A CELLULAR BIOSORBENT FOR ARSENIC REMOVAL AND PROCESS FORPREPERATION THEREOF

Abstract

ABSTRACT This invention relates a cellular biosorbent, from the cellular biomass of Rhodopseudomonas palustris made with polyethyleneimine polymer and a cross-linking agent for adsorption of Arsenic (III) and Arsenic (V) from contaminated water and a process for preparation thereof. Reference Fig 1

Specification

Description:DETAILED DESCRIPTION OF THE INVENTION
Some embodiments of this disclosure, illustrating all its features, will now be discussed in detail. The words "comprising," "having," "containing," and "including," and other forms thereof, are intended to be equivalent in meaning and be open ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items.
Although any methods similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present disclosure, the exemplary methods are now described. The described embodiments are merely exemplary of the disclosure, which may be embodied in various forms.
Various modifications to the embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. However, one of ordinary skill in the art will readily recognize that the present disclosure is not intended to be limited to the embodiments illustrated, but is to be accorded the widest scope consistent with the principles and features described herein.
As referred to herein, all compositional percentages are by weight of the total composition, unless otherwise specified.
The term "adsorption" refers a process that utilizes solids for eliminating substances from either liquid or gaseous solutions, by attraction on the solid's surface.
The term "adsorbent" refers to a material that has the ability to attract and hold molecules of a substance (usually a gas or liquid) on its surface, rather than absorbing it into its bulk. Adsorbents are typically used in purification, separation, and chemical reaction processes.
The term "biosorbent" refers to a biological material that can passively adsorb and remove contaminants, such as heavy metals, dyes, or other pollutants, from aqueous solutions. Unlike traditional adsorbents, biosorbents are often derived from natural or waste materials, including algae, fungi, bacteria, agricultural waste (like rice husks or fruit peels), or other plant-based biomass.
The term "cellular biosorbent" refers to a type of biosorbent made up of living or non-living microbial cells, such as bacteria, fungi, or algae, that adsorb contaminants from solutions. These cells contain various functional groups (such as carboxyl, hydroxyl, and amine groups) on their surfaces, which facilitate the binding of pollutants like heavy metals, dyes, and other toxic substances.
The term "monolithic adsorbent" refers to a single, continuous, solid material with a porous structure designed for efficient adsorption of molecules. Unlike traditional granular or powdered adsorbents, monolithic adsorbents are formed as a single piece or block with interconnected macropores, mesopores, or micropores that allow for easy fluid flow and high surface area. This structure enhances adsorption efficiency and minimizes pressure drop, making monolithic adsorbents especially valuable in applications like chromatography, wastewater treatment, and gas separation.
The invention relates to a cellular biosorbent for removal of arsenic from water. More particularly the cellular biosorbent removes the more toxic form of As (III) through adsorption more efficiently when compared to As (V), at neutral, acidic, and alkaline pH conditions.
An embodiment of the invention relates to a cellular biosorbent, comprising:
? a cellular biomass of Rhodopseudomonas palustris;
? polyethyleneimine polymer stock solution, and;
? a cross-linking agent.
Cellular Biomass
In an aspect of the embodiment, the biosorbent is prepared from a natural source, more particularly a non-sulfur bacteria.
In an aspect of the embodiment, the non-sulfur bacteria used is Rhodopseudomonas palustris. It consists of functional groups that have bioremediation potential for various heavy metals.
In an aspect of the embodiment, a cellular biomass of Rhodopseudomonas palustris is prepared and immobilized in a polymer matrix to form the biosorbent.
In an aspect, cells of Rhodopseudomonas palustris are used in an amount of 30-50 mg, more preferably 40 mg.
In an aspect, the cellular biomass is prepared by growing Rhodopseudomonas palustris cells in nutrient broth with continuous monitoring of optical density. The cells were harvested in the early log phase, The cells were then centrifuged, with the supernatant discarded, and the cell pellet was collected and weighed and used as the cellular biomass.
Polymer
In an aspect of the embodiment, the cellular biomass was embedded in a polymeric network to form the biosorbent. Polyethyleneimine (PEI) is the polymer that is rich in -NH2 groups. Addition of PEI to Rhodopseudomonas palustris biomass makes it into a monolithic adsorbent with high porous properties.
In an aspect of the embodiment, polyethyleneimine (PEI) is used in an amount of 120 µl. In an aspect, the polymer is used as a stock solution.
The polymer stock solution consists of polyethyleneimine in an amount of 120 µl in deionized water.
In an aspect, the stock solution is prepared by diluting PEI solution with deionized water. The solution was sonicated for 60 minutes in an ultrasonic water bath to ensure thorough dispersion and was stored as the PEI stock solution. In an aspect, the PEI stock solution is used in an amount of 100-140 µl, preferably 120 µl.
