Manometric monitoring of biological denitrification

A simple, automated manometric method is here discussed and applied to perform batch experiments for the stoichiometric and kinetic characterization of biological denitrification. The main strength of the proposed methodology is that it requires simple instrumentation, which is usually available in wastewater treatment plant laboratories, being it used in BOD and in BMP tests. The experimental setup consists of a glass bottle, a mixing and termostated system and a manometric bottle-head which can measure and log the overpressure that is caused by denitrified N2. At first, tests were conducted to determine the repeatability of the method; they were performed under low Food-to-Biomass ratio and with both endogenous and externally dosed carbon sources. Later, experimental procedures were performed to assess (1) the anoxic growth yield, (2) the endogenous anoxic decay rate; (3) the anoxic growth rate on acetate; (4) the fraction of anoxic active biomass in the sludge sample. Sludge samples for all these tests were taken from two WWTPs and 6 to 10 replicates were performed each time. Results indicated that the testing procedures is well repeatable and reliable and resulting estimates were within reported literature values

Zymomonas mobilis: biomass production and use as a dough leavening agent

Zymomonas mobilis ferments only glucose, fructose and sucrose via the Entner-Doudoroff pathway, providing an equimolar mixture of ethanol and CO2 and theoretically, as for Saccharomyces cerevisiae, the gas evolved can be used to leaven a dough. However, the capability of Z. mobilis to produce CO2 has rarely been exploited. In the present study we first evaluated the growing performance of two Z. mobilis strains (DSMZ 424 and 3580) in a culture medium lacking yeast extract, with added glucose or fructose (20 and 50 g/L) comparatively; the results demonstrated that biomass yield is 50 % higher with glucose. The best conditions were up-scaled, obtaining a biomass yield of 1.3\u20131.4 g dcw/L in a 14-L fermenter. Leavening trials performed in a model system with the biomass collected from fermenters after 9 or 16 h incubation evidenced that Z. mobilis can leaven a model dough as S. cerevisiae does, and showing a CO2 production rate (9\u201311 mL g dcw 121 min 121) statistically higher than that of S. cerevisiae (6\u20137 mL g dcw 121 min 121), especially when using 9-h-grown biomass. Bakery products leavened with Z. mobilis could thus be available to people with adverse responses to the ingestion of bakery food, providing innovation in the area of yeast-free leavened baked goods

Alkaline pretreatment of sorghum and wheat straw for increasing methane production

The aim of this study was to determine the effect of alkaline pretreatment on fiber composition,biodegradability and methane production rate of sorghum forage and wheat straw. Samples were treated at 40 \ub0C for 24 h with a sodium hydroxide solution. The specific dosages were 1, 3 and 10gNaOH/100gTS. By increasing the alkaline dosage, a reduction in the total fiber content and an increase in COD solubilization is observed. Total sugars content increased up to five times at the highest alkaline dosage with respect to control samples, proving that alkali pretreatment improves substrate swelling and hydrolysis of hemicellulose. Biochemical methane production tests showed that the chemical pretreatment increased both the ultimate anaerobic biodegradability and the methanization rate. The ultimate biodegradability was increased from 66 to 86% for sorghum and from 56 to 72% for wheat straw. The first order kinetic constant for methane production was increased by 33% (from 0.21 to 0.28 d-1) for sorghum and by 170% (from 0.10 to 0.27 d-1) for wheat straw

Effect of sodium hydroxide pretreatment on physical, chemical characteristics and methane production of five varieties of sorghum

Sorghum bicolor [L] Moench, represents an interesting substrate for methane production. The aim of this study was to evaluate the effect of alkaline pretreatment on chemical composition, physical structure and methane production of five varieties of sorghum (S1, S2, S3, S4, and S5). The pretreatment was conducted in closed bottles, at 55 degrees C for 12 h. Samples were soaked in a NaOH solution at 4 and 10 gNaOH/100 gTS, with a solid concentration of 35 gTS/L. Sodium hydroxide pretreatment led to a reduction of lignin (50 -70%), hemicelluloses (18-35%), cellulose (16-45%) and galacturonic acids (up to 100%), for all varieties of sorghum, as also confirmed by Fourier transform infrared spectroscopy analyses. The reduction of lignin content and thereafter the solubilization of cellulose and hemicelluloses, previously observed, can accelerate the disintegration and the hydrolysis steps during anaerobic digestion. Indeed, an increase in the first order kinetic constant was observed by increasing the alkaline dosage (by 40%, 61%, 64%, 54%, and 40% for sorghum S1, S2, S3, S4, and S5, respectively). Nevertheless, the sodium hydroxide pretreatment had no positive effect in enhancing the methane yields (270 +/- 13, 335 +/- 11, 294 +/- 1, 327 +/- 9 and 303 +/- 24 mL CH4/gVS for S1, S2, S3, S4 and 55, respectively)

Benefit of sodium hydroxide pretreatment of ensiled sorghum forage on the anaerobic reactor stability and methane production

The assessment of the pretreatment effect on the anaerobic digestion process is generally based on the results of batch tests, which may fail in truly predicting full-scale anaerobic reactors performance. Therefore, in this study, the effect of alkaline pretreatment on the anaerobic digestion of ensiled sorghum forage was evaluated by comparing the results of two semi-continuous CSTR (Continuously Stirred Tank Reactor) anaerobic reactors. Results showed that an alkaline pretreatment step, prior to the anaerobic digestion of ensiled sorghum forage, can have a beneficial effect both in enhancing methane production (an increase of 25% on methane production was observed, if compared to that of untreated sorghum) and in giving more stability to the anaerobic digestion process

