Environmental Project.docx

Abstract This report will address all the water treatment processes required to improve the characteristics of a given sample of raw water (see table 2) to match the standards of drinking water (see table 3). It will provide an insight into all the water treatment processes required to match the quality standards of drinking water varying from flocculation and coagulation to sedimentation and filtration. The report will further address the design of coagulation, flocculation, and settling tanks along with the design of a rapid gravity sand filter.

Contents Abstract.......................................................................................................................................................1 Introduction.................................................................................................................................................3 Background..................................................................................................................................................3 Project Requirements..................................................................................................................................5 Rapid mixing................................................................................................................................................5 Flocculation.................................................................................................................................................8 Softening.....................................................................................................................................................9 Sedimentation...........................................................................................................................................10 Filtration....................................................................................................................................................11 Biological Treatment..................................................................................................................................12 Treatment of Nitrogen...............................................................................................................................13 Treatment of phosphate............................................................................................................................14 Removal of Fecal Coliform.........................................................................................................................14 Appendix...................................................................................................................................................15 References.................................................................................................................................................16

Introduction The ultimate goal of the design of any water treatment facility is to provide safe water. Safe water in general means colorless, odorless, and clear water with a pleasant taste. Also, safe water has to be non-corrosive and non-staining. High concentrations of some chemical elements such as iron, hydrogen, manganese, sulfides, chlorides, and sulfates must be avoided. There are several factors that affect the design of a water treatment plant. Among the most important factors are the nature of the water source, and the desired quality of treated water. The quality of the treated water depends on the type of end uses which vary from human consumption and irrigation, to hydropower generation and industrial utilization. Typical water sources include but not limited to lakes, rivers, wells, and reservoirs.

Background The type of water source indicates how polluted the raw water which is to be treated. The level of pollution in turn defines the procedures and water treatment processes needed. Table (1) defines the water treatment processes needed to purify raw water based on the type of water source and the level of pollution. Table (1): Water treatment processes based on the type of water source and level of pollution [1]

Water source Ground Water

Level of pollution No pollution and high content of minerals. No pollution and high content of manganese and iron. With pollution.

Water treatment processes Chlorination Iron and manganese chlorination. Coagulation, chlorination.

settling,

removal

and

filtration,

and

Surface water

Ground or surface water

With almost no  Slow sand filtration and chlorination. pollution and low  Coagulation, settling, filtration, and turbidity. chlorination.  Membrane filtration, and chlorination. With moderate  Pre-chlorination, coagulation, settling, level of pollution. filtration, and chlorination.  Membrane filtration, and chlorination.

With high level of  Coagulation, settling, sand filtration, pollution. ozonation, GAC filtration, and chlorination. With high  Softening with a soda ash/lime reactor hardness and a filter or an ion exchange resin.

Polluted water, in addition to having high concentrations of some chemical elements, it contains some organic and inorganic substances that need to be removed as to improve the quality of the treated water. The typical water treatment processes needed to remove these substances include but not limited to: rapid mixing, coagulation, flocculation, sedimentation, sludge collection, filtration, disinfection, chlorination, ozonation, softening, iron and manganese removal, and taste and odor control. However, not all processes are necessary. As previously mentioned the types of water treatment processes needed are selected based on the desired quality of treated water and state or characteristics of raw water. The design of a typical water treatment plant is diagramed in figure (1), in which some of the previously mentioned major processes take place.

Figure (1): typical design of a water treatment plant [2]

Project Requirements The characteristics of the input or raw water in this project are listed in Table 2. Now that the content of each parameter is listed in the table, there is no need to identify the water source. Also, the standards of drinking water which represent the desired quality of treated water are listed in Table 3. Table 2: characteristics of raw water Parameter Unit

Value

Magnesium

mg/L as CaCO3

70

Calcium

mg/L as CaCO3

200

HCO3-

mg/L as CaCO3

150

pH

Table 3: Drinking water standards [3] all values in mg/L

6.0

Flow rate

m3/d

150,000

TSS

mg/L

900

Fine particles

High

Color

High

BOD

mg/L

100

Nitrogen

mg/L

20

Phosphate

mg/L

5

Fecal coliform

#/100ml

10,000

Note that the units and parameters in table 1 and table 2 are not consistent. This inconsistency will be accounted for in later sections of this report.

