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Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG [Abstract] The recent unprecedented increase in energy demand has led to a growing interest in emerging alternatives such as the production of microbial lipids with high energy density and environmentally-friendly characteristics. Oleaginous yeasts represent a versatile and attractive tool for the accumulation of such lipids, also known as single cell oils (SCOs), used to manufacture biofuels (e.g., biodiesel, aviation fuel) and bioproducts. This review provides an overview of the most common oleaginous species, analysing the viability of typical feedstocks and their effect on lipid accumulation. The best results in terms of lipid content using glucose, glycerol, lignocellulose, or acetic acid as substrates are 81.4, 70, 68.2 and 73.4% (w/w), respectively. Besides, an analysis of the parameters that can affect lipid production is also presented. For instance, the optimum conditions for lipid accumulation are usually a C/N ratio between 100 and 200, pH between 5 and 6 (being more alkaline if acids are used as substrates) and temperature around 30 °C. Besides, genetic modifications generally allow to increase the lipid yield, even by up to 400%. Finally, some cost analysis is provided for scaling-up, with feedstock costs estimated at 50–80%, followed by fermenter costs, and downstream costs estimated at around 13%. This study was funded by the Spanish Ministry of Science and Innovation and European FEDER funds (PID2020-117805RB-I00). The manuscript is based on research related to COST action Yeast4Bio. RR thanks the Ministry of Science and Innovation for financial support of his doctoral research (E-15-2019-0344365). CFB (ED481A-2020/028) thanks Xunta de Galicia for financing her doctoral research. The authors, belonging to the BIOENGIN group, thank Xunta de Galicia for financial support to Competitive Reference Research Groups (ED431C 2021/55) Xunta de Galicia; ED481A-2020/028 Xunta de Galicia; ED431C 2021/55

Clostridium carboxidivorans produces alcohols from C1 gases (CO, CO2), converting them first into fatty acids, and subsequently into alcohols. This research identified conditions that allow to selectively produce either fatty acids or alcohols. The conversion of gases into acids and then into alcohols is catalysed by metalloenzymes, stimulated by specific trace metals. Therefore, different bioreactors were set-up, either with or without addition of tungsten (W) or selenium (Se) and at different pHs. Combining the presence of those trace metals with a low pH (5.0) allowed to accumulate high amounts of alcohols as major end products (8038 mg/L total alcohols; 3027 mg/L total acids). Instead, maintaining a higher pH (6.2), in the absence of those trace metals, allowed to selectively produce organic acids (9577 mg/L) and almost no alcohols (676 mg/L). Omitting W, but not Se, at high pH (6.2), led to a still higher concentration of acids (11303 mg/L).

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG [Abstract] An anaerobic mixed culture able to grow on pure carbon monoxide (CO) as well as syngas (CO, CO2 and H2), that produced unusual high concentrations of butanol, was enriched in a bioreactor with intermittent CO gas feeding. At pH 6.2, it mainly produced acids, generally acetic and butyric acid. After adaptation, under stress conditions of CO exposure at a partial pressure of 1.8 bar and low pH (e.g., 5.7), the enrichment accumulated ethanol, but also high amounts of butanol, up to 6.8 g/L, never reported before, with a high butanol/butyric acid molar ratio of 12.6, highlighting the high level of acid to alcohol conversion. At the end of the assay, both the acetic acid and ethanol concentrations decreased, with concomitant butyric acid production, suggesting C2 to C4 acid bioconversion, though this was not a dominant bioconversion process. The reverse reaction of ethanol oxidation to acetic acid was observed in the presence of CO2 produced during CO fermentation. Interestingly, butanol oxidation with simultaneous butyric acid production occurred upon production of CO2 from CO, which has to the best of our knowledge never been reported. Although the sludge inoculum contained a few known solventogenic Clostridia, the relative taxonomic abundance of the enriched sludge was diverse in Clostridia and Bacilli classes, containing known solventogens, e.g., Clostridium ljungdhalii, Clostridium ragsdalei and Clostridium coskatii, confirming their efficient enrichment. The relative abundance of unassigned Clostridium species amounted to 27% with presumably novel ethanol/butanol producers. This publication has emanated from research supported by Science Foundation Ireland (SFI) through the SFI Research Professorship Programme entitled Innovative Energy Technologies for Biofuels, Bioenergy and a Sustainable Irish Bioeconomy (IETSBIO3; grant number 15/RP/2763) and the Research Infrastructure research grant Platform for Biofuel Analysis (Grant Number 16/RI/3401). This research was partly funded by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) through project CTQ2017-88292-R and European FEDER funds. The BIOENGIN group thanks Xunta de Galicia for financial support to its Competitive Reference Research Group (ED431C 2021/55). Funding for open access charge provided by Universidade da Coruña/CISUG Irlanda. Science Foundation Ireland; 15/RP/2763 Irlanda. Science Foundation Ireland; 16/RI/3401 Xunta de Galicia; ED431C 2021/55

