This article was downloaded by: [University of Colorado - Health Science Library] On: 30 March 2015, At: 14:22 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
Effect of Reactor Configuration on Performance During Anaerobic Treatment Low Strength Wastewater Suprotim Das a
ab
b
& Sanjeev Chaudhari
Research & Development, Tata Steel Limited, Jamshedpur-831001, India
b
Centre for Environmental Science and Engineering (CESE), Indian Institute of Technology Bombay, Powai, Mumbai-t400076, |cIndia Accepted author version posted online: 09 Mar 2015.
Click for updates To cite this article: Suprotim Das & Sanjeev Chaudhari (2015): Effect of Reactor Configuration on Performance During Anaerobic Treatment Low Strength Wastewater, Environmental Technology, DOI: 10.1080/09593330.2015.1026845 To link to this article: http://dx.doi.org/10.1080/09593330.2015.1026845
Disclaimer: This is a version of an unedited manuscript that has been accepted for publication. As a service to authors and researchers we are providing this version of the accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proof will be undertaken on this manuscript before final publication of the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to this version also.
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
Publisher: Taylor & Francis Journal: Environmental Technology DOI: 10.1080/09593330.2015.1026845
a
t
Research & Development, Tata Steel Limited, Jamshedpur-831001, India
us c
Centre for Environmental Science and Engineering (CESE), Indian Institute of Technology Bombay, Powai, Mumbai-400076, India
M an
b
rip
Suprotim Das a, b and Sanjeev Chaudhari b
Abstract:
ce
pt e
d
The efficiency of UASB reactor is quite low for the treatment of low strength wastewaters (LSWs) due to less biogas production leading to poor mixing. LSW may be treated efficiently by providing adequate mixing in UASB reactor when gas production is low and sufficient mixing can be achievable by modifying reactor geometry. Hence, modifying UASB reactor geometry for enhanced mixing and evaluating its performance for the treatment of LSWs would be a worthwhile effort. In the present study, UASB reactor configuration was modified by providing a vertical baffle along the height to promote mixing of reactor contents and is termed as modified up-flow anaerobic sludge blanket (MUASB). The performance of on-site pilot scale MUASB reactor was evaluated for 375 days under ambient condition for the treatment of municipal sewage as LSW and compared with the conventional UASB and hybrid UASB (HUASB) reactor. The MUASB reactor showed better performance in terms of chemical oxygen demand (COD) removal efficiency as compared to UASB and HUASB reactor during this study. At 4 h hydraulic retention time (HRT), the total COD removal efficiency of UASB and HUASB reactor were 53.7% and 61% respectively which were much lower than the total COD removal efficiency of MUASB reactor (72.7%). Better performance observed in MUASB reactor possibly due to improved mixing. Depth-wise analysis of reactor liquid showed that better mixing in MUASB reactor enhances the contact of wastewater with biomass which contributes to the improved treatment efficiency. It seems that MUASB holds promise for LSW treatment.
