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Energy-positive nitrogen removal of pharmaceutical wastewater by coupling heterotrophic nitrification and electrotrophic denitrification
Accepted Manuscript Energy-positive nitrogen removal of pharmaceutical wastewater by coupling heterotrophic nitrification and electrotrophic denitrification G.N. Nikhil, P. Suman, S. Venkata Mohan, Y.V. Swamy PII: DOI: Reference:
S1385-8947(17)30934-8 http://dx.doi.org/10.1016/j.cej.2017.05.165 CEJ 17064
To appear in:
Chemical Engineering Journal
Received Date: Revised Date: Accepted Date:
11 May 2016 25 May 2017 28 May 2017
Please cite this article as: G.N. Nikhil, P. Suman, S. Venkata Mohan, Y.V. Swamy, Energy-positive nitrogen removal of pharmaceutical wastewater by coupling heterotrophic nitrification and electrotrophic denitrification, Chemical Engineering Journal (2017), doi: http://dx.doi.org/10.1016/j.cej.2017.05.165
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Energy-positive nitrogen removal of pharmaceutical wastewater by coupling heterotrophic nitrification and electrotrophic denitrification G.N. Nikhil, P. Suman, S. Venkata Mohan, Y.V. Swamy* Bioengineering and Environmental Sciences (BEES), CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad-500 007 Email: [email protected]; Phone: +91-40-27193159
Abstract An attempt was made to cohesively assess the aerobic nitrification treatment (ANT) and bioelectrochemical denitrification treatment (DNT) of real-field pharmaceutical wastewater. The results revealed that ANT resulted in the removal of 73% ammonium and 78.5% organic carbon content. Subsequently, the outlet of ANT was fed to DNT for the evaluation of relative influence of nature of external circuitry influence.. The DNT system with closed circuit mode (CCM) resulted in 82.8% of nitrates and 61.1% of organic content removal even at low C/N ratio of 2.18. The other pollutant concentrations viz., phosphates, sulfates and total dissolved salts were also significantly removed in both ANT and DNT systems. Thus, the outcome of the study proposes for a sequential integration of both the processes that exhibits high potential for selfsustained energy-positive nutrient removal.
Keywords: bioelectrofermentation; biocatalysis; multi-pollutants; external circuitry
1. Introduction In recent years, extensive anthropogenic activities have led to alarmingly over-abundance of nitrogenous compounds (viz., nitrate, nitrite, or ammonium) in water bodies, thus resulting in adverse ecological impact [1]. These compounds like ammonium and nitrate principally together accounts for greater ill-effects on both aquatic as well as a terrestrial ecosystem. In many parts of the world, including India, the potable water is contaminated with nitrate [2]. Therefore, stringent regulations are made mandatory to curtail the concentration of contaminants in industry-discharged water i.e., ammonium and nitrate to 50 mg L-1 and 10 mg L-1, respectively [1]. 1
Conventionally, removal of nitrogenous components from liquid waste is accomplished by employing various physical and chemical methods. However, these methods merely allocate the displacement of ammonium or nitrate from the contaminated solution, instead of destructing these pollutants. Thus, the major shortcoming is the formation secondary wastewater, containing pollutants which is needs to be treated and disposed of safely [3]. Alternatively, the biological approach of nitrification followed by denitrification is found suitable for the removal of ammonium and nitrate [4]. In spite of being eco-friendly and economically viable, the sluggish nature of biological approach of nitrogen removal makes it challenging to consider for water treatment [1]. In recent times, efforts have been focused on driving up nitrification and denitrification technique as it may reduce the complexity of further treatment [5-7].
The complete elimination of nitrogen from water through biological route recruits diversified consortia of microorganisms, wherein essential metabolic steps permit the nitrogen remediation process [8]. The ammonium present in wastewater is converted to nitrate during nitrification and further the nitrate content of wastewater is removed by denitrification [9]. The nitrification process is accomplished by nitrifying bacteria in aerobic condition at the optimum pH, where ammonium undergoes stepwise oxidation to form nitrate as the final product [10]. Later, the ubiquitous denitrifying bacteria carry out biological denitrification by utilizing oxygen present in nitrate during their respiratory process in anoxic condition and produce harmless “N2” by complete reduction [11, 12]. Currently, the scientific fraternity is focusing on denitrification via bio-electrochemical treatment strategies for simultaneous treatment and value-addition [6, 1315].
Earlier studies have documented proficient application of nitrification and denitrification mechanism in treating synthetic wastewater by removing nitrogenous pollutants and organic matter [9, 16]. The present study aimed to investigate the efficacy of integrative aerobic nitrification treatment (ANT) and bioelectrochemical denitrification treatment (DNT) in a sequential manner for the treatment of real-field pharmaceutical effluent. Furthermore, the influence of external circuitry regulation on DNT performance was investigated.
2
2. Experimental Methodology 2.1. Biocatalyst Aerobic mixed culture was collected from aerobic domestic effluent treatment plant and it is used as inoculum for ANT. Prior to experiment, the aerobic culture was enriched with designed synthetic wastewater (DSW) containing glucose as carbon source and ammonium chloride as nitrogen source. Anaerobic mixed culture was collected from anaerobic domestic effluent treatment plant and it is used as inoculum for DNT. Prior to experiment, anaerobic culture was enriched with DSW containing sodium acetate as carbon source and sodium nitrate as nitrogen source. Both the treatment studies were carried out individually with real-field pharmaceutical wastewater which was characterized as follows: pH 6.5-6.7, chemical oxygen demand (COD) 12000-13500 mg L-1, ammonium –170 mg L-1 , nitrate - 985 mg L-1 , phosphates - 215 mg L-1 , sulfates- 190 mg L-1 , TDS- 8450 mg L-1 , TSS- 1630 mg L-1 , VFA- 2500 mg L-1.
2.2. Reactor construction and operation Two single-chambered cylindrical reactors were designed and fabricated using perspex material with working/total volume of 1000/1200 mL. Of these, one reactor was used for ANT and the other was used for DNT that holds a couple of non-catalyzed graphite electrodes (5 cm x 5cm x 1 cm; geometrical surface area 70 cm2) as anode and cathode. The anode was completely submerged at the bottom of the reactor that supports exclusively for oxidation and cathode at the top that enables reduction. The entire study is carried out in two phases i.e. ANT followed by DNT. In the first phase, ANT reactor comprising of aerobic mixed culture with pharmaceutical wastewater was operated under continuous aeration by maintaining the dissolved oxygen (DO) level of above 0.8 mg L-1. In the second phase, the effluent after treatment in ANT reactor was subsequently fed into DNT reactor which was operated in three different circuitry modes viz., open circuit (OCM), closed circuit (CCM) and short circuit (SCM). Initially, the DNT reactor was operated in open circuit mode (OCM) for stabilization of open circuit voltage. After stabilization in OCM, polarization of the DNT reactor was assessed by ramping with a variable external resistor at resistances ranging from 30–0.05 kΩ. The resistance at which maximum power point (MPP) was obtained was subsequently chosen to close the circuit and the DNT reactor was operated in CCM. After attaining the maximum power, consequently, the resistance was removed resulting in short circuit and the DNT reactor was operated in short circuit mode 3
(SCM). All the reactor operations were performed in a batch process with a hydraulic retention time of 12 h for about 60 days. Samples collected from both the reactors at regular time intervals of 4 h were analyzed. Organic matter (chemical oxygen demand, COD; 5220-C), ammonium (4500-NH3) nitrate (4500-B), sulfates (4500-E), phosphates (4500-D) and pH (4500-H+B) were estimated as per the standard procedures [17]. Bioelectrochemical behavior of the DNT reactor was evaluated with standard operating procedures under external applied voltage range (-0.5mV to -0.5mV) with cyclic voltammetric technique [18]. All the experiments were carried out in duplicates, and the average is represented in results.
