(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) obtained from waste/wastewater using a mixed microbial culture (MMC) usually varies in its properties due to daily variation in the waste/wastewater composition applied as feedstock. In the current study, the average molecular weight (MW) of PHBV was purposely reduced from about 1 MDa to about 200 kDa by drying the PHBV-rich biomass at elevated temperature of 120 °C for 18 h to ease extraction and handling. Furthermore, conversion into value-added chemicals such as trans-crotonic acid (trans-CA) and trans-2-pentenoic acid (2-PA) by thermal decomposition (pyrolysis) benefits from the lower MW. For the extraction of low MW PHBV, the use of the bio-based solvents 2-methyltetrahydroxyfuran (2-MTHF) and dihydrolevoglucosenone (cyrene) was studied. The maximum extraction yield of 62 ± 3 % with purity of > 99 % was achieved with 2-MTHF at 80 °C for an hour with high biomass to solvent ratio of 5 % (g/mL). Cyrene-based extractions resulted in the highest yield of 57 ± 2 % with purity of > 99 % at 120 °C in 2 h with 5 % (g/mL) biomass to solvent ratio. The mass balance closure over the extraction process indicated that about 15 % and 10 % of polymer has remained in the residual biomass after extraction by 2-MTHF and cyrene, respectively. The performance of these new solvents to extract polymers with various average MW was compared to the benchmark extractions using chloroform and dimethyl carbonate (DMC). It was found that for the polymers with low average MW the extraction efficiency of the proposed solvents exceeds the benchmark solvents.

Microbial electrosynthesis (MES) allows carbon-waste and renewable electricity valorization into industrially-relevant chemicals. MES has received much attention in laboratory-scale research, although a techno-economic-driven roadmap towards validation and large-scale demonstration of the technology is lacking. In this work, two main integrated systems were modelled, centered on (1) MES-from-CO₂ and (2) MES from short-chain carboxylates, both for the production of pure, or mixture of, acetate, n–butyrate, and n–caproate. Twenty eight key parameters were identified, and their impact on techno-economic feasibility of the systems assessed. The main capital and operating costs were found to be the anode material cost (59%) and the electricity consumption (up to 69%), respectively. Under current state-of-the-art MES performance and economic conditions, these systems were found non-viable. However, it was demonstrated that sole improvement of MES performance, independent of improvement of non-technological parameters, would result in profitability. In otherwise state-of-the-art conditions, an improved electron selectivity (≥36%) towards n-caproate, especially at the expense of acetate, was showed to result in positive net present values (i.e. profitability; NPV). Cell voltage, faradaic efficiency, and current density also have significant impact on both the capital and operating costs. Variation in electricity cost on overall process feasibility was also investigated, with a cost lower than 0.045 € kWh⁻¹ resulting in positive NPV of the state-of-the-art scenario. Maximum purification costs were also determined to assess the integration of a product's separation unit, which was showed possible at positive NPV. Finally, we briefly discuss CO₂ electroreduction versus MES, and their potential market complementarities.

Polyhydroxyalkanoate (PHA) accumulating microbial enrichment was established on volatile fatty acids (VFAs) containing leachate derived from the organic fraction of municipal solid waste (OFMSW). The enrichment was based on a 12-h feast-famine batch cycle and an exchange ratio of 50% in which VFAs were completely consumed in less than 50 min during stable periods of operation. No pH control was applied in the system, and the pH went as high as 9 due to the presence of amongst others, ammonia [500 mg·L-1 total ammonia nitrogen (TAN) on average]. The degree of enrichment was evaluated with fluorescence in situ hybridization (FISH), and a yet unknown genus of large (3-5 μm diameter) beta-proteobacteria appeared dominant in the culture. A method for estimating the fraction of PHA accumulating active biomass in the total volatile suspended solids was established, and the results indicated an increase of this fraction from 25% to 56% after implementing two modifications in the operational protocol: (1) a pretreatment of the substrate removing virtually all settleable solids; and (2) a settling phase in the enrichment reactor after the feast phase, selectively removing nonsettleable solids and slowly degradable substrates. The PHA accumulation potential of the culture was 77±18 wt% PHA (n=3) after 3 h in batch accumulation experiments. The results suggest the potential feasibility of PHA production under conditions that were previously considered economically favorable but technically difficult.

After the first commercial applications of a new biological process for the removal of hydrogen sulfide (H₂S) from low pressure biogas, the need arose to broaden the operating window to also enable the removal of organosulfur compounds from high pressure sour gases. In this study we have selected microorganisms from a full-scale biodesulfurization system that are capable of withstanding the presence of thiols. This full-scale unit has been in stable operation for more than 10 years. We investigated the microbial community by using high-throughput sequencing of 16S rRNA gene amplicons which showed that methanethiol gave a competitive advantage to bacteria belonging to the genera Thioalkalibacter (Halothiobacillaceae family) and Alkalilimnicola (Ectothiorhosdospiraceae family). The sulfide-oxidizing potential of the acclimatized population was investigated under elevated thiol loading rates (4.5-9.1 mM d^-1), consisting of a mix of methanethiol, ethanethiol, and propanethiol. With this biomass, it was possible to achieve a stable bioreactor operation at which 80% of the supplied H₂S (61 mM d^-1) was biologically oxidized to elemental sulfur. The remainder was chemically produced thiosulfate. Moreover, we found that a conventionally applied method for controlling the oxygen supply to the bioreactor, that is, by maintaining a redox potential set-point value, appeared to be ineffective in the presence of thiols. (Chemical Equation Presented).

Haloalkaliphilic microorganisms that grow optimally at high-pH and high-salinity conditions can be found in natural environments such as soda lakes. These globally spread lakes harbour interesting anaerobic microorganisms that have the potential of being applied in existing technologies or create new opportunities. In this review, we discuss the potential application of haloalkaliphilic anaerobic microbial communities in the fermentation of lignocellulosic feedstocks material subjected to an alkaline pre-treatment, methane production and sulfur removal technology. Also, the general advantages of operation at haloalkaline conditions, such as low volatile fatty acid and sulfide toxicity, are addressed. Finally, an outlook into the main challenges like ammonia toxicity and lack of aggregation is provided.