Schmutzdecke- a Filtration Layer of Slow Sand Filter

Int.J.Curr.Microbiol.App.Sci (2018) 7(7): 637-645

International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 7 Number 07 (2018) Journal homepage: http://www.ijcmas.com

Review Article https://doi.org/10.20546/ijcmas.2018.707.077

Schmutzdecke- A Filtration Layer of Slow Sand Filter

Prem Ranjan1* and Manjeet Prem2

1Department of Agricultural Engineering, North Eastern Regional Institute of Science and Technology, Nirjuli, Arunachal Pradesh-791109, India 2Department of Farm Power and Machinery Engineering, College of Agricultural Engineering and Technology, AAU, Godhra- 389001, India *Corresponding author

ABSTRACT

K e yw or ds Slow sand filtration has been an effective means of treating water for the control of

Filtration , Sand bed, microbiological contaminants. Schmutzdecke is the layer of the microbial community that Schmutz decke, is responsible for treating the water through the sand bed. As water passes through this Pseudomonas biological layer, foreign particles are trapped and essentially eaten by bacteria forms on stutzeri this layer. Development of Schmutzdecke layer depends on available microbes in raw water, food supply, oxygen supply, residence time, and wetting of sand bed. Generally, 13 Article Info types of bacterial community are found in the Schmutzdecke layer, in which Pseudomonas

Accepted: stutzeri bacteria are dominant. Many of the researchers observed that water purification is 90 to 99% after the development of Schmutzdecke or maturity of the filter bed. Head loss 06 June 2018 of filter is also increased with the volume of water filter, but it can be easily recovered by Available Online: 10 July 2018 cleaning of the upper layer of the filter bed.

Introduction providing some degradation of soluble organics in the raw water, which is useful for Schmutzdecke is a complex biological layer reducing tastes, odours and colour. It is formed on the surface of a slow sand filter formed in the first few weeks of operation and which means “dirty layer” in German. The consists of organic matter including bacteria, Schmutzdecke is the layer that provides the fungi, protozoa, rotifer and various aquatic effective purification of potable water insect larvae. It consists of alluvial mud, treatment. It is a gelatinous layer or biofilm organic matter, bacteria, diatoms, called the hypogeal layer or Schmutzdecke. zooplankton, thread-like algae formed by the This sticky film, which is reddish brown in excretion of microorganisms. It is the layer of colour, consists of decomposing organic aquatic life that is responsible for purifying matter, iron, manganese and silica and the water. As water passes through this therefore acts as a fine filter media that biological layer, foreign particles are trapped contributes to the removal of turbid particles and essentially eaten by bacteria forms on this in the raw water. It also doubles up as an layer. As the water slowly passes down initial zone of biological activity and through the layers of sand, impurities are left

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Int.J.Curr.Microbiol.App.Sci (2018) 7(7): 637-645 behind, leaving the water between 90% and filtration, the depth of the Schmutzdecke can 99% free from bacteria (Elliott et al., 2008). be said to connect to the penetration zone of solid particles, that is, the top 0.5•2 cm of a Schmutzdecke layer formed due to the filter bed (Ranjan 2017). At this depth, the establishment of a microbial community on Schmutzdecke merges with the deeper the top layers of the fine sand particles. These biological layer, and filter raw water flows microbes usually came from the raw water and into this zone after passing through the establish a community within a matter of a Schmutzdecke layer. This deeper zone is not few days. The sand bed and slow filtration rate largely a mechanical filtration zone but help to the establishment of this microbial somewhat a continuation of the area of community. The majority of the microbial biological action. community are predatory bacteria that feed on water-borne microbes passing through the Filtration processes within the filter. The microbial population is limited by schmutzdecke and the biological zone the amount of organic material available/supplied by the inflowing raw water; As per Huisman and Wood (1974),there are the growth is therefore escorted by an four dominant processes which contribute to equivalent dying off. It turns liberates organic the purification of the raw water: matter, which becomes available to bacteria at lower depths. In this way, the whole of the Hostile Environment: Conditions found within degradable organic matter present in the raw a slow sand filter are generally unsuitable for water is gradually broken down and converted the multiplication of intestinal bacteria. into water, CO2 and relatively inoffensive Normally used to a human body temperature inorganic salts such as sulphates, nitrates, and of 37°C, they do not thrive at temperatures phosphates. The bacteria oxidize part of the below 30°C. food to provide the energy they need for their metabolism, and they convert part of it into Competition for food: Food is required for the cell material for their growth. Thus, dead microbial community for metabolism. organic matters are converted into living Oxidization processes during metabolism matter. The dissimilation of products is carried consume organic matter in the raw water, away by the water, to be used again at greater including dead pathogens. The filter bed does depth by another bacterium. not usually contain adequate organic matter of animal origin to meet their nutritional needs. The bacterial activity is most pronounced in Within the upper layers, there is competition the upper layer of the filter-bed and gradually for food from other microbes while at lower decreases with depth as food becomes scarcer. depths suitable food becomes even scarcer so When a filter is cleaned by scraping off the that they starve, particularly at higher top few millimetres layer, the bacteria in the temperatures when their metabolic rate layer are also removed, and a further ripening increases. period is necessary to bring the population of microbes up to the required depth. The Predation: Many types of predatory organisms bacterial activity below a depth of 30-40 cm it thrive in the upper part of the filter bed and is very small, but biochemical reactions take feed on other cells. place converting such microbiological degradation products as amino acids into Excretion of poisons or toxins: It is reported ammonia and nitrates. The Schmutzdecke have that the microorganisms in a slow sand filter a double function, which includes mechanical produce various substances that act as 638