Influence of alkaline pre-treatment conditions on structural features and methane production from ensiled sorghum forage

Alkaline pre-treatment has been widely applied to lignocellulosic biomass but the tested conditions are quite variable in literature. Results are also quite scattered even when similar substrates are compared. Therefore the aim of this study was to test different alkaline dosages (4% and 10% gNaOH/gTS), temperatures (40 °C and 55 °C), and contact times (12 h and 24 h) in order to investigate the influence of the pre-treatment conditions on the structural features and methane production from ensiled sorghum forage. This study confirms the positive effect of NaOH pre-treatment on fibre reduction, total organic carbon and proteins solubilisation, and thereafter the anaerobic degradability of ensiled sorghum forage. An increase in methane yield, with respect to untreated sample (from 8% to 19%), was observed at all pre-treatment conditions tested. Nevertheless, no significant differences on methane yield were observed by varying NaOH dosage, temperature, and contact time. The increase of sodium hydroxide dosage led to an increase of the soluble total organic carbon (TOC) (from 12% to 29%) and proteins (from 56% to 72%), at each temperature and contact time tested. By increasing the NaOH dosage, a reduction of hemicelluloses (from 37% to 70%) and lignin contents (from 26% to 70%), and an increase of the anaerobic digestion kinetics (with a maximum increase of 43% for samples treated at 55 °C for 24 h), were also observed. Finally, the anaerobic digestion kinetics were improved with the increase of contact time (up to 13%) and temperature (up to 20%)

Alkaline pretreatment of sorghum and wheat straw for increasing methane production

The aim of this study was to determine the effect of alkaline pretreatment on fiber composition,biodegradability and methane production rate of sorghum forage and wheat straw. Samples were treated at 40 \ub0C for 24 h with a sodium hydroxide solution. The specific dosages were 1, 3 and 10gNaOH/100gTS. By increasing the alkaline dosage, a reduction in the total fiber content and an increase in COD solubilization is observed. Total sugars content increased up to five times at the highest alkaline dosage with respect to control samples, proving that alkali pretreatment improves substrate swelling and hydrolysis of hemicellulose. Biochemical methane production tests showed that the chemical pretreatment increased both the ultimate anaerobic biodegradability and the methanization rate. The ultimate biodegradability was increased from 66 to 86% for sorghum and from 56 to 72% for wheat straw. The first order kinetic constant for methane production was increased by 33% (from 0.21 to 0.28 d-1) for sorghum and by 170% (from 0.10 to 0.27 d-1) for wheat straw

Sodium hydroxide pretreatment of ensiled sorghum forage and wheat straw to increase methane production

The aim of this study was to determine the effect of sodium hydroxide pretreatment on the chemical composition and the methane production of ensiled sorghum forage and wheat straw. NaOH pretreatment was conducted in closed bottles, at 40 WC for 24 h. Samples were soaked in a NaOH solution at different dosages (expressed in terms of total solids (TS) content) of 1 and 10% gNaOH/gTS, with a TS concentration of 160 gTS/L. At the highest NaOH dosage the reduction of cellulose, hemicelluloses and lignin was 31, 66 and 44%, and 13, 45 and 3% for sorghum and wheat straw, respectively. The concentration of soluble chemical oxygen demand (CODs) in the liquid phase after the pretreatment was also improved both for wheat straw and sorghum (up to 24 and 33%, respectively). Total sugars content increased up to five times at 10% gNaOH/gTS with respect to control samples, suggesting that NaOH pretreatment improves the hydrolysis of cellulose and hemicelluloses. The Biochemical Methane Potential (BMP) tests showed that the NaOH pretreatment favoured the anaerobic degradability of both substrates. At 1 and 10% NaOH dosages, the methane production increased from 14 to 31% for ensiled sorghum forage and from 17 to 47% for wheat straw. The first order kinetic constant increased up to 65% for sorghum and up to 163% for wheat straw

Effect of particle size on alkaline pretreatment and methane production of ensiled sorghum forage.

Residual and dedicated energy crops, such as sorghum, are suitable substrates for anaerobic digestion in agricultural biogas plants. However, their complex structure justifies the use of a pretreatment to improve their anaerobic biodegradability. Thus, the aim of this study was to investigate the impact of particle size reduction on structural changes and methane production from ensiled sorghum forage, with and without the addition of sodium hydroxide. Sorghum samples were ground into particles with mean diameters of 994, 471, 269 and 169 μm. Milled samples with 471 and 169 μm particle sizes were soaked in a NaOH solution at 10% gNaOH/gTS dosage and maintained at 55°C for 12 h. BMP tests were performed on all samples. All results are discussed both in terms of specific methane production and kinetic constants. The main conclusion is that milling did not improve methane production (275.3± 3.5 mLCH4/gVS) nor kinetic constants (0.11±0.01 d-1) between 994 and 169 μm. On the contrary, by adding sodium hydroxide, an increase in both methane yield (324.5±0.7 mLCH4/gVS) and kinetic constants (0.16 ± 0.00 d-1) was observed, but these results were not influenced by the particle size. Chemical and infra red spectroscopy (FTIR) analysis were performed to characterize the samples and explain these results