# Ethiopian Water Hyacinth Leaf Extract as a Potential Tannery Effluent Treatment Material

Authors: Fitsum Etefa Ahmed; Awoke Fenta Wodag; Gemeda Gebino Gelebo; Belay Meles Gebre
Journal: Journal of Engineering
 (2022)

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## Abstract

Industrial effluents have a serious problem on our ecosystem. Tannery effluent contains a huge amount of pollutant compounds such as toxic substances which need to be treated using either synthetic or natural products. The present study focussed on the treatment of tannery effluents using water hyacinth plant leaf extract. Though some researchers have tried to use this extract for the same, the researchers have experimented only to treat that of Cr3+ and there are a bit of difference in the methodology they followed. In addition, the scope of this research was wider. In this study, fresh raw WH leaves were collected from around Lake Tana, Ethiopia, cleaned and made to powder and then extraction was performed using different solvents. The solvent effects were examined using the ANOVA test. The tannery wastewater was treated with the extracts and parts of the effluents were kept as a control for comparison. Treated and untreated tannery effluents were compared using standard methods such as SLC 22, SLC 8, APHA 2540C, APHA 2540D, and Hack LCK 139 to determine Cr6+, Cr3+, TDS, TSS, and TKN, respectively. The highest amount of Cr6+, Cr3+, and TKN were removed at 30% water hyacinth leaves extracted by distilled water solvent and that of the least was found at hyacinth leaves extract by ethanol solvent but by acetone in BOD and COD treatment. In addition, though it was out of the permissible limit, by using the same amount of the material extracted by distilled water solvent some amounts of BOD and TDS were removed from the wastes compared to that of untreated tannery effluents. Generally, water hyacinth leaf extract is found effective material for the treatment of tannery effluents and can be used in the sector industries. Future studies may be required for setting the most optimum extract concentration for better results.


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## Body

## 1. Introduction

In industries, toxic wastes are released from different chemical processes into the environment [1]. It has negative effects on the health of humans and animals [2]. Leather manufacturing contains chemical and mechanical processes in order to convert raw hides and skins into a stable leather material that will suitable for a wide variety of applications [3]. In the process of turning animal hides into leather, almost every tannery uses a considerable amount of chemicals. Sodium sulfite, basic chromium sulfate, ammonium sulfide, ammonium chloride, bactericides, sodium chloride, wetting agents, enzymes, and other chemicals are used in tanneries in large amounts [4]. In the chrome tanning process, around 276 chemicals and 14 heavy metals are used all of which contribute significantly to water contamination [5]. According to a research findings report, only 20% of the chemicals used in the tanning process are absorbed by the leather and the rest will be released as waste [6]. The several components in the tannery wastewater have an impact on agriculture and livestock as well as creating serious health problems in tannery employees such as eye illnesses, skin irritations, kidney failure, and intestinal problems [7].The majority of tanneries use a chromium-based tanning process that needs a lot of water and chemicals [8], and around 90% of the industries are releasing their effluents into water bodies, streams, and land without any treatment mechanisms [9]. The tanneries produce 30–35 liters of wastewater per kilogram of skin or hide, with an estimated annual amount of 400 million cubic meters of liquid waste discharge [10].For example, the case of Ethiopia’s physicochemical analysis study revealed that most Ethiopian tannery effluents showed that several wastewater quality parameters (COD, BOD, sulfide, total nitrogen, total chromium, TDS, and TSS) are beyond the country’s industrial treatment standards [8]. Basic chromium sulfate is a tanning agent used by 90% of tanning industries [11], and the unabsorbed part of it will be discharged with the wastewater [12]. In Ethiopia, around 10% of the existing tanning industries treat their wastewater to any degree while the majority discharge their wastewater into nearby water bodies, streams, and open land without any kind of treatment [13]. This makes industrial and chemical pollution to become a major problem in the country and one of the great environmental concerns [14]. Therefore, the removal of chromium and related pollutant chemicals and materials from tannery wastewater is highly advisable.According to the World Health Organization for drinking water quality recommendations [15], one of the many metals of most immediate concern is chromium [16]. Although some heavy metals are essential as trace elements, their biotoxic effects on human biochemistry are a major source of concern. If the concentration of heavy metals exceeds their limits in the drinking water, it can affect human health [17]. As a result, heavy metal removal from aqueous solutions has gotten a lot of attention in recent years [18]. Therefore, wastewater treatment is essential to resolve the effects of the mentioned toxic byproducts on the environment. Wastewater treatment is the process of partially removing and changing the solids in wastewater from highly complex putrescible organic solids to mineral or relatively stable organic solids through decomposition [19]. Several conventional treatment methods, such as the biological process was used to treat wastewater from the tannery industry [20–22], oxidation process [23, 24], chemical process [25], etc. One of the biological wastewater treatment systems is phytoremediation [26], and its the concept of removing toxins from the environment using plant-based systems and microbiological processes [27]. The majority of heavy metal removal methods are quite expensive and injurious to health [14]. Natural plant extracts have been used for water purification for many years. The majority of these extracts come from tree and plant seeds, leaves, bark or sap, roots, and fruit [28]. In Ethiopia, water hyacinth plant is harmful to water, and it is invading Lake Tana since 2011 [29], and the area covered at the time of inception was approximately 80 to 100 ha [30]. In addition, water hyacinth plant has recently got a lot of attention in order to use it as a source of income in many parts of the world [30–33].In addition, this plant and its extract have been used for wastewater treatment in phytoremediation techniques using constructed wetland [34, 35]. Sudanese researchers [36] studied the effects of extraction solvents on total contents and activities of extracts from Sudanese medicinal plants because the choice of appropriate extraction solvent is essential for the desired activity of the extracts [36]; however, their study was focused on the plant extract medicinal applications. Likewise, in this study, the researchers believed that the proper choices of extraction solvents are required to extract the WH leaf material for tannery wastewater treatment. In the case of Ethiopia, some researchers have tried to use these plant extracts for wastewater treatment to treat only Cr3+ [37]. However, in this study, in addition to investigating its leaf extracts as a potential treatment material for tannery effluent treatment, the effects of the extraction solvents on the potential of the extracted material to remove different toxic and pollutant chemicals from tannery wastewater are also emphasized. Some other researchers tried to use the same for the treatment of wastewater other than tannery waste but there is a difference between these wastes and tannery wastes in pollutant contents because tannery effluents have many chemicals discharged with the effluents [8]. The research output may result in decreasing the rate of the plant’s attack on water bodies and usage of treated tannery effluents for alternative usages. In the study, the researchers collected water hyacinths plant leaves around Lake Tana, Bahir Dar City, Ethiopia, and cleaned them, dried them, and extracted the required treating material from the leaves by using ethanol acetone, distilled water, and extracting solvents. These solvents have been used by previous researchers in materials extraction from given plants [38–41].