Cross-linking agent
In an aspect of the embodiment, to aid the polymerisation a cross-linking agent is added. In a preferred aspect, the cross-linking agent used is 1,3-diglicidyl ether.
In an aspect the cross-linking agent is used in an amount of 5- 15 µl, preferably 10 µl.
In an aspect of the embodiment, the cellular biosorbent is a microporous biosorbent with pores ranging from 0.09 µm to 54.39 µm in size. The pores are uniformly spread throughout the biosorbent
Process for preparation
An embodiment of the invention relates to a process for the preparation of cellular biosorbent comprising the steps of:
a. Growing cells of Rhodopseudomonas palustris grown in natural broth and centrifuging the cells to form cellular biomass,
b. Sonicating polyethyleneimine polymer in deionized water to form a stock solution;
c. Adding the cellular biomass to the stock solution and vortexing followed by addition of cross-linking agent to form the cellular biosorbent of Rhodopseudomonas palustris.
d. The mixture is ice-templated to form the cellular biosorbent of Rhodopseudomonas palustris.
The present invention relates to a novel biosorbent made by R. palustris biomass with polyethyleneimine polymer. It has the adsorptive capacity of 165 mg g-1 for As (V) and 168 mg g-1 for As (III). It can reduce the concentration of both species of arsenic As (III) and As (V) below the permissible limit of 10 µg/L as prescribed by the USEPA within the time frame of 15 hours at optimum pH and temperature. This biosorbent can highly maintain its efficacy at an alkaline pH of 8.4. It has the potential to remove a more toxic form of arsenic, that is, As (III), more effectively than As (V). The biosorbent exhibited a pore size distribution ranging from 0.09 µm to 54.39 µm, with macropores uniformly spread throughout the material. This configuration provides increased accessible area, enhancing the biosorbent's capacity to adsorb a range of contaminants, including heavy metals and organic pollutants. This biosorbent can be used for up to 4 complete cycles without losing efficacy in arsenic ion removal. The macroporous biosorbent can be deployed in contaminated water sources, wastewater treatment facilities, and industrial effluent systems to adsorb toxic pollutants. It can be easily separated from the water post-treatment due to its solid structure, allowing for potential regeneration and reuse.
EXAMPLES
The invention is illustrated by the following examples which are only meant to illustrate the invention and not to act as limitations. All embodiments apparent to a process there in the art are deemed to fall within the scope of the present invention.
Example 1: Preparation of cellular biosorbent material
The cellular biosorbent was prepared by using the following steps:
a. Rhodopseudomonas palustris cells were grown in nutrient broth. Optical density was measured every 24 hours at ?= 660 nm. Cells were taken during the early log phase (OD = 1.5) and centrifuged at 8000 rpm for 10 minutes. The pellet was collected, and the supernatant was discarded. Rhodopseudomonas palustris biomass was weighed, and 40 mg of its biomass was taken.
b. Polyethyleneimine stock solution was prepared by diluting 2000 mg of polyethyleneimine with deionized water. The mixture was sonicated for 60 minutes in an ultrasonic water bath sonicator. The sonicated solution was kept as the stock solution.
c. A 40 mg biomass of Rhodopseudomonas palustris was taken in a 2 ml Eppendorf tube, followed by the addition of 120 µl of Polyethyleneimine polymer from the stock solution. The contents were vortexed thoroughly for 2 minutes.
d. In order to strengthen the polymer, 10 µl of 1,3-diglicidyl ether was added as a cross-linking agent, followed by vortexing the mixture for 2 minutes.
e. The mixture was ice-templated in the freezer at -16ºC for 36 hours.
Figure 1 shows the image of the cellular biosorbent made up from 40 mg Rhodopseudomonas palustris cells with polyethyleneimine
Example 2: Fourier-transform infrared spectroscopy (FTIR) analysis
FTIR analysis was conducted to investigate the functional groups involved in As (V) and As (III). For this study, 40 mg of Rhodopseudomonas palustris-based polymeric adsorbent was taken as a control. Rhodopseudomonas palustris-based polymeric adsorbent was used in As (V) and As (III) reduction kinetics studies and was selected for FTIR analysis. We chose the adsorbent from a 15-hour experimental design because we found significant As (V) and As (III) reduction at this point. Figure 2 shows the analysis for polymeric cellular adsorbent as control with As (V) and As (III) laden adsorbent after 15 hours.
FTIR analysis proved the mechanism behind the attachment of functional groups of the cellular adsorbents with arsenic compounds. O-H stretching (broad peak around 3200-3600 cm?¹): This may suggest the existence of hydroxyl groups, potentially originating from water or hydroxyl groups present on the adsorbent material.
• C=O stretching (around 1650-1750 cm?¹): Indicates carbonyl groups, which could be part of carboxylic acids, esters, or ketones.
• C-H stretching (around 2800-3000 cm?¹): Associated with alkyl groups (methyl, methylene).
• As-O stretching: Specific to arsenic oxides, peaks around 800-900 cm?¹ indicate As-O bonds.

