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Biogas optimization for fuel improvement, energy balances in EDAR (Spanish acronym for Sewage Treatment Plant) and from micro-algae.

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  • UniversityUniversidad de Valladolid
  • Center
  • DepartmentChemical Engineering and Environmental Technology
  • Investigation GroupEnvironmental technology


BIOGAS UPDATE VIA BIOLOGIC CO2 CONVERSION AND H2 INTO CH4. - Biogas has become one of the main sources of renewable energy in the EU, overtaking petrol by more than 12% for the last 15 years. Currently, the main use of biogas is the combined production of heat and electricity in cogeneration plants. However, some factors are changing this trend: The low efficiency of combustion due to the presence of carbon dioxide (25-50%), the reduction of electrical tariffs originating from biogas and political instabilities in Europe’s natural gas supply are behind the continent’s huge expansion of biogas improvement plants. Improved biogas can be used either as a fuel (pumped into the grille of natural gas) or liquefied as natural gas. PRE-TREATMENT OF BIOGAS EXPLOSIONS IN LOCAL QUAGMIRES IN ORDER TO IMPROVE ENERGY BALANCES IN EDAR. - Political and social demands for the sustainable use of energetic resources have motivated the water industry to intensify energy saving efforts. Besides the huge costs of electricity and other power loads, water companies have been meeting their customers’ environmental awareness. The water resources management confirmed that the energy’s demand for Sewage Treatment Plants (EDAR) constitute an important part of the total power consumption. Part of this energy can be regained by exploiting sewage’s energy potential to transform organic matter into biogas, since mud is the only current able to produce energy in an EDAR. Subsequently, the obtained biogas could be used for elctricity and heat generation or directly consumed for other EDAR processes. The medium term target for turning into an EDAR with neutral or even positive energy seems viable by implementing sludge treatments before anaerobic digestion. In this way, thermal hydrolysis “steam explosion” is widely used to increase methane production. At the same time, the term “explosion of ammonia” is used within the field of straw hydrolysis. OPTIMIZATION OF BIOGAS PRODUCTION THROUGH ALGAE BIOMASS - Microalgae ability to attach CO2, nutrients (N, P) and storing solar energy in theit cells through photosyntesis makes them an interesting alternative of green energy ( (biofuel and biogas) and sewage treatment technologies. In comparison to conventional plants, microalgae have higher growth rates and can be grown in non-arable land. For this reason, microalgae grown for biogas production can’t compete with crops for human nutrition. The use of microalgae in sewage treatment results in bigger amounts of biomass that need to be removed. Likewise, biodiesel production through microalgae would generate huge amounts of algae waste. An alternative to this residual biomass’ waste is anaerobic digestion, which transforms this waste into CH4, which can, in turn, be transformed into different kinds of energy (heat, electricity, etc). - CHARACTERIZATION OF THERMAL HYDROLYSIS AND ANAEROBIC DIGESTION COMBINED PROCESS IN A PILOT PLANT - In a conventional sewage treatment plant, around 60% of sewage waste turns into mud handled in anaerobic digestion for its stabilization and biogas production. However, anaerobic digestion presents some drawbacks, such as a long time of hydraulic retention (over 20 days), a high digestion volume (high cost) and a degradation rate limited by the organic matter during the hydrolytic phase. This way, the procedure’s improvement is linked to the hydrolysis phase’s improvement. A bigger and faster degradation could be achieved by increasing the solubilization of undissolved compounds, breaking them into monomers more accessible to anaerobic bacterias. It is therefore necessary to introduce a pretreatment unit before the digestor. Thermal hydrolysis sticks out among the other alternative treatments (mechanical, biological, ultrasound...). Its main advantage is that the need for thermal energy can be satisfied by the energy generated in the process, thus obtaining an energetically self-sufficient system. Even though thermal hydrolysis has been widely studied in literature, most investigations have examined the point of view of the laboratory scales for the lot biodegradability test. However, in order to obtain reliable technological data and to establish the calculation bases of a future plant, it is necessary that a pilot plant quantifies not only the biogas output but also its characteristics. SECONDARY SLUDGE AUTOHYDROLYSIS PREPARATION FOR ANAEROBIC DIGESTION IMPROVEMENT - Secondary sludge is produced during the biological treatment in the activated sludge process of sewage treatment plants and consists of active micro-organism floccules. The resultant sludge must be treated by trying to reduce the amount of water and organic matter. It also seeks to produce a stabilized and reusable efflluent, mainly using grade A biosolids and using the energetic content of organic matter. Anaerobic digestion is the most popular treatment for sludge elimination in EDAR. The biogas production has been tied to renewable energy sources and a low energy requirement. Hydrolisis is the limiting step for anaerobic digestion of secondary sludge, since it is necessary to break the sludge floc and the membrane cell. Several techniques have been proposed to improve sludge hydrolysis if anaerobic digestion pre-treatments show interesting results. There are many sludge pre-treatments using different mechanic processes (chemical, sonication, thermal and use of hydrolytic enzimes) The option of hydrolytic enzymes includes the possibility of using: (1) commercial enzymes, (2) enzyme producing microorganisms, (3) enzymatic system of pre-treated sludge. If the environmental conditions of sludge were changed, it would be possible to stimulate the production of hydrolytic enzymes such as proteases and then producing a metter hydrolysis of the organic matter. - MICROAEROBIC PROCESSES FOR H2S DISASSEMBLING AND IMPROVEMENT OF THE PROCESS’ CONSISTENCY - Anaerobic digestion (AD) of organic waste is capable of transforming a big part of organic matter into biogas, 60-70 (v / v)% of methane, which can be energetically recovered, thus destroying most pathogens present in the sludge and limiting every possible odor problem related to residual putrefying matter. As a result, AD is a widely used method in the sewage sludge treatment, and in local and agricultural solid waste and high organic waste sewage treatment plants. However, the huge diversity of microorganisms involved in the transformation of complex compounds into simpler compounds that can be turned into methane requires a balance between intermediary products, in a way that environmental conditions allow microorganisms to appropriately use organic matter. Intrinsic variations in organic residual charges may result in the accumulation of intermediaries and consequently, to the process’ failure. In addition, when sulphur compounds are available, hydrogen sulphide is produce in a different degree with several associated problems. Hydrogen sulphide is corrosive and damages considerably the facilities’ shelf life. It’s also toxic for living beings, it causes inhibition problems in microorganisms and has a strong smell. METHANOL PRODUCTION FROM BIOGAS - Nowadays, one of the main environmental problems is the presence of carbon dioxide in the atmosphere, which causes the infamous greenhouse effect. This is why CO2 is trying to be captured and recovered. Some of the techniques used allow this compound to be reused. For example, in metanol production which has a great importance in chemical industries. Also, methanol can be used as a fuel and sometimes even substitues gasoline. Methanol production through selective carbon dioxide hydrogenation is a new technological alternative to capture and reuse CO2. When CO2 and methane are combined (as happens in biogas), it can be used as a carbon source in methanol synthesis in accordance with the reaction of vapor methane, where the gases formed in the methane’s alteration act as an alcohol precursor. - TREATMENT OF SEWAGE WITH MEMBRANE TECHNOLOGY- The main advantage of membrane technology is the capability of disconnecting the hydraulic retention time (HRT) and the sludge retention time (SRT). This can be achieved because the membrane works as a barrier, keeping the solids within the reactor. A sludge trap is not necessary and the concentration of solids in the mixture may be higher. The more solids in the reactor, the bigger the possibility of working with higher organic loading rates, with consequential space reduction. The process of activated sludge operates at an organic charge of 5 to 10 grams of chemical Oxygen Demand (COD) per liter, while a membrane bioreactor can go up to 60 grams of COD/L, which implies a 10 to 12 times bigger reduction in space. A higher SRT is also an advantage, since it allows bacteria with a low growth rate to develop in the liquid phase, thus improving efficiency. -

