T.C. Susitha, M. Ezhilpriya
Department of Civil Engineering, ACCET, Karaikudi
The amount of chlorine left after the disinfection is known as residual chlorine. Though chlorine has been used as disinfectant for many decades, presence of excess chlorine was observed to be very harmful to health. It is advised to avoid direct skin contact to chlorine and not inhale the fumes of oxides of chlorine. Generally chlorination, the disinfection process is placed at the tertiary level in drinking water treatment process. To overcome future contamination little amount of chlorine was allowed to be left in the water even after dechlorination. However this residual chlorine must be removed before the distribution for the reasons cited above. Sugar cane bagasse, an agro industrial waste made activated carbon, was reported to be an effective absorbent in many applications. This study investigates the effective removal of residual chlorine with cheap and easily available adsorbent, bagasse as such without activation. The adsorption capacity of the developed bagasse is comparable to the other available adsorbents, and cost wise it is calculated to be cheaper. Batch adsorption experiments were performed as a function of contact time, adsorbent dose, and pH. Isotherm studies, kinetics and diffusion studies were performed. This study also compares and enumerates the effect of pre-treatment over natural usage of bagasse as such as an adsorbent.
The world Health Organization, WHO, defines potable water as water that is limpid and transparent, odourless with no objectionable taste, and free from any kind of micro organism or chemical substance in concentration that can cause a risk to human health. For disinfection in many public water treatment facilities, chlorine and chlorine compounds (sodium hypochlorite, chlorine dioxide and calcium hypochlorite) are used. Chlorine is a powerful oxidising agent, able to penetrate cells and to act on vital cellular substances, and thus killing micro organisms. The concentration of residual chlorine in drinkable water should be in the range of 1.5 to 2.0 mg/L [1
In industries, the water from city distribution plants receives an additional dosage of chlorine so as to guarantee the level of quality required by the process.
It is also known that there is a natural tendency for chlorine to react with organic substances, forming chloramines, which alters characteristics of the final product such as taste odour, and total trihalomethanes (TTHM) associated with an increased risk of cancer as well as damage to heart , lungs, kidney, liver and central nervous system. For this reason, the water used in all processes which comes into direct contact with living beings free from residual chlorine.
Activated carbon (powdered or granular) is most widely used adsorbent because it has excellent adsorption efficiency for organic compounds. In order to decrease the cost of treatment, attempts have been made to find inexpensive alternative adsorbents. Consequently, a number of low cost and easily available materials, such as waste biomass, are being studied for the removal of residual chlorine from aqueous solutions at different operating conditions. However, as in adsorption capacities of the above adsorbents are not very large, the new adsorbents which are more economical, easily available and highly effective are still needed.
MATERIALS AND METHODS:
Formaldehyde treated sugarcane bagasse:
Sugarcane bagasse was collected from a local market. It was dried under sunlight until all the moisture has evaporated. The material was ground to fine powder. The resulting material was sieved in the size range of 1.456mm mesh. To immobilize the colour and water soluble substances, the ground powder was treated with 1% formaldehyde in the ratio of 1:5 (bagasse: formaldehyde, w/v) at 50ºC for 4 h. The sugarcane bagasse was filtered out, washed with distilled water to remove free formaldehyde and activated at 80ºC in hot air oven for 24 h. The material was placed in an airtight container for further use.
Sulphuric acid treated sugarcane bagasse:
One part of dried sugarcane bagasse was mixed with one part of concentrated sulphuric acid and heated in a muffle furnace for 24 h at 150ºC. The heated material was washed with distilled water and soaked in 1% sodium bicarbonate solution overnight to remove residual acid. The material was dried in an oven at 105ºC for 24 h and sieved in the size range of 1.456 mm mesh and used for the further study. All adsorbents were dried at 110ºC overnight before the adsorption experiments. 
A stock solution of chlorine was prepared by diluting 3mg in 1 litre distilled water and used for adsorption studies. Residual chlorine was analysed using standard materials.
