**Emerging Tools for Energy System Design Increasing Economic and Environmental Sustainability**

**Yee Van Fan 1, Zorka Novak Pintariˇc 2 and Jiˇrí Jaromír Klemeš 1,\***

Received: 12 June 2020; Accepted: 30 July 2020; Published: 5 August 2020

**Abstract:** Energy is a fundamental element supporting societal development, particularly with the increasing dependency on the Internet of Things. It is also the main contributor to environmental impacts and subsequently, a potential sector for mitigation. Sustainable energy system design considers energy savings and energy efficiency, waste and consumption reduction, process efficiency enhancement, waste heat recovery, and integration of renewable energy. Emerging tools range from advanced Process Integration, modelling, simulation, and optimisation, to system analysis and assessment. This review covers selected emerging studies promoting sustainable system design, including the recent developments reported in the Special Issue (SI) of the 22nd Conference on Process Integration, Modelling and Optimisation for Energy Saving and Pollution Reduction (PRES'19). The primary emphasis was to enhance the economic and environmental performance. However, social factors were also highlighted as essential for future sustainable development. The discussion and analysis in this review focus on the most recent developments of (a) heat integration and heat transfer; (b) integrated and newly developed heat exchangers, (c) integration of renewables, and (d) roles in economic and environmental sustainability. The key results are highlighted, and future research ideas are suggested according to their links to a broader context.

**Keywords:** energy system; environmental sustainability; heat integration; economic sustainability; optimisation and modelling tools


**Abstract**

Periodontitis is a globally prevalent inflammation-mediated disease that can result in varying degrees of destruction to the tissues supporting the teeth. The microbial pathogenic dysbiosis, oxidative stress, and deregulated inflammation, found in patients with periodontitis, make it a multifaceted condition that is difficult to fully resolve. Further to this, periodontitis has been associated with other systemic inflammatory conditions. Trans-resveratrol (3,5,4′-trihydroxy-trans-stilbene) is a plant-derived molecule present in many foods, which have been shown to exhibit antimicrobial, antioxidant, anti-inflammatory, and regenerative properties. However, trans-resveratrol has been reported to have physicochemical shortcomings, which make its clinical translation a challenge. This review outlines a critical analysis of identified samples from the scientific literature that was conducted to assess the potential of RES as a viable therapeutic for periodontitis. The potential for the improvement of the limiting pharmacological profile of trans-resveratrol via nanoformulation is also explored.

**Keywords:** periodontitis, trans-resveratrol, nanotechnology, pharmacognosy, pharmacology


**4. Discussion**

Brain has low storing capacity of oxygen though it is a demanding consumer: brain uses about 20 % of oxygen total supply. In degenerative diseases like Alzheimer's, Parkinson's disease the etiology often are not fully known. In Alzheimer's disease pathophysiological theories have been proposed e.g. heat shock protein interactions [4], Tau-protein abnormality [5] neuroin‐ flamation and neuronal loss [6, 7], β-amyloid interactions [8], mitochondrial misfunction [9]. An overlooked possibility may be using ICP-MS for analysis of elemental profiles of erythro‐ cytes as biomarker for Alzheimer 's disease. Small changes in metabolism of oxygen dependent cells may give symptoms difficult to identify due to lack of suitable biomarkers [10, 11, 12. 13, 14]. Erythrocytes carrying excess lead, cadmium, silver and uranium ions may induce damages in cells including brain cells. Accumulation of elements in the human erythrocytes are a result of low exposure and not of a sudden insult which calls for sensitive biomarkers.

#### **4.1. Effects of accumulated lead, cadmium, silver and uranium in the erythrocytes**

**Figure 3.** Distribution of silver in erythrocytes of 13 patients with Alzheimer's disease. Patient 1-9 men, 10-13 women. Error bar 10%. The mean value of Ag in Alzheimer's patients was 7.4 μg/kg, standard error 1.5 μg/kg, mean of con‐ trols 1.3 μg/kg, The concentration of silver in the erythrocytes of patients was significant higher (Wilcoxon, p< 0.005)

**Figure 4.** Concentration of uranium in erythrocytes of 13 patients with Alzheimers disease. Patient 1-9 men, 10-13 women. Error bar 10 %. The mean value of U in Alzheimer's patients was 0.55 μg/kg, standard error 0.16 μg/kg, mean of controls 0.11 μg/kg, The concentration of uranium in the erythrocytes of patients with Alzheimer's disease was sig‐

