Valorization of Sugarcane By-Products through Synthesis of Biogenic Amorphous Silica Microspheres for Sustainable Cosmetics.

Ashes from sugarcane by-product incineration were used to synthesize silica powders through alkaline hot extraction, followed by ethanol/acid precipitation or the sol-gel method. Both production methods allowed amorphous spherical silica microparticles with sizes ranging from 1-15 µm and 97% purity to be obtained. Water absorption ranged from 135-155 mL/100 g and 150-250 mL/100 g for precipitated silica and silica gel, respectively, while oil absorption ranged from 305 to 390 and from 250 to 350 mL/100 g. The precipitation with ethanol allowed the recovery of 178 g silica/kg ash, with a lab process cost of EUR 28.95/kg, while the sol-gel process showed a yield of 198 g silica/kg ash with a cost of EUR 10.89/kg. The experimental data suggest that ash from sugarcane by-products is a promising source to be converted into a competitive value-added product, minimizing the environmental impact of disposal problems.

Functional redundancy ensures performance robustness in 3-stage PHA-producing mixed cultures under variable feed operation.

Polyhydroxyalkanoates (PHA) are biopolymers that can be produced by mixed microbial cultures using wastes or industrial by-products, which represent an economical and environmental advantage over pure culture processes. The use of alternate feedstocks enables using seasonal by-products, providing that the process is resilient to transient conditions. The mixed microbial communities of a 3-stage PHA producing system fed initially with molasses and then cheese whey were investigated through amplicon sequencing of the 16S rRNA gene. The transition in feedstock resulted in an adaptation of the acidogenic community, where Actinobacteria dominated with sugarcane molasses (up to 93% of the operational taxonomic units) and Firmicutes, with cheese whey (up to 97%). The resulting fermentation products profile also changed, with a higher fraction of HV precursors obtained with molasses than cheese whey (7.1±0.5 and 1.7±0.7 gCOD/L, respectively). As for the PHA storing culture, the genera Azoarcus, Thauera and Paracoccus were enriched with fermented molasses (average 89% of Bacteria). Later, fermented cheese whey fostered a higher diversity, including some less characterised PHA-storers such as the genera Paenibacillus and Lysinibacillus. Although the microbial community structure was significantly affected by the feedstock shift, the acidogenic and PHA storing performance of the 3-stage system was very similar once a pseudo steady state was attained, showing that a reliable level of functional redundancy was attained in both mixed cultures.

Strategies for efficiently selecting PHA producing mixed microbial cultures using complex feedstocks: Feast and famine regime and uncoupled carbon and nitrogen availabilities.

Production of polyhydroxyalkanoates (PHAs) by open mixed microbial cultures (MMCs) has been attracting increasing interest as an alternative technology to PHA production by pure cultures, due to the potential for lower costs associated with the use of open systems (eliminating the requirement for sterile conditions) and the utilisation of cheap feedstock (industrial and agricultural wastes). Such technology relies on the efficient selection of an MMC enriched in PHA-accumulating organisms. Fermented cheese whey, a protein-rich complex feedstock, has been used previously to produce PHA using the feast and famine regime for selection of PHA accumulating cultures. While this selection strategy was found efficient when operated at relatively low organic loading rate (OLR, 2g-CODL-1d-1), great instability and low selection efficiency of PHA accumulating organisms were observed when higher OLR (ca. 6g-CODL-1d-1) was applied. High organic loading is desirable as a means to enhance PHA productivity. In the present study, a new selection strategy was tested with the aim of improving selection for high OLR. It was based on uncoupling carbon and nitrogen supply and was implemented and compared with the conventional feast and famine strategy. For this, two selection reactors were fed with fermented cheese whey applying an OLR of ca. 8.5g-CODL-1 (with 3.8g-CODL-1 resulting from organic acids and ethanol), and operated in parallel under similar conditions, except for the timing of nitrogen supplementation. Whereas in the conventional strategy nitrogen and carbon substrates were added simultaneously at the beginning of the cycle, in the uncoupled substrates strategy, nitrogen addition was delayed to the end of the feast phase (i.e. after exogenous carbon was exhausted). The two different strategies selected different PHA-storing microbial communities, dominated by Corynebacterium and a Xantomonadaceae, respectively with the conventional and the new approaches. The new strategy originated a more efficient PHA-production process than the conventional one (global PHA productivity of 6.09g-PHAL-1d-1 and storage yield of 0.96 versus 2.55g-PHAL-1d-1 and 0.86, respectively). Dissociation between the feast to famine length ratio (F/F) and storage efficiency was shown to be possible with the new strategy, allowing selection of an efficient PHA-storing culture with complex feedstock under high organic loading rates.

Response of a three-stage process for PHA production by mixed microbial cultures to feedstock shift: impact on polymer composition.

Polyhydroxyalkanoates (PHA) can be produced by mixed microbial cultures (MMC) using a three-stage process. An attractive feature of MMC for PHA production is the ability to use waste/surplus feedstocks. In this study, the effect of a feedstock shift, mimicking a seasonal feedstock scenario and/or as a strategy for controlling polymer composition, on a MMC PHA production process was assessed using cheese whey (CW) and sugar cane molasses (SCM) as model feedstocks. The acidogenic stage responded immediately to the feedstock shift by changing the fermented products profile, with acetate and butyrate being the main acids produced from CW, while for SCM propionate and valerate were the dominant products. The fermentation process was then quite stable during long term operation. The PHA culture selection stage also responded quickly to the fermented feestocks shift, generating a polymer whose composition was linearly dependent on the concentration of HV and HB precursors produced in the acidogenic stage. The selected culture reached a maximum PHA content of 56% and 65% with fermented SCM and CW, respectively. Mixing fermented CW and SCM, in equal volume proportions, demonstrated the possibility of using different fermented feedstocks for tailoring polymer composition.