Investigation of bio-augmentation of overloaded activated sludge plant operation by computer simulation

Accepted Manuscript Title: Investigation of Bio-Augmentation of Overloaded Activated Sludge Plant Operation by Computer Simulation Author: Hadieh Roohian Nasir Mehranbod PII: DOI: Reference:

S0098-1354(17)30157-6 http://dx.doi.org/doi:10.1016/j.compchemeng.2017.04.004 CACE 5778

To appear in:

Computers and Chemical Engineering

Received date: Revised date: Accepted date:

17-8-2016 30-3-2017 1-4-2017

Please cite this article as: Roohian, H., and Mehranbod, N.,Investigation of Bio-Augmentation of Overloaded Activated Sludge Plant Operation by Computer Simulation, Computers and Chemical Engineering (2017), http://dx.doi.org/10.1016/j.compchemeng.2017.04.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Investigation of Bio-Augmentation of Overloaded Activated Sludge Plant Operation by Computer Simulation

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Hadieh Roohian, Nasir Mehranbod*

Department of Chemical Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz, Iran *

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Corresponding author: Department of Chemical Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz 71345, Iran. E-mail addresses: [email protected]

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Abstract. Based on the essential role of nitrifiers in nitrification process, bio-augmentation of

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nitrifiers in activated sludge process via two configurations is proposed to improve nutrient removal under overloaded conditions. In the first configuration a bio-augmentation batch enhanced reactor was applied to activated sludge. To improve nitrogen removal in overloaded plant, side-stream bio-augmented sequential batch reactor was examined as the second configuration. The simulation of overloaded plant without additional aeration tanks as base-case was performed by ASM1 model. The operation of bio-augmentation configurations and overloaded plant with additional aeration tanks were also simulated. The results reveal that nitrification efficiency can be improved up to 88% under 30% overloading condition compared to the base-case by applying the second configuration to the overloaded plant. Second configuration shows a significant potential for nitrification improvement as a result of N-load reduction compared to the main process as well as augmentation of the endogenous nitrifiers.

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Keywords: Bio-augmentation, Nitrification, Autotrophic nitrifiers, Simulation, ASM models, Overloaded wastewater treatment plant.

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Additional Oxygen Uptake (%) Additional Reactor Volume (%) Biological Oxygen Demand (mg/l) Chemical Oxygen Demand (mg/l) Hydraulic Retention Time (h) Nitrification Efficiency (%) Nitrification Efficiency Improvement (%) Kjeldahl nitrogen (mg/l) Ammonium concentration(mg/l) Overloading percentage (%) Return Activated Sludge Reactor Volume (m3) Reject Water Solid Retention Time (d) Nitrogen gas concentration (mg/l)

SNH4

Ammonium nitrogen concentration (mg/l)

SNO2

Nitrite nitrogen concentration (mg/l)

SNO3

Nitrate nitrogen concentration (mg/l)

SO2 SS X NH 4

Dissolved Oxygen concentration (mg/l) Readily biodegradable COD concentration(mg/l) Soluble Inert COD concentration(mg/l) Ammonia oxidizers concentration (mg/l)

X NO2

Nitrite oxidizers concentration (mg/l)

XH

Heterotrophs concentration (mg/l)

XI XS

WAS

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Nomenclature AOU ARV BOD COD HRT NE NEI N-kj NH4 OL RAS RV RW SRT SN2

Inert suspended COD concentration (mg/l) Slowly biodegradable COD concentration(mg/l) Waste Activated Sludge

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1. Introduction

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Nutrient removal from wastewater is a vital factor to prevent eutrophication and to provide environmental sustainability. The activated sludge process is one of the most widespread biological treatments for nutrient removal from municipal and industrial wastewaters. Different modifications have been suggested for the conventional activated sludge over time to comply strict effluent standards for Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), nitrogen and phosphorus. More stringent standard has been legislated for allowable effluent nutrient concentration as a result of global environmental issues. On the other hand, urban development and rising population result in new challenges such as higher volumes of wastewater generation and therefore overloaded wastewater treatment plants. Overloading is either hydraulic or organic. The former is caused by an increase in the feeding flow rate and the latter is due to an increase in the organic matter content of the same feeding flow rate (Regueiro et al., 2015). Therefore, wastewater treatment plants upgrading will be required to handle increased hydraulic and organic loadings in order to meet existing effluent quality or to meet higher treatment requirements. It is substantial to consider urban land high cost and limitations for upgrading of the overloaded activated sludge plant (Andreottola et al., 2003). Aeration cost is another issue to be considered in upgrading of wastewater treatment plants.

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Aeration is an essential process in biological wastewater treatment plants and accounts for the largest fraction of plant energy expenditure, ranging from 45-75% of it (Longo et al., 2016). Therefore, it is essential to consider process energy expenses for wastewater treatment plants upgrading. As mentioned in the literature, specific energy consumption in the conventional activated sludge processes is in the range of 0.3-0.6 kWh/m3 of treated domestic wastewater with an average of 0.45 kWh/m3 (Gu et al., 2017). Meanwhile, processes with alternative phases of aeration and feed batch processes, such as Sequential Batch Reactor (SBR) can reduce energy consumption due to the customized aeration configuration. Specific energy consumption for SBRs is reported in the range of 0.19- 0.39 kWh/m3 and thus it can save up to 60% of expenses (Li et al., 2016; Longo et al., 2016; Vera et al., 2013). Mathematical modeling has been used extensively in industrial applications for the purpose of process design, process intensification and devising new effective process control strategies (Van Hulle and Ciocci, 2013). Thus, mathematical modeling can be a time and cost-saving tool for evaluation of new treatment concepts and can be used to substantially decrease the time and costs of scaling-up new processes. Similarly, in wastewater treatment industries, mathematical modeling helps for identification of optimal or near optimal a) design configuration such as sizing and arrangement of reactors, b) operating conditions such as sludge age and sludge recycle ratio (Henze et al., 2000). It is a long time that there has been a significant increase of the interest in modeling and simulation of wastewater treatment plants (Van Hulle and Ciocci, 2013). Essential role of bacteria in the conversion of organic compounds and nutrient removal explains the necessity of having an accurate biological model as part of process model. This necessity has gained attention of researchers to investigate microbial conversion models which are necessary 4