## 2. Materials and Methods

### 2.1. Materials

The raw leaves and stems of healthy water hyacinths were collected from around Lake Tana near Kristos Samra Monastery, Gonder, Ethiopia. The plant leaves were cleaned from physical foreign bodies, rinsed to remove impurities, and chopped into small chips for faster drying. As shown in Figure1, drying the leaves was carried out outdoors for seven days in which the temperature ranges between 25°C and 104°C and oven-dried at 104°C for hrs. Distilled water, acetone, and ethanol were used as solvent materials for the extraction.Figure 1
(a) Freshwater hyacinth leaves in sun drying and (b) water hyacinth parts in oven drying.


### 2.2. Collection of Sample Tannery Wastewater

A sample of tannery wastewater was collected at effluent exit points of Bahir Dar tannery in Ethiopia. Sample bottles were rinsed with water to minimize the risk of external contamination before sampling and the bottles are prelabeled. The samples were collected at 2 : 00 a.m., when the tannery was running at full capacity, and the wastewater flow was expected to be at its peak. The chrome effluent was deep blue in color at the time of sampling, while the general effluent was light brownish in color. During collection, the temperature of the wastewater samples was recorded at 25 degrees Celsius using a calibrated thermometer. The effluent samples were sealed and stored in a refrigerator for further use and later usage.


### 2.3. Preparation of the Plant Extracts

Before extraction, the dried leaves were grounded in a high-speed multifunction grinder with a mesh size of 50–300 mesh shown in Figure2. The main reason behind grounding the plant part was to maximize the surface area available for extractions which increases the extraction rate. The powdered samples are placed in small plastic bags for later experimental usage.Figure 2
(a, b) Water hyacinth leaves in powder grinding and (c) powder form of the WH leaves.Distilled water, acetone, and ethanol solvents were used for different plant extract preparation [38, 40]. Amount of 50 g of water hyacinth leaves powder were soaked with (500 ml) separate solvents of distilled water, acetone, and ethanol in a glass beaker and incubated for 48 hours. The mixtures were then stirred for 1 hour [39] at room temperature and filtered using Whatman 1 paper, 24 cm disc [41]. As shown in Figure 3, the mixtures were then centrifuged (4000 rpm, 25°C) for 15 minutes [42]. Finally, 300 ml active component per one cycle of extraction was obtained. This active component of the extract has a phenolic chemical structure which is the main content of the extract that gives it antioxidant activities [43]. The extracts obtained were kept in bottles at 20°C for further analysis.Figure 3
(a) Magnetic stirrer. (b) Whatman paper filtration. (c) Centrifugation filtration.


### 2.4. Tannery Effluents Treatment Method

The amount 70% and 90% of tannery effluent were treated with 30% (30 ml) and 10% of distilled water and ethanol and acetone extract of water hyacinth leaves, respectively, and the result is presented in Table1. Separate solutions were prepared by treating tannery effluents with 10% (10 ml) and 30% (30 ml) of plant extract of distilled water, ethanol, and acetone for three consequent days [46]. As shown in Figure 4, each solution was then shaken for 24 hrs at room temperature (25 ± 2°C) at 150 rpm using a BioSan multifunctional orbital shaker PSU-20i [47] in order to increase the opportunity for solution reaction. The same mount untreated tannery effluents were used as a control experiment for comparison purposes with the treated one. Each solution was then allowed to stand at 4oC for further analysis.Table 1
The typical characteristics of Tannery wastewater (control) and treated tannery effluents.
Physicochemical waste parametersTreated tannery effluent by water hyacinth (WH) leaves extract using different extraction solventsUntreated samplePermissible discharge limit [44, 45]Distilled water extract of WH leaves (10%)Acetone extract of WH leaves (10%)Ethanol extract of WH leaves (10%)Distilled water extract of WH leaves (30%)Acetone extract of WH leaves (30%)Ethanol extract of WH leaves (30%)Tannery wastewater (control)pH6.647.247.716.987.337.526.96–9Cr3+ (mg/l)2.852.93.01.842.842.853.61.5–2.0Cr6+ (mg/l)0.030.040.190.020.050.150.060.05TDS (mg/l)21632197284821342124276423421000TSS (mg/l)21521025614018224415050TKN (mg/l)11532905.458134660COD9792291313729104229823142501086500BOD57.213516435.3133.3108.338200Figure 4
(a) BioSan multifunctional orbital shaker.


### 2.5. Determination of Waste Parameters

Tannery effluent (control) and treated wastewater characterization were determined using the following standard test procedures and required sample solutions were taken from each stock solution.


