Digestión anaerobia termófila de fangos a escala industrial: Efecto de la co-digestión con residuos agroalimentarios

Se ha llevado a cabo un estudio en un digestor industrial de 2500 m3 con el fin de mejorar la gestión medioambiental de efluentes líquidos y residuos sólidos en una fábrica de alimentos precocinados pasando de la digestión anaerobia de los fangos procedentes del tratamiento de aguas residuales a la co-digestión anaerobia en presencia de residuos agroalimentarios de la misma fábrica, funcionando ambos procesos en condiciones termófilas.El objetivo de tal acción ha sido minimizar la cantidad de residuos a tratar en la misma fábrica (o a enviar fuera de la misma para su gestión ulterior) y, también, recuperar la energía presente en tales residuos mediante generación de biogás. Se ha demostrado que la substitución de fango por residuos agroalimentarios no merma la producción de biogás, al haberse demostrado que el caudal de biogás permanece prácticamenteconstante (1678 ± 99 m3/día y 1623 ± 147 m3/día, medidosen condiciones estándar de 1 bar y 0 ºC, para la digestión y co-digestión, respectivamente). Ahora bien, la co-digestión fue más eficaz en lo que a eliminación de sólidos se refiere y el rendimiento de eliminación de sólidos totales aumentó del 58,8% (digestión) al 65,0% (codigestión) y el rendimiento de eliminación de sólidos volátiles se incrementó del 66,9 al 72,8%. Así pues, se ha demostrado el buen funcionamiento del digestor anaerobio termófilo al añadir residuos agroalimentarios al fango con el que operaba habitualmente. Mediante análisislineal múltiple ha sido posible predecir el caudal de biogás  y el rendimiento de eliminación de sólidos en función de diferentes variables de proceso

Acetogenic inoculum selection for acetate production from waste biomasses via thermal shock treatment

Innovative treatment and utilization of waste biomass streams are crucial for increase environmental sustainability of human activities. Sewage sludge from the biological degradation of biomass can be valorized for the selection of biocatalysts capable to convert CO2 into valuable products. Indeed, chemoautotrophic microorganisms, like methanogens and acetogens, respectively, are able to convert CO2 into CH4 or acetate by using hydrogen as electron donor, i.e., their utilization for several bio-based CO2 reutilization processes has been widely proposed by several authors. Chemoautothrophic acetogens are widely present in waste streams deriving from the organic matter degradation, however, due to the syntrophic relationship between acetogens and acetoclastic methanogens in anaerobic environments, autothropihc acetate results immediately converted into methane. Therefore, the selection of an acetogenic inoculum which allow to obtain CO2 reduction into acetate, requires methanogens inhibition. Among the different methanogen’s inhibition strategies, the most common method is the use of BES (bromo-ethane sulphonate) which results a not scalable technique for large scale application. A most promising and sustainable approach is offered by the adoption of a thermal treatment which allows to the selection of an acetogenic inoculum, thanks ot the sporogenous capacity of acetogenic bacteria. This work presents the results obtained in the thermal pre-treatment of different type of waste biomasses coming from pilot and full-scale biological processes for the selection of an acetogenic inoculum able to convert CO2 into acetate. Each waste biomass was treated by a thermal shock procedure that consisted in the treatment of the dried biomass at 120°C for 2 hours. Acetogenic inoculums obtained by the thermal pre-treatment of an acidogenic fermentate, an activated sludge and a mesophilic anaerobic digestate, were tested under hydrogenophilic conditions in comparison with blank tests and raw inoculums. The results clearly indicate the effectiveness of the thermal pre-treatment in the selection of the acetogenic microorg

Hydrogenophilic and bioelectrochemical production of acetate with a pure culture of Acetobacterium Woodii

In recent years there has been a growing interest in the potential use of autotrophic acetogenic bacteria to produce compounds of interest through CO2 fixation, representing an alternative solution to currently used CO2 storage technologies. This group of microorganisms are ubiquitous in nature and they are characterised by a Wood-Ljungdahl pathway that combines CO2 fixation with adenosine triphosphate (ATP) synthesis by using H2 as electron donor. In this work the autotrophic production of acetate by a pure colture of Acetobacterium woodii has been tested under hydrogenophilic or bioelectrochemical conditions. More in details, the hydrogenophilic tests were conducted at two different pH values (5.5 and 7.5) with an H2 partial pressure of 0.52 atm, while bioelectrochemical tests were performed at an applied cathodic potential of -0.90 V vs. SHE (Standard Hydrogen Electrode). The bioelectrochemical tests were set up in H-type reactors (250 mL), in which graphite rods were used as electrodic material and an anion exchange membrane served to separate the anodic and cathodic chambers while allowing anions migration for electroneutrality maintenance. The hydrogenophilic tests resulted in different kinetics depending on the applied pH value. The bioelectrochemical tests, performed at a pH value of 7.5, reached an acetate production rate 2 times higher than in the hydrogenophilic experiments at pH 7.5, as well as an increase in the efficiency of using the reducing power, suggesting an improvement in hydrogen uptake. At pH 5.5, on the other hand, production is improved by increasing the partial pressure of H

Modelling Mixed Microbial Culture Polyhydroxyalkanoate Accumulation Bioprocess towards Novel Methods for Polymer Production Using Dilute Volatile Fatty Acid Rich Feedstocks

