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

Dry chemo-mechanical pretreatments of lignocellulosic biomass: impact on energy consumption, enzymatic hydrolysis and bioethanol yields

The high crude oil prices, the decline of fossil fuel reserves and the increase of greenhousegas emissions are motivating the development of biorefineries that produce energy fromrenewable resources (i.e. lignocellulosic biomass). However, the key driver for the successfulconversion of biomasses into biofuels is the selection of efficient pretreatments that permit tomaximize the sugars recovery and to minimize the consumption of water, chemicals andenergy. This study proposes the application of “dry” chemo-mechanical pretreatments thatpermit to enhance enzymatic hydrolysis and thereafter bioethanol production fromlignocellulosic biomasses.In a first experiment, wheat straw was pretreated with NH3, NaOH, NaOH-H2O2 and NH3-H2O2 at both high (5 kg L-1) and at low (0.2 kg L-1) biomass concentrations, named “dry” and“diluted” pretreatments. Then, untreated and pretreated samples were subjected to centrifugaland ball milling, followed by enzymatic hydrolysis. Compared to diluted mechano -NaOHpretreatments, dry mechano -NaOH and -NaOH-H2O2 were found to be more effective indecreasing the particle size (up to 55%), increasing the surface area (up to 88%) anddecreasing the total energy requirement (up to 50%). Enzymatic hydrolysis was enhanced bypretreatments, as suggested by higher glucose yields (332, 320, 140, 322, 141 g glucose kg-1biomass for diluted –NaOH, dry – NaOH, dry -NH3, dry -NaOH-H2O2 and dry -NH3-H2O2,respectively), compared to that of untreated wheat straw (118 g glucose kg-1). However, lowerenergy efficiency was obtained for dilute mechano -NaOH treatment, compared to drymechano -NaOH treatments.In a second experiment, sugarcane bagasse was pretreated with NaOH and H3PO4 at highbiomass concentration (5 kg L-1) and then milled by using different methods, such asvibratory milling (VBM), ball milling (BM) and centrifugal milling (CM). Results indicatethat NaOH-BM and NaOH-VBM was preferred to enhance glucose yields and bioethanolproduction (up to 76%), while CM consumed 75% and 58% lesser energy than BM and VBM,respectively. The highest energy efficiency was obtained with NaOH-CM. Therefore, thecombination of dry NaOH and CM appears the most suitable and interesting pretreatment forthe production of bioethanol from SB

Bioethanol fermentation as alternative valorization route of agricultural digestate according to a biorefinery approach

This study investigates the feasibility of producing bioethanol from solid digestate after a mechanical fractionation (i.e. centrifugal milling), in order to improve the energy recovery from agricultural wastes and the sustainability of anaerobic digestion plants. A bioethanol yield of 37 g kg−1 TS was evaluated for the solid digestate fraction. Mass and energetic balances were performed and compared between two scenarios: (A) one-stage bioethanol fermentation and (B) two-stage anaerobic digestion–bioethanol fermentation, in order to evaluate the feasibility and the advantages of the two-stage process. Results revealed that, compared to the one-stage process, the dual anaerobic digestion–bioethanol process permitted: (i) to diversify biofuels production; (ii) to provide the thermal energy sufficient for drying digestate (13,351 kWhth day−1), for the subsequent milling step; (iii) to reduce the electric energy requirement for the milling step (from 23,880 to 3580 kWhel day−1); (iv) to produce extra electrical energy of 8483 kWhel day−1; (v) to improve the reduction of waste streams generated (from 13% to 54% of organic matter removal)

Comparison of Dry Versus Wet Milling to Improve Bioethanol or Methane Recovery from Solid Anaerobic Digestate

Biogas plants for waste treatment valorization are presently experiencing rapid development, especially in the agricultural sector, where large amounts of digestate are being generated. In this study, we investigated the effect of vibro-ball milling (VBM) for 5 and 30 min at a frequency of 20 s−1 on the physicochemical composition and enzymatic hydrolysis (30 U g−1 total solids (TS) of cellulase and endo-1,4-xylanase from Trichoderma longibrachiatum) of dry and wet solid separated digestates from an agricultural biogas plant. We found that VBM of dry solid digestate improved the physical parameters as both the particle size and the crystallinity index (from 27% to 75%) were reduced. By contrast, VBM of wet solid digestate had a minimal effect on the physicochemical parameters. The best results in terms of cellulose and hemicelluloses hydrolysis were noted for 30 min of VBM of dry solid digestate, with hydrolysis yields of 64% and 85% for hemicelluloses and cellulose, respectively. At the condition of 30 min of VBM, bioethanol and methane production on the dry solid separated digestate was investigated. Bioethanol fermentation by simultaneous saccharification and fermentation resulted in an ethanol yield of 98 geth kg−1 TS (corresponding to 90% of the theoretical value) versus 19 geth kg−1 TS for raw solid digestate. Finally, in terms of methane potential, VBM for 30 min lead to an increase of the methane potential of 31% compared to untreated solid digestate

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

Thermo-chemical pretreatments for the combined recovery of extractives and bioethanol production from Douglas-fir bark

The presence of bark in wood can constitute a serious limitation for the bioconversion of forest residues into bioethanol, especially due to the presence of high content of extractives, which may inhibit ethanol fermentation. However, a perfectly debarked wood chip may not represent an economical source of carbohydrates for industrial applications. An option is to utilise bark as a source of renewable energy and chemicals, within a biorefinery platform. In this study, enzymatic hydrolysis and bioethanol fermentation of Douglas-fir bark were studied before and after organosolv and diluted acid pre-treatments performed at 150°C and 180°C. The recovery of valuable platforms molecules was also determined after pre-treatment. Results showed that an organosolv-free acid pre-treatment performed at 150°C gave the best results in terms of platforms molecules recovery (40% w/w) and bioethanol yield (2 g.100g-1 total solids). However, the low glucose and ethanol yields obtained (6% and 16% of the theoretical values, respectively) confirmed that enzymatic hydrolysis remains the limiting step of bioethanol fermentation from bark. Interestingly, ethanol was produced without inhibition of fermentation from the untreated and pretreated substrates

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 1.3–1.4 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 (9–11 mL g dcw−1 min−1) statistically higher than that of S. cerevisiae (6–7 mL g dcw−1 min−1), 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

A new concept for enhancing energy recovery from agricultural residues by coupling anaerobic digestion and pyrolysis process

In a full-scale anaerobic digestion plant, agricultural residues are generally converted into biogas and digestate, the latter usually produced in large amount. Generally, biogas is converted into heat, often lost, and electricity, which is completely valorized or it is sold to the public grid. In this context, the aim of this study was to investigate the feasibility to combine anaerobic digestion and pyrolysis processes in order to increase the energy recovery from agricultural residues and the sustainability of the anaerobic digestion plant. Results revealed that heat excess produced during anaerobic digestion could cover the drying needs for the solid digestate, while pyrolysis of digestate at 500 °C resulted in 8.8 wt.%, 58.4 wt.% and 32.8 wt.% of syngas, oil and char, respectively. The LHV of syngas was 15.7 MJ N m−3, whereas pyrolysis oil exhibited a HHV of 23.5 MJ kg−1 after water extraction. The hybrid system operating in symbiosis could increase the production of electricity from 9896 kWhel day−1 to 14,066 kWhel day−1 corresponding to an increase of 42% compared to AD stand-alone plant