Rapid mixing Rapid mixing is represented in the first stage in figure 1. It is the process at which a coagulant is spread through the act of mixing. Usually the duration of coagulation is between 10-

30 seconds. This process takes place in the coagulation basin. It is mainly used to improve the homogeneity of the input water. The mixing of the water is accomplished by means of pumps and turbines. In this project, the mixer is assumed to be an axial flow turbine. The parameters of coagulation are mixing intensity, detention time, power, diameter of the impeller and dimensions of coagulation basins. The following calculations illustrate the design parameters for rapid mixing: Mixer: Axial flow turbine Tank: -

1 to 3 m diameter Flow through, top to bottom 30 to 90 second detention time

Coagulant: Aluminum sulfate: Al2(S04)3 (Alum) since alum tends to work best at a dosed-water pH of 5.8-6.5 which is our case. If the pH is lower or higher than this optimum, then problems of high residual color and aluminum or disinfection by-products may occur in the finished water. Al2(SO4)3.14 H2O  2Al(OH)3+ 8H2O + 3H2SO4-2

√

P μ∀ G=velocity gradient ,[ s−1 ] P=input power,[ W ] ∀=volume of water in mixing tan k ,[ m3 ] μ=fluid vis cosity ,[ Pa⋅s or N⋅s/m2 ] G=

G value for coagulation: 600 to 1000 S-1

Take G =600 S-1

Mixing time: 30 to 90 sec

Take =60 sec Q=150,000 m3/d=50000 m3/d per basin

Design Considerations: Three rapid mix basin (Coagulation)

12 flocculator trains(Flocculation) Volume= Q=60 sec*1.7361 m3/s= H=2T

Volume=

104.166 m 3 =34.7 m3 per basin 3

π∗T 3 =34.722 m3 2

T=2.8m and H=5.6m

Where,

Assume

μ ( water viscousity )=1.002 ×10−3

2

2

Assume B is one third of the depth H Allowable Range 0.14-0.5 2.0-4.0 0.28-2.0 0.7-1.6

at temperature=20 0C

34.7 =12.517 kW

−3

p=G × μ × ∀=600 × 1.002× 10 ×

Geometric Ratio D/T H/D H/T B/D

Ns 2 m

B= 1.867 m 0.8 0.3 7.0 2.0 2.3

Impeller Diameter, m 1.4 0.5 4.0 2.0 1.3

Use Impeller Diameter D=1.4 m 

Rotational Speed (n):

Np=0.31

p N p× D 5 × ρ ) 1/3=1.958 rps=117.5 rpm n=¿

Alum dose: For PH equal to 6, assume alum dosage 20 mg/L [4]

2.0 0.7 2.8 2.0 0.9

Amount needed= dosage x Q= 20 mg/L * 150,000 m3/d=3000 Kg/d

Flocculation Flocculation is a physical process characterized by slow mixing of the input water. This process occurs in the flocculation basin which is highlighted as stage 2 in figure 1. The slow mixing of row water along with the coagulant will result in floc formation. The mixing time of the flocculation process should be within the range of 20-60 mins. In this process, turbulence should be avoided as much as possible, through providing laminar flow condition to enhance the floc formation. The main design parameters of this process are the same as the design parameters of the coagulation process in the previous section, and they are computed as follows: Mixer: Axial flow turbine G value for coagulation: 30 to 90 s-1

Take G =30 s-1

Mixing time: 20 to 60 min

Take =20 min

Use G=30 s-1 for the 12 basins Q= 12500 m3/d per basin Volume= Q=20 min *8.68 m3/min= 173.6 m3 per basin Assume 3 compartments per basin Volume per basin=57.87 m3 H=2T

