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emoval of iron, arsenic and coliform bacteria from watery novel constructed soil filter system

ravin D. Nemade, Avinash M. Kadam, H.S. Shankarepartment of Chemical Engineering, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India

a b s t r a c t

The present paper presents results of the study in removal of iron, arsenic and total coliform from drinkingwater using single-pass constructed soil filter (CSF). Results indicated that arsenic levels ranged from0.5 to less than 10 �g l−1 levels; iron from 5 to less than 0.3 mg l−1 and coliform from 10−5 to less than

eywords:rsenic

ronoliform bacteria

5 CFU/100 ml. The results revealed very high removal efficiency, i.e., over 99% and water quality as perWHO standard.

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onstructed soil filterrinking water

. Introduction

About 80% of communicable diseases in the world are water-orne. Among the various undesirable and naturally occurringollutants in water, coliform bacteria, iron, fluoride and arsenic areery important as these pose severe health problems (Joshi andhaudhuri, 1996).

Iron is a troublesome element in water supplies. Making up ateast 5% of the earth’s crust, iron is one of the earth’s most plentifulesources. Rainwater, as it infiltrates soil, the underlying geologicormations, dissolves iron, causing it to seep into aquifers that serves sources of groundwater for wells. Iron is seldom found at con-entrations greater than 10 milligrams per liter (mg l−1) or 10 partser million. However, as little as 0.3 mg l−1 can cause water to turnreddish brown color (Das et al., 2007). Thus, the removal of iron

s necessary. Iron is mainly present in water in two forms: eitheroluble ferrous iron or insoluble ferric iron. Water containing fer-ous iron is clear and colorless because iron is completely dissolved.

hen exposed to air in the pressure tank or atmosphere, the waterurns cloudy and a reddish brown substance begins to form. Thisediment is the oxidized or ferric form of iron that will not dis-

olve in water. There are several methods for removal of iron fromrinking water like ion exchange and water softening (Vaaramaand Lehto, 2003), activated carbon and other filtration materialsMunter et al., 2005), bioremediation (Berbenni et al., 2000), oxi-

caatrt1

ation by aeration, chlorination, ozonation followed by filtrationEllis et al., 2000), by ash (Das et al., 2007), by aerated granularlter (Cho, 2005) and by adsorption (Tahir and Rauf, 2004).

Arsenic is a brittle-natured and gray or white-colored toxicetalloid that cannot be found as a free element in the earth’s

rust. There are more than 245 species of arsenic-bearing miner-ls, mostly ores containing sulphide along with copper, nickel, lead,obalt and other metals as well as some oxides that exist in nature.here are also anthropogenic sources of arsenic such as insecticides,esticides and wastes from mine, smelter and tannery industries.oth organic and inorganic compounds of arsenic are present in thenvironment. The inorganic arsenic is highly toxic (Rahaman et al.,008). In high concentrations, arsenic poisoning can also lead ton acute condition called arsenicosis (Hering et al., 1997; Gregor,001; Saha et al., 1999).

Coliform bacteria is the indicator of water contaminated withuman or animal wastes and if these are absent, only then can watere considered safe for drinking purpose. Generally not all bacte-ia are harmful but other microbes along with these bacteria canause short-term effects like diarrhoea, cramps, nausea, headaches,r other symptoms (Jerzy et al., 1999).

Many methods have been used to remove iron, arsenic andoliforms from water. Conventional methods for removal of iron,rsenic and coliform bacteria involve coagulation followed by sep-

ration of the produced insoluble settling or by direct filtrationhrough sand beds. Arsenic removal by various methods includeseverse osmosis, ion exchange, lime softening, flotation and adsorp-ion on iron oxides or activated alumina (Kartinen and Martin,995); waste materials (Rahaman et al., 2008); iron oxide fungal

1153

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ig. 1. Simplified chemistry of the fundamental natural processes in construct= 0.02–0.002; the lower value for terrestrial and higher value for aquatic productio

iomass (Pokhrel and Viraraghavan, 2008), aquatic macrophytesRai et al., 1995) and hydrous ferric oxide (HFO) (Nemade etl., 2007). These conventional water treatment methods are notffordable in rural communities of developing countries. So othermall-scale economical methods are required for decentralizedommunities.

