Microalgae biorefineries offer a route to sustainable fuels, yet most techno-economic analyses (TEAs) and life cycle assessments (LCAs) address narrow product portfolios within cradle-to-gate boundaries. This study presents the first cradle-to-grave TEA and LCA of a commercial-scale, continuous-mode, wastewater-fed photobioreactor (PBR) biorefinery producing 1,000,000 gal/yr biodiesel while treating approximate to 8.9 million m(3)/yr of tertiary wastewater through five-tier cascading valorization of Chlorella vulgaris biomass. Three scenarios were modeled in SuperPro Designer and SimaPro: a biodiesel-plus-fertilizer baseline (S1); added pigment extraction and enzymatic protein hydrolysis (S2); and a full cascade adding two-stage biohythane recovery via dark fermentation and co-digestion (S3). Cascading valorization raised co-product revenue by similar to 600%, cutting the minimum fuel selling price (MFSP) from $198.22 to $158.06/gal (-20.3%); S3 yielded a statistically indistinguishable $159.99/gal, and Monte Carlo simulation confirmed robust separation of S2/S3 from S1. The LCA (ReCiPe Midpoint) showed that PBR cultivation electricity (345 kWh/gal; 90.4% of process-electricity demand) dominated 17 of 18 impact categories, making grid decarbonization the primary improvement lever. Absolute impacts are specific to the fossil-dominated GCC grid, whereas the cultivation-electricity hotspot and the relative effects of cascading valorization generalize across electricity mixes. Valorization deepened land-use credits 3.2-fold via soy-protein displacement but shifted burdens toward water consumption and terrestrial ecotoxicity. Pigment price and electricity cost dominated the sensitivity analysis; under moderate co-product pricing ($7/kg protein, $300/kg pigments), MFSP fell to $16.92-18.73/gal (similar to 89% reduction). Economic allocation per ISO 14044 reduced the biodiesel-attributed GWP to approximate to 13.5-13.8 kg CO2-eq/gal, approaching fossil-diesel parity as co-products absorb most of the burden.
Recently, CO2 emissions have been identified as the primary contributor to climate change; therefore, there is an urgent need to remove excess CO2 from the atmosphere. CO2 capture is the most promising approach to address this problem and is considered one of the best potential solutions. The synthesis of mesoporous MgO nano-particles modified with carbon as effective, high-capacity CO2 adsorbents was carried out using various surfactants, including CTAB, F127, P123, Triton X-100, and SDBS, which served as both carbon sources and structure-directing agents. The resulting powder was calcined at 800 degrees C in N2 to produce MgO-N2-CTAB, MgO-N2-F127, MgO-N2-SDBS, MgO-N2-P123, and MgO-N2-X100. Another portion of powder was calcined directly at 450 degrees C in air, yielding MgO-O2-CTAB, MgO-O2-F127, MgO-O2-SDBS, MgO-O2-P123, and MgO-O2-X100. Results showed that the CO2 adsorption capacity of MgO-O2-SDBS (1.781 mmol/g) was 4.68 times greater than that of unmodified MgO nanoparticles (0.38 mmol/g). The highest CO2 capture capacity, approximately 3.755 mmol/g, was achieved with the MgO-N2-SDBS adsorbent at 273 K and 760 mmHg. Interestingly, the CO2 adsorption capacity of MgO-N2-SDBS (3.755 mmol/g) was 2.11 times higher than that of MgO-O2-SDBS prepared in oxygen (1.781 mmol/g). This difference is attributed to the increased presence of C1s (1.33% atomic percentage) in the MgO lattice, as confirmed by XPS analysis. Additionally, S 2p signals were detected for MgO-O2-SDBS, corresponding only to the oxidized state of sulfur (SOx), since SDBS contains sulfur. The presence of accessible pores, combined with the sufficient Lewis basicity of MgO, played a crucial role in enhancing CO2 adsorption over MgO-O2-SDBS. The MgO-N2-SDBS sample exhibited the highest adsorbent capacity among all synthesized samples according to the results of Henry's law constants and isosteric heats of adsorption, indicating its strong ability to interact with CO2 molecules. The prepared sorbents maintained only slight reductions in capacity over ten consecutive CO2 sorption-desorption cycles, demonstrating good recyclability and stability.
The current study numerically investigates the impact of twist angle on the performance of a twisted double-tube latent heat storage (LHS) system, evaluating first- and second-law efficiencies during melting and solidification. Water serves as the heat transfer fluid (HTF) circulating within the inner tube, while the phase change material (PCM) RT35 is situated in the annular space. Performance is evaluated by examining the PCM temperature, liquid fraction, and the rates of thermal and frictional entropy generation over time. The findings indicate that lower twist angles result in reduced melting and solidification durations. A notable exception is the 360° case during melting, which achieves the shortest melting time among all configurations due to the dominance of vortex-enhanced convective heat transfer over the minor stagnation-zone penalty at this twist angle. Frictional entropy generation is consistently negligible compared to thermal entropy generation. Thermal entropy generation exhibits an increasing-then-decreasing trend during solidification, with peak values of 7.8 W/m3/K and 1.8 W/m3/K recorded during solidification and melting, respectively. At higher twist angles, both phase-change durations are extended.
A subgraph of the square lattice with all of its inner faces being 4-cycles is called a square-cell configuration. Prior work has provided explicit expressions for the total and average distances between vertex pairs in symmetric square-cell configurations, including well-structured families such as hexagonal square-cell configurations H(n), trapezium square-cell configurations T(n,k), and bitrapezium square-cell configurations BT(n,k_1,k_2). In this article, we further extend the square-cell configuration from regular boundaries to irregular boundaries, which do not exhibit complete regularity or symmetry in their structure. We find the generalized expressions for the Wiener index and average distance of such irregular configurations, incorporating combinatorial and structural variations. Our results demonstrate how irregularity affects the growth and distribution of pairwise distances and provide a unifying framework that includes both symmetric and asymmetric square-cell graphs as exceptional cases. This generalization provides novel insights into the structural behaviour of square-cell frameworks characterized by complex or perturbed geometries.
Abstract Hydrogen sulfide (H 2 S) is a highly toxic gas often encountered in various industrial settings, including the construction industry. When H 2 S is encountered in construction environments, it not only poses severe health risks to workers but also causes project delays and economic losses. In this study, a quantitative survey was conducted to assess construction professionals’ awareness of H 2 S hazards, evaluate the impacts of regulatory measures on project performance, and identify effective mitigation measures. A structured online survey was administered to 59 construction engineers and professionals in Kuwait, and the responses were analyzed using descriptive and inferential statistics in SPSS. The results revealed significant gaps in hazard awareness, with 41.1% of the respondents incorrectly identifying H 2 S as a harmless gas. While 61.4% reported preemptive testing of H 2 S concentrations during groundwater pumping, nearly half of the participants reported no regular training on H 2 S management. H 2 S emissions negatively impact safety (81.0%), cost (79.3%), and schedule (75.9%). Effective mitigation measures identified include implementing water treatment systems (59.6%), installing on-site gas monitoring labs (49.1%), and utilizing exhaust ventilation in confined spaces (54.4%). The findings underscore the need for enhanced training protocols, stricter enforcement of safety regulations, and the integration of proactive engineering controls to reduce occupational hazards, protect worker health, and ensure project delivery in H 2 S-prone environments.