π∗T 3 Volume= =57.87 m3 2

p=G 2 × μ × ∀=302 × 1.002×10−3 ×

T=3.25m and H=6.5m

57.87 =52.2 W per compartment

B= 2.167 m

Geometric Ratio D/T H/D H/T B/D

Allowable Range 0.14-0.5 2.0-4.0 0.28-2.0 0.7-1.6

0.8 0.2 8.1 2.0 2.7

Impeller Diameter, m 1.1 0.3 5.9 2.0 2.0

1.4 0.4 4.6 2.0 1.5

Use D=1.4 m Np=0.31 p N p× D 5 × ρ ) 1/3=0.315 rps= 19 rpm n=¿

Softening Required: Soften the water to 70 mg/L as CaCO3

TH=200+70=270 mg/L as CaCO3 CH=150 mg/L as CaCO3 NCH=270-150=120 mg/L as CaCO3 Lime requirement= 150+(70-40) +(70-40) =210 mg/L as CaCO3

NCHi=70-40=30 mg/L as CaCO3 NCH=120-30=90 mg/L as CaCO3

210 mg/L as CaCO3 of lime (

28 )=117.6 mg/L as CaO 50

90 mg/L as CaCO3 of soda (

53 50

)=95.4 mg/L as Na2CO3

Sedimentation Sedimentation, also known as clarification, is the process of removing very small particles, flocs, and precipitates. This process takes place in the settling tank (clarifier) represented in stage 3 in figure 1. The sedimentation occurs right after coagulation and flocculation to remove solids which have been created through the addition of chemicals in the softening process. Typically, the settling tanks are divided into four zones: the inlet zone, the sludge zone, the settling zone, and the outlet zone. The inlet and outlet zones should behave as transitional zones for the influent and effluent flows respectively. The sludge zone is the zone where the sludge material settles, and thus is prevented from getting mixed with the small particles in the settling zone. The efficacy of the of the sedimentation tank mainly depends on the behavior of the suspended particles that are to be settled in the sedimentation tank. The most two important factors in the design of the sedimentation tank are the geometry and the type of flow. As for the geometry, the most common two types of sedimentation tanks are rectangular or circular. On the other hand, the most common flow type in settling tanks is the horizontal flow. Figure 2 shows a rectangular settling tank profile with a steady horizontal flow.

Figure 2: Rectangular settling tank [4]

The design criteria of sedimentation tanks as per the Recommended Standard of Water Works [5] are listed as follows:

i. ii. iii. iv.

The depth of the settling tank should lie within the range of 8 to 16 ft. The detention time should be more than 4 hours. The velocity inside the settling tank should be less than 0.5ft/min. The bottom of the basin should be prepared such that dewatering of the settling basin is possible. The settling tanks should be designed such that sludge can be removed.

v.

No details about the number and size of the sedimentation tanks were provided. Thus, we will assume 15 rectangular clarifiers that are 50 m in length, 10 m in width, and 3.6 m in depth. The design of the settling tanks is illustrated down below: Flow rate=150000m3/day Detention time= volume / flow rate= (15 x 50 x 10 x 3.6)/150000=0.18 days= 4.32 hrs Horizontal velocity= Flow rate / Area= 150000 / (15 x 50 x 10)=20m/day= 0.05 ft/min

Filtration Filtration is the process in which small impurities and suspended particles are removed by the passage of water through a porous medium. A typical porous medium to filter out impurities is sand. The water passes through the sand filter, meanwhile all the impurities are stuck in the pores. In fact, there are too many different types of sand filters. Among the most common ones are slow sand filters, and rapid gravity sand filters. In this project, the use of rapid sand filters is proposed. The proposed filter material is silica sand. Also, the face velocity is assumed to be 200 m/d and the surface area of each filter is assumed to be 50 m2. which satisfies the Recommended Standards for Water Works [5]. A=

Q v

Where,

v= rate of filtration or face velocity, m/d = loading rate, m3/(m2.d) Q= flow rate onto filter surface, m3/d A= Total surface area of filter, m2 The total surface area=150000/160= 938m2 Number of filters needed= 938/50= 18.76= 19 filter