3. Results and Discussion 3.1 Ammonium removal in ANT Operation of ANT reactor showed decrement of ammonium concentration from 160 ± 10 mg L-1 to 75 ± 5 mg L-1 amounting to 56% removal after 8 batch cycles (Fig. 1a). After 12 batch cycles, the ammonium concentration reduced to 42 ± 2 mg L-1 which is 73% removal. Ammonium Degradation Rate (ADR) was calculated to be 3.66 mg L-1 h-1 during start-up phase that later rose to 6.66 mg L-1 h-1 at the end of 8th cycle; finally, stabilized to 9.42 ± 0.05 mg L-1 h-1 at the end of 12th cycle (Fig. 1a). Consequently, the nitrates increased from 930 ± 13 to 1420 ± 17 mg L-1 augmenting to about 53% after 8 cycles of operation and finally to 1470 ± 10 mg L-1 resulting in 69% at the end of the 12th cycle (Fig. 1b). Table 1 summarizes the result of ammonium removal through nitrification in ANT. The reduction in ammonium synchronized with increase in the nitrates; signifying the efficacy of nitrification process which was considered as a major marker to evaluate the performance of the ANT [5].
3.2 Influence of external circuit over denitrification The DNT reactor was operated in three circuitry modes – OCM, CCM, and SCM and the reactor performance was observed in the following trend – CCM>OCM>SCM (Fig. 2). Initially, the DNT reactor was kept in OCM for stabilization of open circuit voltage. During this phase, electro-active bacteria are selectively enriched and a biofilm is formed over the anode. These bacteria respire by shuttling electrons to the electrode [19]. Likewise, at cathode, denitrifying bacteria are enriched to reduce the nitrates to nitrogen. After stabilization, the maximum open circuit voltage (OCV) obtained was 253 mV; thereafter polarization analysis was carried out. 4
During OCM, the nitrate removal rate was 82.16 mg L-1 h-1 resulting in removal efficiency of 69.5%. The resistance at which maximum power point (MPP) was obtained was subsequently chosen to close the circuit of DNT reactor. In this study, the MPP was 11.2 mWm-2 at 200 Ω resistance. During CCM, nitrate removal rate increased to 92.5 mg L-1 h-1 resulting in 82.8% removal
which is attributed to the enrichment of electro-active denitrfying bactria during
circuitry operation of DNT reactor. The external resistance obtained from polarization is considered to be equivalent to the internal resistance of the DNT system. This optimized resistance provided a stabilized and steady electron flow from anode to cathode resulting in notable nitrate removal [20]. After few cycles, the resistance was removed resulting in short circuit. In this case, the electron flow from anode to cathode becomes uncontrolled resulting in maximum current density and formation of capacitance over the cathode. During SCM, the nitrate removal rate decreased to 55.16 mg L-1 h-1 resulting in removal efficiency of 50.4% attributing to the intolerance of denitryfing bacteria to the electrochemical charge colud (capacitance) to thrive over the cathode. Biological route of nitrate elimination (via denitrification) principally depends on the presence or absence of organic matter. During heterotrophic denitrification, the oxidation of organic matter at the anode is a source of electrons for denitrification process at the cathode. While, in autotrophic condition, inorganic chemical compounds can be a source of electrons for denitrification [8, 21]. In the present study, nitrate removal at cathode is composite of bioelectrochemical reactions of electrotrophic denitrifying microorganisms owing to the availability of organic substrate [22]. The inadequate performance of DNT in OCM/SCM is ascribed to hysterical electron flow between anode and cathode during membrane-less condition.
3.3 Wastewater treatment 3.3.1 Substrate removal The organic content in pharmaceutical wastewater is estimated as chemical oxygen demand (COD). The inlet COD value of 13500 mg L-1 decreased to 2970 mg L-1 resulting in 78.5% removal efficiency with a removal rate of 877.6 mg L-1 h-1 at the end of the 12th cycle of ANT (Fig. 3). Subsequently, further COD removal was observed in DNT reactor but varied with circuit operation. Operation in CCM resulted in maximum COD removal efficiency of 61.1%, followed by OCM with 53.6% and then SCM with 46.7%. Substrate oxidation in DNT is carried 5
out at the anode where anode respiring bacteria utilizes the organic matter present in the feed. At the cathode, electro-active denitrifying bacteria reduce nitrate to nitrogen [23]. During these redox metabolic processes, protons and electrons are released out and these electrons are captured as bioelectricity when the circuit is closed with a defined external resistance [24].
3.3.2 C/N ratio The denitrification potential of biocatalyst is a function of available organic carbon, which is usually expressed as the C/N ratio. Earlier studies reported on conventional denitrification process for wastewater exhibited a low C/N ratio. The conventional denitrification is challenging; since, the process requires C/N ratio typically in the range of 7-10 [8]. A few recent studies have reported bioelectrochemical denitrification resulted in high nitrate removal with average C/N ratio ranging from 2.65 to 3.01 but with synthetic feed [3]. Besides, in bioelectrochemical systems an increase in the removal rate of both ammonium and nitrate was observed with the decreasing C/N ratio [25]. A comparative table is presented to illustrate the effect of C/N on nitrate removal (Table 2). In the present study with real field pharmacetical wastewater, ANT operation resulted in COD removal with increased nitrates resulting in decreased C/N ratio (4.02 to 2.18). Thereafter, the effluent of ANT was fed to bioelectrochemical DNT reactor operated in different circuitry modes and finally CCM of operation resulted in 82.8% nitrates removal even at low C/N ratios.
3.3.3 pH During ANT, it was observed that the pH rose from an initial value of 7.00 ± 0.02 to 8.16 ± 0.03 at the end of batch cycle. Later, the initial pH was set to 7.5 ±0.02 which increased to a final value of 8.64 ±0.04 at the end of the batch cycle. Certain studies suggested that change in pH can influence the nitrification rate; for instance: pH range of 6.45–8.95 results in complete nitrification and pH beyond the range might cause inhibition [26, 27]. In this study, decrease in ammonium concentration was noticed with increase in nitrates concentration at the end of ANT operation. Perhaps, a certain amount of ammonium removal through volatilization due to pH fluctuations that arise below the dissociation constant (pKa) of ammonia i.e. 9.24 [28].
3.3.4 Multi-pollutant removal 6
During the ANT operation, besides ammonia; sulfates, phosphates and total dissolved salts (TDS) removal was also observed. The maximum removal efficiencies of sulfates, phosphates and TDS are 43 ± 0.5%; 49.6% and 24.5%, respectively (Fig. 4). Further removal of sulfates, phosphates and TDS was also observed in DNT system operated in different circuitry modes. The order of removal efficiencies are as follows: CCM (30.1%, 33.6%, 35.3%) > OCM (23.6%, 24.9%, 28.6%) > SCM (19.7%, 18.4%, 24.2%). On the whole, integrated sequential approach showed notable removal efficiencies of multi-pollutants viz., sulfates, phosphates, and TDS. It is understood that these inorganic salts present in wastewater act as a source of electron donors and acceptors during the process of biological and electrochemical remediation [14, 29].
