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Journal of Environmental Management 91 (2010) 1055–1062

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Journal of Environmental Management

journal homepage: www.elsevier .com/locate/ jenvman

Impact of riverbank filtration on treatment of polluted river water

P. Singh a, P. Kumar a,*, I. Mehrotra a, T. Grischek b

a Indian Institute of Technology, Roorkee, Indiab University of Applied Sciences, Dresden, Germany

a r t i c l e i n f o

Article history:Received 11 June 2008Received in revised form5 November 2009Accepted 27 November 2009Available online 22 January 2010

Keywords:Riverbank filtrationRadial wellPre-chlorinationColourDissolved organic carbonTristimulus valuesUV-absorbanceOzonation

* Corresponding author. Tel.: þ91 1332 285446, 28275568.

E-mail address: pkumafce@iitr.ernet.in (P. Kumar)

0301-4797/$ – see front matter � 2009 Elsevier Ltd.doi:10.1016/j.jenvman.2009.11.013

a b s t r a c t

The impact of riverbank filtration (RBF) on the treatment of water from the River Yamuna at Mathura,which has disagreeable visual properties, has been investigated. The dissolved organic carbon (DOC) andcolour of the river water were 4.0–6.8 mg/L and 40–65 colour units (CU), respectively. Pre-chlorination isin practice to improve raw water quality. Chlorine doses as high as 60 mg/L ahead of the water treatmentunits reduced colour by about 78%. Removal of DOC and UV-absorbance was less than 18%. In comparisonto direct pumping of the river water, collection of water through RBF resulted in the reduction of DOC,colour, UV-absorbance and fecal coliforms by around 50%. However, riverbank filtrate did not conform tothe drinking water quality standards. Therefore, riverbank-filtered water along with the Yamuna waterwere ozonated for different durations. To reduce DOC to the desired level, the dose of ozone required forthe riverbank filtrate was found to be considerably less than the ozone required for the river water. RBFas compared to direct pumping of Yamuna water appears to be effective in improving the quality of theraw water.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

River water exhibiting a wide range of spatio-temporal varia-tions is treated by a series of processes to provide safe water forhuman consumption. The degree of treatment depends on thenature of the river water. The conventional raw water treatmentscheme followed in India is as under (Manual of Water Supply andTreatment, 1991).

Raw water/Coagulation/Flocculation/

Sedimentation/Filtration/Post� chlorination/Treated water

In case of polluted rivers, raw water is generally pre-chlorinatedand then subjected to a treatment sequence given above. Chlori-nation of waters polluted with organics is a potential source for theformation of disinfection by-products (DBPs). Removal of organicsto minimize formation of DBPs is a regulatory requirement indeveloped countries (NHMRC and ARMC, 1996). The interimmaximum acceptable concentration for trihalomethanes (THMs) assuggested by Health Canada (1996) for drinking water is 0.1 mg/L. If

5021; fax: þ91 1332 273560,

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the total organic carbon (TOC) concentration in a water sample isless than 2 mg/L, there is a high probability that the THMs guidelineof 0.1 mg/L will not exceed (Martin, 1994). It, therefore, necessitatesreducing TOC of polluted river waters to a value �2 mg/L toeliminate or reduce pre-chlorination and the probability of theformation of unacceptable levels of DBPs.

Alternatives to pre-chlorination are ultraviolet (UV) irradiationand ozonation. Natural purification of polluted river water throughriverbank/riverbed filtration (RBF) is also one of the alternatives toattenuate organic, microbial and other pollutants. RBF is a processin which subsurface water under the direct influence of surfacewater flows through the aquifer. During the flow, surface water issubjected to a combination of physical, chemical, and biologicalprocesses such as filtration, dilution, sorption, and biodegradationthat significantly improve the raw water quality. In comparison tomost groundwater sources, alluvial aquifers, hydraulicallyconnected to rivers are typically easier to exploit as they aresupposed to be shallow and highly productive for drinking waterproduction (Doussan et al., 1997).