#### 2.5.1. pH Values Measurement

pH indicates the acidic or alkaline nature of any water body. The pH of untreated and treated wastewater was determined by using a pH meter.


#### 2.5.2. Chromium (III) Determination

The amount of chromium (III) in controlled and treated tannery wastewater was measured using a titrimetric method according to the Society of Leather Chemistry (SLC 8) [48].


#### 2.5.3. Chromium (VI) Measurement

the volume of chromium (IV) of both wastewaters was measured using a UV-visible spectrometer and the SLC 22 method (Society of Leather Chemists).


#### 2.5.4. Total Dissolved Solids (TDSs) Measurement

TDS in the initial and treated tannery wastewater was determined according to the APHA 2540C (American Public Health Association) standard procedure.Total suspended solids (TSSs) measurement: the TSS treated and untreated tannery wastewater was determined using the APHA 2540D standard method. The crucible and filter paper were first dried for 1 hour at 104°C, then cooled in a desiccator, and the weight was measured and registered. 100 ml wastewater was filtered onto filter paper after being weighed in a measuring cylinder. The residue sample on the filter paper was placed in an oven at 105°C for 1 hr, the filter paper and crucible in the desiccator were cooled, the weight was measured, and then, the TSS was determined by calculation using the following equation and is expressed in mg/l [49, 50]:(1)TSSmg/l=0,1Weight of filter paper+residue after drying–weight of crucible beforeD∗1000∗1000Volume of sample takenml.


#### 2.5.5. Total Kjeldahl Nitrogen (TKN)

The TKN values of both wastes were determined according to the Hack LCK 139 standard method.


#### 2.5.6. Biochemical Oxygen Demand (BOD)

Biochemical oxygen demand (BOD) of an effluent is the milligram of oxygen required to biologically stabilize one liter of that in 5 days at 20oC [51, 52]. The BOD concentration in the untreated and treated tannery wastewater was determined using an open reflux procedure.


#### 2.5.7. Chemical Oxygen Demand (COD) Determination

COD is the amount of oxygen needed to oxidize the oxidizable chemicals contained in one liter of effluent under specific conditions, expressed in milligrams [52, 53]. A bottom flask was filled with 20 mL of sample wastewater and 1 g of H2SO4, and the 5 mL sulfuric acid reagent was slowly added to dissolve H2SO4. After that, a 25 ml solution of 0.04167 M K2Cr2o7 was applied to the mixture. Cooling water was turned on and the bottom flask was connected to the condenser. Swirling and mixing were continued while applying the remaining sulfuric acid reagent (70 ml) through the open end of the condenser. The excess K2Cr2o7 was then titrated with FAS using 6 drops of ferroin indicator after cooling to room temperature.(2)CODmgO2/L=ml of FAS used for blank–ml of FAS used for sample∗M∗8000Sample volumeml.where 8000 = milli equivalent weight of oxygen (8) × 1000 mL/L.


## 2.1. Materials

The raw leaves and stems of healthy water hyacinths were collected from around Lake Tana near Kristos Samra Monastery, Gonder, Ethiopia. The plant leaves were cleaned from physical foreign bodies, rinsed to remove impurities, and chopped into small chips for faster drying. As shown in Figure1, drying the leaves was carried out outdoors for seven days in which the temperature ranges between 25°C and 104°C and oven-dried at 104°C for hrs. Distilled water, acetone, and ethanol were used as solvent materials for the extraction.Figure 1
(a) Freshwater hyacinth leaves in sun drying and (b) water hyacinth parts in oven drying.


## 2.2. Collection of Sample Tannery Wastewater

A sample of tannery wastewater was collected at effluent exit points of Bahir Dar tannery in Ethiopia. Sample bottles were rinsed with water to minimize the risk of external contamination before sampling and the bottles are prelabeled. The samples were collected at 2 : 00 a.m., when the tannery was running at full capacity, and the wastewater flow was expected to be at its peak. The chrome effluent was deep blue in color at the time of sampling, while the general effluent was light brownish in color. During collection, the temperature of the wastewater samples was recorded at 25 degrees Celsius using a calibrated thermometer. The effluent samples were sealed and stored in a refrigerator for further use and later usage.


## 2.3. Preparation of the Plant Extracts

Before extraction, the dried leaves were grounded in a high-speed multifunction grinder with a mesh size of 50–300 mesh shown in Figure2. The main reason behind grounding the plant part was to maximize the surface area available for extractions which increases the extraction rate. The powdered samples are placed in small plastic bags for later experimental usage.Figure 2
(a, b) Water hyacinth leaves in powder grinding and (c) powder form of the WH leaves.Distilled water, acetone, and ethanol solvents were used for different plant extract preparation [38, 40]. Amount of 50 g of water hyacinth leaves powder were soaked with (500 ml) separate solvents of distilled water, acetone, and ethanol in a glass beaker and incubated for 48 hours. The mixtures were then stirred for 1 hour [39] at room temperature and filtered using Whatman 1 paper, 24 cm disc [41]. As shown in Figure 3, the mixtures were then centrifuged (4000 rpm, 25°C) for 15 minutes [42]. Finally, 300 ml active component per one cycle of extraction was obtained. This active component of the extract has a phenolic chemical structure which is the main content of the extract that gives it antioxidant activities [43]. The extracts obtained were kept in bottles at 20°C for further analysis.Figure 3
(a) Magnetic stirrer. (b) Whatman paper filtration. (c) Centrifugation filtration.