This research was funded by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) through project CTQ2017-88292-R and European FEDER funds, and through European ERA-IB7 project OBAC and PCIN2016-148. The authors, belonging to the BIOENGIN group, thank Xunta de Galicia for financial support to Competitive Reference Research Groups (ED431C 2017/66)

Fish canning industries generate a significant amount of solid waste that can be digested anaerobically into volatile fatty acids (VFA). The aim of this research was to study the effect of various pHs, ranging from 5.0 to 10.0, and percentage of total solids on the anaerobic digestion of tuna waste into VFA, both in batch assays and continuous reactor. The production of VFA was affected by pH and was significantly higher under alkaline conditions. At pH 8.0, the VFA production reached 30,611mgCOD/L. The VFA mainly consisted of acetic, propionic, n-butyric and i-valeric acids. Acetic acid was the main product at all the pHs tested. In terms of total solids (TS) the best results were obtained with 2.5% total solids, reaching 0.73gCODVFA/gCODwaste. At higher TS concentrations (5 and 8% TS) lower yields were reached probably due to inhibition at high VFA concentration.

Fermentation medium and fermentation pH are among the main parameters that control acidogenesis and solventogenesis in clostridia during CO bioconversion. The approach of cyclic pH shifts from high (pH 5.75) to low (pH 4.75) levels, in continuous gas-fed bioreactors, allowed Clostridium autoethanogenum to consume and convert CO and the produced acetic acid from CO to alcohols using one single bioreactor. Increasing amounts of ethanol accumulate after each pH shift cycle, while acids are used up and converted during each cycle. In this study, a total of three cyclic pH shifts along with partial medium replenishment, resulted in a high ethanol production, reaching a concentration of 7143 mg/L. The mixotrophic fermentation using xylose as additional carbon source besides carbon monoxide allowed to conclude that xylose is a preferred carbon source compared to CO and that it allows to increase the cell mass concentration (421 mg/L).

Ethanol production from C1 compounds, such as carbon monoxide, using acetogenic bacteria is an attractive alternative to produce renewable fuels. However, the process is generally associated with acetic acid accumulation, which is often produced in larger quantities than ethanol itself. This study shows the continuous production of ethanol and complete conversion of produced acetic acid to ethanol, which is possible through pH shifts from high pH to low pH using an optimized medium and one single gas-fed bioreactor. A first study with a single pH shift resulted in the production of 2408 mg/L of ethanol without any accumulation of acetic acid. In a next study a final ethanol concentration of 4260 mg/L was reached with just one pH shift and one partial medium renewal. These results indicate that maintaining an optimal growth pH at the beginning of the process in order to obtain a high cell mass, and later shifting the pH to a low value will improve ethanol productivity and avoid any acetic acid accumulation.

