Estudio en planta piloto de la aplicación de la tecnología de membranas para el tratamiento anaerobio de aguas residuales urbanas. estudio de la condiciones críticas de filtracion

[ES] El tratamiento de aguas residuales urbanas en la mayoría de países desarrollados se basa en los tradicionales fangos activos aerobios como núcleo del proceso de depuración. Este sistema de tratamiento presenta dos inconvenientes principales: un alto consumo energético derivado de las necesidades de aireación y una gran generación de fangos que necesitan, a su vez, ser tratados para su eliminación o reutilización. En un contexto de aumento de la sensibilización medioambiental y de un previsible incremento de los costes energéticos, el estudio de las posibilidades de un cambio a tratamientos anaerobios de aguas residuales está justificado. Estos tratamientos reducen el consumo de energía, al no necesitar de aireación, y producen menores cantidades de fango, debido al menor rendimiento en el crecimiento de la biomasa anaerobia. Como ventaja adicional, se produce biogás que sirve como fuente de energía. Sin embargo, los procesos anaerobios presentan también desventajas, como son la menor velocidad de crecimiento de la biomasa a temperatura ambiente y la baja sedimentabilidad de los fangos. La combinación del tratamiento anaerobio con un proceso de separación por membranas permite solventar parte de estos inconvenientes, aunque añade otros relacionados con los problemas intrínsecos de los procesos de membrana, como es el ensuciamiento. Es por ello que se hace necesario el estudio de los parámetros de operación relacionados con la tecnología anaerobia de membranas a escala industrial, con el fin de conocer las condiciones que permitan su correcto funcionamiento a largo plazo, minimizando los efectos del ensuciamiento, con un bajo coste energético y económico. En esta línea, la aplicación del conocido como ¿Flux-step method¿ para determinar las condiciones críticas de filtración permitiría conocer las condiciones de operación bajo las cuales se minimizarían los problemas de ensuciamiento.[EN] Waste water treatment is based on traditional aerobic activated sludge in most of the developed countries. This treatment system has two main disadvantages: high energy consumption because of its aeration needs and high sludge production, which needs to be managed. In a context, where environmental sensibility and energy costs will improve its levels, studying the posibility of changing to anaerobic waste water treatment is justified. This system reduces energy consumption, because no aeration is needed, and reduces sludge production, because of the lower grow yield of anaerobic biomass. In addition, biogas is produced, and it is an energy source. However, anaerobic prcesses have also disadvantages, such as its lower biomass grow rate in ambient temperature and the low sludge sedimentability. A combination between anaerobic treatment and a membrane filtration system can deal with these problems in order to solve them, but it introduces new desadvantage, such as membrane fouling. That is why studying operation parameters related to anaerobic membrane technology is needed, in order to know how to operate it correctly, minimizing fouling and with low energy consumption an costs. In this line, flux-step method will be used to determine critic filtration conditions, so fouling can be minimize.Jiménez Benítez, AL. (2012). Estudio en planta piloto de la aplicación de la tecnología de membranas para el tratamiento anaerobio de aguas residuales urbanas. estudio de la condiciones críticas de filtracion. http://hdl.handle.net/10251/27700Archivo delegad

Production of microalgal external organic matter in a Chlorella-dominated culture: influence of temperature and stress factors

Although microalgae are recognised to release external organic matter (EOM), little is known about this phenomenon in microalgae cultivation systems, especially on a large scale. A study on the effect of microalgae-stressing factors such as temperature, nutrient limitation and ammonium oxidising bacteria (AOB) competition in EOM production by microalgae was carried out. The results showed non-statistically significant differences in EOM production at constant temperatures of 25, 30 and 35 °C. However, when the temperature was raised from 25 to 35 °C for 4 h a day, polysaccharide production increased significantly, indicating microalgae stress. Nutrient limitation also seemed to increase EOM production. No significant differences were found in EOM production under lab conditions when the microalgae competed with AOB for ammonium uptake. However, when the EOM concentration was monitored during continuous outdoor operation of a membrane photobioreactor (MPBR) plant, nitrifying bacteria activity was likely to be responsible for the increase in EOM concentration in the culture. Other factors such as high temperatures, ammonium-depletion and low light intensities could also have induced cell deterioration and thus have influenced EOM production in the outdoor MPBR plant. Membrane fouling seemed to depend on the biomass concentration of the culture. However, under the operating conditions tested, the behaviour of fouling rate with respect to the EOM concentration was different depending on the initial membrane state

Life cycle assessment of AnMBR technology for urban wastewater treatment: A case study based on a demo-scale AnMBR system