Prakash (2006) studied the quality of water from infiltrationwells situated adjacent to the River Ganga at Haridwar, India.Filtrate collected through the RBF was generally free from theturbidity, organic substances and fecal contamination. Microbialmonitoring of different RBF systems on Ohio, Missouri and WabashRivers revealed occasional presence of Cryptosporidium and Giardia

P. Singh et al. / Journal of Environmental Management 91 (2010) 1055–10621056

in river waters but never in any sample from wells hydraulicallyconnected to the rivers (Weiss et al., 2005). Sontheimer (1980)demonstrated the removal of heavy metals from the River Rhine byRBF. Herbicides such as triazine and acetamide in the Platte River inNebraska have been shown to reduce by RBF. However, theriverbank-filtered water had elevated concentration of metabolitesof herbicides (Verstraeten et al., 2000). Effective removal ofdissolved organic constituents along with heavy metals, nitrate,pathogens, viruses, etc. by RBF has also been reported by Schmidtet al. (2003).

RBF has special relevance for India whose 14 major, 55 minorand several hundred small rivers receive domestic, industrial andagricultural wastes. Realizing potentials of RBF and hazards asso-ciated with the pre-chlorination, a project was undertaken tocompare the quality of water produced from the two treatmentschemes: (i) with pre-chlorination (without RBF) and (ii) withoutpre-chlorination (with RBF). Two such water supply schemesexisting at Mathura town (about 150 km from Delhi) were selectedfor the study. The quality of water from both the schemes did notconform to the drinking water quality standards. Therefore, anattempt was made to study ozonation of the river water andriverbank filtrate. The impact of RBF on the ozonation of thepolluted river water having distinct disagreeable visual propertieshas also been demonstrated.

2. Site description

The River Yamuna originating from the Yamnotri Glacier inHimalayas runs through several major cities and towns such asDelhi, Mathura, Agra, etc. covering a distance of 1376 km. It finallyjoins the River Ganga at Allahabad (Fig. 1). On the basis of hydro-geo-morphological, ecological and pollutional characteristics, the490 km long stretch of the Yamuna River upstream and down-stream of Mathura has been recognized as a eutrophic segmentmainly due to the release of sewage and industrial effluents into it(Agarwal and Trivedi, 1995). Several water supply schemes utilizethe river water even in this stretch as source water. In Mathura,there are two water supply schemes. One of the schemes (desig-nated as Site 1) is with pre-chlorination and the other, designatedas Site 2, has a radial well (RBF system). Site 1 is located about 4 kmupstream of Site 2. At Site 1, an intake well pumps river water,which is aerated, pre-chlorinated, coagulated, flocculated, settled

Fig. 1. Map of Northern part of In

and filtered through rapid sand filters. Post-chlorination, wheneverneeded, is carried out prior to the supply. Generally, chlorine addedduring pre-chlorination is adequate to maintain free residual in thewater supplied for drinking. At Site 2, subsurface water is collectedfrom a radial well having 13 radials (total length of 522 m) laid at15.5–18 m below the bed of the river (Fig. 2). Filtrate is aerated,filtered, chlorinated and supplied. Water is neither pre-chlorinatednor coagulated. Only post-chlorination is practiced. Schematicflow-diagrams of collection and treatment works at the two sitesare given in Fig. 3

3. Materials and methodology

Water samples from the Yamuna at several locations aroundSites 1 and 2, treated water at Site 1 and riverbank filtrate alongwith treated water at Site 2 were collected 5 times starting from themonth of November 2006 to May 2007. Temperature, pH,conductivity, DO and ORP were measured on site by Thermo Orion4 Star pH and conductivity meter, DO meter (Hach HQ10) and ORPmeter (Thermo Orion model 420 Aþ). Samples were transported tothe Environmental Engineering Laboratory, IIT Roorkee andanalyzed for turbidity, major ions, residues, DOC, colour, UV-absorbance, most probable number (MPN) of coliform bacteria andchlorine demand in accordance with the procedures laid down inthe Standard Methods (APHA, 2005). Dissolved organic carbon(DOC) concentrations of water samples (filtered through 0.45 mmfilter) were determined by the TOC-V CSN total organic carbonanalyzer (Shimadzu). UV-absorbance at 254 nm was measuredusing Hach DR/4000U spectrophotometer with 10 mm quartz cell.Hach 2100AN turbiditimeter was used to measure turbidity. Colouron Pt–Co scale (expressed in colour units, CU) was determined inHach DR/890 colorimeter with 25 mm cell.