The present research explored the optimization of volatile fatty acids (VFA) production from cheese whey in an anaerobic sequencing batch reactor (AnSBR). For that purpose, changes of solid and hydraulic retention times (SRT and HRT) were applied. Moreover, the experiments were coupled to metagenomic analyses by 16S rRNA sequencing. The results showed an enhancement of the process effectiveness at longer SRT and shorter HRT. The degree of acidification (DA) improved from 0.73 to 0.83 when increasing the SRT from 5 to 15 days. It also increased from 0.79 to 0.83 when lowering the HRT from 3 to 1 day. The acidification yield (YVFA/S) improved from 0.78 to 0.87 and from 0.86 to 0.90 g COD-VFA g COD-Lactose−1 when increasing the SRT from 5 to 15 days and decreasing the HRT from 3 to 1 day, respectively. Hydrolytic bacteria dominated the microbial community at the shortest SRT, although they were replaced by acidogenic bacteria at longer SRT.

The effect of trace metals, namely tungsten and selenium, on the production of acids and alcohols through gas fermentation by a CO-enriched anaerobic sludge in a continuous gas-fed bioreactor was investigated. The CO-enriched sludge was first supplied with a tungsten-deficient medium (containing selenium) and in a next assay, a selenium-deficient medium (containing tungsten) was fed to the bioreactor, at a CO gas flow rate of 10 mL/min. In the absence of tungsten (tungstate), an initial pH of 6.2 followed by a pH decrease to 4.9 yielded 7.34 g/L acetic acid as the major acid during the high pH period. Subsequently, bioconversion of the acids at a lower pH of 4.9 yielded only 1.85 g/L ethanol and 1.2 g/L butanol in the absence of tungsten (tungstate). A similar follow up assay in the same bioreactor with two consecutive periods at different pH values (i.e., 6.2 and 4.9) with a selenium deficient medium yielded 6.6 g/L acetic acid at pH 6.2 and 4 g/L ethanol as well as 1.88 g/L butanol at pH 4.9. The results from the microbial community analysis showed that the only known CO fixing microorganism able to produce alcohols detected in the bioreactor was Clostridium autoethanogenum, both in the tungsten and the selenium deprived media, although that species has so far not been reported to be able to produce butanol. No other solventogenic acetogen was detected.

The use of biological techniques for the removal of hydrophobic and recalcitrant volatile compounds at industrial scale has recently significantly increased. In the present work, studies were undertaken aimed at comparing the performance of a continuous stirred tank bioreactor (CSTB) with either a single liquid phase or in the presence of a solid non-aqueous phase (NAP), for the biodegradation of α-pinene. Specifically, 3.5mm diameter beads of Hytrel G3548L were selected as solid NAP based on their affinity for α-pinene. Performance was evaluated over a period of 322 days. However, the experimental results showed no significant enhancement of α-pinene biodegradation in presence of the NAP compared to the reactor with a single liquid phase. Under steady-state conditions, when Hytrel G3548L (5%) was added to the CSTB, the maximum elimination capacity (ECmax) achieved was ∼60 g m(-3)h(-1), which was similar as in the absence of the NAP. Under transient shock-load conditions similar results were obtained with or without NAP, although attenuation was observed in the decrease of the removal efficiency (RE) during overload when polymer beads were present.

The removal of α-pinene from polluted air was examined under thermophilic conditions (50 °C) in one- and two-liquid phase continuous stirred tank bioreactors (CSTBs). Steady-state experiments were performed at different gas residence times, and α-pinene concentrations, corresponding to inlet loading rates between 0.5 and 38 g m−3 h−1 in the one-liquid phase CSTB, and between 2.9 and 176 g m−3 h−1 in the two-liquid phase CSTB. The presence of a second liquid-phase (5% v/v silicone oil) increased the maximum elimination capacity (85.7 g m−3 h−1) by ∼6-fold compared to the one-liquid phase CSTB. During transient-state experiments, the CSTB with silicone oil could withstand a higher α-pinene shock load (110 g m−3 h−1) than the CSTB operated without silicone oil (70 g m−3 h−1). Besides, the thermophilic specific substrate utilization rates were estimated from batch assays, reaching 89 and 340 μ g α -pinene mg biomass - 1 d - 1 , in the absence of or presence of silicone oil, respectively.

