This article was downloaded by: [New Jersey Institute of Technology] On: 05 February 2015, At: 13:51 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Kinetics of autotrophic denitrification process and the impact of sulphur/limestone ratio on the process performance a
b
c
Arzu Kilic , Erkan Sahinkaya & Ozer Cinar a
Bioengineering and Science Department, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey b
Bioengineering Department, Faculty of Engineering and Architecture, Istanbul Medeniyet University, Goztepe, Istanbul, Turkey c
Click for updates
Environmental Engineering Department, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey Accepted author version posted online: 14 May 2014.Published online: 09 Jun 2014.
To cite this article: Arzu Kilic, Erkan Sahinkaya & Ozer Cinar (2014) Kinetics of autotrophic denitrification process and the impact of sulphur/limestone ratio on the process performance, Environmental Technology, 35:22, 2796-2804, DOI: 10.1080/09593330.2014.922127 To link to this article: http://dx.doi.org/10.1080/09593330.2014.922127
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2014 Vol. 35, No. 22, 2796–2804, http://dx.doi.org/10.1080/09593330.2014.922127
Kinetics of autotrophic denitrification process and the impact of sulphur/limestone ratio on the process performance Arzu Kilica∗ , Erkan Sahinkayab and Ozer Cinarc a Bioengineering and Science Department, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey; b Bioengineering Department, Faculty of Engineering and Architecture, Istanbul Medeniyet University, Goztepe, Istanbul, Turkey; c Environmental Engineering Department, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey
Downloaded by [New Jersey Institute of Technology] at 13:51 05 February 2015
(Received 9 February 2014; final version received 2 May 2014 ) Kinetics of sulphur–limestone autotrophic denitrification process in batch assays and the impact of sulphur/limestone ratio on the process performance in long-term operated packed-bed bioreactors were evaluated. The specific nitrate and nitrite reduction rates increased almost linearly with the increasing initial nitrate and nitrite concentrations, respectively. The process performance was evaluated in three parallel packed-bed bioreactors filled with different sulphur/limestone ratios (1:1, 2:1 −1 d −1 ) and 3:1, v/v). Performances of the bioreactors were studied under varying nitrate loadings (0.05 − 0.80 gNO− 3 -N L −1 −1 and hydraulic retention times (3–12 h). The maximum nitrate reduction rate of 0.66 g L d was observed at the loading −1 −1 in the reactor with sulphur/limestone ratio of 3:1. Throughout the study, nitrite concentrations rate of 0.80 g NO− 3 -N L d remained quite low (i.e. below 0.5 mg L−1 NO− 2 -N). The reactor performance increased in the order of sulphur/limestone ratio of 3:1, 2:1 and 1:1. Denaturing gradient gel electrophoresis analysis of 16S rRNA genes showed quite stable communities in the reactors with the presence of Methylo virgulaligni, Sulfurimonas autotrophica, Sulfurovum lithotrophicum, Thiobacillus aquaesulis and Sulfurimonas autotrophica related species. Keywords: denitrification; sulphur–limestone autotrophic denitrification; drinking water; sulphur/limestone ratio; microbial community
1. Introduction Nitrate is a priority pollutant due to its toxicity related to methemoglobinemia and to the possible formation of N-nitroso compounds in the gastric system.[1] In many countries, nitrate concentrations in the groundwater used as drinking water source exceed the maximum allow− able concentration of 10 mg L−1 NO− 3 N.[2] Some wells in Harran Plain, Sanliurfa, Turkey, contain nitrate as − high as 180 mg L−1 NO− 3 N, and the average concentra− tion for the entire plain is 35 mg L−1 NO− 3 N.[3] The most important sources of nitrate in ground waters are nitrogen-containing fertilizers, and industrial and domestic wastewaters discharged without being treated properly.[4, 5] Physical–chemical technologies that can be used for nitrate removal include reverse osmosis, ion exchange and electrodialysis.[6] The main important disadvantages of these processes are their poor selectivity, high operation and maintenance costs, and the generation of brine wastes after treatment.[7,8] Consequently, biological treatment processes to convert nitrates to benign dinitrogen gas could be an interesting alternative for the remediation of groundwater contaminated with nitrates.[6] Biological denitrification is commonly used for the treatment of wastewater. ∗ Corresponding
author. Email: [email protected]
© 2014 Taylor & Francis
