Standardized protocol for determination of biohydrogen potential.

Biohydrogen production potential (BHP) depends on several factors like inoculum source, substrate, pH, among many others. Batch assays are the most common strategy to evaluate such parameters, where the comparison is a challenging task due to the different procedures used. The present method introduces the first internationally validated protocol, evaluated by 8 independent laboratories from 5 different countries, to assess the biohydrogen potential. As quality criteria, a coefficient of variation of the cumulative hydrogen production (H max) was defined to be <15 %. Two options to run BHP batch tests were proposed; a manual protocol with periodic measurements of biogas production, needing conventional laboratory materials and analytical equipment for biogas characterization; and an automatic protocol, which is run in a device developed for online measurements of low biogas production. The detailed procedures for both protocol options are presented, as well as data validating them. The validation showed acceptable repeatability and reproducibility, measured as intra- and inter-laboratory coefficient of variation, which can be reduced up to 9 %.

Sequential adaptation of Nannochloropsis gaditana to table olive processing water.

The main objective of this study was to evaluate the suitability of Nannochloropsis gaditana to grow by sequential adaptation to TOPW (Table olive processing water) at increased substrate concentrations (10-80%). Sequential adaptation allows growing Nannochloropsis gaditana up to 80% TOPW, although the maximum microalgae biomass productions were achieved for percentages of 20-40%, i.e. 0.308 ± 0.005 g VSS (Volatile Suspended Solids)/L. In all growth experiments, proteins were the majority compound in the grown microalgae biomass (0.44 ± 0.05 g/g VSS), whereas phenols were retained up to a mean concentration of 12.1 ± 1.9 mg total phenols/g VSS. The highest microalgae biomass production rate at rate of 80% TOPW took place in the first two days when most nutrients were also removed. Average removal efficiencies at this percentage of TOPW were 69.1%, 50.9%, 54.3% and 71.8% for total organic carbon, total soluble nitrogen, phosphate and total phenols, respectively. Sequential adaptation can ensure the obtaining of a sustainable microalgae culture as a treatment method for TOPW.

Microbial ecology of fermentative hydrogen producing bioprocesses: useful insights for driving the ecosystem function.

One of the most important biotechnological challenges is to develop environment friendly technologies to produce new sources of energy. Microbial production of biohydrogen through dark fermentation, by conversion of residual biomass, is an attractive solution for short-term development of bioH2 producing processes. Efficient biohydrogen production relies on complex mixed communities working in tight interaction. Species composition and functional traits are of crucial importance to maintain the ecosystem service. The analysis of microbial community revealed a wide phylogenetic diversity that contributes in different-and still mostly unclear-ways to hydrogen production. Bridging this gap of knowledge between microbial ecology features and ecosystem functionality is essential to optimize the bioprocess and develop strategies toward a maximization of the efficiency and stability of substrate conversion. The aim of this review is to provide a comprehensive overview of the most up-to-date biodata available and discuss the main microbial community features of biohydrogen engineered ecosystems, with a special emphasis on the crucial role of interactions and the relationships between species composition and ecosystem service. The elucidation of intricate relationships between community structure and ecosystem function would make possible to drive ecosystems toward an improved functionality on the basis of microbial ecology principles.

Assessment of microalgae and nitrifiers activity in a consortium in a continuous operation and the effect of oxygen depletion

Background: Industrial wastewaters with a high content of nitrogen are a relevant environmental problem. Currently, treatments to remove nitrogen are not efficient, so is necessary to develop alternative methods. The objective of this study is to investigate a consortium of microalgae - nitrifying, that due to the symbiosis between them could be an interesting alternative. Results: In this study, it was possible to obtain a consortium of nitrifying bacteria (NB) and microalgae (MA) capable of operating with low requirements of dissolved oxygen, using aerobic sludge from wastewater treatment plants. During the operation, this consortium presents removal percentages above 98% of ammonia, even at concentrations of DO of 0.5 mg O2 L-1. It is estimated that the removal was caused both by the action of nitrifying bacteria and microalgae. It was determined that approximately 60% of the ammonia feed was oxidized to nitrate by nitrifying bacteria, while the algae assimilated 40% of the nitrogen feed at steady state. A methodology for measuring the specific activities of nitrifying bacteria and microalgae by comparing the rates in the variation inorganic nitrogen compounds was established with satisfactory results. An average specific activity of 0.05 and 0.02 g NH4 + gVSS-1 d-1 for nitrifying bacteria and microalgae was determined, respectively. Conclusions: The consortium it can be obtained in a single continuous operation, and has a high capacity for nitrogen removal with low oxygen content. The consortium could prove to be a more economical method compared to traditional.