Various low-cost materials like kaolinite, bentonite, lignite andumice were investigated to assess their capacity for removal of

ron, arsenic and coliform bacteria from water by batch adsorp-ion studies (Tekerlekopoulou et al., 2006; Meng et al., 2001;urhanettin et al., 2003). Slow sand diatomaceous earth (DE) fil-ration and sand filled glass columns with grown plants were alsosed for removal of Giardia muris, cryptosporidium and coliform bac-eria from water (Peter et al., 1991; Garcia and Beı̌cares, 1997; Jerzyt al., 1999; Wand et al., 2007). Also high-performance compactlter system removes bacteria and domestic wastewater is alsoreated (Heistad et al., 2006). Surface-flow wetlands constructedith Acorus and Typha plants, connected to a wastewater treat-ent plant, were investigated by Park et al. (2008) with respect

o organics (dissolved organic matter), anions (nitrate, sulphate,nd phosphate), metals (Cu, Ni, Zn, Fe, and Mn), and metalloidsArsenic).

Several small-scale water treatment techniques are practicedo alleviate these problems especially for rural communities ofeveloping countries. Constructed wetland (Vymazal, 2009) andomestic slow sand filter (SF) is one of the options which hadeen practiced for a long time and this is also economical to con-truct, operate and maintain, but the filtrate of this domestic slowand filter does not meet the recommended guidelines in remov-

ng pathogens. Also it does not successfully remove some chemicalsike arsenic. This work uses CSF so called soil biotechnology whereinundamental chemical reaction of nature such as respiration, pho-osynthesis and mineral weathering are integrated and synergizedogether (Shankar et al., 2005) as shown in Fig. 1.

FA5fe

l filter for conversion of As(III) to As(V). Where x = 0.16–0.016; y = 0.01–0.001;

The inorganic transformations such as Fe2+ to Fe3+ and Mn2+ ton4+ serve as oxygen carrier in soils (Langmuir, 1997). In CSF, respi-

ation serves to bring about oxidation of organics and inorganic andeduced oxygen demand substantially. The mineral weathering reg-lates to enable these reactions to occurred at required rates, whilehotosynthesis serves as a bio-indicator of process performance.BT houses an engineered ecology of formulated media contain-ng selected micro- and macro-organisms such as earth wormsnd indicator plants. Bio-conversion takes place by bacterial pro-ess of organic and inorganic solids. CSF efficiently removes BOD,OD, suspended solids, phosphate, bacteria and carbon (Kadam etl., 2008a,b). Shankar et al. (2005) provided details of formulatededia, culture and additives used in CSF.The present work shows excellent results for coliform removal,

early complete removal of iron (Fe) and nearly complete naturalxidation of As(III) to As(V). Subsequent co-precipitation by ironomplex, gives residual arsenic levels in treated water of less than0 �g/l (or 10 ppb) conforming to WHO, 1996 standards for drinkingater.

. Materials and methods

.1. Experimental set-up

The experiment was conducted in a bioreactor which is fabri-ated by aluminium mounted on metal grid filled with formulatededia and under drain. The total height of bioreactor is 30 cm with a

iameter of 28.5 cm. The weight of the media is 26.5 kg as shown in

ig. 2. The details of bioreactor (CSF) contents are shown in Table 1.sand filter containing gravel (size: 8–12 mm), thin gravel (size:

–8 mm), sand (size: 1–2 mm) without media was used as controlor the experiments as shown in Fig. 3. Six run on control (SF) andxperimental (CSF) unit were conducted with continuous flow rate

1154

Fig. 2. Process schematics of (a) constructed soil filter (CSF); (b) control unit without media. Sand filter (SF) for removal of iron, arsenic, coliform removal from water.

Table 1Details of bioreactor (CSF).

Details Length from base

Media (6–8 mm) 240 mmSand (1–2 mm) 20 mmThin gravel (6–8 mm) 20 mmThick gravel (8–12 mm) 20 mm

Fig. 3. XRD of formulated media (PWDTB) used in constructed soil filter (CSF).