Brain has low storing capacity of oxygen though it is a demanding consumer: brain uses about 20 % of oxygen total supply. In degenerative diseases like Alzheimer's, Parkinson's disease the etiology often are not fully known. In Alzheimer's disease pathophysiological theories have been proposed e.g. heat shock protein interactions [4], Tau-protein abnormality [5] neuroin‐ flamation and neuronal loss [6, 7], β-amyloid interactions [8], mitochondrial misfunction [9]. An overlooked possibility may be using ICP-MS for analysis of elemental profiles of erythro‐ cytes as biomarker for Alzheimer 's disease. Small changes in metabolism of oxygen dependent cells may give symptoms difficult to identify due to lack of suitable biomarkers [10, 11, 12. 13, 14]. Erythrocytes carrying excess lead, cadmium, silver and uranium ions may induce damages

than that of controls.

**4. Discussion**

nificant higher (Wilcoxon, p<0.01) than that of controls

408 Pharmacology and Nutritional Intervention in the Treatment of Disease

At present there is lack of methods to describe the accumulated effects of metal ions in erythrocytes in terms of stability constants or conditional constants. There is lacking informa‐ tion of e.g. solvent properties, pH, temperature, redox properties, lack of knowledge of interacting compounds. Elemental profiles of erythrocytes may be an alternative to estimate changes of trace elements and metal ions at the cellular level. The discussion below will be focused on some effects on membrane integrity by lead, cadmium, silver and uranium because it is not fully known how these ions are associated to other compounds.

#### **4.2. Initiation of eryptosis by accumulated lead, cadmium silver and uranium in erythrocytes**

It has been suggested that mature erythrocytes may enter programmed death without the aid of caspase systems [15,16]. Heavy metal ions and organic compounds may be involved in early senescence [17, 18, 19]. When erythrocytes are growing old they will change gradually, fragments will be cleaned up [20, 21], mainly in spleen, liver, bone marrow by the macro‐ phages. Most material of captured senescent erythrocytes e.g. iron and metabolized organic material will be reused [22, 23].

Silver, cadmium ions induce suicidal erythrocyte death [24, 25] and it is likely that erythro‐ cytes and cells dependent on erythrocytes of patients with Alzheimer's disease with accumulated silver and also lead, cadmium and uranium may show early eryptosis. Eryptosis may also be initiated via formation of phosphatidylserine by lead, cadmium, hemin as stimulator [26, 27, 28].

#### **4.3. Erythrocyte channels exposed to accumulated ions of lead, cadmium, silver and uranium**

The accumulated lead, cadmium, silver and uranium may interfere the activity in the eryth‐ rocyte channels for cations, anions and water. Cadmium, lead, silver may interfere with potassium, calcium [29, 30] and other ions in erythrocyte membranes [31, 32]. Binding in vitro of cadmium to β-amyloid channels was reported by [33]. Exposure to accumulated lead, cadmium, silver, uranium ions to β-amyloid or other compounds is likely to support the pathophysiological process by association to available binding sites.

Anions e.g. chlorides, carbonates ions are transported in anion channels [34, 35, 36] may react with silver, lead, cadmium and uranium disturbing channel transport and oxygen handling.

Aquaporin channels in the erythrocyte membrane are important for flow of water and shape [37, 38, 39]. Accumulated cadmium, lead, silver, uranium ions associated to erythrocyte aquaporin channels may decrease the capacity to shrink and expand. Water exchange may also be important for osmotic regulation when the erythrocytes enter capillaries. It cannot be excluded that lead, cadmium, silver, uranium may release important elements. e.g. calcium from their association sites. Released calcium may form non-selective channels in membranes [40].

#### **4.4. Accumulated cadmium, lead, silver and uranium ions may compete with essential elements in carrier systems**

secondary messengers. More research is needed to interpret early symptoms of Alzheimer

Metabolism Changes as Indicated by the Erythrocytes of Patients with Alzheimer's Disease

http://dx.doi.org/10.5772/57511

411

Monitoring changes of elements in the erythrocytes by ICP-MS may be used as an early biomarker of Alzheimer's disease and may support the pharmaceutical treatment. The accumulated lead, cadmium, silver and uranium may interfere with channel activities, have effects on apoptosis, react with secondary messenger and support pathophysiological

