Freshwater is a beneficial resource for the nourishment of human and industrial life. Environment as an unlimited source for raw materials an unlimited sinks for waste freshwater supplies, and eventually human existence. Wastewater contains toxic contaminants, which, if continuously discharged to water bodies, will seriously affect the marine ecosystem [1].

Environmental pollution is the release of unwanted substances to the environment by the man in such quantities that damage either the health or the resource itself. Environmental pollution affects the quality of the pedosphere, hydrosphere, atmosphere, lithosphere, and biosphere [2].

Environmental pollution and water pollution is a problem of worldwide concern. Groundwater is too polluted due to the unplanned disposal of untreated domestic sewage. Heavy metal is referred to as any metallic chemical element that has relatively high-density Heavy metal ions are used in various industries due to their technologies and may become part of wastewater change, both natural and man-made ecosystems. According to WHO [3] the metals of most immediate concerns are cadmium, chromium, cobalt, copper, iron, lead, nickel, mercury, and zinc. These heavy metals bio-accumulate readily in marine organisms, most of which are food to man, and consequently affects man when ingested, as they are carcinogenic, interfering with the growth or metabolism of cells in the body. Industrial pollution is one of the significant concerns about corruption. The significant reasons for industrial pollution are that people are not sensitive to their environment. The quantity of life on earth is linked with the overall quality of the domain. Increasing industrialization and population development results in a highly polluted atmosphere due to the drainage and wastage from these industries [4].

 Effluents from industries that usually are generally considered as the primary industrial pollutants containing organic and inorganic compounds are discharged into the nearby water bodies. It makes the water bodies toxic as various industries release the suspended solids, toxic chemicals, oils, greases, dyes, radioactive wastes, and thermal pollutants. As a result, the high level of contaminants, mainly organic matter in river water, causes an increase in BOD, COD, TDS, TSS, etc. It makes the water unsuitable for drinking, irrigation, or other uses. Heavy metals are being released from various industries like electroplating, fertilizer, leather, paint, pesticide, pharmaceuticals, pulp & paper, mining, oil refinery, etc. The accumulation of these heavy metals in plants causes physiological and biochemical changes [5-6].

Steel is widely used for domestic, agriculture, industrial, and defense purposes. Per capita, steel consumption is a significant indicator of the economic status of any country. Growth of the steel industry significantly contributes to economic growth as it generates employment both directly and also due to the development of downstream sectors [7].

 Wastewater from the steel production processes has a high level of contaminations containing a variety of heavy metal ions. Various techniques employing chemical treatment [8], biosorption, and bioremediation [9-10] and physical removal [11] have been reported to remediate heavy metals in wastewater. However, most chemical and physical engineering technologies fail to remove heavy metals from effluents altogether. Many technologies are used to prevent water pollution and to utilize it for beneficial purposes, including precipitation, reduction, artificial membranes, and ion exchange. These methods are used to remove heavy metals from industrial effluents but are expensive and may generate a huge amount of waste. Hence, developing cost-effective and environmentally friendly technologies to remediate heavy metals from polluted wastewaters is a topic of global interest. Naturally occurring biological tools are being substituted as an alternative in pollution control programs due to their harmless nature [12]. Bioremediation is one of the important technologies that can provide cleaner and suitable alternatives to many polluted products. With the help of this technology, the environment altered by contaminants is changed to its original position. It stimulates microorganisms with nutrients and chemicals, which enable them to eliminate pollutants. In this technique, those microorganisms are used, which are native to the contaminant site. It is the cheaper, efficient, and environmentally friendly method for wastewater treatment. It is used for the reduction of pollution such as; industrial effluents. As this technique utilizes living sources, for example, plants and microorganisms like fungi, algae, etc. so it is environmentally friendly and economically feasible [13].

Phytoremediation is the process that introduces plants into an environment and allows them to assimilate the contaminants into their roots and leaves. Such an approach has been used to clean up heavy metals, pesticides, and xenobiotics [14].

organic compounds [15] toxic aromatic pollutants [16] and acid mine drainage [17].

It is considered to be an environmentally friendly technology that is safe and also a cheap way to remove contaminants, in some cases doing the same job as a group of engineers for one-tenth of the cost. It is one new approach that offers more ecological benefits and a cost-efficient alternative. Although it is a cheaper method but requires technical strategy, expert project designers with field experience choose the proper species and cultivars for particular metals and regions [18].

