• International Journal of Technology (IJTech)
  • Vol 14, No 4 (2023)

Biosorption of Hexavalent Chromium Cr(VI) using Microalgae Scenedesmus sp as Environmental Bioindicator

Biosorption of Hexavalent Chromium Cr(VI) using Microalgae Scenedesmus sp as Environmental Bioindicator

Title: Biosorption of Hexavalent Chromium Cr(VI) using Microalgae Scenedesmus sp as Environmental Bioindicator
Rudi Kartika, Ahmad Hafizullah Ritonga, Lilik Sulastri, Siti Nurliana, Deddy Irawan, Partomuan Simanjuntak

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Cite this article as:
Kartika, R., Ritonga, A.H., Sulastri, L., Nurliana, S., Irawan, D., Simanjuntak, P., 2023. Biosorption of Hexavalent Chromium Cr(VI) using Microalgae Scenedesmus sp as Environmental Bioindicator. International Journal of Technology. Volume 14(4), pp. 791-799

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Rudi Kartika Faculty of Mathematics and Natural Science, Mulawarman University, Samarinda-75119, Indonesia
Ahmad Hafizullah Ritonga Institut Kesehatan Medistra Lubuk Pakam, Deli Serdang-20512, Indonesia
Lilik Sulastri Sekolah Tinggi Teknologi Industri dan Farmasi, Bogor-16151, Indonesia
Siti Nurliana Balai Riset dan Standarisasi Industri Samarinda, Samarinda-75124, Indonesia
Deddy Irawan Departement of Chemical Engineering, Politeknik Negeri Samarinda, Samarinda-75131, Indonesia
Partomuan Simanjuntak Research Center for Pharmaceutical Ingredient and Traditional Medicine, National Research and Innovation Agency (BRIN), KST Soekarno Cibinong 16911, Indonesia
Email to Corresponding Author

Abstract
Biosorption of Hexavalent Chromium Cr(VI) using Microalgae Scenedesmus sp as Environmental Bioindicator

Scenedesmus sp. is a freshwater green alga that functions as an ionic biosorbent and can also be a bioindicator for water contaminated with hexavalent chromium Cr(VI) ion. This study aimed to observe the growth of Scenedesmus sp. exposed to Cr(VI) ion at various concentrations and analyze the remaining Cr(VI) ion that did not undergo biosorption by microalgae. This research was conducted on Scenedesmus sp. microalgae growth media using five bioreactors, each with a different Cr(VI) ion exposure concentration. The remaining ion in the growth media was analyzed for its concentration with an ultraviolet-visible spectrophotometer at time variations with an interval of two days. Maximum biosorption with exposure to Cr(VI) occurred at a concentration of 1.0 ppm on day 12 of 99.93%. At concentrations of 5.0 ppm and 7.0 ppm, microalgae growth was very poor, indicating the medium was toxic.

Biosorption; Hexavalent Chromium; Scenedesmus sp; Toxicity

Introduction

      The microalga Scenedesmus sp. is highly competent at binding inorganic ions such as carboxyl, amine, sulfate, and sulfonate, which lends itself viable to treat aquatic waste. Microalgae have the advantage of being environmentally friendly, recyclable, and low maintenance costs (Wilan et al., 2020)Scenedesmus sp. is a cosmopolitan microalga that lives in colonies within brackish water and soil with a humid climate. Their cells are cylindrical (8-20 m in length and 3-9 m in width) and are surrounded by three layers consisting of an inner layer (cellulose), a middle layer (membrane structure), and an outer layer net of pectin and fine hairs (Prihantini, Damayanti, and Yuniati, 2007).

      Scenedesmus sp. is widely utilized as a supplement, fish feed, pollutant removal agent for wastewater treatment, a source of biofuel, and a bio-indicator of water pollution using herbicides as a determinant (Fodorpataki, Bartha, and Keresztes, 2009; Makareviciene et al., 2011; Sudibandriyo and Putri, 2020).
        Industrial activities often pollute their surrounding with various classes of contaminants, of which heavy metals are particularly concerning since they persist in the environment and do not decompose or degrade into benign compounds as most organic pollutants do. Heavy metal ions are toxic to aquatic ecosystems and human health above a certain concentration level (Suprapto et al., 2020).

     Heavy metal ions can be removed from water through several methods, such as physical adsorption, chemical sedimentation, mechanical filtration, and ion exchange. However, these processes have their drawbacks, such as secondary pollution due to the chemicals used and high cost. An environmentally friendly alternative is using microorganisms to adsorb the ions out of the water, a technique known as biosorption. This method is highly efficient in wastewater detoxification, and it has a simple implementation and a low cost. Microorganisms' adsorption of heavy metal ions is a rapid and reversible process in which the cell wall serves as a binding site, which means that the microorganism does not even need to be alive for this purpose. Using dead microbial cells could be more cost-efficient because they do not require a supply of nutrients during the process. Several factors affect biosorption: characteristics of biomass, temperature, pH, biosorbent concentration, contact time, and biomass surface area. The biomass must be immobilized to avoid blockage of the reaction (Wilan et al., 2020).