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tools to better understand the complex nutrient removal systems (Moussa et al., 2005). Since 1987, the most applied and reliable model developed to describe biological degradation processes in the activated sludge plants is Activated Sludge Models (ASM) that have been made more comprehensive over years. The ASM1 is the first version which is a structured model based on Monod kinetics describing organic carbon and nitrogen compounds removal under aerobic and anoxic conditions. Thus far, the ASM1 has been applied as a reliable reference in most of the scientific and practical studies and also executed in commercial software for dynamic modeling and simulation of municipal activated sludge wastewater treatment plants (Gernaey et al., 2004). ASM1 was extended by including biological phosphorus removal processes in the ASM2 and ASM2d, consist denitrifying Phosphorus-Accumulating Organisms (PAOs). Finally, in 1998 a new modeling platform, the ASM3, was developed in order to create a sound basis for use in the next of activated sludge models that will rely on metabolism of microorganisms. ASM3 was the result of applying modifications to ASM1 to correct the deficiencies of it, though it describes the same phenomena as does ASM1. The role of storage of organic substrates is introduced in ASM3 and also the death-regeneration process for heterotrophic organisms in ASM1 is replaced by an endogenous respiration process in ASM3. The most important modification introduced in ASM3 is inclusion of different oxygen consumption rates that facilitates model calibration (Van Loosdrecht et al., 2015). Activated sludge processes that handle high load of nitrificationdenitrification with relatively short anoxic residence time is one of the cases for which modeling by ASM3 is recommended. Other cases include those involve supporting selector, step-feed operation, and industrial wastewater with significant storage of readily biodegradable substrate. For an activated sludge process under operating conditions that does not match any of these cases, ASM1 is mentioned to be an equally effective model as ASM3 (Van Loosdrecht et al., 2015). A survey is also performed in order to obtain an estimate of the ASM models potential application. The yearly number of publications referring to each model revealed that ASM1 is the most used model, followed by ASM3, ASM2 and ASM2d (Van Loosdrecht et al., 2015). Review of recent open literature publications on activated sludge modeling is also showing that ASM1 has been used more often than ASM3. All ASM models include biomass concentrations of different microorganisms as state variables. This indicates the importance of biomass concentrations in treatment performance of biological systems and thus keeping it as close as possible to optimum conditions is of great interest (Gernaey et al., 2004; Henze et al., 2000). Bacterial augmentation or bio-augmentation describes the direct addition of a specific biomass in order to rectify certain biological properties of a particular ecosystem. Bio-augmentation can promote performance of biological systems especially when it is implemented for slow-growing bacteria that are required in the system. Autotrophic nitrifiers have slow growth rate and are extremely sensitive to several environmental and operating conditions. It has been shown that bio-augmentation of nitrifiers is a cost-effective technique to enhance nitrogen removal efficiency under specific Solid Retention Time (SRT) and to prevent wash out phenomena (Leu and Stenstrom, 2010; Zhou et al., 2014). Rittmann and Whiteman (1994) introduced bioaugmentation with nitrifying bacteria as a tool to relieve serious and long-term water-quality violations. They initiated a bio-augmentation plan for a municipal wastewater treatment plant as a trial to test the effluent ammonium during winter conditions. They concluded the application of fully integrated bio-augmentation with rational analysis and design of the biological process can 5

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play an important role in improving process performance (Rittmann and Whiteman, 1994). Reject Water (RW) is the supernatant from the dewatering stage of sludge treatment which is usually recycled to the head of the wastewater treatment process. The RW flow is relatively small, around 2% of the activated sludge plant influent, and contains low organic carbon concentration. However it contributes approximately 10% to 30% of the total nitrogen load that is around 500-1500 mg NH4/l and considerable. Accordingly, nitrogen removal from this highly concentrated stream in a separated process will save cost significantly for plant upgrading purposes (Dosta et al., 2007; Hwang et al., 2015; Karwowska et al., 2014; Van Loosdrecht and Salem, 2006). Kos (1998) published a study in which a side-stream reactor was used to treat RW but he did not elaborate on the design of the side stream reactor. His simulation showed a decrease of 60% in aerobic SRT in the main wastewater treatment process is achievable due to addition of the sludge formed in the side-stream reactor (Kos, 1998). Plaza et al. (2001) also studied theoretically and experimentally a bio-augmentation system. The results showed the advantageous effect of seeding sludge from a separate nitrification reactor into an activated sludge system. It should be mentioned that the separate nitrification reactor is similar in size to activated sludge aeration tank, and a separate settler is needed that led to high investment costs (Plaza et al., 2001). The concept of bio-augmentation of conventional activated sludge has been investigated through bench, pilot and full-scale tests and proven effective in reducing the start-up time and the SRT necessary for desired nitrification in cold temperatures (Head and Oleszkiewicz, 2004; Krhutková et al., 2006). As mentioned in the literature, it is possible to use either isolated strains (Nancharaiah et al., 2008; Olaniran et al., 2006; Park et al., 2008; Plangklang and Reungsang, 2011) or consortia of microorganisms (Chen et al., 2006; Mrozik and Piotrowska-Seget, 2010) for bio-augmentation of activated sludge processes. Although enriched mixed cultures are preferred as degradation of contaminants is more likely to be obtained by active mixed culture rather than pure (Ikeda-Ohtsubo et al., 2013; Martin-Hernandez et al., 2012; Munz et al., 2012). Bio-augmentation can be conducted ex-situ by adding external source of nitrifiers and in-situ by an internal process for nitrifier population enrichment. Variations in conditions such as temperature, substrate and biomass composition in ex-situ approach may affect the bio-augmentation efficiency. However, internal bio-augmentation is reported to be more efficient as the same conditions are applied to both main-stream and sidestream reactors (Head and Oleszkiewicz, 2004; Leu and Stenstrom, 2010; Parker and Wanner, 2007). The Bio-Augmentation Batch Enhanced (BABE) reactor is an example wastewater treatment technology for upgrading purpose. This technology comprises a side stream reactor in the sludge return line which operates batch wise. The BABE reactor was proposed by DHV-Water with a relatively short SRT which treated ammonium-rich flow of RW along with the bio-augmentation of nitrifiers (Zilverentant, 2003). High temperature of reject water provides high specific growth rate for nitrifiers in this side-stream reactor to enhance nitrification process. Salem et al. (2003) developed a mathematical model based on ASM1 model to evaluate the potential of bioaugmentation of the nitrifying bacteria. They used RW as internal ammonium source and an artificial ammonium-rich stream as external source for BABE reactor to study the differences between the two origins of ammonium and found an internal ammonium source is more effective. They implied that reactivating endogenous nitrifiers in the BABE reactor with short 6

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SRT, ensuring growth of nitrifiers in the main stream (Salem et al., 2003). Salem et al. (2004) also reported full scale test of the BABE to be an effective and stable operation especially at lower ambient temperatures and smaller volume of the side-stream reactor (Salem et al., 2004).

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This assay set out to investigate the concept of bio-augmentation of an activated sludge plant to cope with overload operating conditions. Upgrading of the overloaded wastewater treatment plant is considered to meet local environmental criteria, 5 mg/l for ammonium and 50 mg/l for nitrate, for effluent quality. Two different configurations are discussed to verify this idea for the purpose of the bio-augmentation of an overloaded plant and thus nitrification process improvement. The implementation of these configurations for enhancement of nitrification process at different incremental overloading conditions was simulated in MATLAB based on ASM models. The following sections are describing the process specifications, mathematical models and simulation results.

2. Process description

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In this investigation, a conventional activated sludge process in a municipal wastewater treatment plant located in south of Iran was considered. As presented in Figure 1, the plant has physical, biological and sludge treatment units for treating incoming daily flow of 69120 m3 of wastewater.

Figure 1. Schematic diagram of the municipal wastewater treatment plant under study

The inlet wastewater is first treated in the physical treatment unit comprising of two primary clarifiers to remove settleable solids. The effluent stream from primary clarifiers that is referred 7

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to as “Influent” is then divided over four parallel trains each containing an aeration tank and a secondary clarifier. Each aeration tank consists of five compartments to aerobically degrade organic contaminants. The required oxygen for metabolism of the aerobic microorganisms is supplied by a surface aerator for each compartment such that a Dissolved Oxygen (DO) concentration of approximately 2 mg O2/l is maintained in aeration tanks. The biomass formed in the aerobic biodegradation reaction is removed from treated wastewater in the secondary clarifier to produce clarified stream for discharging to the environment after disinfection. A part of the settled biomass is returned to the aeration tank as Return Activated Sludge (RAS) and the remaining forms Waste Activated Sludge (WAS) that is treated in the sludge treatment unit that comprises of anaerobic digester and drying beds. WAS is then digested under anaerobic condition and the ammonium-rich supernatant from dewatering stage that is RW is recycled to the head of the biological treatment unit. The characteristics of the influent stream to the biological treatment and reject water stream are summarized in Table 1. Table 1. The characteristics of the influent and reject water streams. Influent 69120 515 50 40

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Reject water 1382 630 522 456

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Parameters Flow COD N-kj NH4+

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For this plant two different process modifications are considered and studied as competitive bioaugmentation alternatives to cope with overload operating conditions to determine advantages of each on a comparative basis. An increase of up to 30% in the influent flow rate is considered here as overloaded conditions. In order to study the effect of the proposed alternative configurations for improving the hydraulically overloaded plant performance, only one train of biological treatment unit was considered as main wastewater treatment process and simulated in MATLAB with specifications presented in Table 2.