Example 3: Surface morphology
The surface morphologies of the adsorbent material were examined by the FESEM instrument.
For this study, 40 mg of Rhodopseudomonas palustris-based polymeric structure was selected and treated as a control.
The Rhodopseudomonas palustris-based polymeric structure used in the As (V) and As (III) reduction kinetics study was selected for FE-SEM/EDAX analysis. The adsorbent was chosen from a 15-hour experimental design since significant As (V) and As (III) reduction was found at this point.
The FESEM-EDAX analysis depicted the percentage for As (III) in cellular monolith to be 26.84% in comparison to As (V) in cellular monolith to be 23.77%. This proves that As (III) is reduced from drinking water through the process of adsorption, which is evident from the FE-SEM results as the percentage of As (III) found in the adsorbed biosorbent is higher in comparison to As (V). (Figure 3)
Example 4: Arsenic reduction kinetics study / Adsorption efficiency
• 30 ppb of As (V) solution was prepared by diluting 1000 ppm of AAS-grade arsenic. Similarly, 30 ppb of As (III) was prepared by diluting 1 ppm of sodium arsenite solution. 40 mg of Rhodopseudomonas palustris based polymeric cellular adsorbent was administered to the freshly prepared arsenic solutions.
• As (V) and As (III) reduction kinetics study was done at different time intervals ranging from 3 hours to 72 hours.
• The final concentrations after each interval were detected with the help of a hydride Atomic Absorption Spectroscopy.
• The above kinetic study was repeated, at different pH. pH 4.6 was achieved by adding a 0.5 M concentration of HCl. Similarly, pH 8.4 was maintained by adding 0.5 M NaOH. The first-order kinetics study was applied, and the value of the adsorption constant K was calculated.
It was observed that the cellular monolithic adsorbents of the present invention can bring down the As (V) level to 0.86 ppb concentration from the initial concentration of 30 ppb. Applying the first-order kinetics model revealed a adsorption rate constant (K) of 0.1347 h-1. In the instance of As (III), the cellular adsorbent lowers the concentration of As (III) from the initial 30 ppb to 0.61 ppb. When the first-order kinetics model was applied, the rate constant (K) was found to be 0.1493 h-1, which is higher than the first-order kinetics of As (V); this shows that the cellular adsorbent can effectively adsorb As (III) better than As (V).
Figure 4 shows the As (V) and As (III) reduction kinetics study by polymeric cellular monolithic structures along with their first-order kinetics
Figure 5 shows the efficacy of the polymeric cellular monolithic structure of the present invention in removing As (V) and As (III) under different pH conditions.
Example 5: Adsorption study
To determine the adsorption capacity of an adsorbent material, adsorption isotherm fitting is commonly used. Adsorption isotherms describe the relationship between the concentration of adsorbate in the liquid (or gas) phase and the amount adsorbed on the adsorbent surface at equilibrium and at a constant temperature: Solutions of the adsorbate (e.g., a pollutant) at varying initial concentrations were prepared. Each solution was contacted with a fixed amount of adsorbent for a sufficient period to reach equilibrium. The concentration of adsorbate remaining in solution after equilibrium is reached was measured and the adsorbed per unit mass of adsorbent (qe) was measured, using
qe = (Co-Ce)V/W (1)
Where, qe is the quantity of adsorbate per unit mass of adsorbent at equilibrium (mg/g) , V is the volume of solution (L), Co (mg L-1) and Ce (mg L-1) are the initial concentrations of As (III) and As (V) and final concentration at equilibrium respectively. W is the mass of the adsorbent material (g).
Adsorption isotherm models were applied for As (V) and As (III) adsorption. The R-square value for the Freundlich isotherm is highest when it is compared to other models; this typically indicates multilayer adsorption. Temkin Isotherm Accounts for interactions between adsorbate molecules and assumes that adsorption heat decreases linearly with coverage. The R-square value for the nonlinear Temkin isotherm is the lowest.
It was observed that adsorptive capacity of the biosorbent was 165 mg/ g for As (V) and 168 mg/g for As (III).
Figure 6 shows the Adsorptive capacity and adsorption isotherm fitting of cellular polymeric structure laden with As (V).
Figure 7 shows the Adsorptive capacity and adsorption isotherm fitting of cellular polymeric structure laden with As (III).