We thank Crafoord foundation for economic support and Åbo Academy for putting instru‐ mental facilities to our disposal. We also thank dr Sture Brishammar, Evert Karlsson for

, Paul Ek3

[1] Johansson E, Westermarck T, Hasan MY, Nilsson B et.al. Alterations in nickel and cadmium concentrations in erythrocytes and plasma of patients with Parkinson's dis‐

[2] Johansson E and Liljefors T. Heavy elements in root tips from teeth with amalgam

\*Address all correspondence to<EMAIL_ADDRESS>
4 Department of Pharmacology and Toxicology, University of Helsinki, Finland

ease. Trends in Biomedicine in Finland 2007; XXI 2(4),17-32.

fillings: in TEMA 7 (ed. Momcilovic B), pp 11-18-11-20. Zagreb 1991.

and Faik Atroshi4

disease and pathophysiological processes.

**5. Conclusions**

**Acknowledgements**

processes.

discussions.

**Author details**

**References**

Erland Johansson1\*, Tuomas Westermarck2

1 EJSelenium Consultant Ltd, Uppsala, Sweden

2 Rinnekoti Research Center, Helsinki, Finland

3 Laboratory of Analytical Chemistry, Åbo Academy, Finland

Cadmium is known to compete with zinc in e.g. metallothionein (MT), carrier of zinc. Metal ions having higher affinity than zinc may interact with the binding sites in MT or other carrier. Lead and uranium ions is known to compete with calcium metabolism. Magnesium and calcium ions in calmodulin (calcium carrier) may be displaced by accumulated lead, cadmium, silver, uranium ions and release essential elements e.g. Mg, Ca, Zn. Release of secondary messenger e.g. Mg may disturb ATP metabolism, Ca may activate translocases flippases, floppases, scramblases and start apoptosis signals. Ca may also activate platelets and make them sticky, ready for clot. Sticky platelets may associate to proteins and form placks.

#### **4.5. Sources of cadmium, lead, silver and uranium — Food and implants**

The food intake is not known for individual patients. In Finland cadmium uptake from food is about 5-10 µg/day, lead 20-66 µg /day, uranium and, silver was not mentioned [41]. In Sweden is reported cadmium uptake from wheat, rice, potatoes, root-crops 10-20 µg /day, lead 15-30 µg /day, uranium 1-4 µg /day, silver not indicated [42]. Cd uptake from nutrition may disturb the heme synthesis. Cadmium rich diet in Nigeria decreased Hb and erythrocyte counts in mice [43]. It cannot be excluded that cadmium, lead, silver, uranium contaminated food may accumulate in human erythrocytes and in similar manner decrease erythrocyte counts and hemoglobin synthesis. Smoker may have higher cadmium values in blood but there was no information about smoking habits. Elevated uranium in drinking water may damage the kidneys and increase protein loss in urine [44, 45].

In Finland some districts have drinking water with high uranium concentrations (> 100 µg/L) which together with cadmium, lead and silver may increase kidney damage and disturb erythrocyte metabolism. Uranium in the drinking water may explain the significant elevated uranium concentrations of erythrocytes of Alzheimer patients.

Implants may be a source of metal ion supply. Amalgam is an alloy which is not stable [2, 3, 46, 47, 48] (release mercury, silver). Guttapercha may sometime contain cadmium [2] but the released amount is not known for the examined patients. Mercury was not analyzed as mercury will associate strong to liver, kidney also to pituary, low mercury will be found in blood. Mercury has also capacity to displace secondary messenger e.g. Mg, Ca, Zn, Fe when not properly associated.

#### **4.6. Elemental profiles of erythrocytes as biomarkers of Alzheimer's disease by ICP-MS**

The early diagnosis of a neurological disease like Alzheimer's and Parkinson's disease is difficult. In Parkinson's disease about 25 % of the patients may get wrong diagnosis [49]. The present study indicate that the elemental profile of erythrocytes may be used as a support in the diagnosis and pathophysiology of Alzheimer's disease. Changes in the elemental profile should be possible to identify earlier due to high sensitivity of ICP-MS. Monitoring elements in the erythrocytes may also be used to observe effects of applied pharmacy and effects on secondary messengers. More research is needed to interpret early symptoms of Alzheimer disease and pathophysiological processes.


**3. Results and discussion**

Due to limitation of convergence of the classical DTM which is only valid near *η* ¼ 0, the multi-step transformation is used.  The transformation of the associated boundary conditions follows as:

Where *i* = 0, 1, 2, 3 … . n indicates the *i*

equations, and the results obtained are shown in **Table 1**.