3.4 Bioelectrochemical assessment The designed DNT system showed power generation when operated under an external load of 750Ω in CCM resulting in power density of 31.43mWm-2 (Fig. 5a). The operating load was obtained by polarization analysis of the DNT reactor that resulted in MPP at 750Ω (Fig. 5b). Empirical observation from the slopes of polarization curve gave an understanding about the electron losses (activation, ohmic and concentration) that inherently exists [30]. It is ascribed that the disparity in DNT performance was noticed by external circuit regulation. In typical microbial fuel cells, oxygen acts as a terminal electron acceptor (TEA) for the cathodic reduction reaction; thus, enabling for power generation [31, 32]. In the present study, the bioelectrochemical denitrification of nitrate-rich effluent was carried out, where nitrate functioned as TEA facilitating the removal of nitrate.
The biocatalytic activity of enriched electroactive bacteria was analyzed by measuring anode potential. The anode potential was noticed to be maximum at CCM (-430mV) followed by OCM (-380 mV) and then SCM (-275mV) (Fig. 5c). Further, the bioelectrochemical activity of biocatalyst was evaluated by carrying out cyclic voltammetry (CV). Cyclic voltammetry infers the synergistic interaction of anodic biofilm and external circuitry influencing the electron transfer capacity of the biocatalyst [9, 33]. The working electrode was connected to the anode; the counter electrode was connected to the cathode and a reference was connected with Ag/AgCl electrode (+0.197 V vs. SHE) [33]. Voltammograms (vs. Ag/AgCl) showed a variation of redox currents (iox, oxidation; ired, reduction) in all the three circuit modes at 0th h and 12th h. In OCM, 7
the iox was higher than ired ,similarly noticed in CCM as well (Sfig.1). Effective treatment was noticed in DNT under CCM due to the slow discharge of electrons which was substantially evidenced through voltammetric measurements.
4. Conclusion The designed ANT reactor resulted in considerable ammonia removal and nitrates production even at low C/N ratio of 2.18. Subsequently, the effluent of ANT was fed to the DNT reactor operated in three circuitry modes. Among which, CCM operation resulted in significant denitrification along with power generation. The study inferred that sequential integration of ANT and DNT reactors are efficient in removing nitrogen compounds and other multi-pollutants at higher rate than the conventional treatment strategies.
Conflict of interest All the authors have declared no conflict of interest.
Acknowledgements The authors wish to thank the Director, CSIR-IICT for support and encouragement in carrying out this work. The research was funded by CSIR in the form of XIIth five year plan project on ‘Development of Sustainable Waste Management Technologies for Chemical and Allied Industries’ (SETCA; CSC-0113).
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[5] A. Sotres, M. Cerrillo, M. Viñas, A. Bonmatí, Nitrogen removal in a two-chambered microbial fuel cell: Establishment of a nitrifying–denitrifying microbial community on an intermittent aerated cathode, Chemical Engineering Journal 284 (2016) 905-916. [6] A. Al-Mamun, O. Lefebvre, M. Baawain, H. Ng, A sandwiched denitrifying biocathode in a microbial fuel cell for electricity generation and waste minimization, International Journal of Environmental Science and Technology 13 (2016) 1055-1064. [7] A. Hussain, M. Manuel, B. Tartakovsky, A comparison of simultaneous organic carbon and nitrogen removal in microbial fuel cells and microbial electrolysis cells, Journal of environmental management 173 (2016) 23-33. [8] A. Vilar-Sanz, S. Puig, A. García-Lledó, R. Trias, M.D. Balaguer, J. Colprim, L. Bañeras, Denitrifying bacterial communities affect current production and nitrous oxide accumulation in a microbial fuel cell, PloS one 8 (2013) e63460. [9] F. Zhang, Z. He, Simultaneous nitrification and denitrification with electricity generation in dual‐cathode microbial fuel cells, Journal of Chemical Technology and Biotechnology 87 (2012) 153-159. [10] F. Fang, B.-J. Ni, X.-Y. Li, G.-P. Sheng, H.-Q. Yu, Kinetic analysis on the two-step processes of AOB and NOB in aerobic nitrifying granules, Applied microbiology and biotechnology 83 (2009) 1159-1169. [11] P. De Filippis, L. Di Palma, M. Scarsella, N. Verdone, Biological denitrification of highnitrate wastewaters, Chemical Engineering Transactions 32 (2013) 319-324. [12] O. Lefebvre, A. Al-Mamun, H. Ng, A microbial fuel cell equipped with a biocathode for organic removal and denitrification, Water Science and Technology 58 (2008) 881. [13] Y. Li, I. Williams, Z. Xu, B. Li, B. Li, Energy-positive nitrogen removal using the integrated short-cut nitrification and autotrophic denitrification microbial fuel cells (MFCs), Applied Energy 163 (2016) 352-360. [14] G. Velvizhi, R.K. Goud, S.V. Mohan, Anoxic bio-electrochemical system for treatment of complex chemical wastewater with simultaneous bioelectricity generation, Bioresource technology 151 (2014) 214-220. [15] S.V. Mohan, G. Velvizhi, K.V. Krishna, M.L. Babu, Microbial catalyzed electrochemical systems: a bio-factory with multi-facet applications, Bioresource technology 165 (2014) 355364. 9
[16] B. Virdis, K. Rabaey, R.A. Rozendal, Z. Yuan, J. Keller, Simultaneous nitrification, denitrification and carbon removal in microbial fuel cells, Water Research 44 (2010) 2970-2980. [17] W.E. Federation, A.P.H. Association, Standard methods for the examination of water and wastewater, American Public Health Association (APHA): Washington, DC, USA (2005). [18] G. Velvizhi, S.V. Mohan, Bioelectrogenic role of anoxic microbial anode in the treatment of chemical wastewater: microbial dynamics with bioelectro-characterization, Water research 70 (2015) 52-63. [19] G. Mohanakrishna, S.K. Butti, R.K. Goud, S.V. Mohan, Spatiometabolic stratification of anoxic biofilm in prototype bioelectrogenic system, Bioelectrochemistry (2017). [20] S. Srikanth, S.V. Mohan, P. Sarma, Positive anodic poised potential regulates microbial fuel cell performance with the function of open and closed circuitry, Bioresource technology 101 (2010) 5337-5344. [21] A. Al-Mamun, M.S. Baawain, F. Egger, A.a.H. Al-Muhtaseb, H.Y. Ng, Optimization of a baffled-reactor microbial fuel cell using autotrophic denitrifying bio-cathode for removing nitrogen and recovering electrical energy, Biochemical Engineering Journal (2017). [22] H. Zhao, J. Zhao, F. Li, X. Li, Performance of denitrifying microbial fuel cell with biocathode over nitrite, Frontiers in Microbiology 7 (2016). [23] Z.P. Zhang Jiqiang, Zhang Meng, LI Wei, Chen Hui, CAI Chen, Xie Zuofu, Coupling process and mechanism of methanol oxidation and nitrate reduction in an anodic denitrification microbial fuel cell(AD-MFC), CIESC Journal 64 (2013) 3404-3411. [24] G. Velvizhi, S.V. Mohan, Biocatalyst behavior under self-induced electrogenic microenvironment in comparison with anaerobic treatment: evaluation with pharmaceutical wastewater for multi-pollutant removal, Bioresource technology 102 (2011) 10784-10793. [25] F. Zhang, Z. He, Integrated organic and nitrogen removal with electricity generation in a tubular dual-cathode microbial fuel cell, Process Biochemistry 47 (2012) 2146-2151. [26] P.M. Kyveryga, A.M. Blackmer, J.W. Ellsworth, R. Isla, Soil pH effects on nitrification of fall-applied anhydrous ammonia, Soil Science Society of America Journal 68 (2004) 545-551. [27] G. Ruiz, D. Jeison, R. Chamy, Nitrification with high nitrite accumulation for the treatment of wastewater with high ammonia concentration, Water Research 37 (2003) 1371-1377. [28] Z. He, A. Alva, D. Calvert, D. Banks, Ammonia volatilization from different fertilizer sources and effects of temperature and soil pH1, Soil Science 164 (1999) 750-758. 10
[29] S.V. Mohan, S. Srikanth, Enhanced wastewater treatment efficiency through microbially catalyzed oxidation and reduction: synergistic effect of biocathode microenvironment, Bioresource technology 102 (2011) 10210-10220. [30] D.K. Yeruva, G. Velvizhi, S.V. Mohan, Coupling of aerobic/anoxic and bioelectrogenic processes for treatment of pharmaceutical wastewater associated with bioelectricity generation, Renewable Energy (2016). [31] S. Srikanth, S.V. Mohan, Influence of terminal electron acceptor availability to the anodic oxidation on the electrogenic activity of microbial fuel cell (MFC), Bioresource technology 123 (2012) 480-487. [32] G. Nikhil, D.K. Yeruva, S.V. Mohan, Y. Swamy, Assessing potential cathodes for resource recovery through wastewater treatment and salinity removal using non-buffered microbial electrochemical systems, Bioresource Technology (2016). [33] G. Nikhil, G.V. Subhash, D.K. Yeruva, S.V. Mohan, Closed circuitry operation influence on microbial
electrofermentation:
Proton/electron
Bioresource technology 195 (2015) 37-45.
