Camphor-Soothed Banana Stem Biowaste in the Productivity and Sustainability of Solar-Powered Desalination

Abstract

The increasing need for clean water can be attributed to a number of reasons, such as population growth, industrial development, and climate change. As a result of modern industrial and agricultural methods, the amount of trash generated daily is also on the rise. Waste management and increasing demand for freshwater are two of the most pressing problems facing the human race today and in the future. This study makes an attempt to strike a balance between these two concerns by repurposing a common biowaste, the banana stem, to collect solar energy for a desalination application. Banana stems work well for interfacial solar desalination because of their capillarity and the fact that they float. Camphor-soothed banana stems were placed in a solar still to collect solar thermal energy and to transfer it to the water surrounding them, speeding up the evaporation process and resulting in more freshwater. Over the course of three days, measurements were taken with the water level held constant and the stem thickness of the bananas varied between 0.5 and 1.5 cm. Enviro-economic studies and water quality analysis were used to calculate greenhouse gas emissions, carbon dioxide mitigation, and the carbon credits obtained. Compared to a standard still, a maximum yield of 934 mL was achieved at an efficiency of 36.35 percent. The CPLs (costs per liter) for the MSS (modified solar still) and the CSS (conventional solar still) were USD 0.0503 and USD 0.0665. In comparison to its CSS counterpart, the MSS had a CPL that was 32.21 percent lower. The treated water retained a 95.77% reduction in TDS compared to salt water. The MSS is predicted to release 219.62 kg of carbon dioxide, 1.67 kg of sulfur dioxide, and 0.69 kg of nitrous oxide over its lifetime. In addition, the MSS saved USD 20.94 in carbon credits after avoiding the emission of 2.09 tonnes of CO₂.

1. Introduction

Providing humanity with clean water to drink is one of the biggest concerns facing the globe today. Groundwater levels are steadily dropping as a result of the uninterrupted extraction of water resources from the Earth for residential and commercial use [1,2]. Despite being readily available, surface water is mostly brackish and unsafe for human consumption. It takes a sophisticated procedure to purge salts and other contaminants from water in order to obtain it to the right pH level for human use. The traditional desalination methods not only consume a lot of energy but also cost a lot of money [3,4]. Therefore, it is necessary to develop a water desalination method that is affordable, environmentally responsible, and renewable. The most effective and practical solution seems to be solar energy.

Solar stills are affordable and simple devices that use energy from the sun to transform saline water into drinkable water. A rectangular basin covered in black on the inside of the solar still collects the maximum amount of solar radiation and uses that energy to heat the water within [5]. To prevent heat loss to the surroundings, the basin is completely enclosed with heatproof material on the sides and bottom. The solar still’s top is covered with transparent glass to provide an airtight seal [6]. The basin liner captures solar irradiance that has already passed via the glass cover. The heated basin liner transports heat to the surrounding water in the basin via convection and conduction. When water is heated, some of it evaporates and forms condensation on the inner side of the glass cover. The condensed water is eventually collected in a container after travelling via a channel. The water that has been collected in this manner is completely free of all pollutants and salts [7].

To increase distillate yield, researchers have carried out a variety of modifications in solar stills. For example, Kumar et al. [8] deployed magnets to improve distillate yield and they obtained a 21.66% higher yield in contrast to conventional stills due to the magnetic effect. Bilal et al. [9] obtained distillate of 1950 mL by employing pumice stones in a solar still as a heat storage material. Kumar et al. [10] enhanced the performance of a solar still by 104.54% via augmenting magnets with charcoal. Siva et al. [11] increased distillate output by fabricating hierarchical structures for solar desalination. They developed these structures using anodization and additive manufacturing. Additionally, they investigated how these structures at room temperature were affected by the anodization time [12]. Peyman et al. [13] improved a solar still’s yield output by nanocoating on a condensed surface. Afzal et al. [14] improved their distillate yield by 25% via utilizing non-contact nanostructures. These structures have a long life span due to the prevention of salt deposition. Arun et al. [15] enhanced a solar still’s productivity by 32% via utilizing PVA sponges. Raja et al. [16] examined the energy and exergy of truncated and parabolic conic fins to study solar still performance and they concluded that parabolic fins are less efficient when compared to truncated conic fins.

