Behdad Moghtaderi

To address global water scarcity, desiccant coated heat exchanger (DCHE) based atmospheric water generators (AWG) have been identified as an efficient method of extracting water vapour from the atmosphere for use in remote, arid and developing regions. Previous studies have modelled DCHE-AWG systems, evaluated their specific water production (SWP) and specific energy consumption (SEC) for various operational and geometric parameters, compared dual and secondary channel heating, and investigated various desiccant coatings. To further improve performance, the process arrangement can be modified by closing the primary and secondary channel loops to conserve heat and water vapour within the system. This study compared different closed loop process arrangements through mathematical modelling, optimisation via the genetic algorithm, and a parametric study. Dual channel heating with dual channel closed loops led to an increase in SWP by up to 76% and a decrease in SEC by up to 85% compared to the same system without closed loops. The relative improvement in performance was larger for lower ambient humidity conditions. The SWP increased with increasing primary channel desorption velocity as the DCHE outlet humidity was consistently above the saturation humidity ratio. The primary channel closed loop design led to a decrease in SEC by up to 20%, however, it also led to a decrease in SWP by up to 25% compared to the dual channel closed loop design. Therefore, the primary channel closed loop design should be used for applications requiring reduced energy consumption, cost, complexity or footprint. In 100% RH conditions, the primary closed loop design achieved an SEC of 3.9 MJ L-1 and is a promising method to reduce the energy consumption and operating costs of AWG systems.

To address global water scarcity, desiccant coated heat exchanger (DCHE) based atmospheric water generators (AWG) have been identified as an efficient method of extracting water vapour from the atmosphere for use in remote, arid and developing regions. Previous studies have modelled DCHE-AWG systems, evaluated its specific water production (SWP) and specific energy consumption (SEC) for various operational and geometric parameters, compared dual and secondary channel heating and compared various desiccant coatings. To further improve performance, the process arrangement can be modified by closing the primary and secondary channel loops in order to conserve heat and water vapour within the system. From this, different closed loop arrangements were compared based on a mathematical model and the optimum performance was determined using the genetic algorithm. Additionally, a parametric study was conducted for the dual channel closed loop and primary channel closed loop arrangements. Dual channel heating with dual channel closed loops led to an increase in SWP by up to 76% and a decrease in SEC by up to 85% compared to the same system without closed loops. The relative improvement in performance was larger for lower ambient humidity conditions. The SWP increased with increasing primary desorption velocity as the outlet humidity was consistently above the saturation humidity ratio. The primary channel closed loop design led to a decrease in SEC by up to 20%, however, it also led to a decrease in SWP by up to 25% compared to the dual channel closed loop design. From this, the primary channel closed loop design should be used for applications requiring reduced energy consumption, cost, complexity or footprint. In 100% RH conditions, the primary closed loop design achieved an SEC of 3.9 MJ L-1 and is a promising method to reduce the energy consumption and operating costs of AWG systems.

Microalgae have been identified as a sustainable and versatile source of natural pigments. Their ability to convert carbon dioxide and sunlight into high-value bioproducts make them both an environmentally beneficial and commercially attractive resource. However, the commercialisation of microalgal pigment production remains constrained by several challenges, including high production costs, low pigment yields under standard conditions, and inefficient downstream processing. This review provides all aspects of pigment production from microalgae and not covered in previous reviews. The review encompasses pigment classification, cultivation strategies, factors affecting extraction, as well as extraction and purification processes. Environmental and operational parameters, such as light, temperature, nutrient availability, salinity, and pH, significantly affect pigment biosynthesis and must be optimised for each strain. The choice of cultivation mode (autotrophic, heterotrophic, mixotrophic) and system (open ponds, photobioreactors, hybrid) also plays a crucial role in determining biomass productivity and pigment quality. Downstream processing, including harvesting, cell disruption, extraction, and purification, remains a bottleneck due to high energy costs and pigment instability. Advanced extraction techniques, such as supercritical fluid extraction and microwave-assisted extraction, offer promise for more sustainable and efficient recovery. To advance the field, future research should focus on strain improvement via metabolic engineering, development of energy-efficient processing methods, and implementation of integrated biorefineries. Additionally, pigment stabilisation and public awareness of the benefits of natural pigments will support wider market adoption. With these advancements, microalgae can become a competitive and eco-friendly source of natural pigments.

The separation of synthesised ammonia from unreacted nitrogen and hydrogen is a crucial step in producing high-purity ammonia and enabling the efficient recycling of unreacted gases in the ammonia synthesis process. The separation of ammonia from nitrogen and hydrogen was studied using zeolite 13X. Experiments were performed using a custom-designed experimental apparatus developed specifically for this study. Adsorption isotherm data for ammonia, hydrogen, and nitrogen were obtained over a temperature range of 293–313 K and pressures up to 5 bar. The results show that the adsorption capacity of zeolite 13X for ammonia is significantly higher than for nitrogen and hydrogen. This indicates a substantially stronger affinity toward ammonia molecules, enabling highly selective adsorption. The experimental isotherm data were successfully fitted using the Sips model, which accurately described the adsorption behaviour of the gases and showed good agreement with the measured data. The adsorption performance of zeolite 13X was further evaluated through a series of dynamic breakthrough experiments under varying pressures and gas compositions. The results confirmed the high selectivity of zeolite 13X for ammonia, with negligible adsorption of nitrogen and hydrogen. Ammonia breakthrough time was found to increase with system pressure, reflecting enhanced adsorption capacity. These findings highlight zeolite 13X as an effective and reusable adsorbent for selective ammonia separation in multi-component gas streams, with promising potential for industrial applications.

This paper presents the first integrated technical, economic, and environmental assessment of ammonia as a reductant for green steel production. Decarbonising primary iron and steelmaking is critical for meeting global climate‑mitigation goals, as the sector contributes ~7% of global direct CO₂ emissions and remains reliant on carbon‑intensive reductants. Hydrogen‑based direct reduced iron (H₂‑DRI) is currently the leading low‑carbon pathway, yet its large‑scale adoption is limited by the high cost of green hydrogen and challenges associated with storage, transport, and long‑term handling. Ammonia has emerged as a promising alternative or complementary reductant due to its higher volumetric energy density, mature global transport infrastructure, favourable safety profile, and potential for cost‑effective production from renewable electricity. Despite growing interest, the techno‑economic and environmental implications of direct ammonia utilisation remain poorly understood. This study addresses that gap through the first integrated assessment of ammonia‑based reduction. Part A develops and validates kinetic correlations for hematite reduction in ammonia and hydrogen using 198 experiments conducted at 600-800°C, supplemented by additional literature data. Results show that ammonia reduction proceeds via mixed direct and indirect pathways, with utilisation maximised at ~800°C and 30 min residence time. Part B incorporates these utilisation figures into a Levelized Steel Production Cost (LSPC) model across 22 scenarios in the USA, Australia, and India, demonstrating that reductant price is the dominant cost driver and that green ammonia must fall to ~$150-200/t to reach parity with NG‑DRI under current energy prices. Part C evaluates Scope 1-3 emissions, showing that although ammonia‑ and hydrogen‑based routes nearly eliminate plant‑level emissions, lifecycle emissions depend strongly on upstream energy sources. Overall, the study concludes that ammonia, particularly low‑cost green ammonia, can be a viable reductant for green steelmaking, contingent on improved utilisation, supply‑chain decarbonisation, and advances in renewable ammonia production.