Table 2Characteristics of formulated media.

Physicochemical properties Values

Moisture content (%) 23.4 ± 5.1Clay (g/kg) 11 ± 1.7Silt (g/kg) 550 ± 25Sand (g/kg) 400 ± 20Gravel (g/kg) 38.0 ± 5.0Soil texture (USDA scheme) Sandy loamHydraulic conductivity (KLa; cm/s) 4.2 × 10−5

pH soil suspension(1:5) 7.0 ± 0.20Organic matter (g/kg) 1.3 ± 0.1Total carbon (g/kg) 4.8 ± 0.4

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Cation exchange capacity (m.e./100 g) 41.0 ± 5.8Anion exchange capacity (m.e./100 g) 1.9 ± 0.4

0 ml min−1. Effluents in continuous tank were analyzed for iron,rsenic, and coliform. In case of arsenic, the effluent is taken andreated with ferric chloride and then analysis after filtration.

.2. Characterization of (PWDTB) media

The media is formulated from partially weathered Deccanrap basalt (PWDTB). The characteristics of formulated mediare shown in Table 2. X-ray diffraction (XRD) of analysis ofhe medium (PWDTB) has shown the presence of Al2O3, Fe2O3,

nO, MgO, CaO, SiO2, TiO2, P2O5 minerals and XRD analy-is as shown in Fig. 4 and XRF analysis presented in Table 3.WDTB showed the presence of albite (NaAlSi3O8), calcium

luminosilicate (CaAl2Si2O8), quartz (SiO2), pyroxene, diopsideNa118Ca553Mg1.087Fe125FeO25Al119Si1.973O6), ferrosilite (FeSiO3),yrolusite (MnO2), and zeolite (Na8Al6Si6O24) particularly natrolite(Ca,Mg,Fe,Al)2(Si,Al)2O6}.

1155

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This media contains innumerable fine-quality zeolites, a groupf silicate minerals characterized by crystallographic structures andre marked by distinct channels at the atomic level which markshem as chemical filter. Quarries of the Deccan Basalts are in factmong top 12 mineral localities in the world. Quarries in the Malad,estern suburb of Mumbai has even reported finest zeolite and

eolite related specimens such as natrolite (Wise and Moller, 1990).

.3. Reagent preparation

Stock solutions of arsenite were prepared by dissolving appro-riate quantity of arsenic trioxide, As2O3 (S.D. Fine Chem Ltd., India)

n tap water containing 1% (w/w) NaOH and the solution was theniluted up to 1 l. Iron (II) sulphate (FeSO4) with a purity of 99%as selected as a source of iron because of good solubility in water.

he arsenate stock solution was prepared from sodium arsenate,a2HAsO4·7H2O (Loba Chemie, India). The working solutions con-

aining arsenic were prepared by dissolving appropriate amountf arsenic from stock solutions in tap water. Experiments wereerformed at ambient temperatures ranging from 29 to 31 ◦C.

.4. Experimental plan

In the bioreactor, all tests were conducted in gravity flowode and at normal pH (7.3). The process schematic for CSF and

F are shown in Figs. 2 and 3 respectively. Arsenic water wasumped through the bioreactor by a peristaltic pump (Cole Parmer

nstrument Company, Ontario). The packed volume has enougheadspace to allow for expansion of the medium during backwash-

ng. The flow rate was kept constant at 60 ml min−1. The liquidold up was 2.25 l (drainage method) and mean residence time was.92 min (tracer method).

The synthetic water containing arsenite, As(III), and iron was

repared in laboratory. The initial As(III) concentrations was keptt 300 �g l−1 in the water. Six runs of down-flow column testsere conducted. In each run a known volume of water is passed

40–60 l). Samples were collected at regular time intervals and co-recipitated by FeCl3 followed by filtration and then analyzed for

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able 3ineral composition of PWDTB used in CSF.

aterial Al2O3 (%) CaO (%) K2O (%) MgO (%) SiO2 (%)

WDTB 13.52 7.63 0.23 4.3 44.71

used in constructed soil filter (CSF).

esidual As(III), iron, coliform and As(V). Before commencement ofach run, the column was washed with tap water until the residualrsenic levels reached less than 10 �g l−1.

