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© IWA Publishing 2015 Water Science & Technology
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71.8
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2015
Biodiesel from wastewater: lipid production in high rate algal pond receiving disinfected effluent Paula Peixoto Assemany, Maria Lucia Calijuri, Eduardo de Aguiar do Couto, Aníbal Fonseca Santiago and Alberto José Delgado dos Reis
ABSTRACT The production of different species of microalgae in consortium with other micro-organisms from wastewaters may represent an alternative process, to reduce the costs, for obtaining biofuels. The aim of this study was to evaluate the influence of pre-ultraviolet disinfection (UV) in the production of lipids from biomass produced in high rate ponds. Two high rate algal ponds were evaluated: a pond that received domestic sewage without disinfection and the other receiving domestic sewage previously disinfected by UV radiation (uvHRAP). The UV disinfection did not lead to significant differences in fatty acid profile and total lipid productivities, although it increased algal biomass concentration and productivity as well as lipid content. Moreover, the overall biomass concentrations and productivities decreased with the UV disinfection, mostly as a consequence of a loss in bacterial load. We thus conclude that uvHRAP disinfection may represent a potential strategy to promote the cleaner and safer growth of algal biomass when cultivated in consortium with other microorganisms. Mainly regarding the use of wastewater as culture medium, together with a cheaper
Paula Peixoto Assemany (corresponding author) Maria Lucia Calijuri Eduardo de Aguiar do Couto Aníbal Fonseca Santiago Avenida PH Rolfs, s/n, Campus Universitário, Department of Civil Engineering, Universidade Federal de Viçosa, Viçosa, 36570-900, Minas Gerais, Brazil E-mail: [email protected] Alberto José Delgado dos Reis National Laboratory of Energy and Geology, I.P. LNEG – Unidade de Bioenergia, Estrada do Paço do Lumiar, 22- Edifício F R/C, 1649-038, Lisbon, Portugal
production of lipids for biodiesel, pre-disinfection may represent an advance since extraction costs could be significantly trimmed due to the increase in lipid content. Key words
| bioenergy, domestic sewage, fatty acid, microalgae, ultraviolet disinfection
INTRODUCTION The cultivation of microalgae for biofuels production is an extremely promising issue, since it represents a method to diversify sources of energy, and also is a potential renewable and carbon-neutral alternative to petroleum fuels, as is any biofuel derived from oil crops (Chisti ; Batten et al. ). However, the production of algal biomass is still costly, which is one of the main challenges for its use on a large scale (Ozkan et al. ). To resolve this issue, the use of wastewater as a growth medium can eliminate the competition with agriculture for space, water and nutrients for microalgae production, with the added benefit of contributing to a closed loop process, adding value to the process, towards no waste generation, contributing to an increasingly greener biotechnology. The production of algal biomass for energy purposes by reusing water can be made in high rate algal ponds (HRAPs), which are at the same time used for treating the effluent (Craggs et al. ). The production of doi: 10.2166/wst.2015.087
microalgae in consortium with other micro-organisms may also contribute to the reduction of the costs involved in the process of obtaining biofuels, since it presents competitive advantages such as less influence of environmental fluctuations and easier harvesting and processing of the biomass (Pires et al. ). Conversely, competition between algae and bacteria for nutrients and space may represent a negative factor for the production of algal biomass and lipids from wastewater (Peccia et al. ). Cho et al. () concluded after laboratory studies that a pretreatment to remove micro-organisms can be applied for the efficient production of algal biomass. Santiago et al. () showed that disinfection by ultraviolet (UV) radiation may be an effective pre-treatment to enhance the production of algal biomass using HRAPs with domestic sewage as growth medium. The objective of this study was to evaluate the influence of UV pre-disinfection on the lipid productivity of a high rate
1230
P. P. Assemany et al.
|
Biodiesel from wastewater: lipid production in high rate pond
pond treating domestic sewage in pilot scale, having in view a potential energy valuation for biodiesel production.
