Sulfate- and pH-driven metabolic flexibility in sugarcane vinasse dark fermentation stimulates biohydrogen evolution,sulfidogenesis or homoacetogenesis

Dark fermentation of sugarcane vinasse can be used as a “cleaning” step to remove sulfate prior to methanogenesis because sulfidogenic conditions can be successfully established in parallel with biohydrogen production. Using a 2² central composite rotational design (CCRD) and response surface methodology (RSM), this study assessed the impacts of bicarbonate and sulfate availability on the establishment of sulfidogenesis in the thermophilic (55 °C) fermentation of vinasse in batch reactors, equally assessing the impacts on biohydrogen evolution. CCRD-RSM results indicated the favoring of biohydrogen production at the lowest sulfate and bicarbonate concentrations, whilst the opposite was observed for sulfidogenesis. Glycerol, lactate, and hydrogen were the preferential electron donors utilized by sulfate-reducing bacteria (SRB), whilst ethanol was markedly consumed only at high sulfate concentrations. SRB were inhibited by sodium when dosing excess NaHCO₃ and Na₂SO₄. Complementary tests revealed maximum biohydrogen production (2.40 mmol) out of the CCRD, at pH exceeding 7.5 with no interference of sulfidogenesis. Non-efficient biohydrogen production was observed at low pH (<5.0; ～1.90 mmol) because the uptake of lactate was inhibited. Meanwhile, homoacetogenesis was established under intermediate pH range (5.5–6.5), as revealed by the accumulation of acetate (up to 2.5 g L^?1). 16S rRNA gene amplicon sequencing further revealed the genera Thermoanaerobacterium/Pseudoclostridium, Desulfotomaculum/Desulfohalotomaculum and Sporomusaceae/Moorella as the main biohydrogen-producing, sulfate-removing and biohydrogen-consuming (homoacetogens) microbial groups, respectively. Hence, using a single inoculum source, vinasse may provide a butyrate-rich (along with biohydrogen-rich biogas) or a sulfate-free and acetate-rich fermented effluent, depending mainly on proper pH control.     

Coastal trapped waves in the southern Caspian Sea

Previous studies reported coastal trapped waves (CTWs) in the Caspian Sea (CS). This study deals with the generation mechanisms, the temporal and spatial variability of CTWs in this area, and their transformations during propagation from the origin to the destination using recent measurements and high-resolution numerical simulations. CTWs are observed at all stations with periods of 2–6 days after northerly storms. The Absheron Peninsula, old Sefidrud delta, and Nur coasts were identified as the CTWs prone regions. The generation of CTWs in these locations was confirmed using numerical experiments. The propagation away from the generating location of CTWs was analyzed using a representative real wind storm. In the west part of the CS, the generation mechanism of CTWs is mainly similar to the barotropic Kelvin waves; in contrast, it is similar to the continental shelf waves in the southern shelves. The results can be used to study the contribution of generated CTWs to the transport of sediment and biological materials in all large lakes.     

A multi-start central force optimization for global optimization

Central force optimization (CFO) is an efficient and powerful population-based intelligence algorithm for optimization problems. CFO is deterministic in nature, unlike the most widely used metaheuristics. CFO, however, is not completely free from the problems of premature convergence. One way to overcome local optimality is to utilize the multi-start strategy. By combining the respective advantages of CFO and the multi-start strategy, a multi-start central force optimization (MCFO) algorithm is proposed in this paper. The performance of the MCFO approach is evaluated on a comprehensive set of benchmark functions. The experimental results demonstrate that MCFO not only saves the computational cost, but also performs better than some state-of-the-art CFO algorithms. MCFO is also compared with representative evolutionary algorithms. The results show that MCFO is highly competitive, achieving promising performance.     

Chlorophyll derivatives/MXene hybrids for photocatalytic hydrogen evolution: Dependence of performance on the central coordinating metals

Development of efficient photocatalytic hydrogen evolution reaction (HER) with illumination of visible light is challenging. In this work, five chlorophyll derivatives (M-Chls; M = H₂/Cu/Ni/Co/Zn) with different central ions in its cyclic tetrapyrrole ring including free base, copper, nickel, cobalt, and zinc were synthesized and employed as the effective visible-light harvester for efficient HER. In addition, two-dimensional (2D) noble metal-free co-catalyst Ti₃C₂T_x MXene was used as an excellent electron capturer due to its outstanding conductivity property. These M-Chls are modified on the surface of Ti₃C₂T_x MXene with 2D accordion-like morphology by means of a simple deposition process to form noble metal-free Chl/Ti₃C₂T_x-based photocatalysts for HER. It is found that the best HER performance as high as 49 μmol/h/g_cat was achieved with the Co-Chl@Ti₃C₂T_x hybrid, which was much higher than those of other M-Chl@Ti₃C₂T_x composites. This research provides a specific way to synthesize low-cost and environmentally friendly natural Chls for developing highly efficient photocatalytic HER through molecular engineering.     

