Integrated Filtration System for Iron-Free Water in Small Public Buildings

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1 SUST Journal of Science and Technology, Vol. 19, No. 5, 2012; P:54-59 Integrated Filtration System for Iron-Free Water in Small Public Buildings (Submitted: June 10, 2012; Accepted for Publication: November 29, 2012) M. A. Islam, M. S. A. Amin*, M. S. Rahman, A. I. H. Laskar, M. A. Khan, A. Khan Center for Environmental Process Engineering, Dept. of Chemical Engineering and Polymer Science, Shahjalal University of Science and Technology, Sylhet, Bangladesh * Abstract An integrated filtration system has been developed for drinking and washing purposes. This is a bench scale unit made of locally available low-cost materials. The unit can remove iron and bacteria, and produce household water maintaining the accepted standard. The operation and maintenance of the plant is simple and could be done by unskilled labor. Based on the experimental results, techno-economical evaluation has also been done for a large-scale plant. The academic building B of SUST is selected as a model object for water supply and the technical target is to reduce iron to standard level. Cost calculation is based on the analysis of its several components such as construction materials with their respective quantities, mechanical equipment, energy consumption, chemical consumption, and operational and maintenance expenses. The result can be extended for quick financial evaluation of the similar systems as well as for the general decision making plan. Keywords: Filtration, Iron removal, Drinking water, Washing water, Disinfection 1. Introduction Iron occurs naturally in water, especially in groundwater. It does not cause adverse health effects. In fact, it is to some extend essential to the human diet. However, water containing excessive amounts of iron can stain clothes, discolor plumbing fixtures, and sometimes add a rusty taste and look to the water. Iron in water also promotes the growth of iron bacteria, a group of organisms that obtain its energy for growth from the chemical reaction that occurs when iron mixes with dissolved oxygen. These bacteria form thick slime growths on the walls of the piping system and on well-screens. Such shines are rust-colored from the iron and black-colored from the manganese. Variations in flow can cause these slime growths to come loose, resulting in dirty water in the system [1]. In Bangladesh, the population depends mainly on the underground water (collected mainly by shallow pumps) for drinking and household purposes. The water from most of the regions, including Sylhet region exceeds the maximum contaminant level with respect to iron [2]. The concentration of iron in underground water varies in the range of mg/l around the Sylhet city and is higher than 1 mg/l in SUST campus [3]. Different methods are proposed in the literature for the removal of iron from ground water, and they include aeration, filtration, ion-exchange, adsorption, ozonation, chlorination, etc. [4-7]. Few commercial firms are also proposing some solutions [8-11]. These methods and solutions seem not appealing to the population due to financial, spatial and technical regions. As a consequence, people are compelled to use high iron-contaminated water for household purposes and to drink water treated with family-size filtration unit. The objective of the present work is to develop: 1) a simple iron removal technology and to test it with bench scale continuous unit, and based on the experimental results 2) to design large-scale facilities with possibilities of servicing and maintenance with unskilled labor and to make techno-economical evaluation of the plant. For the purpose, an integrated filtration system is designed, which is unique in perspective of SUST as well as Sylhet region. It is supposed to serve the employees and students of the Building B, SUST and is anticipated that it is capable of filtering 2500 liters of water per day (750 liters/day for drinking purpose and 1750 liters/day for washing) [12].

Integrated Filtration System for Iron-Free Water in Small Public Buildings 55 2.