Studies demonstrate that biological denitrification may also be used for the remediation of drinking water.[4,6,9–11] Autotrophic denitrification has been receiving more attention in recent years due to two major advantages compared with heterotrophic denitrification: (1) no external organic carbon (methanol or ethanol) is needed, which lowers the cost and risk of the process and (2) less sludge production, which minimizes the handling of sludge.[6,12] Due to its low cost, elemental sulphur is an attractive source of energy for biological denitrification of nitrate-contaminated groundwater. In this process, the elemental sulphur and nitrate act as an electron donor and an acceptor, respectively. Furthermore, elemental sulphur is non-toxic and stable under normal conditions.[13] Therefore, elemental sulphur is oxidized to sulphate and nitrate is reduced to nitrogen gas (Reaction 1) [4] + 55 S0 + 50 NO− 3 + 38 H2 O + 20 CO2 + 4 NH4 + → 4 C5 H7 O2 N + 55 SO−2 4 + 25 N2 + 64 H
(1)
In sulphur-based autotrophic denitrification, the most important disadvantages are the formation of acid and sulphate.[9,14] One of the important factors is pH in
Downloaded by [New Jersey Institute of Technology] at 13:51 05 February 2015
Environmental Technology denitrification.[15] Reaction 1 shows that 4.57 g alkalinity − (as CaCO3 ) will be consumed on reducing 1 g of NO− 3 N to nitrogen gas (Reaction 1). Therefore, pH will decrease during autotrophic denitrification. Previous studies showed that the optimum pH for denitrification of drinking water using sulphur-oxidizing bacteria is between 6.8 and 8.2.[9] Therefore, an appropriate alkalinity source is required to keep pH neutral in the autotrophic denitrification processes. Limestone is the most commonly used alkalinity source due to availability, low-cost and efficiency.[9] Hence, the SLAD (sulphur–limestone autotrophic denitrification) process may be a powerful alternative for the denitrification of drinking water sources. Alternatively, hydrogen or thiosulphate can be used as electron sources in autotrophic denitrification processes.[16,17] Although hydrogen is an excellent electron donor for denitrification, need for complex hydrogen delivering systems increases the capital costs and may create explosion risks.[16] Another alternative is the use of soluble sulphur compounds as an electron source to reach high denitrification rates. Thiosulphate may be used for this purpose according to the following reaction [17]:
+ + 0.086 HCO− 3 + 0.086 NH4 → 0.086 C5 H7 O2 N + + 0.5 N2 + 1.689 SO2− 4 + 0.697 H
2. Materials and methods 2.1. Kinetic tests The kinetic tests were conducted at 25 ◦ C using 150 mL serum bottles filled with 100 mL medium. The serum bottles were supplemented with excess amount of elemental sulphur (3 g) and limestone (3 g) not to limit the nitrate and nitrite reduction. The kinetic assays were conducted with tap water supplemented with 0.05 g L−1 K2 HPO4 and varying concentrations of nitrate or nitrite (10–100 mg L−1 N). The batch bottles were inoculated with the column bed obtained from the fixed-bed reactor packed with sulphur and limestone with a volume ratio of 1:1 (C1).The initial biomass concentration in the serum bottles was 400 ± 100 mg volatile suspended solids (VSS) L−1 . Before inoculation, the medium was purged with N2 gas for 5 min to remove oxygen. The serum bottles were sampled regularly for the nitrate, nitrite and sulphate measurements. At the end of the study, the biomass was analysed for organic nitrogen for the calculation of biomass concentration.
2.2.
− 0.844 S2 O2− 3 + NO3 + 0.347 CO2 + 0.434 H2 O
(2)
Although thiosulphate is an effective electron donor,[17] − 11.58 mg sulphate is generated per mg NO− 3 N removed. The production of higher amount of sulphate compared with sulphur-oxidizing autotrophic denitrification (7.54 mg sul− phate per mg NO− 3 N removed (Reaction 1)) is the major disadvantage of the process. The process efficiency depends on the ratio of sulphur/limestone in the bioreactor.[9,10] The optimum ratio may depend on nitrate concentration and the operational conditions (such as hydraulic retention time (HRT)). The impact of sulphur/limestone ratio on the process performance has been generally evaluated in batch-type reactors, which may not allow the determination of optimum ratio for future full-scale applications.[9,10] Sulphur/limestone ratio should be determined in terms of both cost and denitrification efficiency for future full-scale applications. Hence, this study aims at determining the kinetics of sulphur-based autotrophic denitrification process in batch assays and the optimum sulphur/limestone ratio in continuously fed-up flow column bioreactors under varying operational conditions. Additionally, the change of microbial community in long-term operating bioreactors was evaluated under varying sulphur/limestone ratios (i.e. 1:1, 2:1, 3:1 on volume basis). Hence, the results of this study may be used for the design of full-scale SLAD systems for the remediation of drinking water.