Yang et al. [17] developed a melanin-inspired aerogel evaporator which demonstrated a remarkable evaporation rate of 1.42 kg m⁻² h⁻¹ under the illumination of one sun with an evaporation efficiency of 91%. Xu et al. [18] reviewed various polyphenolic composite materials such as hydrogels, membranes, and nanofibers for water remediation by emphasizing their functional and structural characteristics. Yiyan et al. [19] fabricated a stable and long-lasting clean water remediation system using a bio-inspired photothermal and antibacterial membrane. They reported a 1.61 kg m⁻² h⁻¹ evaporation rate with greater than 90% efficiency. Zhang et al. [20] manufactured a 3D-printed interfacial evaporator and achieved an efficiency of 94.4%; the 3D-printed evaporator with a tall cone structure could evaporate water at a rate of 1.96 kg m^–2 h^–1. Huiying et al. [21] utilized the oxidation process to develop metal–organic framework materials such as nanorods for interfacial solar evaporation and reported a 2.25 kg m^–2 h^–1 evaporation rate. Chen et al. [22] developed inexpensive, mass-produced xerogel foam for the production of thermoelectric power and photothermal water desalination and recorded an average daily production of 8.9 kg m² and a maximum water collection rate of 1.2 kg m⁻² h⁻¹ in outdoor experiments.

The recent literature above utilized magnets, charcoal, fins, evaporators such as melanin-inspired aerogels, antibacterial membranes, foams, 3D-printed nanostructures, nanocoatings, and PVA sponges as substances for storing energy to enhance the distillate yield of solar stills. Slowly, researchers are focusing on utilizing natural materials in solar stills as energy absorption materials due to them being cost effective and environmentally viable.

Kumar and Kousik [23], who improved the condensation and evaporation rates of pure water via utilizing natural fibers and energy storage, achieved 126% distillate yield enhancement. Subbarama and Sendhil [24] utilized Luffa acutangula fiber in a solar still and enhanced the yield by 4.09%, 16.64%, 22.69%, 22.04%, 17.45% and 12.27% with 25, 20, 16, 14, 13, and 10 fibers in the absorber basin in contrast to a traditional solar still. Suraparaju et al. [25] investigated the natural sisal fiber’s effect on a solar still’s condensation rate and improved the distillate output by 19.1% in contrast to a traditional still. Natarajan et al. [26] evaluated a single slope still’s performance by utilizing ridge gourd natural fiber and concluded that the 0.6 m² absorber basin produced 1550 mL using the system without fibers, whereas the solar still using the ridge gourd fiber produced 1500 mL. Kousik et al. [27] employed pond fibers to increase the performance of a single slope still and the results disclosed that the solar still with five dried pond fibers increased freshwater production by 29.67%.

So far, researchers have utilized ridge gourd, pond, Luffa acutangula, sisal, and natural fibers to improve the performance of solar stills. In this work, banana stems were utilized as a biowaste for harvesting solar energy. The pros and cons of the pseudo stem are as follows: the banana stem has a good capillarity and floating nature, which is viable for interfacial solar desalination. Furthermore, utilizing banana stem biowaste is cost-effective and eco-friendly. However, the life span of these stems is limited due to the continuous exposure to solar irradiation over a period of time. A pseudo stem was soothed with camphor to absorb solar energy. The banana stems were placed in a solar still to capture thermal energy from the sun and transfer it to the surrounding water to improve the evaporation rate in order to obtain more freshwater. Studies were carried out over three days by varying the thickness of the banana stems such as 0.5 cm, 1 cm, and 1.5 cm and keeping the depth of water constant (1 cm). The results revealed that the banana stems with a 0.5 cm thickness performed better in contrast to those that were 1 cm and 1.5 cm thick. Furthermore, a water quality analysis was also carried out to make sure that the pure water did not contain any kinds of harmful pathogens and the results were compared to the standard limits provided by the WHO and the BIS. Moreover, enviro-economic investigations have disclosed that desalination has 2.09 tonnes of CO₂ mitigation for 10 years of life.