Simultaneous production and separation of biohydrogen in mixed culture systems by continuous dark fermentation.

Hydrogen production by dark fermentation is one promising technology. However, there are challenges in improving the performance and efficiency of the process. The important factors that must be considered to obtain a suitable process are the source of the inoculum and its pre-treatment, types of substrates, the reactor configurations and the hydrogen partial pressure. Furthermore, to obtain high-quality hydrogen, it is necessary to integrate an effective separation procedure that is compatible with the intrinsic characteristics of a biological process. Recent studies have suggested that a stable and robust process could be established if there was an effective selection of a mixed microbial consortium with metabolic pathways directly targeted to high hydrogen yields. Additionally, the integration of membrane technology for the extraction and separation of the hydrogen produced has advantages for the upgrading step, because this technology could play an important role in reducing the negative effect of the hydrogen partial pressure. Using this technology, it has been possible to implement a production-purification system, the 'hydrogen-extractive membrane bioreactor'. This configuration has great potential for direct applications, such as fuel cells, but studies of new membrane materials, module designs and reactor configurations are required to achieve higher separation efficiencies.

Microbial ecology in anaerobic digestion at agitated and non-agitated conditions.

To investigate the distribution and dynamics of microbial community in anaerobic digestion at agitated and non-agitated condition, 454 pyrosequencing of 16s rRNA was conducted. It revealed the distinct community compositions between the two digesters and their progressive shifting over time. Methanogens and syntrophic bacteria were found much less abundant in the agitated digester, which was mainly attributed to the presence of bacterial genera Acetanaerobacterium and Ruminococcus with relatively high abundance. The characterization of the microbial community corroborated the digestion performance affected at the agitated condition, where lower methane yield and delayed methane production rate were observed. This was further verified by the accumulation of propionic acid in the agitated digester.

A methodology for a quantitative interpretation of DGGE with the help of mathematical modelling: application in biohydrogen production.

Molecular biology techniques provide valuable insights in the investigation of microbial dynamics and evolution. Denaturing gradient gel electrophoresis (DGGE) analysis is one of the most popular methods which have been used in bioprocess assessment. Most of the anaerobic digestion models consider several microbial populations as state variables. However, the difficulty of measuring individual species concentrations may cause inaccurate model predictions. The integration of microbial data and ecosystem modelling is currently a challenging issue for improved system control. A novel procedure that combines common experimental measurements, DGGE, and image analysis is presented in this study in order to provide a preliminary estimation of the actual concentration of the dominant bacterial ribotypes in a bioreactor, for further use as a variable in mathematical modelling of the bioprocess. This approach was applied during the start-up of a continuous anaerobic bioreactor for hydrogen production. The experimental concentration data were used for determining the kinetic parameters of each species, by using a multi-species chemostat-model. The model was able to reproduce the global trend of substrate and biomass concentrations during the reactor start-up, and predicted in an acceptable way the evolution of each ribotype concentration, depicting properly specific ribotype selection and extinction.

Identification in an anaerobic batch system: global sensitivity analysis, multi-start strategy and optimization criterion selection.

Several mathematical models have been developed in anaerobic digestion systems and a variety of methods have been used for parameter estimation and model validation. However, structural and parametric identifiability questions are relatively seldom addressed in the reported AD modeling studies. This paper presents a 3-step procedure for the reliable estimation of a set of kinetic and stoichiometric parameters in a simplified model of the anaerobic digestion process. This procedure includes the application of global sensitivity analysis, which allows to evaluate the interaction among the identified parameters, multi-start strategy that gives a picture of the possible local minima and the selection of optimization criteria or cost functions. This procedure is applied to the experimental data collected from a lab-scale sequencing batch reactor. Two kinetic parameters and two stoichiometric coefficients are estimated and their accuracy was also determined. The classical least-squares cost function appears to be the best choice in this case study.

Biofilm formation for organic matter and sulphate removal in gas-lift reactors

A start-up strategy was presented and evaluated to obtain a well-established biofilm in a gas lift-reactor capable both for the removal of organic matter and sulphate. Pumice stone was used as material support. The influence of shear forces, given by the biogas recirculation, the effect of the COD/SO4-2 ratio and the OLRs increase were evaluated on the reactor performance. From the first stages, cell colonization was observed along with the presence of extracellular polymeric substances. The COD and sulphate removal was over 70 percent, for all conditions. The increase of gas flow did not have an adverse effect on biofilm development even though there was some detachment. Specific methanogenic activity of the biofilm increased along the experiments. Operational parameters as alkalinity and alkalinity ratio were within the recommended values for the operation with sulphate-rich wastewater. For gas-lift reactors operation it becomes fundamental to have a suitable start-up strategy that takes into account the initial biofilm development from a non-acclimatized biomass.