2 Integrated Filtration System for Iron-Free Water in Small Public Buildings Methodology The type of treatment largely depends on the quality of the raw water, the purposes for which the treated water is to serve, the availability of financial resources and the philosophy of the water company. Iron is easily oxidized by atmospheric oxygen. Aeration supplies the dissolved oxygen necessary to convert the iron from their ferrous forms to their insoluble oxidized ferric forms. It takes 0.14 ppm of dissolved oxygen to oxidize 1 ppm of iron [1]. The precipitated iron can be separated from water primarily by sedimentation and then filtered by coarse filters. This water can be used for washing purposes. For drinking purposes, however, the washing quality water must undergo fine filtration, disinfection or membrane filtration. In view of this, a bench scale unit was designed to test the treatment technology. The photograph of the unit, which is tested in the Laboratory of CEPE is shown in Figure 1. This tap water is practically aerated one containing large amount of colloidal iron particles. Through a regulated valve, this water is fed to the pre-filter packed with stone chips from the bottom. The water exits from this pre-filter almost free of iron particles and enters into secondary storage tank. This water can be used for washing purposes without further treatment. Portion of the water exists the secondary storage tank and enters into the disinfection tank through a control valve. In the disinfection tank the water is filtered through fine filter, and the filtrate meets the drinking water quality. Figure 1: Bench scale set up of the integrated filtration system 3. Results from the bench scale unit All the experiments were conducted in the Laboratory of the CEPE at the Department of Chemical Engineering and Polymer Science, Academic Building B with the tap water as raw water. The performance of the bench scale Integrated Filtration System was continuously monitored in terms of the quality and production rate of both the drinking and washing water. The aesthetic view of the feed water (after exposure to air for more than half an hour), the water for house hold purposes (undergone coarse filtration only) and the drinking water (passed through fine filter/disinfection unit) is presented in Figure 2. Laboratory test of both types of water satisfy the accepted standard for drinking and washing purposes.

cleaning of the filtration unit is an important element in operation and maintenance of a water treatment plant.

3 56 M. A. Islam, M. S. A. Amin, M. S. Rahman, A. I. H. Laskar, M. A. Khan and A. Khan Figure 2: Comparison of water quality (from left to right): a) iron contaminated water exposed to air for half an hour, b) water for household purposes and c) water for drinking purposes The cleaning of the filtration unit is an important element in operation and maintenance of a water treatment plant. The system proposed in this work requires interruption of the operation of the filtration unit followed by the addition of a very cheap chemical (developed in the Laboratory of CEPE). After 15 minutes, the filter is washed with water from the top and the dirty water is collected at the bottom of the filtration unit. Figure 3 represents the dirt collected from the cleaning operation. A large amount of sludge (with high iron content) is recovered from the unit. The sludge is rich in almost pure iron, which can be treated at high temperature and used as adsorbent for different purposes such as treatment of arsenic containing water. Figure 3: Regenerated water from the filtration unit with sludge precipitated at the bottom of the beaker 4. Description of the Large Scale Plant The bench scale unit is practically a prototype of a large-scale plant, which will be scaled up based on the results from the operation of the prototype tested in the Laboratory of CEPE. Thus, the large-scale plant has been designed, which is also an integrated system, in which a high pressure head tank is needed from which water flows under gravity to keep the power consumption to minimum. The already built water reservoir at the top of the