ð Þ *Z*3ð Þ*i :Z*2ð Þ *k* � *i*

2 X *k*

*i*¼0

½ � *Z*3ð Þ*i Z*7ð Þ *k* � *i*

4 *θ*0 ð Þ*η*¼0

*y*2 *Ra*∗ ð Þ*y* 3*=*4

4 *C*0 ð Þ*η*¼0

*u*2 *y*2 2 *f* 00 � � *η*¼0

*Pr*1*=*4 *f* 00 � � *η*¼0

*Z*1ð Þ*k cosα* � 1

X *k*

*i*¼0

*i*¼0

*i*¼0

*k*

*i*¼0

the number of terms of the power series. *Hi*represents the sub-domain interval, and

*Z*1ð Þ¼ 0 1, *Z*2ð Þ¼ 0 *a*, *Z*3ð Þ¼ 0 0, *Z*4ð Þ¼ 0 0, *Z*5ð Þ¼ 0 *b*, *Z*6ð Þ¼ 0 1, *Z*7ð Þ¼ 0 *c* where *a*, *b*, and *c* are obtained by solving the system of algebraic simultaneous

*Z*4ð Þ*i Z*4ð Þþ *k* � *i* 3

4 X *k*

" #

*i*¼0

transformations, we have:

*Computational Fluid Dynamics Simulations*

*F*

*i*ð Þ*k* , *θi*ð Þ*k* ,*C*

*Z*1ð Þ¼ *k* þ 1 *Z*2 ð Þ*k*

*Z*3ð Þ¼ *k* þ 1 *Z*4 ð Þ*k*

*Z*4ð Þ¼ *k* þ 1 *Z*5 ð Þ*k*

*Z*6ð Þ¼ *k* þ 1 *Z*7 ð Þ*k*

Parameters Domain:

*Z*2ð Þ¼ *k* þ 1

*Z*5ð Þ¼ *k* þ 1

*Z*7ð Þ¼ *k* þ 1

**Table 1.**

**30**

*k* þ 1

*k* þ 1

*k* þ 1

1 *k* þ 1

*k* þ 1

*Pr* < 1, *Le* ≫ 1, *Le* ≪ 1, and *N* ≥ 0

The local Nusselt number: *Nu* � ½ � *Gr* ∗ ð Þ*y* 1

The shearing stress on the plate: *τw* ¼ ∝

*Important dimensionless parameters of interest.*

The Local Sherwood number: *Sh* ¼ �½ � *Gr* ∗ ð Þ*y* 1

The coefficient of skin friction: *Cf* ¼ ∝*ϑPr*1*=*4*Ra*∗ ð Þ*y* 3*=*4

� 3 4 *:*Pr*:Le k* þ 1

X *k*

*i*¼0

� 3 4 Pr *k* þ 1

**Table 1** shows the expressions for the dimensionless parameters that are of interest in this work. The solutions to Eqs. (13)–(15) subjected to Eq. (16) solved using the multi-step DTM method are presented graphically in the figures below. The results shown are for Prandtl numbers of 0.01, 0.1, 0.5, and 0.72, respectively.

**Figure 2** shows the profiles of local skin friction against Prandtl number for various angles of inclination at a constant Lewis number. It could be observed from the plots that the shearing stress decreases as the Prandtl number increases for all the plate angles considered. More importantly, it is illustrated by the graphs that the local skin friction also decreases with increase in the buoyancy ratio and also with respect to the angle of inclination of the wall.

**Figure 3** shows the plots of local Nusselt number against Prandtl number for various angles of inclination at a constant Lewis number. It is clearly seen from the results that the rate of heat transfer (Nusselt number) increases as the Pr increases for all the wall inclination angles. Also to note is the fact that Nusselt number increases as the buoyancy ratio is increased.

**Figure 4** shows the results of how the local Sherwood number changes as the Lewis number is increased for various angles of inclination at a constant Prandtl number. It is noted from the graphs that the local Sherwood number increases as the Lewis number increases for all angles of inclination. Also, it is observed from the figures that the rate of increase of Sherwood number is dependent on N as well as the angle of inclination of the wall.