Colour was also analysed in accordance with the CIELAB colourspace method proposed by ‘‘Commission Internationale deL’Eclairage’’ (CIE) (CIE, 1986; Rivas et al., 2006). In this method ofmeasurement, the observer and the light that illuminates the objectare specified. The entirety of all the possible colours is consideredas a tri-dimensional space, where each colour is defined by threecolorimetric co-ordinates, calculated from the values of trans-mission of the visible spectrum. This space defines the colours bythe geometrical coordinates L* (lightness; z-axis), a* (red/green;x-axis) and b* (yellow/blue; y-axis). However, these parameters are

dia showing River Yamuna.

Fig. 2. Sketch of radial well constructed in the bed of river Yamuna at Mathura.

P. Singh et al. / Journal of Environmental Management 91 (2010) 1055–1062 1057

not sufficient to obtain a good characterization of the colour. Forthis, it is necessary to consider the psycho-physical parameters,which correspond with the cylindrical coordinates: hue andchroma (hab and C*ab). Chromaticity coordinates: L*, a* and b* wereobtained using Hach Program no. 1666 (Hach, 1999) as specified inthe Standard Methods (APHA, 2005) by Hach DR/4000U spectro-photometer. The transmittance was measured from 780 to 380 nmin 5 nm intervals with Illuminant C and the Standard 2� Observer.Other parameters such as chroma (C*ab) and hue (hab) weredetermined by Eqs. (1) and (2) (ASTM, 2001)

C�ab ¼hða�Þ2þ

�b��2i1=2

(1)

hab ¼ arctan�

b*=a*�

(2)

Chroma ðC�abÞ is considered the quantitative attribute ofcolorfulness. Hue (hab) is qualitative attribute according to whichcolours have been traditionally defined as reddish, greenish, etc.It is the attribute, which allows distinguishing a colour withreference to a grey colour with the same lightness. This attributeis related to the differences in absorbance at differentwavelengths.

Ozonation of river and radial well waters was carried out main-taining the ozone flow rate of 1 L/min. Ozone generated in Oraipl,Indoz-5 ozonator was bubbled through the samples for time inter-vals of 1, 2, 3 and 5 min. Ozonation was monitored by measuringcolour, DOC, UV-absorbance and chromaticity parameters.

4. Results and discussions

Treated waters at Site 1 (without RBF i.e. direct pumping of riverwater, pre-chlorination before treatment as shown in Fig. 3) andSite 2 (with RBF, no pre-chlorination, treatment as shown in Fig. 3)have been referred as Treated Waters 1 and 2, respectively. Range ofvalues of different water quality parameters for the River Yamuna,Treated Water 1, riverbed filtrate and Treated Water 2 are presentedin Tables 1a and 1b. Desirable and permissible limits for drinkingwater as specified in Indian Standard IS:10500 (1991) are also givenin Tables 1a and 1b. Permissible limits represent the relaxations,which can be permitted in the desirable limits in the absence of analternate source at a particular location.

4.1. River water quality

The turbidity of the river water in pre- and post-monsoonperiods has been found to vary from 3.83 to 13.6 NTU (Table 1b).

Site 1: Without RBF Site 2: With RBF

River Yamuna

Intake well/Pump house

Aeration

Flocculation

Sedimentation

Rapid sand filtration

Post Chlorination

Treated Water 1

Alum coagulation Prechlorination

River Yamuna

Horizontal collector well (RBF)

Aeration

Filtration

Chlorination

Treated Water 2

Fig. 3. Water supply schemes at Site 1 (without RBF) and Site 2 (with RBF).

P. Singh et al. / Journal of Environmental Management 91 (2010) 1055–10621058

However, turbidity of the Yamuna water during monsoon rangedfrom 70 to 180 NTU. pH of the river water varied from 7.7 to 8.2.River water on an average contained dissolved salts of 840 mg/Lwhich is more than the desirable limit of 500 mg/L. Averageconductivity (1360 mS/cm at 25 �C) and alkalinity (320 mg/L asCaCO3) were also high. Average values of DOC (5.20 mg/L), UV-absorbance (0.20 cm�1 at 254 nm) and colour (45 CU) indicated thepresence of organic compounds in the Yamuna water. The colourdue to inorganic metal ions at pH 7.7 to 8.2 is unlikely. The MPN oftotal coliform were found in the range from 23�102 to 15�105 per100 mL.

4.2. Quality of Treated Water 1 (with pre-chlorinationand without RBF)

The alkalinity of the Treated Water 1 in the range 190–260 mg/Las CaCO3 was less than the alkalinity of the Yamuna water (248–360 mg/L as CaCO3). Alkalinity is neutralized or reduced during

Table 1aWater quality parameters at Site 1 and Site 2.

