Clean Technol., Volume 1, Issue 1 (December 2019) – 22 articles

The Allam cycle is the latest advancement in power generation technologies with a high cycle efficiency, zero NO_x emission, and carbon dioxide available at pipeline specification for sequestration and utilization. The Allam cycle plant is a semi-closed, direct-fired, oxy-fuel Brayton cycle that uses high pressure supercritical carbon dioxide as a working fluid with sophisticated heat recuperation. This paper conducted process analyses including exergy analysis, sensitivity analysis, air separation unit (ASU) oxygen pump/compressor option analysis, and carbon footprint analysis for the integrated Allam power plant (natural gas)/ASU complex with a high degree of heat and work integration. Earlier works on exergy analysis were done on the Allam cycle and ASU independently. Exergy analysis on the integrated plants helps identify the equipment with the largest loss of thermodynamic efficiency. Sensitivity analysis investigated the effects of important ASU operational parameters along with equipment constraint limits on the downstream Allam cycle. Energy efficiency and carbon footprint are compared among the state-of-the-art fossil-fuel power generation cycles. Full article

Fish scales (FS), a byproduct of the fish processing industry, are often discarded carelessly. In this present study, FS were used as a promising bio-sorbent for the removal of anionic acid dyes (acid red 1 (AR1), acid blue 45 (AB45) and acid yellow 127 (AY127)) from the wastewaters of textile coloration. Here, physiochemical characterizations of the FS were investigated by SEM-EDS, TGA and FI-IR analyses, and dye absorption and removal efficiency were evaluated and optimized considering different process parameters such as concentration of initial dye solution, amount of FS used, contact time, FS size, process temperature, additives, stirring and vacuum. SEM images and EDS elemental analyses showed architectural variation and heterogeneous composition of FS at different places. TGA identified the 50% minerals, 33% organic matters and 17% moisture and volatile components. FI-IR evidenced considerable absorption of acid dyes. Process optimization revealed that additives and fine pulverized FS had significant positive and negative impact on the dye removal efficacy, respectively. Temperature and stirring improved dye removal efficiency, and dye absorption by FS was very fast at the beginning and became almost constant after an hour indicating saturation of absorption. The maximum dye absorptions in scales for AR1, AB45, and AY127 were noted as 1.8, 2.7 and 3.4 mg/g, respectively, and removal percentages were 63.5%, 89.3% and 93%. The effects of the process parameters were consistent across all three acid dyes used in this study. Two-way ANOVA model showed that dye type, process parameters and ‘dye type X process parameters’ interactions had significant effect on the dye removal efficiency. Full article

Managing certain by-products of the nuclear fuel cycle, such as the radioactive isotopes of caesium: ¹³⁴Cs, ¹³⁵Cs and ¹³⁷Cs is challenging due to their environmental mobility and radioactivity. While a great many materials can isolate Cs+ ions from neutral or basic aqueous solutions via ion exchange, few of these, with the exception of ammonium phosphomolybdate (AMP), function effectively in acidic media. The use of AMP, and its porous composite in polyacrylonitrile (PAN) for management of Cs radioisotopes in various nuclear wastes have been known for decades and are well studied, yet the effects of radiation on the physiochemical properties of such composites have only received limited attention to date. In a previous publication, we demonstrated that a 100 kGy gamma irradiation dose has negligible effect on the ion exchange performance of AMP and AMP–PAN with respect to capacity or kinetics under the Cs+ concentrations and acidity found in spent nuclear fuel (SNF) recycling. As a continuation of this prior study, in this publication we explore the effects of gamma irradiation on the physiochemical properties of AMP and AMP–PAN using a range of characterisation methods. The effects of the same gamma dose on the oxidation state of Mo in AMP and AMP–PAN, the thermal degradation of both AMP and AMP–PAN, combined with a first study into the high-temperature degradation AMP, are reported. The implications of irradiation, its possible mechanism, the conditions present in SNF recycling, and for the end-of-life disposal or recycling of these materials are also discussed. Full article