       Many techniques have been applied to improve the performance of a biosorbent. The chemical composition of the adsorbing surface may be modified by adding or removing certain functional groups to improve specificity and binding energy. The binding surface area may be expanded by increasing porosity (Anuar et al., 2019). Several researchers have used the biosorption method to remove heavy metals in solution using dead biomass to bind pollutants through simultaneous adsorption, complex formation, micro-surface deposition, and ion exchange (Kusrini et al., 2019; Fomina and Gadd, 2014; Ekmekyapar et al., 2012). Certain bacteria can absorb Pb ions, such as micrococcus sp. and flavobacterium sp., by up to 100% at an initial concentration varying from 2.0 ppm to 10 ppm after an exposure of 3 to 30 days (Susanto, Kartika, and Koesnarpadi, 2019).

       Chromium is a very toxic and dangerous heavy metal. Among the valence range of chromium from -2 to +6, only hexavalent chromium (Cr VI) and trivalent chromium (Cr III) have environmental significance due to their stability in the form of oxidation in water and poor absorption by soil and organic matter, making them slow to sediment out of the solution (Mnif et al., 2017).

      Cr (VI) compounds are generated by various industries such as metallurgy, leather tanning, paint, textile, pulp, ore and petroleum refining, metal corrosion, and electroplating. Those compounds may be released into the environment due to leakage, poor storage, or improper disposal. Chromium ions are toxic in the human body because they can irritate the respiratory tract, blood vessels, kidneys, and skin at high levels. According to the World Health Organization (WHO) drinking water guidelines, the maximum recommended limit for total chromium is 0.05 ppm (Rahman and Singh, 2019; Khatoon and Rai, 2016; Khatoon et al., 2013).
       This study aims to observe the growth of Scenedesmus sp. exposed to Cr(VI) ion at various concentrations in the growth medium, during which the alga should adsorb the ions, and then analyze the remaining Cr(VI) ion in the growth medium at an interval of two days. The extent of absorption of Cr(VI) ion can be a bioindicator for the environment by providing information about the growth of the microalgae Scenedesmus sp., which is disturbed at a certain concentration and is characterized by a colorless growth media (not growing or dying). However, if the growth medium is green, the growth is normal (not disturbed by Cr(VI) ion).

Experimental Methods

2.1. Microalga Cultivation Process and Exposure to Bioreactors
       2.13 g of the growth media for algae or bold basal medium (BBM) was dissolved in 3 L of distilled water to obtain a BBM solution (Figure 1a). Five photobioreactors were prepared and charged with potassium dichromate (K2Cr2O7) solution to obtain a Cr(VI) solution with a concentration of 0 ppm, 1 ppm, 3 ppm, 5 ppm, and 7 ppm. The Scenedesmus sp. culture was inoculated into the five photobioreactors that had been filled with BBM solution and aerated. The microalgae were cyclically illuminated with fluorescent lighting (1500 lux), receiving 12 hours of light and 12 hours of darkness at 25°C. The Cr(VI) with variation concentration (0 ppm, 1 ppm, 3 ppm, 5 ppm, and 7 ppm) was measured in each bioreactor every two days for a total of 12 days (Figure 1b).


Figure 1 Scheme of (a) Microalgae Cultivation, (b) Exposed to Bioreactors

2.2.  Preparation of Cr(VI) Standard Solution

        A mass of K2Cr2O7 weighing 0.1414 g was dried in an oven and dissolved in 100 mL distilled water in a volumetric flask to yield a Cr(VI) 500 ppm solution. 10 mL of the Cr(VI) 500 ppm solution was diluted with 100 mL distilled water in a volumetric flask to obtain a Cr(VI) 50 ppm solution. 10 mL of Cr(VI) 50 ppm solution was diluted with 100 mL distilled water in a volumetric flask to obtain a standard Cr(VI) 5 ppm solution.

2.3.  Curve Calibration

        2 mL of the Cr(VI) 5 ppm standard solution was added into a 100 mL volumetric flask, followed by five drops of H3PO4. The pH of the mixture was adjusted by adding 0.2 M H2SO4 until it reached pH 2. Next, 2 mL of diphenylcarbazide was added, and the flask was filled with distilled water up to the marked line, resulting in a 0.1 ppm standard solution for the calibration curve. The procedure was repeated with the volume of the Cr(VI) 5 ppm standard solution incremented by 2 mL up to 20 mL, resulting in standard solutions with a concentration of 0.2 ppm, 0.3 ppm, 0.4 ppm, 0.5 ppm, 0.6 ppm, 0.7 ppm, 0.8 ppm, 0.9 ppm, and 1.0 ppm. The solutions were each rested for 10 min before their absorbances were measured at a wavelength of 540 nm.