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In research and development phase

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The Environmental Technology Research Group have several technical equipment in their facilities to perform their research. For each activity, this equipment consists of: -Pilot studies of biodegradability: Upflow Anaerobic Sludge Bed (UASB) (0.5 - 200L), membrane bioreactors, dry digestion. - Sludge pre-treatment and solid waste:Thermal hydrolysis, ultrasound, enzymatic incubation - Pilot studies of biofiltration for VOC and odor treatment: Biofilters activated sludge difussion, biotricking filters, two-phase partitioning bioreactors. - Dynamic surveillance of microbian population for EDAR - Microalgae culture in high-speed algae ponds Besides of the already mentioned research activities supported by public institutions, the research group has actively collaborated with several companies with the aim of strengthening the transfer of knowledge between the University and the Industry. In this context, the Environmental Technology Research Group has participated in 40 publicly funded projects (with a total budget of €4,879,217 and 47 privately financed projects (with a total budget of €6,155,167). The Group currently consists of 10 Major Researchers, 5 PostDocs, 15 Doctorates, 2 Researches and 5 Technicians. Besides, the Group has defended 26 thesis, 174 ISI publications, 16 non-ISI publications, 178 international congresses and 6 patents.


3310 - Industrial technology

Other members:

Pedro Antonio García Encina
Mar Peña Miranda
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María Fernández Polanco
Sara I. Pérez Elvira
Raúl Muñoz Torre
Rubén Irusta
Raquel Lebrero
Aitor Aizpuru
Nuria Martín
Araceli Crespo
Enrique Marco
Mónica Gay Martín
Daniel Fernández Planillo
Miguel Ángel Mouriz
Jonatan Prieto
Patricia Ayala
Rebeca Pérez
Esther Arnáiz
Rebeca López Serna
Elisa Rodríguez
Esther Posadas
Rodolfo Travaini
Sonia Martínez Páramo
Israel Díaz
José Manuel Estrada
Ieva Sapkaite
Juan Carlos López
Natalia Alfaro
Osvaldo Frutos
Sara Cantera
Judit Martín
Dimas García
Ilker Arkmirza
Ana Lorenzo
Thiago Do Nascimiento
Ricardo Saavedra Concha
David Marín de Jesús
María del Rosario Rodero
Roxana Ángeles Torres
Yadira Rodríguez
Cristina Álvarez Requena
Jaime Benito
Nereida Pérez



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