The need to reduce CO₂ emissions makes companies find new sustainable solutions for energy production. Diverse multiple sourcing energy production value chains became an important strategical development used at a regional level in Finland. This article presents a social sustainability state data visualization framework that allows us to communicate key social aspects to stakeholders and local communities. Core social aspects are defined through the assessment of multiple sourced electricity supply chains available within one region. This framework was tested on a case study covering regional electricity production supply chains in the Oulu sub-region, Finland. The evaluation of social indicators and their impacts presented along regional electricity production supply chains was performed via the conversion of collected data into visual objects. A cumulative social impact assessment of a local energy supply chain revealed that social sustainability impacts have the tendency to accumulate within the region. The results indicate that multiple sourced electricity supply chains are a socially sustainable solution that improve energy security and provide affordable electricity to local communities. The results indicate how by using multiple-sourcing value chains, companies can improve regional social resilience and balance socio-efficiency through building an effective relation between a company’s value added and its social impact on local communities. Full article

Hydrogel microfibers have great potential for applications such as tissue engineering or three-dimensional cell culturing. Their favorable attributes can lead to tissue models that can help to reduce or eliminate animal testing, thereby providing an eco-friendly alternative to this unsustainable process. In addition to their highly tunable mechanical properties, this study shows that varying the viscosity and flow rates of the prepolymer core solution and gellator sheath solution within a microfluidic device can affect the surface topology of the resulting microfibers. Higher viscosity core solutions are more resistant to deformation from shear force within the microfluidic device, thereby yielding smoother fibers. Similarly, maintaining a smaller velocity gradient between the fluids within the microfluidic device minimizes shear force and smooths fiber surfaces. This simple modification provides insight into manufacturing microfibers with highly tunable properties. Full article

In this paper we test for convergence in access to clean energy and clean technology among nations in order to study the economic determinants of access to clean energy and clean technologies. This is important because without access to clean fuels, no global development strategy can be environmentally sustainable. After obtaining an estimated convergence rate under a conditional $\beta$ -convergence model, we use a more sophisticated club convergence econometric framework and ultimately reject the hypothesis of $\beta$ -convergence in favor of subgroups exhibiting intra-group convergence tendencies that are distinct from the other groups. We then employ a club convergence algorithm which groups the 93 nations studied into 8 convergence clubs based on characteristics including the percentage of the population with access to clean energy in the household and the growth rate of this percentage. Evidence that household access to clean energy and clean technology is tied to economic development and institutional quality is provided by showing that the convergence clubs not only reflect distinct strata in access to clean energy but are also strongly tied to important indicators of institutional quality. Full article

The textile and fashion industries account for a significant part of global business. Textile wet processing (TWP) is a crucial stage in textile manufacturing. It imparts aesthetics as well as functional appeal on the textile fabric and ultimate products. Nevertheless, it is considered as one of the most polluting industries and threatens sustainability. There have been different approaches to transform this polluting industry to a sustainable industry. Many researchers have found this challenging, as sustainable, eco-friendly, green or cleaner wet processing might not be always applicable and relevant from the perspective of industrial applications. The present work helps us understand the current state of research of cotton-based textile processes including proposed sustainable approaches. It also examines the achievement of the degree of sustainability of those proposed processes with the lens of the triple bottom line (TBL) framework, identifies existing limitations, and suggests future research scopes that might pave ways for young researchers to learn and undertake new experimental and theoretical research. Full article

