Biodegradability and toxicity of styrene in the anaerobic digestion process

Start-up and operation of an Upflow Anaerobic Sludge Blanket (UASB) reactor fed with an industrial effluent from a polymer synthesis plant containing 6 mg styrene 1ˉ¹ was unstable. In batch assays with 200 mg styrene 1ˉ¹, 74% of styrene was degraded at a rate of 7 ml methane gˉ¹ volatile suspended solids.day, without a lag phase. The toxicity limit (IC50) of styrene was 1.4 mM for the acetoclastic activity, 0.45 and 1.6 mM for the methanogenic activity in the presence of 30 mM of propionate and ethanol respectively. Instability of UASB operation was attributed to other compounds such as acrylates or detergents present in the industrial effluent.Project ALFA - ALR/B-73011/94.04-4.0181.9

Recovery of acetoclastic activity in anaerobic granular sludge, monitored by methanogenic activity measurements and image analysis

The specific acetoclastic activity (SAA) of anaerobic granular sludge was recovered in a lab scale EGSB reactor. The inoculum presented a very low acetoclastic activity (0.81+/-2.48mg COD-CH4/gVSS.day). Ethanol was fed at a COD concentration of 1.5g/L, as sole organic carbon source to promote the biogas production through the hydrogenophilic pathway. During the operation period the specific methanogenic activity (SMA)1 in the presence of acetate, propionate, butyrate, ethanol and H2/CO2, and the biomass morphology were quantified. The SAA steadily increased as expected by the reactor performance, achieving a value of 183+/-13mg COD-CH4/gVSS.day at day 108. From the SMA results it was suggested that, until day 62, the initial methane production rate was dominated by the hydrogenotrophic population and afterwards, the developed acetoclastic activity started to play a role in the initial methane production from ethanol. Until day 62 the ratio between the filaments length and aggregates projected area (LfA)2 increased due to the breakdown of granules inside the reactor, after that decreased and granules development was simultaneous with the increase of the SAA. Percentage of aggregates in size range 0.1 to 1mm (equivalent diameter) increased until day 40 due to granules fragmentation. When the system achieved a steady state, the aggregates size increased

Análisis de imagen para la cuantificación de cambios morfológicos en biomasa granular, inducidos por la presencia de nitrato en reactores EGSB

Cuatro reactores EGSB (R1-R4) fueron operados a velocidades de carga orgánica de 10 kgCOD/(m³.d), tiempos de retención hidráulicos de 3.6 h, velocidades superficiales de 10 m/h y diferentes concentraciones de nitrato a la entrada, 0, 20, 60 y 100 mgN-NO3-/L en R1, R2, R3 and R4, respectivamente. Después de 20 días de operación continua, la biomasa granular fue caracterizada en términos de: (i) morfología por análisis de imagen cuantitativo; (ii) actividad metanogénica específica en presencia de acetato, butirato, propionato, etanol y una mezcla gaseosa de H2CO2; velocidad de sedimentación. El parámetro LfA, definido como el cuociente entre la longitud total de filamentos y el área total proyectada, fue determinado y se observó que es suficientemente sensible para la cuantificación de diferencias morfológicas inducidas por la presencia de nitrato. Aunque el crecimiento de estructuras filamentosas en la superficie de los gránulos fue evidente, no hubo una disminución notable en la velocidad de sedimentación de los gránulos, probablemente porque durante el período de operación los gránulos crecieron en tamaño. En el reactor R4 se observó un mayor washout que en R1, R2 y R3.Fundação para a Ciência e Tecnologia (FCT

Quantitative image analysis as a diagnostic tool for identifying structural changes during a revival process of anaerobic granular sludge