Int.J.Curr.Microbiol.App.Sci (2018) 7(7): 637-645 chemical or biological poisons to intestinal acidicelersmzd-5, B. megateriumsmzd-6, B. bacteria. altitudinissmzd-7, B. pumilussmzd-9, B. subtilissmzd-10, B. subtilissmzd-11, B. The combined effects of this selectively licheniformissmzd-12, dan B. cereus smzd-13. hostile environment result in the death and inactivation of many pathogens. The overall Development of Schmutzdecke layer result is a substantial reduction in the number of indicator bacteria such as E. coli, and an For the development of the Schmutzdecke even greater proportional decrease in layer on filter bed, the presence of adequate pathogens themselves. food, oxygen, and suitable temperatures is required. The bacterial population is limited Biological populations found in by the amount of organic material supplied by Schmutzdecke layer the inflowing raw water.

Buzunis (1995) found that the schmutzdecke Depth of Schmutzdeckelayer layer is made up of a variety of microorganisms. These include algae, Slow sand filters show that the majority of bacteria, protozoa and small life cells. The biological processes occur in the top layer of types of microorganisms and the relative the sand bed. They also cleared that the number of each species are specifically bacteriological purification occurs mostly in adapted to the characteristics of the raw water the top 40 cm of the sand bed below the source and the environment of the filter. schmutzdecke. Biological activity occurs Different types of bacteria are normally found within this active filtration bed. Below a depth at various depths below the filter surface. of 30•40 cm, bacterial activity is small, but Lazarova and Manem (1995) reported that the biochemical reactions take place converting many research identified the bacterial in organic materials such as amino acids into schmutzdecke by insulated the biofilm from ammonia, nitrites, and nitrates. These amino schmutzdecke using scanning electron acids are liberated from the bacterial life cycle microscopy (SEM). This research found in the upper filter layer (Huisman and Wood, Pseudomonas stutzeri bacterial community. 1974). This result has been confirmed by test Bryan et al., (1999) reported that the data where oxidation of nitrogenous organic Pseudomonas stutzeri is Gram-negative compounds at depths lower than 40 cm was bacteria, commonly found in soil, and it also found to be incomplete (Muhammad et al, de-nitrifiers because it can change nitrate to 1996). For irregularly operated sand filters, the nitrogen gas.Also, other studies have shown depth of biological processes is also dependent that the result of DNA isolated from bacteria on how much water is standing on top of the in schmutzdecke has 98% similarity with sand during gap times. A lower water depth Sphingopyxiswit flariensis. Fitriani et al., means that more oxygen can diffuse to the (2014) found that in schmutzdecke 13 different biological layer, and as a result, the bacterial isolates based on colony morphology biologically active zone can grow deeper in observation is only 11 isolates identified. It the sand. because of the amount of DNA extracted is less than 60bp, thus the primary can’t be Keeping the sand bed wet attached when the annealing process occurs while the nucleotide amplification. The total For the survival of the microbial community of 11 isolates identified as B. subtilissmzd-1, within the biological zone, the sand bed must S. sciurismzd-2, A. baumanniismzd-3, B. be kept wet. The sand bed is kept wet by sand 639