This study aims at assessing the environmental performance of a projected full-scale anaerobic membrane bioreactor (AnMBR) treating urban wastewater (UWW) at ambient temperature. To this aim, data from an AnMBR demonstration plant equipped with commercially available equipment, including industrial hollow fiber and degassing membranes, was used for projecting a full-scale facility. The use of real operation data allows to obtain robust results that contribute to improve the knowledge of the environmental performance of this technology, pointing out its strengths and the challenges that still need to be addressed. Life cycle assessment (LCA) was applied by means of Ecoinvent data base and ReCiPe2016 methodology considering 1 kg of removed COD as functional unit. Additionally, sensitivity and uncertainty analysis were conducted. Energy balance showed AnMBR performing as energy producer (net energy surplus up to - 0.688 kWh⋅kg CODrem - 1 ) and carbon sink (emissions credit up to 0.223 kgCO2eq⋅kgCODrem - 1). Results also showed energy recovery, heavy metals in sludge, dissolved methane in the effluent, and effluent nutrient content as the most important aspects affecting LCA outcome. Construction phase affected some impact categories significantly (e.g., 51-71% in mineral resource scarcity, 18-27% in fossil resource scarcity, 21-28% in water consumption), therefore its exclusion should be carefully evaluated. CHP efficiency, dissolved methane recovery, filtration productivity, membrane scouring, reactor mixing, HRT and SRT appeared most influencing parameters. Finally, actions leading to increase the recovery and valorization of dissolved methane and/or of nutrients through, for instance, fertigation, improve the environmental performance of AnMBR for UWW treatment

Calcium-Looping performance of mechanically modified Al2O3-CaO composites for energy storage and CO2 capture

This work reports the Calcium-Looping (CaL) multicycle performance under energy storage and CO2 capture conditions of different Al-composites prepared by milling mixtures of nanoalumina and natural limestone powders. The micro- and nanostructure of the composites have been analyzed by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy as affected by the type of CaL conditions employed, either for energy storage in Concentrated Solar Power (CSP) plants or for post-combustion CO2 capture. Two types of calcium aluminates are formed under these diverse CaL conditions. A calcium aluminate with ratio Ca/Al 1) under CaL-CO2 capture conditions presumably due to the higher calcination temperature, which withdraws from the sorbent a relatively higher amount of active Ca. Moreover, the addition of nano-alumina, and the consequent generation of calcium aluminate, affects in a diverse way the microstructure and morphology of the CaO particles as depending on the CaL application, which critically modifies the performance of the composites.Ministerio de Economia y Competitividad CTQ2014-52763-C2, CTQ2017-83602-C

Optimising an outdoor membrane photobioreactor for tertiary sewage treatment

The operation of an outdoor membrane photobioreactor plant which treated the effluent of an anaerobic membrane bioreactor was optimised. Biomass retention times of 4.5, 6, and 9 days were tested. At a biomass retention time of 4.5 days, maximum nitrogen recovery rate:light irradiance ratios, photosynthetic efficiencies and carbon biofixations of 51.7 ± 14.3 mg N·mol−1, 4.4 ± 1.6% and 0.50 ± 0.05 kg CO2·m3influent, respectively, were attained. Minimum membrane fouling rates were achieved when operating at the shortest biomass retention time because of the lower solid concentration and the negligible amount of cyanobacteria and protozoa. Hydraulic retention times of 3.5, 2, and 1.5 days were tested at the optimum biomass retention times of 4.5 days under non-nutrient limited conditions, showing no significant differences in the nutrient recovery rates, photosynthetic efficiencies and membrane fouling rates. However, nitrogen recovery rate:light irradiance ratios and photosynthetic efficiency significantly decreased when hydraulic retention time was further shortened to 1 day, probably due to a rise in the substrate turbidity which reduced the light availability in the culture. Optimal carbon biofixations and theoretical energy recoveries from the biomass were obtained at hydraulic retention time of 3.5 days, which accounted for 0.55 ± 0.05 kg CO2·m−3influent and 0.443 ± 0.103 kWh·m−3influent, respectively

Low-cost Ca-based composites synthesized by biotemplate method for thermochemical energy storage of concentrated solar power

An ever more environmentally conscious society demands the use of green, sustainable and high-efficiency renewable energy resources. However, large-scale energy storage remains a challenge for a deep penetration of power produced from renewables into the grid. The Calcium-Looping (CaL) process, based on the reversible carbonation/calcination of CaO, is a promising technology for thermochemical energy storage (TCES) in Concentrated Solar Power (CSP) plants. Natural limestone to be used as CaO precursor is cheap, non-toxic and abundant. Nevertheless, recent works have shown that carbonation of CaO derived limestone at optimum conditions for TCES is limited by pore-plugging, which leads to severe deactivation for large enough particles to be employed in practice. In our work, we have synthesized inexpensive CaO/SiO2 composites by means of a biotemplate method using rice husk as support. The morphological and compositional features of the biomorphic materials synthesized help improve the CaO multicycle activity under optimum CSP storage conditions and for particles sufficiently large to be managed in practical processes.Ministerio de Economía y Competitividad CTQ2014-52763-C2, CTQ2017-83602-C

Improving membrane photobioreactor performance by reducing light path: operating conditions and key performance indicators

