Homoacetogenesis and solventogenesis from H2/CO2 by granular sludge at 25, 37 and 55 °C.

Abstract CO2 fermentation is a promising process to produce biofuels like ethanol. It can be integrated in third generation biofuel production processes to substitute traditional sugar fermentation when supplied with cheap electron donors, e.g. hydrogen derived from wind energy or as surplus gas in electrolysis. In this study, granular sludge from an industrial wastewater treatment plant was tested as inoculum for ethanol production from H2/CO2 via non-phototropic fermentation at submesophilic (25 °C), mesophilic (37 °C) and thermophilic (55 °C) conditions. The highest ethanol concentration (17.11 mM) was obtained at 25 °C and was 5-fold higher than at 37 °C (3.36 mM), which was attributed to the fact that the undissociated acid (non-ionized acetic acid) accumulation rate constant (0.145 h−1) was 1.39 fold higher than at 25 °C (0.104 h−1). Methane was mainly produced at 55 °C, while neither acetic acid nor ethanol were formed. Ethanol production was linked to acetic acid production with the highest ethanol to acetic acid ratio of 0.514 at 25 °C. The carbon recovery was 115.7%, 131.2% and 117.1%, while the electron balance was almost closed (97.1%, 110.1% and 109.1%) at 25 °C, 37 °C and 55 °C, respectively. The addition of bicarbonate inhibited ethanol production both at 25 °C and 37 °C. Clostridium sp. were the prevalent species at both 25 and 37 °C at the end of the incubation, which possibly contributed to the ethanol production

Effect of methanol-organosolv pretreatment on anaerobic digestion of lignocellulosic materials

Abstract Lignocellulosic materials are the most abundant biomass on the planet, representing a great opportunity for energy valorisation. This work investigated the effect of methanol-organosolv pretreatment on the methane production from hazelnut skin (HS), spent coffee grounds (SCG), and almond shell (AS). The pretreatment on the three lignocellulosic materials was performed at 130, 160, and 200 °C for 60 min using a 50% (v/v) methanol solution, with and without the addition of sulfuric acid as a catalyst. The biomethane potential of raw and pretreated substrates was evaluated under wet-mesophilic conditions in batch reactors, achieving 17.3 (±32.3), 293.4 (±46.6), and 23.2 (±9.6) mL CH4/g VS for HS, SCG, and AS, respectively. The methanol-organosolv pretreatment was particularly effective on HS, increasing its biomethane potential up to 310.6 (±22.2) CH4/g VS. On the contrary, all pretreatment conditions were ineffective on SCG and AS in terms of cumulative methane production. Among the three substrates, only HS showed significant composition changes due to the pretreatment, with the lignin content decreasing from 39.66 to 34.73% and the amount of bioavailable sugars increasing. An energy assessment confirmed the pretreatment efficacy on HS, with a maximum net positive energy recovery of 1.35 kWh/kg VS

Silicone membrane contactor for selective volatile fatty acid and alcohol separation

The effect of pH and extraction temperature on flux, recovery, mass transfer coefficient and separation factor of volatile fatty acids (VFAs) and alcohols from synthetic solutions and cheese whey fermentate was investigated using a silicone membrane contactor with water as extractant. The silicone membrane allowed extraction of undissociated acids only, resulting in substantially higher recovery efficiencies at pH 3 than at pH 5. Furthermore, the non-porous silicone membrane favoured extraction of longer chain over shorter chain acids. Caproic acid was extracted with the highest flux of 1.30 (± 0.02) g m−2 h−1 in short time (32 h), with a 41.5 % recovery efficiency at pH 3 and 20 °C, indicating the feasibility of its selective separation from the VFA mixture. A similar trend was observed for alcohols, with butanol being extracted with a 39 % recovery efficiency at 40 °C, against 32 % and 19 % of propanol and ethanol, respectively, while the mass transfer coefficients were not affected by temperature. When applying the silicone membrane contactor to real cheese whey fermentate at pH 3, butyric and acetic acid were extracted with 21.5 % and 7% recovery efficiency, respectively, suggesting the feasibility of the contactor for VFA recovery from real fermentate

Radioactivity concentrations and their radiological significance in sediments of the Tema Harbour (Greater Accra, Ghana)