Some examples of plants used in phytoremediation practices are water hyacinths (Eichornia crassipes); poplar trees (Populus spp.); forage Kochia (Kochia spp); alfalfa (Medicago sativa); Kentucky bluegrass (Poa pratensis); Scirpus spp, coontail (Ceratophyllum demersum L.); American pondweed (Potamogeton nodosus); and the common emergent arrowhead (Sagittaria latifolia) amongst others.

Water Hyacinth is among one of the essential phytoremediators and has great potential in being used in wastewater treatment systems. Studies on water hyacinth showed that it improves the wastewater effluent from oxidation ponds and integrated treatment systems [19]

and that it uses appreciable amounts of the inorganic forms of nitrogen and phosphorus found in domestic sewage, industrial and municipal [20].

 Water hyacinth’s quest for nutrients has also been exploited to clean wastewater in small-scale sewage treatment plants where it absorbs and digests wastewater pollutants, converting sewage effluents to relatively clean water [21].

It removes biochemical oxygen demand (BOD) and suspended solids (S.S.) when used in the secondary treatment of domestic wastewater [22] and textile mill effluents [23].

 In the process of studying water hyacinth’s capabilities in sewage treatment, it has been discovered that the plant is highly effective in absorbing and accumulating various heavy metals [24] and this capability is the reason for this study for industrial wastewater treatment. It is well known for its phytoremediation potential. One study was conducted in which pollutants removal by water hyacinth, grown on the overbank, and flood bare soils of the river, were studied [25]

They observed that the roots of water hyacinth growing in the over bank soils accumulate several metals except for Co, Al, and Fe. The ash of water hyacinth is also significant for the removal of heavy metals from the wastewater. It is excellent phytoremediation and metal absorber. 40-44 % cellulose is present in the plant so that the absorbent capacity of the plant increases. That is why ash is being used in this study [26].

The aims of the study are reduction in the contamination of Steel Industry effluents through Water Hyacinth ash and to make wastewater beneficial for industries.

Materials and Methods

Study Area

Ittehad steel mills are located at plot no.417, sector I/9 industrial areas, Islamabad, Pakistan.

Sample Collection

Wastewater from the discharge point of the industry was collected triplicate in 3 bottles (washed with distilled water and dried) of 500ml size. The water hyacinth plant was collected from the bank of Korang Nala.

Sampling Strategy

Glass bottles were used for storage purposes. The sample was stored at 4⁰C in the nanoscience and catalyst laboratory, department of National Centre for Physics, Islamabad, Pakistan.

Experimental Setup

455g of the fresh plant was taken. The plant was then dried in the sunlight to remove its moisture. The plant was then added to the beaker and was put in box furnace large to make ash. The plant was burnt entirely; it was placed in the lab until cooled down. The burnt plant was ground by using Pestle and mortar.  Ash was washed with distilled water for 7-8 times until all the contaminants and color was removed.

Analytical Work

The analytical work was carried out at Geo-Science Laboratory, Bio-Chemistry Laboratory of Quaid-e-Azam University, and Wet Lab of International Islamic University, Islamabad, Pakistan.

Laboratory Work

The laboratory work was carried out at the National Centre for Physics, located at Shahdra Valley Road, Islamabad. It comprises of standardized laboratories where laboratory work was conducted during April and May 2015.

Determination of Physico-Chemical Parameters from Industrial Wastewater

Physico-chemical parameters; pH, electrical conductivity (EC), total dissolved solids (TDS), temperature, turbidity, dissolved oxygen (DO) were determined by using instruments according to the American Public Health Association (APHA) method, 2005. The mentioned parameters were recorded before and after the treatment of industrial wastewater with ash.

Preparation of Solutions

Solutions of different concentrations of salts were prepared. Salts of lead, chromium, and nickel were used to make solutions. Salts used were lead acetate, chromium (III) chloride, and nickel (II) bromide, respectively. The concentrations of heavy metals were recorded before and after the treatment with ash. Each solution was prepared by the same method as explained below:

Standard solutions of 20, 40, and 60 ppm were prepared in triplicate for metals analysis. By adding 20 mg of salts in 1000 ml of distilled water, a 20 ppm solution was prepared. Similarly, by adding 40 mg and 60 mg of salts in 1000ml of distilled water, 40 ppm and 60 ppm solutions were prepared, respectively.

Treatment of Solutions with Ash

100ml of each of the above solutions was taken in the beaker, and 5 g of ash was added in each solution. Then these solutions were gently shaken by using an electrical stirrer for 20 minutes. The solutions were then filtered by using filter paper, and the filtrate was taken in a flask. After that, the filtrate was transferred to the sample bottles. The sample bottles were sealed to avoid evaporation. All samples were labeled for identification. All the pieces were checked by Atomic Absorption Spectrometer (A.A.S.) to determine how much amount of metals was removed from each solution by the ash.