Example 6: Reusable analysis of biosorbent material in the removal of Arsenic:
The reusability of an adsorbent is considered as an important parameter for deciding its cost-effectiveness and economic applicability. In order to examine the long-term usability of the synthesized adsorbent material, reusability was studied up to five cycles for the removal of As (III) and As (V). The experimental results presented in Figure 8 confirmed that the biosorbent possesses excellent As (III) and As (V) removal properties and can be reused multiple times without any significant decrease in its arsenic sorption capacity
, Claims:
CLAIMS
We claim:
1. A cellular biosorbent, comprising:
? a cellular biomass of Rhodopseudomonas palustris;
? polyethyleneimine polymer stock solution, and;
? a cross-linking agent.
2. The biosorbent as claimed in claim 1, wherein the adsorbent consists of Rhodopseudomonas palustris biomass in an amount of 30-50 mg.
3. The biosorbent as claimed in claim 1, wherein the polyethyleneimine polymer stock solution comprises of polyethyleneimine in an amount of 1800-2200 mg in deionised water.
4. The biosorbent as claimed in claim 1, wherein the polymer stock solution is used in an amount of 100-140 µl.
5. The biosorbent as claimed in claim 1, wherein cellular biosorbent has adsorptive capacity of 165 mg g-1 for As (V) and 168 mg g-1 for As (III).
6. The biosorbent as claimed in claim 1, wherein the cross-linking agent is 1,3-diglicidyl ether in an amount of 5-15 µl.
7. The biosorbent as claimed in claim 1, wherein the biosorbent consists of pores ranging from 0.09 µm to 54.39 µm in size.
8. A system of cellular biosorbent preparation, comprising:
? Rhodopseudomonas palustris cellular biomass in an amount of 40 mg;
? polyethyleneimine polymer stock solution in an amount of 120 µl, and;
? 1,3-diglicidyl ether in an amount of 10 µl.
9. A process for preparing cellular biosorbent comprising steps:
a. Growing cells of Rhodopseudomonas palustris grown in natural broth and centrifuging the cells to form a cellular biomass,
b. Sonicating polyethyleneimine polymer in deionised water to form a stock solution;
c. Adding the cellular biomass to the stock solution and vortexing followed by addition of cross-linking agent to form a mixture,
d. The mixture is ice-templated to form the cellular biosorbent of Rhodopseudomonas palustris.

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