COMPARATIVE BIOSORPTION STUDY OF ARSENIC AND CADMIUM FROM AQUEOUS SOLUTION USING COCONUT SHELL AND GROUNDNUT SHELL

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COMPARATIVE BIOSORPTION STUDY OF ARSENIC AND CADMIUM FROM AQUEOUS SOLUTION USING COCONUT SHELL AND GROUNDNUT SHELL

ABSTRACTS

Comparative biosorption of heavy metals (Cd, and As) in batch system using agro-mass obtained from groundnut shell and coconut shell was carried out. The heavy metal adsorption was found to be dependent on the initial pH, contact time, initial concentration of heavy metal and agro-mass dose. Activated carbon from coconut shell and groundnut shell using phosphoric acid (H₃PO₄) as activating agents by means of a two step activation process was characterised. The result of the analysis indicate the percentage of dry matter, moisture contents, Ash contents, bulk density and surface area of the samples were shown as 97.78%, 2.22%, 1.85%, 0.58g/cm³ and 179.30m² while 98.93%, 1.07%, 1.46%, 0.20g/cm³ and 289.10m² for coconut shell and groundnut shell respectively. The groundnut shell sample gave different results on analysis to that of coconut shell sample. The percentage removal efficiency of Cd²⁺ and As³⁺ before and after with the activated carbon of the samples and the amount Cd²⁺ and As³⁺ adsorbed at different contact time range was determined using the Atomic Adsorption Spectrophotometer (AAS) “ICE 3000 AA02134104v130”. Langmuir and Freundlinch model were used to study the adsorption isotherms. Langmuir was found to be better fit for adsorption of Cd²⁺ and As³⁺ ions with good correlation coefficient (0.936) and (0.958) for coconut shell than for groundnut shell (0.084) and (0.906) respectively. These results reveal that activated carbon made from groundnut shell with good characteristic are better than activated carbon made from coconut shell for the adsorption of heavy metal ions from aqueous solution.

CHAPTER ONE

INTRODUCTION

1.1.     BACKGROUND OF THE STUDY

The natural environment is constantly contaminated by various pollutants coming from domestic, industrial and agricultural sectors, which in turn showed a considerable change. Poisonous metals are widespread hazardous and affect the environment with a negative impact on the ecosystem, causing life threaten diseases to both animals and humans. Among heavy metals, Arsenic, Mercury, Cadmium, Chromium, e.t.c. (Cd, As, Hg, Cd, As, Cr, As) are cited (Salem et al. 2012) which must be removed before discharge to the aquatic environment. Unlike organic pollutants, heavy metals are refractory and cannot be degraded  and accumulate  in living organisms (Ali and Ateeg 2015).The elimination  of heavy metals has been the theme of several works using different techniques like adsorption (Abolhasani and Behbahani 2015); ion electrodialysis (Esalah et al. 2000), coagulation/flocculation (Yue et al. 2009), sedimentation (Gupta et al. 2001), ionexchange   (Dabrowski et al. 2004; Kang et al. 2008), biological operations (Rashid et al. 2014), nano filtration (Hafiane et al. 2000), solid-phase extraction (Khezami and Capart 2005), (Behbahani et al. 2014) and electro kinetic remediation (Sawada et al. 2004).

However, all these techniques suffer from high costs of capitals and operations as well as the elimination of metallic sludge (Malairajan 2011). On the other hand, the adsorption has become advantageous for removing poisonous metals because of its environmentally friendly characteristic, efficiency and low cost. In this regard, many agricultural wastes were used as adsorbents for both inorganic and organic pollutants (Copat et al. 2012; Izquierdoetal.2014; Samiey and Ashoori 2012; Vilar et al.2008).

In this respect, coconut shell and groundnut shell will be utilize to see their efficacy in adsorbing heavy metals from solution because of their  specific characteristics that motivate their utilization for the elimination of various pollutants, including metals. The present study is devoted specifically to the adsorption of heavy metals. (As and Cd) onto coconut shell and groundnut shell. The optimization of the operating conditions (initial pH value, contact time, metal concentration and adsorbent dose) in batch system allow an elimination a good percentage of the metals. The Langmuir and Freundlich, adsorption isotherm were applied to the experimental data to get information on the interaction metals/coconut   shell and groundnut shell. (Ashoori 2012).

