1,721,139 research outputs found
Coupling acid pretreatment and dosing of Ni and Se enhances the biomethane potential of hazelnut skin
No full textThis study offers new insights and promising perspectives in view of the energy valorization of hazelnut skin (HS) as a potential feedstock for renewable biomethane production. The process originally comprised the coupling of chemical pretreatments and individual dosing of cobalt (Co), nickel (Ni) and selenium (Se) as enhancement strategies of the biochemical methane potential (BMP) of HS. The anaerobic digestion (AD) of the untreated HS resulted in a biomethane production of 299 ± 3 mL CH4·g VS−1. This was not positively nor negatively influenced by the addition of the three trace elements (TEs). Performing a 1% H2SO4 pretreatment on HS, a 104% increase of the biomethane yield (i.e. 612 ± 20 mL CH4·g VS−1) was obtained. Under the same pretreatment conditions, a peak of 66.2 mg HAc g VS−1 of total volatile fatty acids (VFAs) was achieved. The BMP of the H2SO4-pretreated HS was further improved by 12 and 16% through the addition of 90 μg Ni·g TS−1 and 270 μg Se·g TS−1 of HS, respectively. The application of a 1.6% NaOH pretreatment on HS led to a 41% higher BMP (i.e. 423 ± 24 mL CH4·g VS−1) compared to that achieved with the untreated material. However, not statistically significant effects were observed when dosing the TEs. In conclusion, a positive synergy between chemical pretreatments and TE supplementation was only observed with the H2SO4- pretreated HS. This was due to the higher VFA production and the more effective VFA conversion to methane in the presence of Ni and Se
Biological inverse fluidized-bed reactors for the treatment of low pH- and sulfate-containing wastewaters under different COD/SO42- conditions.
No full textThe feasibility of removing sulfate using low-density polypropylene beads as carrier material in two lactate-fed sulfidogenic inverse fluidized-bed reactors was investigated. Two different COD/sulfate ratios and two different feed-sulfate concentrations were used for the operation of the reactors. During the 242 days of operation, the robustness of the system was studied by suddenly decreasing the feed pH to 3.00. A 10% fluidization degree was used since the carrier material adopted showed not to be adequate to attain a satisfactory immobilization of the biomass with higher fluidization degrees. This resulted in a failure of the process when the feed pH was intentionally decreased to 3.00 in reactor 2, operated with a COD/sulfate ratio of 4.00. On the contrary, when a slightly acidic feed solution was fed to reactor 2, a 97% sulfate reduction efficiency was obtained. In reactor 1, operated with a COD/sulfate ratio of 0.67 throughout the experiment, COD removal and sulfate reduction efficiencies reached the highest values of 75% and 35%, respectively. Higher efficiencies were not achieved also due to the accumulation of acetate and the most likely presence of microbial competition between sulfate reducers and other microorganisms
Column leaching of low-grade sulfide ore from Zijinshan copper mine
No full textCopper and iron dissolution of Zijinshan low-grade copper sulfide ores was investigated in ore-packed columns. At 60 degrees C and pH 1.0, 37.1 g Fe(III) L-1 permitted effective copper dissolution and inhibited the activity of iron-oxidizing microorganisms. At 30 degrees C, microorganisms stimulated Fe(II) and pyrite oxidation, resulting in 85 and 54% of copper and pyrite extraction yields, respectively. Bacteria belonging to the genera Acidithiobacillus and Leptospirillum were dominant as observed by real-time PCR assay. Aeration and inoculation of columns were not necessary. Solutions had a higher pH of 1.7 in the columns operated without recirculation. Under these conditions, copper extraction was not affected and Fe(III) precipitated as jarosite, indicating a novel method for iron control in Zijinshan copper mine. (c) 2015 Elsevier B.V. All rights reserved
Enhanced lignocellulosic component removal and biomethane potential from chestnut shell by a combined hydrothermal–alkaline pretreatment