Abstract Studies on environmental radioactivity in tropical Africa are scarce. Therefore, a baseline study of natural ( 238 U, 210 Pb, 226 Ra, 232 Th, 228 Ra, 228 Th, 40 K) and anthropogenic ( 137 Cs) radionuclides was carried out on Tema Harbour (Greater Accra, Ghana) surface sediments and on their radiological significance. Grab surface sediment samples were collected from 21 stations within the Tema Harbour and their radioactivity concentrations measured by gamma spectrometry. The mean sediment radioactivity concentrations (Bq kg −1 dw) were 34 for 238 U, 210 for 210 Pb, 14 for 226 Ra, 30 for 232 Th, 29 for 228 Ra, 31 for 228 Th, 320 for 40 K, and 1.5 for 137 Cs. Large 238 U/ 226 Ra disequilibria were observed in the harbour sediments and a complex dynamics of several mixed sources of sediments within the Tema Harbour can be inferred from the spatial variations in the radioactivity concentrations. The estimated total absorbed dose rate in air ( D ), radium equivalent activity (Ra eq ), external hazard index ( H ex ), annual gonadal dose equivalent (AGDE) and annual effective dose equivalent (AEDE) indicated no significant radiological risks from the sediment radioactivity concentrations. Application of the Environmental Risk from Ionising Contaminants Assessment and Management tool (ERICA) confirmed that the potential dose rates to biota from the sediment radioactivity concentrations are unlikely to pose appreciable ecological risks. The radioactivity levels are compared with levels reported in sediments from other coastal areas of the world

Settling fluxes and sediment accumulation rates by the combined use of sediment traps and sediment cores in Tema Harbour (Ghana)

Settling fluxes and sediment accumulation rates in coastal Tema Harbour (Ghana) were investigated by the combined analyses of results in sediment traps and sediment cores. Sediment traps were deployed at 5 stations within the Tema Harbour at two sampling depths and were retrieved every two weeks till the end of 12 weeks to estimate the Settling Fluxes (SFs). Four sediment cores from the harbour were analysed for their radioactivity (7Be, 234Th, 210Pb, 212Pb, 226Ra, 40K and 137Cs) profiles to quantify Sediment Accumulation Rates (SARs). The sediment cores exhibited variable bulk density profiles, indicating highly dynamic and non-steady sedimentation conditions. 7Be-derived gross-estimates of very recent SARs using the constant flux-constant sedimentation (CF-CS) model were in the range of 2.5–9.0 g·cm− 2·y− 1. These values were much lower than the estimated average SFs (15.2–53.8 g·cm− 2·y− 1), indicating sediment resuspension plays an important role. On a decadal time scale, conventional 210Pb sediment dating models did not allow any estimation of SARs in the Tema Harbour. Thus, the 210Pb-based TERESA model was applied to depict a reliable scenario for sedimentation with time-averaged SARs in the range of 1.4–3.0 g·cm− 2·y− 1 and fluxes of matter contributed by the marine inflow and local sources. Sediment accretion rates of 1.7–3 cm·y− 1 were also inferred, which may pose a moderate problem of sustainability for the Tema Harbour. This study reveals how the geochemical behaviour of different radionuclides with Gamma spectrometry in the marine environment can be used to obtain reliable information on the complex dynamics of Suspended Particulate Matter (SPM), even in a very disturbed and anthropic environment as a coastal harbour area where (1) conventional 210Pb-based dating methods fail and (2) the use of sediment traps and 234Th and 7Be profiles in sediment cores show serious constraints.University of Ghana UGFD/7/2012-2013/00

Autotrophic denitrification of nitrate rich wastewater in fluidized bed reactors using pyrite and elemental sulfur as electron donors

This study compared denitrification performances and microbial communities in fluidized bed reactors (FBRs) carrying out autotrophic denitrification using elemental sulfur (S0) and pyrite (FeS2) as electron donors. The reactors were operated for 220 days with nitrate loading rates varying between 23 and 200 mg N-NO 3 − /L ⋅ d and HRT between 48 and 4 h. The highest denitrification rates achieved were 142.2 and 184.4 mg N-NO 3 − /L ⋅ d in pyrite and sulfur FBRs, respectively. Pyrite-driven denitrification produced less SO 4 2 − and no buffer addition was needed to regulate the pH. The sulfur FBR needed instead CaCO3 to maintain the pH neutral and consequentially more sludge was produced (CaSO4 precipitation). The active community of pyrite-based systems was investigated and Azospira sp., Ferruginibacter sp., Rhodococcus sp. and Pseudomonas sp. were the predominant genera, while Thiobacillus sp. and Sulfurovum sp. dominated the active community in the sulfur FBR. However, Thiobacillus sp. became more dominant when operating at elevated nitrogen loading rate. Patterns of diversity and microbial community assembly were assessed and revealed three distinct stages of microbial community succession which corresponded with the operation of a period of high influent nitrate concentration (13 5 mg N-NO 3 − /L). It is proposed that a high degree of functional redundancy in the initial microbial communities may have helped both reactors to respond better to such high influent nitrate concentration

