The aim of this study was to assess the environmental impact of three alternatives for wastewater treatment in small communities. To this end, a Life Cycle Assessment (LCA) was carried out comparing a conventional wastewater treatment plant (i.e. activated sludge system) with two nature-based technologies (i.e. hybrid constructed wetland and high rate algal pond systems). Moreover, an economic evaluation was also addressed. All systems served a population equivalent of 1500 p.e. The functional unit was 1 m3 of water. System boundaries comprised input and output flows of material and energy resources for system construction and operation. The LCA was performed with the software SimaPro® 8, using the ReCiPe midpoint method. The results showed that the nature-based solutions were the most environmentally friendly alternatives, while the conventional wastewater treatment plant presented the worst results due to the high electricity and chemicals consumption. Specifically, the potential environmental impact of the conventional wastewater treatment plant was between 2 and 5 times higher than that generated by the nature-based systems depending on the impact category. Even though constructed wetland and high rate algal pond systems presented similar results in terms of environmental impact, the latter showed to be the less expensive alternative. Nevertheless, the constructed wetland system should be preferred when land occupation is of major concern, since it has a smaller footprint compared to the high rate algal pond alternative.
Eskicioglua, C.; Monlau, F.; Barakat, A.; Ferrer, I.; Kaparaju, P.; Trably, E.; Carrère, H. Water Research Vol. 120, p. 32-42 DOI: 10.1016/j.watres.2017.04.068 Data de publicació: 2017-09 Article en revista
Hydrothermal pretreatment of five lignocellulosic substrates (i.e. wheat straw, rice straw, biomass sorghum, corn stover and Douglas fir bark) were conducted in the presence of CO2 as a catalyst. To maximize disintegration and conversion into bioenergy (methane and hydrogen), pretreatment temperatures and subsequent pressures varied with a range of 26–175 °C, and 25–102 bars, respectively. Among lignin, cellulose and hemicelluloses, hydrothermal pretreatment caused the highest reduction (23–42%) in hemicelluloses while delignification was limited to only 0–12%. These reductions in structural integrity resulted in 20–30% faster hydrolysis rates during anaerobic digestion for the pretreated substrates of straws, sorghum, and corn stover while Douglas fir bark yielded 172% faster hydrolysis/digestion due to its highly refractory nature in the control. Furans and phenolic compounds formed in the pretreated hydrolyzates were below the inhibitory levels for methane and hydrogen production which had a range of 98–340 ml CH4/g volatile solids (VS) and 5–26 ml H2/g VS, respectively. Results indicated that hydrothermal pretreatment is able to accelerate the rate of biodegradation without generating high levels of inhibitory compounds while showing no discernible effect on ultimate biodegradation.
This study aimed at analyzing the anaerobic co-digestion of microalgal biomass grown in wastewater and wheat straw. To this end, Biochemical Methane Potential (BMP) tests were carried out testing different substrate proportions (20–80, 50–50 and 80–20%, on a volatile solid basis). In order to improve their biodegradability, the co-digestion of both substrates was also evaluated after applying a thermo-alkaline pretreatment (10% CaO at 75 °C for 24 h). The highest synergies in degradation rates were observed by adding at least 50% of wheat straw. Therefore, the co-digestion of 50% microalgae – 50% wheat straw was investigated in mesophilic lab-scale reactors. The results showed that the methane yield was increased by 77% with the co-digestion as compared to microalgae mono-digestion, while the pretreatment only increased the methane yield by 15% compared to the untreated mixture. Thus, the anaerobic co-digestion of microalgae and wheat straw was successful even without applying a thermo-alkaline pretreatment.
Sole, M.; Carrère, H.; Marianna Garfi'; Ferrer, I. Algal research: biomass, biofuels and bioproducts Vol. 24, part A, p. 199-206 DOI: 10.1016/j.algal.2017.03.025 Data de publicació: 2017-06 Article en revista
The aim of this study was to evaluate for the first time the effect of a thermo-alkaline pretreatment with lime (CaO) on microalgae anaerobic digestion. The pretreatment was carried out by adding different CaO doses (4 and 10%) at different temperatures (room temperature (25 °C), 55 and 72 °C). The exposure time was 4 days for pretreatments at 25 °C, and 24 h for pretreatments at 55 and 72 °C. Following, a biochemical methane potential test was conducted with pretreated and untreated microalgae. According to the results, the pretreatment enhanced proteins solubilisation by 32.4% and carbohydrates solubilisation by 31.4% with the highest lime dose and temperature (10% CaO and 72 °C). Furthermore, anaerobic digestion kinetics were improved in all cases (from 0.08 to 0.14 day- 1 for untreated and pretreated microalgae, respectively). The maximum biochemical methane potential increase (25%) was achieved with 10% CaO at 72 °C, in accordance with the highest biomass solubilisation. Thus, lime pretreatment appears as a potential strategy to improve microalgae anaerobic digestion.
Sole, M.; Cucina, M.; Folch, M.; Tapias, J.; Gigliotti, G.; Marianna Garfi'; Ferrer, I. Science of the total environment Vol. 586, p. 1-9 DOI: 10.1016/j.scitotenv.2017.02.006 Data de publicació: 2017-05 Article en revista
Microalgae anaerobic digestion produces biogas along with a digestate that may be reused in agriculture. However, the properties of this digestate for agricultural reuse have yet to be determined. The aim of this study was to characterise digestates from different microalgae anaerobic digestion processes (i.e. digestion of untreated microalgae, thermally pretreated microalgae and thermally pretreated microalgae in co-digestion with primary sludge). The main parameters evaluated were organic matter, macronutrients and heavy metals content, hygenisation, potential phytotoxicity and organic matter stabilisation. According to the results, all microalgae digestates presented suitable organic matter and macronutrients, especially organic and ammonium nitrogen, for agricultural soils amendment. However, the thermally pretreated microalgae digestate was the least stabilised digestate in comparison with untreated microalgae and co-digestion digestates. In vivo bioassays demonstrated that the digestates did not show residual phytotoxicity when properly diluted, being the co-digestion digestate the one which presented less phytotoxicity. Heavy metals contents resulted far below the threshold established by the European legislation on sludge spreading. Moreover, low presence of E. coli was observed in all digestates. Therefore, agricultural reuse of thermally pretreated microalgae and primary sludge co-digestate through irrigation emerges a suitable strategy to recycle nutrients from wastewater.