Detection of Metals from Industrial Wastewater

Atomic Absorption Spectrometer (A.A.S.) was used to detect heavy metals like Lead, Zinc, Cadmium, Nickel, and Chromium in industrial wastewater.

Results and Discussion

Water Hyacinth ash showed excellent tolerance for steel industry wastewater. When the ash was passed through the steel industry wastewater, heavy metals, e.g., Cr, Cd, Zn, Ni, As, Pb, and physicochemical parameters like pH, temperature, electrical conductivity, total dissolved solids were reduced and turbidity, dissolved oxygen increased. 

Analysis of Physico-Chemical Parameters

1. Temperature

The higher recorded value of temperature was 27.5°C. After treatment with ash, the temperature of the water was still 27.5°C as shown in fig. 1. No change in temperature is because of any thermo-dynamical effect.

Fig. 1 Change in Temperature of Steel Effluents before and after Treatment with Water Hyacinth Ash

2. pH

Initially the pH of effluent was basic (8.32) in nature and after treatment it became approximately neutral as shown in fig. 2. According to Mahmood, et al (2005), the reduction in pH and conductivity might be due to the absorption of pollutant by plant. The pH of wastewater was decreased because of the removal of metal ions by Water hyacinth ash. 

Fig. 2 Change in pH of Steel Effluents before and after Treatment with Water Hyacinth ash

3. Electrical Conductivity (E.C.)

Conductivity (E.C.) values in the present study were found high (665µS/cm) and usually, high E.C. value indicates the presence of high contents of heavy metals in water. A significant decrease in E.C. value (285µS/cm) was observed after the remediation process as shown in fig. 3.

Fig. 3 Change in E.C. of Steel Effluents before and after Treatment with Water Hyacinth Ash

4. Total Dissolved Solid (TDS)

The TDS value was recorded as 442mg/L before treatment with ash and after the treatment, it was decreased to 182.5mg/L as shown in figure 4. The TDS was decreased because the total soluble salts were adsorbed on ash.

Fig. 4 Change in TDS of Steel Effluents before and after Treatment with Water Hyacinth Ash

5. Dissolved Oxygen (DO)

Fig. 5 Change in D.O. of Steel Effluents before and after Treatment with Water Hyacinth Ash

In figure 5, it is shown that before treatment with ash, D.O. of the industrial wastewater was 3mg/L and it was increased to 6mg/L after treatment with ash of Water hyacinth plant. This increase in D.O. is because of the removal of microbes and pollutants.

6. Turbidity

The turbidity of the wastewater was 0.42NTU before the treatment with Water hyacinth ash and after treatment; it was increased to 3.29NTU as shown in figure 6. The increase in turbidity was due to the presence of nanoparticles that decreased the transmittance and increased the turbidity.

Fig. 6 Change in Turbidity of Steel Effluents before and after Treatment with Water Hyacinth Ash

Solutions and their Absorption on Ash

1. Lead

In 0ppm solution of lead acetate, no lead was present before treatment. In 20, 40 and 60ppm of solution, 9.72, 19.04 and 18.77 ppm of lead was analyzed before treatment and after treatment, these amounts were reduced to 0.48, 0 and 0.15ppm respectively resulting in 95, 100 and 99 percent removal of lead as shown in in figure 7.

Fig. 7 Percentage of Removal of Lead from Lead Acetate Solutions

2. Chromium

Like the previous metal, the concentration of chromium was also reduced. In 0 ppm solution of chromium (III) chloride, no chromium was present before treatment. In 20, 40, and 60 ppm of the solution, 7.144, 12.338, and 0.181 ppm of chromium was analyzed before treatment. After treatment, these amounts were reduced to 0.258, 0.128, and 12.338 ppm, respectively, resulting in 96.40, 99, and 98.8 percent removal of chromium, as shown in figure 8.

Fig. 8 Percentage of Removal of Chromium from Chromium (III) Chloride Solution

1. Nickel

Like the above two metals, the concentration of nickel was also reduced. In 0 ppm solution of nickel (II) bromide, no nickel was present before treatment. In 20, 40, and 60 ppm of the solution, the concentration of nickel was reduced to 0.52, 0.13, and 0.628ppm from 10.01, 13.22, and 27.124 ppm respectively after treatment resulting in 94.91, 99.1, and 97.68 percent removal of nickel as shown in figure 9.

