, and causes this sudden decrease in the ORP (Plisson-Saune et al., 1996). Point C signifies the beginning of the oxic phase. ARTICLE IN PRESSInfluent2520151058.18.0J.-H. Kim et al. / Water Research 38 (2004) 3340-3348Anoxic phaseOxic phaseNH4-N NO2-N NO3-Nd3343150100507.9A7.8B7.77.67.5pHORP7.47.30255075100125150cC175200225Time (min)e250275300325f3500-50-100-150-200-250-300-350375400 Fig. 2.Real-time control points in high C=N ration load cycles (TOC/TN ratio of the influent: 1.4) A: Feeding, B: Nitrate knee point,C and c: Beginning of the oxic phase, e: Ammonia valley point, f: End of the oxic phase.The initial rise on the pH curve (from c point to d point) is caused by carbon dioxide stripping from the system and the rapid consumption of VFA that is produced during the anoxic phase (Ra et al., 1998). Under oxic condition, NH4-N decreases with time. Nitrate concen-tration increases with time as ammonia is converted through nitrification. The decrease in pH is caused by the removal of ammonia from the system. Point e represents the end of nitrification and it is known as the ammonia valley. During nitrification, NH4-N is con-verted into NO3-N, as shown in Eqs. (1) and (2) (EPA, 1975).55NH4 76O2 109HCO3-C5H7NO2 54NO2 57H2O 104H2CO31400NO2 NH4 4H2CO3 HCO3 195O2-C5H7NO2 3H2O 400NO32Alkalinity is required in the ammonia-nitrate oxida-tion process (7.14 mg of alkalinity as CaCO3 to 1 mg of ammonia-N). The reduction of alkalinity and the acid production during nitrification decrease the pH. The complete removal of ammonia indicates the end of alkalinity consumption in the wastewater, hence the end of further pH decrease.3.2. Real-time control point in low C/N ratio load cyclesThe designation of a control point in low C=N ratio load cycles was very important for integrated real-time control strategy. The track analysis with low C=N load influent is shown in Fig. 3. Point A is the beginning of the anoxic phase. From the nutrient profile, it can be seen that NO3-N that is produced from nitrification during the previous oxic phase is slowly denitrified using the carbon source provided by the feed. After 2 h, complete denitrification was not reached due to insuffi-mpHORP (mV)Concentration (mgl-1) ARTICLE IN PRESS33442520151058.18.07.9J.-H. Kim et al. / Water Research 38 (2004) 3340-3348InfluentAnoxic phaseOxic phaseNH4-N NO3-N NO2-NS150c100A507.8Swine waste additionBf0-50 7.7S-1007.6e-1507.5pH-200ORP7.4C-2507.3-300025507597122147 172 197 222 247272 297322347 372 397Time (min)Fig. 3.Real-time control points in low C=N ratio load cycles (TOC/TN ratio of the influent: 0.7) A: Feeding, B: Nitrate knee point, Cand c: Beginning of the oxic phase, e: Ammonia valley point, f: End of the oxic phase, S: Beginning of the swine waste addition.cient carbon source provided by the influent, and at point S, the addition of swine waste was started. The NO3-N is gradually denitrified using swine waste with every pulsed addition, and the denitrification rate rapidly increases. Ten minutes after the first addition of swine waste, the concentration of NO3-N in the reactor decreased from 11.7 to 9.6 mg L 1. The complete denitrification was not reached, and the second addition of swine waste was started. The program was cycled to provide external carbon source for complete denitrifica-tion. After the third addition of swine waste, the concentration of nitrate was decreased to zero, and an abrupt change in the slope of the ORP curve was appeared at point B, denoting the complete disappear-ance of the NOx-N through denitrification in the anoxic phase. Until point B, the program of swine waste addition was stopped automatically. Integrated strategy of real-time control with pulsed input control of theswine waste based on the nitrate breakpoint that occurred in the ORP-time profile enables the optimiza-tion of swine waste addition. Point C signifies the beginning of the oxic phase. The d point apparently did not appear because insufficient carbon dioxide and VFA were produced in the anoxic phase due to low C=N ratio influent. Under oxic conditions, NH4-N decreases with time. Nitrate concentration increases with time as ammonia is converted through nitrification. The de-crease in pH is caused by the removal of ammonia from the system, as ammonia is strongly related to alkalinity of the wastewater. Point e represents the end of nitrification and it is known as the ammonia valley. The complete removal of ammonia indicates that the alkalinity consumption in the wastewater has stopped, hence the end of further pH decrease. The rise in pH beyond point e might be caused by air stripping of carbon dioxide (Chen et al., 2002). pHORP (mV)Concentr