Download Turbidity Removal of Water-Challenging Criteria Abstract: Surface

Asian Journal of Biochemical and Pharmaceutical Research Issue 3(Vol. 6) 2016 ISSN: 2231-2560
CODEN (USA): AJBPAD
Research Article
Asian Journal of Biochemical and Pharmaceutical Research
Turbidity Removal of Water-Challenging Criteria
K. S. Beenakumari
Department of Chemistry, All Saints College, Kerala University, Thiruvananthapuram, India
Received: 08 July 2016; Revised: 14 July 2016; Accepted: 16 July 2016
Abstract: Surface water contains different kind of suspended materials which cause turbidity and
colour. In drinking water, the higher the turbidity level, the higher the risk for the people to develop
gastrointestinal diseases. This is especially problematic for immune- compromised people, because
contaminants like bacteria can become attached to the suspended solids. Coagulation and flocculation
using alum and lime are the physical and chemical processes in which small particles causing turbidity
and colour change into giant particles and finally eliminated. It is very important to ensure that
coagulation is optimized to prevent excessive amount of chemicals remaining in the drinking water. It
is not easy to calculate the amount of chemicals required to maintain the turbidity in the standard level
by simply conducting jar test in different environmental conditions like rainy falls, since the turbidity of
raw water will change within seconds in the river during these times. This study determines the exact
quantity of alum and lime required to maintain the quality of water at varied turbid and pH levels. This
ratio will help to add lime and alum only by measuring the turbidity and pH of the raw water without
conducting the jar text experiments. This ratio of lime and alum to maintain the water quality is very
useful for persons working in water treatment plants.
Keywords: Water quality, Turbidity, Jar test, Lime-Alum ratio
INTRODUCTION:
Surface water contains different kind of suspended materials which cause turbidity and colour
[1,2]. One of the physical characteristics of potable water that should meet the drinking water standard
is turbidity. The usual source of turbidity is clay particles resulting from the erosion of soil in the
catchment area [1]. The size of the colloidal particles which causes turbidity may range from 0.001
microns to 10 microns. The time to settle down these particles in surface waters range from half an hour
to 63 years [3].
Turbidity in open water may causes by growth of phytoplankton. Human activities like civil
constructions and land altering can lead to high sediment levels in water. Natural calamities like storm
rain etc. will also create turbidity conditions. Urbanized areas contribute large amounts of turbidity to
nearby waters, through storm water pollution from paved surfaces bridges and parking lots. Certain
industries such as quarrying, mining and coal recovery can generate very high level of turbidity in water.
In drinking water, the higher the turbidity level, the higher the risk for the people to develop
gastrointestinal diseases. This is especially problematic for immune compromised people, because
contaminants like bacteria can become attached to the suspended solids. The suspended solids interfere
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Asian Journal of Biochemical and Pharmaceutical Research Issue 3(Vol. 6) 2016 ISSN: 2231-2560
CODEN (USA): AJBPAD
with water disinfection with chlorine as this particle acts as shields for bacteria against the chlorine and
also protect bacteria from UV sterilization of water.
Coagulation and flocculation are the physical and chemical processes in which small particles
causing turbidity and colour change into giant particles and finally their elimination will be preferred by
different physical methods such as sedimentation and filtration [1]. Coagulants were used many years
ago and Egyptians used alum in 2000 year B. C. [1,4] onwards. The colloidal particles in the surface
water carry same electrical charges and hence they cannot get together and form heavier particle for
settlement [3]. The coagulants unstabilize this stable system, so that they will get enough close to each
other to make heavier and bigger particles [3]. There are various techniques for turbidity removal [5].
The best management strategy for both aluminium and iron when used in treatment is to ensure
that coagulation is optimized to prevent excessive amount remaining in the drinking water. It is very
essential to ensure the quality of chemicals added so that the treated water does not contain unacceptable
concentrations of unwanted chemicals.
Conducting jar test is the common way to find out the amount of alum and lime at different pH
and turbid conditions. It is not easy to calculate the amount of chemicals required for maintain the
turbidity in the standard level by simply conducting jar test in different environmental conditions like
rainy falls etc. since, the turbidity of raw water will change within seconds in the river during these
times. It is hence very important to find out the relation between the amount of chemicals to be added
to maintain pH and turbidity of water.
The aim of this study was to determine the exact quantity of alum and lime required to maintain
the quality of water at varied turbid and pH levels. The addition of optimum quantity of lime and alum
in the water not only avoid the over dosage of chemicals usually happens in many practical situations
but also reduce the quantity of aluminium in water coming out from the alum.
