The microalgae–bacteria consortium is a promising and sustainable alternative for industrial wastewater treatment, since it may allow good removal of organic matter and nutrients, as well as the possibility of producing products with added value from the algae biomass. This research investigated the best bacterial and microalgae inoculation ratio for system start-up and evaluation of removing organic matter (as chemical oxygen demand (COD)), ammoniacal nitrogen (NH₄⁺–N), nitrite nitrogen (NO₂⁻–N), nitrate nitrogen (NO₃⁻–N), phosphate phosphorus (PO₄³⁻–P) and biomass formation parameters in six photobioreactors with a total volume of 1000 mL. Reactors were operated for 14 days with the following ratios of pulp mill biomass aerobic (BA) and Scenedesmus sp. microalgae (MA): 0:1 (PBR1), 1:0 (PBR2), 1:1 (PBR3), 3:1 (PBR4), 5:1 (PBR5), and 1:3 (PBR6). Results show that COD removal was observed in just two days of operation in PBR4, PBR5, and PBR6, whereas for the other reactors (with a lower rate of initial inoculation) it took five days. The PBR5 and PBR6 performed better in terms of NH₄⁺–N removal, with 86.81% and 77.11%, respectively, which can be attributed to assimilation by microalgae and nitrification by bacteria. PBR6, with the highest concentration of microalgae, had the higher PO₄³⁻–P removal (86%), showing the advantage of algae in consortium with bacteria for phosphorus uptake. PBR4 and PBR5, with the highest BA, led to a better biomass production and sedimentability on the second day of operation, with flocculation efficiencies values over 90%. Regarding the formation of extracellular polymeric substances (EPS), protein production was substantially higher in PBR4 and PBR5, with more BA, with average concentrations of 49.90 mg/L and 49.05 mg/L, respectively. The presence of cyanobacteria and Chlorophyceae was identified in all reactors except PBR1 (only MA), which may indicate a good formation and structuring of the microalgae–bacteria consortium. Scanning electron microscopy (SEM) analysis revealed that filamentous microalgae were employed as a foundation for the fixation of bacteria and other algae colonies.

BACKGROUND: Chlorella vulgaris is being explored for several applications such as biodiesel production, nutrient supplementation, animal feed and pharmaceutical products. In this study, the performance of a batch culture under progressive light intensity and the effect of hydrogen peroxide (H₂O₂) concentration on lipid accumulation were investigated.RESULTS: Under progressive light intensity (60 to 300 μmol m⁻² s⁻¹), a 43% biomass increase was achieved in comparison with the control light conditions (60 μmol m⁻² s⁻¹), whereas a 300 μmol m⁻² s⁻¹ light intensity caused growth inhibition to the culture. In addition, an increase in carotenoid content from 0.102 mg g⁻¹ biomass (control) to 0.460 mg g⁻¹ (progressive light) and lipid accumulation from 31.0 mg g⁻¹ (control) to 36.5 mg g⁻¹ (progressive light) was observed. However, the moderate illumination conditions (60 μmol m⁻² s⁻¹) induced a very significant increase of chlorophyll b, regarding the progressive light mode, increasing the photosynthetic efficiency. After the growth phase, the biomass was subjected to stress conditions by adding H₂O₂ to the culture medium at different concentrations: 0.75 mmol L⁻¹ increased the lipid content of the biomass from 3.6% to 10.3% in a 3‐day test, reaching lipid productivity of 70.4 mg L⁻¹ day⁻¹, an increase of ≈40% compared to the phosphate starvatiod for the same culture time.CONCLUSION: The progressive light system allowed an increase in biomass and lipid accumulation. Together with the exposure to H₂O₂, this work provides a new approach for lipid and pigment production from microalgae. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Microwave (MW) drying of wood has gained popularity in the field of wood modification. The rise in temperature during MW drying leads to increased steam pressure, enhancing wood permeability but potentially decreasing mechanical properties. Understanding temperature and moisture behaviors during MW drying is crucial for its industrial application in wood drying. Therefore, this study aimed to characterize the temperature and moisture behaviors during MW drying of small Portuguese maritime pine (Pinus pinaster Aiton.) wood samples to support a wider use of this technology. The effects on water uptake and the compressive strength parallel to the grain were also investigated. The results indicated three distinct phases in the MW drying rates, with an average of 0.085% of water removed per second. Moreover, the temperature underwent three distinct stages: an initial rapid increase, a period of constant temperature, and a slight decrease until drying was complete. At the beginning of MW drying, the temperatures were below 100 °C, with average temperatures ranging from 126 to 145 °C. Specimens with lower initial moisture content had higher temperatures, and a positive correlation was found between initial moisture content and drying time. In contrast, negative correlations were found between the initial moisture content and average temperature, as well as average temperature and MW drying time. Additionally, the operating condition parameters used in MW drying of pine samples enhanced water impregnability by 65%, generating a slight reduction of 11% in compressive strength. It was also noticed that the initial moisture content did not impact MW-dried samples’ water uptake or compressive strength. Finally, although small clear wood samples of maritime pine were utilized, the temperature and moisture patterns observed closely matched real-scale specimens. Thus, the findings corroborate a wide utilization of MW technology for wood drying, mainly demonstrating positive possibilities for structural-sized wood specimens.