## 2.4. Tannery Effluents Treatment Method

The amount 70% and 90% of tannery effluent were treated with 30% (30 ml) and 10% of distilled water and ethanol and acetone extract of water hyacinth leaves, respectively, and the result is presented in Table1. Separate solutions were prepared by treating tannery effluents with 10% (10 ml) and 30% (30 ml) of plant extract of distilled water, ethanol, and acetone for three consequent days [46]. As shown in Figure 4, each solution was then shaken for 24 hrs at room temperature (25 ± 2°C) at 150 rpm using a BioSan multifunctional orbital shaker PSU-20i [47] in order to increase the opportunity for solution reaction. The same mount untreated tannery effluents were used as a control experiment for comparison purposes with the treated one. Each solution was then allowed to stand at 4oC for further analysis.Table 1
The typical characteristics of Tannery wastewater (control) and treated tannery effluents.
Physicochemical waste parametersTreated tannery effluent by water hyacinth (WH) leaves extract using different extraction solventsUntreated samplePermissible discharge limit [44, 45]Distilled water extract of WH leaves (10%)Acetone extract of WH leaves (10%)Ethanol extract of WH leaves (10%)Distilled water extract of WH leaves (30%)Acetone extract of WH leaves (30%)Ethanol extract of WH leaves (30%)Tannery wastewater (control)pH6.647.247.716.987.337.526.96–9Cr3+ (mg/l)2.852.93.01.842.842.853.61.5–2.0Cr6+ (mg/l)0.030.040.190.020.050.150.060.05TDS (mg/l)21632197284821342124276423421000TSS (mg/l)21521025614018224415050TKN (mg/l)11532905.458134660COD9792291313729104229823142501086500BOD57.213516435.3133.3108.338200Figure 4
(a) BioSan multifunctional orbital shaker.


## 2.5. Determination of Waste Parameters

Tannery effluent (control) and treated wastewater characterization were determined using the following standard test procedures and required sample solutions were taken from each stock solution.


### 2.5.1. pH Values Measurement

pH indicates the acidic or alkaline nature of any water body. The pH of untreated and treated wastewater was determined by using a pH meter.


### 2.5.2. Chromium (III) Determination

The amount of chromium (III) in controlled and treated tannery wastewater was measured using a titrimetric method according to the Society of Leather Chemistry (SLC 8) [48].


### 2.5.3. Chromium (VI) Measurement

the volume of chromium (IV) of both wastewaters was measured using a UV-visible spectrometer and the SLC 22 method (Society of Leather Chemists).


### 2.5.4. Total Dissolved Solids (TDSs) Measurement

TDS in the initial and treated tannery wastewater was determined according to the APHA 2540C (American Public Health Association) standard procedure.Total suspended solids (TSSs) measurement: the TSS treated and untreated tannery wastewater was determined using the APHA 2540D standard method. The crucible and filter paper were first dried for 1 hour at 104°C, then cooled in a desiccator, and the weight was measured and registered. 100 ml wastewater was filtered onto filter paper after being weighed in a measuring cylinder. The residue sample on the filter paper was placed in an oven at 105°C for 1 hr, the filter paper and crucible in the desiccator were cooled, the weight was measured, and then, the TSS was determined by calculation using the following equation and is expressed in mg/l [49, 50]:(1)TSSmg/l=0,1Weight of filter paper+residue after drying–weight of crucible beforeD∗1000∗1000Volume of sample takenml.


### 2.5.5. Total Kjeldahl Nitrogen (TKN)

The TKN values of both wastes were determined according to the Hack LCK 139 standard method.


### 2.5.6. Biochemical Oxygen Demand (BOD)

Biochemical oxygen demand (BOD) of an effluent is the milligram of oxygen required to biologically stabilize one liter of that in 5 days at 20oC [51, 52]. The BOD concentration in the untreated and treated tannery wastewater was determined using an open reflux procedure.


### 2.5.7. Chemical Oxygen Demand (COD) Determination

COD is the amount of oxygen needed to oxidize the oxidizable chemicals contained in one liter of effluent under specific conditions, expressed in milligrams [52, 53]. A bottom flask was filled with 20 mL of sample wastewater and 1 g of H2SO4, and the 5 mL sulfuric acid reagent was slowly added to dissolve H2SO4. After that, a 25 ml solution of 0.04167 M K2Cr2o7 was applied to the mixture. Cooling water was turned on and the bottom flask was connected to the condenser. Swirling and mixing were continued while applying the remaining sulfuric acid reagent (70 ml) through the open end of the condenser. The excess K2Cr2o7 was then titrated with FAS using 6 drops of ferroin indicator after cooling to room temperature.(2)CODmgO2/L=ml of FAS used for blank–ml of FAS used for sample∗M∗8000Sample volumeml.where 8000 = milli equivalent weight of oxygen (8) × 1000 mL/L.


## 2.5.1. pH Values Measurement

pH indicates the acidic or alkaline nature of any water body. The pH of untreated and treated wastewater was determined by using a pH meter.


## 2.5.2. Chromium (III) Determination

The amount of chromium (III) in controlled and treated tannery wastewater was measured using a titrimetric method according to the Society of Leather Chemistry (SLC 8) [48].


## 2.5.3. Chromium (VI) Measurement

the volume of chromium (IV) of both wastewaters was measured using a UV-visible spectrometer and the SLC 22 method (Society of Leather Chemists).


## 2.5.4. Total Dissolved Solids (TDSs) Measurement

TDS in the initial and treated tannery wastewater was determined according to the APHA 2540C (American Public Health Association) standard procedure.Total suspended solids (TSSs) measurement: the TSS treated and untreated tannery wastewater was determined using the APHA 2540D standard method. The crucible and filter paper were first dried for 1 hour at 104°C, then cooled in a desiccator, and the weight was measured and registered. 100 ml wastewater was filtered onto filter paper after being weighed in a measuring cylinder. The residue sample on the filter paper was placed in an oven at 105°C for 1 hr, the filter paper and crucible in the desiccator were cooled, the weight was measured, and then, the TSS was determined by calculation using the following equation and is expressed in mg/l [49, 50]:(1)TSSmg/l=0,1Weight of filter paper+residue after drying–weight of crucible beforeD∗1000∗1000Volume of sample takenml.


