Factor-based assessment of continuous bio-H2 production from cheese whey.

Despite having been widely investigated, dark fermentative H2 production from organic residues is still limited by process-related issues which may hamper the perspectives of full-scale process implementation. Such constraints are mainly due to the process complexity, which is largely affected by multiple and often mutually interacting factors. In the present work, the results of continuous fermentative H2 production experiments using synthetic cheese whey as the input substrate were used to gain detailed knowledge of the process features and identify suitable and critical operating conditions. Specifically, innovative process interpretation involved a combination of analytical characterization of the fermentation broth, mass balance calculations and statistical methods (correlation and principal component analyses) to derive systematic considerations for process characterization and scale-up. The metabolic products mainly included acetate and butyrate, which however were likely to derive (in different proportions depending on the operating conditions) from both hydrogenogenic and competing pathways. For some tests, lactate and succinate were also found to have been formed. It was observed that the main features of the process (H2 yield and rate, stability condition) were correlated with the operational and analytical parameters. The first three principal components identified by the statistical analysis were able to account for: 1) the effect of retention time and total metabolites produced; 2) biogas (H2 and CO2) generation, butyrate production and stability condition; and 3) organic loading rate and propionate production. The results suggested that the main features of hydrogenogenic fermentation can be described by a reduced set of factors that may be usefully adopted for both process monitoring and prediction purposes.

Control of fermentation duration and pH to orient biochemicals and biofuels production from cheese whey.

Batch dark fermentation tests were performed on sheep cheese whey without inoculum addition at different operating pHs, relating the type and production yields of the observed gaseous and liquid by-products to the evolution of fermentation. Cheese whey fermentation evolved over time in two steps, involving an initial conversion of carbohydrates to lactic acid, followed by the degradation of this to soluble and gaseous products including short-chain fatty acids (mainly acetic, butyric and propionic acids) and hydrogen. The operating pH affected the production kinetics and yields, as well as the fermentation pathways. By varying the duration of the fermentation process, different cheese whey exploitation strategies may be applied and oriented to the main production of lactic acid, hydrogen or other organic acids.

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.

An experimental study on fermentative H2 production from food waste as affected by pH.

Batch dark fermentation experiments were performed on food waste and mixtures of food waste and wastewater activated sludge to evaluate the influence of pH on biological H2 production and compare the process performance with and without inoculum addition. The effect of a preliminary thermal shock treatment of the inoculum was also investigated as a means to harvest the hydrogenogenic biomass. The best performance in terms of both H2 generation potential and process kinetics was observed at pH=6.5 under all experimental conditions (no inoculum, and untreated or thermally treated inoculum added). H2 production from food waste was found to be feasible even without inoculum addition, although thermal pre-treatment of the inoculum notably increased the maximum production and reduced the lag phase duration. The analysis of the fermentation products indicated that the biological hydrogen production could be mainly ascribed to a mixed acetate/butyrate-type fermentation. However, the presence of additional metabolites in the digestate, including propionate and ethanol, also indicated that other metabolic pathways were active during the process, reducing substrate conversion into hydrogen. The plateau in H2 generation was found to mirror the condition at which soluble carbohydrates were depleted. Beyond this condition, homoacetogenesis probably started to play a role in the degradation process.

A review of dark fermentative hydrogen production from biodegradable municipal waste fractions.

Hydrogen is believed to play a potentially key role in the implementation of sustainable energy production, particularly when it is produced from renewable sources and low energy-demanding processes. In the present paper an attempt was made at critically reviewing more than 80 recent publications, in order to harmonize and compare the available results from different studies on hydrogen production from FW and OFMSW through dark fermentation, and derive reliable information about process yield and stability in view of building related predictive models. The review was focused on the effect of factors, recognized as potentially affecting process evolution (including type of substrate and co-substrate and relative ratio, type of inoculum, food/microorganisms [F/M] ratio, applied pre-treatment, reactor configuration, temperature and pH), on the fermentation yield and kinetics. Statistical analysis of literature data from batch experiments was also conducted, showing that the variables affecting the H2 production yield were ranked in the order: type of co-substrate, type of pre-treatment, operating pH, control of initial pH and fermentation temperature. However, due to the dispersion of data observed in some instances, the ambiguity about the presence of additional hidden variables cannot be resolved. The results from the analysis thus suggest that, for reliable predictive models of fermentative hydrogen production to be derived, a high level of consistency between data is strictly required, claiming for more systematic and comprehensive studies on the subject.

Combined use of a transformed red mud reactive barrier and electrokinetics for remediation of Cr/As contaminated soil.