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
Effect of Reactor Configuration on Performance During Anaerobic Treatment Low Strength Wastewater
Keywords:
Anaerobic process; Wastewater treatment; Anaerobic reactor; UASB; Municipal sewage
1.0 Introduction Anaerobic wastewater treatment process has significant advantages over aerobic one like- low energy consumption, low sludge production, biogas production in form of methane (CH4) and formation of stabilized sludge [1, 2]. Several complex sequential and parallel biological reactions
t rip
as the substrate for the next which results in the conversion of organic matter into biogas (CH4
us c
and CO2). Among various anaerobic reactor, up-flow anaerobic sludge blanket UASB is most widely used for treating different types of wastewater through out the world since 1980s [3-5]. The formation of densely packed granular sludge allows UASB reactor to achieve high chemical
M an
oxygen demand (COD) removal efficiency without the need of any support material. In addition, the turbulence caused by the rising gas bubbles enhance the contact of sludge biomass with incoming wastewater, thus improves mixing without any additional energy requirement and its
d
associated cost [5]. The UASB process has proven effective for the treatment of medium strength
pt e
wastewaters (MSWs) and high strength wastewaters (HSWs) [6]. The potential of UASB reactor is not restricted for the treatment of MSWs and HSWs. The UASB reactor can also be useful for
ce
low strength wastewater (LSW) treatment [7]. However, despite several advantages many researchers have pointed out that UASB reactors have some inherent limitations for the treatment of LSW [5, 7, 8]. Researchers [7, 9] have described LSWs are those which contain COD below
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
occur in anaerobic reactor during the treatment of wastewater. The product of one reaction serves
2,000 mg L-1. It has been reported that food processing, chemicals, dyeing industries release
LSWs in large quantities [10]. Sewage can be considered as an example of low strength complex wastewater [11] which also contains significant fraction of suspended solids (SS). The presence
of SS in wastewater affects the UASB process adversely as degradation of suspended organic matter is difficult as compared to soluble organic matter. The presence of SS also decreases sludge activity due to adsorption and entrapment on granular surface of sludge biomass, thereby inhibiting granulation process in UASB reactor [12]. Thus the efficiency of the UASB system is
limited as it has low SS removal capability mainly for the treatment of LSWs [13]. The diffusion rate of substrate to anaerobic biomass is also lower under this condition [7, 13]. Previous investigation [14] showed that mixing is important to improve reactor efficiency. During the treatment of MSWs and HSWs, gas production inside the UASB reactor provides good mixing. Well mixed conditioned lead to higher dispersion thus resulting in limited plug-flow behaviour of
rip
t
the gas bubbles with the granules [15] which is not achieved during the treatment of LSW as low volume of biogas is produced. In UASB reactor, low mixing may cause channelling of
us c
wastewater through the bed and therefore a poor wastewater–sludge contact, which results in low treatment efficiencies [15, 16]. Tracer studies revealed that internal mixing was not optimal in a
M an
pilot scale UASB reactor treating sewage [17]. Moreover, dilute complex wastewaters provides low mass transfer between wastewater and biomass due to the presence of considerable amount of suspended matter. Therefore, sufficient mixing is essential in order to eliminate mass transfer limitations in microbial aggregates [18]. Different feed inlet systems, more feed inlet points per
d
unit area and high superficial velocities of incoming liquid have been proposed by researchers in
pt e
order to improve the sludge-wastewater contact.
ce
The performance of bioreactor is influenced by several factors, among them mass transfer of organic matter to biomass and residence time of liquid are governed by hydrodynamics of bioreactor. Thereby reactor hydrodynamic has influence on the performance [19]. Reactor
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
the sludge bed [7]. Turbulence of sludge bed is enhanced under this condition due to collision of
configuration and hydrodynamics has significant impact on sludge biomass characteristics such as size distribution, compressibility and the settling rate in suspended aerobic growth
bioreactor system [20].
The aim of this study was to improve the performance of UASB reactor for the treatment of LSW by changing the reactor geometry. Therefore, modification of UASB reactor was done and the reactor is termed as modified up-flow anaerobic sludge blanket (MUASB). The
performance of pilot scale MUASB reactor for on-site treatment of municipal sewage as LSW was evaluated mainly in terms of total COD removal efficiency and TSS removal and was compared with conventional UASB and hybrid UASB (HUASB) reactor.
rip
t
2.1 Description of the pilot-scale Up-flow Anaerobic Sludge Blanket (UASB), Hybrid Up-flow Anaerobic Sludge Blanket (HUASB) and Modified Up-flow Anaerobic Sludge Blanket (MUASB) reactors
On-site pilot-scale experiment with domestic sewage as real low strength wastewater (LSW)
us c
was carried out by using UASB, HUASB and MUASB reactors. The reactors were fabricated in the laboratory using transparent acrylic sheet (thickness 8 mm). The model schematics of
M an
UASB, HUASB and MUASB reactors are shown in Figure 1. The detailed specifications of the models are presented in Table 1. The pilot-scale study was conducted under ambient condition with reactor liquid temperature in the range of 240C to 280C. The detailed
d
specifications of the reactors are as follows-
pt e
2.1.1 Up-flow Anaerobic Sludge Blanket (UASB) Reactor The UASB model was fabricated by using acrylic sheet in a square cross-sectional form. The
ce
total height of the reactor was 270 cm included the height of hopper bottom. The gas liquid solid separator (GLSS) with deflector beam was also made of acrylic and provided at the top
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
2.0 Materials and Methods
of the reactor.