Microalgae are nowadays regarded as a potential biomass feedstock to help reducing our dependence on fossil fuels for transportation, electricity and heat generation. Besides, microalgae have been widely investigated as a source of chemicals, cosmetics and health products, as well as animal and human feed. Among the cutting-edge applications of microalgae biomass, anaerobic digestion has shown promising results in terms of (bio)methane production. The interest of this process lies on its potential integration within the microalgae biorefinery concept, providing on the one hand a source of bioenergy, and on the other hand nutrients (nitrogen, phosphorus and CO2) and water for microalgae cultivation. This article reports the main findings in the field, highlighting the options to increase the (bio)methane production of microalgae (i.e. pretreatment and co-digestion) and bottlenecks of the technology. Finally, energy, economic and environmental aspects are considered.
The final publication is available at Springer via http://dx.doi.org/10.1007/s12649-016-9604-3
Gutierrez, R.; Ferrer, I.; González-Molina, A.; Salvado, H.; Garcia, J.; Uggetti, E. Water research (Oxford) Vol. 106, p. 539-549 DOI: 10.1016/j.watres.2016.10.039 Data de publicació: 2016-12 Article en revista
Microalgal biomass harvesting by inducing spontaneous flocculation (bioflocculation) sets an attractive approach, since neither chemicals nor energy are needed. Indeed, bioflocculation may be promoted by recycling part of the harvested microalgal biomass to the photobioreactor in order to increase the predominance of rapidly settling microalgae species. The aim of the present study was to improve the recovery of microalgal biomass produced in wastewater treatment high rate algal ponds (HRAPs) by recycling part of the harvested microalgal biomass. The recirculation of 2% and 10% (dry weight) of the HRAPs microalgal biomass was tested over one year in an experimental HRAP treating real urban wastewater. Results indicated that biomass recycling had a positive effect on the harvesting efficiency, obtaining higher biomass recovery in the HRAP with recycling (R-HRAP) (92–94%) than in the control HRAP without recycling (C-HRAP) (75–89%). Microalgal biomass production was similar in both systems, ranging between 3.3 and 25.8 g TSS/m2d, depending on the weather conditions. Concerning the microalgae species, Chlorella sp. was dominant overall the experimental period in both HRAPs (abundance >60%). However, when the recycling rate was increased to 10%, Chlorella sp. dominance decreased from 97.6 to 88.1%; while increasing the abundance of rapidly settling species such as Stigeoclonium sp. (16.8%, only present in the HRAP with biomass recycling) and diatoms (from 0.7 to 7.3%). Concerning the secondary treatment of the HRAPs, high removals of COD (80%) and N-NH4+ (97%) were found in both HRAPs. Moreover, by increasing the biomass recovery in the R-HRAP the effluent total suspended solids (TSS) concentration was decreased to less than 35 mg/L, meeting effluent quality requirements for discharge. This study shows that microalgal biomass recycling (10% dry weight) increases biomass recovery up to 94% by selecting the most rapidly settling microalgae species without compromising the biomass production and improving the wastewater treatment in terms of TSS removal.
Hom, A.; Passos, F.; Ferrer, I.; Vicent, T.; Blánquez , P. Algal research: biomass, biofuels and bioproducts Vol. 19, p. 184-188 DOI: 10.1016/j.algal.2016.08.006 Data de publicació: 2016-11 Article en revista
Coupling microalgae production to wastewater treatment can reduce the costs of microalgae production for non-food bioproducts and energy consumption for wastewater treatment. Furthermore, microalgae anaerobic digestion can be enhanced by applying pretreatment techniques. The aim of this study is to improve the biogas production from microalgal biomass grown in urban wastewater treatment systems by applying an enzymatic pretreatment with crude fungal broth and commercial laccase. To this end, the fungus Trametes versicolor was cultured, and the enzymatic activity of the culture broth analysed by measuring laccase concentration. The results showed that both the fungal broth and commercial laccase pretreatment (100 U L- 1) over an exposure time of 20 min increased the methane yield in batch tests. Indeed, the fungal broth pretreatment increased the methane yield by 74%, while commercial laccase increased the methane yield by 20% as compared to non-pretreated microalgal biomass. In this manner, laccase addition enhanced microalgal biomass anaerobic biodegradability, and addition of T. versicolor broth further improved the results. This fact may be attributed to the presence of other molecules excreted by the fungus.
This study evaluated the environmental impacts caused by drinking water consumption in Barcelona (Spain) using the Life Cycle Assessment (LCA) methodology. Five different scenarios were compared: 1) tap water from conventional drinking water treatment; 2) tap water from conventional drinking water treatment with reverse osmosis at the water treatment plant; 3) tap water from conventional drinking water treatment with domestic reverse osmosis; 4) mineral water in plastic bottles, and 5) mineral water in glass bottles. The functional unit was 1 m3 of water. The water treatment plant considered in scenarios 1, 2 and 3, treats around 5 m3 s-1 of surface water. The water bottling plants considered in scenarios 4 and 5 have a production capacity of 200 m3 of bottled water per day. The LCA was performed with the software SimaPro®, using the CML 2 baseline method. The results showed how tap water consumption was the most favourable alternative, while bottled water presented the worst results due to the higher raw materials and energy inputs required for bottles manufacturing, especially in the case of glass bottles. The impacts generated by domestic reverse osmosis were between 10 and 24% higher than tap water alternative depending on the impact category. It was due to the higher electricity consumption. Reverse osmosis at the water treatment plant showed impacts nearly twice as high as domestic reverse osmosis systems scenario, mainly because of the higher energy inputs. Water treated by domestic reverse osmosis equipment was the most environmentally friendly solution for the improvement of tap water organoleptic characteristics. An economic analysis showed that this solution was between 8 and 19 times cheaper than bottled water.
This review aims to provide an overview of household biogas digester implementation in rural areas of Latin America. It considers the history of household-digesters in Latin America, including technical, environmental, social and economic aspects. Several successful experiences have been promoted during the last decade, including the creation of the Network for Biodigesters in Latin America and the Caribbean (RedBioLAC) that provides a forum to coordinate implementation and research programmes throughout the continent. Although the potential of this technology is well demonstrated, some barriers are identified, such as the need for technical improvements, lack of social acceptance and high investment costs. Thus, further efforts should be undertaken to overcome these barriers and improve the technical performance, social acceptance, economic benefits and environmental impact in order to enhance its wide-spread dissemination in energy poor communities. (C) 2016 Elsevier Ltd. All rights reserved.