Regression analysis of surface roughness and micro-structural study in rotary ultrasonic drilling of BK7

Ceramic materials have tremendous demand in manufacturing sectors. However, poor machinability impedes their widespread applications on an industrial scale. BK-7 falls in the same category and is normally processed by ultrasonic machining. But nowadays rotary ultrasonic machining is overtaking the ultrasonic machining for processing difficult to cut materials because of its superlative material removal mechanism. Current study aims to improve the surface quality of BK7 by studying the effect of input factors on surface roughness during rotary ultrasonic machining. Response surface methodology has been used to observe the effect of input variables ― spindle speed, feed rate and ultrasonic power ― on surface roughness (SR). Thereafter, central composite design was employed to estimate the regression coefficients of quadratic model for surface roughness. Fitness of developed quadratic model was checked by ANOVA test, which also revealed that all the model terms of input factors were significant except feed and speed interaction. Feed has the maximum impact over surface roughness descended by moderate impact of power and spindle speed. The study was further reinforced on observing the surface integrity of processed surfaces using scanning electron microscopic images. Mixed flow of material was observed to occur at lower feed rate and higher levels of rpm and ultrasonic power.     

Dry reforming of methane over Ni/dendritic fibrous SBA-15 (Ni/DFSBA-15): Optimization,mechanism, and regeneration studies

Dendritic fibrous type SBA-15 (DFSBA-15) was recently discovered with its outstanding catalytic performance and coke resistance as compared to the conventional SBA-15. The operating conditions for dry reforming of methane (DRM) over 10Ni/DFSAB-15 were optimized by using response surface methodology (RSM), followed by stability and regeneration study. Characterization results (TEM and FESEM) confirmed the homogenous distribution of NiO particles with no morphological change in spherical DFSBA-15 upon Ni addition. Process parameters, such as reaction temperature (X₁, 700 °C–900 °C), gas hourly space velocity (X₂, 15,000 mL/g.h ‒ 35,000 mL/g.h), and CH₄/CO₂ ratio (X₃, 1–3) were studied over CO₂ conversion (Y₁), CH₄ conversion (Y₂), and H₂/CO ratio (Y₃). The optimal reaction conditions were found at X₁ = 794.37 °C, X₂ = 23,815.022 mL/g.h, and X₃ = 1.199, with Y₁ = 95.67%, Y₂ = 93.48%, and Y₃ = 0.983. The in-situ FTIR studies of adsorbed CH₄, CO₂, and CH₄ + CO₂ confirmed the formation of unidentate carbonate, bidentate carbonate, and linear carbonyl species as intermediate species. 10Ni/DFSBA-15 presented good reproducibility by using both regeneration medium (air and CO₂/N₂) with two-fold regeneration by air as compared to CO₂/N₂. It was proven that the synthesized 10Ni/DFSBA-15 was appreciably stable and prone to be regenerated by air for DRM under optimal conditions.     

Total mercury levels in crustacean species from Italian fishery

This study investigated mercury contamination levels in eight commercially valuable crustacean species caught off the Central Adriatic and Tyrrhenian coasts of Italy. Total mercury levels were measured by Thermal Decomposition-Amalgamation-Atomic Absorption Spectrophotometry. Results showed a high variability among species with values ranging from 0.070 to 1.24 (mg kg^?1 wet weight). The lowest mercury levels were detected in caramote prawn (Penaeus kerathurus), warty crab (Eriphia verrucosa) and European spider crab (Maja squinado), decapods living in shallow waters. Levels exceeding the limits established by the European Commission were found in species living in close contact with bottom sediments: deepwater rose shrimp (Parapenaeus longirostris), blue and red shrimp (Aristeus antennatus) and Norway lobster (Nephrops norvegicus). For shrimps, the inter-individual variability observed was mostly related to the body size, indicating the accumulation of mercury with age. An estimation of the human intake of mercury associated to the consumption of the crustaceans sampled and its comparison with the Tolerable Weekly Intake are provided.     

Multivariate analysis of subjective evaluation of indoor lighting environment

Though subjective feelings affected by lighting have been studied a lot, multivariate experimental studies are lacking in this research field. Central composite rotatable design (CCRD) was applied to investigate the influence of illuminance, correlated color temperature (CCT) and illuminance uniformity on satisfaction in this study. A series of subject experiments were carried out and polynomial regression models of luminous satisfaction for different activity scenarios were generated. Illuminance and CCT affected the satisfaction significantly in visual task scenarios, and the effect of them was independent with each other, which was demonstrated by the regression model (R² = 0.89). The variation of luminous satisfaction in general activity scenarios cannot be fully explained by the three investigated factors. The results contributed to the knowledge of multivariate analysis of luminous environment and indicated that much could be expected referring to the application of CCRD in this field.