11
effluxes
on
electro-fuels
productivity,
10
A
140
9
ADR 120
8 7
100
6 80
5
60
4 3
40
+ ADR (mg-NH4 /L/h)
+ Ammonium concentration (mg-NH4 /L)
+
[NH4 ]
2 20 0
1 0
2
4
6
8
10
12
0
Cycle number 1500
Nitrates pH
B
10 9 8
1400
7 1300
6
1200
5
1100
4
1000
3
900
2
pH
Nitrates concentration (mg-NO3 /L)
1600
1
800
0 0 12 24 36 48 60 72 84 96 108 120 132 144 156 Operation time (h) Fig.1 Nitrification performance of ANT reactor: (A) ammonium removal and ammonium degradation rate (ADR); (B) Variation in nitrate concentration and pH.
12
OCM
CCM
SCM
- -1 -1 Nitrate removal rate(mg-NO3 L h )
100 90 80 70 60 50 40 30 20 10 0 Cycle1
Cycle2
Cycle3
Cycle4
Cycles operation Fig. 2 Denitrification performance of DNT reactor (as nitrate removal rate) at different circuitry connections: OCM (Open Circuit Mode), CCM (Closed Circuit Mode) and SCM (Short Circuit Mode).
13
100
OCM
90
ANT
DNT
Cumulative
80 COD removal (%)
70 60 50 40 30 20 10 0 Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle Operation 100
ANT
DNT
Cumulative
CCM
90
COD removal(%)
80 70 60 50 40 30 20 10 0 Cycle 1
Cycle 2
Cycle 3
Cycle Operation
14
Cycle 4
100
ANT
DNT
Cumulative
SCM
90
COD removal(%)
80 70 60 50 40 30 20 10 0 Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle operation Fig. 3 Cumulative performance of ANT and DNT reactors with respect to organic content degradation (as COD removal efficiency) during (A) OCM (B) CCM (C) SCM.
15
100 90
OCM
CCM
SCM
A
Sulphates removal(%)
80 70 60 50 40 30 20 10 0 ANT
DNT
Cumulative
100 90
OCM
CCM
SCM
B
Phosphates removal (%)
80 70 60 50 40 30 20 10 0
ANT
DNT
16
Cumulative
100 90
OCM
CCM
SCM
C
80 TDS removal(%)
70 60 50 40 30 20 10 0
ANT
DNT
Cumulative
Fig.4 Cumulative assessment of multi-pollutant removal by both ANT and DNT reactors: (A) sulphates removal (B) Phosphates removal (C) TDS removal.
17
OCM
Anode potential(mV) vs Ag/AgCl
0
CCM
SCM
A -100
-200
-300
-400
-500
0
5000
10000 15000 20000 25000 30000 Resistance (Ω)
300
14 V-I Curve
Power Curve B
12 10
200
8 150 6 100
4
50 0
2
0
25
50
75
100
-2 Current density (I, mAm )
18
125
0
-2 Power density (P, mWm )
Voltage (V, mV)
250
40 C 35
-2
Power density (mWm )
30 25 20 15 10 5 0 0
10
20
30
40
50
60
Operation time (h) Fig. 5 Bioelectrochemical performance evaluation of DNT reactor: (A) Anode potential; (B) Polarization curve; (C) Power density.
19
Table
Table 1: Relative performance of ANT reactor for ammonium removal
Cycle Number
Outlet Ammonium (mg-NH4+ l-1) 123
Ammoniu m removal (%) 25.45
Outlet Nitrate (mg-NO3--N l-1) 1024
Increase in nitrates (%) 18.38
Outlet pH
Cycle 2
Inlet Ammonium (mg-NH4+ l-1) 165
Cycle 8
160
70
56.25
1384
41.89
8.21
Cycle 12
152
42
72.36
1451
64.24
8.41
1
7.91
Table 2: Influence of C/N ratio on nitrate removal S. No
Substrate
Carbon Source
Organic Nitrogen load (mg/L) source
Circuit connection
Nitrogen removal %
References
1
Synthetic Wastewater (SW)
Sodium Acetate
127.3± 4.6
Ammonium Chloride
16.9 ± 1.4
8.1 ± 0.4
Open circuit
42.2 ± 1.4
(Virdis et al., 2010)
2
SW
Sodium Acetate
745 ± 231
Sodium Nitrate
29.6 ± 5.3
34.9
Closed circuit
18.9
(Vilar-Sanz et al., 2013)
3
SW
Sodium Acetate
500
Sodium Nitrate
21.4 ± 0.2
23.6 ± 0.4
Poised 55.8 Potential(-0.8V)
(Tong and He, 2014)
4
SW
Glucose
300
Sodium Nitrate
100
3
Open circuit
>80
(Xiao et al., 2013)
5
SW
Methanol
400
Sodium Nitrate
200
2
Nil (Batch Study)
79
(Foglar et al., 2005)
6
SW
Sodium Acetate
50-320
Sodium Nitrate
20-110
2.5-2.9 Closed circuit (1.1Ω)
72.8
(Clauwaert et al., 2009)
7
SW
Methanol
250 ± 0.01 – Sodium 176,00 ± Nitrate 135.41
50 ± 0.02 3560 ± 36.80
5
Closed circuit (1000 Ω)
>95
(Zhang et al., 2013)
8
Pharmaceutical wastewater
ANT Effluent
3100
1381
2.18
Closed circuit (750Ω)
80.24
Present study
Nitrates
2
Nitrogen C/N inlet (mg/L) ratio
Highlights •
Substantial bioelectrochemical denitrification was noticed under closed circuitry.
•
The designed bioelectrochemical DNT system performed at low C/N ratios.
•
Sequential integration of ANT & DNT resulted in remarkable multi-pollutant removal.
22
Energy-positive nitrogen removal of pharmaceutical wastewater by coupling heterotrophic nitrification and electrotrophic denitrification G.N.Nikhil, P.Suman, S.Venkata Mohan, Y.V.Swamy* Bioengineering and Environmental Sciences (BEES), CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad-500007 Email: [email protected]; Phone: +91-40-27193159
Schematic view of (A) ANT (Aerobic Nitrification Treatment) reactor and (B) DNT (Denitrification Treatment) reactor (1: nitrifying organisms, 2: Anode Oxidizing Bacteria, 3: Nitrate reducing bacteria, P1 & P2: Pumps).
