Biohydrogen production from used diapers: Evaluation of effect of temperature and substrate conditioning.

This research assessed the viability to use disposable diapers as a substrate for the production of biohydrogen, a valuable clean-energy source. The important content of cellulose of disposable diapers indicates that this waste could be an attractive substrate for biofuel production. Two incubation temperatures (35 °C and 55 °C) and three diaper conditioning methods (whole diapers with faeces, urine, and plastics, WD; diapers without plastic components, with urine and faeces, DWP; diapers with urine but without faeces and plastic, MSD) were tested in batch bioreactors. The bioreactors were operated in the solid substrate anaerobic hydrogenogenic fermentation with intermittent venting mode (SSAHF-IV). The batch reactors were loaded with the substrate at ca. 25% of total solids and 10% w/w inoculum. The average cumulative bioH2 production followed the order WD > MSD > DWP. The bio-H2 production using MSD was unexpectedly higher than DWP; the presence of plastics in the first was expected to be associated to lower degradability and H2 yield. BioH2 production at 55 °C was superior to that of 35 °C, probably owing to a more rapid microbial metabolism in the thermophilic regime. The results of this work showed low yields in the production of H2 at both temperatures compared with those reported in the literature for municipal and agricultural organic waste. The studied process could improve the ability to dispose of this residue with H2 generation as the value-added product. Research is ongoing to increase the yield of biohydrogen production from waste disposable diapers.

Cheese whey as substrate of batch hydrogen production: effect of temperature and addition of buffer.

The aim of this work was to evaluate the effect of buffer addition and process temperature (ambient and 35°C) on H2 production in batch fermentation of cheese whey (CW). When the H2 production reached a plateau, the headspace of the reactors were flushed with N2 and reactors were re-incubated. Afterwards, only the reactors with phosphate buffer showed a second cycle of H2 production and 48% more H2 was obtained. The absence of a second cycle in non-buffered reactors could be related to a lower final pH than in the buffered reactors; the low pH could drive the fermentation to solvents production. Indeed a high solvent production was observed in non-buffered bioreactors as given by low ρ ratios (defined as the ratio between sum of organic acid production and sum of solvents production). Regarding the process temperatures, no significant difference between the H2 production of reactors incubated at ambient temperature and at 35°C was described. After flushing the headspace of bioreactors with N2 at the end of the second cycle, the H2 production did not resume (in all reactors).

Effect of culture conditions on fatty acids composition of a biosurfactant produced by Candida ingens and changes of surface tension of culture media.

This work investigated the effect of culture medium composition on a biosurfactant production and their total fatty acids content, as well as the surface tension of media, and biomass production by Candida ingens. A factorial experimental design was used to evaluate the combined effect of C/P, C/N(inorganic), C/Fe, C/Mg ratios and yeast extract concentration. The highest biosurfactant production was reached when high C/Fe and high C/P ratio variables were combined; biosurfactant concentration increased by a 3.42 fold. The variable with the highest effect on net decrease surface tension (DeltaST) and fatty acids percentage of C. ingens biosurfactant was yeast extract. The average of DeltaST (25 mN/m) and fatty acids percentage (34.7%) values were enhanced at high yeast extract concentration of 1g/l. The main conclusion of this study was that the culture composition affected the biosurfactant production by C. ingens. It was also observed that the surface tension and total fatty acids of the biosurfactant were modified as the media composition changed.

Semi-continuous treatment of recalcitrant anaerobic effluent from pulp and paper industry using hybrid pellets of Trametes versicolor.