Volatile fatty acid (VFA) rich streams from fermentation of organic residuals and wastewater are suitable feedstocks for mixed microbial culture (MMC) Polyhydroxyalkanoate (PHA) production. However, many such streams have low total VFA concentration (1–10 gCOD/L). PHA accumulation requires a flow-through bioprocess if the VFAs are not concentrated. A flow through bioprocess must balance goals of productivity (highest possible influent flow rates) with goals of substrate utilization efficiency (lowest possible effluent VFA concentration). Towards these goals, dynamics of upshift and downshift respiration kinetics for laboratory and pilot scale MMCs were evaluated. Monod kinetics described a hysteresis between the upshift and downshift responses. Substrate concentrations necessary to stimulate a given substrate uptake rate were significantly higher than the concentrations necessary to sustain the attained substrate uptake rate. A benefit of this hysteresis was explored in Monte Carlo based PHA accumulation bioprocess numerical simulations. Simulations illustrated for a potential to establish continuous flow-through PHA production bioprocesses even at a low (1 gCOD/L) influent total VFA concentration. Process biomass recirculation into an engineered higher substrate concentration mixing zone, due to the constant influent substrate flow, enabled to drive the process to maximal possible PHA production rates without sacrificing substrate utilization efficiency

Bioelectrochemical chlorinated aliphatic hydrocarbons reduction in synthetic and real contaminated groundwaters

The widespread contamination of chlorinated aliphatic hydrocarbons (CAHs) as Perchloroethylene (PCE) and Trichloroethylene (TCE) over the past recent years and their uncorrected disposal and storing brought these substances to become one of the most common contaminants of subsoils and groundwater in the world. In recent years, more sustainable remediation and cost-effective technologies involving groundwater’s indigenous microorganism such as the dehalorespiring microorganisms. Dehalorespiring microorganisms can reduce PCE and TCE via reductive dechlorination (RD) while aerobic dechlorinating microorganisms oxidized low chlorinated compound such as cis-dichloroethylene (cDCE) and vinyl chloride (VC) into non harmful products. The integration of reductive dechlorination and aerobic dechlorination results in an efficient approach for the complete mineralization of high chlorinated compounds, which usually led to a build-up of VC. Bioelectrochemical systems, which exploit the capability of microorganisms to interact with a polarized electrode, provide an effective strategy to promote reductive and oxidative environments by the regulation of the applied potentials. Indeed, the complete mineralization of high chlorinated CAHs, can be obtained by a sequential reductive/oxidative bioelectrochemical process which allows for the optimization of the reductive and oxidative dechlorinating conditions. In this study the performances of the reductive reactor, devoted to the reductive dechlorination has been presented with three different contaminated feeding solutions. The three different feeding solutions included an optimized mineral medium, a synthetic groundwater (constituted by tap water added with nitrate and sulphate) and a real contaminated groundwater. Moreover, different operating conditions like hydraulic retention time (HRT) and applied cathodic potential have been investigated to assess the performance of the reductive dechlorination and on side reactions. The analysis of the coulombic efficiencies for the reductive dechlorination in the reductive reactor showed an important effect of the feeding solution composition and operating conditions (applied potential and HRT), namely strongly decreasing under when using real contaminated groundwater. Despite the progressive decrease of the coulombic efficiency obtained using more complex matrixes, the CAHs removal rates along with the energetic consumption of the process showed an advantageous perspective in the adoption of the bioelectrochemical process for the stimulation of the reductive dechlorination reaction

Financing social and cohesion policy in an enlarged EU: plus ça change, plus c'est la même chose?

The development of the Open Method of Coordination, agreement on the Lisbon Agenda and EU enlargement offered the prospect of a new and substantial EU social policy agenda. This article considers EU social and cohesion policies in the context of the recent negotiation of the EU budget for 2007—13. We find the Commission's wish to redistribute EU spending in favour of these policy areas and new member states was thwarted by key political features of EU budget making: CAP spending levels which are downwardly sticky; institutional arrangements which provide for budget making as, at best, a zero-sum game; and the preferences of contributor member states in the EU-15 to contain overall spending while preserving their net budget positions. Questions are thus raised as to the ability of the EU to make any progress, from a budgetary perspective, on the social and cohesion policy agenda in an enlarged EU

Polyhydroxyalkanoates production by mixed microbial cultures in sequencing batch reactors operated under different feeding conditions

The production of polyhydroxyalkanoates (PHA) by mixed microbial cultures (MMC) requires a multistage process, whereby the microbial selection of PHA-storing microorganisms plays a key role on the overall performance. A strategy to favor the microbial selection consists in the alternance of excess (feast phase) and absence (famine phase) of the external carbon source. In this work, three runs of a lab-scale Sequencing Batch Reactor (SBR) operated under different working conditions for the establishment of the feast and famine (F/F) regime were analyzed. A fixed organic loading rate of 4.25 gCOD (Chemical Oxygen Demand)/L d, and a fixed cycle length of 12 h were applied to the SBR. The F/F regime consisted of fully aerobic dynamic (ADF) or aerobic/anoxic (AE/ANOX) conditions. Results showed an intracellular PHA content as high as 40 ± 2 (%, w/w) when ADF conditions were applied with the organic feeding solution made of acetate (85 % on COD basis) and propionic (15%) acids. The hydroxyvalerate content in the stored polymer increased (from 25 ± 1 to 41 ± 3, % w/w) by increasing the propionic fraction (up to 35%) in the feeding solution. The AE/ANOX condition resulted in a lower PHA-storing ability which warrants further investigations

Bioelectrochemical dechlorination of trichloroethene: From electron transfer mechanisms to process scale-up

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Field distribution and activity of chlorinated solvents degrading bacteria by combining CARD-FISH and real time PCR

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