4 Integrated Filtration System for Iron-Free Water in Small Public Buildings 57 building-roof of the Academic Building B may ensure the high pressure head. The reservoir is exposed to natural air stream for the oxidation of Fe 2+ to Fe 3+ ions. The technological sketch of the plant is presented in Figure 4. Error! Reservoir Valve: 1 A B Valve: 2 D Reservoir Valve: liter Valve: 4 C 800 liter Drinking Water Figure 4: Schematic diagram of the proposed integrated filtration plant A. Sedimentation Tank The tank is fed by the water coming from the water reservoir through a control valve (controlling flow rate) and a nozzle (for aeration of the incoming water) by gravitational force. Stokes eq uation is used to determine the settling velocity assuming that the particle diameter is 0.05 mm and the average specific gravity of the particle present in the water is 2.65 gm/cm 3 [13]. Under these conditions, the settling velocity is found to be 13.2 cm/min. For the sedimentation purpose, the settling velocity should be greater than over flow velocity. In engineering practice, the overflow velocity does not exceed 80% of the settling velocity [14] and thus the overflow is assumed to be 5 cm/min/m 2. The detention time is taken to be 20 minutes as the particles with a diameter of 75 m settle in 5 to 10 minutes [15]. After the sequential calculations, the design parameters of the tank are chosen as follows: length 1m, height 0.4 m (including sludge zone) and width 0.25m. B. Filtration Tank Sedimentation removes a large portion of suspended particles; nonetheless, the resultant water will not be pure and may contain fine particles and impurities. To produce potable water, the water is filtered through the beds of fine granular materials (filters). In this system, water flows from the bottom to the top of the tank, with the expectation that the ferric hydroxide precipitates, co-joining with the iron particles on its way of deposition will form floating coagulation and will accelerate the rate of deposition. It is also beneficial in a way that the iron precipitates can be removed easily from the tank using the discharge valve. When the water leaves the filtration tank, it is almost iron-free and can be used for washing purposes. As the system is designed to produce water at a rate of as low as 104 L/h, a slow filtration system is used as the rate of this type of filtration is L/m 2 h [16]. This filtration effect is attributed to mechanical straining, flocculation and sedimentation in the voids of filter and biological metabolism. The filtration rate varies with the type and size of particles. Assuming that the filtration rate is 200 L/m 2 h and the bed height is 0.5 m, the required surface area for the demand of 2500 L/day is 0.52 m 2. The filter materials are stone chips, which are stratified as follows: mm at the bottom, mm in the middle and 3-5 mm at the top. As the water flows from bottom to the top, a space of 0.3 m is kept both at the bottom and top of the filter bed of the filtration tank and thus the height of the unit is 1.1 m. The service life of filter bed depends on the flow rate, iron content of the raw water, frequency of regeneration and so on, and will be determined in laboratory scale experiments.

5 58 M. A. Islam, M. S. A. Amin, M. S. Rahman, A. I. H. Laskar, M. A. Khan and A. Khan C. Disinfection/fine filtration tank The disinfection tank comprises a disinfection unit and a storage tank. The water inflowing this tank is almost free from iron as most of the iron was separated as colloidal particles in the filtration tank. A traditional disinfection unit consists of hemispheric ceramic filters, which are available in local markets. The disinfection unit has a dimension of 0.68 m 0.68 m 0.3 m, where 72 hemispheric ceramic filter units (diameter 4.5 cm and height 6 cm) are placed onto a fixed surface in two independent levels. The filter balls and the disinfection unit can be mantled and dismantled independently, which permits easy replacement and servicing. This tank should not be exposed to direct sunlight as it tends to form algae and pathogen of cholera. After passing through the disinfection unit the water is totally pure and safe to drink. Occasionally, it can be washed with bleaching agent. D. Storage Tank The water passing through the filtration tank is almost free from iron and can be utilized for washing and household purposes. Based on the designed total consumption of 2500 L/day, 1750 L/day will be used for washing and household purposes and this amount will go directly to the storage tank from the filtration tank. Operation Schedule The operation of the system is simple and is controlled manually. The controlling system consists of four control valves. The operation of the valves is time centric, and the cycle of the operation is in conformity with the working hours of SUST. Valve 1 controls the flow of the water to the sedimentation tank from the reservoir. Valve 2 and valve 3 controls the flows to the storage tank and disinfection unit respectively. At 9:30 am, valve 2 is closed, and valve 3 remains open until 5.00 PM, which delivers water to the disinfection unit. At 5:00 pm, valve 3 closes and valve 2 remains open until 9:30 am, next morning, and this is the time for the water to flow from the filtration tank to the storage tank directly. At 9:30 am, valve 2 closes and valve 3 opens again. The water of the storage tank is pumped to the supply system by a 1.5 HP pump. An additional Valve 4 controls the water flow from the storage tank to a distribution unit, in the event, the water level in the disinfection unit is lowered and needs compensation for steady operation. 5. Techno-economic evaluation The techno-economic evaluation is performed as per the procedure developed by Khan [17]. The results are presented in Table 1. Table 1: Cost analysis of the Integrated Filtration System Cost of the equipments Scrap value of the equipments Amortization calculation and the production Individual equipment Price (in BD Taka) Individual equipment Price (in BD Taka) cost Stands 2500 Stands 1000 Average life-time of the plant 5 years Disinfection 2500 Secondary 100 Life-time of filter ball 1 year chamber storage Secondary 400 Final storage 100 Cost impact of the plant per 2600 taka storage annum Final storage 400 Total production of drinking L/year water (excluding weekly and fixed holidays, approximate 220 days in a year) Filter media 1800 Cost impact on every unit Tk/L drinking water Primary filter 2000 Others 2000 Total Total 1200