2.1.2 Hybrid Up-flow Anaerobic Sludge Blanket (HUASB) Reactor The HUASB reactor contains 5000 numbers of small sponge cube (1 cm x 1 cm) as filter media which was provided in the upper part of the reactor (200 cm to 240 cm from bottom). A uniformly perforated square shaped plate was provided as support for filter media.
2.1.3 Modified Up-flow Anaerobic Sludge Blanket (MUASB) Reactor
In UASB reactor, a slanted rigid acrylic plate, which has been termed as baffle, was fixed between two opposite vertical walls. The baffle was introduced having an angle of 5.7o with the vertical wall. The lower end starts from 60 cm from the bottom and extended up to 170 cm having an opening of 3 cm x 16 cm. The granule along with effluent come out from the narrow opening of the baffle with higher velocity and falls on the other side of the baffle and
t
rip
by enhancing the internal recirculation of sludge biomass and thereby improves reactor
us c
performance due to better mixing. 2.2 Seed Sludge
M an
Seed sludge was collected from a 1.2 million liter per day (MLD) full scale UASB reactor treating effluent of dairy industry where the COD of wastewater was in the range of 3500 mg L-1 to 5000 mg L-1.
d
2.3 Characteristics of Domestic Sewage
pt e
The pilot-scale reactors were fed with the sewage of Indian Institute of Technology Bombay (IIT Bombay) campus-Mumbai (20,000 inhabitants). The average total COD concentration of
ce
raw sewage was 198 mg L-1 which can be classified as “very diluted” [11]. This sewage was withdrawn from sewage pumping station through a stainless steel net (2 cm2 per square holes). The sewage was stored in a plastic tank with a capacity of 1000 L. The hourly
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
thus circulated into the reactor. Baffle increases contact of sludge granules with wastewater
variation of the sewage was avoided by pumping sewage frequently into storage tank. The main characteristics of this sewage are shown in Table 2.
2.4 Analytical Technique
Various analytical technique used in this investigation are presented in the following subsection. In general, for monitoring of pH, COD, total suspended solids (TSS) and volatile
t rip
3.0 Result and Discussion
us c
3.1 Performance comparisons of Up-flow Anaerobic Sludge Blanket (UASB), Hybrid Up-flow Anaerobic Sludge Blanket (HUASB) and Modified Up-flow Anaerobic Sludge Blanket (MUASB) Reactors
M an
On-site pilot-scale reactor performance was evaluated for the treatment of domestic sewage. The reactors were installed at IIT Bombay sewage pumping station and operated for 375 days. Wastewater was taken directly from pumping station through a net basket (2 cm2 per
d
square holes) to prevent coarse materials and was pumped in storage tank. The detention time
pt e
in storage tank was 4 h. Average composition of sewage during the study is presented in Table 2. The influent COD exhibited seasonal variations.
ce
Figure 2 presents the COD removal efficiency of the reactors with time. The average influent total COD varied from 90 mg L-1 (rainy season) to 207 mg L-1 (summer). All three reactors
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
fatty acids (VFA) standard procedure as detailed in standard methods [21] was followed.