Microalgae cultivation has been receiving increasing interest in wastewater remediation due to their ability to assimilate nutrients present in wastewater streams. In this respect, cultivating microalgae in membrane photobioreactors (MPBRs) allows decoupling the solid retention time (SRT) from the hydraulic retention time (HRT), which enables to increase the nutrient load to the photobioreactors (PBRs) while avoiding the wash out of the microalgae biomass. The reduction of the PBR light path from 25 to 10 cm increased the nitrogen and phosphorus recovery rates, microalgae biomass productivity and photosynthetic efficiency by 150, 103, 194 and 67%, respectively. The areal biomass productivity (aBP) also increased when the light path was reduced, reflecting the better use of light in the 10-cm MPBR plant. The capital and operating operational expenditures (CAPEX and OPEX) of the 10-cm MPBR plant were also reduced by 27 and 49%, respectively. Discharge limits were met when the 10-cm MPBR plant was operated at SRTs of 3-4.5 d and HRTs of 1.25-1.5 d. At these SRT/HRT ranges, the process could be operated without a high fouling propensity with gross permeate flux (J20) of 15 LMH and specific gas demand (SGDp) between 16 and 20 Nm3air·m−3permeate, which highlights the potential of membrane filtration in MPBRs. When the continuous operation of the MPBR plant was evaluated, an optical density of 680 nm (OD680) and soluble chemical oxygen demand (sCOD) were found to be good indicators of microalgae cell and algal organic matter (AOM) concentrations, while dissolved oxygen appeared to be directly related to MPBR performance. Nitrite and nitrate (NOx) concentration and the soluble chemical oxygen demand:volatile suspended solids ratio (sCOD:VSS) were used as indicators of nitrifying bacteria activity and the stress on the culture, respectively. These parameters were inversely related to nitrogen recovery rates and biomass productivity and could thus help to prevent possible culture deterioration

High-performance and low-cost macroporous calcium oxide based materials for thermochemical energy storage in concentrated solar power plants

High energy density, cycling stability, low cost and scalability are the main features required for thermochemical energy storage systems to achieve a feasible integration in Concentrating Solar Power plants (CSP). While no system has been found to fully satisfy all these requirements, the reversible CaO/CaCO3 carbonation reaction (CaL) is one of the most promising since CaO natural precursors are affordable and earth-abundant. However, CaO particles progressively deactivate due to sintering-induced morphological changes during repeated carbonation and calcinations cycles. In this work, we have prepared acicular calcium and magnesium acetate precursors using a simple, cost-effective and easily scalable technique that requires just the natural minerals and acetic acid, thereby avoiding expensive reactants and environmentally unfriendly solvents. Upon thermal decomposition, these precursors yield a stable porous structure comprised of well dispersed MgO nanoparticles coating the CaO/CaCO3 grains that is resistant to pore-plugging and sintering while at the same time exhibits high long term effective conversion. Process simulations show that the employment of these materials could significantly improve the overall CSP-CaL efficiency at the industrial level.Ministerio de Economía y Competitividad CTQ2014-52763-C2, CTQ2017-83602-C

A semi-industrial AnMBR plant for urban wastewater treatment at ambient temperature: Analysis of the filtration process, energy balance and quantification of GHG emissions

A semi-industrial scale AnMBR urban wastewater treatment plant was operated for 580 days at ambient temperature (ranging from 10-30 ○C) to assess its long-term filtration performance, energy balance and GHG emissions. The applied 20ºC-standardized transmembrane flux (J20) was varied between 15 and 25 LMH and the specific gas demand per m2 of membrane (SGDm) was modified between 0.10 to 0.40 Nm3·m-2·h-1 (corresponding to a specific gas demand per permeate volume (SGDP) between 10 to 20 Nm3·m-3). The filtration strategy allowed successful long-term operations without any chemical cleaning requirements and little fouling for 233 days. The plant operated as a net energy producer for more than 50 % of the experimental period, with an average net energy demand of -0.169±0.341, -0.190±0.376 and -0.205±0.447 kWh·m-3, considering 0 %, 50 % and 70 % of dissolved methane recovery, respectively. Finally, demethanization of AnMBR effluent is needed to achieve an environmentally sustainable operation of the technology. Therefore, the combination of AnMBR with degassing membranes appears as a suitable alternative to conventional wastewater treatment

A semi-industrial scale AnMBR for municipal wastewater treatment at ambient temperature: performance of the biological process

A semi-industrial scale AnMBR plant was operated for more than 600 days to evaluate the long-term operation of this technology at ambient temperature (ranging from 10 to 27 ºC), variable hydraulic retention times (HRT) (from 25 to 41 h) and influent loads (mostly between 15 and 45 kg COD·d−1). The plant was fed with sulfate-rich high-loaded municipal wastewater from the pre-treatment of a full-scale WWTP. The results showed promising AnMBR performance as the core technology for wastewater treatment, obtaining an average 87.2 ± 6.1 % COD removal during long-term operation, with 40 % of the data over 90%. Five periods were considered to evaluate the effect of HRT, influent characteristics, COD/-S ratio and temperature on the biological process. In the selected periods, methane yields varied from 70.2±36.0 to 169.0±95.1 STP L CH4·kg−1 CODinf, depending on the influent sulfate concentration, and wasting sludge production was reduced by between 8 % and 42 % compared to conventional activated sludge systems. The effluent exhibited a significant nutrient recovery potential. Temperature, HRT, SRT and influent COD/-S ratio were corroborated as crucial parameters to consider in maximizing AnMBR performance