Int.J.Curr.Microbiol.App.Sci (2018) 7(7): 637-645 filter design, where the outlet level is made allowed to maintain a long enough contact above the level of the sand. This will be time with the sand bed. About the daily always ensuring that the sand filter bed does amount of water put through the filter, they not dry out. found that microbial reductions were greater with a greater residence time within the filter, Food supply especially for water retained in the filter bed overnight. The many researchers showed this For the survival of the microbial community through taking samples of filtered water at within the biological zone, there needs to be a various stages when the filter was re•started supply of food in the raw water. Seeding the after gap time – a significant drop infiltrates filter with biologically productive raw water quality was noted after the pore volume ensures more efficient biological filtration threshold had been filtered which in their case (Palmateer et al., 1999). was 18.3 litres. This showed that water that had been standing in the filter during gap time Oxygen supply had a much better quality, and this appears to be largely due to the increased contact time for For the survival of the microbial community biological and chemical processes in the sand. within the biological zone, there needs to be a Elliott et al., (2008) confirmed that the supply of sufficient oxygen demand. Oxygen importance of residence time of water in a is used in the metabolism of biodegradable filter. During six to eight-week-long studies components and the inactivation and conducted on the sand filter, filters were fed consumption of pathogens. If it falls to zero with surface water spiked with E. coli, during filtration anaerobic decomposition echovirus type 12 and bacteriophages (MS2 occurs, with consequent production of and PRD•1). He found that the performance of hydrogen sulphide, ammonia, and other taste the filter in reducing microbial concentrations and odour producing substances together with in water fed into the filter depended largely on dissolved iron and manganese, which make the amount of time that the filter bed had to the treated water unsuitable for washing ripen, and the daily volume of water put clothes and other purposes. Huisman and through the filter each day. Also, Jenkins et Wood (1974) found that the average oxygen al., (2009 and 2011) have built on this content of the filtered water should not be understanding about the importance of allowed to fall below 3 mg/l if anaerobic residence time. They investigated the effect of conditions are to be avoided throughout the gap time on efficiency at removing viruses, whole area of the filter bed. This requirement bacteria and turbidity but also looked at other may call for aeration of the raw water to parameters that influence flow rate and increase its oxygen content or pre-treatment to therefore residence time, namely hydraulic lower its oxygen demand. Develop a way to loading and sand size. They established allow enough oxygen transfer to sustain the previous findings on the impact of gap time on biological layer has been essential in the water quality. They found that water quality design of the intermittent slow sand filter. improved with longer residence times (i.e., mean 16 hours) compared to shorter residence Contact time times (i.e., mean of 5 hours). They also tested filters with varying levels of hydraulic loading For satisfactory biochemical oxidation of above the sand surface (10, 20 and 30 cm) and organic matter by the organisms in the two sand sizes (0.17 mm and 0.52 mm). They biological layer, enough time must also be found that bacteria and virus removal was