6 Integrated Filtration System for Iron-Free Water in Small Public Buildings Conclusions 1. An integrated filtration system is developed for the production of iron free water for drinking as well as household purposes. 2. The system is cheap and sustainable, and can be maintained and operated by unskilled labor. 3. The capital and maintenance cost of the plant is significantly low and the poor population of the country could afford it. References [1] A. G. Tekerlekopoulou, D. V. Vayenas, Ammonia, iron and manganese removal from potable water using trickling filters. Desalination, 210(1 3) (2007), [2] M. D. Hossain, M. K. Huda, Study of the iron content in ground water of Bangladesh. J. Civil Engg, IEB, CE 25 (2), (1997) [3] Unpublished Data, CEPE Laboratory, SUST [4] D. van-halem, S. Olivero, W. W. J. M. de Vet, J. Q. J. C. Verberk, G. L. Amy, J. C. van Dijk, Subsurface iron and arsenic removal for shallow tube well drinking water supply in rural Bangladesh. Water Research, 44(19), (2010) [5] B. Das, P. Hazarika, G. Saikia, H. Kalita, D. C. Goswami, H.B. Das, S.N. Dube, R.K. Dutta, Removal of iron from groundwater by ash: A systematic study of a traditional method. Journal of Hazardous Materials, 141(3), (2007) [6] S. Chaturvedi, P. N. Dave, Removal of iron for safe drinking water Review Article. Desalination, 303, (2012) 1-5. [7] D. van-halem, S. Olivero, W. W. J. M. de-vet, J. Q. J. C. Verberk, G. L. Amy, J. C. van Dijk, Subsurface iron and arsenic removal for shallow tube well drinking water supply in rural Bangladesh. Water Research, 44(19), (2010) [8] G. D. Michalakos, J. M. Nieva, D. V. Vayenas, G. Lyberatos, Removal of iron from potable water using a trickling filter. Water Research, 31(5), 1(997) [9] Water Treatment (Accessed date April 30, 2012). [10] Water Treatment Solutions, Lenntech (Accessed date April 30, 2012). [11] P. Mondal, C. Balomajumder, B. Mohanty, A laboratory study for the treatment of arsenic, iron, and manganese bearing ground water using Fe 3+ impregnated activated carbon: Effects of shaking time, ph and temperature Original Research Article. Journal of Hazardous Materials, 144 (1 2), (2007), [12] S. K. Garg, Water Supply Engineering, 12 th Edition, Khanna Publishers, New Delhi, [13] Degremont (Ed.), Water Treatment Handbook, Vol. 1 and 2, Sixth Edition, Lavoisier, France, [14] T. Gass, Removing iron from a water supply. Water Well Journal, 31(10), (1977) [15] Metcalf & Eddy, Wastewater Engineering, Third edition, Tata McGraw-Hill, New Delhi, [16] A. Colter, R. L. Mahler, Iron in drinking water, A Pacific North West Extension Publication, PNW 589, [17] M. R Khan, Techno-economic evaluation of Chromium recovery pilot plant installed at Kasur Tanneries Complex, Pakistan. The Pakistan Development Review, 46 (4), (2007)

Mechanism of filtration : 1- Straining action: strain particles that has a big size on the sand surface.

Mechanism of filtration : 1- Straining action: strain particles that has a big size on the sand surface. Filtration Purpose of filtration : Removal of remaining 4% of suspended solids. Removal of odor, color and taste. Removal of iron and manganese. Removal of 90 % of bacteria. Mechanism of filtration : 1-