Fig. 9 Percentage of Removal of Nickel from Nickel (II) Bromide Solutions

From these results, it can be assumed that at room temperature, 5g of Water hyacinth ash has the maximum capacity to remediate a 40 ppm solution. After this concentration, its efficiency decreases. In the above figures, it is shown that till 40ppm, the line goes straight upward, but after 40 ppm, there is a decline in the removal of metal from the metal solution because saturation occurs after 40 ppm.

Desorption of Heavy Metals of Solutions from Ash

20.13 ppm of the total lead, 19.58 ppm of the total chromium, and 21.01 ppm of the full nickel were desorbed from the ash, respectively, resulting in 42.92, 57.67, and 42.81 percent of desorption as shown in the fig. 10.

Fig. 10 Percentage of Desorption of Heavy Metals by Ash

Fig. 11 The Comparison of Adsorption and Desorption Percentage of Heavy Metals from Solutions

Figure 11 compares the percentage of adsorption of chromium, lead, and nickel from their solutions on ash and their desorption by using HNO₃ solution as a catalyst.

Detection of Metals from Industrial Wastewater

1. Lead

According to E.P.A., the permissible limits for lead in the industrial discharge are 0.5 mg/L. The recorded concentration of metal (0.61 ppm) was above the allowable limits reduced to 0 ppm after treatment with Water hyacinth ash, as shown in fig. 12. Hence 100 % of the metal was removed from the wastewater.

2. Zinc

According to E.P.A., the permissible limit for zinc in industrial discharge is 5.0 mg/L. The concentration of metal (2.7 ppm) in industrial wastewater was within allowable limits reduced to 0 ppm, as shown in fig. 12.

3. Cadmium

NEQS for cadmium is 0.1mg/L. The concentration of cadmium in the industrial wastewater before treatment with ash was reported as 1.1ppm, and after treatment, it was reduced to 0 ppm as shown in fig. 12.

4. Nickel

According to E.P.A., the permissible level of nickel is 1.0 mg/L. The concentration of metal in the sample of industrial wastewater (2.5ppm) was above the allowable limit reduced to 0 ppm as shown in fig. 12.

5. Chromium

The concentration of chromium was a bit higher than the permissible limit. Results indicate that the level of chromium was reduced to 0ppm from 1.1 ppm, as shown in fig. 12. It means that 100% of the chromium contaminants were removed.

Fig. 12 Change in Concentration of Heavy Metals in Industrial Wastewater after Treatment with Water Hyacinth Ash

Desorption of Heavy Metals of Industrial Wastewater from Ash

The heavy metals were desorbed from ash using nitric acid (HNO₃) from industrial wastewater containing metals in triplicate.

0.439ppm of the lead, 1.971 ppm of the zinc, 0.858 ppm of the cadmium, 2.075 ppm of the nickel, and  0.825 ppm of the chromium was desorbed from the ash respectively which means that 71.97, 73, 78, 83 and 75 percent of the metals were desorbed respectively as shown in the fig. 13.

Fig. 13 Percentage of Desorption of Heavy Metals from Water Hyacinth Ash by Using HNO₃ Solution

Conclusion

Heavy metals affect plants, animals, and humans in different ways. The various techniques are available to reduce the number of heavy metals from wastewater, but all these chemical techniques have limitations and drawbacks. Phytoremediation and biosorption techniques could be cost-effective methods for massive metal uptake and removal from contaminated sites. Furthermore, biosorption and phytoremediation have been reported as appropriate techniques without causing any environmental impact. The current study reports that the wastewater of the steel industry contains various heavy metals in the different concentrations found above the permissible level, and its remediation by using the Water hyacinth, ash.

Water hyacinth (Eichhornia crassipes) could effectively remediate contaminated water containing metals such as, zinc (Zn⁺²), Lead (Pb⁺²), Cadmium (Cd⁺²), Chromium (Cr⁺²), and Nickel (Ni⁺²), thus; reducing the environmental hazard that could arise, from untreated wastewater to the ecosystem. The ash of water hyacinth often several advantages, including cost-effectiveness, high efficiency, minimizing the chemical/biological sludge, and regeneration of bio-sorbent with the possibility of metal recovery, the adsorption capacity of E. Crassipes ash to metals is more than that of the other plant materials. Biosorption and desorption by the ash of Water hyacinth is a technique can be used for removal and recovery of the metal pollutant from water.

From present research work, we found that Ash of Water hyacinth has excellent potential for reducing heavy metal pollution from the environment.

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this pape.

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