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Table 2. The specifications of the simulated aeration tank

Specification Influent flow Aeration volume Dissolved oxygen concentration Temperature SRT

Unit m3/day m3 mg O2/l °C days

17280 5125 2 20 15

As discussed in the introduction, previous studies have confirmed the effective implementation of the BABE technology for promoting endogenous nitrifiers, and hence upgrading a full-scale activated sludge plant at low ambient temperature. It can thus be suggested that the BABE technology will be efficient for enhancing the nitrification process in an overloaded plant. Therefore, the application of the so-called BABE reactor with the schematic diagram shown in Figure 2a was considered and simulated as an alternative configuration. In this configuration a 8

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BABE reactor was considered as a pretreatment reactorwhich was fed with a mixture of high ammonium loaded stream, RW, and small fraction of RAS. The effluent of the BABE reactor after one batch treatment in combination with enriched sludge of endogenous nitrifiers was divided equally to four parallel streams to direct to the inlet of aeration tank as shown in Fig. 2a. Thus, the nitrification potential of the plant increases and may compensate effectively the extra load of wastewater to the plant. The BABE reactor was simulated under cyclic aeration condition (aerobic/anoxic) during each batch of 6h. The volume of the suggested BABE reactor was considered 12% of the total aeration capacity of the main process to convert ammonium efficiently. The SRT in the BABE was selected 5 days to assure restoration of considerable amount of ammonia oxidizers for bio-augmentation purposes (Zilverentant, 2003). Since reject water has a relatively higher temperature than influent and the released metabolic heat from the nitrification process of high ammonium loaded solution is significant, the temperature in BABE reactor is higher than the aeration tank temperature. The temperature of the BABE was presumed 35°C and the kinetic parameters of the model were corrected for this temperature (Zilverentant, 2003).

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Figure 2. The schematic diagram of the simulated bio-augmentation configurations (a) First configuration: application of the BABE reactor, (b) Second configuration: application of side-stream SBRs in addition to the BABE reactor.

The flow rate of the return sludge and reject water to the suggested BABE should be such that it can treat 5-30% of the main process total nitrogen load. Therefore, considering the wastewater 9

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influent flow, Qi, the flow of reject water to the BABE should be considered to be 0.01-0.2 times the wastewater influent flow while the flow of return sludge to the BABE reactor can be 0.1-2 times of reject water flow (Salem et al., 2003; Zilverentant, 2003). Therefore, to assure higher temperature in the BABE compared to the aeration tank, the volumetric flow rate of RAS fed to the BABE was set to be 1% of influent wastewater (Salem et al., 2003).

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In order to have more efficient nitrogen removal in the overloaded plant, implementation of sidestream SBRs in addition to the BABE reactor was considered as the second configuration that is shown schematically in Figure 2b. In this configuration the advantageous characteristics of SBR that is flexibility in operation is suggested to be employed to handle the incremental increase in overload of wastewater as well as bio-augmentation of the main stream. In this way the number of necessary SBRs employed can be increased from three to seven as the percent of overload wastewater increased from 10% to 30% of the influent. For the 10% increase three SBRs were employed and for every other 5% increments one SBR was added. The proposed SBRs were operated in parallel and bio-augmented with the enriched flow of nitrifiers from the BABE reactor. The effluent of the BABE reactor was introduced to the influent stream, extra load of wastewater, to the SBRs instead of being directly fed to the aeration tanks as in the first configuration. The effluent streams from the SBRs were mixed with each other, then divided equally to four parallel streams to each of the aeration tanks. In this way the aeration tanks were bio-augmented by an enriched stream of nitrifiers from SBRs. Design parameters of a SBR are important and can affect its performance and in this study these parameters were adopted from those provided by Artan et al. 2001 (Artan et al., 2001). Each SBR had a volume of 1000 m3 and fed every 6 h in a cycle consisting of a 3 h anoxic phase, for filling and anoxic reaction, a 1.5 h aerobic reaction phase and a 1.5 h for settling, effluent discharge and idle phase. As the nitrate concentration in the effluent of the BABE is significant, the anoxic phase time was considered such that sufficient time was applied for denitrification process in SBRs. Although both BABE reactor and SBRs were simulated in batch mode, the role of each in bio-augmentation configuration is different. The BABE reactor was fed with ammonium-rich flow of RW, whereas the SBRs were fed with incremental overload of wastewater and enriched stream of nitrifiers from the BABE reactor. In the first configuration shown in Figure 2a, nitrification in the main stream was enhanced just as a result of bio-augmentation from the BABE rector. However, in the second configuration shown in Figure 2b, combination of both treatment of incremental overload of wastewater in the side-stream SBRs and bio-augmentation of the main stream was investigated to improve nitrogen removal in the main stream.

3. Mathematical models and equations 3.1. Main process

As mentioned in the introduction, there are cases of activated sludge processes for which modeling by ASM3 is recommended. In other cases ASM1 which is less complex than ASM3 can be used effectively to describe the dynamics of activated sludge process (Van Loosdrecht et al., 2015). The main process as depicted in Figure 1 and detailed in the process description matches none of the cases outlined in introduction thus ASM1 model was used to simulate the wastewater plant under study in MATLAB. All model parameters used for simulation were 10

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similar to those values for municipal wastewater with common composition at 20°C as reported by Henze et al. (2000).

(b)

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Figure 3. (a) ASM1 reaction network for main process, (b) modified ASM1 reaction network for BABE.

As shown in Figure 3a, the ASM1 consists of growth and decay of heterotrophs and autotrophs and hydrolysis of particulate organics. The ASM1 model considers nitrification as a one-step process carried out by the autotrophs under aerobic condition that oxidize ammonia nitrogen directly to nitrate nitrogen. Denitrification is also considered to be a one-step process performed by the heterotrophs that reduce nitrate directly to nitrogen gas through anoxic condition. The mass balance equations for each component as well as oxygen involved in the ASM1 model 11

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were considered in the form of ordinary differential equations. The transient concentrations during process simulations were calculated through solving these differential equations. The main characteristics of the influent and RW streams which were used in the ASM1 model is illustrated in Table 3. Table 3. The characteristics of the influent and RW streams for ASM1 model. RW 500 456 40 90 0

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Influent 125 40 40 100 250

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Unit g COD/m3 g N/m3 g COD/m3 g COD/m3 g COD/m3

