TOOL FOR DESIGN OF STP BASED ON ANAEROBIC AND FACULTATIVE PONDS 25
Capacity Average Flow
MLD
Guidance: Yellow cells are the input information to be suitably filled. Green cells are to be reviewed and modified/updated if need be. Red letters to be suitably corrected. Ground level at STP Site at Inlet chamber
209. 209.5 5 Mtr Mtr
Drain level at outlet at chainage 11325
206. 206.2 2 Mtr Mtr 215. 215.68 68 Mtr Mtr
IL of Out fall Sewer(1000 Sewer(1000 mm) with with slope 1 in 1100 at STP Average Flow
25 MLD
Average Flow
0.29 M /sec
Peak Flow :
3
Peak Factor
2 .2 5
3
0.65 M /sec
Peak Flow : Minimum Flow
56.25 ML MLD
Factor
Minimum Flow
2
12.5 MLD 3
0.14 M /sec
DESIGN OF INLET CHAMBER Peak Flow Peak Flow Detention time Volume required Liquid depth taken Area
56.2 56.25 5 MLD MLD 3
0.65 M /sec 15 Sec 9.77 9.77 cum cum 0.8 0.8 Mtr 2
12.2 12.21 1M
Width taken
3.5 3.5 Mtr
Length
3.5 3.5 Mtr
Provide free board to ensure that raw sewage will not overflow even when the 1000 mm out fall sewer run full
0.8 0.8 Mtr
DESIGN OF COARSE SCREEN Peak Flow
0.65 0.65 M3/s M3/sec ec
Coarse Screen Opening
50 mm
Depth of water in screen
0.9 0.9 Mtr. Mtr.
velocity through screen
0.7 0.7 M/se M/secc
Area of screen Angle of inclination with the horizontal
0.93 0.93 M2 45 degr degree ee
Sin (Angle of Inclination)
0.71
Free Board
0 .6 0 m
Length of screen
2.12
Width of opening
1.03 1.03 mtr mtr
No of opening
21 nos
Number of bars
20 nos
Let width of each bar be
10 mmx7 mmx75 5 mm
Total width of channel Let width of each side be
1230 1230 mm 50 mm
Total width of channel: Provide
1331 mm
Openings
22
No of bars Size of Coarse Screen-Width
21 1.3 m
Size of Coarse Screen-Length Velocity in Channal u/s of Screen Velocity through Screen Head Loss No Clogging Velocity when 50% clogging Head Loss when 50% clogging
4 0.54 0.65 0.006 1.29 0.070
m
m m/sec m
DESIGN OF FINE SCREEN 0.65 M3/sec
Peak Flow Nos of screen(Each for handling peak flow) Velocity(taking) through screen, Assume
2 Nos 0.8 M/sec 0.81 M2
Area Depth of flow taken Hence width of opening
0.7 Mtr. 1.16 Mtr.
No of Openings
78
No of Bars
77
Width of Channal
1928
Angle of inclination with the horizontal
75 degree
Clear opening between adjacent bars of screen
15 mm
Bars thickness of screen
10 mm x50mm
Taking width of screen Nos of opening will be
2000 mm 80 Nos
Nos of bars(10 mm thickness)
79 Nos
Free Board
0.6 m
Sin (Angle of Inclination with horizontal)
0.966
Inclined length of Screen Length of chamber before screen
1.35 m 1.5 m
Total Length of chamber Total width of channel
2.85 2 Mtr.
Velocity in Channal u/s of Screen
0.47 m/sec
Velocity through Screen
0.77 m/sec
Head Loss through screen
0.019 m
Velocity through screen when 50% clogged
1.542
Head Loss when 50% clogging
0.110
Size-2.85 (L)x2(W)x1.7(D)
DESIGN OF GRIT CHAMBER GRIT REMOVAL SYSTEM
Two grit removal tank (1 w +1 S) each capable of handling peak flow, will be provided. They are designed to remove grit particle of size of 0.15 mm size and above with a specific gravity of 2.3 -n
Q/A=VS x n/(1-η) -1
Where-η-Desired efficiency of removal of grit particle VS -settling velocity of minimum size of grit particle to be removed Q/A--Design surface overflow rate applicable for grit chamber to be designed n-an index which a measure of the basin performance Here η value taken Say Here VS value taken
75 % 0.75 1225 m3/m2/day
Here n value taken-1/8(for very good performance)
0.13
Hence surface over flow rate(Q/A)=(Vs*n)/(((1-η)^-n)-1) Say This Q/A value has to be reduced to allow for deposition of sand during sand strom by Then design overflow rate 3/
Peak flow(m day) Hence area required for peak flow Each side of square grit chamber Hence provide tank length Hence provide tank Width Detention time taken is Depth of tank will be However in order to provide adequate depth for the grit scraping mechanism, increase to
3 2 806.42 m /m /day
810 m3/m2/day 10.00% % 729 m3/m2/day 56250 (m3/day) 77.16 m2 8.78 9.00 9 1 0.48 0.9
mtr. mtr. mtr. minute mtr. mtr.