Biofilm carrier type affects biogenic sulfur-driven denitrification performance and microbial community dynamics in moving-bed biofilm reactors

Autotrophic denitrification with biosulfur (ADBIOS) provides a sustainable technological solution for biological nitrogen removal from wastewater driven by biogenic S0, derived from biogas desulfurization. In this study, the effect of different biofilm carriers (conventional AnoxK™ 1 and Z-200 with a pre-defined maximum biofilm thickness) on ADBIOS performance and microbiomics was investigated in duplicate moving bed-biofilm reactors (MBBRs). The MBBRs were operated parallelly in continuous mode for 309 days, whilst gradually decreasing the hydraulic retention time (HRT) from 72 to 21 h, and biosulfur was either pumped in suspension (days 92–223) or supplied in powder form. Highest nitrate removal rates were approximately 225 (±11) mg/L·d and 180 (±7) mg NO3−-N/L·d in the MBBRs operated with K1 and Z-200 carriers, respectively. Despite having the same protected surface area for biofilm development in each MBBR, the biomass attached onto the K1 carrier was 4.8-fold more than that on the Z-200 carrier, with part of the biogenic S0 kept in the biofilm. The microbial communities of K1 and Z-200 biofilms could also be considered similar at cDNA level in terms of abundance (R = 0.953 with p = 0.042). A relatively stable microbial community was formed on K1 carriers, while the active portion of the microbial community varied significantly over time in the MBBRs using Z-200 carriers

Organic waste biorefineries: looking towards implementation

The concept of biorefinery expands the possibilities to extract value from organic matter in form of either bespoke crops or organic waste. The viability of biorefinery schemes depends on the recovery of higher-value chemicals with potential for a wide distribution and an untapped marketability. The feasibility of biorefining organic waste is enhanced by the fact that the biorefinery will typically receive a waste management fee for accepting organic waste. The development and implementation of waste biorefinery concepts can open up a wide array of possibilities to shift waste management towards higher sustainability. However, barriers encompassing environmental, technical, economic, logistic, social and legislative aspects need to be overcome. For instance, waste biorefineries are likely to be complex systems due to the variability, heterogeneity and low purity of waste materials as opposed to dedicated biomasses. This article discusses the drivers that can make the biorefinery concept applicable to waste management and the possibilities for its development to full scale. Technological, strategic and market constraints affect the successful implementations of these systems. Fluctuations in waste characteristics, the level of contamination in the organic waste fraction, the proximity of the organic waste resource, the markets for the biorefinery products, the potential for integration with other industrial processes and disposal of final residues are all critical aspects requiring detailed analysis. Furthermore, interventions from policy makers are necessary to foster sustainable bio-based solutions for waste management

Microbial electrochemical technologies: Electronic circuitry and characterization tools

Microbial electrochemistry merges microbiology, electrochemistry and electronics to provide a set of technologies for environmental engineering applications. Understanding the electronic concepts is crucial for effectively adopting these systems, but the importance of electronic circuitry is often overlooked by microbial electrochemistry researchers. This review provides the background on the electronics and electrochemical concepts involved in the study of microorganisms interacting with electricity, and their applications in microbial electrochemical technology (MET). The potentiostat circuitry is described along with its working principles. Electrochemical analyses are presented together with the rational and parameters employed to study MET devices and electroactive microorganisms. Finally, future directions are delineated towards the adoption of MET, and the related electronics, in environmental engineering applications.This work has been financed by the Science Foundation Ireland (SFI) Research Professorship Programme Innovative Energy Technologies for Biofuels, Bioenergy and a Sustainable Irish Bioeconomy (award no. 15/RP/2763). The authors thank Uwe Schröder group (Technische Universität Braunschweig, Germany) for kindly permitting re-using their data to plot the graphs shown on Fig. 8.peer-reviewed2021-11-1