Water quality parameters River water(na¼ 15)

Site 1: Treated water 1b

(n¼ 5)

Temperature (�C) 19.8–21.6 20–24Conductivity (mS/cm at 25 �C) 1170–1454 –Total dissolved solids (mg/L) 725–902 –Total hardness (mg/L CaCO3) 260–358 210–298Alkalinity (mg/L CaCO3) 248–360 190–260Sodium (mg/L) 115–153 –Sulfate (mg/L) 50–53 –Bromide (mg/L) 0.263 0.189Chloride (mg/L) 175–237 250–330

a n Indicates the number of samples analyzed.b Without RBF, with pre-chlorination.c Values in parenthesis in the last column indicate permissible limit in the absence of

alum coagulation and pre-chlorination. At Site 1, the chlorinedemand of the water directly pumped from the river ranged from15 to 65 mg/L on different days (based on unpublished datacollected from U.P. Jal Nigam). Drop in pH by 0.5–0.7 could also beassociated with the drop in the alkalinity. Heavy dose of chlorine atthe pre-chlorination stage resulted in the increase in chlorideconcentration of the treated water. It was found to be more than theprescribed desirable limit of 250 mg/L (IS:10500, 1991). Colourremoval by pre-chlorination and coagulation was around 78%. TheUV-absorbance, however, did not follow the trend shown by colourremoval. The UV-absorbance of the Treated Water 1, i.e. with pre-chlorination, ranged from 0.14 to 0.23 cm�1 at 254 nm. It wasnearly of the same order of magnitude as that of the river water.DOC removal during pre-chlorination was 7–18%. It indicates thechange in the nature of the organic substances to chloro-organicsand not the reduction of organic compounds during pre-chlorination.

4.3. Quality of riverbank filtrate

Mineral content of the riverbank filtrate was found to be morethan that of water from the Yamuna River. The organic pollution,coliform bacteria and turbidity, however, were substantiallyreduced. TDS, hardness and alkalinity exceeded the desirable limitbut remained less than the permissible limits specified for theseparameters. Bed filtration reduced colour, UV-absorbance and DOCby around 50%. Accordingly, radial well water was found to have onan average UV-absorbance of 0.096 cm�1 at 254 nm, DOC of2.35 mg/L and colour of 22 CU. Total coliform of the river water(23�102 to 15�105 MPN/100 mL) reduced to 43 to 75�103 MPN/100 mL. The coliform removal was around two logs due to RBF. Bedfiltered river water is post-chlorinated to maintain a residualchlorine concentration of 0.2 mg/L.

4.4. Quality of Treated Water 1, riverbank filtrate and TreatedWater 2: comparative assessment

Perusal of the data given in Tables 1a and 1b reveals thesimilarity between the quality of riverbank filtrate and TreatedWater 2. Colour removal by pre-chlorination and coagulation atSite 1 was around 78%, whereas colour removal by RBF rangedfrom 55 to 62%. At Site 2, colour removal during post-chlorinationwas marginal. The decrease in UV-absorbance due to RBF, at Site 2,ranged from 36 to 61% while in case of pre-chlorination, reductionin UV-absorbance was marginal (0–18%). UV-absorbance ofa water sample at 254 nm is a measure of the presence of organiccompounds. These observations, therefore, suggest that organics

Site 2 Indian standards(IS:10,500: 1991) desirablelimits for drinking water

Riverbed filtrate(n¼ 11)

Treated water 2(n¼ 30)

21.4–24.7 21.6–24.4 –1356–1483 1406–1515 –

840–934 872–954 500 (2000)c

324–396 320–380 300 (600)312–349 310–342 200 (600)130–170 134–160 –

62–80 66–76 200 (400)0.371 0.372 –

203–244 221–252 250 (1000)

alternate source.

y = -0.04x + 0.27R2 = 0.98

y = -0.02x + 0.11R2 = 0.87

0

0.05

0.1

0.15

0.2

0.25

0.3

0 1 2 3 4 5 6

)m

n

45

2

ta

m

c/

1(

e

cn

ab

ro

sb

a

VU

y = -0.38x + 4.65R2 = 0.95

y = -0.38x + 2.83R2 = 0.86

0

1

2

3

4

5

6

0 1 2 3 4 5 6

)L/

gm

(

CO

D

60

70

a

b

c

Table 1bWater quality parameters at Site 1 and Site 2: other parameters.