Traditionally, remote and urban communities worldwide have been supplied electricity almost completely by fossil fuel generators to accommodate for electricity needs. Currently, the integration of renewable energy sources (RESs) into the current power generation systems can offer attractive economic and environmental merits, including considerable fuel savings and carbon dioxide emission reductions. In relation to sustainability, efficiency and economic feasibility, solar photovoltaic (PV) is one of the most promising sources of RESs which is being touted as a leading solution to long-term electrification and development problems in rural and urban parts of Pacific Island Countries (PICs). In this work, a grid-tie PV system is instigated at a residential scale. The idea of this research is not to claim the power output from the PV system but to show the feasibility of a grid-tie system at a residential scale. This will help the PICs, non-profit organisations and the government better share scarce resources towards achieving their energy goals and be in line with Sustainable Development Goal (SDG) 7, ensuring access to affordable, reliable, sustainable and modern energy for all. Full article

The objective of the current review is to present the development of a large vertical axis wind turbine (VAWT) since its naissance to its current applications. The turbines are critically reviewed in terms of performance, blade configuration, tower design, and mode of failure. The early VAWTs mostly failed due to metal fatigue since the composites were not developed. Revisiting those configurations could yield insight into the future development of VAWT. The challenges faced by horizontal axis wind turbine (HAWT), especially in the megawatt capacity, renewed interest in large scale VAWT. VAWT provides a solution for some of the immediate challenges faced by HAWT in the offshore environment in terms of reliability, maintenance, and cost. The current rate of research and development on VAWT could lead to potential and economical alternatives for HAWT. The current summary on VAWT is envisioned to be an information hub about the growth of the Darrieus turbine from the kW capacity to megawatt scale. Full article

Small wind turbines are key devices for micro generation in particular, with a notable contribution to the global wind energy sector. Darrieus turbines, despite being highly efficient among various types of vertical axis turbines, received much less attention due to their starting characteristics and poor performance in low wind speeds. Radically different concepts are proposed as a potential solution to enhance the performance of Darrieus turbine in the weak wind flows, all along the course of Darrieus turbine development. This paper presents a comprehensive review of proposed concepts with the focus set on the low wind speed performance and critically assessing their applicability based on economics, reliability, complexity, and commercialization aspects. The study is first of its kind to consolidate and compare various approaches studied on the Darrieus turbine with the objective of increasing performance at low wind. Most of the evaluated solutions demonstrate better performance only in the limited tip speed ratio, though they improve the low wind speed performance. Several recommendations have been developed based on the evaluated concepts, and we concluded that further critical research is required for a viable solution in making the Darrieus turbine a low speed device. Full article

Clean energy technologies have been developed to address the pressing global issue of climate change; however, the functionality of many of these technologies relies on materials that are considered critical. Critical materials are those that have potential vulnerability to supply disruption. In this paper, critical material intensity data from academic articles, government reports, and industry publications are aggregated and presented in a variety of functional units, which vary based on the application of each technology. The clean energy production technologies of gas turbines, direct drive wind turbines, and three types of solar photovoltaics (silicon, CdTe, and CIGS); the low emission mobility technologies of proton exchange membrane fuel cells, permanent-magnet-containing motors, and both nickel metal hydride and Li-ion batteries; and, the energy-efficient lighting devices (CFL, LFL, and LED bulbs) are analyzed. To further explore the role of critical materials in addressing climate change, emissions savings units are also provided to illustrate the potential for greenhouse gas emission reductions per mass of critical material in each of the clean energy production technologies. Results show the comparisons of material use in clean energy technologies under various performance, economic, and environmental based units. Full article

In this short communication, we demonstrate that the performance of a typical air source heat pump (ASHP), exploiting a relatively stable air temperature within a subway environment, is high, even during the peak heating months. After a nine-month operational run, the coefficient of performance is demonstrated to be 3.5. The design and installation difficulties are stated together with the lessons learnt following this trial. The actual energy and carbon savings are discussed. Full article