2. Experimentation

A conventional solar still (CSS) and modified solar still (MSS) were constructed with comparable specifications for size and operation. Plywood was used for the SSs’ exterior construction. The shorter side was 20 cm tall, while the long side was 36 cm in height. The outside construction serves simply as an insulator and was only designed to prevent heat from escaping into the surroundings. Galvanized iron with dimensions of 50 cm × 50 cm × 0.1 cm was used to construct the inside framework of the solar still. There was a 0.25 m² surface area exposed to solar radiation. For saltwater delivery and drainage, a 1.27 cm-diameter entrance was built into the galvanized iron on the back side of the solar still. The water yield production was collected through a channel connecting to the solar still’s shorter side. Figure 1 depicts the experimental setup.

The studies were conducted in Hyderabad’s climate (longitude 78.49° E and latitude 17.39° N). Banana stems were taken and sliced into the desired thicknesses and soothed with camphor. The process of camphor soothing of the banana stems is described in Figure 2. Initially, fresh banana stems were considered and washed with distilled water several times to remove the surface impurities present on them. Later, they were sliced into several pieces (stems) with variation in the required thickness. The sliced stems were washed with deionized water to clean up the microstructure surface, to become ready for soothing and were dried at room temperature. After drying, the stems were exposed to camphor soothing. For soothing of the banana stems, we considered 5 gm of camphor and kept the stems at a height of 4 cm for uniform soothing. The camphor pellets were placed in a crucible and then ignited with a matchbox; the camphor pellets began to melt instantly. Camphor fumes were formed; they grabbed the flame and began to burn vigorously above the crucible. The flame height significantly decreased after 8–9 s, although it continued to burn around the crucible’s opening for 10–16 s. The banana stem was positioned over the top of the flame in order to deposit a thin layer of camphor soot on the surface of the stem. A single coating procedure iteration resulted in a very tiny film of camphor soot on the banana stems. Three such repetitions were performed, resulting in a clearly visible, thin soot coating on the stems. The process was repeated to sooth all of the banana stems with the required quantity to carry out the desalination experiment.

The desalination studies were carried out over three days by varying the thickness of the banana stems such as 0.5 cm, 1 cm, and 1.5 cm and keeping the depth of the water constant. The average diameter of the banana stems was 52 mm. The stems were arranged in the still to cover the entire basin area. Different measurement tools were used to assess the various factors that affected the SSs’ performance, as indicated in

Table 1. Measuring instruments used.

Measuring Device	Standard Uncertainty	% Error	Accuracy
Hukseflux pyranometer (SR05-D1A3)	5.77 W/m2	10	±10 W/m2
RTD sensors	0.5 ℃	0.25	±0.8 ℃
Data logger	0.06 ℃	1.3	±0.1 ℃
Measuring jars	3 mL	5	±5 mL
Anemometer	0.06 m/s	10	±0.1 m/s

. RTD sensors were utilized in each still with an accuracy of ±0.8 °C; the temperatures were recorded at three separate locations using a 16-channel data logger. The points were the basin plate (T_b), the water (T_w), and the inner glass (T_g) cover temperatures. A Hukseflux pyranometer (accuracy 10 W/m²) was utilized to monitor the solar intensity and ambient temperature. To gauge the wind speed, an anemometer with a ±0.1 m/s accuracy was used. The water production was determined utilizing 1 L calibrated measuring jars with a 5 mL accuracy.

3. Results and Discussion

Solar irradiance is directly related to the ambient temperature of the environment. Solar irradiance is affected by wind speed and the values will be recorded with a lower value than the corresponding ambient temperature. The solar irradiance values were recorded on day 1 (with a 0.5 cm-thick banana stem) from 585 W/m² at 10:00 a.m. to 89 W/m² in the evening at 17:00 p.m. with a peak value at 12:00 p.m. as 800 W/m². On day 2 (with a 1.0 cm-thick banana stem), the values ranged from 570 W/m² at 10:00 a.m. to 60 W/m² at 17:00 p.m., and at noon, the peak value of the day was achieved as 785 W/m². On day 3 (with a 1.5 cm-thick banana stem), the values were recorded as 516 W/m² at 10:00 a.m., 754 W/m² at 12:00 p.m., and 110 W/m² at 17:00 p.m. Similarly, the ambient temperature was 22–25 °C at 9:00 a.m. and reached a high of 30–33 °C around mid-day for all three days. On all of the days, the solar irradiance showed little variation, which concludes that all of the days had the same solar intensity conditions with minimal variation which was just negligible. The solar irradiance and ambient temperature variation for all three days are depicted in Figure 3.