The biodegradation of gas-phase mixtures of methanol, α-pinene and H2S was examined in a biotrickling filter (BTF), inoculated with a microbial consortium composed of an autotrophic H2S-degrading culture, and pure strains of Candida boidinii, Rhodococcus erythropolis, and Ophiostoma stenoceras. The inlet concentrations of methanol, α-pinene and H2S varied from 0.05 to 3.3 gm(-3), 0.05 to 2.7 gm(-3), and 0.01 to 1.4 gm(-3), respectively, at empty bed residence times (EBRT) of either 38 or 26s. The maximum elimination capacities (ECmax) of the BTF were 302, 175, and 191 gm(-3)h(-1), with 100%, 67%, and >99% removal of methanol, α-pinene and H2S, respectively. The presence of methanol showed an antagonistic removal pattern for α-pinene, but the opposite did not occur. For α-pinene, inlet loading rates (ILRs) >150 gα-pinenem(-3)h(-1) affected its own removal in the BTF. The presence of H2S did not show any declining effect on the removal of both methanol and α-pinene.

The effect of relative humidity (RH: 30% to >95%) of a gas-phase mixture composed of benzene, toluene, ethylbenzene and para-, meta- and ortho-xylenes (BTEX), inlet concentrations (0.2–12.6 g m−3), and empty bed residence times (EBRTs) (48–144 s) was tested in a fungi-dominant biofilter. A maximum elimination capacity (ECmax) of 244.2 gBTEX m−3 h−1 was achieved at a total inlet loading rate (ILRT) of 371.2 gBTEX m−3 h−1 (RH: 65%). The transient-state response was tested by increasing the ILRT, in two steps, from ∼50 to 850 g m−3 h−1 and from ∼50 to 320 g m−3 h−1, at a constant EBRT of 41.7 s. Increasing the ILRT reduced the total BTEX removal efficiency (RET) from >97% to 35%, and from >90% to 60% during medium and high shock-load, respectively. When subjected to short (4 d) and long-term (7 d) shut-down periods, the biofilter was able to recover high ECmax of, respectively, 200 and 72 gBTEX m−3 h−1 after resuming operation. Ministerio de Educación y Ciencia; CTM2004-00427/TECNO Ministerio de Educación y Ciencia; SB-2004-0135 Ministerio de Ciencia e Innovación; JCI-2008-0385

Acetone, toluene and styrene (ATS) are representative air pollutants emanating during the production process in fibreglass and composite manufacturing industries. In this study, the performance of a steady-state biofilter inoculated with the fungus Sporothrix variecibatus was tested at different empty bed residence times (EBRTs), and at different inlet concentrations of ATS, corresponding to total pollutant loading rates ranging from 30 to 490 g m −3 hour −1 . Styrene was somewhat better removed (47–100%) in the biofilter than acetone (34–100%) and toluene (42–100%), with maximum elimination capacities (EC max ) of 108, 72 and 144 g m −3 hour −1 , for ATS, respectively. Besides, it was observed that, although increasing the concentration of ATS decreased their removal, the presence of toluene also decreased the EC max of both acetone and toluene in the ternary mixture. During transient operations, the biofilter was subjected to intermittent shutdown and re-start operations where the gas-phase pollutant flow was stopped for either 5 or 16 d. It was observed that, for longer shutdown periods (16 d), the biofilter required nearly 8–10 d to reach similar removal patterns to those observed before the shutdown phase. Batch biodegradation tests were conducted, using Sporothrix -like microorganisms present in the leachate of the biofilter, with a mixture of ATS as the sole carbon source. Complete removal of ATS was observed within the test period of 168 hours. Styrene was degraded faster, with a specific substrate utilization rate of 0.9 mg styrene mg biomass −1 hour −1 , followed by toluene (0.6) and acetone (0.44). The effectiveness of the biofilter to reach high total EC (321.3 g m −3 hour −1 ), and withstand transient operations shows the robustness of this fungal-bioreactor and its suitability to handle emissions from a fibreglass and composite manufacturing industry.