23
S1385-8947(17)30934-8 http://dx.doi.org/10.1016/j.cej.2017.05.165 CEJ 17064
To appear in:
Chemical Engineering Journal
Received Date: Revised Date: Accepted Date:
11 May 2016 25 May 2017 28 May 2017
Please cite this article as: G.N. Nikhil, P. Suman, S. Venkata Mohan, Y.V. Swamy, Energy-positive nitrogen removal of pharmaceutical wastewater by coupling heterotrophic nitrification and electrotrophic denitrification, Chemical Engineering Journal (2017), doi: http://dx.doi.org/10.1016/j.cej.2017.05.165
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.
Energy-positive nitrogen removal of pharmaceutical wastewater by coupling heterotrophic nitrification and electrotrophic denitrification G.N. Nikhil, P. Suman, S. Venkata Mohan, Y.V. Swamy* Bioengineering and Environmental Sciences (BEES), CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad-500 007 Email: [email protected]; Phone: +91-40-27193159
Abstract An attempt was made to cohesively assess the aerobic nitrification treatment (ANT) and bioelectrochemical denitrification treatment (DNT) of real-field pharmaceutical wastewater. The results revealed that ANT resulted in the removal of 73% ammonium and 78.5% organic carbon content. Subsequently, the outlet of ANT was fed to DNT for the evaluation of relative influence of nature of external circuitry influence.. The DNT system with closed circuit mode (CCM) resulted in 82.8% of nitrates and 61.1% of organic content removal even at low C/N ratio of 2.18. The other pollutant concentrations viz., phosphates, sulfates and total dissolved salts were also significantly removed in both ANT and DNT systems. Thus, the outcome of the study proposes for a sequential integration of both the processes that exhibits high potential for selfsustained energy-positive nutrient removal.
Keywords: bioelectrofermentation; biocatalysis; multi-pollutants; external circuitry
1. Introduction In recent years, extensive anthropogenic activities have led to alarmingly over-abundance of nitrogenous compounds (viz., nitrate, nitrite, or ammonium) in water bodies, thus resulting in adverse ecological impact [1]. These compounds like ammonium and nitrate principally together accounts for greater ill-effects on both aquatic as well as a terrestrial ecosystem. In many parts of the world, including India, the potable water is contaminated with nitrate [2]. Therefore, stringent regulations are made mandatory to curtail the concentration of contaminants in industry-discharged water i.e., ammonium and nitrate to 50 mg L-1 and 10 mg L-1, respectively [1]. 1
Conventionally, removal of nitrogenous components from liquid waste is accomplished by employing various physical and chemical methods. However, these methods merely allocate the displacement of ammonium or nitrate from the contaminated solution, instead of destructing these pollutants. Thus, the major shortcoming is the formation secondary wastewater, containing pollutants which is needs to be treated and disposed of safely [3]. Alternatively, the biological approach of nitrification followed by denitrification is found suitable for the removal of ammonium and nitrate [4]. In spite of being eco-friendly and economically viable, the sluggish nature of biological approach of nitrogen removal makes it challenging to consider for water treatment [1]. In recent times, efforts have been focused on driving up nitrification and denitrification technique as it may reduce the complexity of further treatment [5-7].
The complete elimination of nitrogen from water through biological route recruits diversified consortia of microorganisms, wherein essential metabolic steps permit the nitrogen remediation process [8]. The ammonium present in wastewater is converted to nitrate during nitrification and further the nitrate content of wastewater is removed by denitrification [9]. The nitrification process is accomplished by nitrifying bacteria in aerobic condition at the optimum pH, where ammonium undergoes stepwise oxidation to form nitrate as the final product [10]. Later, the ubiquitous denitrifying bacteria carry out biological denitrification by utilizing oxygen present in nitrate during their respiratory process in anoxic condition and produce harmless “N2” by complete reduction [11, 12]. Currently, the scientific fraternity is focusing on denitrification via bio-electrochemical treatment strategies for simultaneous treatment and value-addition [6, 1315].
Earlier studies have documented proficient application of nitrification and denitrification mechanism in treating synthetic wastewater by removing nitrogenous pollutants and organic matter [9, 16]. The present study aimed to investigate the efficacy of integrative aerobic nitrification treatment (ANT) and bioelectrochemical denitrification treatment (DNT) in a sequential manner for the treatment of real-field pharmaceutical effluent. Furthermore, the influence of external circuitry regulation on DNT performance was investigated.
2
2. Experimental Methodology 2.1. Biocatalyst Aerobic mixed culture was collected from aerobic domestic effluent treatment plant and it is used as inoculum for ANT. Prior to experiment, the aerobic culture was enriched with designed synthetic wastewater (DSW) containing glucose as carbon source and ammonium chloride as nitrogen source. Anaerobic mixed culture was collected from anaerobic domestic effluent treatment plant and it is used as inoculum for DNT. Prior to experiment, anaerobic culture was enriched with DSW containing sodium acetate as carbon source and sodium nitrate as nitrogen source. Both the treatment studies were carried out individually with real-field pharmaceutical wastewater which was characterized as follows: pH 6.5-6.7, chemical oxygen demand (COD) 12000-13500 mg L-1, ammonium –170 mg L-1 , nitrate - 985 mg L-1 , phosphates - 215 mg L-1 , sulfates- 190 mg L-1 , TDS- 8450 mg L-1 , TSS- 1630 mg L-1 , VFA- 2500 mg L-1.
2.2. Reactor construction and operation Two single-chambered cylindrical reactors were designed and fabricated using perspex material with working/total volume of 1000/1200 mL. Of these, one reactor was used for ANT and the other was used for DNT that holds a couple of non-catalyzed graphite electrodes (5 cm x 5cm x 1 cm; geometrical surface area 70 cm2) as anode and cathode. The anode was completely submerged at the bottom of the reactor that supports exclusively for oxidation and cathode at the top that enables reduction. The entire study is carried out in two phases i.e. ANT followed by DNT. In the first phase, ANT reactor comprising of aerobic mixed culture with pharmaceutical wastewater was operated under continuous aeration by maintaining the dissolved oxygen (DO) level of above 0.8 mg L-1. In the second phase, the effluent after treatment in ANT reactor was subsequently fed into DNT reactor which was operated in three different circuitry modes viz., open circuit (OCM), closed circuit (CCM) and short circuit (SCM). Initially, the DNT reactor was operated in open circuit mode (OCM) for stabilization of open circuit voltage. After stabilization in OCM, polarization of the DNT reactor was assessed by ramping with a variable external resistor at resistances ranging from 30–0.05 kΩ. The resistance at which maximum power point (MPP) was obtained was subsequently chosen to close the circuit and the DNT reactor was operated in CCM. After attaining the maximum power, consequently, the resistance was removed resulting in short circuit and the DNT reactor was operated in short circuit mode 3
(SCM). All the reactor operations were performed in a batch process with a hydraulic retention time of 12 h for about 60 days. Samples collected from both the reactors at regular time intervals of 4 h were analyzed. Organic matter (chemical oxygen demand, COD; 5220-C), ammonium (4500-NH3) nitrate (4500-B), sulfates (4500-E), phosphates (4500-D) and pH (4500-H+B) were estimated as per the standard procedures [17]. Bioelectrochemical behavior of the DNT reactor was evaluated with standard operating procedures under external applied voltage range (-0.5mV to -0.5mV) with cyclic voltammetric technique [18]. All the experiments were carried out in duplicates, and the average is represented in results.