Using three distinct thermocouples, the temperatures of the water (T_w), glass (T_g), and basin (T_b) were monitored and are graphically depicted in Figure 4a–c. For the modified still, the maximum water temperatures were obtained at 61 °C, 58 °C, and 59 °C for the 0.5 cm-, 1.0 cm-, and 1.5 cm-thick banana stems, respectively. For the conventional still, the highest water temperatures were 56 °C, 54 °C, and 55 °C for all three consecutive days, respectively. Due to the presence of camphor-soothed banana stems, the temperatures of the water readings between the CSS and the MSS deviate from one another. More solar energy is absorbed by the banana stems in the solar basin, which leads to heat localization and transfers a significant amount of the energy flux from the sun to the water available on the surface of the banana stems. For the modified still with the 0.5 cm-, 1.0 cm-, and 1.5 cm-thick banana stems, the highest basin temperatures were 60 °C, 59 °C, and 57 °C, respectively, while for the conventional still, they were 57 °C, 58 °C, and 56 °C, respectively. This is owing to the energy interactions that occurred between the basin of the solar stills and the camphor-soothed banana stems. A maximum distillate yield was achieved by the improved evaporation rates, which were aided by the aforementioned water and basin temperatures. For the modified still, the highest glass interior temperatures were 54 °C for the 0.5 cm-, 55 °C for the 1.0 cm-, and 56 °C for the 1.5 cm-thick banana stems. The maximum glass interior temperatures for the conventional still were 52 °C, 54 °C, and 53 °C, respectively. Moreover, the evaporation of rate of saline water depends on the difference in temperature (T_w-g) between the water (T_w) and the glass (T_g). As this difference in temperature increases, the evaporation rate will also increase. This difference in the case of 0.5 cm and 1.0 cm was about 7 °C and 3 °C, respectively, in the MSS at the peak time. For the present study, the camphor-soothed stems absorbed the incoming solar energy and transferred it to the water surrounding them. As a result, the water temperatures are higher when compared to the basin temperatures in the MSS, whereas in the CSS, the basin temperatures are more in contrast to the water temperatures. For all three consecutive days, the highest temperature values were reached at mid-day and followed a similar pattern to the ambient temperature and solar irradiance.

With three different thicknesses of banana stems, the hourly yield and cumulative yield of both the CSS and MSS have been graphically depicted in Figure 5 and Figure 6, respectively. It is shown from the graphs that the distillate yield generated was more for the 0.5 cm-thick banana stems in contrast to the 1.0 cm- and 1.5 cm-thick banana stems. This is due to the capillary action of the banana stems. As the banana stem thickness increases, the time required for water vapor to reach the evaporation surface also increases. Another reason is that only a layer of water is available on the banana stem surface which rapidly evaporated as the camphor soothing of the banana stem readily absorbs energy from the sun. The maximum hourly water production was achieved at mid-day and those values were 0.88 kg m⁻² h⁻¹, 0.88 kg m⁻² h⁻¹, and 0.84 kg m⁻² h⁻¹ for the MSS and 0.48 kg m⁻² h⁻¹, 0.66 kg m⁻² h⁻¹, and 0.68 kg m⁻² h⁻¹ for the CSS for the 0.5 cm-, 1.0 cm-, and 1.5 cm-thick banana stems, respectively. The maximum hourly water purification production efficiency of 83% was attained for the 0.5 cm-thick banana stems in the MSS in contrast to the CSS. The conventional still produced 685 mL, 670 mL, and 680 mL of distillate on three different days, but the modified still produced 934 mL, 865 mL, and 780 mL of distillate with the 0.5 cm-, 1.0 cm-, and 1.5 cm-thick banana stems, respectively. The banana stem with a 0.5 cm thickness produced yields of 36.35%, 7.97%, and 19.74% more in contrast to the CSS for the studies of 1.0 cm and 1.5 cm thickness.