In the present study, the photocatalytic degradation of alachlor was investigated using TiO₂ under sunlight irradiation. The effects of some operational parameters, such as photocatalyst concentration, temperature, pH, sunlight intensity and irradiation time, were optimized. The kinetics of photodegradation was found to follow a pseudo-first-order kinetic law, and the rate constant at optimal condition is 0.245 min⁻¹. The activation energy (E_a) is 6.4 kJ/mol. The alachlor mineralization can be completed under sunlight irradiation after 10 h. The formations of chloride, nitrate and ammonium ions are observed during the photocatalytic degradation. The eight photoproducts were identified by the GC–MS technique. The photodegradation reaction pathways are proposed based on the evidence of the detected photoproducts and the calculated frontier electron densities of the alachlor structure. The photocatalytic degradation treatment for the alachlor wastewater under solar irradiation is simple, convenient and low cost. Full article

Water pollutant removal by biomass adsorbent has been considered innovative and cost-effective, and thus commendable for application in industry. However, certain important aspects have been overlooked by researchers, namely the efficiency in the operation time and pollutant removal. In this research, landfill leachate samples with organic components were treated using a bentonite-enriched sawdust-augmented sequencing batch reactor (SBR) process. By modifying the pH, the sawdust samples were categorized into three groups: the acidic, the alkaline, and the neutral. To bentonite samples, the pH-adjusted sawdust was added at 10%, 20%, and 30% amounts by mass, respectively. At the optimum aeration rate of 7.5 L/min and contact period of 22 h, the treatment achieved 99.28% and 95.41% removal of chemical oxygen demand (COD) and NH₃-N with bentonite, respectively. For both pollutants, in the presence of sawdust, the removal was only reduced by about 17% with the contact period reduced to 2 h, which was a considerable achievement. Full article

The prevalence of antibiotics in water creates microbial resistance and has a negative impact on the ecosystem. Biomaterials such as spent tea leaves are rich in functional groups and are suitable for chemical modification for diverse applications. This research proposes the use of spent tea leaves of chamomile (CM), green tea (GT), and peppermint (PM) as structural scaffolds for the incorporation of carboxyl, sulfonyl, and thiol groups to improve the adsorption of Penicillin G (Pe). Adsorbents characterization reported a higher number of acidic functional groups, mainly in thiolated products. Scanning electron microscopy (SEM) analysis showed changes on the surfaces of the adsorbents due to reaction conditions, with a stronger effect on thiolated and sulfonated adsorbents. Elemental analysis by Energy dispersive X-ray spectrophotometry (EDS) corroborated the chemical modification by the presence of sulfur atoms and the increase in oxygen/carbon ratios. Batch experiments at different pH shows a strong pH-dependence with a high adsorption at pH 8 for all the adsorbents. The adsorption follows the trend CMs > GTs > PMs. Thiolation and sulfonation reported higher adsorptions, which is most likely due to the sulfur bridge formation, reaching adsorption percentages of 25%. These results create a new mindset in the use of spent tea leaves and their chemical modifications for the bioremediation of antibiotics. Full article

A numerical simulation model for a novel concept of a hybrid composed of photovoltaic-thermal solar panels and a heat pump is presented. This concept was developed to assess the performance and energy conversion efficiency of the hybrid system used to produce domestic hot water and electricity. A two-dimensional heat transfer and fluid flow dynamic model was developed to describe the behavior of the hybrid system under different solar irradiance, heat pump boundary conditions and different refrigerants. The model is based on dynamic mass and energy equations coupled with the heat transfer coefficients, and the thermodynamic properties of refrigerants as well as material properties. The model compared fairly to experimental data. Full article

Currently, renewable energy development is emphasized for sustainable development goals accomplishment and the better realization of sustainable development globally. Tanzania, like other developing countries, is striving to adopt different ways of ensuring affordable and accessible energy supply to its socioeconomic and political sectors to achieve renewable energy development. To secure affordable and accessible energy in the country, renewable energy is termed as an alternative energy source because of it is environmentally friendly. If renewable energy is produced and utilized in a modern and sustainable manner, it will help to eliminate energy problems in Tanzania. Thus, this study aims to review the current potential renewable energy for the achievement of sustainable development in Tanzania. Moreover, challenges of renewable energy development are examined. Full article