Improved sanitary landfill design using recirculation of anaerobically treated leachates: generation of advanced design criteria

In Latin America, the most accepted disposal systems for Municipal Solid Waste (MSW) are landfills, which nowadays have low rates of stabilization. The objective of this study was to develop design criteria for sanitary landfills which lead to a reduction in the stabilization times of MSW, based on experiment results obtain from a pre-pilot scale operation of two sanitary landfills (0.5 Ton), one with recirculation of leachates treated in an anaerobic digester and the other with recirculation of untreated leachates. This was complemented by another pilot scale sanitary landfill (1440 Ton) with recirculation of leaches treated in an anaerobic filter, and additionally by a computer simulation of leachate generation through the water balance of a theoretical cell of MSW (850 Ton), in which the initial humidity of the MSW and the type of final cover were evaluated. The results obtained on the pre-pilot scale indicate that recirculation of anaerobically treated leachates, when compared to the recirculation of untreated leachates, increased the rate of MSW stabilization, projecting a stabilization time reduction of 72 percent. In the pilot sanitary landfill an increase in the settling rate of around 200 percent was observed when operating with the recirculation of anaerobically treated leachates as opposed to operation without recirculation. The water balance carried out on the theoretical cell of MSW demonstrated the importance to leachate generation of both the initial landfill water saturation and the type of final barrier. From these results it may be stated that it is important for landfill design to maintain waste humidity close to its field capacity along with an adequate leachate application rate.

Simultaneous effects of pH and substrate concentration on hydrogen production by acidogenic fermentation / Efectos simultáneos del pH y la concentración de sustrato en la producción de hidrógeno mediante fermentación acidogénica

The present research examined the effects of initial substrate concentration and pH on the yield and productivity of hydrogen production by acidogenic fermentation. Assays were carried out at three different initial pH levels (5.5, 6.5 and 7.5) and three initial substrate concentrations (3, 5 and 10 g COD/L). Glucose was used as carbon source and the experiments were conducted at 37°C in batch tests, after a thermal pretreatment to eliminate methanogenic microorganisms. Conversions of glucose into hydrogen were between 16.75 and 27.25 percent of theoretical maximum, and high values of hydrogen productivity were obtained. An optimum value for the yield of glucose between initial pH of 6.3 and 3.7 g COD/L and productivity of the 5.95 H2/gVSS h and initial pH of 6.7 and 10 g COD/L were obtained from the response surface.

Anaerobic sequencing batch reactor as an alternative for the biological treatment of wine distillery effluents.

The goal of this study was to assess the effect of different modes of operation and configurations of Anaerobic Sequencing Batch Reactors (ASBRs) treating phenolic wastewater. Several lab-scale reactors were used in the mesophilic range. The reactors were fed with synthetic wastewater with a COD of 5 g/L using phenol as a carbon source (variable concentration) and glucose as a co-substrate. One and two-phase (hydrolytic/acidogenic-methanogenic) systems in batch and fed-batch operation were evaluated. The one-stage reactor operated by the fed batch (which was the only configuration using phenol as a sole carbon source), presented better results for the removal of phenol, reaching 100% removal in 10 days at a concentration of 210 mg/L. The two-stage configuration had removal percentages near 100%, but the methanogenic reactor presented greater degradation of the remaining phenol not removed in the hydrolytic/acidogenic reactor. ASBRs might be a feasible alternative to treat this type of effluent due to their operational flexibility.

Treatment of low strength sewage with high suspended organic matter content in an anaerobic sequencing batch reactor and modeling application

In this work, an anaerobic sequencing batch reactor (ASBR) was operated for 8 months to treat low strength sewage with high suspended organic matter content. Three phases of operation with increasing organic loading rates (OLR) were performed: 0.4 kg COD/m³ x d (phase I), 0 .8 kg COD/m³ x d (phase II) and 1.2 kg COD/m³ x d (phase III). Adequate stability parameters (pH, total alkalinity) were obtained through all three experimental phases. During phases I and II, the removal efficiencies of organic matter (expressed as total chemical oxygen demand (COD) and total suspended solids ranged between 50-60 percent. However, these values decreased to 15-25 percent in phase III. In addition, a non-complex model, including hydrolysis, acidogenesis and methanogenesis, was applied to predict the reactor behavior.