No full textThis study proposes new perspectives for the management and biorefinery of wastes deriving from the agri–food sector such as chestnut shell (CS), which was here used as an organic feedstock for biomethane production through anaerobic digestion (AD). 1–5% alkaline (i.e. NaOH and KOH), hydrothermal (i.e. at 100 °C) and combined hydrothermal–alkaline pretreatments were employed to enhance the CS biodegradability prior to biochemical methane potential (BMP) tests conducted under mesophilic conditions. The hydrothermally–pretreated CS with 3% NaOH achieved the highest biomethane yield of 253 (±9) mL CH4·g VS−1 coupled to a volatile solid reduction of 48%. The hydrothermal–alkaline pretreatment positively affected both delignification and hemicellulose polymerization, promoting an approximately 2.4–fold higher substrate biodegradability compared to the untreated CS, which only reached a CH4 production of 104 (±5) mL CH4·g VS−1. AD proceeded via volatile fatty acid accumulation, subsequently followed by methane production that was effectively simulated via the modified Gompertz kinetic having a R2 of 0.974–0.999. Among the physical–chemical parameters characterizing the CS, the soluble chemical oxygen demand (sCOD) was highly correlated with the BMP showing a Pearson coefficient of 0.952. The cumulative biomethane yield, the sCOD and the cellulose, hemicellulose and lignin amount of CS were also processed through the least square method, obtaining a useful regression equation to predict the BMP. The economic assessment indicated that the hydrothermal–alkaline pretreatment is a cost–effective method to improve the BMP of CS, also for future full–scale applications
Impact of Ni2+ on denitrification of mining waters in fluidized-bed reactors
No full textIn mining processes, nitrate is released into the environment due to the use of N-based explosives and leaching agents such as cyanide. The present study assessed the effect of Ni on denitrification in fluidized-bed reactors (FBRs) at 7-8 and 22oC. In absence of nickel, the feed acidic pH was neutralized due to the pH buffering produced by denitrification and the FBR internal recycling. At feed pH of 2.5 and 5.5 mg/L of Ni, nitrate and nitrite removals were not inhibited. However, effluent pH decreased to 5.0. At feed pH of 5.5, denitrification was efficiently maintained even at 100 mg/L Ni, resulting in complete nitrate removal and stable effluent pH of 7.1. In summary, denitrification tolerated high nickel concentrations demonstrating to be suitable for mining water treatment
Nitrification of arsenic-containing mining waters
No full textThe oxidation of arsenic-containing minerals in mine sites results in the spreading of arsenic into the environment. In gold mining, arsenic often co-occurs with ammonium deriving from the degradation of cyanide used for gold recovery. In the present work, batch bioassays were used for assessing the feasibility of maintaining nitrification in presence of arsenic. Ammonium was completely oxidized even at total As concentrations up to 100 mg/L. At 150 and 200 mg/L of dissolved As, nitrification was partially inhibited resulting in 75% of ammonium oxidation. As(III) was chemically oxidized to As(V) during the first 3h alleviating nitrification. Candidatus Nitrospira defluvii and other species belonging to Nitrospirae were the main nitrifying microbial species revealed by PCR/DGGE analyses. In summary, microorganisms tolerated high As levels making nitrification a potent process for ammonium oxidation in mining waters
Influence of liquid-phase hydrogen on dark fermentation by Thermotoga neapolitana
No full textHydrogen is a strong inhibitor of dark fermentation. We aimed at directly correlating the hydrogen production by Thermotoga neapolitana with the supersaturation of hydrogen in the liquid phase (H2aq), which is often disregarded. Different agitation speeds, biogas recirculation and bubble induction by AnoxKTM K1 carrier were tested to prevent the supersaturation of H2aq. At 100 rpm agitation, the H2aq was 29.7 (± 1.4) mL/L, which is 3-times higher than 9.7 mL/L, i.e. the equilibrium concentration given by Henry’s law. Increasing the agitation speed up to 600 rpm reduced the H2aq until 8.5 (± 0.1) mL/L in 2 h and increased the hydrogen production rate (HPR) from 39 (± 2) mL/L/h at 0 rpm to 198 (± 4) mL/L/h at 600 rpm. Similar to 600 rpm, biogas recirculation and the presence of K1 carrier at 200 rpm maintained the H2aq below the equilibrium concentration. This study demonstrates the reciprocal influence of HPR and H2aq and revealed an inverse nonlinear correlation between the two parameters. Therefore, we conclude that an adequate gas-liquid mass transfer, efficiently provided by biogas recirculation or the presence of solid materials (e.g. a biomass carrier), is essential to remove H2 from the liquid phase and prevent H2 supersaturation