Water quality parameters River water (na¼ 15) Site 1:Treated water 1b

(n¼ 5)

Site 2 Desirable limits for drinkingwater as per the IndianStandards (10,500: 1991)

Riverbed filtrate(n¼ 11)

Treated water 2(n¼ 30)

Turbidity (NTU) 3.83–13.6 – 0.9–4.29 0.15–3.48 5 (10)c

pH 7.7–8.2 7.18–7.46 7.93–8.23 7.97–8.2 6.5–8.5Colour unit (CU) 40–65 9.0–14.0 18–25 15–20 5 (25)

[77.5–78.5%]d [55–62%] [62.5–69%]UV-absorbance (cm�1 at 254 nm) 0.11–0.28 0.14–0.23 0.07–0.13 0.07–0.11 –

[0–18%] [36–54%] [36–61%]DOC (mg/L) 4.04–6.80 3.75–5.53 1.65–3.28 2.32–2.75 –

[7–18.6%] [52–59%] [43–60%]SUVA (L/(m) (mg)) 3.0–4.7 3.2–4.5 3.0–4.8 3.0–4.8 –DO (mg/L) 5.14–7.17 – 0.22–0.97 5.36–6.68 –ORP (mV at 25 �C) 353–390 663–684 354–364 379–432 –Tristimulus values L*¼ 99.5 to 99.8 L*¼ 99.98 L*¼ 99.7–99.93 L*¼ 99.8–99.9 –

a*¼�0.3 to �0.18 a*¼�0.05 to 0.11 a*¼�0.12 to �0.15 a*¼�0.12 to 0.13b*¼ 0.97–1.25 b*¼ 0.09–0.21 b*¼ 0.42–0.68 b*¼ 0.32–0.53

TC (MPN/100 mL) 23� 102–15� 105 <3 43–75� 103 <3 < 3FC (MPN/100 mL) 150–23� 104 – 43–93� 102 – < 3

a n Indicates the number of samples analysed.b Without RBF, with pre-chlorination.c Values in parenthesis () in the last column indicate the permissible limit in the absence of an alternate source.d Values in parenthesis [ ] in the 3rd , 4th and 5th columns indicate percent decrease.

P. Singh et al. / Journal of Environmental Management 91 (2010) 1055–1062 1059

during RBF are diluted, sorbed and/or degraded, whereas duringpre-chlorination and coagulation, the form or the nature of theorganics is changed. This is supported by the observations madeon the DOC concentration of the samples. DOC of the river waterranging from 4 to 6.8 mg/L reduced to 3.7–5.5 mg/L and 1.6–3.3 mg/L due to the pre-chlorination and bank filtration, respec-tively. During chlorination DOC due to humic and fulvic acids isconverted to the DOC of THMs, trichloroacetic acid, dichloroaceticacid, haloketones and haloacetonitriles (Reckhow and Singer,1990).

The primary reason for reducing organic carbon in drinkingwater is not related to the toxicity of the organic carbon compoundsthemselves. Their reduction lowers the potential of the formationof THMs and other DBPs following chlorination (Rathbun, 1996).Results from the present study suggest that the RBF has potentialsof attenuating organic compounds and subsequently the concen-tration of DBPs in the treated water.

The data in Table 1b suggest a correlation between DOC andUV-absorbance and a dependence of colour units on the nature ofthe organics. DOC and UV-absorbance of Treated Water 1(without RBF, with pre-chlorination) were more than that of theTreated Water 2 (with RBF). The upper limits of DOC in surfaceand treated water have been recommended to be 4 and 2 mg/L,respectively (BC Environment, 1995). Although RBF producedwater of lower DOC, however, both raw river water pre-treatedwith heavy dose of chlorine as well as collected through RBF didnot meet this guideline. Further treatment with ozone has beenevaluated.

y = -12.9x + 63.2R2 = 0.96

y = -4.82x + 25R2 = 0.99

-10

0

10

20

30

40

50

0 1 2 3 4 5 6

)U

C(

ru

ol

oC

Ozonation Time(min)

Fig. 4. (a–c) River (A) and radial well waters (-): variation of (a) UV-absorbance, (b)DOC and (c) colour with ozonation time (solid lines indicate computed curves).