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Compounds Ss SNH SI XI XS

3.2. Side-stream reactors for bio-augmentation

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The side-stream reactors for both proposed alternative configurations were modeled as completely mixed during all phases of reaction. No removal of substrates is assumed to take place during settle, decant and idle periods in SBRs. The RW stream that is the influent of the BABE is high in ammonium load thus an appropriate model is required to handle effectively transient behavior of BABE. The developed model by Moussa et al. 2005 with two-step nitrification for nitrogen removal from ammonium-rich RW was applied in MATLAB programming to describe the performance of the BABE reactor. The model is based on the ASM1 model and reaction network is shown schematically in Figure 3b. The model has been developed for growth, maintenance and removal of organic and nitrogen substrates for which BABE is designed and biological phosphorus removal has not been considered. Nitrification is considered as a two-step process in this model, which is carried out by two types of nitrifiers, ammonia and nitrite oxidisers. However, denitrification is modeled as a one-step process as nitrite presents for a short time under aerobic conditions. Moreover, substrate is utilized for growth and maintenance of the ammonia oxidisers, nitrite oxidisers and heterotrophs in this model. The model includes concentration of six soluble compounds that are dissolved oxygen ( SO2 ), nitrogen gas ( SN2 ), ammonium (SNH), nitrite ( SNO2 ), nitrate ( SNO3 ) and COD (SS). Four particulate compounds were also included in BABE mode that are ammonia oxidizers ( X NH 4 ), nitrite oxidisers ( X NO2 ), heterotrophs ( X H ) and inert biomass ( X I ). Model process kinetics as a result of simplifying assumptions is presented in Table 4. Process stoichiometry in the form of a Petersen matrix and numerical values of kinetic parameters of this model are illustrated in Appendices A and B, respectively. (Moussa et al., 2005). The following six assumptions have been applied to ASM1 to simplify it for modeling the BABE reactor: 1. At temperature above 20°C a two-step nitrification model with nitrite as intermediate might be useful. Since the RW temperature is relatively high, the BABE was operated at 35 °C and therefore nitrification was considered as a two-step process. As can be seen from reaction kinetics presented in Table 4, two-step nitrification is carried out by two types of nitrifying 12

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biomass: ammonia oxidizers (Processes 1-4) and nitrite (Processes 5-8) oxidizers (Hellinga et al. 1998, Hellinga et al. 1999, Nowak et al. 1995, Brouwer et al. 1998).

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2. Heterotrophic organisms were considered to be responsible for COD utilization under both aerobic and anoxic conditions. These two conditions are similar, except that under anoxic conditions nitrate is used as electron acceptor instead of oxygen (processes 10 and 12 in Table 4) (Henze et al. 2000). Nitrite was not considered in the denitrification process in the BABE modeling. Table 4. Process kinetics for enriched culture of nitrifiers in the BABE reactor Rate equation

Ammonia Oxidizers 1. Growth of X NH 4





S

cr

Process



S

4

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max NH O µ NH  K + S   K NH + S  X NH NH NH O O

4

   S NH SO mNH 4  X NH 4 NH  K NH + S NH   K O + SO 

3. Aerobic decay of X NH 4

 K NH   KONH  bNH 4  X NH 4 NH  K NH + S NH   KO + SO  

4. Anoxic decay of X NH 4



K NH



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4



max µ NO  2

4

  SO X NO2  NO2  + S NO2   K O + So 

S NO2

 K NO2

  S NO2  SO mNO2   NO2   X NO2  K NO2 + S NO2   K O + So 

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6. Maintenance of X NO2

K

NH O η NH bNH  X NH NH  K NH + S NH   KO + SO  4

Nitrite Oxidizers 5. Growth of X NO2

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2. Maintenance of X NH 4

   K ONO2  K NO2 bNO2    NO2  X NO2  K NO2 + S NO2   K O + So 

8. Anoxic decay of X NO2

   K ONO2  K NO2 η NO2 bNO2    NO2  X NO2  K NO2 + S NO2   K O + So 

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7. Aerobic decay of X NO2

Heterotrophs 9. Aerobic growth of X H 10. Anoxic growth of X H

11. Aerobic maintenance of X H



SS   SO  XH H  K S + SS   K O + SO 

µ Hmax 

 S NO3 S S   K OH     X B,H H     K S + S S   K O + SO   K NO3 + S NO3  

ηH µ Hmax 

 SS   SO  mH  XH H  K S + SS   K O + SO  13

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 S NO3  S S   K OH   mH    X B, H H  K S + S S   K O + SO   K NO3 + S NO3 

13. Decay of X H

 KS  bH  X B.H  K S + S S 

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12. Anoxic maintenance of X H

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3. According to reaction kinetics presented in Table 4, the substrate utilization for growth and maintenance processes of the ammonia oxidizers (Processes 1 and 2), nitrite oxidizers (Processes 5 and 6) and heterotrophs (Processes 9-12) that were used are those described and suggested by Beeftink et al. (1990) and also applied by De Gooijer et al. (1991) and Hunik et al. (1994).

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4. The kinetic expressions in the model are based on switching functions, Monod equations, for all soluble compounds consumed (Henze et al. 2000)

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5. Aerobic decay rate (Processes 3 and 7 in Table 4) was considered for bacteria starvation under aerobic condition as well as anoxic decay rate for biomass starvation in the absence of oxygen and presence of nitrate (Processes 4 and 8 in Table 4) (Leenen et al. 1997, Siegrist et al. 1999).

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6. The generation of inert biomass (Fxi) without any further degradation results from the decay processes of the active biomass.

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It should be mentioned that growth of nitrifiers is the rate limiting step in nitrification process in ASM models. Therefore, nitrification process plays essential role in determining required SRT to achieve desired nitrification and prevent washout of the nitrifiers. Consequently, upgrading of a wastewater treatment plant for the purpose of improving nitrification process usually requires enlargement of aeration reactors to allow operation at higher SRTs. On the other hand nitrification process rate will be increased as a function of temperature in the range of practical interest (Tang and Chen, 2015).

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As illustrated in the Figure 2b, the parallel SBRs used in the second alternative configuration were designed to treat extra load of wastewater to the plant. Therefore, the characteristics of the influent to the SBRs in this configuration were presumed identical with the influent to the wastewater plant. Consequently, the same model as used for the modeling the wastewater plant was applied for parallel SBRs. 4. Results and discussion

As explained in the previous section, application of the proposed configurations has been evaluated by computer simulation. The simulation was applied for an existing plant under overloaded operating conditions to evaluate process intensification by two alternative bioaugmentation configurations. Simulation results of ammonium and nitrate concentration in the bio-augmented process effluent for different incremental overloading conditions demonstrate treatment improvement and bio-augmentation efficiency. The computer simulation can be used to generate transient profile for all state variables under different incremental overloading

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conditions. Concentration profiles for 30% overloading condition are presented in the following subsections for the sake of brevity. 4.1. Overloaded plant bio-augmentation through the BABE reactor

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As shown in Figure 2a, application of the side-stream BABE reactor in the return sludge line is an alternative configuration to cope with overload operating conditions. Figure 4 presents ammonium and nitrate profile during one SRT in the BABE reactor. During aerobic phase of each cycle, ammonium concentration decreases from 79 mg/l to 29 mg/l while nitrate concentration increases from 60 mg/l to 88 mg/l. It can be seen that under steady state conditions ammonium removal of approximately 60% was achieved due to the nitrifiers metabolism during aerobic phase. The BABE anoxic phase was 1 h/cycle that is not relatively long enough to provide complete denitrification process, consequently nitrate reduction is low and nitrate concentration is high, 82 mg/l, in the effluent of the BABE reactor. The positive effect of the BABE side-stream reactor on ammonium removal in the 30% overloaded condition is illustrated in Figure 6a. Concentration profiles in this figure indicate that nitrification process initially caused to ammonium concentration decrease and simultaneously nitrate concentration increase and afterwards, ammonium concentration rises slightly as a result of heterotrophs ammonification. Figure 6b also allows comparison of nitrate concentration in the effluent before and after bio-augmentation with BABE reactor during one SRT for the overloaded main process. Figure 6a illustrates that feeding the effluent of the BABE reactor to the main reactor as a source of reactivated nitrifiers decreases ammonium concentration from 27.83 mg/l in the overloaded main process to 18.76 mg/l in the bio-augmented process. Comparison of nitrification efficiency improvement for different overloading conditions which will be discussed later, demonstrates that bio-augmentation under 30% overloaded condition is the most efficient. However, nitrate concentration in the bio-augmented plant effluent compared to overloaded plant increased from 26.27 to 34.37 mg/l. This is a consequence of increasing nitrification process efficiency and incomplete denitrification process in the BABE reactor.