MATERIALS AND METHODS Experimental unit The HRAPs were installed downstream of a full-scale upflow anaerobic sludge blanket (UASB) reactor, with the following characteristics: average flow ¼ 115 m3 day1, volume ¼ 48 m3, height ¼ 5.7 m and hydraulic holding time ¼ 7 h. Part of the effluent from this reactor was sent to the pilot system of two high rate ponds evaluated in this study. The HRAP received effluent from the UASB reactor and the uvHRAP received the same effluent after being submitted to the UV disinfection process. The culture medium used in this study was domestic sewage anaerobically treated and no inoculum was added to the ponds, characterising an outdoor experiment under natural conditions. The experimental HRAPs had the following characteristics: width ¼ 1.28 m, length ¼ 2.86 m, total depth ¼ 0.5 m, culture depth ¼ 0.3 m, surface area ¼ 3.3 m2, culture volume ¼ 1 m3 and a hydraulic retention time (HRT) of 4 days. The paddlewheels were driven by a 1 horsepower electric motor. Rotation was reduced by a reduction gear coupled to the motor and controlled by a frequency inverter (WEG, series CFW-10) to provide a mean horizontal water velocity of approximately 0.10–0.15 m s1. The inlet flow was manually regulated to 10.4 L h1 to maintain an HRT of 4 days. The disinfection system was designed to achieve a final concentration of 103 MPN (100 mL)1 of Escherichia coli, with an adopted effective dose of 21 mJ cm2 and absorbance of 42%, as suggested by Gonçalves et al. (), who studied E. coli removal from UASB effluent by UV disinfection. Thus, an applied dose of 203.1 mJ cm2 and applied dose per volume of 5.64 Wh m3 were used in the disinfection unit. The characteristics of the disinfection reactor were: width ¼ 0.16 m, length ¼ 0.76 m, water depth ¼ 0.10 m and HRT ¼ 8.4 s. On the longitudinal axis, three low-pressure UVC lamps (
© IWA Publishing 2015 Water Science & Technology
|
71.8
|
2015
Biodiesel from wastewater: lipid production in high rate algal pond receiving disinfected effluent Paula Peixoto Assemany, Maria Lucia Calijuri, Eduardo de Aguiar do Couto, Aníbal Fonseca Santiago and Alberto José Delgado dos Reis
ABSTRACT The production of different species of microalgae in consortium with other micro-organisms from wastewaters may represent an alternative process, to reduce the costs, for obtaining biofuels. The aim of this study was to evaluate the influence of pre-ultraviolet disinfection (UV) in the production of lipids from biomass produced in high rate ponds. Two high rate algal ponds were evaluated: a pond that received domestic sewage without disinfection and the other receiving domestic sewage previously disinfected by UV radiation (uvHRAP). The UV disinfection did not lead to significant differences in fatty acid profile and total lipid productivities, although it increased algal biomass concentration and productivity as well as lipid content. Moreover, the overall biomass concentrations and productivities decreased with the UV disinfection, mostly as a consequence of a loss in bacterial load. We thus conclude that uvHRAP disinfection may represent a potential strategy to promote the cleaner and safer growth of algal biomass when cultivated in consortium with other microorganisms. Mainly regarding the use of wastewater as culture medium, together with a cheaper
Paula Peixoto Assemany (corresponding author) Maria Lucia Calijuri Eduardo de Aguiar do Couto Aníbal Fonseca Santiago Avenida PH Rolfs, s/n, Campus Universitário, Department of Civil Engineering, Universidade Federal de Viçosa, Viçosa, 36570-900, Minas Gerais, Brazil E-mail: [email protected] Alberto José Delgado dos Reis National Laboratory of Energy and Geology, I.P. LNEG – Unidade de Bioenergia, Estrada do Paço do Lumiar, 22- Edifício F R/C, 1649-038, Lisbon, Portugal
production of lipids for biodiesel, pre-disinfection may represent an advance since extraction costs could be significantly trimmed due to the increase in lipid content. Key words
| bioenergy, domestic sewage, fatty acid, microalgae, ultraviolet disinfection