This review aims to provide an overview of household biogas digester implementation in rural areas of Latin America. It considers the history of household digesters in Latin America, including technical, environmental, social and economic aspects. Several successful experiences have been promoted during the last decade, including the creation of the Network for Biodigesters in Latin America and the Caribbean (RedBioLAC) that provides a forum to coordinate implementation and research programmes throughout the continent. Although the potential of this technology is well demonstrated, some barriers are identified, such as the need for technical improvements, lack of social acceptance and high investment costs. Thus, further efforts should be undertaken to overcome these barriers and improve the technical performance, social acceptance, economic benefits and environmental impact in order to enhance its wide-spread dissemination in energy poor communities.
Taking into account the current global water scarcity and the expensive operation and maintenance cost of wastewater treatment, INCOVER concept has been designed to move wastewater treatment from being primarily a sanitation technology towards a bio-product recovery industry and a recycled water supplier. A wastewater specific Decision Support System methodology will be tailored to the INCOVER technologies and provide data and selection criteria for a holistic wastewater management approach.
Three added-value plants treating wastewater from three case-studies (municipalities, farms and food and beverage industries) will be implemented, assessed and optimised concurrently. INCOVER plants will be implemented at demonstration scale in order to achieve Technology Readiness Level(TRL) of 7-8 to ensure straightforward up scaling to 100,000 population equivalents (PE). INCOVER added-value plants will generate benefits from wastewater offering three recovery solutions: 1) Chemical recovery (bio-plastic and organic acids) via algae/bacteria and yeast biotechnology; 2) Near-zero-energy plant providing upgraded bio-methane via pre-treatment and anaerobic co-digestion systems; 3) Bio-production and reclaimed water via adsorption, biotechnology based on wetlands systems and hydrothermal carbonisation. To improve added-value production efficiency, INCOVER solutions will include monitoring and control via optical sensing and soft-sensors.
INCOVER solutions will reduce at least a 50% overall operation and maintenance cost of wastewater treatment through the use of wastewater as a source for energy demand and added-value production to follow UE circular economy strategy. In addition, strategies to facilitate the market uptake of INCOVER innovations will be carried out in order to close the gap between demonstration and end-users.
An estimated turnover of 188 million€ for INCOVER lead-users is expected after the initial exploitation strategy of 5 years implementing 27 INCOVER solutions.
Gutierrez, R.; Ferrer, I.; Uggetti, E.; Arnabat, C.; Salvado, H.; Garcia, J. Algal research: biomass, biofuels and bioproducts Vol. 16, p. 409-417 DOI: 10.1016/j.algal.2016.03.037 Data de publicació: 2016-06 Article en revista
The aim of this study was to evaluate the settling velocity distribution of microalgal biomass with and without flocculant (Tanfloc SG). Microalgal biomass was obtained from two experimental wastewater treatment high rate algal ponds (HRAPs) operated with 4 and 8 days of hydraulic retention time. Two sets of dynamic sedimentation tests were carried out using a water elutriation apparatus. In the first set, most of the biomass of the 8 days-HRAP (63%) had settling velocities between 16.5 and 4 m/h, while most of the biomass of the 4 days-HRAP (65%) had settling velocities between 16.5 and 1 m/h. In the second set, most of the biomass from both HRAPs (60% from the 8 days-HRAP and 80% from the 4 days-HRAP) had settling velocities between 6.5 and 0.4 m/h. In this second set, settling velocities of <0.4 m/h were reached by 20% and 40% of the biomass from 4 days-HRAP and 8 days-HRAP, respectively. The addition of flocculant at optimal doses ranging from 20 to 40 mg/L had impressive effects on the settling velocity distribution in this second set. 70% and 84% of biomass reached velocities of >6.5 m/h, compared to 10% and 14% of microalgal biomass without flocculant for the 8 days-and 4 days-HRAPs, respectively. With flocculant, a very small amount of biomass (3% for the 4 days-HRAP and 8% for the 8 days-HRAP) had settling velocities of <0.4 m/h. Microscopic examination of samples from sedimentation tests showed how an important amount of microalgae settled in the system. Indeed, <1500 microalgae individuals/mL were found in all outlet samples from the elutriation apparatus (inlet samples of >10(5) microalgae individuals/mL). According to our results, a settler designed with a critical settling velocity of 1m/h would reach biomass recoveries as high as 90-94% with flocculant compared to 77-88% without flocculant.