EXPERIMENTAL METHODS:
The raw water obtained from the Aruvikkara River during different seasons was selected for this
study. The pH of water was monitored using a digital pH meter MK VI of Systronics. The turbidity is
measured using Nephalo turbidity meter of Systronics India. All experiments were conducted at room
temperature (28oC). AR grade of Hydrazinium sulphate and Hexamethylene teraammine of Qualigens
were used to prepare the standard solutions of turbid water. Buffer capsules of pH 4.00, 7.00, and 9.20
are used to prepare standard solution for pH meter standardization. Flocculator of model KEMI was
used to conduct the jar test. The volume of turbid water was 500 ml for all jar test experiments.
The alum solution was prepared by dissolving 1g of alum having aluminium concentration above
15%, iron below 1.0% and insoluble matter below 0.5% in 1 litre of distilled water
Preparation of lime solution was carried out by dissolving 1 g of lime (concentration of Ca(OH)2
above 86.0% and insoluble below 1.0%) in 1 litre distilled water.
Jar test experiments were carried out in the following manner. 500 ML of water samples were
taken into a beaker. Then note down its pH and turbidity. Add lime stepwise to increase the pH above
8.5, measure the lime required for increasing the pH to 8.5. Then add alum solution step wise to decrease
the pH to 7.5. Note the amount of alum required to bring down the pH 7.5. Calculate the lime-alum ratio
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Asian Journal of Biochemical and Pharmaceutical Research Issue 3(Vol. 6) 2016 ISSN: 2231-2560
CODEN (USA): AJBPAD
for the above process by ratio fixation method. Take 500 ML of water samples in different jars and add
lime and alum in multiplies of above ratio to each jar in the flocculator. Then rotate the flocculator at an
rpm of 100 for 1 minute and at 10 rpm for next 14 minutes. Allowed to stand the water samples for 10
minutes and note down the pH and turbidity of the supernatant solution. The amount of lime and alum
for which the turbidity below10 and pH between 6.5 and 8.5 was noted. A table is created for different
turbidity levels showing their corresponding alum and lime amount at different pH conditions.
RESULTS AND DISCUSSIONS:
Jar test experiment is conducted at different pH and turbidity levels. The resulted turbidity and
ph are noted. Table 1 shows the relation between the raw water turbidity and amount of alum added per
1000 L of water sample
As the turbidity level increases, the amount of alum also increases. This rise in alum is noted up
to the turbidity of 100 NTU in raw water. Above the turbidity limit of 100 NTU the consumption of
alum was very high. This is because the alum needed to coagulate the colloidal particles is very high
above the turbidity level of 100 NTU. The addition of alum not only decreases the turbidity but also
decreases the pH value also. Lime is to be added to maintain the pH level for drinking water. From the
table it was noted that amount of lime required was 3/4th of amount of alum if the raw water pH is below
6.5. If the raw water pH is in the range of 6.5 to 7.0, the amount of lime required was ½ of the alum
used. If the raw water pH was above 7.5, the quantity of lime consumed to maintain the quality of water
was found to be 1/4th of alum used.
CONCLUSION:
The amount of alum and lime required for maintain the quality of drinking water at different
turbidity and pH conditions were optimized. The relation between alum and lime during different
turbidity and pH conditions were also established. Used jar test experiments the quantity of alum
required increases with increase in the turbidity of water. A very sharp increase in consumption of alum
was noted to maintain the turbidity of the water to the standard value if the raw water turbidity is above
100 NTU. Irrespective of the turbidity of raw water, the amount of lime required was 3/4th of amount of
alum if the raw water pH is below 6.5. If the raw water pH is in the range of 6.5 to 7.0, the amount of
lime required was ½ of the alum used and the quantity of lime consumed was 1/4 th of alum if the raw
water pH was above 7.5. This ratio will help to add lime and alum only by measuring the turbidity and
pH of the raw water without conducting the jar text experiments. By establishing this ratio of lime and
alum to maintain the water quality is very useful for persons working in water treatment plants.
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Asian Journal of Biochemical and Pharmaceutical Research Issue 3(Vol. 6) 2016 ISSN: 2231-2560
CODEN (USA): AJBPAD
Table 1: The relation between the raw water turbidity and amount of alum added
Raw water
Amount of
Turbidity (NTU) Alum (g)
Amount of lime (g)
pH of raw water below 6.5 pH of raw water
between 6.5 -7.5
pH of raw
water above 7.5
10-20
20
15
10
5
20-30
22
16.5
11
5.5
30-40
24
18
12
6
40-50
26
19.5
13
6.5
50-60
28
21
14
7
60-70
30
22.5
15
7.5
70-80
32
24
16
8
80-90
34
25.5
17
8.5
90-100
36
27
18
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A. H. Mahvi and M. Razavi, American Journal of Applied Sciences, 2005, 2(1), 397-399.
A. A. Shahmansuri and A. A. Neshat, Water and Wastewater Journal, 2003, 48, 39-44.
C. Y. Yin, Process Biochemistry, 2010, 45(9), 1437-1444
Corresponding Author: K. S. Beenakumari
Department of Chemistry, All Saints College, Kerala University, Thiruvananthapuram, India.
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