The presence of sulfur compounds in fossil fuels has been an important concern in recent decades as an environmental risk due to the increase of greenhouse gases in the atmosphere and accentuation of acid rain. This study evaluates modified clays as low-cost and efficient adsorbents for the removal of dibenzothiophene (BT) and 4,6-dibenzothiophene (DBT). Adsorption was investigated in a batch system with synthetic fuels (gasoline and diesel) as a function of type of clay modification, adsorbent dosage, initial concentration of the pollutants, desorption, and isotherm modeling. Maximum adsorption was observed with clays modified with benzyltrimethylammonium ion (BM), achieving a maximum adsorption capacity (qmax) of BT of 11.3 mg/g in gasoline and 31.3 mg/g in diesel. The formation of Van der Waals interaction as well as aromatic forces as the main mechanism is proposed based on the results. A 40% desorption was accomplished in 0.1 N HCl. Adsorbents were characterized by scanning electron microscopy (SEM) and Fourier transform-infrared spectroscopy (FT-IR), indicating their optimum properties as adsorbents in fuels. This work highlights the potential use of reverse polarity clays in the elimination of sulfur compounds from model fuels as a low-cost and environmentally friendly purification technique. Full article

The coupling of fuel cell technology with wastewater treatment plants (WWTPs) is within the sustainable development imperative for the integration of energy production purposes and recovery of materials, even if research is still under development in this field. The anaerobic digestion process can be used for fuel cell feeding, only if trace contaminants are removed continuously. The most harmful and frequent contaminant is H₂S. This article shows the results of H₂S adsorption on activated carbon fixed-beds (dry process), since it is one of the best solutions from both the complexity and costs perspectives. Inside the wide range of commercial activated carbons, a specific commercial carbon has been used in test campaigns, since it is also used in the Società Metropolitana Acque Torino (SMAT) real plant. Thermal regeneration of spent carbons was exploited, using different conditions of temperature, treatment time and atmosphere, since it is a better cost-effective and environmentally sound option than immediate carbon disposal after adsorption. Regeneration with CO₂ showed the best regeneration ratio values. In particular, the best conditions achieved were 300 °C and 75 min of thermal treatment time, with a regeneration ratio of 30%. Full article

Following the increasing global awareness of the dangers posed by the present state of climate change, many countries such as Uganda have adapted long-term plans for a transition to decarbonised economies. A major strategy for decarbonisation is to replace fossil fuels with renewable energy (RE) sources as the fundamental energy source. Uganda has substantial RE resources for the provision of energy services and production, yet these resources remain untapped. It is therefore crucial that the use of these abundant resources should be heightened. This paper examines and discusses the potential and current RE utilization and development in Uganda from the perspective of sustainable development. The status of the different RE resources and their application/utilization, including details of existing projects in the country, are carefully explored and discussed. The possible drivers for a huge advancement of RE applications and development in Uganda are also discussed before elucidating the major barriers and challenges faced by the energy sector as regards RE. Measures and policies required to facilitate the utilization of RE in Uganda are proposed. These evidence-based policies could guide the delivery of affordable and sustainable energy solutions for all by 2030 in Uganda. Full article

In industrial processes, recycling and reusing of process streams—and of water, in particular—is necessary for minimizing fresh water requirements. Water supply issues are increasing in importance for new and existing industrial plants because the freshwater supply is limited and the forecast are that by 2025 two-thirds of people will live in regions with water scarcity. In this short note, the potentialities of a membrane-assisted condenser for the recovery of evaporated waste water from industrial gases are presented. The modelling of the process was carried out for predicting the membrane-based process performance. The experimental data were compared with the results achieved through the simulations. The comparison showed good agreement confirming the validity of the realized model and its suitability for a screening of the operative conditions to be utilized. Full article