TREATMENT OF TANNERY EFFLUENT USING ACTIVATED CARBON

TREATMENT OF TANNERY EFFLUENT USING ACTIVATED CARBON

ABSTRACT

This research work  was done using granulated activated carbon (GAC) to treat tannery effluent and Atomic Absorption Spectroscopy (AAS) was used to determined heavy metals namely; chromium (Cr), Cadmium (Cd) and Lead (Pb) and the result showed the reduction of Chromium by the used of activated carbon from 62.9466mg/L to 17.4221mg/L, the reduction of Cadmium 0.0723mg/L to 0.0419mg/L while Lead was 2.1807mg/L to 1.7644mg/L in both the untreated and treated sample. Then various physico–chemical parameters were analysed such as pH, conductivity, COD, and BOD. The parameters were carried out on both the untreated and treated sample. The result of the pH of both the untreated and treated samples showed that the activated carbon best reduced the pH from 7.46 to 7.15 and the conductivity from 104.95µS/cm to 101.30µS/cm, while the COD reduced from 56.00ppm to 34.10ppm and the BOD reduced from 144.47ppm to 138.00ppm. 

CHAPTER ONE

INTRODUCTION

1.0.      BACK GROUND OF THE STUDY

A tannery is the term for a place where the skins are processed. Tanning into leather involved a process which permanently alters the protein structure of skin.

Effluent means liquid waste or sewage discharge into a river or sea.

Wastewater from tannery effluents attracts the attention of environmental protection agencies all over the world which are highly toxic (Chu, 2001). Tannery industries used a large number of chemicals (i.e. natural and synthetic tanning agents, surfactants, salts etc.) for the treatment of skins and consequently produce large quantities of effluents (about 10m³ of waste per tone of leather) which have to be purified before being discharged into the environment. Tanning industry contributes significantly towards exports, employment generation and occupies an important role in many countries. On the other hand; tannery wastes are ranked as the highest pollutants among all the industrial waste (Laconi et al, 2002).

Some dyes are reported to harm mammalian cells by causing kidney tumours\ and reproductive difficulties these days are also potentially carcinogenic, genotoxic or tetratonic in many animals’ species (Nimrat et al, 2004).

Dyes and heavy metals which are major pollutant species usually exist side by side in effluents and waste (Saffaj et al, 2004). This gave rise to different mixtures or complexes which makes the treatment of effluents difficult to handle (Vista et al, 2010)

 1.1.      TREATMENT OF TANNERY EFFLUENTS

The degree of damage of the environment depends on the nature and amounts of the hazardous species present. Indiscriminate discharge of effluents into the environment can have far reaching consequences. (Abdulrasaq et al, 2010).

There are acceptable standards/levels to which the pollutant load from tannery effluents should be reduced to before discharge into the environment.

Various techniques can be used to regulate the pollutant load of raw effluents. Some of them are; precipitation, filtration, bisorption, chemical coagulation and flocculation, oxidation and adsorption (Kadrivelu et al, 2003). However, adsorption using activated carbon is considered efficient for the dye removal and is also widely used for heavy metal removal or recovery.

1.2.   USE OF ACTIVATED CARBON FOR TANNERY EFFLUENT TREATMENT

In an effort to develop an optimal method for treating effluents, the feasibility of combining the Granulated Activated Carbon (GAC) and photocatalytic systems has recently been studied. Effluents are generally comprised of organic and inorganic species. The versatile nature of activated carbon makes it usable for uptake of various pollutant species from effluents. It has high degree of porosity and an extended inter-particulate surface area. Activated carbon is a much preferred choice of adsorbent due to the fact that it can easily been produced with not much complicated procedure which therefore, makes it relatively easy to use and a less expensive adsorbent to employ compared to others(Ocholi,O. 2012).

Activated carbon is used in the adsorption of heavy metals like Pb, Cd, Cr and others and also in the recovery of certain precious metals like Ag and Au.

1.3.      ADSORP TION THEORY

The phenomenon of attracting and retaining the molecules of a substance on the surface of a liquid or a solid resulting into a higher concentration of the molecules on the surface is called adsorption. The substance thus adsorbed on the surface is called adsorbate and the substance on which it is adsorbed is called adsorbent. The adsorptive or ion exchange mechanisms process is predominantly dissolved metabolism independent. Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or solid to a surface. This process creates a film of the adsorbate of the adsorbent. This process differs from adsorption, in which a fluid (the adsorbate) permeates or is dissolved by a liquid or a solid (the adsorbent).

Note that adsorption is a surface-based process while adsorption involves the whole volume of the material. The term ‘sorption’ encompasses both processes, while desorption is the reverse of adsorption. It is a surface phenomenon. A number of mechanisms by which micro-organisms tolerate and removed heavy metals have been proposed. Micro-organisms modulate metal toxicity by maintaining and allow intracellular concentration of toxic metals via precipitation, adsorption to the cell surface, or accumulation in the pericellular or endocellular region of the cell. The cell walls of the microbial biomass are mainly composed of polysaccharides, proteins and lipids and often contain functional groups such as carboxylate, hydroxyl, sulphate, phosphate and amino groups that bind to heavy metals.

1.4.      AIM OF THE STUDY

The aim of this research is to determine if tannery effluent using activated carbon  will yield efficient and effective result for use in further treatment method.

1.5.      OBJECTIVES OF THE STUDY

To determine if tannery effluent can be treated efficiently by using activated carbon.

To determine if treated effluent can be suitably reused in tanning industries for further leather production.

To determine if treated effluent is safe for human consumption.

1.6.      STATEMENT OF THE PROBLEM

The discharge of chromium (vi) into aquatic ecosystems has become a matter of concern in all the tannery areas across the world over the last few decades (Singh et al, 2001). This pollutant is introduced into the aquatic systems of leather processing units as a result of chrome tanning of leather. The presence of heavy metals in industrial and urban wastes water is one of the main causes of water and soil pollution. Tremendous increase in the use of heavy metals over the past decades has invariably resulted in an increased flux of metallic substances in the environment (Gupta et al, 2009)

1.7.      JUSTIFICATION

The common laboratory practice is to carry out adsorption studies using a single adsorbate system (Meesavana and Pavsant, 2008). Environmental pollution is a global challenge with industrial effluent as major contributors (Garg et al., Kadrivelu et al., 2003). These effluent are normally a mixture of atleast two or more pollutant species i.e.aqueous binary or multi-component mixtures (Meesaavan and pavasant 2008).

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