Biological Treatment

For all assumptions made, refer to table 1 in the appendix BOD0=100 mg/L Take k value to be 0.15 day-1 F/M=0.3 Aeration period is 6hrs, with BOD removal efficiency is 90% V= Q=6hr*6250m3/hr=37500 m3 Five activated sludge aeration tanks are operated in series. Each tank has the following dimensions: 15.0m wide by 80m long by 6.0m effective liquid depth. The plant operating parameters are as follows: F Q∗S = M V∗X

X=1333.3g/m3

Ks=60 mg BOD per L km=5 mg BOD per mg VSS per day Y=0.6

X=

θc × Y ×( So−S) θ(1+kd∗θc)

S=100-0.9*100=10 mg/L

assume kd=0.06

θc=9.8 d

where um=3

BODeffluent=3.42mg/L

Treatment of Nitrogen 

Nitrification – Aerobic condition:



Denitrification – Anoxic condition:

The denitrification requires a source of carbon, and methanol (CH 3OH) is often used for this purpose.

−¿ NO¿3 ¿ NH ¿ +¿ ¿ ¿4 ¿ ¿ ¿ ¿

[CH 3OH ] =10 mg/L

Treatment of phosphate Phosphate may be removed chemically or biologically. But the most practical methods use lime and alum. CaCO3

CO2 +CaO

CaO, is then slaked by adding H2O and forming lime: CaO + H2O

Ca2(OH)

The aluminum ion from alum precipitates as very slightly soluble aluminum phosphate: Al3+ +PO43-

AlPO4

Removal of Fecal Coliform A radio-frequency plasma system (RF) can be used to remove the microorganisms from water. Plasma generated by RF radiation can yield dynamic compounds that have a high oxidation potential and can kill microorganisms present in water (fecal coliforms and TSS etc.) [2]. The death rate of microorganisms is calculated using the first order equation:

where N is the number of microorganisms (MPN/100mL)

N(t)=Ne-kt Where k= 2.73h-1 for frequency equal to 3.7MHz t is taken between 1 to 2 hrs use t=1.5 hr N (1.5) =10000e-(1.5) (2.73) =166 microorganism Removal efficiency 98%

Appendix

Table 4 Parameter values for activated sludge systems using a completely mixed flow reactor

Table 5 BOD Removal as function of the process involved

References

[1]

K. Tomono and Y. Magara, "Environmental and health aspects of water treatment and supply," in Design of water treatment facilitiesParis, France: Eolss Publishers.

[2]

R. F. Weiner, R. A. Matthews, and P. A. Vesilind, Environmental engineering, 4th ed. ed. Amsterdam ;: Butterworth-Heinemann, 2003. [Online].

[3]

F. J. Thakor, S. N. Pandya, D. K. Bhoi, H. R. Dabhi, and N. B. Chauhan, "Water Quality Index (W.Q.I.) of Pariyej Lake Dist. Kheda - Gujarat," Current World Environment, vol. 6, no. 2, pp. 225-231, 2011.

[4]

D. Ryan, A. Gadd, J. Kavanagh, M. Zhou and G. Barton, "A comparison of coagulant dosing options for the remediation of molasses process water", Separation and Purification Technology, vol. 58, no. 3, pp. 347-352, 2008.

[5]

P. Enterprises. (2002). Design of Water Treatment Plants.

[6]

E. Great Lakes--Upper Mississippi River Board of State Sanitary and H. New York . Department of, Recommended standards for water works : adopted ... May 25, 1962. A report of Committee of the Great Lakes-Upper Mississippi River Board of State Sanitary Engineers on policies for the review and approval of plans and specifications for public water supplies. States represented: New York ... [et al.] January, 1953, Rev. ed. [Albany] :: New York State Health Dept., 1962. [Online]. Available: Google http://books.google.com/books?id=B8tQAAAAYAAJHathiTrust Digital Library, Full view http://catalog.hathitrust.org/api/volumes/oclc/4604687.html.

[7]

R. Desmiarti, A. Hazmi and Y. Trianda, "Fecal Coliforms and Total Coliforms Removal in Water Using Radio-Frequency (RF) Plasma System", Modern Applied Science, vol. 9, no. 7, 2015.