.5. Analysis

The residual arsenic in water sample was determined usingapid colorimetric method (Dhar et al., 2004) with detection limit�g l−1. The method was used to estimate As(III) and As(V) con-entrations in treated water samples. Arsenic was determinedy double beam UV Spectrophotometer (Shimadzu, Japan) andeasurements were made at a wavelength of 880 nm. Total iron

nalysis was performed by 1, 10 phenanthroline method (APHA,998). Water temperature, conductivity and total dissolved oxygenTDS) were measured using WTW (Germany) Inolab1 conductiv-ty meter; pH and dissolved oxygen (DO) were measured using

TW (Germany) Inolab1 pH/Oxi meter; turbidity was measured onTW (Germany) Turb 550. Indicator organism viz., total coliformas enumerated as per the procedure given in Standard Meth-ds for the Examination of Water and Wastewater (APHA, 1998)sing membrane filtration technique. Appropriately diluted (10−3

o 10−7) sample (100 ml in volume) was filtered through 0.45 �membrane filters and subsequently these filters were mounted on

pecific media supplied from Hi Media Laboratory Pvt. Ltd., India.lates were then incubated for 24 h at 44.5 ◦C on M-Endo agar forotal coliform. Results are reported as number of Colony Formingnit (CFU) per 100 ml. Initial characteristics of water are shown inable 4.

. Results and discussion

The hydrodynamic characteristics of bioreactor were studiedrst in the laboratory. At the flow of 60 ml min−1, the hold up was

.85 l (drainage method) with a mean residence time of 9.92 minpotassium bromide tracer method). In all the experiments, aeaction time of 9.9 min was maintained. Available experimentaltudies on oxygen transfer showed transfer coefficient in the rangef 10−2 to 10−3 s−1, almost similar to agitated vessels. In this study,

FeO + Fe2O3 (%) Na2O (%) TiO2 (%) MnO (%) P2O5 (%)

16.46 0.83 2.10 0.25 0.25

1156

Table 4Physico-chemical analysis of water sample.

Sr. no. Parameters Values Maximum permissible limits (WHO)

1 pH 7.2 6.8–8.52 Temperature (◦C) 29.7 16–323 Turbidity (NTU) 285 5–104 Iron (mg/l) 5.0 0.305 Arsenic (mg/l) 0.30 0.016 MPN (coliform cells/100 ml) 2 × 105 Nill

Table 5Removal of iron from water by constructed soil filter (CSF) and SF having an initialconcentration of 5 mg/l having flow rate of 60 ml/min.

Run time (h) Residual iron (mg/l) CSF Residual iron (mg/l) SF

2 0.128 3.914 0.089 2.606 0.077 1.75

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Table 7Removal of coliform bacteria from drinking water by SF and CSF having an initialconcentration of 2 × 105 (coliform cells/100 ml).

Run time (h) Residual total coliform bacteria(coliform cells/100 ml) SF(without media)

Residual total coliform bacteria(coliform cells/100 ml) CSF(with media)

0 105 105

2 104 104

4 104 103

6 104 102

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8 0.067 1.1210 0.056 0.75

he authors were concerned only with iron, arsenic and coliformacteria removal using CSF with formulated media and SF withoutedia as a control. The water was treated under continuous mode

peration having flow rate of 60 ml min−1. The iron, arsenic andoliform bacteria concentrations were measured before and afterreatment for each run separately.