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Int.J.Curr.Microbiol.App.Sci (2018) 7(7): 637-645 significantly better for filters with finer sand due to the low hydraulic loading and smaller and those with a lower head, independently sand size found in slow sand filters. It mostly from each other and for both short and long- develops within the top 0.5•2 cm of the sand term residence times, but that results were filter. enhanced with longer residence times. The best combination was 0.17 mm sand with 10 Bellamy et al., (1985a) reported that the filter cm head over longer residence times. ripening is a complex process that involves both biological and physical mechanisms. As Effect of temperature filtration progresses, biological growth consisting of algae, bacteria, and zooplankton The temperature of the water must not be occurs in the sand bed and gravel layer. allowed to fall too low for satisfactory During this period, the filter does not biochemical oxidation of organic matter to effectively remove bacteria. It also concluded take place by the microbes in the biological that a new sand bed will remove 85% of the layer. The efficiency of slow sand filtration coliform bacteria in the raw water. As the may also be seriously reduced due to low sand bed matures, the percent removal temperatures, due to the influence of improves to more than 99% for coliform temperature both on the speed at which bacteria. The ripening period for the bio-sand chemical reactions take place and on the rate filter is usually one to two weeks. However, of metabolism of bacteria and other for slow sand filters, the ripening process can microorganisms. At low temperatures, the be accelerated by using synthetic polymers to activity of bacteria consuming protozoa and agglomerate particles in the raw water and nematodes drops abruptly, and at the same accelerate their removal at the filter surface so time the metabolism of the intestinal bacteria as to quickly develop the filter cake. themselves slows down, increasing the chance However, the addition of chemicals to the of survival of those that are carried through sand filter would complicate the originally the bed. The factor by which the numbers of simple filtration process. E. coli or other microbes are reduced, which is normally in the range 100•1000, may fall as Hirschi and Sims, (1991) reported that the low as 2 at temperatures of 2°C or less, and maturity of the sand bed, the development of chlorination is then essential if the quality of the schmutzdecke is an important process of the delivered water is to be maintained. removing pollutants. The thickness of the schmutzdecke is an increase, thus the A schmutzdecke layer takes some time to filtration efficiency value is raised. Farooq et develop naturally. This is usually at least al., (1994) reported that the formation of around 2•3 weeks. schmutzdecke or colmation layer on the surface of the sand bed as filtration progresses Palmateer et al., (1998) measured the is considered as the important process of development of a biofilm or schmutzdecke purification mechanism of slow sand filters. and found that at 210C, it acquired 16 days for Jellisonet al., (2000) reported that while the biological film to develop to 85•90% successful in removing turbidity and cover. They noted that having a raw water pathogens from drinking water, slow sand that is more biologically productive will mean filters require ripening periods at the starting that the biofilm will develop more quickly of each filter run. The principle of this and that the filter will operate more research was that it should be possible to efficiently. Schmutzdecke layer development enhance the ripening of slow sand filters.

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Potential ripening agents were screened by the region where most biological treatment is assessing their interaction with the surface of achieved. Thus, pathogen removal and other filtration media and turbidity particles. Four impurities removal occur in this region. Ellis natural organic polymers and nine synthetic (1987) reported that that most of removal of polymers were investigated for their potential suspended solids, BOD, and coliform to enhance filter ripening of the 13 modifying organisms occurred at the surface sand layer, agents considered, none conclusively sorbed “Schmutzdecke”. When raw water passing to to the filter media, and only one, a synthetic this layer, the organic materials can be polymer, interacted with kaolin particles. A removed by conversion into living matter, and filter modified with a continuous feed of the the pathogens, protozoa, parasite, and polymer ripened successfully and produced suspended solids are removed(Schuler et al., water with turbidity below 1.0 NTU in about 1991). Chapetta (2008) observed that the 24 hours. Most turbidity removal in the removal of coliforms including E. Coli from treated filter occurred in the schmutzdecke raw untreated water must then be attributed to rather than within the depth of the filter bed. some other mechanism inside the slow sand Hence, the mechanism of enhanced ripening filters that remains invisible and that lies in this case probably was particle within the sand column itself. The causative agglomeration with resulting acceleration of agent most likely responsible for the massive particle deposition at the filter surface amount of coliform removal from untreated accompanied by straining or attachment to water within the slow sand filters is kinetic previously removed particles. adhesion of the bacterial cells to the sand itself. The shape and size of the bacterial cell Prakash et al., (2003) found that the also contribute to the efficacy of particulate Schmutzdecke development period generally adhesion including the porous media that is occurs in a few hours to weeks depending on used. Elliott et al., (2008) showed that the type of bacteria in raw water and the other microbial reductions improved over time with microorganisms attached on the sand ripening, but a greater reduction was noted medium. As long as the length of the filter is after 30 days. Microbial reductions continued operated, the diversity of microorganisms in to improve even up to 53 days during the Schmutzdecke also increased. Joubert et al., research, indicating that the longer the better (2008) reported that the Schmutzdecke and that ripening can take some time. development period generally occurs in a few hours to weeks depending on the type of Limitations of schmutzdecke layer bacteria and the other microorganisms attached to the sand medium. Zhu and Bates The efficiency of sand filters slowly reduced (2013) reported that the in a fixed-film as the schmutzdecke thickness is increased biological process, biofilms are developed on and thereby reduces the rate of flow through media such as sand, anthracite, granular the filter. Ultimately, it is necessary to clean activated carbon (GAC), or membranes. A the top layer of the filter. After cleaning of biofilm process mainly consists of two sand water is decanted back into the filter and simultaneous steps, substrate diffusion and re‐ circulated for a few hours to allow a new biological reaction. biofilm to develop. A decline in ﬂow rate is expected due to head-loss accumulation as the Filtration of bacteria and fine particles ﬁlter ripens or matures. Particle accumulation and biological growth in the topmost layer of The Schmutzdeckeis developing where the the media bed is typically responsible for highest concentration of biomass exists, hence ripening. The concentration of organic 642