3. Results and Discussion 3.1 Ammonium removal in ANT Operation of ANT reactor showed decrement of ammonium concentration from 160 ± 10 mg L-1 to 75 ± 5 mg L-1 amounting to 56% removal after 8 batch cycles (Fig. 1a). After 12 batch cycles, the ammonium concentration reduced to 42 ± 2 mg L-1 which is 73% removal. Ammonium Degradation Rate (ADR) was calculated to be 3.66 mg L-1 h-1 during start-up phase that later rose to 6.66 mg L-1 h-1 at the end of 8th cycle; finally, stabilized to 9.42 ± 0.05 mg L-1 h-1 at the end of 12th cycle (Fig. 1a). Consequently, the nitrates increased from 930 ± 13 to 1420 ± 17 mg L-1 augmenting to about 53% after 8 cycles of operation and finally to 1470 ± 10 mg L-1 resulting in 69% at the end of the 12th cycle (Fig. 1b). Table 1 summarizes the result of ammonium removal through nitrification in ANT. The reduction in ammonium synchronized with increase in the nitrates; signifying the efficacy of nitrification process which was considered as a major marker to evaluate the performance of the ANT [5].
3.2 Influence of external circuit over denitrification The DNT reactor was operated in three circuitry modes – OCM, CCM, and SCM and the reactor performance was observed in the following trend – CCM>OCM>SCM (Fig. 2). Initially, the DNT reactor was kept in OCM for stabilization of open circuit voltage. During this phase, electro-active bacteria are selectively enriched and a biofilm is formed over the anode. These bacteria respire by shuttling electrons to the electrode [19]. Likewise, at cathode, denitrifying bacteria are enriched to reduce the nitrates to nitrogen. After stabilization, the maximum open circuit voltage (OCV) obtained was 253 mV; thereafter polarization analysis was carried out. 4
During OCM, the nitrate removal rate was 82.16 mg L-1 h-1 resulting in removal efficiency of 69.5%. The resistance at which maximum power point (MPP) was obtained was subsequently chosen to close the circuit of DNT reactor. In this study, the MPP was 11.2 mWm-2 at 200 Ω resistance. During CCM, nitrate removal rate increased to 92.5 mg L-1 h-1 resulting in 82.8% removal
which is attributed to the enrichment of electro-active denitrfying bactria during
circuitry operation of DNT reactor. The external resistance obtained from polarization is considered to be equivalent to the internal resistance of the DNT system. This optimized resistance provided a stabilized and steady electron flow from anode to cathode resulting in notable nitrate removal [20]. After few cycles, the resistance was removed resulting in short circuit. In this case, the electron flow from anode to cathode becomes uncontrolled resulting in maximum current density and formation of capacitance over the cathode. During SCM, the nitrate removal rate decreased to 55.16 mg L-1 h-1 resulting in removal efficiency of 50.4% attributing to the intolerance of denitryfing bacteria to the electrochemical charge colud (capacitance) to thrive over the cathode. Biological route of nitrate elimination (via denitrification) principally depends on the presence or absence of organic matter. During heterotrophic denitrification, the oxidation of organic matter at the anode is a source of electrons for denitrification process at the cathode. While, in autotrophic condition, inorganic chemical compounds can be a source of electrons for denitrification [8, 21]. In the present study, nitrate removal at cathode is composite of bioelectrochemical reactions of electrotrophic denitrifying microorganisms owing to the availability of organic substrate [22]. The inadequate performance of DNT in OCM/SCM is ascribed to hysterical electron flow between anode and cathode during membrane-less condition.
3.3 Wastewater treatment 3.3.1 Substrate removal The organic content in pharmaceutical wastewater is estimated as chemical oxygen demand (COD). The inlet COD value of 13500 mg L-1 decreased to 2970 mg L-1 resulting in 78.5% removal efficiency with a removal rate of 877.6 mg L-1 h-1 at the end of the 12th cycle of ANT (Fig. 3). Subsequently, further COD removal was observed in DNT reactor but varied with circuit operation. Operation in CCM resulted in maximum COD removal efficiency of 61.1%, followed by OCM with 53.6% and then SCM with 46.7%. Substrate oxidation in DNT is carried 5
out at the anode where anode respiring bacteria utilizes the organic matter present in the feed. At the cathode, electro-active denitrifying bacteria reduce nitrate to nitrogen [23]. During these redox metabolic processes, protons and electrons are released out and these electrons are captured as bioelectricity when the circuit is closed with a defined external resistance [24].
3.3.2 C/N ratio The denitrification potential of biocatalyst is a function of available organic carbon, which is usually expressed as the C/N ratio. Earlier studies reported on conventional denitrification process for wastewater exhibited a low C/N ratio. The conventional denitrification is challenging; since, the process requires C/N ratio typically in the range of 7-10 [8]. A few recent studies have reported bioelectrochemical denitrification resulted in high nitrate removal with average C/N ratio ranging from 2.65 to 3.01 but with synthetic feed [3]. Besides, in bioelectrochemical systems an increase in the removal rate of both ammonium and nitrate was observed with the decreasing C/N ratio [25]. A comparative table is presented to illustrate the effect of C/N on nitrate removal (Table 2). In the present study with real field pharmacetical wastewater, ANT operation resulted in COD removal with increased nitrates resulting in decreased C/N ratio (4.02 to 2.18). Thereafter, the effluent of ANT was fed to bioelectrochemical DNT reactor operated in different circuitry modes and finally CCM of operation resulted in 82.8% nitrates removal even at low C/N ratios.
3.3.3 pH During ANT, it was observed that the pH rose from an initial value of 7.00 ± 0.02 to 8.16 ± 0.03 at the end of batch cycle. Later, the initial pH was set to 7.5 ±0.02 which increased to a final value of 8.64 ±0.04 at the end of the batch cycle. Certain studies suggested that change in pH can influence the nitrification rate; for instance: pH range of 6.45–8.95 results in complete nitrification and pH beyond the range might cause inhibition [26, 27]. In this study, decrease in ammonium concentration was noticed with increase in nitrates concentration at the end of ANT operation. Perhaps, a certain amount of ammonium removal through volatilization due to pH fluctuations that arise below the dissociation constant (pKa) of ammonia i.e. 9.24 [28].
3.3.4 Multi-pollutant removal 6
During the ANT operation, besides ammonia; sulfates, phosphates and total dissolved salts (TDS) removal was also observed. The maximum removal efficiencies of sulfates, phosphates and TDS are 43 ± 0.5%; 49.6% and 24.5%, respectively (Fig. 4). Further removal of sulfates, phosphates and TDS was also observed in DNT system operated in different circuitry modes. The order of removal efficiencies are as follows: CCM (30.1%, 33.6%, 35.3%) > OCM (23.6%, 24.9%, 28.6%) > SCM (19.7%, 18.4%, 24.2%). On the whole, integrated sequential approach showed notable removal efficiencies of multi-pollutants viz., sulfates, phosphates, and TDS. It is understood that these inorganic salts present in wastewater act as a source of electron donors and acceptors during the process of biological and electrochemical remediation [14, 29].
3.4 Bioelectrochemical assessment The designed DNT system showed power generation when operated under an external load of 750Ω in CCM resulting in power density of 31.43mWm-2 (Fig. 5a). The operating load was obtained by polarization analysis of the DNT reactor that resulted in MPP at 750Ω (Fig. 5b). Empirical observation from the slopes of polarization curve gave an understanding about the electron losses (activation, ohmic and concentration) that inherently exists [30]. It is ascribed that the disparity in DNT performance was noticed by external circuit regulation. In typical microbial fuel cells, oxygen acts as a terminal electron acceptor (TEA) for the cathodic reduction reaction; thus, enabling for power generation [31, 32]. In the present study, the bioelectrochemical denitrification of nitrate-rich effluent was carried out, where nitrate functioned as TEA facilitating the removal of nitrate.
