MSU -Iligan Institute of Technology College of Engineering Department of Chemical Engineering and Technology
Batch Sedimentation
A Laboratory Report
In Partial Fulfillment For the requirements of
CHE 159: Particle Technology
Prof. Arniel Ching O. Dizon
KIMBER S. CELICIOUS ROMEO T. DOCOR HOPE MARIE N. GOCOTANO NOVI KENN C. LAVISORES
March 2018
Abstract
Wastewater treatment is vital nowadays in order to lessen the p ollution in the environment. With the aid of sedimentation process, treatment becomes easier and more economical. A volume of wastewater from Permites Compound creek, San Miguel Iligan city was obtained and homogenized in a graduated cylinder. The settling particulates were then observed and recorded in Table 1. Data obtained were used to calculate the areas of the thickener which is found to be 10.9 m2 and a clarifier area of 368 m2. Results obtained in area calculations gave us the idea of the quantity of wastewater particles present and the time it will totally settle down.
I. Introduction
Sedimentation, or clarification, is the process of letting suspended material settle by gravity. It is a physical water treatment process using gravity to remove suspended solids from water . Sedimentation has been used to treat wastewater for millennia. The particles that settle out from the suspension become sediment, and in water treatment is known as sludge. When a thick layer of sediment continues to settle, this is known as consolidation. When consolidation of sediment, or sludge, is assisted by mechanical means then this is known as thickening. In water treatment sedimentation might be used to reduce the concentration of particles in suspension before the application of coagulation, to reduce the amount of coagulating chemicals needed, or after coagulation and, p ossibly, flocculation. When sedimentation is applied after coagulation, its purpose is usually to reduce the concentration of solids in suspension so that the subsequent filtration can function most effectively. Sedimentation is one of several methods for application prior to filtration: other options include dissolved air flotation and some methods of filtration. Generically, such solids-liquid separation processes are sometimes referred to as clarification processes. There is a variety of methods for applying sedimentation and include: horizontal flow, radial flow, inclined plate, ballasted floc and floc blanket sedimentation. Wastewater is composed of all the water used in the home that goes down the drains or into the sewage collection system. This includes water from baths, showers, sinks, dishwashers, washing machines, and toilets. Small businesses and industries often contribute large amounts of wastewater to sewage collection systems; others operate their own wastewater treatment systems.
Primary treatment of sewage is removal of floating and settleable solids through sedimentation, as well as the precipitates formed in coagulation and flocculation. After plain sedimentation, simple settlement of the solid material in sewage can reduce the polluting load by significant amounts. It is important to know how fast or slow particles settle in order to conclude the time it takes to get a compacted solid at the bottom. The area being occupied by the compacted solids by a certain time is calculated using the Talmadge and Fitch Method. A successful sedimentation is crucial for the overall efficiency of the wastewater plant. Common examples include the removal of grit and particulate matter in the primary settling tanks that receive raw wastewater prior to biological treatment and sludge from the bioreactor. Using the Talmadge and Fitch method it is possible to plot the solid flux versus the solids concentration without implementing multiple tests. The point at which the settled particles of the solid are compacted is called the compression point and its concentration is said to be critical. These are all important in wastewater treatment in order to calculate the area of the clarifier and the area of the thickening. Thickening is the part which the solid particles settles and compressed, and the clarifier is the part which is clearer and is subjected to secondary treatment. The rate of flux can also be calculated using this method. The objectives of this experiment are to estimate the area of a thickener/clarifier from the batch settling data of the waste water.
II. Background
The use of gravitational sedimentation is one of the economical and practical method s used in removing the solids from waste water. The process emplo yed in this method is a batch settling process where particles settle by gravity to the bottom of a liquid forming sediment.
Two possible occurrences of settling are present, the free settling and the hindered settling. Each particle is not affected by the movements of the other particles is the working principle of free settling and the forces involve in the interaction of particles in the fluid or with the container walls of considerable magnitudes is for hindered settling. The Talmadge and Fitch Method is applied in this experiment which is a graphical method of estimating the area needed for clarification and thickening from the settling curve. The area
, and the area needed for clarification, , are given by,
needed for thickening,
=
(2.1)
=
(2.2)
, and is the flow rate of the mixed liquor, time required to reach the desired
where Q, s,
underflow concentration, initial height of the column is the clarification rate and interface subsidence velocity III. Experimental Procedure
In the experiment, the wastewater was obtained in Permites Compound creek in barangay San Miguel, Iligan City. The batch settling was proceeded in a 500-ml graduated cylinder. The collected wastewater was transferred to the cylinder, was inserted with a stopper and was shaken manually to allow homogenization of the sample. The initial height of the clear liquid-interface was noted and the cylinder was left to stand in a flat surface taking notice of the height of the clear liquid-interface at different time. Height measurement were done using a ruler placed at the cylinder at specified periods. Interpretation of data were done using Microsoft Excel.
Wastewaster was collected in Permites Compound creek
Laboratory scale sedimetation experiment
Interpretation of data in the experiment by applying the thories and principles above mentioned.
Figure 3. Process flowchart
IV. Results
The batch settling test results are shown in table 4.1. Table 4.1 Clear liquid-interface height and time data Time, min
Height, cm
Time, min
Height, cm
0.00 5.05 10.06 15.05 20.03 25.02 30.00 35.10 60.01
29.00 19.82 15.00 11.78 8.80 5.32 4.90 4.41 3.99
90.10 120.08 150.05 180.03 210.10 240.02 300.05 360.03 375.03
3.66 3.41 3.00 2.83 2.58 2.09 1.92 1.70 1.70
Plotting the values from table 4.1, a batch settling curve reflected on figure 4.1 is obtained.