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Figure 4. Ammonium and nitrate profiles in the BABE reactor cycles.

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These results match those observed in the earlier studies (Munz et al., 2012; Salem et al., 2003) and confirm a considerable potential of bio-augmentation for reducing ammonium concentration in the effluent of the overloaded plant. These results confirm that the effect of the BABE reactor for nutrient removal enhancement in an overloaded plant contributes to two factors: removal of ammonium from concentrated flow, RW, and also bio-augmentation of nitrifiers in the main process.

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4.2. Overloaded plant bio-augmentation through combination of BABE and SBRs

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It is widely acknowledged that the SBR is a low-cost and viable alternative to continuous-flow systems for carbon removal as well as for nutrient and suspended solids removal. The SBR offers a great deal of operational flexibility as it allows for easy adjustment of aerobic, anoxic and anaerobic periods through temporal control of aeration and filling. As discussed in section 2, the advantageous characteristics of SBR are suggested to be employed in the second alternative configuration to handle the overload of wastewater feed. Nitrogen removal occurs in aerobic and anoxic phases in SBRs. While nitrification is carried out in an aerobic phase by autotrophic nitrifiers oxidizing ammonium to nitrate and nitrite, denitrificatin occurs under anoxic condition by facultative heterotrophic bacteria using nitrate as electron acceptor. The autotrophic population constitutes only a small fraction of the total biomass and longer SRT are required for efficient nitrification, since the growth rate of nitrifiers is slow compared to heterotrophs (Ikeda-Ohtsubo et al., 2013; Salem et al., 2003). It can thus be suggested that bio-augmentation of autotrophic nitrifiers will improve the nitrification process efficiently. Hence, in this study, each SBR was considered to be bio-augmented with reactivated nitrifiers in the BABE reactor. On the other hand, side-stream SBRs which were bio-augmented

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with enriched flow of nitrifiers from the BABE reactor can be considered as an effective alternative for excess flow wastewater treatment.

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The effect of bio-augmentation on population of nitrifiers in bio-augmented SBR is illustrated in Figure 5a. This figure shows simulated concentration of nitrifiers during aerobic and anoxic phases. Concentration of nitrifiers increases slightly during short aerobic phase and decreases in anoxic phase due to oxygen deficiency. It can be seen that concentration of nitrifiers increases during one SRT as a result of bio-augmentation and therefore provide an enriched sludge of nitrifiers to augment bioactivity in the aeration tanks. Consequently, on the basis of same level of wastewater treatment, nitrification enhancement due to bio-augmentation decreases required SRT compared to the case in which bio-augmentation is not implemented.

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Also COD, ammonium and nitrate concentration during aerobic and anoxic phases of bioaugmented side-stream SBR are shown in Figure 5b and 5c. It is apparent from Figure 5b that COD decreased from 226 to 60 mg/l as a consequence of the heterotrophs activity during both aerobic and anoxic phases. In addition, Figure 5c illustrates ammonium removal and nitrate formation which occurred simultaneously as a result of nitrification process in the aerobic phase as well as nitrate reduction during anoxic phase. It can be seen that ammonium concentration decreases from 34.40 mg/l to 28 mg/l and nitrate concentration increases from 0.26 mg/l to 7.81 mg/l during aerobic phase under steady state conditions. The anoxic phase duration in SBR cycle was defined 3 h/cycle so that denitrification process can proceed toward completion. It can be seen in Figure 5c that nitrate concentration is less than 1 mg/l at the end of each cycle.

(a)

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Figure 5. a) nitrifiers ,b) COD and c) nitrogen concentration profile in the side-stream bio-augmented SBR in the second configuration.

Ammonium and nitrate concentrations in the effluent of the overloaded main process and the two alternative bio-augmentation configurations are compared in Figures 6a and 6b, respectively. It is apparent from Figure 6a that suggested bio-augmentation configurations are both effective for decreasing effluent ammonium concentration of the overloaded plant. Application of the first suggested configuration with BABE reactor improved ammonium removal from 25.73 mg/l in the main process to 16.83 mg/l in the bio-augmented process from the BABE reactor. However, bio-augmentation via the second suggested configuration effluent is more efficient as effluent ammonium concentration decreased by 81% and providing less than 5 mg/l, for ammonium concentration.

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(a)

(b)

Figure 6. a) Ammonium and b) Nitrate profile for 30% overloading condition Overloaded plant before bio-augmentation, after bio-augmentation from the BABE and after bioaugmentation from side-stream SBRs.

Consequently, the simulation results reveal that bio-augmentation of the second alternative configuration is the most efficient one to improve nutrient removal efficiency. This significant decrease in ammonium concentration in the plant effluent is due to N-load decrease to the main process which is the result of pre-processing of overload wastewater by SBRs as part of the second configuration. Considering this figure, it can be seen that ammonium concentration profile for the main process and the first bio-augmentation configuration have an initial decrease and then increase slightly as a result of heterotrophs activity and ammonification. On the other hand, this profile for the second bio-augmentation configuration is completely different and ammonium concentration decreased progressively until steady state concentration is reached. 19

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Ammonium profile in the second configuration can be explained as a consequence of autotrophs population increase and accordingly nitrification improvement due to bio-augmentation as well as decrease of heterotrophs growth and ammonification according to the available oxygen depletion. As can be seen in Figure 3b, the most likely cause of this approach is the nature of competition between autotrophs and heterotrophs for oxygen uptake under aerobic condition. In comparison with the first bio-augmentation configuration, oxygen uptake increases by larger amount of bio-augmented nitrifiers, and hence heterotrophs growth is rather limited in the second configuration.

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Furthermore, Figure 6b illustrates nitrate concentration increase due to improved nitrification process in the bio-augmented overloaded plant. Nitrate concentration increased from 28 mg/l in the main process to around 37 mg/l in both bio-augmentation configurations. In the case of nitrate concentration advantage of second configuration over first one is infinitesimal. Although effluent ammonium concentration decreases significantly as a result of bio-augmentation, nitrate concentration in the effluent does not increase accordingly. It can be concluded that nitrate reduction during anoxic phase of side-stream reactors predominates nitrate formation in the nitrification process. Consequently, bio-augmentation configurations both are efficient in improving ammonium removal as well as nitrate removal.

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Ammonium concentration profile for incremental increase in wastewater influent after application of the second alternative configuration is presented in Figure 7 to compare nitrogen removal performance. Calculating nitrification efficiency from these data indicates significant increase, in nitrification efficiency from 42% to 106% in comparison with main process for incremental rise of overloading percentage of 10-30%, respectively. It means that the bioaugmentation is much more efficient for upgrading nitrification process at higher overloading conditions as the hydraulic retention time for the main process decreases significantly under these conditions.

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Figure 7. Effluent ammonium concentration of the overloaded plant+ BABE+ SBRs before (---) and after ( ̶ ̶ ̶ ) implementation of the side-stream SBRs.