In **Figure 5**, the similarity profiles of the effect of the buoyancy ratio and the angles of inclination on the dimensionless velocities at fixed Prandtl and Lewis numbers is presented. It could be interpreted from the results for N = 0 that a maximum velocity is obtained for a vertical wall while at an angle of 60°, the minimum velocity. Also, it is clearly seen from the plots that aside from the vertical wall possessing the maximum velocity, its vertical velocity value for N = 1 is higher when compared to the case when N = 0. When the buoyancy ratio N is further increased to 1.5, the velocity for the vertical wall also increases. The trend in the figure also shows that increasing the inclination angle increases the velocity boundary layer thickness for all buoyancy ratio.

In **Figure 6**, the similarity profiles of dimensionless temperature for the wall angles of inclinations considered in this study at constant Lewis number are presented. The temperature profiles show that despite the varying buoyancy ratio, the thermal boundary layer thickness increases as the inclination angle of the wall increases.

**Figure 7** presents the similarity profiles of dimensionless species concentration distributions for the angles of inclination of the wall at a constant Lewis number. It is clearly seen that as the buoyancy ratio is increased, the concentration boundary layer thickness has a decreasing trend under this same flow configuration but as the angle of inclination increases, *δc* increases.

**Figure 8** shows the plots of the coupled similarity profiles of dimensionless temperature, species concentration, and velocity for wall inclination angle of 60° under the constant Lewis number of 10. It can be seen from the results that increasing N has negligible effect on the trio of velocity, concentration and temperature boundary layer thicknesses for a fixed wall angle. However, the effect of N is very noticeable in the vertical velocity values which is clearly higher when N = 1.5 compared to when N = 0.

**Figure 2.**

*Similarity profiles of effects of Prandtl number on skin friction for (a) N = 0; (b) N = 1; (c) N = 1.5 at constant Lewis number of 10.*

**Figure 3.**

**33**

*constant Lewis number of 10.*

*Similarity profiles of effects of Prandtl number on Nusselt number for (a) N = 0; (b) N = 1; (c) N = 1.5 at*

*Scaling Investigation of Low Prandtl Number Flow and Double Diffusive Heat and Mass…*

*DOI: http://dx.doi.org/10.5772/intechopen.90896*

*Scaling Investigation of Low Prandtl Number Flow and Double Diffusive Heat and Mass… DOI: http://dx.doi.org/10.5772/intechopen.90896*

**Figure 3.** *Similarity profiles of effects of Prandtl number on Nusselt number for (a) N = 0; (b) N = 1; (c) N = 1.5 at constant Lewis number of 10.*

**Figure 2.**

**32**

*Lewis number of 10.*

*Computational Fluid Dynamics Simulations*

*Similarity profiles of effects of Prandtl number on skin friction for (a) N = 0; (b) N = 1; (c) N = 1.5 at constant*

**Figure 5.**

**35**

*Similarity profiles of dimensionless velocity for (a) N = 0, (b) N = 1, (c) N = 1.5 at Pr = 0.1 and Le = 10.*

*Scaling Investigation of Low Prandtl Number Flow and Double Diffusive Heat and Mass…*

*DOI: http://dx.doi.org/10.5772/intechopen.90896*

**Figure 4.** *Similarity profiles of effects of Lewis number on Sherwood number for (a) N = 0; (b) N = 1; (c) N = 1.5 at constant Pr of 0.1.*

*Scaling Investigation of Low Prandtl Number Flow and Double Diffusive Heat and Mass… DOI: http://dx.doi.org/10.5772/intechopen.90896*

**Figure 5.** *Similarity profiles of dimensionless velocity for (a) N = 0, (b) N = 1, (c) N = 1.5 at Pr = 0.1 and Le = 10.*

**Figure 4.**

**34**

*constant Pr of 0.1.*

*Computational Fluid Dynamics Simulations*

*Similarity profiles of effects of Lewis number on Sherwood number for (a) N = 0; (b) N = 1; (c) N = 1.5 at*

i. The velocity boundary layer thickness is maximum when the plate is in the vertical position, while it is minimum when the plate is at the inclined angle of 60° to the vertical for any value of Lewis number but within a certain

*Scaling Investigation of Low Prandtl Number Flow and Double Diffusive Heat and Mass…*

ii. The thermal boundary thickness is maximum when the wall is inclined at 60° to the vertical and minimum when in a vertical position while keeping

iii. Thermal boundary thickness decreases with increase in Prandtl number for all angles of inclination while keeping both the Lewis number and

*Similarity profiles of dimensionless concentration for (a) N = 0, (b) N = 1.5 at Pr = 0.1 and Le = 10.*

buoyancy ratio.