Actualmente, la investigación de nuevas fuentes de energía ha centrado la atención hacia las microalgas. El principal desafio para la producción de microalgas a gran escala es realizar una recuperación de la biomasa algal eficente y rentable para su posterior valorización. En el contexto del tratamiento de aguas residuales, el proceso de coagulación-floculación seguido de la sedimentación representa la técnica de recuperación de microalgas más adecuada debido al bajo consumo energético y a los bajos costes asociados.El objetivo principal de la tesis doctoral fue evaluar y mejorar la eficiencia de separación de la biomasa algal cultivada en lagunas de alta carga (LAC) para el tratamiento de agua residual urbana. Esto se consiguió aplicando técnicas de pre-concentración basadas en procesos de floculación. A posteriori, se evaluó el balance energético de un sistema de tratamiento de aguas residuales a gran escala situado en la región Mediterránea, formado por un sistema de LAC seguido de un proceso de digestión anaeróbica de la biomasa.En primer lugar, la coagulación-floculación y sedimentación con dos floculantes naturales poliméricos (Ecotan y Tanfloc) se evaluó por medio de ensayos de sedimentación estáticos en columnas de sedimentación convencionales. Ambos floculantes obtubieron dosis ótimas bajas (10-50 mg / L) que permitieron la recuperación del 90% de la biomasa. Además, estos aumentaron la velocidad de sedimentación de la biomasa algal, implicando una recuperación de la biomasa rápida y eficiente (> 90% de recuperación en 10 a 20 min). Posteriormente, los tests de sedimentación dinámica se realizaron en un dispositivo dotado de tres columnas de sedimentación con el fin de evaluar la distribución de velocidades de sedimentación de la biomasa con y sin el efecto de floculantes. Esta vez, se evaluaró un floculante polimérico (Tanfloc) y un almidón catiónico. En estos ensayos, se auménto del 10-14% (son floculante) al 70-84% (con coagulante) la fracción de biomasa con unas velocidades de sedimentación mayores a 6,5 m/h tras la adición de 20-40 mg/L de Tanfloc. Por otra parte, entre10 y 25 mg / L de almidón fueron necesarios para recuperar más del 95% de la biomasa,incrementando del 46% a 78% la fracción de partículas con velocidades de sedimentación mayores a 6,5 m / h. Según los resultados, un decantador diseñado con una velocidad de sedimentación de 1 m / h (valor típico en decantadores secundarios) permitiría la recuperación del 90% de la biomasa, reduciendo el tiempo de retención hidráulico y la superficie de los decantadores, tras la adición de los floculantes naturales estudiados. La separación de la biomasa también se evaluó mediante la recirculación de una fracción de la biomasa cosechada (2% y 10% del peso en seco) en un sistema de LAC para el tratamiento de aguas residuales con el fin de aumentar el predominio de aquellas especies con altas tasas de sedimentación. Los resultados indicaron que la recirculación aumento la eficiencia de recuperación, obteniendo mayores recuperaciones en la LAC con recirculación (91-93%) que en LAC sin recirculación (75-88%), y aumentando el porcentaje de la biomasa con velocidad de sedimentación elevadas. Esto fue debido a la aparación de especies con altas tasas de sedimentación tales como Stigeoclonium sp. y diatomeas presentes cuando se recirculó el 10% de biomasa cosechada. Por último, el balance energético de una planta de tratamiento de aguas residuales a base de microalgas situada en la región Mediterránea se evaluó a partir de resultados experimentales de la biomasa algal crecida en LAC y sometida a la digestión anaerobia (con o sin tratamiento térmico previo) para producir biogás y generar electricidad y / o calor. El estudio concluyó que se debe lograr una mínima producción de biomasa algal de 15 g SST / m2d y / o unas producciones de metano de 0,5 m3CH4 / kgVS para obtener un sistema energéticamente autosuficiente durante todo el año
Research of new sources of bioenergy is nowadays driving attention to microalgae. Cost-effective biomass harvesting poses a challenge for full-scale microalgae production for biofuels. In the context of wastewater treatment with microalgae cultures, coagulation-flocculation followed by sedimentation seems to be the most suitable option for microalgae harvesting as low energy and no extra materials are required.
The main objective if this PhD thesis was to evaluate and improve the harvesting efficiency of microalgal biomass grown in wastewater treatment high rate algal ponds (HRAPs) by means of flocculation-based pre-concentration techniques (i.e. coagulation-flocculation with organic flocculants and biomass recycling). Moreover, the energy assessment of a full-scale wastewater treatment system based on HRAPs followed by anaerobic digestion of harvested microalgal biomass located in a Mediterranean Region was assessed.
Firstly, coagulation-flocculation and sedimentation with two tannin-based polymeric flocculants (Ecotan and Tanfloc) was evaluated by means of static sedimentation tests in conventional settling columns. Low flocculants doses (10-50 mg/L) enabled over 90% biomass recovery. Furthermore, both flocculants increased microalgae settling velocity, leading to fast and efficient biomass recovery (> 90% recovery in 10-20 min).
Subsequently, dynamic sedimentation tests were performed in a water elutriation apparatus in order to evaluate the settling velocities distribution of microalgal biomass with and without flocculants. This time, a tannin-based flocculant (Tanfloc) and a cationic starch were evaluated. The amount of biomass reaching settling velocities higher than 6.5 m/h increased from 10-14% (without flocculant) to 70-84% when 20-40 mg/L of Tanfloc were added. On the other hand, 10-25 mg/L of starch enabled more than 95% biomass recovery, increasing from 46% to 78% the amount of particles with settling velocities higher than 6.5 m/h. According to the results, a settler designed with a critical settling velocity of 1 m/h (which is a typical value in secondary settlers) would enable over 90% biomass recovery while reducing the hydraulic retention time and the settler surface as compared to biomass harvesting without flocculants.
Microalgal biomass harvesting was also tested by recycling some of the harvested microalgal biomass (2% and 10% dry weight) to the pilot wastewater treatment HRAP in order to increase the predominance of rapidly-settling microalgae species. Results indicated that biomass recycling had a positive effect on the harvesting efficiency, obtaining higher recoveries in the pilot HRAP with recycling (91-93%) than in the pilot HRAP without recycling (75 ¿ 88%), and increasing the percentage of biomass with high settling velocity. This was due to the fact that the abundance of rapidly-settling strains such as Stigeoclonium sp. and diatoms increased when 10% (dry weight) of harvested biomass was recycled.
Experimental results from this PhD thesis suggested that either flocculation with natural organic flocculants or biomass recycling improves harvesting efficiency of microalgal biomass with high biomass recoveries (>90%), increasing by 2-8-folds the amount of biomass with high settling velocities (6.5 m/h) and obtaining the best results in those experiments in which rapidly settling species (e.g. Stigeoclonium sp. and diatoms) were dominant. Finally, the energy balance of a microalgae-based wastewater treatment plant located in the Mediterranean Region was assessed based on experimental results. The harvested microalgal biomass grown in wastewater HRAPs would undergo anaerobic digestion (with or without thermal pretreatment) to produce biogas and generate electricity and/or heat. The energy assessment concluded that the system should achieve microalgal biomass production of at least 15 g TSS/m2d and/or a methane yield of 0.5 m3CH4/KgVS all over the year to be energy self-sufficient.