The biocatalytic activity of enriched electroactive bacteria was analyzed by measuring anode potential. The anode potential was noticed to be maximum at CCM (-430mV) followed by OCM (-380 mV) and then SCM (-275mV) (Fig. 5c). Further, the bioelectrochemical activity of biocatalyst was evaluated by carrying out cyclic voltammetry (CV). Cyclic voltammetry infers the synergistic interaction of anodic biofilm and external circuitry influencing the electron transfer capacity of the biocatalyst [9, 33]. The working electrode was connected to the anode; the counter electrode was connected to the cathode and a reference was connected with Ag/AgCl electrode (+0.197 V vs. SHE) [33]. Voltammograms (vs. Ag/AgCl) showed a variation of redox currents (iox, oxidation; ired, reduction) in all the three circuit modes at 0th h and 12th h. In OCM, 7
the iox was higher than ired ,similarly noticed in CCM as well (Sfig.1). Effective treatment was noticed in DNT under CCM due to the slow discharge of electrons which was substantially evidenced through voltammetric measurements.
4. Conclusion The designed ANT reactor resulted in considerable ammonia removal and nitrates production even at low C/N ratio of 2.18. Subsequently, the effluent of ANT was fed to the DNT reactor operated in three circuitry modes. Among which, CCM operation resulted in significant denitrification along with power generation. The study inferred that sequential integration of ANT and DNT reactors are efficient in removing nitrogen compounds and other multi-pollutants at higher rate than the conventional treatment strategies.
Conflict of interest All the authors have declared no conflict of interest.
Acknowledgements The authors wish to thank the Director, CSIR-IICT for support and encouragement in carrying out this work. The research was funded by CSIR in the form of XIIth five year plan project on ‘Development of Sustainable Waste Management Technologies for Chemical and Allied Industries’ (SETCA; CSC-0113).
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[5] A. Sotres, M. Cerrillo, M. Viñas, A. Bonmatí, Nitrogen removal in a two-chambered microbial fuel cell: Establishment of a nitrifying–denitrifying microbial community on an intermittent aerated cathode, Chemical Engineering Journal 284 (2016) 905-916. [6] A. Al-Mamun, O. Lefebvre, M. Baawain, H. Ng, A sandwiched denitrifying biocathode in a microbial fuel cell for electricity generation and waste minimization, International Journal of Environmental Science and Technology 13 (2016) 1055-1064. [7] A. Hussain, M. Manuel, B. Tartakovsky, A comparison of simultaneous organic carbon and nitrogen removal in microbial fuel cells and microbial electrolysis cells, Journal of environmental management 173 (2016) 23-33. [8] A. Vilar-Sanz, S. Puig, A. García-Lledó, R. Trias, M.D. Balaguer, J. Colprim, L. Bañeras, Denitrifying bacterial communities affect current production and nitrous oxide accumulation in a microbial fuel cell, PloS one 8 (2013) e63460. [9] F. Zhang, Z. He, Simultaneous nitrification and denitrification with electricity generation in dual‐cathode microbial fuel cells, Journal of Chemical Technology and Biotechnology 87 (2012) 153-159. [10] F. Fang, B.-J. Ni, X.-Y. Li, G.-P. Sheng, H.-Q. Yu, Kinetic analysis on the two-step processes of AOB and NOB in aerobic nitrifying granules, Applied microbiology and biotechnology 83 (2009) 1159-1169. [11] P. De Filippis, L. Di Palma, M. Scarsella, N. Verdone, Biological denitrification of highnitrate wastewaters, Chemical Engineering Transactions 32 (2013) 319-324. [12] O. Lefebvre, A. Al-Mamun, H. Ng, A microbial fuel cell equipped with a biocathode for organic removal and denitrification, Water Science and Technology 58 (2008) 881. [13] Y. Li, I. Williams, Z. Xu, B. Li, B. Li, Energy-positive nitrogen removal using the integrated short-cut nitrification and autotrophic denitrification microbial fuel cells (MFCs), Applied Energy 163 (2016) 352-360. [14] G. Velvizhi, R.K. Goud, S.V. Mohan, Anoxic bio-electrochemical system for treatment of complex chemical wastewater with simultaneous bioelectricity generation, Bioresource technology 151 (2014) 214-220. [15] S.V. Mohan, G. Velvizhi, K.V. Krishna, M.L. Babu, Microbial catalyzed electrochemical systems: a bio-factory with multi-facet applications, Bioresource technology 165 (2014) 355364. 9
[16] B. Virdis, K. Rabaey, R.A. Rozendal, Z. Yuan, J. Keller, Simultaneous nitrification, denitrification and carbon removal in microbial fuel cells, Water Research 44 (2010) 2970-2980. [17] W.E. Federation, A.P.H. Association, Standard methods for the examination of water and wastewater, American Public Health Association (APHA): Washington, DC, USA (2005). [18] G. Velvizhi, S.V. Mohan, Bioelectrogenic role of anoxic microbial anode in the treatment of chemical wastewater: microbial dynamics with bioelectro-characterization, Water research 70 (2015) 52-63. [19] G. Mohanakrishna, S.K. Butti, R.K. Goud, S.V. Mohan, Spatiometabolic stratification of anoxic biofilm in prototype bioelectrogenic system, Bioelectrochemistry (2017). [20] S. Srikanth, S.V. Mohan, P. Sarma, Positive anodic poised potential regulates microbial fuel cell performance with the function of open and closed circuitry, Bioresource technology 101 (2010) 5337-5344. [21] A. Al-Mamun, M.S. Baawain, F. Egger, A.a.H. Al-Muhtaseb, H.Y. Ng, Optimization of a baffled-reactor microbial fuel cell using autotrophic denitrifying bio-cathode for removing nitrogen and recovering electrical energy, Biochemical Engineering Journal (2017). [22] H. Zhao, J. Zhao, F. Li, X. Li, Performance of denitrifying microbial fuel cell with biocathode over nitrite, Frontiers in Microbiology 7 (2016). [23] Z.P. Zhang Jiqiang, Zhang Meng, LI Wei, Chen Hui, CAI Chen, Xie Zuofu, Coupling process and mechanism of methanol oxidation and nitrate reduction in an anodic denitrification microbial fuel cell(AD-MFC), CIESC Journal 64 (2013) 3404-3411. [24] G. Velvizhi, S.V. Mohan, Biocatalyst behavior under self-induced electrogenic microenvironment in comparison with anaerobic treatment: evaluation with pharmaceutical wastewater for multi-pollutant removal, Bioresource technology 102 (2011) 10784-10793. [25] F. Zhang, Z. He, Integrated organic and nitrogen removal with electricity generation in a tubular dual-cathode microbial fuel cell, Process Biochemistry 47 (2012) 2146-2151. [26] P.M. Kyveryga, A.M. Blackmer, J.W. Ellsworth, R. Isla, Soil pH effects on nitrification of fall-applied anhydrous ammonia, Soil Science Society of America Journal 68 (2004) 545-551. [27] G. Ruiz, D. Jeison, R. Chamy, Nitrification with high nitrite accumulation for the treatment of wastewater with high ammonia concentration, Water Research 37 (2003) 1371-1377. [28] Z. He, A. Alva, D. Calvert, D. Banks, Ammonia volatilization from different fertilizer sources and effects of temperature and soil pH1, Soil Science 164 (1999) 750-758. 10
[29] S.V. Mohan, S. Srikanth, Enhanced wastewater treatment efficiency through microbially catalyzed oxidation and reduction: synergistic effect of biocathode microenvironment, Bioresource technology 102 (2011) 10210-10220. [30] D.K. Yeruva, G. Velvizhi, S.V. Mohan, Coupling of aerobic/anoxic and bioelectrogenic processes for treatment of pharmaceutical wastewater associated with bioelectricity generation, Renewable Energy (2016). [31] S. Srikanth, S.V. Mohan, Influence of terminal electron acceptor availability to the anodic oxidation on the electrogenic activity of microbial fuel cell (MFC), Bioresource technology 123 (2012) 480-487. [32] G. Nikhil, D.K. Yeruva, S.V. Mohan, Y. Swamy, Assessing potential cathodes for resource recovery through wastewater treatment and salinity removal using non-buffered microbial electrochemical systems, Bioresource Technology (2016). [33] G. Nikhil, G.V. Subhash, D.K. Yeruva, S.V. Mohan, Closed circuitry operation influence on microbial
electrofermentation:
Proton/electron
Bioresource technology 195 (2015) 37-45.
