Effect of pH on the Removal of Chromium ( Cr ) ( VI ) by Sugar Cane Bagasse

The industrial estates in India are dominated by small and medium scale industries, which are posing a serious threat to the environment by virtue of discharging effluents of a polluting nature. The problems become severe due to the presence of heavy metals in the effluents. Chromium is widely used in a number of industries such as electroplating, metal finishing, cooling towers, dyes, paints, anodising and leather tanning industries. The toxicity of chromium (VI) is well known and is considered a hazard to the health of humans and animals. The presence of chromium (VI) in aquatic environments at high concentrations is also lethal to marine species. The treatment of chromium bearing effluents have been reported through several methods, such as chemical reduction, precipitation, ion exchange, electrochemical reduction, evaporation, reverse osmosis and adsorption. However among these, adsorption is found to be highly effective, inexpensive and an easy method to operate. India is an agricultural country and generates a considerable amount of agricultural wastes such as sugar cane bagassess, coconut jute, nut shell, rice straw, rice husk, waste tea leaves, ground nut husk, crop wastes, peanut hulls and fertilizer wastes. Successful studies on these materials could be beneficial to developing countries and could be easily applied as adsorbents for the removal of chromium from wastewater. Most of the previous work highlights the use of commercial activated carbon but these adsorbents are relatively expensive and less feasible to be used in developing countries. Keeping these in view batch experiments have been designed to study the feasibility of sugar cane bagasse to remove chromium (VI) from the aqueous solutions. While evaluationg the impact of various parameters, such as adsorbent does, contact time, initial concentration and pH on chromium removal efficiency, the results indicate a prominent effect of pH on the chromium reduction by the adsorbent used in the present study.


Effect of pH on the Removal of Chromium (Cr) (VI) by Sugar Cane Bagasse
ABSTRACT: The industrial estates in India are dominated by small and medium scale industries, which are posing a serious threat to the environment by virtue of discharging effluents of a polluting nature.The problems become severe due to the presence of heavy metals in the effluents.Chromium is widely used in a number of industries such as electroplating, metal finishing, cooling towers, dyes, paints, anodising and leather tanning industries.The toxicity of chromium (VI) is well known and is considered a hazard to the health of humans and animals.The presence of chromium (VI) in aquatic environments at high concentrations is also lethal to marine species.The treatment of chromium bearing effluents have been reported through several methods, such as chemical reduction, precipitation, ion exchange, electrochemical reduction, evaporation, reverse osmosis and adsorption.However among these, adsorption is found to be highly effective, inexpensive and an easy method to operate.India is an agricultural country and generates a considerable amount of agricultural wastes such as sugar cane bagassess, coconut jute, nut shell, rice straw, rice husk, waste tea leaves, ground nut husk, crop wastes, peanut hulls and fertilizer wastes.Successful studies on these materials could be beneficial to developing countries and could be easily applied as adsorbents for the removal of chromium from wastewater.Most of the previous work highlights the use of commercial activated carbon but these adsorbents are relatively expensive and less feasible to be used in developing countries.Keeping these in view batch experiments have been designed to study the feasibility of

Introduction
Most of the wastewater in industrial estates contains trace quantities of many heavy metals such as nickel, manganese, lead, chromium, cadmium, zinc, copper, iron and mercury.Some of these metals are essential to the growth of biological life and absence of sufficient quantities of them could limit their growth (Metacalf and Eddy et al, 1994).Larger concentrations, however, could cause adverse effects on humans, animals and plants.The rapid industrialization has resulted in accelerating the flux of heavy metals into surfacial environment.Pollution, due to these heavy metals, has been a major source of concern to scientists and environmental engineers.The presence of any of the above mentioned heavy metals in excessive quantity will interfere with many usages of water because of their toxicity.Therefore, it is desirable to measure and control the concentrations of these substances.Several mishaps related to heavy metal concentrations in the aquatic environment have increased the awareness about heavy metal toxicity.Among these, Minamata tragedy in Japan  due to metallic mercury escaping from the laboratories and industries, mainly from chlorine manufacturing.It was acquired by aquatic life and passed along through natural food chains to humans, largely by fish.Another disease "Itai-Itai" that occurred among the farmers who drank water-containing cadmium supplied from the Jentsu River in Japan (Benefield ;Jadleins and Weand et al, 1982).
Chromium (VI) causes many adverse effects on humans, aquatic life and soil.Some of the effects are summarized as follows; Humans: Nausea, vomiting (Kerishnamurthy and Vishwanathan) , epiesgestric pain, severe diarrhoea, haemorrhage, dermatitis by skin contact, nasal mucous membrane, ulcer (Satyanarayan et al, 1995), lung cancer and tissue necrosis.Aquatic life: reduction in fish production at high concentrations, chromium accumulates in fish tissues and reaches to consumers.Gold fish and trout are killed at a concentration of 180 mg/l.Land: Soil fertility is reduced if chromium-bearing effluents are discharged on land (Sohail, 1997).