## 2.5.5. Total Kjeldahl Nitrogen (TKN)

The TKN values of both wastes were determined according to the Hack LCK 139 standard method.


## 2.5.6. Biochemical Oxygen Demand (BOD)

Biochemical oxygen demand (BOD) of an effluent is the milligram of oxygen required to biologically stabilize one liter of that in 5 days at 20oC [51, 52]. The BOD concentration in the untreated and treated tannery wastewater was determined using an open reflux procedure.


## 2.5.7. Chemical Oxygen Demand (COD) Determination

COD is the amount of oxygen needed to oxidize the oxidizable chemicals contained in one liter of effluent under specific conditions, expressed in milligrams [52, 53]. A bottom flask was filled with 20 mL of sample wastewater and 1 g of H2SO4, and the 5 mL sulfuric acid reagent was slowly added to dissolve H2SO4. After that, a 25 ml solution of 0.04167 M K2Cr2o7 was applied to the mixture. Cooling water was turned on and the bottom flask was connected to the condenser. Swirling and mixing were continued while applying the remaining sulfuric acid reagent (70 ml) through the open end of the condenser. The excess K2Cr2o7 was then titrated with FAS using 6 drops of ferroin indicator after cooling to room temperature.(2)CODmgO2/L=ml of FAS used for blank–ml of FAS used for sample∗M∗8000Sample volumeml.where 8000 = milli equivalent weight of oxygen (8) × 1000 mL/L.


## 3. Result and Discussion

### 3.1. pH Values

The required pH measurement and analysis were to understand whether the pH of the treated wastes is within the required range or not. From the previously documented research findings, the pH of the tannery wastewater is basic and its high organic content can pollute the environment significantly and that of pure water is near neutral (7.0) [54, 55]. Its value before and after treatments with 10% and 30% water hyacinth leaves extracts with any type of extraction solvents used is basic and within the permissible limits (6–9). As results presented in Table 1, the pH values of treated wastes are near neutral, particularly that of treated effluent by the material extracted by 30% distilled water solvent was near to the pH of pure water which indicates the treated effluent by that amount of extract was near to clean/pure water stage. This shows that if the pH of the effluent is within the permissible limits for parameters in the tannery effluents, it is acceptable and the extracts have a promising result as a potential tannery effluent treatment material.According to the results presented in Table1 and Figure 5, the concentration of Cr3+ and Cr6+ in the untreated tannery wastewater was 3.6 mg/l and 0.06 mg/l, respectively. The permissible limit for Cr3+ in the tannery effluents mentioned in the rightmost column of Table 1 is 1.5–2.0 mg/l and that of Cr6+ is 0.05 mg/l which is stipulated by the World Health Organization and Ethiopian Environmental Protection Authority [44, 45]. However, after treatment of the effluents using the extracts, the amounts of the pollutant chemicals and materials reduced below that of untreated values and lie within the permissible limits. In the present study, 30% of WH material extracted by distilled water had the highest Cr3+ removal efficiency (37.2%), which has given a better result compared to that of Nath et al. [56]. In their study of pollutant removal efficiency of water hyacinth plants in the batch treatment of Calcutta city sewage, the removal efficiency of chromium was 32% [57]. However, another study conducted by Narain et al. [58] revealed 80.26% and revealed 79% chromium removal from tannery effluent through phytoremediation, respectively. The different results may be due to the difference between the methods and amounts which the researchers followed in their studies. In addition, other researchers reported that better Cr(VI) removal was achieved by phytoremediation [59], and Kumar and Chauhan [60] reported on the removal of Cr(VI) by adsorption using dried WH root. Generally, this research discovered an interesting result in the removal of chromium ions using leaf extracts compared to previous results. However, it has resulted in a lower efficiency compared to that of other researchers based on the phytoremediation method.Figure 5
The effect of extraction solvents on chromium (III) and chromium (VI) removal of the tannery waste samples.As the data analyzed in Table2, based on ANOVA rule of a single factor analysis, if F>F is critical or if P value is less than 0.005, it indicates that the factors have a significant effect. As the statement is true in this research analysis of Table 1, therefore, when changing the solvent types used during the leaf material extraction, it significantly affects the material efficacy to treat the toxic/pollutant materials of the tannery wastes. Therefore, it can be concluded that the extraction solvent type has a significant effect on the waste (Cr3+ and Cr6+) treatment efficacy of the materials.Table 2
ANOVA results of the effect of the solvent on the WH leaf extract efficacy.
SummaryGroupsCountSumAverageVarianceChromium III (Cr3+)616.282.7133330.186626667Control of III (Cr3+)621.63.60Chromium VI (Cr6+)60.480.080.00512Control of VI (Cr6+)60.360.060ANOVASource of VariationSSdfMSFP-valueF critBetween Groups59.5248319.8416413.91280160.00013.098391Within Groups0.958733333200.047937Total60.4835333323