Novel photo-chemoautotrophic system combining microalgae and hydrogen oxidizing bacteria for microbial protein production from carbon dioxide
Full text linkThis study investigated the production of microbial protein (MP) using a novel microbial consortium composed of microalgae and hydrogen-oxidizing bacteria (HOB). This photo-chemoautotrophic consortium was aimed at capturing and valorising carbon dioxide (CO2) while overcoming typical limitations of each microbial group. Batch tests were run under varying gas mixtures of oxygen (O2), CO2 and hydrogen (H2) to assess process performance in terms of biomass growth, nitrogen assimilation, gas consumption, final biomass and microbial community composition. The consortium was compared to the single microalgae and HOB cultures grown under photo- and chemoautotrophic conditions, respectively. The consortium achieved significant growth (5.5 g VSS/L) under a non-explosive gas mixture, reaching a protein content of 40.3 ± 8.5 %. The consortium achieved up to 1.8- and 10-times higher biomass growth compared to the single microalgae and HOB cultures, respectively, showing a higher CO2 consumption and stimulating photosynthetic O2 production
Ammonia stripping from buffalo manure digestate for future nitrogen upcycling into bio-based products
No full textMitigating ammonia emissions from the livestock sector offers the opportunity to combine environmental protection with resource recovery through emerging circular bioeconomy approaches. In this work, we tested the potential of low-rate stripping techniques to enable techno-economically feasible nitrogen recovery and valorization from buffalo manure digestate. The proposed process achieved more than 80% ammonia stripping at mild temperatures (35-55 °C) and without the need of caustic agents to increase pH. Coupling such low-rate ammonia stripping with innovative biological resource valorization processes could offer interesting future perspectives
Phenanthrene biodegradation in a fed–batch reactor treating a spent sediment washing solution: Techno–economic implications for the recovery of ethanol as extracting agent
No full textThe continuous dredging of sediments contaminated by polycyclic aromatic hydrocarbons such as phenanthrene (PHE) has required the employment of high–efficiency technologies, including sediment washing (SW). However, the large amount of generated spent SW effluents requires the development of effective, eco–friendly and cost–saving approaches, which can tackle the waste formation in favor of the recovery of chemicals. This study proposes the treatment of a spent SW solution containing ethanol (EtOH) as extracting agent, by testing different initial PHE concentrations (i.e. 20–140 mg L−1) within six consecutive cycles in a fed–batch bioreactor under aerobic conditions. The biological process achieved a PHE removal of 63–91% after the enrichment of PHE–degrading bacteria and the proper supplementation of nutrients, and was mainly affected by the initial PHE concentration value and the excessive decrease of pH and dissolved oxygen. Achromobacter, Sphingobacterium and Dysgonomonas genera were mainly involved in PHE degradation, which followed a first–order kinetic model (R2 = 0.652–0.928) with a degradation rate and half–life time of 0.127–1.177 d−1 and 0.589–2.912 d, respectively. A techno–economic assessment revealed that a virtuous operation of SW, EtOH recovery and biodegradation of the SW solution can allow the recovery of up to 1.35 tons of EtOH per ton of remediated sediment and the decrease of the overall costs by 50%
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