achieved quasi-steady state after 35-40 days. In this study, HRT was reduced from 8 to 4 h in stepwise manner. At 8 h HRT (day 1-89), the total COD removal efficiencies were 61%, 65% and 81.2% and the average effluent COD concentrations were 70 mg L-1, 66 mg L-1 and 38 mg L-1 for UASB, HUASB and MUASB reactors, respectively. When the HRT was reduced from
8 h to 6 h (after 89 days), the average total COD removal was found to be 63%, 69% and 82% and total COD of effluent was 76 mg L-1, 68 mg L-1 and 39 mg L-1 for UASB, HUASB
and MUASB reactors, respectively. In between 135 to 214 days, the average total sewage COD was 90 mg L-1 due to monsoon and total sewage COD was in the range of 77 mg L-1 to 110 mg L-1. The low influent COD adversely affected the reactor performance. The efficiency of UASB and HUASB reactor dropped to about 32% and 36% respectively (average effluent COD 71 mg L-1 and 57 mg L-1 respectively) at this stage. The decrease in COD removal
t
rip
average COD removal in MUASB reactor was 51% with average total effluent COD of 42 mg L-1. From day 214 (post rainy season), the average influent sewage COD was 160 mg L-1.
us c
The average COD removal efficiency was increased to 51%, 57% and 69%in UASB, HUASB and MUASB reactors respectively when the reactors were operated with the same
M an
HRT of 6 h (day 214-270). To evaluate the pilot-scale reactors behaviour at rather high hydraulic loading rate, the reactor performances were examined at 4 h HRT (day 271-375). The total COD removal efficiencies were 53.7% and 61.3% for UASB and HUASB reactors
d
respectively, which was much lower than the total COD removal efficiency of MUASB
pt e
reactor (72.7%). A compilation of quasi-steady state reactor performance is given in Table 3. It may be noted from the Table 3, that the effluent soluble COD was similar in all three
ce
reactors. However, the average effluent total COD was significantly lower in MUASB (42 mg L-1) as compared to UASB (71 mg L-1) and HUASB (61 mg L-1) reactor. Higher total
COD removal and lower TSS concentration (Figure 3 in MUASB as compared to UASB and
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
efficiency was probably due to very low influent COD concentration. However, at this stage
HUASB reactor indicates effective removal/degradation of suspended organic matter. Improved performance obtained in MUASB during this study was perhaps due to higher mixing that promoted better sludge wastewater contact. Analysis of variance (ANOVA) test confirmed that the differences in total COD removal efficiencies were significant (p
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Effect of Reactor Configuration on Performance During Anaerobic Treatment Low Strength Wastewater Suprotim Das a
ab
b
& Sanjeev Chaudhari
Research & Development, Tata Steel Limited, Jamshedpur-831001, India
b
Centre for Environmental Science and Engineering (CESE), Indian Institute of Technology Bombay, Powai, Mumbai-t400076, |cIndia Accepted author version posted online: 09 Mar 2015.
Click for updates To cite this article: Suprotim Das & Sanjeev Chaudhari (2015): Effect of Reactor Configuration on Performance During Anaerobic Treatment Low Strength Wastewater, Environmental Technology, DOI: 10.1080/09593330.2015.1026845 To link to this article: http://dx.doi.org/10.1080/09593330.2015.1026845
Disclaimer: This is a version of an unedited manuscript that has been accepted for publication. As a service to authors and researchers we are providing this version of the accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proof will be undertaken on this manuscript before final publication of the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to this version also.
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
Publisher: Taylor & Francis Journal: Environmental Technology DOI: 10.1080/09593330.2015.1026845
a
t
Research & Development, Tata Steel Limited, Jamshedpur-831001, India
us c
Centre for Environmental Science and Engineering (CESE), Indian Institute of Technology Bombay, Powai, Mumbai-400076, India
M an
b
rip
Suprotim Das a, b and Sanjeev Chaudhari b
Abstract:
ce
pt e
d
The efficiency of UASB reactor is quite low for the treatment of low strength wastewaters (LSWs) due to less biogas production leading to poor mixing. LSW may be treated efficiently by providing adequate mixing in UASB reactor when gas production is low and sufficient mixing can be achievable by modifying reactor geometry. Hence, modifying UASB reactor geometry for enhanced mixing and evaluating its performance for the treatment of LSWs would be a worthwhile effort. In the present study, UASB reactor configuration was modified by providing a vertical baffle along the height to promote mixing of reactor contents and is termed as modified up-flow anaerobic sludge blanket (MUASB). The performance of on-site pilot scale MUASB reactor was evaluated for 375 days under ambient condition for the treatment of municipal sewage as LSW and compared with the conventional UASB and hybrid UASB (HUASB) reactor. The MUASB reactor showed better performance in terms of chemical oxygen demand (COD) removal efficiency as compared to UASB and HUASB reactor during this study. At 4 h hydraulic retention time (HRT), the total COD removal efficiency of UASB and HUASB reactor were 53.7% and 61% respectively which were much lower than the total COD removal efficiency of MUASB reactor (72.7%). Better performance observed in MUASB reactor possibly due to improved mixing. Depth-wise analysis of reactor liquid showed that better mixing in MUASB reactor enhances the contact of wastewater with biomass which contributes to the improved treatment efficiency. It seems that MUASB holds promise for LSW treatment.