INTRODUCTION The cultivation of microalgae for biofuels production is an extremely promising issue, since it represents a method to diversify sources of energy, and also is a potential renewable and carbon-neutral alternative to petroleum fuels, as is any biofuel derived from oil crops (Chisti ; Batten et al. ). However, the production of algal biomass is still costly, which is one of the main challenges for its use on a large scale (Ozkan et al. ). To resolve this issue, the use of wastewater as a growth medium can eliminate the competition with agriculture for space, water and nutrients for microalgae production, with the added benefit of contributing to a closed loop process, adding value to the process, towards no waste generation, contributing to an increasingly greener biotechnology. The production of algal biomass for energy purposes by reusing water can be made in high rate algal ponds (HRAPs), which are at the same time used for treating the effluent (Craggs et al. ). The production of doi: 10.2166/wst.2015.087
microalgae in consortium with other micro-organisms may also contribute to the reduction of the costs involved in the process of obtaining biofuels, since it presents competitive advantages such as less influence of environmental fluctuations and easier harvesting and processing of the biomass (Pires et al. ). Conversely, competition between algae and bacteria for nutrients and space may represent a negative factor for the production of algal biomass and lipids from wastewater (Peccia et al. ). Cho et al. () concluded after laboratory studies that a pretreatment to remove micro-organisms can be applied for the efficient production of algal biomass. Santiago et al. () showed that disinfection by ultraviolet (UV) radiation may be an effective pre-treatment to enhance the production of algal biomass using HRAPs with domestic sewage as growth medium. The objective of this study was to evaluate the influence of UV pre-disinfection on the lipid productivity of a high rate
1230
P. P. Assemany et al.
|
Biodiesel from wastewater: lipid production in high rate pond
pond treating domestic sewage in pilot scale, having in view a potential energy valuation for biodiesel production.
MATERIALS AND METHODS Experimental unit The HRAPs were installed downstream of a full-scale upflow anaerobic sludge blanket (UASB) reactor, with the following characteristics: average flow ¼ 115 m3 day1, volume ¼ 48 m3, height ¼ 5.7 m and hydraulic holding time ¼ 7 h. Part of the effluent from this reactor was sent to the pilot system of two high rate ponds evaluated in this study. The HRAP received effluent from the UASB reactor and the uvHRAP received the same effluent after being submitted to the UV disinfection process. The culture medium used in this study was domestic sewage anaerobically treated and no inoculum was added to the ponds, characterising an outdoor experiment under natural conditions. The experimental HRAPs had the following characteristics: width ¼ 1.28 m, length ¼ 2.86 m, total depth ¼ 0.5 m, culture depth ¼ 0.3 m, surface area ¼ 3.3 m2, culture volume ¼ 1 m3 and a hydraulic retention time (HRT) of 4 days. The paddlewheels were driven by a 1 horsepower electric motor. Rotation was reduced by a reduction gear coupled to the motor and controlled by a frequency inverter (WEG, series CFW-10) to provide a mean horizontal water velocity of approximately 0.10–0.15 m s1. The inlet flow was manually regulated to 10.4 L h1 to maintain an HRT of 4 days. The disinfection system was designed to achieve a final concentration of 103 MPN (100 mL)1 of Escherichia coli, with an adopted effective dose of 21 mJ cm2 and absorbance of 42%, as suggested by Gonçalves et al. (), who studied E. coli removal from UASB effluent by UV disinfection. Thus, an applied dose of 203.1 mJ cm2 and applied dose per volume of 5.64 Wh m3 were used in the disinfection unit. The characteristics of the disinfection reactor were: width ¼ 0.16 m, length ¼ 0.76 m, water depth ¼ 0.10 m and HRT ¼ 8.4 s. On the longitudinal axis, three low-pressure UVC lamps (