### 3.2. Total Dissolved Solids (TDSs) and Total Suspended Solids (TSSs)

The values presented in Figure6 are discussed below.Figure 6
TDS and TSS values of controlled and treated wastes by using leaf 10% materials extracted by different extraction solvents.Total dissolved solids (TDSs) are either naturally present in water or are the consequence of industrial water treatment. TDS contains minerals and chemical compounds that may provide benefits such as nutrition or are contaminants such as harmful metals and organic pollutants [61]. According to the result presented in Figures 6 and 7, the TDS value in untreated tannery wastewater was 2342 mg/l, which is out of the discharge limit (1000 mg/L) set by the Ethiopian Environmental Protection Authority [45] and World Health Organization [44]. In the present study, tannery effluents waste treatment with 10% and 30% of distilled water leaves extract reduced the untreated tannery wastewater TDS concentration from 2342 mg/l to 2163 mg/l (7.6%) and to 2134 mg/l, respectively, and 10% and 30% of acetone leaves extract reduced to 2197 mg/l and 2124 mg/l, respectively. On the other hand, the treatment efficacy of ethanol extracted material has the lowest TDS removal values.Figure 7
TDS and TSS values of controlled and treated wastes by using leaf 30% materials extracted by different extraction solvents.As presented in Table1 and Figure 7, the TSS in the original effluents of the tannery wastes was found at 150 mg/l and after it is treated with 10% and 30% leaves extract by distilled water solvents were found at 215 mg/l and 140 mg/l, respectively, and treatment of the effluent with 10% and 30% of acetone extracted leaves were found at 210 mg/l and 182 mg/l, respectively, and that of ethanol extracted leaves of 10% and 30% were 256 mg/l and 244 mg/l, respectively, as these results show the TSS values in all treated effluents were not properly treated. The most possible reason is due to the type of the extractive solvent used and incompatibility of the newly extracted material with the TSS of the effluents. Similarly, Lissy and Madhu [62] observed an increment in TDS and TSS values after treatment with a water hyacinth plant using a phytoremediation method. The increment of the TDS and TSS in this study might be due to the presence of tannery chemicals such as carbonates, bicarbonates, calcium, sodium, potassium, and iron in the effluent. However, still, the researchers believed that the WH leaf extract can reduce the TSS and TDS values at their best ratio.


### 3.3. Total Kjeldahl Nitrogen (TKN)

The total Kjeldahl nitrogen (TKN) of the untreated tannery wastes was 6 mg/l and can be improved to 5.4 mg/l after its treatment with 30% extracted material by distilled water extraction solvent. On the other side, the wastes treated with 10% and 30% acetone extract yielded 53 mg/l and 58 mg/l, respectively. Comparatively, in the current study, the treatment using 30% extracted material using distilled water as a solvent of extraction improved the TKN reduction recorded by previous researchers by the phytoremediation method [63] by 8.4%. The results of all trials using these different extraction solvents but the same amount of extracts except that of 30% distilled water solvents TKN values have not shown improvement, and they were beyond the wastewater permissible limit (60 mg/L) set by the Ethiopian Environmental Protection Authority [45]. However, the material extracted with 30% distilled water solvents can reduce TKN to 16.6% and was higher than the 8.4% TKN reduction recorded by Cornwell et al. [63] using the same plant extract. However, by performing phytoremediation using water hyacinth, Schulz et al. [64] reported 19% TKN removal, Bramwell and Devi Prasad [65] reported 27.6% TKN removal, and Jianbo et al. [34] reported 21.78% TKN removal in their wastewater treatment study. The most possible reason is due to the treatment process in phytoremediation and methods are different from that of the WH leaf extract as well as the contaminants in the wastes being treated were different compared to tannery wastewater. In addition, it clearly indicates that the type of solvents used during material extraction greatly affects the effectiveness of the material.


### 3.4. Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD)

According to the results presented in Table1, a relative best result was found by treating the effluents with the materials extracted by 10% and 30% distilled water extraction solvent. Even though 9.79% and about 4% of the COD levels of waste were reduced by the newly extracted materials by 10% and 30% distilled water, respectively, the COD levels of the tannery waste treated by the extracted material by acetone and ethanol extraction solvents exceeded the Ethiopian Environmental Protection Authority’s allowable limit (500 mg/L) [45]. Using the same extracts, BOD was changed to 35.3.2 mg/l and 57.2 mg/l compared to ineffective leave extracts by acetone and ethanol solvents, as the values are presented in Table 1. Water hyacinth acetone and ethanol extract will not be used as a potential extraction solvent for COD reduction from wastewater based on the findings of this report. The reason is due to high levels of COD in tannery wastewater indicate that the effluent is not appropriate for the existence of aquatic species [66] and the COD results of treated wastewater were higher than the World Health Organization's provisional discharge limit for tannery effluent to water bodies [44]. However, the extract of water hyacinth leaves has limited potential in removing COD from tannery wastewater, and further research is required to determine the optimal concentration of the extract. In case of BOD levels of this study, as presented in Table 1, all of the BOD results of the treated effluents were under the permissible limit (200 mg/L) set by the Ethiopian Environmental Protection Authority [45].Based on the existed literature, the treated wastewater had more BOD than the untreated wastewater. Gamage and Yapa [67] and Chakrabarty et al. [68] introduced water hyacinth on tannery wastewater using phytoremediation using constructed wetlands and it has shown a reduction in BOD after 15 days of sedimentation. All of the treated effluent BOD findings in this study were within the Ethiopian Environmental Protection Authority's permissible limit (200 mg/L) [45]. However, as compared to the control effluent, the BOD value of treated wastewater increased to some extent in the current report but was not effective as required as it is due to the reason stated by Raj et al. [66]. Therefore, this study recommends the WH leaf extracts remove Cr3+, Cr6+, and TKN than TDS, TSS, BOD, and COD from tannery effluents using distilled water extraction solvents.