This gives detention time is 1.87 minute the detention time of 1.87(slightly higher) minute is immaterial for mechanically cleaned grit removal tank Hence size of grit removal chamber is 9 x9x0.9 Flow height above, H 0.12 m weir,Q=(2/3)*Cd*L*H^1.5*((2g)^.5),Cd=.6,L=9
DESIGN OF CHANNEL FROM GRIT CHAMBER TO DISTRIBUTION CHAMBER Peak flow velocity taken
0.65 M3/sec 0.8 M/sec
Depth taken
0.81 m2 0.7 mtr.
Then width of channel will be
1.16 mtr.
Area required
DESIGN OF ANAEROBIC POND No of Anaerobic ponds to provide flexibility in O&M of these ponds
3 Nos
Each handling flow of(25000m3 per day/3)
8333 (m3/day)
say
8333 (m3/day)
Volume of anaerobic pond V=Li xQ/λ Li-Raw sewage BOD(1000 XB/q)
300 mg/l
8333 (m3/day)
Q- average flow λ- volumetric BOD loading(Range between 100-400 gm/m3/day) λ=20T-100(as per MEAFNRCD) 0
T=mean temperature in coldest month in C (The manual by DANIDA ENRECA suggests T as mean in coldest month or quarter. In quarter it is 15.55)
13.89
hence λ is
177.8 kg/ha/day
Hence Volume of tank(V)
14061 m3 1.69 day
Detention time Detention time of 2 days or more is desirable to achieve sufficient BOD removal
2.00 day 16667 m3
Hence Volume of each tank (V) Hence Volumetric BOD loading(λ) is
150 gm/m3/day
BOD removal efficiency(in %)=2T+20
47.78 %
For liquid depth
4 mtr. 4167 m2
Area at mid depth Length shall be L=2B Hence mid depth width B=(area/2)
1/2
45.6 mtr.
Hence mid length L-
91.3 mtr.
Side slope of pond is 1V :2.5 H
2.5 mtr.
Depth for Sludge
1 mtr.
bottom below Mid depth
2.5 mtr.
Free Board
1 mtr.
Top of embankment above mid depth
3.5
Hence total top length(L)
108.8 mtr.
Hence total top width(W)
63.1 mtr.
Area at top Hence total bottom length (L)
6869 m2 78.8 mtr.
Hence total bottom width(W)
33.1 mtr.
Area at Bottom
2611 m2
Provide three anaerobic pond each of 108.8mx63.1m at top surface and 78.8mx33.1 m surface at bottom
DESIGN OF FACULTATIVE POND Nomber of Tanks
2 No
Average flow in each tank
12500 cum/sec
BOD enter at Facultative pond after 2 days detention period at anaerobic pond
156.66 mg/l
0
Minimum mean monthly temperature c Volumetric BoD loading:λs=350 x(1.107-0.002T)
(T-20)
this value of BOD loading rate
13.89 219.67 kg/ha/day
recommended as MEAFNRCD( Refer DANIDA) λs=60(1.099)^T (Refer Jodhpur design)
222.64
λs=20 T-120 λs=20T-60 λs=375-6.25L, where L-latitude(28.73), Refer manual
157.80 217.80 195.44 kg/ha/day
Correction for above MSL=(1+(3 x10-5)xE)
where E is elevation in meters=
210
1.0063
then λs is Influent BOD to facultative pond
194.21 kg/ha/day 156.66 mg/l
value of λs is considered recommended as MEAFNRCD
219.67 kg/ha/day
From equation (as per world bank paper) facultative mid depth area can be calculated as(A) A=10 x Li x Q/λs A-facultative area at mid depth in m
2
Li-influent BOD concentration in mg/l, Li is BOD to be removed Effluent to be used for restricted irrigation as such 100 effluent BOD is ok however on safe side design for effluent BOD of
75
Li=
81.66
then A is
85356 M2
Divide the area in two ponds(area of each facultative pond) at middle of tank
42678 M2
Take L=2B 1/2
146 M
Then L is at mid depth
292 M
Then width B=(A/2)
Hence area at mid depth is Adopt liquid depth Adopt depth for sludge Adopt Free Board
42678 M2 1m 0.5 m 1m
Total Depth of tank
2.5
Area at bottom embankment slope H/V
2.5
Length at bottom
285.9 m
width at bottom
139.8 m
Hence area at bottom is -
39978 m2
Length at top including 1.0 mt free board
298.4 m
width at top including 1.0 mt free board
152.3 m
Area at top including 1.0 mtr free board-
45456 m2
Volume of pond V=h/6(S0+4S1+S2) h-height(liquid depth)
1.5 m
S0-area at top
45456 m2
S1-area at mid water depth S2-area at bottom Hence V of each tank is
42678 m2 39978 m2 64037 m3 5.12 days
Then detention time of each tank is Total detention time of anaerobic + f acultative pond is
7.12 days
Total area of ll afacultative ponds at top
90912 m2
Total area of all anaerobic ponds at top
20608 m2
Total area
111520 m2
Assuming footprint area of units as % of total area