35 m30 c , t h g25 i e h e c20 a f r e t n15 i d i u q i l 10 r a e l C 5
0 0
50
100
150
200
250
300
350
400
time, minutes
Figure 4.1 Batch settling test results, Height – time curve
According to 2010 census population and housing, barangay San Miguel Iligan city has a total population of 4117 with 862 number of households. The average water usage per person of
265 (Eddy, 1991) thus the water usage per day is =4117×265 × =1091
(4.1)
4.1 Clarifier area
In figure 4.1, a tangent line to the initial (black solid line) and final (black dashed line) leg is constructed. The two lines were then bisected (red solid line) and was projected up to the batch settling curve. The intersection of the bisection and the curve corresponds to the critical height, H c, and concentration, C c. Projecting the intersection to the height axis (red dashed line), the critical height was determined equal to H c = 4.2 cm. These lines are shown in Figure 4.2 and Figure 4.3.
35 m30 c , t h g 25 i e h e c 20 a f r e t n 15 i d i u q i 10 l r a e 5 l C Hc
0 0
50
100
150
200
250
300
time, minutes
Figure 4.2 Talmadge-Fitch method to determine Hc
350
400
10 m c , t h g i e h e c a f r e t n i d i u q i l r a e l C
9 8 7 6 5 4
Hc =
4.2 cm
3 2 1 0 0
10
20
30
40
50
60
70
time, minutes
Figure 4.3 Enlarge view of Figure 4.2.
The area of the clarifier is determined using equation 4.2 and 4.3.
= =
(4.2)
(4.3)
Accordingly, the clarifier rate is
. =1091 . =158.0 The velocity is determined from the straight line o n figure 4.1, from time 0 to 20.03 minutes.
− = .∆ = .−. .−
(4.4)
=14.5 / From equation 4.2, the area of the clarifier is,
/ = . . /
= 10.9 4.2 Thickening Area
The thickening area, At , can be calculated using equation 4.5.
= Assuming a sludge concentration
(4.5)
with ten times the initial concentration, that is =10
,
the sludge height can be calculated using equation 4.6.
=
(4.6)
= . = 2.9
To determine s, a tangent line (balck solid line) intersecting the curve at point (H c , Cc) and a line of height
(black dashed line) were drawn on figure 4.1. The intersection was projected
downwards at time t s. These lines are shown on figures 4.4 and 4.5.
35 m30 c , t h g i 25 e h e c 20 a f r e t n 15 i d i u q i 10 l r a e l C 5
0 0
50
100
t s
150
200
250
300
350
400
time, minutes
Figure 4.4 Talmadge-Fitch method to determine t s .
5 m c , 4 t h g i e h e 3 c a f r e t n i - 2 d i u q i l r a 1 e l C
t s = 141 min
0 0
50
100
150
200
time, minutes
Figure 4.5 Enlarge view of figure 4.4
From figure 4.5, t s is equal to 141 minutes, which by conversion is equal to
= 141 = 0.0 979
250
Form equation 4.5, the thickening area is
). ( = .
= 368 . V. Discussion
In this experiment, the waste water was taken from San Miguel, Iligan City. It has a population of 4,117 as of 2013. Average usage of water per person is 265 L/day. Based on these data, the total usage of water per day is
. This value roughly represents the amount of 1091
wastewater generated in San Miguel, Iligan City. The slope of the settling curve represents the settling rate of the particles. From figure 4.1, the settling velocity is constant during the early stage, as observed from the straight line after 25 minutes. This gradually decrease at the later time, gaining again a visually constant velocity after 60 minutes. The part of constant velocity is considered the free settling zone and fluid below is the hindered settling zone wherein the velocity decreases because of the interactions of the neighbouring particles. This statement is reflected in the results as shown on curve figure 4.1. The clarifier and thickener area was found using the Talmadge and Fitch method. From figures 4.1 to 4.5, their areas are 10.9 and 368 m2, respectively. Moreover, the area needed for clarification is much less compared to the area needed for thickening, thus it should be considered in the design for the clarifier and thickener. A source of error is inherent in using the Talmadge and Fitch Method. This relies on graphical inspection which is prone to error introduction. A difficulty was especially experienced
in constructing the lines for the determination of the critical height and s. The nature of the curve greatly affects the values obtained, as well as the researcher’s judgement as where to draw the lines, especially the tangent line of figure 4.4. The graph, as observed in a close-up view in figure 4.5, is not smooth creating complication in the tangent line construction since there are several orientations that appears tangent to the curve at the critical point. This decision-making part
significantly affect the values of the critical height and s. The calculation may not be representative to the whole stream since poor sampling was done and standard water sampling procedure was not followed. The changes, however, can be readily substituted to procedure in calculating the clarifying and thickening areas. VI. Conclusion
In conclusion, the use of Talmadge and Fitch method is a fast way fit in designing thickener/clarifier in the sedimentation process of wastewater treatment facilities. In line with this, there is a need of consideration for the area needed for thickening and based on the graph above, the domination of hindered settling in the curve is quite obvious, thus the sample coming from Permites Compound wastewater contains high concentration of solids.
VII. Bibliography
Eddy, M. a. (1991). Wastewater Engineering. Treatment Disposal Reuse. New York: McGrawHill. (2013, July 17). Retrieved March 27, 2018, from https://psa.gov.ph/content/population-iligan-citywas-recorded-323-thousand-results-2010-census-population-and-housing Quantity of Wastewater. (n.d.). Retrieved March 27, 2018, from https://www.globalspec.com/reference/80578/203279/4-quantity-of-wastewater
Appendix A Documentation
Figure 8: Inversion of sedimentation cylinder
Figure 9: Start of experiment
Figure 10: After 6 hours