Adsorption of Heavy Metals on Agricultural Wastes
The treatment of chromium bearing effluents has been reported through several methods, such as, chemical reduction and precipitation, ion exchange, electrochemical reduction, evaporation and reverse osmosis.Most of these methods need high capital costs and recurring expenses such as chemicals.Less attention has been paid towards the treatment of effluent containing chromium by means of the adsorption technique using agricultural wastes.(Sohail et al, 1998).Potential Agricultural waste adsorbents are activated ground nut husk carbon (Periasamy, 1991), calcinate coke (Satyanarayan, 1995), bagasse ash , activated coconut jute, waste tea leaves carbon, activated charcoal, fly ash and rice husk, and rice straw (Deo, 1992).The comparative studies of different adsorbents are shown in Table 1 (Lal, 1992;Huang, 1975;Sharma, 1993;Shrichand, 1994).

Materials and Methods
The wastewater to be used in the investigation was prepared by dissolving a known amount of potassium dichromate in a known volume of distilled water in order to have waste of uniform characteristics and to avoid the interference with other elements.To evaluate the potential of bagasse to remove hexavalent chromium, batch experiments were carried out.Wastewater containing known concentrations of Cr (VI) were prepared from the stock solution and taken separately in glass stoppered conical flasks.Then known quantities of the adsorbent were added to the wastewater.The system was equilibrated by shaking the contents of the flask at room temperature so that adequate contact time between adsorbent and the metal ion was maintained.The suspension was filtered through Whatman No.1 filter paper and the filtrate was analyzed to evaluate the concentration of Cr (VI) metal in the treated wastewater.All the analyses were performed according to Standard Methods (Standard Methods, 1989).Metal analysis was carried out by using Atomic Absorption Spectrometry (model: GBC-902).

Results and Discussion
While evaluating the effect of adsorbent dose, contact time and pH on chromium removal, the initial concentration of Cr (VI) was kept as 50 mg/l because in chrome plating wastes, chromium concentrations vary from 3-30 mg/l [ISI 7453-1977].

Effects of Contact Time at Different Adsorbent Doses on Cr (VI) Removal
The response of contact time on the removal of Cr (VI) is presented in Figure1.The observations reveal that the percentage of removal of Cr (VI) increases with an increase in contact

CONTACT TIME IN HOURS % REMOVAL OF Cr(VI)
0.1 g 0.2 g 0.3 g 0.4 g 0.5 g 0.6 g 0.7 g 0.8 g 0.9 g time.The removal efficiency is further increased as the dose of bagasse increases from 0.1 to 0.9 g and the contact time varies from 0.5 to 3.5 hr.It is also observed that at 0.5 hr the removal efficiency increased from 27-80% as the adsorbent dose increased from 0.2 to 0.8 g.If the contact time is raised to 1.0 hr, the removal efficiency varies from 38 to 93% for the same variation of dose (0.2 to 0.8 g).
A removal efficiency of 94% of Cr (VI) is observed at a contact time of 1.5 hr with a dose of 0.70 g/50 ml.Chand et al. (Shrichand, 1994) observed 30% removal efficiency of Cr (VI) having initial Cr (VI) concentration of 10 mg/l, at pH 4.38, the contact time was 1.5 hr and dose of adsorbent was 1.2 g/100 ml.

Effects of Adsorbent Dose at Different Contact Time on Chromium Cr (VI) removal
The effect of various bagasse dose on the removal of Cr (VI) from the wastewater are shown in Figure 2 .The results indicate an increase in the removal efficiency of Cr (VI) with increase in the dose of raw bagasse up to a certain level, beyond which the removal efficiency remains constant.It is evident that a dose of 0.8 g/50 ml is sufficient to remove 75-100% Cr (VI) in 0.5-3.5 hr.The increase in the removal efficiency with a simultaneous increase in adsorbent dose is due to the increase in surface area and hence more active sites are available for the adsorption of Cr (VI).

Effect of pH on Chromium (VI) Removal
Effect of pH on Cr (VI) removal shows that at lower pH, the Cr (VI) removal efficiency is higher and at higher pH the removal efficiency is reduced considerably (Figure 3).At pH 1.0 the removal efficiency is 100%, whereas on increasing the pH to 3.0 the removal efficiency is reduced to 15%.One of the reasons for the better adsorption capacity observed at low pH values may be attributed to the large number of H + ions present at these pH values, which in turn neutralizes the negatively charged hydroxyl groups (-OH) on the adsorbed surface thereby reducing hindrance to the diffusion of dichromate ions.At higher pH, the reduction in adsorption may be due to an abundance of OH -ions causing increased hindrance to diffusion of positively charged dichromate ions.

Effects of Various Initial Cr (VI) Concentrations on Cr (VI) Removal
The results of Figure 4 show that at low initial concentrations of chromium (VI) ( 5 to 10 mg/l) the removal efficiency is higher (70-100%).The removal efficiency of chromium decreases when chromium concentration is increased beyond 10 mg/l.The removal efficiency is 60% at a concentration of 20 mg/l and it decreases to 47% when chromium concentration was increased to 50 mg/l.In a similar study Chand et al. (Shrichand, 1994) obtained 90% removal efficiency at a Cr (VI) concentration of 10 mg/l in a dose of 1.0 g/100 ml at a contact time of 1.5 hr when the pH of the solution was 2.0.

Figure 1 .
Figure 1.Effects of contact time at different adsorbent (bagasse) doses on Cr (VI) removal.

Figure 2 .
Figure 2. Effects of adsorbent dose at different contact time on Cr (VI) removal.

Figure 3 .
Figure 3. Effects of pH on Cr (VI) removal.

Fig. 4
Fig.4 EFFECTS OF INITIAL Cr (VI) CONCENTRATION ON Cr (VI) REMOVAL