The most widespread wood species in the Portuguese forest and the most widely utilized are maritime pine (Pinus pinaster) and eucalyptus (Eucalyptus globulus Labill). In the case of eucalyptus, except for the pulping sector, it might have limited usage due to drying issues and low permeability. Microwave (MW) treatment is a technology that has been used to improve wood species’ permeability. Therefore, the present paper aimed to evaluate the MW treatment of both Portuguese wood species and to investigate the effects of different MW treatments on wood’s density, water uptake capability, modulus of rupture (MOR), and modulus of elasticity (MOE). Using small clear wood specimens, two MW powers were used, 700 and 1200 W, and the samples were submitted to successive MW cycles of 2 min till they reached the required dryness. The results showed that each wood species had a different behavior during the MW drying in terms of drying rate, supply, and consumption of energy. In general, with the increase in MW power, the densities of both species decreased and the water uptake increased, as a possible indicator that a certain level of microstructural damage might have occurred. Regarding the mechanical properties of MW-treated maritime pine and eucalyptus wood specimens, under the harshest conditions (MW power of 1200 W), MOR and MOE were reduced compared with the wood sample without MW treatment.

Dissolving-grade pulps serve as the primary material for producing regenerated cellulose fibers, and their utilization is steadily increasing. Despite extensive research efforts, it remains necessary to deepen our understanding of the inherent factors that impact pulp reactivity apart from the well-known degree of polymerization. The Fock reactivity test is commonly used to quantify the reactivity of cellulose pulp by measuring the percentage of cellulose that reacts with carbon disulfide. Dissolving pulps typically require a reactivity of over 90%. Hemicellulose content, intrinsic viscosity, cell wall porosity, crystallinity, and accessible area of four different pulps were characterized and distinct treatments were employed to try to separate the effect of different pulp properties and assess their effect on Fock reactivity. Hemicelluloses removal by xylanase and cold caustic treatments (86% removal) increased the Fock reactivity by 30%, from 55.7% to 71.3%. Assuming the hemicelluloses are fully accessible by the CS₂, cellulose reactivity increased from 35.6% to 69.5%,but at the expense of an intrinsic viscosity decrease from 990 cm³/g to 689 cm³/g. This unexpected intrinsic viscosity decrease can be due to the cellulose de-shielding effect provoked by hemicellulose removal and some cellulose degradation during cold caustic extraction. Vibrational impact ball-milling applied on a pulp with 5% hemicellulose content notably boosted Fock reactivity by 56%, from 54% to 84.5%, but two pulp properties, intrinsic viscosity, and crystallinity, decreased concurrently due to the high-energy treatment. This phenomenon complicates identifying a direct correlation between heightened reactivity and a single parameter. To address this, endoglucanase treatment was used to separate intrinsic viscosity from crystallinity, clarifying their contributions to changes in Fock reactivity. Unfortunately, the effect of a given physical or bio/chemical pulp treatment affects more than one pulp property, always including the cellulose degree of polymerization, which has made it difficult to isolate the pulp properties that affect Fock reactivity. Several processes have been tested to obtain pulp with dissolving potential.