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
Effect of Reactor Configuration on Performance During Anaerobic Treatment Low Strength Wastewater
Keywords:
Anaerobic process; Wastewater treatment; Anaerobic reactor; UASB; Municipal sewage
1.0 Introduction Anaerobic wastewater treatment process has significant advantages over aerobic one like- low energy consumption, low sludge production, biogas production in form of methane (CH4) and formation of stabilized sludge [1, 2]. Several complex sequential and parallel biological reactions
t rip
as the substrate for the next which results in the conversion of organic matter into biogas (CH4
us c
and CO2). Among various anaerobic reactor, up-flow anaerobic sludge blanket UASB is most widely used for treating different types of wastewater through out the world since 1980s [3-5]. The formation of densely packed granular sludge allows UASB reactor to achieve high chemical
M an
oxygen demand (COD) removal efficiency without the need of any support material. In addition, the turbulence caused by the rising gas bubbles enhance the contact of sludge biomass with incoming wastewater, thus improves mixing without any additional energy requirement and its
d
associated cost [5]. The UASB process has proven effective for the treatment of medium strength
pt e
wastewaters (MSWs) and high strength wastewaters (HSWs) [6]. The potential of UASB reactor is not restricted for the treatment of MSWs and HSWs. The UASB reactor can also be useful for
ce
low strength wastewater (LSW) treatment [7]. However, despite several advantages many researchers have pointed out that UASB reactors have some inherent limitations for the treatment of LSW [5, 7, 8]. Researchers [7, 9] have described LSWs are those which contain COD below
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
occur in anaerobic reactor during the treatment of wastewater. The product of one reaction serves
2,000 mg L-1. It has been reported that food processing, chemicals, dyeing industries release
LSWs in large quantities [10]. Sewage can be considered as an example of low strength complex wastewater [11] which also contains significant fraction of suspended solids (SS). The presence
of SS in wastewater affects the UASB process adversely as degradation of suspended organic matter is difficult as compared to soluble organic matter. The presence of SS also decreases sludge activity due to adsorption and entrapment on granular surface of sludge biomass, thereby inhibiting granulation process in UASB reactor [12]. Thus the efficiency of the UASB system is
limited as it has low SS removal capability mainly for the treatment of LSWs [13]. The diffusion rate of substrate to anaerobic biomass is also lower under this condition [7, 13]. Previous investigation [14] showed that mixing is important to improve reactor efficiency. During the treatment of MSWs and HSWs, gas production inside the UASB reactor provides good mixing. Well mixed conditioned lead to higher dispersion thus resulting in limited plug-flow behaviour of
rip
t
the gas bubbles with the granules [15] which is not achieved during the treatment of LSW as low volume of biogas is produced. In UASB reactor, low mixing may cause channelling of
us c
wastewater through the bed and therefore a poor wastewater–sludge contact, which results in low treatment efficiencies [15, 16]. Tracer studies revealed that internal mixing was not optimal in a
M an
pilot scale UASB reactor treating sewage [17]. Moreover, dilute complex wastewaters provides low mass transfer between wastewater and biomass due to the presence of considerable amount of suspended matter. Therefore, sufficient mixing is essential in order to eliminate mass transfer limitations in microbial aggregates [18]. Different feed inlet systems, more feed inlet points per
d
unit area and high superficial velocities of incoming liquid have been proposed by researchers in
pt e
order to improve the sludge-wastewater contact.
