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 VS_AS/g TOC_FW]) 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 TOC_FW (pH = 7.5, ISR = 1.74) and 156-160 L H₂/kg TOC_FW (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 TOC_FW 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.

Application of accelerated carbonation on MSW combustion APC residues for metal immobilization and CO2 sequestration

The present study focuses on the application of an aqueous phase accelerated carbonation treatment on air pollution control (APC) residues from municipal solid waste combustion, aimed at assessing its influence on the environmental behaviour of the residue under concern, as well as the potential of the process in terms of sequestration of the CO2. APC residues are considered hazardous waste and must be treated before final disposal in order to achieve the immobilization/mobilization of critical contaminants such as heavy metals as well as mobilization of soluble salts. The treatment applied proved to be effective in reducing the mobility of Pb, Zn, Cr, Cu and Mo, the optimum final pH for the carbonated APC residues being in a range of 10-10.5, whilst a mobilization effect was noticed for Sb and no effect was assessed for chlorides. The effect of carbonation treatment on the contaminant release was further evaluated by means of a sequential extraction procedure, indicating that the distribution of contaminants on water soluble, exchangeable and carbonate fraction was modified after treatment. The CO2 sequestration potential assessed for the APC residues showed that the carbonation technology could be a technically viable option in order to reduce emissions from WtE plants.

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.

Landfill gas generation after mechanical biological treatment of municipal solid waste. Estimation of gas generation rate constants

Mechanical biological treatment (MBT) of residual municipal solid waste (RMSW) was investigated with respect to landfill gas generation. Mechanically treated RMSW was sampled at a full-scale plant and aerobically stabilized for 8 and 15 weeks. Anaerobic tests were performed on the aerobically treated waste (MBTW) in order to estimate the gas generation rate constants (k,y(-1)), the potential gas generation capacity (L(o), Nl/kg) and the amount of gasifiable organic carbon. Experimental results show how MBT allowed for a reduction of the non-methanogenic phase and of the landfill gas generation potential by, respectively, 67% and 83% (8 weeks treatment), 82% and 91% (15 weeks treatment), compared to the raw waste. The amount of gasified organic carbon after 8 weeks and 15 weeks of treatment was equal to 11.01+/-1.25kgC/t(MBTW) and 4.54+/-0.87kgC/t(MBTW), respectively, that is 81% and 93% less than the amount gasified from the raw waste. The values of gas generation rate constants obtained for MBTW anaerobic degradation (0.0347-0.0803y(-1)) resemble those usually reported for the slowly and moderately degradable fractions of raw MSW. Simulations performed using a prediction model support the hypothesis that due to the low production rate, gas production from MBTW landfills is well-suited to a passive management strategy.

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.

Engineering and environmental properties of thermally treated mixtures containing MSWI fly ash and low-cost additives

An experimental work was carried out to investigate the feasibility of application of a sintering process to mixtures composed of Municipal Solid Waste Incinerator (MSWI) fly ash and low-cost additives (waste from feldspar production and cullet). The proportions of the three constituents were varied to adjust the mixture compositions to within the optimal range for sintering. The material was compacted in cylindrical specimens and treated at 1100 and 1150 degrees C for 30 and 60 min. Engineering and environmental characteristics including weight loss, dimensional changes, density, open porosity, mechanical strength, chemical stability and leaching behavior were determined for the treated material, allowing the relationship between the degree of sintering and both mixture composition and treatment conditions to be singled out. Mineralogical analyses detected the presence of neo-formation minerals from the pyroxene group. Estimation of the extent of metal loss from the samples indicated that the potential for volatilization of species of Pb, Cd and Zn is still a matter of major concern when dealing with thermal treatment of incinerator ash.

Alpha-amino acid phenolic ester derivatives: novel water-soluble general anesthetic agents which allosterically modulate GABA(A) receptors

In the search for a novel water-soluble general anesthetic agent the activity of an alpha-amino acid phenolic ester lead, identified from patent literature, was markedly improved. In addition to improving in vivo activity in mice, good in vitro activity at GABA(A) receptors was also conferred. Within the series of compounds good enantioselectivity for both in vitro and in vivo activity was found, supporting a protein-mediated mechanism of action for anesthesia involving allosteric modulation of GABA(A) receptors. alpha-Amino acid phenolic ester 19, as the hydrobromide salt Org 25435, was selected for clinical evaluation since it retained the best overall anesthetic profile coupled with improved stability and water solubility. In the clinic it proved to be an effective intravenous anesthetic in man with rapid onset of and recovery from anesthesia at doses of 3 and 4 mg/kg.