4. Monetary Analysis

The following mathematical formulas given by [28,29] were used to assess the monetary analytical modelling, i.e., equations from (1)–(9).

$$\mathrm{CRF} (\mathrm{Capital} \mathrm{recovery} \cos \mathrm{t}=\frac{\mathrm{i}{(1+\mathrm{i})}^{\mathrm{y}}}{[\left(1+\mathrm{i}{)}^{\mathrm{y}}-1\right]}$$

(1)

The following assumptions have been made:

Life of solar still (y) = 10 Years

Interest rate (i) = 12%

Number of sunny days (n) = 250

$$\mathrm{FAC} \left(\mathrm{Fixed} \mathrm{annual} \cos \mathrm{t}\right)=\mathrm{P}\left(\mathrm{Capital} \cos \mathrm{t}\right)\times \mathrm{CRF}$$

(2)

$$\mathrm{S} \left(\mathrm{Salvage} \mathrm{value}\right)=0.2\times \mathrm{P}$$

(3)

$$\mathrm{SFF} \left(\mathrm{Sin}\mathrm{king} \mathrm{fund} \mathrm{factor} \right)=\frac{\mathrm{i}}{[\left(1+\mathrm{i}{)}^{\mathrm{y}}-1\right]}$$

(4)

$$\mathrm{ASV} \left(\mathrm{Annual} \mathrm{salvage} \mathrm{value} \right)=\mathrm{SFF} \times \mathrm{S}$$

(5)

$$\mathrm{AMC} \left(\mathrm{Annual} \mathrm{maintenance} \mathrm{operational} \cos \mathrm{t}\right)=0.15\times \mathrm{FAC}$$

(6)

$$\mathrm{AC} \left(\mathrm{Annual} \cos \mathrm{t} \right)=\mathrm{FAC}+\mathrm{AMC}-\mathrm{ASV}$$

(7)

$$\mathrm{M} \left(\mathrm{Average} \mathrm{annual} \mathrm{productivity} \mathrm{in} \mathrm{liters} \right)=\mathrm{c} \times \mathrm{n}$$

(8)

where

n = sunny days per year

c = yield/day

$$\mathrm{CPL} \left(\mathrm{Distilled} \mathrm{water} \cos \mathrm{t} \mathrm{per} \mathrm{liter} \right)=\frac{\mathrm{AC}}{\mathrm{M}}$$

(9)

The cost of fabricating the CSS and the MSS, which includes all of the materials needed for production which are listed in

Table 2. Costs associated with the manufacture of solar stills.

S. No	Material/Service	Area/Quantity per Still	CSS (USD)	MSS (USD)
1.	Glasses	2.5 m2	15	15
2.	PVC collecting channel	1	5	5
3.	Black powder coating	1 m2	4	4
4.	Glass cover, 0.4 cm	0.5 m2	1	1
5.	Double side foam tape	1.5 m	1	1
6.	Silicon glue	1	3	3
7.	Camphor sooth	200 gm	-	2
8.	Banana stem	0.9 kg	-	-
9.	Fabrication charges	-	30	30
	Total cost	-	59	61

, was USD 59 and USD 61, respectively. The financial analysis parameters included in the mathematical modelling are listed in

Table 3. Economical comparison between the MSS and the CSS in USD.

Parameters in USD	Conventional Still	Modified Still
P	59	61
CRF	0.177	0.177
FAC	10.45	10.80
S	11.8	12.2
SFF	0.05698	0.05698
ASV	0.6723	0.6951
AMC	1.5675	1.6200
AC	11.34	11.72
M	171	233
CPL	0.0665	0.0503

. Due to its higher daily distillate output (934 mL/day) than the CSS, the MSS greatly increased its yearly productivity by 36.25%, further demonstrating its superiority in terms of productivity. The CSS and MSS’s respective CPLs were USD 0.0665 and USD 0.0503. The MSS’s CPL was 32.21% smaller than that of its equivalent CSS. As a result, the MSS became affordable in the perspective of the CPL.

5. Assessment of Water Quality

Before and after desalination, the quality of the CSS and the MSS’s water was evaluated to make sure that the distillate water was within the limits set by the BIS (Bureau of Indian Standards) and the WHO (World Health Organization). The results of the water quality tests, which were completed at Hyderabad’s VNRVJIET Environmental Engineering Laboratory, are summarized in

Table 4. Water quality assessment.

