Assessing the Removal of Turbidity and Coliform Transport through Canal-Bed Sediment at Lab-Scale: Column Experiments

This study was conducted at lab scale to determine the performance of the canal-bed for the removal of turbidity and microorganisms TC (Total Coliforms) from surface water. The canal-bed sediments were collected and analyzed for the characteristics of sediments for grain size distribution, hydraulic conductivity and the POM (Particulate Organic Matter) percent. Canal-bed sediments were containing fine particles<0.075mm in the range of 40-58%, with hydraulic conductivity averaged 7ft/day, and the POM 2.75%. The water samples collected from the canal-water have shown average POM 3.6%. Theremoval-reduction in turbidity and TC were determined through the column experiments on the canal-bed sediments. Three columns were prepared at lab-scale by using prepared canal-bed sediment as a filter-bed in the columns for the filtration of raw water samples. Fine particles of the canal-bed grain size D 10 0.2 and D 10 0.1mm were selected for the filter-bed formation. The prepared concentrated and diluted influent water samples containing turbidity and TC were passed through the washed filter-bed into the columns for 8-weeks filter run. The frequency of sampling and analysis were followedafter the interval of one-week run, the influent (raw water) and effluent (filtered) water samples were collected and analyzed for the turbidity and TC concentrations. The performance of the grain size D 10 0.1mm have shown 95-99.95% reduction in turbidity and TC compared to the larger grain size having D 10 0.2mm particles.


INTRODUCTION
W ater is an essential element for our survival.
Deterioration in water quality and contamination of lakes, rivers and groundwater aquifers has resulted in increased waterborne diseases and other health impacts. The people of developing countries do not have an access to safe drinking water and sanitation [1]. In Sindh 95% of shallow groundwater supplies are bacteriological contaminated [2]. Less than 30% of groundwater of Sindh province is fresh; much of the province is underlain by highly brackish water [3]. It is estimated that 40 million people depend on irrigation water for their domestic usein areas where the groundwater is saline in nature. It is also reported that about 24% of the rural population gets water from irrigation canals or dug wells [3]. Groundwater serves half of the global population as the primary source for drinking water with little or no additional treatment [4,5,6].
Surface water sources with microbial contamination is frequently treated, to remove turbidity and pathogens through conventional methods of water treatment using the filter-bed of porous media, such as, slow sand filtration, and the disinfection process of drinking water treatment.
Surface water is also being treated through the natural process of treatment-filtration such as riverbank filtration [7,8].
A major group of water pollutants are microorganisms, and physiochemical compounds. The microorganisms (Pathogens) are diseases causing bacteria, which includes giardia, lamblia, viruses and parasites, organic compounds include naturally occurring organic matter (dissolved and particulate) and the inorganic contaminants include health related toxic metals and nitrates [4]. The microorganisms (pathogens) have frequently been found to occur in shallow groundwater wells [4,9]. They may be inactivated during the passage of surface water infiltration through porous media towards the aquifer.Various studies have been conducted on the transport of the microorganisms at lab-scale by using the porous media as a filter-bed.
The variable filter-bed design parameters and different porosity of the filter-media are applied to isolate the influence of specific processes and factors [10]. Scott et. al. [11] have discussed the detailed studies on the fate and transport of the pathogens in the subsurface environment these studies have been conducted largely at the laboratory scale.
According to Kanerick and Michail [12], the removal of organic compounds, nitrogen, phosphorus, suspended solids, bacteria, and viruses through a soil-infiltration treatment system is achieved through infiltration, percolation, sorption, chemical reaction, biotransformation, die-off, and predation processes during infiltration of surface water. Phosphorus removal in soil-media is influenced by the properties of the soilmedia, mainly sorption and precipitation [13]. Organic matter is predominantly removed through adsorption and biodegradation. Degradation of oxidizable organic substances is facilitated by microbial metabolism [14].
Coliform bacteria and E.coli are used as indicator bacteria to detect fecal contamination [15]. Reductions of pathogens in water treatment play an important role in minimization of public health risks [16]. The major factors influenced in the performance of soil-media are the raw water quality and the soil properties, during the infiltration process of the water pollutants through the porous media for the attenuation or removal of the water pollutants [17].

Method of Sediments Sampling
The disturb soil (sediment) core composite samples were taken from the canal-bed and six grab sample were collected from the surface of the canal-bed at the depth of 6cm.
Then 6-grab samples were mixed thoroughly in a bucket to make one composite sample of each location as shown in Fig. 1. Then the composite samples of canal-bed sediments were labeled and transferred in the polyethylene bags for further laboratory analysis.

Method of Grain Size Distribution Analysis
The physical analysis of the soil samples, the GSD (Grain Size Distribution) was carried out by applying ASTM methods of sieving [18]. The stack of the sieves was selected for the medium to fine sand particles such as 4.75, 2.0,0.425,0.15, 0.075mm and <0.075mm, the percent passing dry-weight of the sediments through each sieve of the stack was calculated.