*DOI: http://dx.doi.org/10.5772/intechopen.90896*

N constant.

**Figure 7.**

**37**

buoyancy ratio constant.

**Figure 6.** *Similarity profiles of dimensionless temperature for (a) N = 0, (b) N = 1.5 at Pr = 0.1 and Le = 10.*


3.5.3. Regeneration of the Polymer

Finally, regeneration of the polymer and gaining a polymer-free Cu(II) concentrate in a batch process were investigated. Cu(II) was released from HB-PEI by the addition of hydrochloric acid to the filtration circuit until pH 1.0 was reached. Unbound Cu(II) was then rinsed from the filtration circuit by water. The discharge of Cu(II) (Δ) from the filtration circuit, depending on the volume of rinsing solution used (˾), is described with an adaption of Equation (2):

$$
\Delta = 1 - \frac{c\_{i,\bullet}}{c\_{i,0}} = 1 - e^{-\bullet} \tag{3}
$$

Experimental and calculated data for the Cu(II) discharge are given in Figure 8. Cu(II) was efficiently discharged from the pilot plant by rinsing with water, generating a polymer-free Cu(II) concentrate. The regenerated HB-PEI remained in the filtration circuit and was used in further separation cycles.

**Figure 8.** HB-PEI regeneration by pH decrease and Cu(II) discharge from the filtration circuit by rinsing with water. Cu(II) concentration in cumulative permeate is referenced to initial Cu(II) concentration in the filtration circuit.

Due to the decreased Cu(II) concentration in the filtration circuit, Cu(II) concentration in the accumulated polymer-free permeate steadily decreased (Figure 8, calculated by mass balancing) with increasing volume of rinsing water. As the regenerated polymer solution was supposed to be used for Cu(II) retention again, a sufficient discharge of Cu(II) from the filtration circuit was necessary, as remaining unbound Cu(II) in the polymer solution was recirculated to the retention step, reducing the performance of this step. Depending on the polymer concentration in the filtration circuit, Cu(II) concentrations in a polymer-free concentrate, as given in Table 7, can be achieved in a batch regeneration process. An initial polymer loading of 250 mg Cu(II)/g polymer, no Cu(II) retention during rinsing, and 90% Cu(II) discharge are assumed.

**Table 7.** Final Cu(II) concentration in cumulative permeate collected during polymer regeneration and rinsing of the filtration circuit with water. No Cu(II) retention and 90% discharge (ʤ = 2.3) are assumed. Calculation according to Equation (3) and by mass balancing.

### *3.6. Photometric Control of the Cu(II) Enrichment and Release*

For pilot scale operation, control of the Cu(II) enrichment and release in the filtration circuit is highly beneficial. An inline measurement of the Cu(II) enrichment enables an automated pH decrease by acid addition as soon as the Cu(II) loading of the polymer is completed. Then again, as soon as the Cu(II) release is completed, the pH is automatically increased and a new enrichment cycle can be started.

Therefore, the specific change in light absorption of PEI depending on its complex formation can be utilized. Due to the formation of Cu(II) complexes with HB-PEI (tetraamminecopper(II)) [37] and H2O, photometric control of the enrichment and release during PAUF experiments [23] with fly ash extract was investigated.

Figure 9a shows the increasing Cu(II) loading of HB-PEI at pH 4.0 (feed solutions in cuvettes 1–10), followed by a clearly visible color change representing the Cu(II) release at pH 1.0 (feed solution in cuvette 11). Decreasing the pH value, the feed solutions turned colorless to light blue again, indicating the formation of hexaaquacopper(II) and thus the regeneration of HB-PEI.

**Figure 9.** (**a**) PAUF feed samples of Cu(II) enrichment and final Cu(II) release (far right) from HB-PEI using fly ash extract (KEBAG Zuchwil), HB-PEI = 4.6 g L−1. (**b**) Corresponding UV-vis spectra of increasing Cu(II) loading (gray, black, and green graphs) and release (orange graph). Comparable solutions of [Cu(NH3)4] 2+ (blue graph) and [Cu(H2O)6] 2+ (red graph) were additionally analyzed.