2797
Fixed-bed column bioreactors
Three identical glass bioreactors were operated in parallel. The internal diameter and the empty bed volumes of the bioreactors were 55 mm and 500 mL, respectively. Sulphur particles were used both as packing medium and as an electron donor. Sulphur and limestone particles size were
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Kinetics of autotrophic denitrification process and the impact of sulphur/limestone ratio on the process performance a
b
c
Arzu Kilic , Erkan Sahinkaya & Ozer Cinar a
Bioengineering and Science Department, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey b
Bioengineering Department, Faculty of Engineering and Architecture, Istanbul Medeniyet University, Goztepe, Istanbul, Turkey c
Click for updates
Environmental Engineering Department, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey Accepted author version posted online: 14 May 2014.Published online: 09 Jun 2014.
To cite this article: Arzu Kilic, Erkan Sahinkaya & Ozer Cinar (2014) Kinetics of autotrophic denitrification process and the impact of sulphur/limestone ratio on the process performance, Environmental Technology, 35:22, 2796-2804, DOI: 10.1080/09593330.2014.922127 To link to this article: http://dx.doi.org/10.1080/09593330.2014.922127
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2014 Vol. 35, No. 22, 2796–2804, http://dx.doi.org/10.1080/09593330.2014.922127
Kinetics of autotrophic denitrification process and the impact of sulphur/limestone ratio on the process performance Arzu Kilica∗ , Erkan Sahinkayab and Ozer Cinarc a Bioengineering and Science Department, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey; b Bioengineering Department, Faculty of Engineering and Architecture, Istanbul Medeniyet University, Goztepe, Istanbul, Turkey; c Environmental Engineering Department, Kahramanmaras Sutcu Imam University, Kahramanmaras, Turkey
Downloaded by [New Jersey Institute of Technology] at 13:51 05 February 2015
(Received 9 February 2014; final version received 2 May 2014 ) Kinetics of sulphur–limestone autotrophic denitrification process in batch assays and the impact of sulphur/limestone ratio on the process performance in long-term operated packed-bed bioreactors were evaluated. The specific nitrate and nitrite reduction rates increased almost linearly with the increasing initial nitrate and nitrite concentrations, respectively. The process performance was evaluated in three parallel packed-bed bioreactors filled with different sulphur/limestone ratios (1:1, 2:1 −1 d −1 ) and 3:1, v/v). Performances of the bioreactors were studied under varying nitrate loadings (0.05 − 0.80 gNO− 3 -N L −1 −1 and hydraulic retention times (3–12 h). The maximum nitrate reduction rate of 0.66 g L d was observed at the loading −1 −1 in the reactor with sulphur/limestone ratio of 3:1. Throughout the study, nitrite concentrations rate of 0.80 g NO− 3 -N L d remained quite low (i.e. below 0.5 mg L−1 NO− 2 -N). The reactor performance increased in the order of sulphur/limestone ratio of 3:1, 2:1 and 1:1. Denaturing gradient gel electrophoresis analysis of 16S rRNA genes showed quite stable communities in the reactors with the presence of Methylo virgulaligni, Sulfurimonas autotrophica, Sulfurovum lithotrophicum, Thiobacillus aquaesulis and Sulfurimonas autotrophica related species. Keywords: denitrification; sulphur–limestone autotrophic denitrification; drinking water; sulphur/limestone ratio; microbial community
1. Introduction Nitrate is a priority pollutant due to its toxicity related to methemoglobinemia and to the possible formation of N-nitroso compounds in the gastric system.[1] In many countries, nitrate concentrations in the groundwater used as drinking water source exceed the maximum allow− able concentration of 10 mg L−1 NO− 3 N.[2] Some wells in Harran Plain, Sanliurfa, Turkey, contain nitrate as − high as 180 mg L−1 NO− 3 N, and the average concentra− tion for the entire plain is 35 mg L−1 NO− 3 N.[3] The most important sources of nitrate in ground waters are nitrogen-containing fertilizers, and industrial and domestic wastewaters discharged without being treated properly.[4, 5] Physical–chemical technologies that can be used for nitrate removal include reverse osmosis, ion exchange and electrodialysis.[6] The main important disadvantages of these processes are their poor selectivity, high operation and maintenance costs, and the generation of brine wastes after treatment.[7,8] Consequently, biological treatment processes to convert nitrates to benign dinitrogen gas could be an interesting alternative for the remediation of groundwater contaminated with nitrates.[6] Biological denitrification is commonly used for the treatment of wastewater. ∗ Corresponding
author. Email: [email protected]
© 2014 Taylor & Francis