Method of Hydraulic Conductivity Estimation
The hydraulic conductivity of the canal-bed sediments was estimated by using Equation (1) [19].
Where K is the hydraulic conductivity in a ft/day, C is the constant and is equal to 100, and D 10 is the effective size of particles corresponding to 10% passing taken in cm.

Method of Particulate Organic MatterSampling & Preparation
The

Sediments Collection and Preparation for Filter-Bed in Columns
The sediments were collected and passed through sieve The D 10 size of the grains was taken to prepare the filter bed in the columns to know the performance of the filter beds by changing the grain size and the influent water quality, generally the raw water (surface water) is being treated through slow sand filters where the effective grain size of the filter bed is required to treat the pollute water.
In this study the grain size of the sediments was selected as it was found during the analysis of the canal-bed sediments.

Columns Specifications and Operational Parameters
In order to analyze the effect of the removal of turbidity and TC, the laboratory scale columns were designed and fabricated as shown in Fig. 2. The length and thickness of the filter-bed in the columns acts a major role in the water infiltration process, which depends on the covered area of filter-bed whereas water infiltrate through porous media. The columns were exposed to atmospheric air at the inlet of the columns to maintain aerobic conditions during the experimental work. Also the influent water was containing dissolved oxygen and TC during the infiltration process of water through filter-bed in the columns.
Whereas, the attenuation process of physical, chemical and biological pollutants occurs within the porous media. the columns were kept during this study, including the other designed parameters of the laboratory scale columns are given in Table 1. The prepared canal water samples as influent containing the TC and the turbidity was applied to pass through the columns filter-bed. The parameters such as water level over the filter-bed and flow rate at the inlet and outlet was maintained initially around 2-4ml/min for first week run to saturate the filterbed. The outlet flow was controlled through clipper/valve to increase the retention time of the influent water within the filter-bed in the columns. The flow-rate was measured by using the 10 ml measuring cylinder and the stop watch; the readings were recorded as ml/min, flow-rate of the effluent water. The samples were taken from the inlet and outlet of the columns for the turbidity and TC analysis.
Total three columns were fabricated with same specifications. Moreover, the operational parameters for column experiments are summarized in Table 2.

Canal Water Sampling
The canal water was used at each attempt of the sampling and analysis as influent water (raw water) during the column experiments. The prewashed containers were used for the collection of raw water from the canal. The canal water samples were taken from the by-pass bridges manually ( Fig. 1), by inserting the glass bottle into the canal at the depth of three feet below the surface water level.

Raw Water (Influent) Preparation (Dilutions) for Column Experiments
The canal water was used to prepare the three different

Methods of Water Samples Analysis
The US-EPA methods for the analysis of water quality parameters were used in this study and are summarized in

Duration of Column-Experiments
The eight attempts of the sampling and analysis from the inlet and outlet of the columns were carried out to determine the TC and turbidity concentration in the

Canal-Bed Grain Size Distribution
The GSD of canal-bed sediments is shown in Fig. 3. The upper layer of the canal-bed from 0-6cm containing average 32.86% of the fine particle size ranged from 2-72% (0.075mm).The particles <0.075mm were averaging 40-58% passing through ASTM No. 200 sieve, indicates the fine sand and silt deposits over the canal-bed, the percentage of the grain is shown in Fig. 4. The layer of fine grained sediments is considered to be the site of the improvements in water quality that occur at bank filtration sites [22]. Physical filtering and adsorption of contaminants onto grain surfaces, where microbial and chemical transformation occur in the sediment layer [15].
The contaminants of surface water reduced due to the physical filtering, microbial degradation, ion-exchange, precipitation and sorption process through soil-sediments to the groundwater [23]. The fine sediments act as a barrier for the turbid particles and the microorganisms.
On the other hand, the higher concentrations of fine particles reduce the hydraulic conductivity of filter-bed [24]. Due to the clogging of the canal-bed the recharge of aquifer decreases adjacent to the canals. Clogging of the filter-bed decreases the hydraulic conductivity of the riverbed [25]. Low hydraulics of the soil-media increases

Canal-Bed Hydraulic Conductivity
The average Hydraulic Conductivity value of Canal-Bed composite samples is shown in Fig. 5. As per the results, the hydraulic conductivity was ranging from 1. 15-10.38 ft/day, with average hydraulic conductivity 7ft/day.