2.4.  Measurement of Chromium Concentration

       A 10 mL sample of the culture solution was filtered using a folder membrane at 0.45 microns. It was treated according to a calibration curve standard solution, and the concentration was measured at a wavelength of 540 nm.

2.5.  Determination of Remaining Cr(VI) Ion Concentration in Growth Medium with Time Variations

       The concentration of Cr(VI) ion in the culture medium was measured by taking a 10 mL sample and running it through a vacuum filter using a millipore membrane (0.4 microns), then determining the concentration of Cr(VI) ion. The measurement was performed on the initial solution, then every other day up to the twelfth day. The Cr(VI) ion which has undergone biosorption is the concentration of Cr(VI) ion obtained (ppm) reduced with the concentration of Cr(VI) ion remaining in the medium.

Results and Discussion

     Table 1 shows that the Cr(VI) ion concentration decreased with increasing contact time. The longer the exposure time, the larger the possible interactions between the biosorbent material and the metal ions, which allowed more active groups to bind metal ions and increase the number of metal ions absorbed. The biosorption proceeded with increasing contact time until the equilibrium point was reached. The length of contact time affected the metal ion-binding process by the biosorbent surface before the surface reached the saturation point. When the biosorbent has reached the equilibrium point, the biosorbent will not bind any heavier metals because the surface of the cell wall is saturated. 

Table 1 Absorption of Cr(VI) with variations in concentration and time


Based on the concentration of Cr(VI) ion exposed and remaining in the growth medium, the percentage of biosorption can be determined based on the following equation (Vendruscolo, da Rocha Ferreira, and Antoniosi Filho, 2017):

Note    Ce = Concentration of Cr(VI) ion exposed in the growth medium (ppm)

               Cr = Concentration of Cr(VI) ion remaining in the growth medium (ppm)

Based on Table 1 and the percentage of biosorption equation, the calculation results for the percentage of Cr(VI) ion removal are listed in Table 2 below.

Table 2 Percentage of Cr(VI) ion removal with variations in concentration and time

Cr(VI) ions removal (%)

Day

1 ppm

3 ppm

5 ppm

7 ppm

0

0.0000

0.0000

0.0000

0.0000

2

14.7766

7.1836

2.3320

2.6836

4

26.4605

13.5690

3.6351

4.6139

6

35.5670

18.2440

4.4582

5.9322

8

57.6632

33.2953

6.6968

7.7067

10

76.4261

44.2987

7.4273

7.6733

12

99.9313

51.4253

10.2030

8.0410

Figure 2 showed that the growth medium exposed to 1.0 ppm Cr(VI) could absorb almost completely or 99.93%, indicating that the microalgae could grow and multiply in water with this chromium concentration. The growth medium is not yet toxic to the growth of microalgae Scenedesmus sp.

Figure 2 (a) Plots of Cr(VI) concentration as a function of time, (b) plots of the percentage of Cr(VI) removal as a function of time, and (c) the plots of the percentage of Cr(VI) removal as a function of Cr(VI) concentration

        At Cr(VI) 3.0 ppm, the a similar trend of increasing ion absorption throughout the study period. However, the amount of chromium ion absorbed was lower than the Cr(VI) 1.0 ppm exposure, which meant that Cr(VI) ion was still absorbed but was toxic. The growth of Scenedesmus sp. was disrupted when exposed to this level of chromium because the metal ion cofactor required by its enzymes was non-competitively inhibited, and the complex reagents exchange metal ions from the enzyme exceeded their tolerance limit (Daneshvar et al., 2019; Susanto, Kartika, and Koesnarpadi, 2019).

        At Cr(VI) 5.0 ppm, the absorption of Cr(VI) dropped precipitously, indicating that the solution was already highly toxic to the microalga and no microbial growth was occurring. The same result was obtained from the 7.0 ppm medium, and in both media, no green color developed beyond the initial very pale green color. It is a bio-indication that the growth media already contained chromium ions at high concentrations (Susanto, Kartika, and Koesnarpadi, 2019).

        The reduction of ion concentration in the growth media was due to (1) the biosorption with bonds between metallothionein thiol groups, namely polypeptides containing about 30% of the amino acid cysteine (Dewi, Yuniastuti, and Ahmed, 2018), and (2) the non-competitive inhibitory effect of Cr(VI) ion to form mercaptide salts with sulfhydryl groups of enzyme proteins :


Notes: M = Metal, R = Protein radicals from microalgae, and SH = Sulfhydryl

This condition inhibits the action of the enzyme because it is not similar to the cofactor as an activator of the enzyme (Dewi, Yuniastuti, and Ahmed, 2018).