Int.J.Curr.Microbiol.App.Sci (2018) 7(7): 637-645 substrate to support microbial colonization on are found in the schmutzdecke layer, in which the ﬁlters that then leads to head loss is Pseudomonas stutzeri bacteria are dominant. another factor that was not constant among The efficiency of filters reduced as the the three experiments because the percent PE Schmutzdecke thickness is increased.It can be was not the same. This may have confounded recovered by the cleaning of the top layer of the expected order of the decline in ﬂow the sand filter. rates(Elliott et al., 2008). The highest contribution to head loss in the slow sand References filter is located in the top few centimetres of the sand and bottom layers of the Adeniran, A. E., and Akanmu, J. O. (2013). schmutzdecke. The schmutzdecke is found to The Efficiency of Slow Sand Filters in contribute substantially to the total head loss the Treatment of Secondary Effluent compared to the sand bed. The schmutzdecke from a Water Hyacinth Domestic acts as a porous filter medium in open filters, Sewage Plan. NSE Technical preventing the fast clogging of the sand bed. Transactions, 47(2). The necessary period for establishment of the Bellamy, W. D., Hendricks, D. W., and schmutzdecke and its thickness are important Logsdon, G. S. (1985a). Slow sand factors affecting head loss development filtration: influences of selected (Campos et al., 2006). process variables. Journal-American Water Works Association, 77(12), 62- The filter maturation due to thegrowth of the 66. schmutzdecke and particle trapping increases Bryan, J. J., Morris, R., Alexander, L., head loss and thus decreases filtration rate Wyn‐ Jones, P., and Sellwood, J. (Elliott et al., 2015). Adeniran and Akanmu (1999). Sources of faecal bacteria and (2013) found that the schmutzdecke is viruses in surface water and their removed when the head loss becomes impact on recreational water quality. In excessive and the outflow rate becomes slow. Health-Related Water Microbiology, After the filter is drained, the schmutzdecke is Proc. 1st IAWPRC Symposium, removed by scraping about 2 cm from the University of Strathclyde (pp. 97-106). surface of the sand bed. The interval between Buzunis, B. J. (1995). Intermittently operated scrapings depends on the contaminants slow sand filtration: a new water present in the water and the hydraulic loading treatment process. Civil Engineering, rate. University of Calgary. Campos, L. C., Smith, S. R., and Graham, N. In conclusion, Schmutzdecke is the layer of J. D. (2006). 13 Use of a novel the microbial community that is responsible simulation model to define the for purifying the water through thesand bed. behaviour of covered and uncovered As water passes through this biological layer, slow sand filters. Recent Progress in foreign particles are trapped and essentially Slow Sand and Alternative eaten by bacteria forms on this layer. Biofiltration Processes, 104. Development of schmutzdecke layer depends Chapetta, A., (2008). Filtration of Bacterial on available microbes in raw water, food Coliforms Including Escherichia Coli supply, oxygen supply, residence time, and in Water Treated by Slow Sand wetting of sand bed. Its development depends Filtration. Biological Sciences on the organic matter present in raw water. Department, College of Science and Generally, 13 types of bacterial community Math, California Polytechnic State

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Int.J.Curr.Microbiol.App.Sci (2018) 7(7): 637-645