Actualmente, la investigación de nuevas fuentes de energía ha centrado la atención hacia las microalgas. El principal desafio para la producción de microalgas a gran escala es realizar una recuperación de la biomasa algal eficente y rentable para su posterior valorización. En el contexto del tratamiento de aguas residuales, el proceso de coagulación-floculación seguido de la sedimentación representa la técnica de recuperación de microalgas más adecuada debido al bajo consumo energético y a los bajos costes asociados. El objetivo principal de la tesis doctoral fue evaluar y mejorar la eficiencia de separación de la biomasa algal cultivada en lagunas de alta carga (LAC) para el tratamiento de agua residual urbana. Esto se consiguió aplicando técnicas de pre-concentración basadas en procesos de floculación. A posteriori, se evaluó el balance energético de un sistema de tratamiento de aguas residuales a gran escala situado en la región Mediterránea, formado por un sistema de LAC seguido de un proceso de digestión anaeróbica de la biomasa. En primer lugar, la coagulación-floculación y sedimentación con dos floculantes naturales poliméricos (Ecotan y Tanfloc) se evaluó por medio de ensayos de sedimentación estáticos en columnas de sedimentación convencionales. Ambos floculantes obtubieron dosis ótimas bajas (10-50 mg / L) que permitieron la recuperación del 90% de la biomasa. Además, estos aumentaron la velocidad de sedimentación de la biomasa algal, implicando una recuperación de la biomasa rápida y eficiente (> 90% de recuperación en 10 a 20 min). Posteriormente, los tests de sedimentación dinámica se realizaron en un dispositivo dotado de tres columnas de sedimentación con el fin de evaluar la distribución de velocidades de sedimentación de la biomasa con y sin el efecto de floculantes. Esta vez, se evaluaró un floculante polimérico (Tanfloc) y un almidón catiónico. En estos ensayos, se auménto del 10-14% (son floculante) al 70-84% (con coagulante) la fracción de biomasa con unas velocidades de sedimentación mayores a 6,5 m/h tras la adición de 20-40 mg/L de Tanfloc. Por otra parte, entre10 y 25 mg / L de almidón fueron necesarios para recuperar más del 95% de la biomasa,incrementando del 46% a 78% la fracción de partículas con velocidades de sedimentación mayores a 6,5 m / h. Según los resultados, un decantador diseñado con una velocidad de sedimentación de 1 m / h (valor típico en decantadores secundarios) permitiría la recuperación del 90% de la biomasa, reduciendo el tiempo de retención hidráulico y la superficie de los decantadores, tras la adición de los floculantes naturales estudiados. La separación de la biomasa también se evaluó mediante la recirculación de una fracción de la biomasa cosechada (2% y 10% del peso en seco) en un sistema de LAC para el tratamiento de aguas residuales con el fin de aumentar el predominio de aquellas especies con altas tasas de sedimentación. Los resultados indicaron que la recirculación aumento la eficiencia de recuperación, obteniendo mayores recuperaciones en la LAC con recirculación (91-93%) que en LAC sin recirculación (75-88%), y aumentando el porcentaje de la biomasa con velocidad de sedimentación elevadas. Esto fue debido a la aparación de especies con altas tasas de sedimentación tales como Stigeoclonium sp. y diatomeas presentes cuando se recirculó el 10% de biomasa cosechada. Por último, el balance energético de una planta de tratamiento de aguas residuales a base de microalgas situada en la región Mediterránea se evaluó a partir de resultados experimentales de la biomasa algal crecida en LAC y sometida a la digestión anaerobia (con o sin tratamiento térmico previo) para producir biogás y generar electricidad y / o calor. El estudio concluyó que se debe lograr una mínima producción de biomasa algal de 15 g SST / m2d y / o unas producciones de metano de 0,5 m3CH4 / kgVS para obtener un sistema energéticamente autosuficiente durante todo el año
Carrère, H.; Antonopoulou, G.; Affes, R.; Passos, F.; Battimelli, A.; Ferrer, I. Bioresource technology Vol. 199, p. 386-397 DOI: 10.1016/j.biortech.2015.09.007 Data de publicació: 2016-01 Article en revista
When properly designed, pretreatments may enhance the methane potential and/or anaerobic digestion rate, improving digester performance. This paper aims at providing some guidelines on the most appropriate pretreatments for the main feedstocks of biogas plants. Waste activated sludge was firstly investigated and implemented at full-scale, its thermal pretreatment with steam explosion being most recommended as it increases the methane potential and digestion rate, ensures sludge sanitation and the heat needed is produced on-site. Regarding fatty residues, saponification is preferred for enhancing their solubilisation and bioavailability. In the case of animal by-products, this pretreatment can be optimised to ensure sterilisation, solubilisation and to reduce inhibition linked to long chain fatty acids. With regards to lignocellulosic biomass, the first goal should be delignification, followed by hemicellulose and cellulose hydrolysis, alkali or biological (fungi) pretreatments being most promising. As far as microalgae are concerned, thermal pretreatment seems the most promising technique so far.
In this study, enzymatic pretreatment of microalgal biomass was investigated under different conditions and evaluated using biochemical methane potential (BMP) tests. Cellulase, glucohydrolase and an enzyme mix composed of cellulase, glucohydrolase and xylanase were selected based on the microalgae cell wall composition (cellulose, hemicellulose, pectin and glycoprotein). All of them increased organic matter solubilisation, obtaining high values already after 6 h of pretreatment with an enzyme dose of 1% for cellulase and the enzyme mix. BMP tests with pretreated microalgae showed a methane yield increase of 8 and 15% for cellulase and the enzyme mix, respectively. Prospective research should evaluate enzymatic pretreatments in continuous anaerobic reactors so as to estimate the energy balance and economic cost of the process.
The anaerobic digestion of microalgae is hindered by its complex cell wall structure and composition. Thus, several pretreatment methods have been used for increasing microalgae anaerobic biodegradability. Since the methane yield depends on biomass characteristics, pretreatments should be compared using the same microalgal biomass. In this study, physical pretreatments including thermal (95 degrees C; 10 h), hydrothermal (130 degrees C; 15 min), microwave irradiation (900 W; 3 min; 34.3 MJ/kg TS) and ultrasonication (70 W; 30 min; 26.7 MJ/kg TS) were evaluated in terms of microalgae solubilisation and methane yield increase in batch tests. Organic matter solubilisation was improved in all cases, with the highest increase on soluble proteins, followed by soluble carbohydrates and soluble lipids. This was attributed to the macromolecular and cell wall composition of the main microalgae species composing the biomass, i.e. Monoraphidium sp. and Stigeoclonium sp. Furthermore, the methane yield was increased by 72% for thermal, 28% for hydrothermal and 21% for microwave pretreatments, whereas no significant increase was found for ultrasonication as compared to control. Outstanding results of the thermal pretreatment should be validated in prospective pilot-scale studies in order to quantify the potential increase in biogas production upon continuous operation. (C) 2015 Elsevier B.V. All rights reserved.