Studies demonstrate that biological denitrification may also be used for the remediation of drinking water.[4,6,9–11] Autotrophic denitrification has been receiving more attention in recent years due to two major advantages compared with heterotrophic denitrification: (1) no external organic carbon (methanol or ethanol) is needed, which lowers the cost and risk of the process and (2) less sludge production, which minimizes the handling of sludge.[6,12] Due to its low cost, elemental sulphur is an attractive source of energy for biological denitrification of nitrate-contaminated groundwater. In this process, the elemental sulphur and nitrate act as an electron donor and an acceptor, respectively. Furthermore, elemental sulphur is non-toxic and stable under normal conditions.[13] Therefore, elemental sulphur is oxidized to sulphate and nitrate is reduced to nitrogen gas (Reaction 1) [4] + 55 S0 + 50 NO− 3 + 38 H2 O + 20 CO2 + 4 NH4 + → 4 C5 H7 O2 N + 55 SO−2 4 + 25 N2 + 64 H
(1)
In sulphur-based autotrophic denitrification, the most important disadvantages are the formation of acid and sulphate.[9,14] One of the important factors is pH in
Downloaded by [New Jersey Institute of Technology] at 13:51 05 February 2015
Environmental Technology denitrification.[15] Reaction 1 shows that 4.57 g alkalinity − (as CaCO3 ) will be consumed on reducing 1 g of NO− 3 N to nitrogen gas (Reaction 1). Therefore, pH will decrease during autotrophic denitrification. Previous studies showed that the optimum pH for denitrification of drinking water using sulphur-oxidizing bacteria is between 6.8 and 8.2.[9] Therefore, an appropriate alkalinity source is required to keep pH neutral in the autotrophic denitrification processes. Limestone is the most commonly used alkalinity source due to availability, low-cost and efficiency.[9] Hence, the SLAD (sulphur–limestone autotrophic denitrification) process may be a powerful alternative for the denitrification of drinking water sources. Alternatively, hydrogen or thiosulphate can be used as electron sources in autotrophic denitrification processes.[16,17] Although hydrogen is an excellent electron donor for denitrification, need for complex hydrogen delivering systems increases the capital costs and may create explosion risks.[16] Another alternative is the use of soluble sulphur compounds as an electron source to reach high denitrification rates. Thiosulphate may be used for this purpose according to the following reaction [17]:
+ + 0.086 HCO− 3 + 0.086 NH4 → 0.086 C5 H7 O2 N + + 0.5 N2 + 1.689 SO2− 4 + 0.697 H
2. Materials and methods 2.1. Kinetic tests The kinetic tests were conducted at 25 ◦ C using 150 mL serum bottles filled with 100 mL medium. The serum bottles were supplemented with excess amount of elemental sulphur (3 g) and limestone (3 g) not to limit the nitrate and nitrite reduction. The kinetic assays were conducted with tap water supplemented with 0.05 g L−1 K2 HPO4 and varying concentrations of nitrate or nitrite (10–100 mg L−1 N). The batch bottles were inoculated with the column bed obtained from the fixed-bed reactor packed with sulphur and limestone with a volume ratio of 1:1 (C1).The initial biomass concentration in the serum bottles was 400 ± 100 mg volatile suspended solids (VSS) L−1 . Before inoculation, the medium was purged with N2 gas for 5 min to remove oxygen. The serum bottles were sampled regularly for the nitrate, nitrite and sulphate measurements. At the end of the study, the biomass was analysed for organic nitrogen for the calculation of biomass concentration.
2.2.
− 0.844 S2 O2− 3 + NO3 + 0.347 CO2 + 0.434 H2 O
(2)
Although thiosulphate is an effective electron donor,[17] − 11.58 mg sulphate is generated per mg NO− 3 N removed. The production of higher amount of sulphate compared with sulphur-oxidizing autotrophic denitrification (7.54 mg sul− phate per mg NO− 3 N removed (Reaction 1)) is the major disadvantage of the process. The process efficiency depends on the ratio of sulphur/limestone in the bioreactor.[9,10] The optimum ratio may depend on nitrate concentration and the operational conditions (such as hydraulic retention time (HRT)). The impact of sulphur/limestone ratio on the process performance has been generally evaluated in batch-type reactors, which may not allow the determination of optimum ratio for future full-scale applications.[9,10] Sulphur/limestone ratio should be determined in terms of both cost and denitrification efficiency for future full-scale applications. Hence, this study aims at determining the kinetics of sulphur-based autotrophic denitrification process in batch assays and the optimum sulphur/limestone ratio in continuously fed-up flow column bioreactors under varying operational conditions. Additionally, the change of microbial community in long-term operating bioreactors was evaluated under varying sulphur/limestone ratios (i.e. 1:1, 2:1, 3:1 on volume basis). Hence, the results of this study may be used for the design of full-scale SLAD systems for the remediation of drinking water.
2797
Fixed-bed column bioreactors
Three identical glass bioreactors were operated in parallel. The internal diameter and the empty bed volumes of the bioreactors were 55 mm and 500 mL, respectively. Sulphur particles were used both as packing medium and as an electron donor. Sulphur and limestone particles size were
