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Respirometric techniques and an activated sludge model (ASM) were applied for the characterization of tannery wastewater and biomass in a pilot plant membrane bioreactor (MBR) operating at high sludge age. The traditional respirometric tests and the IWA-ASM1 were modified to take into account the specific operating conditions, the solid-liquid separation technology and the wastewater complexity. As a result the wastewater biodegradable COD was fractionated into four components: readily biodegradable, rapidly hydrolysable, slowly hydrolysable and inorganic (due to the presence of reduced sulphur compounds). The kinetic and stoichiometric parameters of the biomass (heterotrophic and nitrifying) were estimated through the integration of model simulations and respirometric tests results. In particular the ammonium and nitrite-oxidizing biomasses were separately characterized: the growth kinetics of ammonium and nitrite-oxidizing bacteria resulted noticeably lower than the traditional reference values (mu(max,AOB)=0.25d(-1)e mu(max,NOB)=0.23d(-1) at 20 degrees C, respectively). The ASM was finally used to confirm that the results of the wastewater and biomass characterization allow to properly simulate the mixed liquor suspended solids in the MBR pilot plant and the COD concentration in the effluent.

Algae are an interesting feedstock for producing biofuel via hydrothermal liquefaction (HTL), due to their high water content. In this study, algae slurries (5-7 wt% daf) from different species were liquefied at 250 and 375 °C in batch autoclaves during 5 min. The aim was to analyze the influence of strain-specific parameters (cell structure, biochemical composition and growth environment) on the HTL process. Results show big variations in the biocrude oil yield within species at 250 °C (from 17.6 to 44.8 wt%). At 375 °C, these differences become less significant (from 45.6 to 58.1 wt%). An appropriate characterization of feedstock appeared to be critical to interpret the results. If a high conversion of microalgae-to-biocrude is pursued, near critical conditions are required, with Scenedesmus almeriensis (freshwater) and Nannochloropsis gaditana (marine) leading to the biocrude oils with lower nitrogen content from each growth environment.

An innovative approach was developed by incorporating high-pressure CO2 into the separate hydrolysis-fermentation of aspen leftover branches, aiming to enhance the bioethanol production efficiency. The high-pressure CO2 significantly increased the 72-h enzymatic hydrolysis yield of converting aspen into glucose from 53.8% to 82.9%. The hydrolysis process was performed with low enzyme loading (10 FPU g-1 glucan) with the aim of reducing the cost of fuel bioethanol production. The ethanol yield from fermentation of the hydrolyzed glucose using yeast (Saccharomyces cerevisiae) was 8.7 g L-1, showing increment of 10% compared with the glucose control. Techno-economic analysis indicated that the energy consumption of fuel bioethanol production from aspen branch chips was reduced by 35% and the production cost was cut 44% to 0.615 USD L-1, when 68 atm CO2 was introduced into the process. These results furtherly emphasized the low carbon footprint of this sustainable energy production approach.

Triacylglycerols recovery from wet microalgae is a key aspect of biodiesel production, because of the energetic balance gained from avoiding biomass drying. In order to isolate TAG from Nannochloropsis cells, the possibility to concentrate biomass and to recover TAG in a single step by membrane process was studied. Different polymeric membranes were selected and screened on the basis of adsorption test and permeation flux. Results showed that membrane of regenerated cellulose (RC) with nominal molecular weight cutoff of 100 kDa and 30 kDa gave the best performance. Indeed, permeate flux was stable during ultrafiltration experiment in concentration mode and no severe fouling/cake deposition was observed. Both membranes allowed to recover permeates with high content of triacylglicerols. However, a more purity of the triacylglicerols from the other co-products was only obtained with the 30 kDa RC membrane because the retention of the unwanted proteins was in the range of 89%.

In biogas plants, huge volumes of digestate are produced daily and stored in uncovered tanks, which leak methane into the atmosphere and cause negative environmental impacts. To better understand the effect that different operating parameters of anaerobic digestion plants have on digestate residual methane yield, four digestate samples collected from plants with very different operations were analysed in batch reactors. Their methane yields were very heterogeneous and varied between 2.88 and 37.63 NL/kgVS. The methane yield was shown to be highly influenced by the A.D. plant Organic Loading Rate and by feedstock quality; hydraulic retention time had only limited effects.

Long chain fatty acids (LCFA) concentrations over 1.0 gL(-1) were inhibiting manure thermophilic digestion, in batch and semi-continuous experiments, resulting in a temporary cease of the biogas production. The aim of the work was to test and evaluate several recovery actions, such as reactor feeding patterns, dilution and addition of adsorbents, in order to determine the most appropriate strategy for fast recovery of the reactor activity in manure based plants inhibited by LCFA. Dilution with active inoculum for increasing the biomass/LCFA ratio, or addition of adsorbents for adsorbing the LCFA and reducing the bioavailable LCFA concentration, were found to be the best recovery strategies, improving the recovery time from 10 to 2 days, in semi-continuously fed systems. Moreover, acclimatization was introduced by repeated inhibition and process recovery. The subsequent exposure of the anaerobic biomass to an inhibitory concentration of LCFA improved the recovery ability of the system, indicated as increasing degradation rates from 0.04 to 0.16 g COD_CH(4)/g VS day. The incubation time between subsequent pulses, or discontinuous LCFA pulses, seems to be a decisive process parameter to tackle LCFA inhibition in manure anaerobic co-digestion.

More than 400 papers in the last 5 years have been published on FW into energy. Food waste complexity and composition affects anaerobic conversion. Scaling up of the AD process is fundamental to assess the real methane potential. Methanogenesis is often rate limiting step leading to pH drop and instability. Strategies to improve AD performances and stability are here reviewed.

Organic waste such as manure is an important resource for biogas production. The biodegradability of manures is however limited because of the recalcitrant nature of the biofibers it contains. To increase the biogas potential of the biofibers in digested manure, we investigated physical treatment (milling), chemical treatment (CaO), biological treatment (enzymatic and partial aerobic microbial conversion), steam treatment with catalyst (H(3)PO(4) or NaOH) and combination of biological and steam treatments (biofibers steam-treated with catalyst were treated with laccase enzyme). We obtained the highest methane yield increase through the chemical treatment that resulted in 66% higher methane production compared to untreated biofibers. The combination of steam treatment with NaOH and subsequent enzymatic treatment increased the methane yield by 34%. To choose the optimal treatment, the energy requirements relative to the energy gain as extra biogas production have to be taken into account, as well as the costs of chemicals or enzymes.