The Research Group on Cooperation and Human Development (GRECDH) of the Technical University of Catalonia (UPC) has long promoted Bachelor, Master and PhD Theses in the framework of sustainable energy projects in low income countries. In this way, students combine their work at UPC with tasks in these countries. The aim of this paper is to present and evaluate the program through the experience of several students who participated in sustainable energy projects in Central and South America.
Passos , F.; Gutierrez, R.; Brockmann, D.; Steyer, J.P.; Garcia, J.; Ferrer, I. Algal research: biomass, biofuels and bioproducts Vol. 10, p. 55-63 DOI: 10.1016/j.algal.2015.04.008 Data de publicació: 2015-07-01 Article en revista
An integrated microalgae-based system for urban wastewater treatment, microalgae production and bioenergy generation through anaerobic digestion was evaluated over a period of one year. The pilot HRAP was effective at removing COD (similar to 80%) and ammonium(similar to 95%) and robust, despite common variations in wastewater composition and weather conditions in the Mediterranean region. Biomass production showed a strong seasonality, reaching an annual average of 10 g TSS/m(2).day and the highest values in spring (23 g TSS/m(2).day). Conversely, the macromolecular composition was fairly constant (58% proteins, 22% carbohydrates and 20% lipids). Predominant microalgae species varied throughout the year, influencing biogas production. Indeed, the anaerobic biodegradability of harvested biomass was 20-25% in July-October 2012 and May-July 2013 and 25-38% in November 2012-April 2013. Adapting the content of particulate inert COD in Anaerobic Digestion Model No. 1 (ADM1) was crucial for model calibration. After adjustment, ADM1 was able to predict microalgae anaerobic digestion performance, which showed an average methane yield of 0.09 L CH4/g COD at 15 days HRT and 0.16 L CH4/g COD at 20 days HRT. (C) 2015 Elsevier B.V. All rights reserved.
In the context of wastewater treatment with microalgae cultures, coagulation-flocculation followed by sedimentation is one of the suitable options for microalgae harvesting. This process is enabled by the addition of chemicals (e.g. iron). However, in a biorefinery perspective, it is important to avoid possible contamination of downstream products caused by chemicals addition. The aim of this study was to evaluate the effect of potato starch as flocculant for microalgal biomass coagulation-flocculation and sedimentation. The optimal flocculant dose (25 mg/L) was determined with jar tests. Such a concentration led to more than 95% biomass recovery (turbidity < 9NTU). The settleability of flocs was studied using an elutriation apparatus measuring the settling velocities distribution. This test underlined the positive effect of starch on the biomass settling velocity, increasing to >70% the percentage of particles with settling velocities >6.5 m/h. Finally, biochemical methane potential tests showed that starch biodegradation increased the biogas production from harvested biomass. (C) 2015 Elsevier Ltd. All rights reserved.
Matamoros Mercadal, Víctor; Gutierrez, R.; Ferrer, I.; Garcia, J.; Bayona, J. Journal of hazardous materials Vol. 288, p. 34-42 DOI: 10.1016/j.jhazmat.2015.02.002 Data de publicació: 2015-05-15 Article en revista
The effect of hydraulic retention time (HRT) and seasonality on the removal efficiency of 26 organic microcontaminants from urban wastewater was studied in two pilot high-rate algal ponds (HRAPs). The targeted compounds included pharmaceuticals and personal care products, fire retardants, surfactants, anticorrosive agents, pesticides and plasticizers, among others. The pilot plant, which was fed at a surface loading rate of 7-29 g of COD m(-2) d(-1), consisted of a homogenisation tank and two parallel lines, each one with a primary settler and an HRAP with a surface area of 1.5 m(2) and a volume of 0.5 m(3). The two HRAPs were operated with different HRTs (4 and 8 d). The removal efficiency ranged from negligible removal to more than 90% depending on the compound. Microcontaminant removal efficiencies were enhanced during the warm season, while the HRT effect on microcontaminant removal was only noticeable in the cold season. Our results suggest that biodegradation and photodegradation are the most important removal pathways, whereas volatilization and sorption were solely achieved for hydrophobic compounds (log Row >4) with a moderately high Henry's law constant values (11-12 Pa m(-3) mol(-1)) such as musk fragrances. Whereas acetaminophen, ibuprofen and oxybenzone presented ecotoxicological hazard quotients (HQs) higher than 1 in the influent wastewater samples, the HQs for the effluent water samples were always below 1. (C) 2015 Elsevier B.V. All rights reserved.
Gutierrez, R.; Passos , F.; Ferrer, I.; Uggetti, E.; Garcia, J. Algal research: biomass, biofuels and bioproducts Vol. 9, p. 204-211 DOI: 10.1016/j.algal.2015.03.010 Data de publicació: 2015-05-01 Article en revista
Research on new sources of bioenergy is nowadays driving attention to microalgae. Cost-effective biomass harvesting and thickening pose a challenge for massive microalgae production for biofuels. In this study, coagulation-flocculation and sedimentation with natural flocculants (Ecotan and Tanfloc) was evaluated on microalgae grown in an experimental high rate algal pond treating urban wastewater. Jar tests showed how flocculant doses of 10 and 50mg/L of Ecotan and Tanfloc enabled over 90% biomass recovery. Furthermore, settling column tests showed that both flocculants increased microalgae settling velocity, performing fast and efficient biomass recovery (>90% recovery in 10-20min). Thus, the use of either flocculant would enhance microalgal biomass reducing the HRT and settler volume. Finally, the potential toxicity of flocculants upon biomass production was assessed in biochemical methane potential tests. Results indicated that doses of 10-50mg/L of Ecotan and Tanfloc did not affect anaerobic digestion, leading to the same methane yield (162-166mL CH4/g VS) with the same methane content (70%) as the control without flocculants. This study demonstrates that Ecotan and Tanfloc flocculants would be appropriate for microalgae biomass harvesting and subsequent biogas generation.
Microalgal biomass grown in wastewater treatment raceway ponds may be valorised producing bioenergy through anaerobic digestion. However, pretreatment techniques seem to be necessary for enhancing microalgae methane yield. In this study, hydrothermal pretreatment was studied prior to batch and continuous reactors. The pretreatment increased organic matter solubilisation (8-13%), anaerobic digestion rate (30-90%) and final methane yield (17-39%) in batch tests. The highest increase was attained with the pretreatment at 130 degrees C for 15 min, which was attested in a laboratory-scale continuous reactor operated at a hydraulic retention time of 20 days with an average organic loading rate of 0.7 g VS/L center dot day. The methane yield increased from 0.12 to 0.17 L CH4/g VS (41%) in the pretreated digester as compared to the control. Microscopic images of microalgal biomass showed that pretreated cells had unstructured organelles and disrupted cell wall external layer, which may enhance the hydrolysis. Indeed, images of the pretreated reactor digestate showed how cells were more degraded than in the control reactor. (C) 2014 Elsevier Ltd. All rights reserved.