EXPERIMENTAL METHODS AND MEASUREMENTS:
In each adsorption experiment, 100 ml of chlorine solution of known concentration and pH was added to 0.4 g of adsorbents (untreated, formaldehyde treated and sulphuric acid treated sugarcane bagasse) in a 250 ml conical flask. This was done at a room temperature (29±1ºC). The mixtures were stirred on a rotary orbital shaker at 160 rpm.
Kinetics of adsorption was determined by analyzing adsorptive uptake of the chlorine from aqueous solution. Therefore, samples were withdrawn from the shaker every 10 minutes and the adsorbent was separated from the solution by centrifugation at 4500 rpm for 5 min. In order to determine the residual chlorine concentration, the absorbance value of the supernatant solution was measured before and after the treatment, at 530 nm with UV spectrophotometer. Two main system variables, initial chlorine concentration in the test solution and adsorbent dosage, were varied to investigate their effects on the adsorption kinetics. Blank runs, with only the adsorbents in 100 ml of distilled water, were conducted simultaneously at similar conditions to account for any colour leached by the adsorbents and adsorbed by glass containers. Samples were diluted with distilled water if absorbance values exceeded 0.900. Each experiment result was an average of three independent adsorption tests.
In order to study the adsorbent dosage required for removal of residual chlorine. The experiment result of chlorine adsorption on baggase with various dosage shows that the increase in the adsorption can be attributed to the increase in adsorbent surface area and availability of more adsorption sites.
In order to study the effect of pH required for removal of chlorine. The initial pH of the mixtures were varied between 2-9, this was controlled by the addition of dilute HCl or NaOH solutions for the optimum adsorbent dosage. With 0.4g/100 ml adsorbent mass at room temperature of 29±1ºC for 3 h equilibrium time.
A known volume of 100 ml of adsorbate was taken in a 250 ml conical flask at optimum adsorbent dosage and pH. At the aliquot are collected and analysed for chlorine content the total reaction time set for 3 hrs. The effect of contact time for the adsorption of chlorine was studies at equilibrium concentration. The time was varied from initial to 180 minutes.
RESULTS AND DISCUSSIONS:
EFFECT OF ADSORBENT DOSAGE:
The study was carried out in 100 ml was taken in 5 different conical flask and adsorbent dosage of 0.1 to 0.9 g of bagasse were added. The adsorption increased from 42.2 to 92% as the sulphuric acid treated dose was increased from 0.2 g to 0.9 g/100 ml at equilibrium time (120 min). For formaldehyde treated sugarcane bagasse, adsorption increased from 9.3 to 63.3% as the adsorbent dose was increased from 0.1 to 0.9 g/100 ml. Maximum chlorine removal was achieved within 90-120 min after which chlorine concentration in the test solution was almost constant.
Fig 1.Effect of adsorbent dose on the residual chlorine adsorption
EFFECT OF pH:
In our studies, maximum chlorine removal was recorded at pH 7 for all three categories and presented in Fig 2. Between pH range of 2-6, the percentage of chlorine removal was nearly equal, ~ 30% for untreated bagasse. Significant increase in chlorine removal efficiency for formaldehyde treated sugarcane bagasse was observed between pH ranges of 2-6. Although dye adsorption efficiency for sulphuric acid treated sugarcane bagasse is higher than the untreated and formaldehyde treated sugarcane bagasse, it was not significantly affected by pH. This may be due to hydrolysis of the adsorbent in water, which creates positively charged sites. Overall, the chlorine adsorption by sulphuric acid treated was 79-90% in the studied pH 7 range followed by formaldehyde treated (52-85%) and untreated sugarcane bagasse (15-33%).
Fig 2.Effect of pH on the residual chlorine adsorption
EFFECT OF TIME:
The adsorption capacity was high compared to the various time intervals with increased contact time and resulted were plotted (Fig 3). 90% removals of residual chlorine were observed in 1hr contact time of adsorption by sulphuric acid treated bagasse. Up to 3 hours the removal efficiency is 92% not beyond that. For formaldehyde treated bagasse 68% removal of residual chlorine was observed and for untreated it is 34.5% removal was observed.