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Supplementary data of the simulation results under steady state conditions is presented in the form of tables that allows comparison of nitrification process improvement. These data are classified in four different operational cases. The data on first simulated case presented in these tables is the existing plant, the main process, without any additional aeration volume treating overloaded influent flow that is considered as base-case. A new activated sludge train was considered to be added to the main process in the second case that require 25% additional aeration volume. Two alternative bio-augmentation configurations, the BABE and the sidestream SBRs, are presented as the 3rd and 4th cases, respectively. Table 5 illustrates the simulation results of these cases for different percentages of overloading in terms of effluent COD, NH4-N, NO3-N. The presented data in Table 5 allows comparing efficiency of the four different cases in terms of effluent quality. Further simulation results such as percentages of COD removal, Nitrification Efficiency, NE, and Nitrification Efficiency Improvement, NEI are reported in Appendix C. As shown in Table 5, effluent COD for all cases is less 115 mg/l and COD removal above 75% is achievable in all cases. It is apparent that bio-augmentation of the overloaded main process from the BABE reactor can decrease ammonium concentration in the effluent to 8-19 mg/l for 10-30% overloading conditions in the overloaded reactor. In comparison with the base-case, nitrate concentration in the plant effluent increases as a consequence of increasing nitrification process efficiency and incomplete denitrification process in the BABE reactor. As can be seen from the 21

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data presented in Table 5 for the side-stream SBRs that is the fourth case improved nitrification as well as denitrification processes notably improved compared to other cases. Moreover, a review of effluent ammonium and nitrate concentrations in Table 5 reveals that though different cases provide nitrate concentration below 50 mg/l, the fourth case is the only one that delivers ammonium concentration less than 5 mg/l in all percentage of overloading.

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3. Overloaded plant +BABE reactor

a

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4. Overloaded plant +BABE reactor+ SBRs

cr

97.33 101.38 105.16 108.76 112.25 66.73 76.39 83.29 88.40 92.55 89.00 94.48 98.98 102.94 106.57 69.86 72.05 74.09 75.91 77.54

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2. Overloaded plant with additional aeration tanks

10 15 20 25 30 10 15 20 25 30 10 15 20 25 30 10 15 20 25 30

Effluent NH4-N Effluent NO3-N (mg/l) (mg/l) 16.98 20.07 22.90 25.48 27.83 3.241 5.53 8.36 11.32 14.19 8.13 10.95 13.70 16.31 18.76 2.81 3.23 3.71 4.24 4.85

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1. Overloaded plant without any additional aeration tanks

Effluent COD (mg/l)

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Configurations

OLa (%)

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Parameters

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Table 5. The simulation results on effluent COD, Ammonium and Nitrate in the overloaded plant under different configurations.

37.57 34.37 31.43 28.74 26.27 52.26 49.66 46.62 43.51 40.51 44.93 42.08 39.35 36.78 34.38 41.61 40.23 38.99 37.78 36.65

Overloading percentage

On the other hand, Figure 8 is illustrated NE and NEI of these four cases under different overloading conditions to compare their performances. The abbreviation NE refers to the percentage of influent ammonium which was oxidized to nitrate during nitrification process and NEI is used to compare NE for each case with that of the base-case which were calculated by Equations (1) and (2), respectively. NE = 100* ( influent ammonia − effluent ammonia ) / influent ammonia NEI k = 100* NEi − NEi , j / NEi

(1)

(2)

i : Basecase ; 22

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j :Operational case (1 − 4) ;

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k : Overloading condition (10 − 30%)

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Figure 8. (a) NE, (b)NEI in the overloaded plant under different configurations.

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It is apparent from Figure 8a, the BABE reactor as an alternative configuration is less efficient in increasing NE in comparison with the second case. However, this proposed configuration caused nitrate concentration decrease according to the activity of denitrifiers during the anoxic phase in the BABE cycle. As Figure 8a shows, there is a significant increase in NE in the fourth case for different overloading conditions. In addition, it is obvious from Figure 8b that nitrogen removal efficiency was improved significantly in both bio-augmentation configurations. Although the fourth case was the most efficient and improved nitrification efficiency by 61-189% in comparison with the base case. As mentioned earlier, comparing nitrification efficiency improvement for different overloading conditions, demonstrates that bio-augmentation under 30% overloaded condition is the most efficient. Appendix D summarizes simulation results for additional reactor volume and oxygen uptake for all cases in comparison with the base-case. Obviously all three cases other than base-case require additional reactor volume which cause additional capital investment cost. The BABE reactor requires least additional reactor volume among others However in comparison with the base case the additional oxygen uptake for nitrification in BABE does not exceed 10.54% whereas fourth case shows up to 16.87% additional oxygen uptake. As discussed in the introduction, reduction of oxygen uptake as a result of sequential aerobic/anoxic phases in the side-stream reactors in both suggested bio-augmentation configurations can be translated in lower energy consumption. A thorough economic analysis is required to determine cost saving in 3rd and 4th cases. However, the fourth case performs much better than other cases in terms of nitrogen removal and it will be

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economically appropriate to improve the performance of the overloaded plants in spite of its large additional reactor volume. 5. Conclusions

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The simulation results of the present investigation indicate adequacy of the proposed bioaugmentation configurations for improving nitrogen removal of an overloaded activated sludge plant. The performance of two alternative configurations is discussed in terms of effluent quality under different overloading conditions. It can be concluded that second configuration has a significant potential for nitrification improvement as a result of N-load reduction to the main treatment reactor as well as augmentation of the existing nitrifiers population. The results reveal that effluent nitrate concentration increases due to improving nitrification after bio-augmentation of the overloaded plant, but does not exceed 50 mg/l. Furthermore, bio-augmentation through application of the side-stream SBRs in addition with BABE reactor has been found far more effective at higher overloading conditions as a result of hydraulic retention time decrease. However, the economic analysis of implementation of the suggested bio-augmentation configurations is necessary for making final decision if it will be considered as an alternative for nitrogen removal enhancement of the overloaded existing wastewater treatment plants.

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Acknowledgment

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Financial support from the Vice Chancellor for Research Affairs of Shiraz University is gratefully acknowledged.

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References

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Andreottola, G., Foladori, P., Gatti, G., Nardelli, P., Pettena, M. & Ragazzi, M. 2003. Upgrading of a Small Overloaded Activated Sludge Plant Using a MBBR System. J. Environ. Sci. Health, Part A, 38(10), 2317-2328. Artan, N., Wilderer, P., Orhon, D., Morgenroth, E. & Özgür, N. 2001. The mechanism and design of sequencing batch reactor systems for nutrient removal – the state of the art. Water Sci. Technol., 43(3), 53–60. Chen, B.-Y., Chen, S.-Y., Lin, M.-Y. & Chang, J.-S. 2006. Exploring bioaugmentation strategies for azo-dye decolorization using a mixed consortium of Pseudomonas luteola and Escherichia coli. Process Biochem., 41(7), 1574-1581. Dosta, J., Gali, A., Benabdallah El-Hadj, T., Mace, S. & Mata-Alvarez, J. 2007. Operation and model description of a sequencing batch reactor treating reject water for biological nitrogen removal via nitrite. Bioresour. Technol., 98(11), 2065-2075. Gernaey, K.V., van Loosdrecht, M.C.M., Henze, M., Lind, M. & Jørgensen, S.B. 2004. Activated sludge wastewater treatment plant modelling and simulation: state of the art. Environ. Model. Softw., 19(9), 763-783. Gu, J., Xu, G. & Liu, Y. 2017. An integrated AMBBR and IFAS-SBR process for municipal wastewater treatment towards enhanced energy recovery, reduced energy consumption and sludge production. Water Res., 110, 262-269. Head, M.A. & Oleszkiewicz, J.A. 2004. Bioaugmentation for nitrification at cold temperatures. Water Res., 38(3), 523-530. Henze, M., Gujer, W., Mino, T. & van Loosdrecht, M.C.M. 2000. Activated Sludge Models ASM1, ASM2, ASM2d and ASM3. In. IWA Publishing, London, UK. Hunik, J.H., Bos, C.G., van den Hoogen, M.P., De Gooijer, C.D. & Tramper, J. 1994. Co-immobilized Nitrosomonas europea and Nitrobacter agilis cells: validation of dynamic model for simultaneous substrate conversion and growth in K-carrageenan gel beads. Biotechnol. Bioeng., 43(1153-1163). Hwang, B., Lu, Q., de Toledo, R.A. & Shim, H. 2015. Enhanced nitrogen removal from sludge reject water by methanol addition using sequencing batch biofilm reactor. Desalin. Water Treat., 1-9. Ikeda-Ohtsubo, W., Miyahara, M., Kim, S.W., Yamada, T., Matsuoka, M., Watanabe, A., Fushinobu, S., Wakagi, T., Shoun, H., Miyauchi, K. & Endo, G. 2013. Bioaugmentation of a wastewater bioreactor system with the nitrous oxide-reducing denitrifier Pseudomonas stutzeri strain TR2. J. Biosci. Bioeng., 115(1), 37-42. Karwowska, B., Sperczyńska, E. & Wiśniowska, E. 2014. Characteristics of reject waters and condensates generated during drying of sewage sludge from selected wastewater treatment plants. Desalin. Water Treat., 57(3), 1176-1183. Kos, P. 1998. Short SRT (solids retention time) nitrification process/flowsheet. Water Sci. Technol., 38(1), 23-29. Krhutková, O., Novák, L., Pachmanová, L., Benáková, A., Wanner, J. & Kos, M. 2006. In situ bioaugmentation of nitrification in the regeneration zone: practical application and experiences at full-scale plants. Water Sci. Technol., 53(12), 39. Leu, S.-Y. & Stenstrom, M.K. 2010. Bioaugmentation to improve nitrification in activated sludge treatment. Water Environ. Res, 82(6), 524-535. Li, W., Li, L. & Qiu, G. 2016. Energy consumption and economic cost of typical wastewater treatment systems in Shenzhen, China. J. Cleaner Prod.(1-5). 26