## 3.1. pH Values

The required pH measurement and analysis were to understand whether the pH of the treated wastes is within the required range or not. From the previously documented research findings, the pH of the tannery wastewater is basic and its high organic content can pollute the environment significantly and that of pure water is near neutral (7.0) [54, 55]. Its value before and after treatments with 10% and 30% water hyacinth leaves extracts with any type of extraction solvents used is basic and within the permissible limits (6–9). As results presented in Table 1, the pH values of treated wastes are near neutral, particularly that of treated effluent by the material extracted by 30% distilled water solvent was near to the pH of pure water which indicates the treated effluent by that amount of extract was near to clean/pure water stage. This shows that if the pH of the effluent is within the permissible limits for parameters in the tannery effluents, it is acceptable and the extracts have a promising result as a potential tannery effluent treatment material.According to the results presented in Table1 and Figure 5, the concentration of Cr3+ and Cr6+ in the untreated tannery wastewater was 3.6 mg/l and 0.06 mg/l, respectively. The permissible limit for Cr3+ in the tannery effluents mentioned in the rightmost column of Table 1 is 1.5–2.0 mg/l and that of Cr6+ is 0.05 mg/l which is stipulated by the World Health Organization and Ethiopian Environmental Protection Authority [44, 45]. However, after treatment of the effluents using the extracts, the amounts of the pollutant chemicals and materials reduced below that of untreated values and lie within the permissible limits. In the present study, 30% of WH material extracted by distilled water had the highest Cr3+ removal efficiency (37.2%), which has given a better result compared to that of Nath et al. [56]. In their study of pollutant removal efficiency of water hyacinth plants in the batch treatment of Calcutta city sewage, the removal efficiency of chromium was 32% [57]. However, another study conducted by Narain et al. [58] revealed 80.26% and revealed 79% chromium removal from tannery effluent through phytoremediation, respectively. The different results may be due to the difference between the methods and amounts which the researchers followed in their studies. In addition, other researchers reported that better Cr(VI) removal was achieved by phytoremediation [59], and Kumar and Chauhan [60] reported on the removal of Cr(VI) by adsorption using dried WH root. Generally, this research discovered an interesting result in the removal of chromium ions using leaf extracts compared to previous results. However, it has resulted in a lower efficiency compared to that of other researchers based on the phytoremediation method.Figure 5
The effect of extraction solvents on chromium (III) and chromium (VI) removal of the tannery waste samples.As the data analyzed in Table2, based on ANOVA rule of a single factor analysis, if F>F is critical or if P value is less than 0.005, it indicates that the factors have a significant effect. As the statement is true in this research analysis of Table 1, therefore, when changing the solvent types used during the leaf material extraction, it significantly affects the material efficacy to treat the toxic/pollutant materials of the tannery wastes. Therefore, it can be concluded that the extraction solvent type has a significant effect on the waste (Cr3+ and Cr6+) treatment efficacy of the materials.Table 2
ANOVA results of the effect of the solvent on the WH leaf extract efficacy.
SummaryGroupsCountSumAverageVarianceChromium III (Cr3+)616.282.7133330.186626667Control of III (Cr3+)621.63.60Chromium VI (Cr6+)60.480.080.00512Control of VI (Cr6+)60.360.060ANOVASource of VariationSSdfMSFP-valueF critBetween Groups59.5248319.8416413.91280160.00013.098391Within Groups0.958733333200.047937Total60.4835333323


## 3.2. Total Dissolved Solids (TDSs) and Total Suspended Solids (TSSs)

The values presented in Figure6 are discussed below.Figure 6
TDS and TSS values of controlled and treated wastes by using leaf 10% materials extracted by different extraction solvents.Total dissolved solids (TDSs) are either naturally present in water or are the consequence of industrial water treatment. TDS contains minerals and chemical compounds that may provide benefits such as nutrition or are contaminants such as harmful metals and organic pollutants [61]. According to the result presented in Figures 6 and 7, the TDS value in untreated tannery wastewater was 2342 mg/l, which is out of the discharge limit (1000 mg/L) set by the Ethiopian Environmental Protection Authority [45] and World Health Organization [44]. In the present study, tannery effluents waste treatment with 10% and 30% of distilled water leaves extract reduced the untreated tannery wastewater TDS concentration from 2342 mg/l to 2163 mg/l (7.6%) and to 2134 mg/l, respectively, and 10% and 30% of acetone leaves extract reduced to 2197 mg/l and 2124 mg/l, respectively. On the other hand, the treatment efficacy of ethanol extracted material has the lowest TDS removal values.Figure 7
TDS and TSS values of controlled and treated wastes by using leaf 30% materials extracted by different extraction solvents.As presented in Table1 and Figure 7, the TSS in the original effluents of the tannery wastes was found at 150 mg/l and after it is treated with 10% and 30% leaves extract by distilled water solvents were found at 215 mg/l and 140 mg/l, respectively, and treatment of the effluent with 10% and 30% of acetone extracted leaves were found at 210 mg/l and 182 mg/l, respectively, and that of ethanol extracted leaves of 10% and 30% were 256 mg/l and 244 mg/l, respectively, as these results show the TSS values in all treated effluents were not properly treated. The most possible reason is due to the type of the extractive solvent used and incompatibility of the newly extracted material with the TSS of the effluents. Similarly, Lissy and Madhu [62] observed an increment in TDS and TSS values after treatment with a water hyacinth plant using a phytoremediation method. The increment of the TDS and TSS in this study might be due to the presence of tannery chemicals such as carbonates, bicarbonates, calcium, sodium, potassium, and iron in the effluent. However, still, the researchers believed that the WH leaf extract can reduce the TSS and TDS values at their best ratio.