Fig 3.Effect of time on the residual chlorine adsorption
Isotherm studies, kinetics and diffusion studies were performed for the removal of residual chlorine by sulphuric acid treated bagasse only.
PSEUDO FIRST ORDER KINETIC MODEL:
The sorption kinetics can be described by a pseudo 1st order equation as suggested by lagergreen. 
Upon integration with limits t=0, t=to and q=0 q=qo the equation is linearised to
k1 = rate constant (per min).
t = time (min).
qe,= amount of residual chlorine at equilibrium. (mg/L).
qt= amount of residual chlorine at time t. (mg/L).
The equilibrium was almost achieved after 3hrs. The regression value was higher for the plot of the pseudo 1st order curve and it’s shown in Fig.4 It appears appreciable to use lagergrean model for the kinetics of chlorine adsorption of treated bagasse
Fig 4.Pseudo first order reaction
The Freundlich isotherm is an empirical equation assuming that the adsorption process becomes a heterogeneous surfaces and adsorption capacity is related to the concentration of chlorine at equilibrium.
= biosorption capacity (mg/L)
n = biosorption intensity.
The values of Freundlich constant ‘n’ is a measure of the deviation from linearity of the biosorption. They were greater than unity, indicating that residual chlorine is favourably adsorbed by bagasse at all temperature studies.
Fig 5. Freundlich isotherm
The adsorption of residual chlorine was dependent on the adsorbent dose. 0.4g/100ml of chlorine solution was the effective dosage of sulphuric acid treated bagasse and 90% removals of residual chlorine were adsorbed in 1hr contact time on neutral pH. Pseudo first order shows that the R2 value is 0.921 and residual chlorine adsorption depends on the concentration of the adsorbent used. In Freundlich isotherm R² value is 0.995 and the ‘n’ is less than 1 as shown in Fig 5, indicating that residual chlorine is not always adsorbed by bagasse at all temperature studies. In W-M model, the graph linear line shows that intraparticle diffusion is involved on the biosorption process Since the line does not passes through the origin it indicates the intraparticle diffusion is not only the rate limiting but also other kinetic models may control the rate of biosorption, all of which may be operating simultaneously.
Sugarcane bagasse is a common biomass waste material and is easily available at small price. The removal of residual chlorine in water using chemical treatment of sugarcane bagasse with sulphuric acid and formaldehyde has been investigated under different experimental conditions in batch mode. Sulphuric acid treated sugarcane baggase showed a better performance compared to formaldehyde treated sugarcane baggase. This study proved that sugarcane bagasse is an attractive option for residual chlorine management.
1. Liew Abdullah AG, Mohd Salleh MA, Siti Mazlina MK, Megat Mohd Noor MJ and Osman MR. Azo dye removal by adsorption using waste biomass: sugarcane bagasse. International Journal of Engineering and Technology. 2(1); 2005: 8-13.
2. Jain BJ, Gupta AK, Bhatnagar VK, Suhas A. The performance of activated carbon from sugarcane bagasse, babassu, coconut shells in removing residual chlorine. Brazilian Journal of Chemical Engineering, 2003.
3. Utilization of industrial waste products as adsorbents for the removal of dyes. Journal of Hazardous Materials B101: 31–42.
4. Bernardo EC, Egashira R and Kawasaki J. Decolorization of molasses wastewater using activated carbon prepared from cane bagasse. Carbon, 35; 1997: 1217.
5. Brunauer S, Emmett PH and Teller E. Adsorption of gases in multimolecular layers. Journal of American Chemical Society, 60; 1938: 309.
6. El-Hendawy A, Samra SE and Girgis BS. Adsorption characteristic of activated carbon obtained corncobs. Colloids and Surfaces, 180; 2001: 209.
7. Perry RH and Green DW. Chemical Engineer’s Handbook, 7th ed., McGraw-Hill Book Company, New York, 1997.
Received on 28.08.2013 Accepted on 01.09.2013
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