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Longo, S., d’Antoni, B.M., Bongards, M., Chaparro, A., Cronrath, A., Fatone, F., Lema, J.M., MauricioIglesias, M., Soares, A. & Hospido, A. 2016. Monitoring and diagnosis of energy consumption in wastewater treatment plants. A state of the art and proposals for improvement. Appl. Energy, 179, 1251-1268. Martin-Hernandez, M., Suarez-Ojeda, M.E. & Carrera, J. 2012. Bioaugmentation for treating transient or continuous p-nitrophenol shock loads in an aerobic sequencing batch reactor. Bioresour. Technol., 123, 150-156. Meijer, S.C.F., van Loosdrecht, M.C.M. & Heijnen, J.J. 2001. Metabolic modelling of full-scale biological nitrogen and phosphorus removing WWTP's. . Water Res., 35, 2711-2723. Moussa, M.S., Hooijmans, C.M., Lubberding, H.J., Gijzen, H.J. & van Loosdrecht, M.C. 2005. Modelling nitrification, heterotrophic growth and predation in activated sludge. Water Res., 39(20), 50805098. Mrozik, A. & Piotrowska-Seget, Z. 2010. Bioaugmentation as a strategy for cleaning up of soils contaminated with aromatic compounds. Microbiol. Res., 165(5), 363-375. Munz, G., Szoke, N. & Oleszkiewicz, J.A. 2012. Effect of ammonia oxidizing bacteria (AOB) kinetics on bioaugmentation. Bioresour. Technol., 125, 88-96. Nancharaiah, Y.V., Joshi, H.M., Hausner, M. & Venugopalan, V.P. 2008. Bioaugmentation of aerobic microbial granules with Pseudomonas putida carrying TOL plasmid. Chemosphere, 71(1), 30-35. Olaniran, A.O., Pillay, D. & Pillay, B. 2006. Biostimulation and bioaugmentation enhances aerobic biodegradation of dichloroethenes. Chemosphere, 63(4), 600-608. Park, D., Lee, D.S., Kim, Y.M. & Park, J.M. 2008. Bioaugmentation of cyanide-degrading microorganisms in a full-scale cokes wastewater treatment facility. Bioresour. Technol., 99(6), 2092-2096. Parker, D. & Wanner, J. 2007. Review of Methods for Improving Nitrification through Bioaugmentation. Water Prac., 1(5), 1-16. Plangklang, P. & Reungsang, A. 2011. Bioaugmentation of carbofuran residues in soil by Burkholderia cepacia PCL3: A small-scale field study. International Biodeterioration & Biodegradation, 65(6), 902-905. Plaza, E., Trela, J. & Hultman, B. 2001. Impact of seeding with nitrifying bacteria on nitrification process efficiency. Water Sci. Technol., 43(1), 155-163. Regueiro, L., Lema, J.M. & Carballa, M. 2015. Key microbial communities steering the functioning of anaerobic digesters during hydraulic and organic overloading shocks. Bioresour. Technol., 197, 208-216. Rittmann, B.E. & Whiteman, R. 1994. Bioaugmentation: A Coming of Age. Water Qual. Int., 1, 12-16. Salem, S., Berends, D.H.J.G., Heijnen, J.J. & Van Loosdrecht, M.C.M. 2003. Bio-augmentation by nitrification with return sludge. Water Res., 37(8), 1794-1804. Salem, S., Berends, D.H.J.G., van der Roest, H.F., van der Kuij, R.J. & van Loosdrecht, M.C.M. 2004. Fullscale application of the BABE technology. Water Sci. Technol., 50(7), 87–96. Siegrist, H., Brunner, I., Koch, G., Leinh, C.P. & Van Chieu, L. 1999. Reduction of biomass decay rate under anoxic and anaerobic conditions. . Water Sci. Technol., 39, 129-137. Tang, H.L. & Chen, H. 2015. Nitrification at full-scale municipal wastewater treatment plants: Evaluation of inhibition and bioaugmentation of nitrifiers. Bioresour. Technol., 190, 76-81. Tappe, W., Laverman, A., Bohland, M., Braster, M., Ritteshaus, S., Groeneweg, J. & van Verseveld, H.W. 1999. Maintenance energy demand and starvation recovery dynamics of Nitrosomonas europaea and Nitrobacter winogradskyi cultivated in a retentostat with complete biomass retention. Appl. Environ. Microbiol., 65, 2471-2477. Van Hulle, S.W.H. & Ciocci, M.C. 2013. Scenario analysis and statistical analysis of simulation results of operation of activated sludge waste water treatment plants. Desalin. Water Treat., 52(22-24), 4154-4164. 27

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Van Loosdrecht, M.C.M., Lopez-Vazquez, C.M., Meijer, S.C.F., Hooijmans, C.M. & Brdjanovic, D. 2015. Twenty-five years of ASM1: past, present and future of wastewater treatment modelling. J. Hydroinf., 17(5), 697-718. Van Loosdrecht, M.C.M. & Salem, S. 2006. Biological treatment of sludge digester liquids. Water Sci. Technol., 53(12), 11. Vera, I., Saez, K. & Vidal, G. 2013. Performance of 14 full-scale sewage treatment plants: comparison between four aerobic technologies regarding effluent quality, sludge production and energy consumption. Environ. Technol., 34(13-16), 2267-2275. Zhou, Z., Hu, D., Jiang, L., Xing, C., Zhu, Y., Jiang, M., Qiao, W. & Li, Z. 2014. Nitrification kinetics of a fullscale anaerobic/anoxic/aerobic wastewater treatment plant. Desalin. Water Treat., 56(8), 20462054. Zilverentant, A.G. 2003. Process for the Treatment of Waste Water Containing Specific Components E.G. Ammonia. In.