4.5. Ozonation

Ozonation of both the river and radial well waters was carried outfor periods of 1, 2, 3 and 5 min maintaining a flow rate of 1 L/min.Coliforms were eliminated from both the samples after ozonationfor 1 min. Fig. 4 represents the linear decrease in the UV-absorbance,DOC and colour with increase in the duration of ozonation of theriver and radial well waters. The decreasing trends in DOC, UV-absorbance and colour of river and filtered waters were different.DOC versus time plots were parallel indicating decrease of the sameamount of DOC per unit dose of ozone for river water and riverbank

P. Singh et al. / Journal of Environmental Management 91 (2010) 1055–10621060

filtrate. On the other hand, colour of the river water decreased morerapidly with the dose of ozone compared to that of the filtrate fromthe radial well. Ozonation for 5 min eliminated the colour of boththe water samples. DOC and UV-absorbance, however, remained inboth the samples.

Organics measured as DOC generally absorb UV-radiationsaround 254 nm. These may or may not absorb visible radiations inthe range from 400 to 700 nm. Colour is due to the absorption ofthe visible range of radiations. Ozonation for 5 min removed thefraction of DOC imparting colour. Residual DOC did not absorblight in the visible range. A good linear correlation existedbetween (a) colour and UV-absorbance, (b) DOC and UV-absor-bance, and (c) colour and DOC (Fig. 5(a–c)). Since the nature ofthe organic compounds in river water (pre-chlorinated) and bankfiltered water is different, slopes of correlation for the twosamples are different. Perusal of the values given in Fig. 5(b and c)does not indicate UV-absorbance and colour at DOC of 2 mg/L and2.73 mg/L in river water. Whereas in case of filtered water, zeroUV-absorbance and colour were observed at DOC of 0.25 and0.62 mg/L.

y = 237x - 3.41

R2

= 0.803

-10

0

10

20

30

40

50

60

70

0 0.05 0.1

)U

C(

ru

ol

oC

UV - absorbanc

y = 0.04 x - 0.01

R2

= 0.99

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0 1 2

4

52

ta

m

c/

1(

ec

na

br

os

ba

-V

U

)m

n

DO

y = 10.5 x - 6.53

R2

= 0.80

01020304050607080

0 1 2

D

)U

C(

r

uo

lo

C

a

b

c

Fig. 5. (a–c) River (A) and radial well waters (-): variation of (a) colour with UV-absorbanccurves).

An ozonation time of w2 min seems to be adequate to reduceDOC concentration to less than 2 mg/L in case of filtrate. However,ozonation of the river water for 5 min was not sufficient. Theresulting DOC was >2 mg/L. RBF reduced the requirement of ozonedose to produce water of desirable quality. In addition, the UV-absorbance, which is a much simpler determination than otherparameters, can indicate DOC and colour for a specific watersample.

The data indicating the effect of the addition of ozone onchromatic parameters (L*, a*, b*, C*, and hab) are compiled in Table 2and shown in Figs. 6 (a–c) and 7. The values of chromatic param-eters for distilled and tap waters (from a multilayer aquifer) havebeen incorporated in Table 2 and Fig. 7. L*, representing the energyof the transmitted light along the z-axis, equal to 100% indicateswhite while a value of zero indicates black. The coloured samples ofriver and filtered waters transmit more than 99% light energy in thez-direction. L* did not change significantly with the increase in timeof ozonation. Values of a* and b*, however, were found to besensitive to the dose of ozone. In a sample of colourless potablewater, values of both a* and b* should be close to zero. Values of a*

y = 307 x - 21.9

R2

= 0.90

0.15 0.2 0.25 0.3

e(1/cm at 254 nm)

y = 0.10 x - 0.20

R2

= 0.96

3 4 5 6

C (mg/L)

y = 32.2 x - 87.9

R2

= 0.92

3 4 5 6

OC (mg/L)

e, (b) DOC with UV-absorbance, and (c) colour with DOC (solid lines indicate computed

Table 2Influence of ozonation time (or dose) on colour parameters (CIELAB).