Figure 9b shows the UV-vis spectra of the PAUF feed samples with increasing Cu(II) concentration from gray to black to green graphs. The prepared solution of [Cu(NH3)4] 2+ (Figure 9b, blue graph) has an absorption maximum at 605 nm. The copper(II) ammine complex formed with HB-PEI absorbs at very similar wavelengths. The intensity of the absorption bands increases until the maximum loading capacity is reached at around 976 mg L−1 of Cu(II). Additional Cu(II) forms Cu(II) aqua complexes. Therefore, UV-vis spectra are shifted more to the right toward the absorption maximum of [Cu(H2O)6] 2+ (810 nm, red graph) and a mixture of ammine and aqua complexes occurs in the feed solution. At pH 1.0, Cu(II) is released from HB-PEI and the Cu(II) aqua complex exists exclusively, showing an absorption maximum at 830 nm (Figure 9b, orange graph).

It is easy to distinguish between the absorption maxima of the ammine and aqua complexes formed within the Cu(II) enrichment and those obtained during the release from HB-PEI. This enables calibrated photometric control of the selective Cu(II) separation from real fly ash extract by PAUF.


*Article* **Gauge Gravity Vacuum in Constraintless Clairaut-Type Formalism**

**Michael L. Walker 1 and Steven Duplij 2,\***

	- D-48149 Münster, Germany

**Abstract:** The gauged Lorentz theory with torsion has been argued to have an effective theory whose non-trivial background is responsible for background gravitational curvature if torsion is treated as a quantum-mechanical variable against a background of constant curvature. We use the CDG decomposition to argue that such a background can be found without including torsion. Adapting our previously published Clairaut-based treatment of QCD, we go on to study the implications for second quantisation.

**Keywords:** gravity; Clairaut equation; Cho–Duan–Ge decomposition; constraintless formalism


**Optimising Soilless Culture Systems and Alternative Growing Media to Current Used Materials**

Editors

**Nazim S. Gruda Juan A. Fern´andez**

MDPI • Basel • Beijing • Wuhan • Barcelona • Belgrade • Manchester • Tokyo • Cluj • Tianjin

*Editors* Nazim S. Gruda University of Bonn Germany

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*Editorial Office* MDPI St. Alban-Anlage 66 4052 Basel, Switzerland

This is a reprint of articles from the Special Issue published online in the open access journal *Horticulturae* (ISSN 2311-7524) (available at: https://www.mdpi.com/journal/horticulturae/special issues/Soilless Culture Systems).

For citation purposes, cite each article independently as indicated on the article page online and as indicated below:

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**ISBN 978-3-0365-3901-0 (Hbk) ISBN 978-3-0365-3902-7 (PDF)**

Cover image courtesy of Juan A. Fernandez ´

© 2022 by the authors. Articles in this book are Open Access and distributed under the Creative Commons Attribution (CC BY) license, which allows users to download, copy and build upon published articles, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications.

The book as a whole is distributed by MDPI under the terms and conditions of the Creative Commons license CC BY-NC-ND.


**5. Disadvantages of electric engines**

## **5.1 Battery**

The typical lithium-ion battery is utilized in electric aircrafts can be associated with hazards such as short-circuit and chemical leakage. There are battery chemistries that perform significantly better than current lithium-ion but are not available in the market. The automotive industry is utilizing hydrogen fuel cells and other forms of energy storage. The flow battery, which NASA is exploring for the Aquifer project, is one illustration of novel energy storage within the early stages of development.

#### **5.2 Weight**

Super-lightweight carbon-fiber construction methods can be used to make airplanes lighter. A better design can be used to reduce required power. For the longer endurance mission requirements of the largest aviation market segments, a hybrid solution that incorporates a small jet-fuel-powered auxiliary power unit can be utilized. While avoiding the expense and weight of an all-electric battery-powered aircraft, this solution offers improved efficiency at a lower cost. The advantages of electric propulsion will be augmented by jet fuel's high energy density. Additionally, lithium-ion batteries, which are lighter, can be utilized.

#### **5.3 Range**

Utilizing electric planes will not be feasible due to their limited range, despite the environmental and financial benefits of not using fossil fuels and the emissions that come with it. Electric planes have the same range as cars on the road, which ranges from 160 to 400 kilometers.

#### **5.4 Thermal runaway**

The electrical drive for an aircraft engine must be thermally stable and reliable to pass airworthiness regulations and be deemed safe for flight. Various electrical concepts can be used to design a fully electric aircraft. With regards to the existing electric engine architecture, the motor does not have a robust high torque and insufficient power density under heavy payloads.