Available online at www.sciencedirect.com Journal of Hazardous Materials 156 (2008) 596���603 Column performance of granular activated carbon packed bed for Pb(II) removal Chandra P. Dwivedi a, J.N. Sahu a, C.R. Mohanty b, B. Raj Mohan a, B.C. Meikap a,��� a Department of Chemical Engineering, Indian Institute of Technology (IIT), P.O. Kharagpur Technology, Kharagpur 721302, West Bengal, India b Orissa State Pollution Control Board, Bubaneswar, Orissa, India Received 14 October 2007 received in revised form 16 December 2007 accepted 17 December 2007 Available online 4 January 2008 Abstract The excessive release of lead from lead acid batteries, smelting plant into the environment is a major concern worldwide. Adsorption process is among the most effective techniques for lead removal from wastewater and activated carbon has been widely used as an adsorbent. In this paper an attempt has been made to investigate the adsorption behaviour of Pb(II) from aqueous systems onto granular activated carbon using the batch mode and continuous mode in a packed bed column with more successive service and regeneration. The experiments were performed at constant temperature and dimensions of column and packed bed of granular activated carbon with variation of flows through the bed and concentrations of lead solutions. Breakthrough points were found out for the adsorption of lead on the adsorbent using continuous-flow column operation by varying different operating parameters like hydraulic loading rate from 4 to 16 m3/h m2 and feed concentrates from 20 to 60 mg/l. Granular activated carbon column regeneration using 0.5 M concentration of HNO3 has been investigated. Results indicate encouraging performance towards removal of Pb(II). �� 2007 Elsevier B.V. All rights reserved. Keywords: Pb(II) removal Granular activated carbon Adsorption Wastewater treatment Packed bed column 1. Introduction Lead is one of the potentially toxic heavy metals when adsorbed into the body [1]. The pollution of water resources due to indiscriminate disposal of lead metals has been causing worldwide concern for the last few decades. The presence of lead in drinking water even at low concentration may cause diseases such as anemia, encephalopathy, hepatitis and nephritic syn- drome [2]. Lead is non-biodegradability and can accumulate in living tissues, thus becoming concentrated throughout the food chain and can be readily absorbed into the human body [3]. Even a very small amount can cause severe physiological or neuro- logical damage to the human body. It is in general metabolic poison and enzyme inhibitor, also cause mental retardation and semipermanent brain damage in young children. ��� Corresponding author. Tel.: +91 3222 283958/2283959 fax: +91 3222 282250. E-mail addresses: bcmeikap@che.iitkgp.ernet.in, bcmeikap@iitkgp.ac.in (B.C. Meikap). Lead, an element which has been used by man for years, can be regarded as a longstanding environmental contaminant. It released into the environment in a number of ways, like as process industries engaged in lead acid batteries, pulp and paper, petrochemicals, refineries, printing, pigments, photo- graphic materials and explosive manufacturing, ceramic, glass, paint, oil, metal, phosphate fertilizer, electronic, wood produc- tion and also combustion of fossil fuel, forest fires, mining activity, automobile emissions, sewage wastewater, sea spray are just few examples [4���6]. The industrial wastewaters are considered to be the main source of lead impurities. The presence of high levels of lead in the environment may cause long-term health risks to humans and ecosystems. It is therefore mandatory that their levels in drinking water, waste water and water used for agricultural and recreational purposesmustbereducedtowithinthemaximumallowablecon- centrations recommended by national and international health authorities such as world health organisation. Its removal from wastewater prior to discharge into environment is, therefore, necessary. Current EPA drinking water standard for lead are 0.05 mg/l, but a level of 0.02 mg/l has been proposed and is under 0304-3894/$ ��� see front matter �� 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2007.12.097

C.P. Dwivedi et al. / Journal of Hazardous Materials 156 (2008) 596���603 597 Nomenclature A0 original adsorptive capacity of the virgin adsor- bent (mg/g) Ar adsorptive capacity of the regenerated column (mg/g) b Langmuir constant (l/g) Ce equilibrium lead concentration (mg/l) Ci initial lead concentration (mg/l) k measure of adsorbent capacity (l/g) KL Langmuir constant (mg/g) M metal adsorbed on adsorbent bed (mg) m mass of adsorbent in column (g) 1/n sorption intensity, dimensionless Q flow rate of the influent ((m3/(h m2)) Q0.5 adsorption column capacity (mg/g) qe amount of lead adsorbed at equilibrium (mg/g) T temperature (���C) t time (h) tb breakthrough time (h) V volume of the solution (l) W weight of adsorbent (g) review [7]. According to Indian Standard Institution, the toler- ance limit for discharge of lead into drinking water is 0.05 mg/l and in land surface waters is 0.1 mg/l [8]. Increasingly strin- gent legislation on the purity of drinking water has created