Mesolimbic dopaminergic reduction outlasts ethanol withdrawal syndrome: evidence of protracted abstinence

Rats chronically administered with ethanol every six hours for six consecutive days show, upon suspension of treatment, a marked somatic withdrawal syndrome characterized by classical neurological signs. The emergence of the behavioral syndrome coincides with a profound decline of dopaminergic mesolimbic neuronal activity which corresponds to a reduction of dopamine outflow in the nucleus accumbens [Diana et al. (1993) Proc. natn. Acad. Sci. U.S.A. 90, 7966-7969]. However, while the behavioral manifestation of the ethanol withdrawal syndrome recedes in about 48 h, electrophysiological indices of mesolimbic dopaminergic function are still reduced 72 h after ethanol discontinuation, thus outlasting the physical signs of ethanol withdrawal syndrome. Dopaminergic neuronal activity is reintegrated by anti-craving drugs such as ethanol itself and gamma-hydroxybutyric acid. It is postulated that the reduced spontaneous activity of mesolimbic dopaminergic neurons may form the neural basis of the dysphoric state which accompanies abrupt interruption of chronic ethanol administration. Pharmacological manipulations of dopaminergic activity targeted at restoring "normal" dopaminergic function after ethanol withdrawal may lead to way to the experimental basis of new therapeutic strategies of alcoholism.

Profound decrease of mesolimbic dopaminergic neuronal activity in morphine withdrawn rats

The spontaneous neuronal activity of meso-accumbens dopaminergic neurons was recorded in unanesthetized rats withdrawn from chronic morphine administration (15 days) by means of single cell extracellular recording techniques coupled with antidromic identification from the nucleus accumbens. Twenty-four h after last morphine administration, firing rate and burst firing were found to be drastically reduced and the relative refractory periods of the same neurons were prolonged in morphine-dependent rats as compared with chronic saline-treated controls. The number of spontaneously active dopaminergic neurons, however, did not differ between the two groups. Administration of morphine restored electrophysiological parameters. When rats were tested 2 h after last morphine administration, i.v. challenge with the opiate antagonist naloxone caused an abrupt and virtually complete reduction of dopaminergic firing rate, burst rate and a prolongation of the relative refractory period. These effects were not observed in control rats. The results indicate that the mesolimbic dopaminergic system is tonically reduced in its activity during morphine withdrawal syndrome and considering its role in the reinforcing properties of opioids, its depressed activity during the morphine withdrawal syndrome may bear relevance for the dysphoric state associated to morphine withdrawal in humans.

Heterogeneous responses of substantia nigra pars reticulata neurons to gamma-hydroxybutyric acid administration

The effect of intravenous administration of gamma-hydroxybutyric acid (GHB) (50-400 mg/kg) on the firing rate of substantia nigra pars reticulata (SN-PR) neurons was studied by making single cell extracellular recordings in unanesthetized rats. For comparison, the effect of intravenous muscimol (0.5-2 mg/kg) and ethanol (0.5-2 g/kg) was also studied. GHB produced variable effects: dose-related inhibition in 7 out of 18 (38.8%) neurons and no significant change in 11 out of 18 (61.2%) neurons tested. In contrast, muscimol and ethanol produced a dose-related inhibition of the SN-PR firing rate. The results indicate that GHB, unlike muscimol and ethanol, has no profound effect on the activity of SN-PR neurons, and thus disinhibition of dopaminergic units, through inhibition of SN-PR neurons, is probably not the mechanism by which GHB stimulates the firing rate of dopaminergic neurons.

Marked decrease of A10 dopamine neuronal firing during ethanol withdrawal syndrome in rats

The electrophysiological activity of mesoaccumbens dopaminergic neurons was monitored during the ethanol-withdrawal syndrome in ethanol-dependent and in control rats. Spontaneous firing was reduced by about half in ethanol-dependent rats as compared to controls. Likewise, the number of spikes/burst was also reduced in ethanol-dependent rats. These results are consistent with the reduction in dopamine release observed during ethanol-withdrawal syndrome and may provide the basis for the aversive effects of the ethanol-withdrawal syndrome.

Secretion of growth hormone releasing hormone in obese children

We have evaluated baseline and l-dopa-stimulated peripheral growth hormone releasing hormone (pGHRH) secretion in 6 obese pre-pubertal children and in 7 age-matched controls. Baseline pGHRH levels were no different between obese (36.6 +/- 9.8 pg/ml, mean +/- SE) and control children (40.6 +/- 10.1 pg/ml). Administration of l-dopa (500 mg po) caused a significant increase of pGHRH levels in both the obese (65.3 +/- 19.8 pg/ml, p less than 0.05) and the control children (84.1 +/- 10.0 pg/ml, p less than 0.003). Mean peak pGHRH levels after l-dopa were not significantly different between the two groups, whereas mean peak GH levels were significantly lower (p less than 0.05) in the obese (7.9 +/- 1.9 ng/ml) than in the control children (20.5 +/- 4.9 ng/ml). We conclude that despite reduced GH secretion, obese children have normal baseline and l-dopa stimulated pGHRH levels.