Adsorption is a surface phenomenon with common mechanism for organic and inorganic pollutants removal.  When a solution containing  absorbable  solute comes into contact with a solid  with a highly  porous  surface  structure,   liquid-solid     intermolecular    forces  of attraction  cause some  of the solute   molecules  from the solution to be concentrated   or deposited  at the solid  surface. The   solute   retained (on the solid surface) in adsorption processes   is called adsorbate, whereas, the solid on which it is retained is called  as an adsorbent.  This surface accumulation   of adsorbate on adsorbent is called adsorption.  This creation of an adsorbed phase having acomposition different from that of the bulk fluid phase  forms the basis of separation  by adsorption technology. (Vilar  et al. 2008).

The  adsorption   technique   has  become   more  popular   in recent  years  for wastewater treatment  owing to its efficiency in the removal of pollutants  too stable for biological methods. Metals   adsorption is a result of six mechanisms    (adsorption, chemical precipitation, ultrafiltration, nanofiltration, electrodialysis and ionexchange)   and is influenced by many factors such as metal/adsorbent interaction, adsorbent’s surface area, particle size, temperature, pH and contact time. The main advantage of adsorption recently became the use of low-cost materials, which reduces the procedure cost. However, following the economic boom in the l970s-where   the procedure cost was not such a big problem (or had not been taken into account) the economic   crisis of the 2000s arose and led researchers  to turn their interest  to other fields  with lower procedure costs. Therefore, different materials were tested as possible wastewater adsorbents. The selection for the most appropriate adsorbent would be based on some major characteristic properties such as:

i.          The low-cost along with the satisfactory adsorption properties (capacity, reuse, industrial-scale use etc.) and

ii.         The environmentally-friendly nature of each adsorbent. It is fundamental to use only materials which either have the lowest impact on environmental balance or are absolutely environmentally friendly (from abundant natural   sources, biodegradable, non toxic etc.). (Salem et al.2012)

Recent  studies  on adsorption  have drawn  the attention  to waste materials  produced  by large-scale   industrial processes. Such materials  are the by-products  of industrial materials produced from natural  resources  such  as peat, wood,  barley,  brown  rice, hay, peanut shell, almond  shell, coconut shell, groundnut    shell, biomass,  soybean,  cotton seed  meal, bark,  sugar  beet pulp, leaves,  green  algae,  wood  chips,  fertilizer,   com  silk, and dried aquatic plants, as well as plant wastes and  other industrial products. All of these materials have been the subject of numerous studies due to their ability to remove trace metals from water. Most of the researches that used adsorbents for organic compounds are based on batch kinetic and batch equilibrium    studies. (Abdessalem et al. 2001).The objective of this research is to study and compare the adsorptive capacities of activated carbon from coconut shell and groundnut shell for the removal of Cd and As from aqueous solution.

1.2.   STATEMENT OF PROBLEM

Arsenic and Cadmium causes toxicity in living cells by following ionic mechanism and that of oxidative stress. These heavy metals have proven to be a major threat and it has several health risks associated with it. Its ability to accumulate in the human body and food chain, exhibiting a health effect (chronic nature) is of immense concern hence the continual search for more effective adsorbent for its removal from effluents and water waste.

1.3       SCOPE AND LIMITATION OF THE STUDY

This research focuses on the use of agricultural waste in the removal of heavy metals particularly Arsenic and Cadmium,   utilizing coconut shell and groundnut shell as adsorbent for removal of Arsenic ion and Cadmium ion from aqueous solution. This study will also investigate the influence of uptake of Arsenic ion and Cadmium ion b coconut shell and groundnut shell at different contact times and concentration of the adsorbent

1.4.      SIGNIFICANCE OF THE STUDY

Several biomasses are considerable for application in adsorption knowing their different adsorption capacity.  Therefore, this study will not only reduce the rate of importation of adsorbent, but would also encourage and promote the use of local raw material as competitive alternatives, also reduce high sludge generating treatment which is prone to environment contamination.

1.5       AIM OF THE STUDY

• To compare the biosorption study of arsenic and cadmium from aqueous    solution using coconut shell and groundnut shell

1.6.      OBJECTIVE OF THE STUDY

•        To identify useful information for the utilization of native agricultural byproduct for the removal of heavy metals (As and Cd).

•        To compare the adsorption capacity of coconut shell and groundnut shell.

•        To illustrate the adsorption by application of isotherm and kinetic    model.

•        To explore optimum experimental conditions for the removal of Cd and As ions from aqueous solution.

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