The time was the important operating parameter considerednder the present study. It is clear from Table 5 that the removalf iron with media CSF was more than control filter SF under allhe treatment times and it was maximum after a treatment timef 10 h with residual values of 0.75 and 0.056 mg l−1, respectivelyor SF and CSF. The concentration of dissolved oxygen in the liquidhase throughout the filter depth was always ranging from 5.0 to.25 mg l−1 which is sufficient to oxidize Fe(II) to Fe(III) forminge(OH)3 which was detained on the support material of the filter.he influent pH was found to be 7.0 ± 0.2 and effluent was foundo be close to neutral (7.4 ± 0.3) showing buffering capacity of SBTnvironment. The residual iron is less than 0.30 mg l−1 which isermissible limit for drinking water. Tekerlekopoulou et al. (2006)bserved iron (1–3 mg l−1) removal from water in trickling filternd residual iron in the outlet was found less than 0.3 mg l−1. Itas clear that the maximum percent removal was achieved with a

reatment time of 10 h and after that the equilibrium was achieved.In CSF, the natural oxidation of As(III) to As(V) nearly takes place,

ith further arsenic removal by co-precipitation with ferric chlo-ide. As(III) is non ionic in natural water having pH between 6.5nd 8; after passing through CSF, it gets converted to As(V) by mediahich is ionic not get adsorbed on media. Table 6 shows the correctass balance of influent and effluent arsenic in water. CSF has very

ood potential for oxidation of As(III) to As(V) and then removal ofrsenic from drinking water as compared to SF under all the treat-ent time conditions. The maximum removal of arsenic for both

he filter media was achieved with a treatment time of 10 h and

wiww

able 6emoval of arsenic from water by SF and CSF having an initial concentration of 300 �g/l.

un time (h) Oxidation of As(III)to As(V) SF (�g/l)

Oxidation of As(III)to As(V) CSF (�g/l)

FeCl3 dose

2 50 294 354 55 295 356 60 296 358 60 296 35

10 60 296 35

8 103 1010 102 5

he residual value of arsenic was 0.008 and 0.24 mg l−1 for CSF andF respectively. In all the experiments the residual arsenic in wateras found to be <10 �g l−1 in compliance with WHO drinking water

tandard. Table 6 shows that there is a very little adsorption of As(V)n the bed. Almost 99% oxidation of As(III) to As(V) took place usingnitial As(III) concentration of 300 �g l−1.

CSF shows excellent results for the removal of coliform bacte-ia from drinking water with CSF as compared to SF as shown inable 7. The maximum removal was achieved under a treatmentime of 10 h for both the filter media and the residual values were00 coliform cells/100 ml and 5 coliform cells/100 ml for SF andSF with formulated media respectively. Formulated media had areat contribution in the removal of coliform bacteria from drink-ng water and under treatment time of 2, 4, 6, 8, and 10 h. Wandt al. (2007) found less coliform removal in sand column. PWDTBsed as formulated media has promising features such as hydrauliconductivity 10−5 ms−1 equivalent to porous sand; oxygen transferoefficient 10−2 s−1; microbial diversity as good as that of soil; andnzymatic activity equivalent to that of virgin soil (Kadam et al.,008b). Treating municipal wastewater gives effluent water qual-

ty of WHO standard for reuse of wastewater and can be used forardening, toilet flushing, car washing, for construction purpose.

It was also found that there was a regular pattern of increasen percent removal of iron, arsenic and coliform bacteria with thencrease of treatment time. The equilibrium was achieved with areatment time of 10 h for iron, arsenic and coliform bacteria. Itas also evident that initially with a treatment time of 2, 4 and 6 h,

t was more efficient for iron removal. On comparing these valuesith the permissible limits of WHO, the values of all the parametersere under the permissible limits.

as Fe (mg/l) Residual arsenic (�g/l) CSF Residual arsenic (�g/l) SF

12 25010 2458 2408 2408 240

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. Conclusions

The CSF technology showed consistent performance towardsemoval of iron, arsenic and coliform from drinking water and theesidual concentrations of these parameters are well under the per-issible limits of the WHO standard. The technology also provides

nvironment for the media without loss of utility. CSF shows aood potential for the removal of iron, arsenic and coliform bacteriarom drinking water and the. The CSF technology can also overcomeome of the limitations of the conventional techniques. The locallyvailable materials are used in the filter, which can treat a reason-ble amount of water within a short time. Moreover, it is also easyo install and operate, even by a laymen after just a few days ofraining.

cknowledgements

The authors would like to extend our sincere thanks to Sophisti-ated Analytical Instrumentation Facility (SAIF), Indian Institute ofechnology Bombay, Mumbai, India for useful assistance in samplenalysis.

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