Watersample

Ozonationtime (min)

Ozonedose (L)

L* a* b* Cab* hab (�)

Distilledwater

– – 100.32 �0.02 �0.07 0.0728 254.05

Tap water – – 100.28 �0.01 0.02 0.0224 116.56River water 0 – 99.76 �0.30 1.19 1.227 104.14

1 1 99.89 �0.29 0.84 0.8887 109.052 2 100.05 �0.27 0.74 0.7877 110.053 3 100.16 �0.13 0.25 0.2818 117.475 5 100.95 0.26 �0.23 0.3471 318.50

Riverbankfiltrate

0 – 99.93 �0.12 0.42 0.4368 105.941 1 99.96 �0.12 0.34 0.3606 109.442 2 99.96 �0.12 0.27 0.2955 113.963 3 100.14 �0.1 0.19 0.2147 117.765 5 101.1 0.27 �0.32 0.4187 310.16

P. Singh et al. / Journal of Environmental Management 91 (2010) 1055–1062 1061

and b* were lower (more close to zero) in case of riverbank filtrate[i.e. at ozonation time of zero minutes in Table 2 and Fig. 6(b–c)]compared to river water. In case of river water, the value of a*displayed a reduction with increase in ozonation time upto 3 min.While in case of riverbank filtrate, the value of a* practicallyremained constant until ozonation time of 3 min. Riverbank filtered

99

99.5

100

100.5

101

101.5

0 1

*L

eul

av

ec

ap

s r

ulo

C

EI

C

L*=100(white)

L*=0(black)

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

*a

ec

ap

s

ru

olo

C EI

C

0 1

-0.4-0.2

00.20.40.60.8

11.21.4

0 1

Ozonatio

*b

e

ca

ps

r

ol

oc

E

IC

a

b

c

Fig. 6. (a–c) River (,) and radial well waters (F): variation of (a) lightness units, L

water appeared to have colour causing organics which are moreresistant to oxidation than those present in river water. Similarobservation has been recorded for decrease in UV-absorbance andcolour [Fig. 4(a and c)].

The value of b* decreased up to ozonation time of 3 min in caseof both the river water and riverbank filtrate. Sharp changes invalues of a* from green (�) to red (þ) and values of b* from yellow(þ) to blue (�) corresponding to ozonation time of 5 min are quitenoticeable. The decrease in chroma (C*ab) and gradual increase ofhue angle (hab) were observed during ozonation of the river waterand riverbank filtrate up to 3 min (Table 2). Ozonation for 5 minresulted an increase in a* from�0.1 to 0.26 and decrease in b* from0.19 to 0.25 to (�0.32) to (�0.23) which eventually led to increasedvalue of chroma (Cab*). The hue angle (hab) increased sharply from117� (yellow) to around 310� (purple). The appearance, neverthe-less, did not change with ozonation for 5 min. It corroborates thefact that the achromatic point (i.e. colourless water) can be ach-ieved with many different mixtures of light, e.g. with comple-mentary colours. Reasons for sign reversals of a* and b* withozonation for 5 min need to be further investigated.

CIELAB is a standard method of colour analysis of water andwastewater samples (APHA, 2005). However, values of chromaticityparameters for wine, textiles, wood, milk, etc. are cited in the

2 3 5

+a*=redness

-a*=greenness

2

5

3

-b = b lu en ess

2 3 5

n time (minute)

+b*=yellowness

-b*=blueness

*, (b) red–green units, a*, and (c) yellow–blue units, b* with time of ozonation.

-1.4

-1.2-1

-0.8

-0.6

-0.4-0.2

0

0.20.4

0.6

0.8

11.2

1.4

-0.4 -0.2 0 0.2 0.4

337.5°

315°

360°0°

45°

22.5°

90°112.5°

135°

157.5°

180°

202.5°

225°247.5° 270°

67.5°

292.5°

a*

b*

Fig. 7. Colour diagram: (a*, b*) distilled water (:), tap water (C), river bank filtrate (�), and river water (-).

P. Singh et al. / Journal of Environmental Management 91 (2010) 1055–10621062

literature. Authors, to the best of their ability, could not get relevantinformation on the water samples.

5. Conclusions

RBF as compared to the direct pumping of river water appears tobe an effective device to attenuate the quality of the water. Organiccontaminants, colour, UV-absorbance and coliform bacteriareduced by around 50% in the filtrate. Accordingly, the dose ofozone or time of ozonation also reduced in case of riverbank filtrateto produce water of potable quality.

Acknowledgements

The authors are grateful to the ‘‘EU-India: Riverbank FiltrationNetwork’’, funded within the Economic Cross Cultural Programme(ECCP) by European Union (ASIE/004/095-733). The authors wishto thank Ms. Nisha L., Research Scholar for providing assistance inthe preparation of the manuscript.

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