ce
The performance of bioreactor is influenced by several factors, among them mass transfer of organic matter to biomass and residence time of liquid are governed by hydrodynamics of bioreactor. Thereby reactor hydrodynamic has influence on the performance [19]. Reactor
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
the sludge bed [7]. Turbulence of sludge bed is enhanced under this condition due to collision of
configuration and hydrodynamics has significant impact on sludge biomass characteristics such as size distribution, compressibility and the settling rate in suspended aerobic growth
bioreactor system [20].
The aim of this study was to improve the performance of UASB reactor for the treatment of LSW by changing the reactor geometry. Therefore, modification of UASB reactor was done and the reactor is termed as modified up-flow anaerobic sludge blanket (MUASB). The
performance of pilot scale MUASB reactor for on-site treatment of municipal sewage as LSW was evaluated mainly in terms of total COD removal efficiency and TSS removal and was compared with conventional UASB and hybrid UASB (HUASB) reactor.
rip
t
2.1 Description of the pilot-scale Up-flow Anaerobic Sludge Blanket (UASB), Hybrid Up-flow Anaerobic Sludge Blanket (HUASB) and Modified Up-flow Anaerobic Sludge Blanket (MUASB) reactors
On-site pilot-scale experiment with domestic sewage as real low strength wastewater (LSW)
us c
was carried out by using UASB, HUASB and MUASB reactors. The reactors were fabricated in the laboratory using transparent acrylic sheet (thickness 8 mm). The model schematics of
M an
UASB, HUASB and MUASB reactors are shown in Figure 1. The detailed specifications of the models are presented in Table 1. The pilot-scale study was conducted under ambient condition with reactor liquid temperature in the range of 240C to 280C. The detailed
d
specifications of the reactors are as follows-
pt e
2.1.1 Up-flow Anaerobic Sludge Blanket (UASB) Reactor The UASB model was fabricated by using acrylic sheet in a square cross-sectional form. The
ce
total height of the reactor was 270 cm included the height of hopper bottom. The gas liquid solid separator (GLSS) with deflector beam was also made of acrylic and provided at the top
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
2.0 Materials and Methods
of the reactor.
2.1.2 Hybrid Up-flow Anaerobic Sludge Blanket (HUASB) Reactor The HUASB reactor contains 5000 numbers of small sponge cube (1 cm x 1 cm) as filter media which was provided in the upper part of the reactor (200 cm to 240 cm from bottom). A uniformly perforated square shaped plate was provided as support for filter media.
2.1.3 Modified Up-flow Anaerobic Sludge Blanket (MUASB) Reactor
In UASB reactor, a slanted rigid acrylic plate, which has been termed as baffle, was fixed between two opposite vertical walls. The baffle was introduced having an angle of 5.7o with the vertical wall. The lower end starts from 60 cm from the bottom and extended up to 170 cm having an opening of 3 cm x 16 cm. The granule along with effluent come out from the narrow opening of the baffle with higher velocity and falls on the other side of the baffle and
t
rip
by enhancing the internal recirculation of sludge biomass and thereby improves reactor
us c
performance due to better mixing. 2.2 Seed Sludge
M an
Seed sludge was collected from a 1.2 million liter per day (MLD) full scale UASB reactor treating effluent of dairy industry where the COD of wastewater was in the range of 3500 mg L-1 to 5000 mg L-1.
d
2.3 Characteristics of Domestic Sewage
pt e
The pilot-scale reactors were fed with the sewage of Indian Institute of Technology Bombay (IIT Bombay) campus-Mumbai (20,000 inhabitants). The average total COD concentration of
ce
raw sewage was 198 mg L-1 which can be classified as “very diluted” [11]. This sewage was withdrawn from sewage pumping station through a stainless steel net (2 cm2 per square holes). The sewage was stored in a plastic tank with a capacity of 1000 L. The hourly
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
thus circulated into the reactor. Baffle increases contact of sludge granules with wastewater
variation of the sewage was avoided by pumping sewage frequently into storage tank. The main characteristics of this sewage are shown in Table 2.