The objective of this work was to evaluate the semi-continuous post-treatment of anaerobically-pre-treated weak black liquor (anaerobic effluent, AnE) by aerobic post-treatment using hybrid pellets of Trametes versicolor. The latter consisted of fungus immobilized onto holm oak sawdust (mixed or double pellets) or a mixture of holm oak sawdust and powdered activated carbon (triple pellets). First, a semicontinuous experiment was run to compare the effectiveness of triple and mixed pellets in agitated flasks for 15 cycles of 7 days each. A second extended batch test was implemented with 500 mL AnE and triple pellets to give 400 mg fungal biomass; some units were spiked with protease inhibitor. In the first experiment, triple pellets displayed consistently higher removal efficiencies of pollutant parameters than double pellets (10 to 15% higher), although overall averages were moderate and no statistical significance to the difference could be set because of the noise of fluctuations. Periodic fluctuations of removal were characterized by three periods of approximately six cycles each with maximum removals occurring at cycles 3-4, 7-9, 13, and 14. Evaluating pooled removals of the latter cycles showed that triple pellets were significantly more effective than double pellets, with removal efficiencies as high as 47% of COD, colour, and absorbance at 254 nm (A254). In general, protease activity seemed to increase in the third period (last six cycles), whereas activities of MnP, LiP and Lac significantly decreased. In the second experiment, pollutant removals and enzymatic activities of triple pellets with protease inhibitor were significantly higher than those of units without added protease inhibitor. These results indicate that protease could be the main cause of periodic falls of pollutant removal efficiencies found in the first experiment.

Removal of phenanthrene from soil by co-cultures of bacteria and fungi pregrown on sugarcane bagasse pith.

Sixteen co-cultures composed of four bacteria and four fungi grown on sugarcane bagasse pith were tested for phenanthrene degradation in soil. The four bacteria were identified as Pseudomonas aeruginose, Ralstonia pickettii, Pseudomonas sp. and Pseudomonas cepacea. The four fungi were identified as: Penicillium sp., Trichoderma viride, Alternaria tenuis and Aspergillus terrus that were previously isolated from different hydrocarbon-contaminated soils. Fungi had a statistically significant positive (0.0001

Integrated biological treatment of recalcitrant effluents from pulp mills.

This work aimed at determining the degree of depuration of a recalcitrant effluent (weak black liquor, WBL) achieved in a series treatment consisting of a first stage methanogenic fluidised bed reactor followed by a second stage aerobic, upflow reactor packed with "biocubes" of Trametes versicolor immobilised onto small cubes of holm oak wood. The mesophilic, lab scale methanogenic fluidised bed reactor contained a microbial consortium immobilised onto granular activated carbon 500 microm average size. The process removed decreasing amounts of organic matter at decreasing hydraulic retention times (HRT), eventually reaching an average of 50% at 0.5 day HRT. Colour and ligninoid removals also decreased with decreasing HRT. Although the methanogenic fluidised bed reactor provided an effective treatment for the degradable organic matter, important concentrations of recalcitrant organic matter and colour still remained in the anaerobic effluent. This anaerobic effluent was fed to the aerobic packed bed reactor. Two HRT were tested in this unit, namely 5 and 2.5 days. The reactor averaged an organic matter removal in the range of 32% COD basis, during an experimental run of 95 days. Colour and ligninoid contents were removed in high percentages (69% and 54%, respectively). There was no significant difference in reactor performance at 5- and 2.5-day HRT. There was a positive correlation between pollutant removal efficiencies and Laccase activity in crude extracts of the reactor liquor. No supplemental soluble carbohydrate was required to sustain the fungus activity and the consistent reactor performance. Overall, the two-stage treatment achieved approximately a 78% removal of the original organic matter of the WBL (COD basis) and ca. 75% of colour and ligninoid contents.

The effect of the supplementation with a primary carbon source on the resistance to oxygen exposure of methanogenic sludge.

Anaerobic methanogenic consortia have a considerable resistance to oxygen exposure. Yet, most research has been focused on the study of the tolerance to oxygen of anaerobic immobilized biomass. Less is known on the potential of the anaerobic suspended biomass for withstanding exposure to oxygen and the effect of a primary degradable substrate on such resistance. Thus, the objective of this work was to determine the effect of the amount of a primary degradable substrate (sucrose) on the resistance of a methanogenic suspended biomass to oxygen exposure. It was found that the inhibition of disperse anaerobic sludge by oxygen exposure decreases when the concentration of the supplemented carbon source increases. This is in agreement with the fact that aerobic respiration of the added substrate by the facultative heterotrophic bacteria, always present in this type of sludge, has been found in previous studies as one of the main mechanisms protecting methanogens against O2. From a practical point of view, this suggests that aeration of anaerobic systems should be possible without inhibiting the activity of methanogenic bacteria if an adequate ratio between oxygen and COD feeding is maintained. Such a ratio will depend however on the wastewater initial COD concentration.