a growing interest in the development of conventional treatment processes. Various chemical and physico-chemical methods for the treatment of wastewaters containing lead wastes are known, such as chemical precipitation, electrochemical reduction, ion exchange, biosorption and adsorption [9���13]. The choice of treatment depends on effluent characteristics such as concentra- tion of lead, pH, temperature, flow volume, biological oxygen demand, the economics involved and the social factor like stan- dardsetbygovernmentagencies.Variousmethodsofwastewater treatment were examined and adsorption emerged as one of the most promising technique [14] as it is generally preferred for the removal of lead due to its high efficiency, easy handling, availability of different adsorbents and cost effectiveness. The use of activated carbon (AC) is still very popular and different grades are available, but are quite expensive and the regeneration of the carbon is not always possible. Activated carbon has been chosen as an adsorptive media for removal of lead, by many researchers [15���18]. Activated carbon is a black solid substance resembling granular or powder charcoal and are carbonaceous material that have highly developed poros- ity, internal surface area of more than 400 m2/g and relatively high mechanical strength. They are widely used as adsorbents in wastewater and gas treatments as well as in catalysis. The increasing usage and competitiveness of activated carbon prices, has prompted, a considerable research work has been done in the search of inexpensive adsorbents especially developed from various agricultural waste materials, i.e. the usage of agricul- tural by-products such as fruit stones [19], coconut shell [20,21], bagasse [22,23], nutshells [24,25] as raw materials to prepare AC. These solid wastes are not only cheap and easily avail- able but are considered as wastes that contribute to disposal problems. In this study coconut shell has been chosen as an adsorptive media. As it is suitable for preparing microporous activated carbon due to its excellent natural structure and low ash content. In practice, activated carbon is found in two general forms: granular activated carbon (GAC) and powdered activated car- bon (PAC). GAC is composed of particles with sizes greater than 0.1 mm, about the size of coarse sand [26]. PAC, of course, is composed of particles smaller than that value. Exact specifi- cations vary, but GAC is generally said to have a larger internal surface area and smaller internal pores, while PAC is thought to have larger pores and a smaller internal surface area. Because PAC has a faster adsorption rate, it was often used in the past, but disposal and handling concerns have made granular activated carbon (GAC) a more popular alternative for most applications. GAC is used in the filtration process in water treatment, and then regenerated when it becomes less effective due to saturation with chemicals. GAC is also usually much easier to handle and trans- port than PAC. The special advantages of packed bed are that it has high residence time to and excellent heat and mass transfer characteristics. GAC is bigger is size and it has no elutriation from the bed and loss is minimum than PAC. In the present batch mode and fixed-bed column adsorp- tion study, GAC coconut shell origin is chosen as an adsorptive media to understand the adsorption behaviour of lead ions from aqueous systems of synthetic waste water of lead contaminated water.Althoughbatchlaboratoryadsorptionstudiesprovideuse- ful information on the application of adsorption to the removal of specific waste constituents, continuous column studies provide the most practical application of this process in wastewater treat- ment. Batch reactors were easy to use in the laboratory study, butlessconvenientforindustrialapplications.Ontheotherhand, fixed-bed columns were widely used in various chemical indus- tries because of their simple operation. Fixed-bed adsorption has been applied to remove organic contaminants for many years with encouraging results. The reason for this is that the high adsorption capacities in equilibrium with the influent concen- tration rather than the effluent concentration can be achieved. In static mode adsorption studies, the same solution remains in contact with a given quantity of the adsorbent. The adsorp- tion process continues, however, till equilibrium between the solute concentration in solution, and the solute adsorbed per unit weight of the adsorbent is reached. This equilibrium established is static in nature, as it does not change further with time. In dynamic column adsorption, solution continuously enters and leaves the column, so that the complete equilibrium is never established at any stage between the solute in solution and the amount adsorbed. Equilibrium has to be continuously estab- lished, as each time, it meets the fresh concentrations, and hence, equilibrium in column mode is termed as dynamic equilibrium. Additional information on the efficiency of the treated adsor- bent in the column mode has been gathered in order to ascertain the practical applicability of the adsorbent for real industrial wastewaters.