Due to unspecified operational problems, the specific acetoclastic activity (SAA) of the anaerobic granular sludge present in an industrial UASB reactor was considerably damaged (from 250 to less than 10mL CH4@STP/gVSS.d), significantly reducing the biogas production of that industrial unit. The hydrogenotrophic methanogenic activity exhibited a value of 600mL CH4@STP/gVSS.d, the settling velocity was 31.479.8 m/h, the average equivalent diameter was 0.9270.43mm, and about 70% of the VSS were structured in aggregates larger than 1mm. In order to study the recovery of the SAA, this sludge was collected and inoculated in a lab-scale expanded granular sludge blanket (EGSB) reactor. Ethanol was fed as the sole carbon source during a trial period of 106 days. Process monitoring included COD removal efficiency, methane production, and periodic determination of the specific methanogenic activity in the presence of acetate, propionate, butyrate, ethanol and H2/CO2. Quantitative image analysis allowed for information to be obtained on granular fragmentation/erosion and filaments release. During the first operational period, biogas production was mainly due to the hydrogenotrophic activity. However, after 40 days, the SAA steadily increased achieving a maximum value of 183713mL CH4@STP/gVSS.d. The onset of SAA recovery, granules breakdown and filaments release to the bulk occurred simultaneously. Further increase in SAA was accompanied by granular growth. In the last 25 days of operation, the size distribution was stable with more than 80% of projected area of aggregates corresponding to granules larger than 1mm (equivalent diameter). Confocal images from FISH hybridized sections of the granules showed that after SAA recovery, the granules developed an organized structure where an acidogenic/acetogenic external layer was apparent. Granular fragmentation and increase of filaments in the bulk, simultaneously with the increase in the acetoclastic activity are described for the first time and might represent a structural response of granular sludge to promote the optimal substrate uptake at minimal diffusion limitations.Fundação para a Ciência e a Tecnologia (FCT) - Grants SFRH/BD/3187/2000, SFRH/BD/13317/2003, Project POCTI/BIO/37934/2001 Grants SFRH/BD/3187/2000, SFRH/BD/13317/200

Bio4gas : evaluation and analysis of wastewater treatment facilities in the scope of biogas production maximization and energy production optimization

The present work presents some of the results of five reports developed in the scope of optimization feasibility studies carried out at 6 small- and medium-sized wastewater treatment plants (WWTP) in Portugal. These 6 WWTP are operated by five companies that belong to the Águas de Portugal holding. The objective of the studies was twofold: to assess to which extent the production of biogas could be increased by means of operational modifications and/or by the implementation of co-digestion regimes; and also to simulate different scenarios for feed-in tariff of electricity taking in account energy prices calculated based upon the DL n.º 225/2007 of 11th May. In this way, several codigestion scenarios were defined based upon standard available organic residues. The results obtained showed that the implementation of co-digestion regimes represent a significative potential to increase the production of biogas, in some cases, over 600%. Even though, it was concluded that in some cases the costs of introducing new regimes of energy management were not supported by the increase of energy production, so a scale factor is associated to the revenues. This study contributed to the establishment of specific needs in terms of information management (digester operation, energy production/consumption, strategy for optimisation)

Image analysis to quantify morphological changes in granular sludge induced by nitrate in EGSB reactors

Four EGSB reactors (R1 to R4) were operated at an organic loading rate of 10 kgCOD/(m³.d), hydraulic retention time of 3.6 h, upflow velocity of 10 m/h and different influent nitrate concentrations (0, 20, 60 and 100 mgN-NO_3-/L for R1, R2, R3 and R4, respectively. After about 20 days of operation, the granular sludge was characterized for: (i) morphology by quantitative image analysis; (ii) specific methanogenic activity in the presence of acetate, propionate, butyrate, ethanol and H_2/CO_2; (iii) settling velocity. LfA parameter, defined as the ratio of total filaments length to total projected area, was determined and was sensitive to quantify the different surface morphology, induced by nitrate to the granular sludge. Although the growth of filamentous structures was evident, no significant decrease on the settling velocity was observed, most likely because granules grew during the trial period. A higher washout occurred in R4, as compared to R1, R2 and R3.Grant SFRH/BD/3187/2000.Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS XXI/BD/20325/99