Les llacunes d'alta càrrega (LAC) es caracteritzen per ser una tecnologia de tractament d'aigua residual econòmica i ambientalment sostenible. Dins les LAC, les microalgues i les bactèries heteròtrofes creixen en relació simbiòtica de manera que l'oxigen que les bactèries necessiten per a la degradació de la matèria orgànica és produït durant la fotosíntesi de les microalgues. Així doncs, en contrast amb els sistemes convencionals de fangs activats, les LAC no requereixen d'aireig mecànic, principal consum energètic de la planta. D'altra banda, la biomassa microalgal, recollida dels decantadors secundaris, pot ser valoritzada en digestors anaerobis alhora que es produeix biogàs. Aquest procés de digestió, però, es veu limitat per la hidròlisi de les macromolècules retingudes dins la paret cel·lular de les microalgues, impedint que aquestes es trobin fàcilment a l'abast dels microorganismes anaerobis. L'objectiu d'aquesta tesi doctoral és doncs investigar la digestió anaeròbia de la biomassa algal cultivada en una LAC i alhora, estudiar possibles mètodes de pretractament per tal de millorar la producció de biogàs.Inicialment, la digestió anaeròbica de la biomassa algal va ser avaluada en una LAC (escala pilot) i en un reactor (escala laboratori) sense aplicar-hi cap pretractament. Quan el reactor fou operat a 15 dies de temps de retenció hidràulica (TRH), la productivitat de metà mitjana fou de 0.13 L CH4/g SV i quan el TRH fou de 20 dies, de 0.17 L CH4/g SV. La biodegradabilitat anaeròbica de les microalgues fou variable i baixa al comparar-la amb d'altres substrats orgànics. Les especies microalgals existents dins la LAC variaren també al llarg del temps, com a conseqüència de les condicions ambientals, la composició de l'aigua residual i les interrelacions amb d'altres microorganismes. Per últim, els resultats suggeriren que la biodegradabilitat de les microalgues depenia de les característiques de les cèl·lules que composaven la biomassa en cada període i que, per tant, era específica segons l'espècie.Com a conseqüència d'aquests resultats, i per tal de millorar la digestió anaeròbica de la biomassa, es van avaluar quatre tècniques de pretractament (microones, tèrmic, hidrotèrmic i ultrasons) utilitzant testos en discontinu. En cada cas, diversos paràmetres operacionals (temperatura, temps d'exposició, potencia consumida i energia específica aplicada), van combinar-se i, posteriorment, les millors condicions s'estudiaren utilitzant reactors en continu. En tot els casos estudiants, el pretractament augmentà tant la solubilització de la biomassa com la productivitat de metà. El pretractament termal a 95 ºC (0.31 L CH4/g SV), fou el que presentà un augment superior (70%) en relació a les microalgues no pretractades. Els anàlisis amb el microscopi indicaren que els mètodes de pretractament estudiats no van aconseguir trencar les parets cel·lulars de les microalgues; tot i això, la majoria de les cèl·lules queden malmeses, augmentant la biodegradabilitat i la bioaccessibilitat de les molècules orgàniques. Les espècies de microalgues que contenien proteïnes i carbohidrats a les parets cel·lulars resultaren en un augment de la productivitat de metà superior a aquelles especies amb parets cel·lulars més resistents, tals com les diatomees. El balanç energètic del procés suggerí que els pretractaments calorífics (tèrmic i hidrotèrmic), més que els elèctrics (microones), foren més eficients a nivell energètic. Els millors resultats s'aconseguiren amb l'aplicació del pretractament tèrmic a 75 i 95 ºC, assolint un balanç energètic positiu (es produí un 30% més d'energia de la consumida). Finalment, la realització d'un balanç energètic estimat del sistema complet, mostrà com les plantes de tractament d'aigua residual basades en les microalgues serien neutrals a nivell energètic amb una producció mitjana de biomassa de 15 g SST/m2¿d en les LAC i amb una producció de biomassa de 10 g SST/m2·d si s'apliqués el pretractament tèrmic.
Microalgae have been intensively studied as a source of biomass for replacing conventional fossil fuels in the last decade. The optimization of biomass production, harvesting and downstream processing is necessary for enabling its full-scale application. Regarding biofuels, biogas production is limited by the characteristics of microalgae, in particular the complex cell wall structure of most algae species. Therefore, pretreatment methods have been investigated for microalgae cell wall disruption and biomass solubilization before undergoing anaerobic digestion. This paper summarises the state of the art of different pretreatment techniques used for improving microalgae anaerobic biodegradability. Pretreatments were divided into 4 categories: (i) thermal; (ii) mechanical; (iii) chemical and (iv) biological methods. According to experimental results, all of them are effective at increasing biomass solubilization and methane yield, pretreatment effect being species dependent. Pilot-scale research is still missing and would help evaluating the feasibility of full-scale implementation. (C) 2014 Elsevier Ltd. All rights reserved.
High rate algal ponds are an economic and sustainable alternative for wastewater treatment, where microalgae and bacteria grow in symbiosis removing organic matter and nutrients. Microalgal biomass produced in these systems can be valorised through anaerobic digestion. However, microalgae anaerobic biodegradability is limited by the complex cell wall structure and therefore a pretreatment step may be required to improve the methane yield. In this study, ultrasound pretreatment at a range of applied specific energy (16-67. MJ/kg. TS) was investigated prior to microalgae anaerobic digestion. Experiments showed how organic matter solubilisation (16-100%), hydrolysis rate (25-56%) and methane yield (6-33%) were improved as the pretreatment intensity increased. Mathematical modelling revealed that ultrasonication had a higher effect on the methane yield than on the hydrolysis rate. A preliminary energy assessment indicated that the methane yield increase was not high enough as to compensate the electricity requirement of ultrasonication without biomass dewatering (8% VS).