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2. Maintenance of X NH 4

−3.43 / YNH 4 + 1 -3.43

SNO3

SS

X NH 4

X NO2

XH

(mg COD/L)

(mg COD/L)

(mg COD/L)

(mg COD/L)

−i NBM − 1/ YNH4

1/ YNH 4

-1

1

XI (mg COD/L)

SNO2

(mg N/L)

SNH4

(mg N/L)

(mg O2/L)

te

ep

Ammonia oxidizers 1. Growth of X NH 4

d

Unit

SN2

(mg N/L)

SO2

Process

Compounds (Unit)

(mg N/L)

M an

Appendix A. Process stoichiometry for enriched culture of nitrifiers in the BABE reactor

1

i NBM − i Nxi Fxi

1 − Fxi

-1

Fxi

4. Anoxic decay of X NH 4

i NBM − i Nxi Fxi

1 − Fxi

-1

Fxi

Ac c

3. Aerobic decay of X NH 4 Nitrite oxidizers 5. Growth of X NO2

6. Maintenance of X NO2

−i NBM

−1.14 / YNO2 + 1 -1.14

−1/ YNO2 1/ YNO2

-1

1

1

7. Aerobic decay of X NO2

i NBM − i Nxi Fxi

1 − Fxi

-1

Fxi

8. Anoxic decay of X NO2

i NBM − i Nxi Fxi

1 − Fxi

-1

Fxi

−i NBM

−1/ YH

1

1 − YH −1/ YH 2.86Y

1

Heterotrophs 9. Aerobic growth of X H 10. Anoxic growth of X H

− (1 − YH ) / YH 1 − YH 2.86YH

−i NBM

−

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1/2.86

-1 -1/2.86

i NBM − i Nxi Fxi

-1

1 − Fxi

Ac c

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d

13. Decay of X H

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11. Aerobic maintenance of

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Fxi

Appendix B. Kinetic parameters for simulation of the nitrification in the BABE reactor Unit

Definition

YNH 4

gCOD/gNO2 –N

Yield of ammonia oxidizers

35°C 0.18

30°C 0.18

(Hunik et al., 1994)

YNO2

gCOD/gNO3 –N

Yield of nitrite oxidizers

0.06

0.06

(Hunik et al., 1994)

YH

g COD/gCOD

Yield of hetrotrophic biomass

0.63

0.63

(Henze et al., 2000)

Fxi

g COD/g COD

0.15

0.15

i Nxi

gN/gCOD

Fraction of inert COD generated in biomass lysis Nitrogen content of XI

0.02

0.02

i NBM

gN/gCOD

Nitrogen content of biomass

0.07

Maximum growth rate of ammonia oxidizers Affinity constant for oxygen of ammonia oxidizers Affinity constant for ammonia of ammonia oxidizers Maintenance coefficient of ammonia oxidizers

2.25

mg O2/l

K NH

mg NH4 _N/l

mNH 4

mg NH4_N/ (g X NH 4 _COD.day)

bNH 4

day-1

ηNH

— 4

max µ NO

day-1

K ONO2

mg O2/l

K NO2

mg NO2 _N/l

mNO2

mg NO2 _N/ (g X NO2 _COD.day)

bNO2

day-1

2

µ Hmax K OH KS

—

day-1

mg O2 /l

mg COD/l

K NO3

mg NO3_N/l

mH

ηH

mg COD/ (gXH_COD.day) —

bH

h-1

cr 1.4

(Hunik et al., 1994)

1

1

5

5

(Moussa et al., 2005) (Moussa et al., 2005) (Tappe et al., 1999)

Aerobic decay rate of ammonia oxidizers Anoxic reduction factor for ammonia oxidizers decay Maximum growth rate of nitrite oxidizers Affinity constant for oxygen of nitrite oxidizers Affinity constant for nitrite of nitrite oxidizers Maintenance coefficient of nitrite oxidizers

0.48

0.3

0.5

0.5

1.21

0.9

1

1

2

2

1.54

1.15

Aerobic decay rate of nitrite oxidizers Anoxic reduction factor for nitrite oxidizers decay Maximum growth rate of heterotrophic biomass Affinity constant for oxygen of heterotrophic biomass Affinity constant for organic carbon of heterotrophic biomass Affinity constant for NO3 of heterotrophic biomass Maintenance coefficient of heterotrophic biomass Anoxic reduction factor of heterotrophic growth Aerobic decay rate of heterotrophic biomass

0.27

0.2

0.5

0.5

16.12

12

(Moussa et al., 2005) (Siegrist et al., 1999) (Henze et al., 2000)

0.2

0.2

(Henze et al., 2000)

2

2

(Henze et al., 2000)

0.5

0.5

(Henze et al., 2000)

0.16

0.12

(Meijer et al., 2001)

0.8

0.8

(Henze et al., 2000)

1.1

0.8

(Henze et al., 2000)

pt

Ac ce

ηNO

(Henze et al., 2000)

0.35

ed

2

(Moussa et al., 2005) (Henze et al., 2000)

0.56

M

K ONH

Reference

0.07

us

day

4

an

max µ NH

-1

Numerical value

ip t

Symbol

(Moussa et al., 2005) (Siegrist et al., 1999) (Hunik et al., 1994) (Moussa et al., 2005) (Moussa et al., 2005) (Tappe et al., 1999)

31

Page 31 of 34

Appendix C. The simulation results on COD removal and nitrification efficiency in the overloaded plant under different configurations.

OL (%)

COD removal (%)

NE (%)

10 15 20 25 30 10 15 20 25 30 10 15 20 25 30 10 15 20 25 30

79.37 78.51 77.71 76.95 76.21 85.86 83.81 82.35 81.26 80.38 78.85 77.55 76.49 75.56 75.00 83.33 82.15 80.99 79.86 78.76

57.55 49.83 42.76 36.31 30.42 91.90 86.18 79.10 71.71 64.51 79.67 72.63 65.76 59.24 53.10 92.97 91.93 90.73 89.39 87.87

ed

3. Overloaded plant +BABE reactor

0 0 0 0 0 59.67 72.96 84.99 97.51 112.06 38.42 45.75 53.80 63.16 74.56 61.53 84.5 112.20 146.21 188.85

Ac ce

pt

4. Overloaded plant +BABE reactor+ SBRs

us

an

2. Overloaded plant with additional aeration tanks

M

1. Overloaded plant without any additional aeration tanks

NEI (%)

cr

Configurations

ip t

Parameters

32

Page 32 of 34

Appendix D. The simulation results of aeration requirements in the overloaded plant for different configurations

2. Overloaded plant with additional aeration tanks

AOU [%]

10 15 20 25 30 10 15 20 25 30 10 15 20 25 30 10 15 20 25 30

20500 20500 20500 20500 20500 25625 25625 25625 25625 25625 23000 23000 23000 23000 23000 26000 27000 28000 29000 30000

0 0 0 0 0 5125 (25%) 5125 (25%) 5125 (25%) 5125 (25%) 5125 (25%) 2500 (12%) 2500 (12%) 2500 (12%) 2500 (12%) 2500 (12%) 5500 (27%) 6500 (32%) 7500 (36%) 8500 (41%) 9500 (46%)

0 0 0 0 0 98.55 99.78 100.32 100.57 100.73 42.43 42.68 42.88 43.04 43.16 47.56 48.76 56.28 64.51 72.35

0 0 0 0 0 22.20 23.67 24.28 24.56 24.71 10.00 10.27 10.39 10.49 10.54 9.79 10.47 12.57 14.78 16.87

a

pt

4. Second suggested configuration: Overloaded plant +BABE reactor+SBRs

cr

ip t

AOUd [mg/(l.day)]

ed

3. First suggested configuration: Overloaded plant +BABE reactor

ARVc [m3 (%)]

us

1. Overloaded plant without any additional aeration tanks

RVb (m3)

an

Configurations

OLa (%)

M

Parameters

Overloading percentage Reactor Volume c Additional Reactor Volume d Additional Oxygen Uptake

Ac ce

b

33

Page 33 of 34

34

Page 34 of 34

ed

pt

Ac ce us

an

M

cr

ip t