POM of Canal-Bed Sediments
POM is also referred as non-dissolved organic carbon, the fraction of organic matter retained on 0.45µm filter.
The average POM% dry weight 2.25% ranged from 1.96-

POM of Canal-Water Sediments
Canal-water containing POM percentage in the range from

Canal Water Quality Characteristics
The average concentrations of canal water quality characteristics such as Turbidity, pH, N-NH 3 , N-NO 3 , P-PO 4 , POM, and TC were recorded during the sampling and analysis of water samples taken from the canal Table 4.

Column Experiments
Analyses were done in the water and soil laboratories,

Turbidity Measurement
Turbidity refers cloudiness of water caused by the suspension of small particles; usually silt, clay, and microorganisms. It even quantifies the degree to which the light traveling through a water column is scattered by suspended organic, inorganic or microbial contaminants.
Excessive turbidity or cloudiness in drinking water is aesthetically unappealing and may also represent a health concern. Turbidity can provide food and shelter for pathogens, if not removed; turbidity can promote regrowth of pathogens leading to waterborne disease outbreaks, which have caused significant cases of gastroenteritis throughout the world [1]. Although, turbidity is not a direct indicator of health risk, numerous studies show a strong relationship between removals of turbidity and pathogens during the treatment process.

Turbidity is measured in NTU (Nephlometric Turbidity
Units). The WHO (World Health Organization) guideline for the non-microbial turbidity level in drinking water is set at 0-5 NTU, and for the effective disinfection process turbidity should be <1NTU [1].
The turbidity removal through the column experiments is shown in Fig. 9. Turbidity removal or the reduction % in

Total Coliforms Reduction
TC removal achieved through column experiments is shown in Fig. 10. The minimum reduction in column C-1 was observed during the fourth week of the experiment, this indicates the biofilm development was started after the 4 th week, and the maximum reduction was observed at the 8 th week of column experiment. The column C-2 has shown a better reduction compared to the C-1, the minimum reduction was observed as (9.09%) during the 3 rd week of the experiment, and it was increased to 75.22-100% during the 5-8 week, respectively. Column C-3 containing the same grain size and the depth of the soilsediments, where, the diluted influent water was applied shown lesser reductions in the TC comparedto the column C-2. This may be due to the biofilm development which was developed during the 6 th week in the column C-3. The minimum reduction in TC was 25%, which was increased up to 96% during the 8 th week of column experiment.

Effect of Grain Size on Performance of Filter-Bed
The large particles having a low surface area compared to the smaller particles. Therefore, the surface area required for the attachment (adsorption) of microorganisms over the particles may be increased which enhances the reduction in the filtered water through porous media. On the other hand, the movement of microorganisms' increases due to the space between the particles of filterbed, which favors the microorganisms pass through a filter-bed and may reduce the treatment efficiency of the filter-bed due to the low adsorption of microorganisms.
The filter-bed for the water filtration-treatment needs porous material, which retains the larger particles compared to the pore (voids) of the filter-bed and passes the smaller particles. process is applied to kill the microorganisms, to make it fit for drinking physically and biologically.
The results obtained during the soil-packed columns study for the removal-reduction of TC and turbidity from contaminated water, the filter-bed in the columns was prepared by using grain size (D 10 0.2 and D 10 0.1mm) of the sand particles. Out of three columns, two columns C-2 and C-3 were containing 0.1mm, and C-3 was containing 0.2mm grain size.

Effect of Influent Water Quality on Performance of Filter-Bed
The lower concentration of the chemical and the low density of the bacteria have also effect on the filter-bed performance, because the biofilm layer development is necessary to retain the bacteria and the turbidity from water during infiltration. In this study the concentration of the influent water applied in the column experiments was different, the concentrated water, undiluted water and diluted water was prepared for the column C-1, C-2 and C-3, respectively as given in Table 2. The undiluted water for column C-2 has shown better results compared to the diluted water for column C-3. The reason may be because of the biofilm layer development over the filter bed, which was started to develop during the 3 rd week with the 10-100% reduction of TC in column C-2.While in the column C-3 the biofilm layer was developed during the 6 th week of run with 25-96% reduction of TC concentration, as shown in Fig. 10. The high number of bacteria seemed to improve the adsorption mechanisms that enhance bacterial removal. Stevik et. al. [29] mentioned that the increase of bacteria (TC) concentration leads to improve the collisions between bacteria and media surface and subsequently increase the likelihood of the process within the media. The rate of adsorption increases linearly with the microbial concentrations. Stevenson et. al. [30] examined the transport and retention behavior of microorganisms through porous media, the results suggests that indicators of specific pathogens are not solely based on similar size, morphology and or surface charge but may be dependent on site-specific conditions where the other factors are involved during the process.

CONCLUSIONS
The canal-bed sediments contain fine clay, sand-silt deposits and the appreciable concentration of particulate organic matter that may enhance the growth of microorganisms to develop the biofilm layer over the bed, which can also reduce the hydraulic conductivity of the canal-bed to percolate the surface water into the aquifer.