## 3.3. Total Kjeldahl Nitrogen (TKN)

The total Kjeldahl nitrogen (TKN) of the untreated tannery wastes was 6 mg/l and can be improved to 5.4 mg/l after its treatment with 30% extracted material by distilled water extraction solvent. On the other side, the wastes treated with 10% and 30% acetone extract yielded 53 mg/l and 58 mg/l, respectively. Comparatively, in the current study, the treatment using 30% extracted material using distilled water as a solvent of extraction improved the TKN reduction recorded by previous researchers by the phytoremediation method [63] by 8.4%. The results of all trials using these different extraction solvents but the same amount of extracts except that of 30% distilled water solvents TKN values have not shown improvement, and they were beyond the wastewater permissible limit (60 mg/L) set by the Ethiopian Environmental Protection Authority [45]. However, the material extracted with 30% distilled water solvents can reduce TKN to 16.6% and was higher than the 8.4% TKN reduction recorded by Cornwell et al. [63] using the same plant extract. However, by performing phytoremediation using water hyacinth, Schulz et al. [64] reported 19% TKN removal, Bramwell and Devi Prasad [65] reported 27.6% TKN removal, and Jianbo et al. [34] reported 21.78% TKN removal in their wastewater treatment study. The most possible reason is due to the treatment process in phytoremediation and methods are different from that of the WH leaf extract as well as the contaminants in the wastes being treated were different compared to tannery wastewater. In addition, it clearly indicates that the type of solvents used during material extraction greatly affects the effectiveness of the material.


## 3.4. Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD)

According to the results presented in Table1, a relative best result was found by treating the effluents with the materials extracted by 10% and 30% distilled water extraction solvent. Even though 9.79% and about 4% of the COD levels of waste were reduced by the newly extracted materials by 10% and 30% distilled water, respectively, the COD levels of the tannery waste treated by the extracted material by acetone and ethanol extraction solvents exceeded the Ethiopian Environmental Protection Authority’s allowable limit (500 mg/L) [45]. Using the same extracts, BOD was changed to 35.3.2 mg/l and 57.2 mg/l compared to ineffective leave extracts by acetone and ethanol solvents, as the values are presented in Table 1. Water hyacinth acetone and ethanol extract will not be used as a potential extraction solvent for COD reduction from wastewater based on the findings of this report. The reason is due to high levels of COD in tannery wastewater indicate that the effluent is not appropriate for the existence of aquatic species [66] and the COD results of treated wastewater were higher than the World Health Organization's provisional discharge limit for tannery effluent to water bodies [44]. However, the extract of water hyacinth leaves has limited potential in removing COD from tannery wastewater, and further research is required to determine the optimal concentration of the extract. In case of BOD levels of this study, as presented in Table 1, all of the BOD results of the treated effluents were under the permissible limit (200 mg/L) set by the Ethiopian Environmental Protection Authority [45].Based on the existed literature, the treated wastewater had more BOD than the untreated wastewater. Gamage and Yapa [67] and Chakrabarty et al. [68] introduced water hyacinth on tannery wastewater using phytoremediation using constructed wetlands and it has shown a reduction in BOD after 15 days of sedimentation. All of the treated effluent BOD findings in this study were within the Ethiopian Environmental Protection Authority's permissible limit (200 mg/L) [45]. However, as compared to the control effluent, the BOD value of treated wastewater increased to some extent in the current report but was not effective as required as it is due to the reason stated by Raj et al. [66]. Therefore, this study recommends the WH leaf extracts remove Cr3+, Cr6+, and TKN than TDS, TSS, BOD, and COD from tannery effluents using distilled water extraction solvents.


## 4. Conclusion

From the study results, it can be concluded that the Ethiopian water hyacinth leaf extract has a very good ability to remove toxic pollutants such as Cr6+, Cr3+, and TKN from tannery effluents. The effect of aqueous and solvent-based extracts of water hyacinth leaves for tannery effluent treatment was investigated using ANOVA and implied that the solvent types and amounts used during extraction greatly affect the effectiveness of the leaf extracts. Distilled water, acetone, and ethanol were used as solvents to extract the active components present in the WH plants leaf. The highest amount of Cr6+, Cr3+, and TKN were removed at 30% WH leaf extract by distilled water solvents Their values were within the permissible discharge limit (1.5–2.0 mg/l for Cr3+, 0.05 mg/l for Cr6+, and 60 mg/l for TKN) and the values of Cr6+, Cr3+, and TKN of the treated effluent by the WH leaf materials extracted by distilled water extraction solvent were 1.84 mg/l of Cr3+, 0.02 mg/l Cr6+, and 5.4 mg/l for TKN compared to that of the untreated effluent values which have 3.6 mg/l Cr3+, 0.06 mg/l Cr6+, and 6 mg/l, TKN respectively. The 30% WH leaf extract using ethanol solvent was ineffective to treat mentioned chemicals compared to the same quantity of the WH leaf extracts by the other solvents. Though the result was out of the permissible limit, by using the same amount of the WH leaf extract using distilled water extraction solvent, 7.6% of BOD and 8.8% of TDS were removed from the tannery wastes. Treatment using the leaf extracts was almost ineffective to remove TDS, TSS, BOD, and COD of the tannery effluent compared to the control waste and permissible limits. The pH of the treated effluent is more neutral than that of the untreated wastes. Comparatively, the leaf extracts with acetone and distilled water as extraction solvents have shown the best result compared to that of the extract with ethanol solvent extracts. According to the results of this study, it is recommended that water hyacinth plant leaf extract can be used for removing pollutants such as Cr3+, Cr6+, and TKN than TDS, TSS, BOD, and COD in the tannery effluents and distilled water extraction solvents is recommended to extract the material. Generally, the findings of the research are very important to the tanneries and act as a base for future researchers for the best results.



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*Source: 8783255-2022-04-23.xml*