Water Quality Metrics	Prior to Desalination	After Desalination (CSS)	After Desalination (MSS)	Maximum Allowable Levels in Drinking Water (WHO and BIS Standards) [30]
pH	8.16	7.50	7.25	8.5
Fluoride (mg/L)	0.579	0.426	0.348	1.5
Hardness (mg/L)	330	160	125	200
TDS (ppm)	440	30	18.6	500
Chloride (mg/L)	57.6	10.45	7.68	250

.

The CSS and the MSS were able to reduce the pH of the brine water from 8.16 to 7.50 and 7.25, respectively. Prior to desalination, the total dissolved solids (TDS) were at 440 ppm; however, following desalination, the TDS levels were substantially decreased to 30 ppm for the CSS and 18.6 ppm for the MSS. When compared to saline water, the TDS levels of the MSS decreased by 95.77%. The hardness values for brine water were 330 mg/L, the CSS was 160 mg/L, and the MSS was 125 mg/L. Brine water had 0.579 mg/L of fluoride ions, while the MSS and the CSS had values of 0.348 mg/L and 0.426 mg/L, respectively. All of the water quality metrics for the MSS and the CSS fell within the BIS and WHO, India, permissible levels [30].

6. Enviro-Economic Investigation

The investigation determines the amount of SO₂, CO₂, and NO released by the MSS throughout its lifespan. Furthermore, it includes data on the overall embodied energy utilized to generate the MSS. Additionally, it provides information about the overall CO₂ reduction and the proportionate credit of carbon generated. The aforementioned parameters may be computed using the following equations [31,32]:

The following empirical formula is used to estimate the total amount of CO₂ emissions during the lifetime of the MSS.

$${\mathrm{CO}}_2 \mathrm{emission}=1.58\times \mathrm{Embodied} \mathrm{energy}$$

(10)

Likewise,

$${\mathrm{SO}}_2 \mathrm{emission}=0.012\times \mathrm{Embodied} \mathrm{energy}$$

(11)

$$\mathrm{NO} \mathrm{emission}=0.005\times \mathrm{Embodied} \mathrm{energy}$$

(12)

The net CO₂ reduction during the life of the MSS may be determined using the equation below:

$${\mathrm{Net} \mathrm{CO}}_2 \mathrm{mitigation} \mathrm{for} \mathrm{lifetime} =\frac{\left[ \left(\mathrm{Embodied} \mathrm{energy} \left(\mathrm{out}\right)\times \mathrm{y}\right)-\mathrm{Embodied} \mathrm{energy} \right]\times 1.58}{1000}$$

(13)

where y = 10 (lifespan in years)

The desalination system’s carbon credit and overall system embodied energy are determined by:

$$\mathrm{Embodied} \mathrm{energy} \left(\mathrm{out}\right)=\frac{\mathrm{Annual} \mathrm{yield} \times \mathrm{latent} \mathrm{heat}}{3600}$$

(14)

For a 0.25 m² area, the yearly production is 233.5 L, and a latent heat of vaporization of 2260 kJ/kg is considered [33].

$$\mathrm{Carbon} \mathrm{credit} \mathrm{earned}={\mathrm{Net} \mathrm{CO}}_2 \mathrm{mitigated} \mathrm{for} \mathrm{lifespan} \times 9.99$$

(15)

Table 5. The MSS’s overall embodied energy.

Components	Weight/Volume	Energy Density (kWh/kg or kWh/m3)	Embodied Energy (kWh)
Galvanized iron sheet (0.1 cm thickness)	8 kg	10.83	86.64
Plywood sheet (1.8 cm thickness)	8 kg	4.167	33.34
Glass cover	0.51 m × 0.6 m × 0.004 m	11,127.8	13.62
Foam tape on two sides and silicon glue	0.25 kg	3.3	0.83
PVC channel	0.2 kg	18.75	3.75
Banana stem + Camphor soothing	0.9 kg	0.95	0.85
Total embodied energy			139.03

compiles the embodied energy (EE), components of a variety of materials, and energy density (ED) employed in the MSS [34,35]. The total EE is required to calculate CO₂ emissions, sulfur emissions, nitrogen emissions, and other environmental and economic characteristics. When compared to the other materials employed in the system, glass had the highest value of 11,127.8 kWh/m³ ED and accounted for 13.62 kWh of embodied energy. With 4.167 kWh/kg ED and an 8 kg mass, a plywood sheet with a thickness of 1.8 cm produced 33.34 kWh, the highest EE. An ED of 10.83 kWh/kg and an EE of 86.64 kWh were measured on 8 kg of galvanized iron which was utilized to manufacture a solar still inside walls and a basin liner.