The Research Group on Cooperation and Human Development of the Technical University
of Catalonia (UPC) has long promoted Bachelor, Master and PhD Thesis in the framework
of sustainable energy projects in low income countries. In this way, students combine their
work at UPC with tasks in the low income countries. The aim of this paper is to present and
evaluate the program through the experience of several students who participated in
sustainable energy projects in Central and South America.
This paper describes the anaerobic digestion of microalgal biomass from high rate ponds in continuous anaerobic reactors for biogas production. With hydraulic retention times (HRT) of 15 and 20 days, the volatile solids (VS) removal did not exceed 30%, and the methane production rate ranged between 0.12 and 0.14 L CH4/L day. To improve process performance, microwave irradiation at 900 W for 3 min (specific energy similar to 70,000 kJ/kg VS) was applied as a pretreatment step. The VS removal increased to 40 and 45% at 15 and 20 days HRT, respectively. Consequently, the methane production rate increased to 0.16 and 0.20 L CH4/L day at 15 and 20 days HRT, respectively. Microscopic analysis confirmed cell wall damage, although generally without lysis, after irradiating microalgal biomass. However, the energy consumption was much higher than the extra energy production of the process. Indeed, microalgal biomass should not only be thickened but also dewatered if microwave irradiation was to be applied as a pretreatment to anaerobic digestion for biogas production. (C) 2013 Elsevier Ltd. All rights reserved.
This study was carried out in response to the growing interest on household biogas digesters in Latin America, particularly in rural Andean communities. The aim was to compare the fixed dome and plastic tubular digester in terms of biogas production, cost and environmental impact, using the life cycle assessment methodology. Design and operational parameters, construction materials and implementation costs were based on our previous research and literature results for plastic tubular and fixed dome digesters, respectively. According to this analysis, the main advantage of the plastic tubular digester was
its ease of implementation and handling, and lower investment cost compared to the fixed dome digester, which appeared to be more environmentally friendly.
This work studied the anaerobic conversion of neutralized volatile fatty acids (VFA) into biogas under Autogenerative High Pressure Digestion (AHPD) conditions. The effects of the operating conditions on the biogas quality, and the substrate utilisation rates were evaluated using 3 AHPD reactors (0.6 L); feeding a concentration of acetate and VFA (1-10 g COD/L) corresponding to an expected pressure increase of 1-20 bar. The biogas composition improved with pressure up to 4.5 bar (>93% CH4), and stabilized at 10 and 20 bar. Both, acetotrophic and hydrogenotrophic methanogenic activity was observed. Substrate utilisation rates of 0.2, 0.1 and 0.1 g CODCH4/g VSS/d for acetate, propionate and butyrate were found to decrease by up to 50% with increasing final pressure. Most likely increased Na+-requirement to achieve CO2 sequestration at higher pressure rather than end-product inhibition was responsible. (C) 2013 Elsevier Ltd. All rights reserved.
'Subsurface-flow constructed wetlands have become a very popular cost effective and green technology for treatment of waste water throughout Europe and the rest of the world. Original predictions over the longevity of constructed wetlands were approximately 50 -100 years (Conley et al 1991). However, it has become disappointingly apparent that these systems are clogging and have on average a lifetime of less than 10 years (Griffin et al 2008). Currently when a wetland becomes clogged, the whole site has to be refurbished and the reeds regrown, which takes several years and has significant economic consequences for the operators.
Our project ARBI aims to develop and trial an Autonomous Reed Bed Installation containing a magnetic resonance probe, can be deployed in several locations within a wetland to give measurements at different depths. By measuring the relaxation times of MR, sufficient information can be obtained to determine the clog state of the gravel bed of a wetland. This would enable the operators to isolate those areas of the bed where the problem resides and make a partial intervention, without the need to remove and re-plant the whole reed bed. When the system is developed, we will have potential for application in other water treatment systems based on subsurface flows like: slow rate sand filters, and river bank filtration.
The project will have major benefits for those organisations who would like to install reedbeds but have resisted doing because of concerns over performance and maintenance costs. These will increase the potential size of the market for reedbed installers and benefit the SMEs in the consortium who currently are operating in a constrained market which has not achieved its true potential.'
The aim of this study was to evaluate the effect of microwave pretreatment on the solubilisation and anaerobic digestion of microalgae-bacterial biomass cultivated in high rate algal ponds for wastewater treatment. The microwave pretreatment comprised three specific energies (21,800, 43,600 and 65,400. kJ/kg TS), combining three output power values with different exposure times. Response surface analysis showed that the main parameter influencing biomass solubilisation was the applied specific energy. Indeed, a similar solubilisation increase was obtained for the same specific energy, regardless of the output power and exposure time (280-350% for 21,800. kJ/kg TS, 580-610% for 43,600. kJ/kg TS and 730-800% for 65,400. kJ/kg TS). In biochemical methane potential tests, the initial biogas production rate (27-75% increase) and final biogas yield (12-78% increase) were higher with pretreated biomass. A linear correlation was found between biomass solubilisation and biogas yield.
This study was carried out in response to the growing interest on household biogas digesters in Latin America, particularly in rural Andean communities. The aim was to compare traditional and novel digester designs, in terms of biogas production, cost and environmental impact. Three household digesters were compared: 1) fixed dome – Chinese model; 2) fixed dome – Camartec model and 3) plastic tubular – Taiwanese model. Data concerning design and operational parameters, construction materials and costs were obtained from our previous results on plastic tubular digesters and from the literature on fixed dome digesters. The biogas production rate
ranged around 0.07-0.5 m3 biogas m-3 digester d-1 in plastic tubular digesters and around 0.35-0.7 m3 biogas m-3 digester d-1 in fixed dome digesters. The novel design of the Camartec model reduced construction materials and capital cost by 27 % compared to the Chinese model. The cost of plastic tubular digesters was mainly attributed to the geomembrane. The life cycle assessment showed how the Camartec model caused the lowest impact, while the plastic tubular digester had the highest impact; which was mainly attributed to plastic materials (greenhouse and biogas reservoir) and geomembrane (digester). In the Chinese model, the main impact was caused by concrete and bricks, which were respectively 38 and 22 % higher than in the Camartec system. The highest impact of the tubular digester may be explained by the lifespan of construction materials. From an economic and environmental perspective, the Camartec model seems the best option; the main advantage of plastic tubular digesters being its ease of implementation and handling.