11
effluxes
on
electro-fuels
productivity,
10
A
140
9
ADR 120
8 7
100
6 80
5
60
4 3
40
+ ADR (mg-NH4 /L/h)
+ Ammonium concentration (mg-NH4 /L)
+
[NH4 ]
2 20 0
1 0
2
4
6
8
10
12
0
Cycle number 1500
Nitrates pH
B
10 9 8
1400
7 1300
6
1200
5
1100
4
1000
3
900
2
pH
Nitrates concentration (mg-NO3 /L)
1600
1
800
0 0 12 24 36 48 60 72 84 96 108 120 132 144 156 Operation time (h) Fig.1 Nitrification performance of ANT reactor: (A) ammonium removal and ammonium degradation rate (ADR); (B) Variation in nitrate concentration and pH.
12
OCM
CCM
SCM
- -1 -1 Nitrate removal rate(mg-NO3 L h )
100 90 80 70 60 50 40 30 20 10 0 Cycle1
Cycle2
Cycle3
Cycle4
Cycles operation Fig. 2 Denitrification performance of DNT reactor (as nitrate removal rate) at different circuitry connections: OCM (Open Circuit Mode), CCM (Closed Circuit Mode) and SCM (Short Circuit Mode).
13
100
OCM
90
ANT
DNT
Cumulative
80 COD removal (%)
70 60 50 40 30 20 10 0 Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle Operation 100
ANT
DNT
Cumulative
CCM
90
COD removal(%)
80 70 60 50 40 30 20 10 0 Cycle 1
Cycle 2
Cycle 3
Cycle Operation
14
Cycle 4
100
ANT
DNT
Cumulative
SCM
90
COD removal(%)
80 70 60 50 40 30 20 10 0 Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle operation Fig. 3 Cumulative performance of ANT and DNT reactors with respect to organic content degradation (as COD removal efficiency) during (A) OCM (B) CCM (C) SCM.
15
100 90
OCM
CCM
SCM
A
Sulphates removal(%)
80 70 60 50 40 30 20 10 0 ANT
DNT
Cumulative
100 90
OCM
CCM
SCM
B
Phosphates removal (%)
80 70 60 50 40 30 20 10 0
ANT
DNT
16
Cumulative
100 90
OCM
CCM
SCM
C
80 TDS removal(%)
70 60 50 40 30 20 10 0
ANT
DNT
Cumulative
Fig.4 Cumulative assessment of multi-pollutant removal by both ANT and DNT reactors: (A) sulphates removal (B) Phosphates removal (C) TDS removal.
17
OCM
Anode potential(mV) vs Ag/AgCl
0
CCM
SCM
A -100
-200
-300
-400
-500
0
5000
10000 15000 20000 25000 30000 Resistance (Ω)
300
14 V-I Curve
Power Curve B
12 10
200
8 150 6 100
4
50 0
2
0
25
50
75
100
-2 Current density (I, mAm )
18
125
0
-2 Power density (P, mWm )
Voltage (V, mV)
250
40 C 35
-2
Power density (mWm )
30 25 20 15 10 5 0 0
10
20
30
40
50
60
Operation time (h) Fig. 5 Bioelectrochemical performance evaluation of DNT reactor: (A) Anode potential; (B) Polarization curve; (C) Power density.
19
Table
Table 1: Relative performance of ANT reactor for ammonium removal
Cycle Number
Outlet Ammonium (mg-NH4+ l-1) 123
Ammoniu m removal (%) 25.45
Outlet Nitrate (mg-NO3--N l-1) 1024
Increase in nitrates (%) 18.38
Outlet pH
Cycle 2
Inlet Ammonium (mg-NH4+ l-1) 165
Cycle 8
160
70
56.25
1384
41.89
8.21
Cycle 12
152
42
72.36
1451
64.24
8.41
1
7.91
Table 2: Influence of C/N ratio on nitrate removal S. No
Substrate
Carbon Source
Organic Nitrogen load (mg/L) source
Circuit connection
Nitrogen removal %
References
1
Synthetic Wastewater (SW)
Sodium Acetate
127.3± 4.6
Ammonium Chloride
16.9 ± 1.4
8.1 ± 0.4
Open circuit
42.2 ± 1.4
(Virdis et al., 2010)
2
SW
Sodium Acetate
745 ± 231
Sodium Nitrate
29.6 ± 5.3
34.9
Closed circuit
18.9
(Vilar-Sanz et al., 2013)
3
SW
Sodium Acetate
500
Sodium Nitrate
21.4 ± 0.2
23.6 ± 0.4
Poised 55.8 Potential(-0.8V)
(Tong and He, 2014)
4
SW
Glucose
300
Sodium Nitrate
100
3
Open circuit
>80
(Xiao et al., 2013)
5
SW
Methanol
400
Sodium Nitrate
200
2
Nil (Batch Study)
79
(Foglar et al., 2005)
6
SW
Sodium Acetate
50-320
Sodium Nitrate
20-110
2.5-2.9 Closed circuit (1.1Ω)
72.8
(Clauwaert et al., 2009)
7
SW
Methanol
250 ± 0.01 – Sodium 176,00 ± Nitrate 135.41
50 ± 0.02 3560 ± 36.80
5
Closed circuit (1000 Ω)
>95
(Zhang et al., 2013)
8
Pharmaceutical wastewater
ANT Effluent
3100
1381
2.18
Closed circuit (750Ω)
80.24
Present study
Nitrates
2
Nitrogen C/N inlet (mg/L) ratio
Highlights •
Substantial bioelectrochemical denitrification was noticed under closed circuitry.
•
The designed bioelectrochemical DNT system performed at low C/N ratios.
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Sequential integration of ANT & DNT resulted in remarkable multi-pollutant removal.
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Energy-positive nitrogen removal of pharmaceutical wastewater by coupling heterotrophic nitrification and electrotrophic denitrification G.N.Nikhil, P.Suman, S.Venkata Mohan, Y.V.Swamy* Bioengineering and Environmental Sciences (BEES), CSIR-Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad-500007 Email: [email protected]; Phone: +91-40-27193159
Schematic view of (A) ANT (Aerobic Nitrification Treatment) reactor and (B) DNT (Denitrification Treatment) reactor (1: nitrifying organisms, 2: Anode Oxidizing Bacteria, 3: Nitrate reducing bacteria, P1 & P2: Pumps).
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