A Sporothrix variecibatus -inoculated biotrickling filter (BTF) was examined for styrene removal, without and with the addition of silicone oil, at different empty bed residence times. The highest elimination capacities (ECs) were 172.8 (without silicone oil) and 670 g m −3 h −1 (with silicone oil), respectively, corresponding to a 4-fold improvement in presence of oil. The addition of silicone oil formed a well-coalesced emulsion of fungi and silicone oil, resulting in filter-bed clogging. Clogging prevention strategies adopted were; (i) lowering the volume ratio of silicone oil from 10% to 2% (v/v), and (ii) periodic increase in trickling rate of the medium from 50 to 190 mL min −1 . During shock-load experiments, the BTF with silicone oil (2% v/v) could withstand high styrene loads, of up to 1900 g m −3 h −1 , when compared to the BTF without silicone oil (400 g m −3 h −1 ).

This work is the first extensive study on the removal of carbon monoxide from polluted air in biofilters. It compares the performance of two packing materials, namely lava rock alone and a mixture of peat and lava rock. The results show that the biofilter packed with the mixture of peat and lava rock performed much better than the other one. The effect of operating conditions as, among others, the inlet concentration and the empty bed residence time (EBRT) were studied. A maximum elimination capacity of 33 g m −3 h −1 was obtained with the mixed packing with more than 85% removal efficiency at EBRT of 3 min or more. Somewhat lower performances were reached at shorter EBRT. The results presented here suggest that the mixture of lava rock and peat, subject to further optimization, offers potential for the biological removal of CO from polluted gas streams.

In this study, effluent from the biological treatment of wastewater from a resin-producing factory containing recalcitrant compounds was ozonated under different conditions. Afterwards, the biodegradability of the ozonated effluent was studied under anoxic conditions. The post-ozonation of the industrial effluent was performed using a wide range of ozone doses, from 1.8 to 29.5 mg L−1 min−1. After the biological treatment of the ozonated effluent, organic carbon and nitrogen removals from 27 to 97% and from 27 to 80%, respectively, were achieved. The effect of the contact time was studied at a constant ozone dose of 13.0 ± 1.2 mg L−1 min−1 and contact times ranging from 30 to 180 min. In this case, organic carbon removals from 55 to 100% and organic nitrogen removals from 41 to 77% were obtained after biological treatment.

A study was performed to assess the feasibility of anaerobic treatment of slaughterhouse wastewaters in a UASB (Upflow Anaerobic Sludge Blanket) reactor and in an AF (Anaerobic Filter). Among the different streams generated, the slaughter line showed the highest organic content with an average COD of 8000 mg/l, of which 70% was proteins. The suspended solids content represented between 15 and 30% of the COD. Both reactors had a working volume of 21. They were operated at 37°C. The UASB reactor was run at OLR (Organic Loading Rates) of 1–6.5 kg COD/m3/day. The COD removal was 90% for OLR up to 5 kg COD/m3/day and 60% for an OLR of 6.5 kg COD/m3/day. For similar organic loading rates, the AF showed lower removal efficiencies and lower percentages of methanization. At higher OLR sludge, flotation occurred and consequently the active biomass was washed out from the filter. The results indicated that anaerobic treatment systems are applicable to slaughterhouse wastewaters and that the UASB reactor shows a better performance, giving higher COD removal efficiencies than the AF.

On the basis of an analysis, in terms of desirable characteristics and main sources of error, of existing apparatus for measuring biogas production by laboratory anaerobic digesters, we have developed a new device that is precise, inexpensive, easily constructed and capable of functioning autonomously for long periods. A slightly costlier version suitable for use in automatic control systems is also described.