The system gained 3.75 kWh of EE from the 0.2 kg of the PVC collecting channel, which had an 18.75 kWh/kg ED. A minimum EE of 0.83 kWh was produced by the additional parts such as the silicon glue and double-sided foam tape. Banana stems as a biowaste that were also employed in the MSS for the purpose of enhancing water productivity account for 0.85 kWh. Consequently, the overall EE for the entire MSS will be 139 kWh by summing the EE for each individual material. This study’s projected total EE will be used as an input source for the determination of enviro-economic metrics.

Table 6. Emissions of SO₂, CO₂, and NO, CO₂ reduction, and earned carbon credits for the MSS.

S. No	Parameters	Values
1.	Embodied energy (out)	146.58 kWh
2.	Lifespan CO2 emission	219.62 kg
3.	Lifespan SO2 emission	1.67 kg
4.	Lifespan NO emission	0.69 kg
5.	Embodied energy	139 kWh
6.	Net CO2 reduction for 10 years	2.09 tonnes
7.	Earned carbon credit for 10 years	USD 20.94

shows the MSS’s CO₂, SO₂, and NO emissions in tonnes, as well as the amount of carbon credits gained in US dollars. The MSS is estimated to release 219.62 kg of CO₂, 1.67 kg of SO₂, and 0.69 kg of NO throughout its lifetime. For ten years of life duration, the net CO₂ mitigation from the MSS was 2.09 tonnes. Carbon credit is a straightforward translation of the net amount of CO₂ reduced to the economic value. The amount of carbon credits obtained for reducing CO₂ by 2.09 tonnes was USD 20.94. The reason behind the poor carbon credit and net CO₂ reduction obtained was that the desalination system required a large amount of embodied energy; 86.64 kWh was utilized by the galvanized iron. Finally, it is suggested that constituents with lower EE values should be used to reduce the emissions of SO₂, CO₂, and NO, boost the carbon credits, and enhance the value of net CO₂ reduction.

7. Conclusions

As the thickness of the banana stems increases, the distillate yield of the still decreases. The maximum yield of 934 mL was obtained with an efficiency of 36.35% in contrast to the conventional still. The modified still with 0.5 cm-thick banana stems enhanced its performance by 7.97% and 19.74% when compared to the 1.0 cm- and 1.5 cm-thick banana stems, respectively. The maximum hourly evaporation rate of 0.88 kg m⁻² h⁻¹ was obtained for the MSS (0.5 cm-thick banana stems) with a conversion efficiency of 83% in contrast to the CSS. The CPLs for the MSS and the CSS were USD 0.0503 and USD 0.0665, respectively. The CPL of the MSS was 32.21% lower in contrast to its counterpart CSS. As a result, the MSS became more inexpensive in terms of CPL.

The CSS and MSS were able to reduce the pH of the brine water from 8.16 to 7.50 and 7.25, respectively. The total dissolved solids (TDS) were at 440 ppm before desalination; however, after desalination, the TDS levels were significantly reduced to 30 ppm for the CSS and 18.6 ppm for the MSS. The modified still’s TDS levels were 95.77% lower than those of saline water. Over the course of its lifespan, the MSS is predicted to emit 219.62 kg of CO₂, 1.67 kg of SO₂, and 0.69 kg of NO. The modified still’s net CO₂ mitigation for 10 years of life was 2.09 tonnes.

The presented study is a small but significant step towards the feasibility to deploy biowaste in solar desalination systems. Biowaste has the benefit of acting as a thermal absorber on one side and as an insulator on the other. It is extremely desirable to transfer heat to a thin layer of water on one side while avoiding heat loss on the other. Apart from banana stems, this investigation opens the pathway to assess several other forms of biowaste which would not only enhance the efficacy of solar desalination systems but will also aid in sustainable and eco-friendly waste management practices.