A reactive barrier (RB) of transformed red mud (TRM), a by-product of the refinement of bauxite in alumina production, was placed adjacent to the anode of an electrokinetic (EK) system with the aim of enhancing removal of chromium or arsenic, added singly to a low permeability clayey soil, and favouring entrapment. The innovative study focused on evaluation of the synergic interaction between the EK system and the RB, and of the efficiency when compared to traditional EK remediation (control tests). The results obtained underlined the successful outcome of treatment of the Cr(VI)-contaminated soil. In presence of the TRM RB, 19.4% wt. of total Cr content was detected in the anolyte and 20.6% wt. trapped in the anodic RB after 6d, versus 6.6% wt. in the anolyte and 8.8% wt. in the soil adjacent to the anode following the control run without RB. On increasing duration of treatment up to 12d, 60.8% wt. of total initial Cr was found in the anolyte and 25.5% wt. trapped in the RB, versus 9.1% wt. and 5.3% wt., respectively, after a control run of the same duration. Finally, on increasing the mass of TRM in the RB, 60.6% wt. of initial Cr content was found to have accumulated in the RB, with Cr being completely absent from the anodic chamber. Conversely, combined treatment was much less effective on As contaminated soil, at least under the operative conditions applied. Low initial As concentration and interference with iron oxides in the soil were likely the reasons underlying low efficiency while attempting As decontamination.

Effects of the cometabolite/growth substrate ratio on the aerobic degradation of 4-monochlorophenol.

Chlorinated phenolic compounds like 4-monochlorophenol (4CP) are characterized by high toxicity even at relatively low concentrations and by strong persistency in both water and soils. Since cometabolism was proved to enhance 4CP biological removal, a conventional Sequencing Batch Reactor (SBR) was used in this study for the cometabolic aerobic degradation of 4CP at different influent concentrations and volumetric organic loading rates (40-50 mg/L and 0.129-0.323 kgCOD-4CP/m3·d, respectively), with sodium acetate (NaAc) as the growth substrate. The effects of different 4CP/NaAc ratios on SBR performances were evaluated in terms of 4CP removal efficiencies and maximum specific removal rates in order to maximize reactor performances: a decrease in NaAc dosage as external growth substrate would lead to definitely lower operating costs. A positive correlation was observed between 4CP maximum specific removal rates and the applied 4CP/NaAc ratios, thus making further reduction in NaAc dosage possible.

Acetate-fed aerobic granular sludge for the degradation of chlorinated phenols.

In this study, the possibility to use acetate-fed aerobic granular sludge for the degradation of low chlorinated 4-mono-chlorophenol (4CP) and highly chlorinated 2,4,6-tri- chlorophenol (TCP) was investigated. A Granulated Sequencing Batch Reactor (GSBR) was used to carry out the experiments, with acetate as growth substrate. 4CP concentration in the influent ranged between 0 and 50 mg/l, while TCP concentration varied between 0 and 15 mg/l. Different operating conditions were applied in order to obtain the complete aerobic degradation of 4CP. For TCP degradation, anaerobic feeding and control of dissolved oxygen concentration in the bulk liquid were used to keep the granules core under anaerobic conditions due to diffusion limitations: the possibility to obtain TCP reductive dechlorination under aerated conditions was thus investigated. Differences in granules shape and size were observed with 4CP and TCP dosed in the influent, and the effects of such toxic compounds on acetate removal were evaluated.Aerobic granules grown on acetate as carbon source proved to be an interesting solution for the degradation of 4CP, showing good resistance to high 4CP concentrations in the influent even if unacclimated. The presence of TCP did not irreversibly inhibit biomass activity, and complete TCP degradation was achieved after acclimation.

Two-phase anaerobic digestion within a solid waste/wastewater integrated management system.

A two-phase, wet anaerobic digestion process was tested at laboratory scale using mechanically pre-treated municipal solid waste (MSW) as the substrate. The proposed process scheme differs from others due to the integration of the MSW and wastewater treatment cycles, which makes it possible to avoid the recirculation of process effluent. The results obtained show that the supplying of facultative biomass, drawn from the wastewater aeration tank, to the solid waste acidogenic reactor allows an improvement of the performance of the first phase of the process which is positively reflected on the second one. The proposed process performed successfully, adopting mesophilic conditions and a relatively short hydraulic retention time in the methanogenic reactor, as well as high values of organic loading rate. Significant VS removal efficiency and biogas production were achieved. Moreover, the methanogenic reactor quickly reached optimal conditions for a stable methanogenic phase. Studies conducted elsewhere also confirm the feasibility of integrating the treatment of the organic fraction of MSW with that of wastewater.

Dynamic transformations of nitrogen during mechanical-biological pre-treatment of municipal solid waste.

Mechanical-biological pre-treatment (MBP) of municipal solid waste (MSW) has gained evidence as a practice capable of accomplishing the requirements for environmental sustainable landfilling. In particular, MBP is effective in reducing the ammoniacal nitrogen content in the leachate. However, few data are available on the modifications of the nitrogen forms occurring during MBP and on the role played by processes such as nitrification and generation of refractory organic compounds. The dynamic transformations of nitrogen were investigated during the MBP. MSW was mechanically and biologically pre-treated; samples were collected at different stages of the process and analysed to investigate the evolution of nitrogen forms; batch and column leaching tests were performed as well. The results indicate that nitrification is negligible and volatilization can only partially explain the low ammoniacal nitrogen content in the leachate. Incorporation of ammoniacal nitrogen into a refractory organic form was assessed and is likely to play an important role. The maximum content of refractory organic nitrogen in the solid waste was achieved after about 60 days of aerobic pre-treatment; therefore, the minimal duration of the MBP should be about 8-9 weeks in order to optimize the ammoniacal nitrogen incorporation, unless the waste is characterized by a low C/N ratio.