Fermentative H2 production from food waste: Parametric analysis of factor effects.

Factorial fermentation experiments on food waste (FW) inoculated with activated sludge (AS) were conducted to investigate the effects of pH and the inoculum-to-substrate ratio (ISR [g VSAS/g TOCFW]) on biohydrogen production. The two parameters affected the H2 yield, the fermentation rate and the biochemical pathways. The minimum and maximum yields were 41 L H2/kg TOCFW (pH = 7.5, ISR = 1.74) and 156-160 L H2/kg TOCFW (pH = 5.5, ISR = 0.58 and 1.74). The range of carbohydrates conversion into H2 was 0.37-1.45 mol H2/mol hexose, corresponding to 9.4-36.2% of the theoretical threshold. A second-order predictive model for H2 production identified an optimum region at low pHs and high ISRs, with a theoretical maximum of 168 L H2/kg TOCFW at pH = 5.5 and ISR = 1.74. The Spearman's correlation method revealed several relationships between the variables, suggesting the potentially governing metabolic pathways, which turned out to involve both hydrogenogenic pathways and competing reactions.

Effect of ultrasonication on anaerobic degradability of solid waste digestate.

This paper evaluates the effect of ultrasonication on anaerobic biodegradability of lignocellulosic residues. While ultrasonication has been commonly applied as a pre-treatment of the feed substrate, in the present study a non-conventional process configuration based on recirculation of sonicated digestate to the biological reactor was evaluated at the lab-scale. Sonication tests were carried out at different applied energies ranging between 500 and 50,000kJ/kg TS. Batch anaerobic digestion tests were performed on samples prepared by mixing sonicated and untreated substrate at two different ratios (25:75 and 75:25 w/w). The results showed that when applied as a post-treatment of digestate, ultrasonication can positively affect the yield of anaerobic digestion, mainly due to the dissolution effect of complex organic molecules that have not been hydrolyzed by biological degradation. A good correlation was found between the CH4 production yield and the amount of soluble organic matter at the start of digestion tests. The maximum gain in biogas production was 30% compared to that attained with the unsonicated substrate, which was tentatively related to the type and concentration of the metabolic products.

The influence of iron concentration on biohydrogen production from organic waste via anaerobic fermentation.

Different micronutrients are essential for bacterial fermentative metabolism. In particular, some metallic ions, like iron, are able to affect the biological H2production. In this study, batch tests were carried out in stirred reactors to investigate the effects of Fe²âº concentration on fermentative H2production from two different organic fractions of waste: source-separated organic waste (OW) from a composting plant including organic fraction of municipal solid waste and food waste (FW) from a refectory. Iron supplementation at 1000 mg/L caused twofold increment in the cumulative H2production from OW (922 mL) compared with the control (without iron doping). The highest H2production (1736 mL) from FW occurred when Fe²âº concentration was equal to 50 mg/L. In addition, the process production from OW was modelled through the modified Gompertz equation. For FW, a translated Gompertz equation was used by the authors, because the initial lag-time for H2production from FW was almost negligible.

Development and calibration of a model for biohydrogen production from organic waste.

Existing models for H2 production are capable of predicting digester failure caused by a specific disturbance. However, they are based on studies using simple sugars, while it is known that H2 production and fermentation kinetics vary with the composition and characteristics of the substrate used. Because the behaviour of biological processes may differ significantly when the digesting material is a complex matrix, such as organic waste, the aim of this study was to develop and calibrate a mathematical model for the prediction of hydrogen production on the basis of the results obtained from a laboratory scale experimental study using source-selected organic waste. The calibration was carried out for the most important kinetic parameters in mesophilic anaerobic digestion processes and also served as a sensitivity analysis for the influence of both the specific growth rate (µmax and the half velocity constant (k(s)), both of which are strongly dependant on the substrate used. High values of µmax led to a shorter lag-time and to an overestimate of the cumulative final H2 production relative to the experimentally measured production. Additionally, high values of ks associated with amino acid and sugar fermentation corresponded to a lower rate of substrate consumption and to a greater lag-time for growth of hydrogen-producing microorganisms. In this case, a lower final H2 production was predicted than that which was experimentally observed. Because the model development and calibration provided useful information concerning the role of the kinetic constants in the analysis of a fermentative H2 production process from organic wastes, they may also represent a good foundation for the analysis of fermentative H2 production from organic waste for pilot and full-scale applications.

Biodegradation of 3-chlorophenol in a sequencing batch reactor.

The present paper shows the results obtained through a study on the biodegradation of 3-chlorophenol (3-CP) in a Sequencing Batch Reactor (SBR). To such a purpose a lab-scale SBR was fed a synthetic wastewater containing 3-CP and nutrients (nitrogen and phosphorus) diluted in tap water. The operating strategy, in terms of both the duration of either the cycle or the react phase, was changed throughout the experimental activity in order to find out the optimal one allowing to ensure constant and high removal efficiency despite the increasing 3-chlorophenol concentration in the feed. Biomass collected from a full-scale continuous flow activated sludge facility treating domestic wastewater was used as seed, after being acclimated to 3-CP by means of several batch tests. The results showed that a periodically operated activated sludge system can be successfully used for the biodegradation of chlorophenol compounds, after the needed members of the microbiological consortium are selected and enriched.

Fast determination of phenols in contaminated soils.

An extraction method for the determination of phenols in contaminated soils, based on the application of solid-phase microextraction (SPME) coupled with GC-flame ionization detection analysis, was developed and tested. This method was developed using a natural soil spiked with phenol to a concentration level typical of an acute contamination event that can occur in an industrial site. The effects of the extraction parameters (pH, extraction time and salt concentration) on the extraction efficiency were studied and the method was then applied to determine the pollutant concentration at the beginning and during the biological treatment of a soil, contaminated with phenol and 3-chlorophenol, respectively. The SPME results were validated by comparison with those obtained with an US Environmental Protection Agency certified extraction method. The SPME method was also successfully applied to the determination of the adsorption behavior of 3-chlorophenol on a natural clay soil and was shown to be suitable for different matrices and phenolic compounds. Application of SPME technique results in a sharp reduction of the extraction times with negligible solvent consumption.