60.00% %
Hence total area is-
185867 sqm
Hence total area in hectare taken as
18.59 hactare 19
Total BOD removal in facultative pond
81.66 mg/l
Hence Effluent BOD is
75 mg/l
Sludge Storage andCleaning requirement Population equivalent at 108 LPCD waste
231481
For anaerobic pond sludge volume For anaerobic pond sludge volume Sludge volume provided in all anaerobic ponds Cleaning required period say
0.04 9259.26 8692.08 1.07 1
cum per capita/year cum/year
cum years years
Distribution tank for Anaerobic Pond Consider one anerobic pond not working, Flow height above weir, H ,Q=(2/3)*Cd*L*H^1.5*((2g)^.5),Cd=.6,L=1.2 Q per tank Assume weir length H Allow free fall of Total Head loss Free Board
0.325520833 1.5 0.24 0.1 0.34 0.30
cum/sec m m m m m
Pipe from distribution tank to anaerobic pond inlet Flow when one tank not working Pipe dia velocity of flow Length of pipe head loss flq^2/10*d^5 entry/exit loss Total Losses
0.33 0.75 0.74 60.00 0.027 0.042 0.068
cum/sec m m/sec m m m m
Overflow Weir for Inlet to Anaerobic Pond Flow when one tank not working Length of weir Flow height above weir, H ,Q=(2/3)*Cd*L*H^1.5*((2g)^.5),Cd=.6 Allow free fall Total Head loss
0.326 cum/sec 3 m 0.15 m 0.1 m 0.25 m
Pipe from Anaerobic Pond Inlet to Anaerobic Pond Peak Flow when one tank not working Pipe dia velocity in pipe Length of pipe head loss flq^2/10*d^5 entry/exit loss Total Losses
0.326 0.750 0.74 40.00 0.018 0.042 0.059
cum/sec m m/sec m m m m
Overflow Weir for Inlet to Facultative Pond Average flow when one tank not working Length of weir Flow height above weir, H
0.145 cum/sec 3 m 0.09 m
Allow free fall Total Head loss Half flow from one anaerobic pond, Length of weir
0.1 m 0.19 m 1.50 m
Pipe from Facultative Pond Inlet to Facultative Pond Average flow when one tank not working Pipe Dia velocity of flow Length of pipe head loss flq^2/10*d^5 entry/exit loss Total Losses
0.145 0.600 0.51 40.00 0.011 0.020 0.031
cum/sec m m/sec m m m m
0.145 3 0.09 0.1 0.19
cum/sec m m m m
0.145 0.600 0.51 40.00 0.011 0.020 0.031
cum/sec m m/sec m m m m
0.145 0.600 0.51 40.00 0.011 0.020 0.031
cum/sec m m/sec m m m m
0.289 0.80 0.58 160.00 0.041 0.025 0.066
cum/sec m
Overflow Weir for Outlet to Facultative Pond Average flow Length of weir Flow height above weir, H Allow free fall Total Head loss
Pipe from Facultative Pond outlet to Outlet Chamber 1 Average flow Assume pipe dia velocity of flow Length of pipe head loss flq^2/10*d^5 entry/exit loss Total Losses
Pipe from outlet Chamber 1to outlet Chamber 2 Flow Assume pipe dia velocity of flow Length of pipe head loss flq^2/10*d^5 entry/exit loss Total Losses
Pipe from Outlet Chamber 2 to Sewage Pump House Flow Pipe dia velocity Length of pipe head loss flq^2/10*d^5 entry/exit loss Total Losses Alternately Provide channal Velocity Area Taking, Width=2*Height, H= Width Slope required, V=1/n*R^.67*S*.5, n=0.013, S= say
Sewage pumping for Irrigation and Disposal
1.0 0.289 0.4 0.8 0.000090 0.1
m m m m m/sec sqm m m in 1000
Flow Flow in LPS say Head Pump working Pump stand bye Flow in each pump pump efficiency Pump KW Motor KW Say Total No of pumps working + stand by Delivery Pipe velocity Pipe Area for combined flow of two pumps Pipe dia Say Pipe dia of delivery for each pump, velocity Pipe Dia Say Suction Pipe dia
0.289 289.35 290.00 15.00 2.00 2.00 145.00 60.00 35.54 39.09 40.00 4.00 0.75 0.387 0.702 750 2.25 0.29 300 250
cum/sec LPS LPS m No No lps % KW
25 30 521 4 12.88 13.00 531
MLD minutes cum m m m cum
m/sec sqm m mm m/sec m mm mm
Sump for Effluent pumping station flow Sump storage Sump Capacity Sump depth Sump Dia Provide Sump Dia Sump Capacity Provided
Free Board F=(log10 A)^.5-1, F=
1.16
Wave height,H, (g*H)/V^2=.0026((gFe/V^2)^0.47, Fe is fetch,V is wind velocity, H=
0.06
Faecal Coliform Removal Ne/Ni=1/(1+ktθa)(1+Ktθf), Ni=5*10^7, Ne= Kt=2.6(1.19)^(T-20), T=13.89, kt=
2798412.9 0.898
Helminth Removal R % removal=100(1-0.14 Exp(-0.38 θ)) R % removal as per the table in book by DANIDA
99.33 % 98.6 %