University, (San Luis Obispo). (2011). Bacterial, viral and turbidity Elliott, M. A., Stauber, C. E., Koksal, F., removal by intermittent slow sand DiGiano, F. A., and Sobsey, M. D. filtration for household use in (2008). Reductions of E. coli, developing countries: Experimental echovirus type 12 and bacteriophages investigation and modeling. Water in an intermittently operated research, 45(18), 6227-6239. household-scale slow sand filter. Jenkins, M. W., Tiwari, S. K., Darby, J., Water Research, 42(10), 2662-2670. Nyakash, D., Saenyi, W., and Elliott, M., Stauber, C. E., DiGiano, F. A., Langenbach, K. (2009). The bio-sand Aceituno, A. F., and Sobsey, M. D., filter for improved drinking water (2015). Investigation of E. Coli and quality in high-risk communities in the Virus Reductions Using Replicate, Njoro watershed, Kenya. Research Bench-Scale Biosand Filter Columns Brief, SUMAWA, Global livestock and Two Filter Media. International collaborative research support Journal of Environmental Research program. University of California, and Public Health, 12, 10276-10299. Davis, USA. Ellis, K. V. (1987). Slow sand filtration as a Joubert, E.D. dan Pillay, B., (2008). technique for the tertiary treatment of Visualisation of the microbial municipal sewages. Water Research, colonisation of a slow sand filter using 21(4), 403-410. an environmental scanning electron Farooq, S. H., Al‐ Yousef, A. K., Al‐ Layla, microscope. Journal of Biotechnology R. I., and Ishaq, A. M. (1994). Tertiary 11(2): 1-7. treatment of sewage effluent via pilot Lazarova, V., and Manem, J. (1995). Biofilm scale slow sand filtration. characterization and activity analysis Environmental technology, 15(1), 15- in water and wastewater treatment. 28. Water Research, 29(10), 2227-2245. Fitriania, N., Hamidaha, L. N., Muhammad, N. Ellis, K. Parr, J. and Smith, Trihadiningruma, Y., Hadia, W., and M.D. (1996) Optimization of slow Redjekib, S. (2014). Bacterial sand filtration. Reaching the Communities in Schmutzdecke of unreached: challenges for the 21st Slow Sand Filter of Water Supply century. 22nd WEDC Conference New Treatment Facility in Surabaya City, Delhi, India, 1996. pp.283285. Indonesia. International Journal, 5(3). Palmateer, G. (1999). Toxicant and parasite Hirschi, S.D., and Sims, R.C. (1991). challenge of Manz intermittent slow Particles and microorganisms in slow sand filter. Environmental Toxicology, rate sand filtration. International sand 14(2), 217-225. filtration workshop (USA), 27-30. Prakash, B., Veeregowda, B. M., and Huisman, L., and Wood, W. E. (1974). Slow Krishnappa, G. (2003). Biofilms: a sand filtration (Vol. 16). Geneva: survival strategy of bacteria. Current World Health Organization. science, 1299-1307. Jellison, K. L., Dick, R. I., and Weber-Shirk, Ranjan, P. (2017). Effect of Multi-Column M. L. (2000). Enhanced ripening of Sand Filter on the Turbidity and slow sand filters. Journal of Escherichia Coli Count of Wastewater environmental engineering, 126(12), (M. Tech Thesis under the guidance of 1153-1157. Vashisht, A. K. submitted to College Jenkins, M. W., Tiwari, S. K., and Darby, J. of Agricultural Engineering and Post-

644

Int.J.Curr.Microbiol.App.Sci (2018) 7(7): 637-645

Harvest Technology (CAU, Imphal) manage the water scarcity in Ranipool, Sikkim). Himalayan region–a practical Schuler, P.F., Ghosh, M.M., and Cropalan, P., approach. Water Utility Journal, 11, (1991). Slow sand and diatomaceous 93-98. earth filtration of cysts and other Zhu, I. X., and Bates, B. J. (2013). particulates. Journal of Water Conventional Media Filtration with Research 25(8): 995-1005. Biological Activities. In Water Vashisht, A. K. (2015). Adaption of seepage Treatment. InTech. spring development technique to

How to cite this article:

Prem Ranjan and Manjeet Prem. 2018. Schmutzdecke- A Filtration Layer of Slow Sand Filter. Int.J.Curr.Microbiol.App.Sci. 7(07): 637-645. doi: https://doi.org/10.20546/ijcmas.2018.707.077

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