2.4 Analytical Technique
Various analytical technique used in this investigation are presented in the following subsection. In general, for monitoring of pH, COD, total suspended solids (TSS) and volatile
t rip
3.0 Result and Discussion
us c
3.1 Performance comparisons of Up-flow Anaerobic Sludge Blanket (UASB), Hybrid Up-flow Anaerobic Sludge Blanket (HUASB) and Modified Up-flow Anaerobic Sludge Blanket (MUASB) Reactors
M an
On-site pilot-scale reactor performance was evaluated for the treatment of domestic sewage. The reactors were installed at IIT Bombay sewage pumping station and operated for 375 days. Wastewater was taken directly from pumping station through a net basket (2 cm2 per
d
square holes) to prevent coarse materials and was pumped in storage tank. The detention time
pt e
in storage tank was 4 h. Average composition of sewage during the study is presented in Table 2. The influent COD exhibited seasonal variations.
ce
Figure 2 presents the COD removal efficiency of the reactors with time. The average influent total COD varied from 90 mg L-1 (rainy season) to 207 mg L-1 (summer). All three reactors
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
fatty acids (VFA) standard procedure as detailed in standard methods [21] was followed.
achieved quasi-steady state after 35-40 days. In this study, HRT was reduced from 8 to 4 h in stepwise manner. At 8 h HRT (day 1-89), the total COD removal efficiencies were 61%, 65% and 81.2% and the average effluent COD concentrations were 70 mg L-1, 66 mg L-1 and 38 mg L-1 for UASB, HUASB and MUASB reactors, respectively. When the HRT was reduced from
8 h to 6 h (after 89 days), the average total COD removal was found to be 63%, 69% and 82% and total COD of effluent was 76 mg L-1, 68 mg L-1 and 39 mg L-1 for UASB, HUASB
and MUASB reactors, respectively. In between 135 to 214 days, the average total sewage COD was 90 mg L-1 due to monsoon and total sewage COD was in the range of 77 mg L-1 to 110 mg L-1. The low influent COD adversely affected the reactor performance. The efficiency of UASB and HUASB reactor dropped to about 32% and 36% respectively (average effluent COD 71 mg L-1 and 57 mg L-1 respectively) at this stage. The decrease in COD removal
t
rip
average COD removal in MUASB reactor was 51% with average total effluent COD of 42 mg L-1. From day 214 (post rainy season), the average influent sewage COD was 160 mg L-1.
us c
The average COD removal efficiency was increased to 51%, 57% and 69%in UASB, HUASB and MUASB reactors respectively when the reactors were operated with the same
M an
HRT of 6 h (day 214-270). To evaluate the pilot-scale reactors behaviour at rather high hydraulic loading rate, the reactor performances were examined at 4 h HRT (day 271-375). The total COD removal efficiencies were 53.7% and 61.3% for UASB and HUASB reactors
d
respectively, which was much lower than the total COD removal efficiency of MUASB
pt e
reactor (72.7%). A compilation of quasi-steady state reactor performance is given in Table 3. It may be noted from the Table 3, that the effluent soluble COD was similar in all three
ce
reactors. However, the average effluent total COD was significantly lower in MUASB (42 mg L-1) as compared to UASB (71 mg L-1) and HUASB (61 mg L-1) reactor. Higher total
COD removal and lower TSS concentration (Figure 3 in MUASB as compared to UASB and
Ac
Downloaded by [University of Colorado - Health Science Library] at 14:22 30 March 2015
efficiency was probably due to very low influent COD concentration. However, at this stage
HUASB reactor indicates effective removal/degradation of suspended organic matter. Improved performance obtained in MUASB during this study was perhaps due to higher mixing that promoted better sludge wastewater contact. Analysis of variance (ANOVA) test confirmed that the differences in total COD removal efficiencies were significant (p
