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**Sedimentation Tank**

**Settling Velocity**

for d < 0.1 mm

Where,

V_{s}= The velocity of the settlement of particle or settling velocity in m/sec.

d = The diameter of the particle in the meter.

G = Specific gravity of the particle.

v = Kinematic viscosity of water in m^{2}/sec.

Y = Dynamic viscosity

δ = Density

where,

→ For laminar flow

R_{e}= Reynolds number

for transition flow.

for turbulent flow.- Newtons Equation for Turbulent Settling
- Modified Hazen’s Equation for Transition Zone

(i)

Where T = Temperature in^{ o}C.

(ii) Putting G = 2.65 for Inorganic Solids

(iii) Putting G = 1.2 for Organic Solids

**Critical Scour Velocity in Constant Velocity Horizontal Flow**

**Grit Chamber **(V_{H})

**Proportional Flow Weir**

Where,

B = Width of the channel.

V_{h} = Horizontal flow velocity.

C_{d} = Coefficient of discharge.

x and y are coordinates on weir profile.

**Parabolically or V-Shaped Grit Chamber Provided with a Parshall Flume**

**Parshall Flume**

Where,

W = Width of the throat in the meter.

Flow in (m^{3}/sec) through Parshall flume.

H_{a}= Depth of flow in the upstream leg of a flume of one-third portion in the meter.**Parabolic Grit Channel**

Where,

n = Discharge coefficients of the control section.

= 1.5 for partial flume.

= 1 for proportional flow weir.**(i)****Aerated Grit Channels****(ii) Detritus Tank**

**Skimming Tank**

- Detention Period = 3 to 5 minutes.
- Amount of compressed air required = 300 to 6000 m
^{3}per million liters of sewage. - Surface Area,

Where,

q = Rate of flow of sewage in m3/day.

V_{r}= Min. rising velocity of greasy material to be removed in m/min

= 0.25 m/min mostly.

**Vacuators**

Vacuum Pressure = 0 to 25 cm of Hg

For 10 to 15 minutes.

**Sedimentation Tank****(i)**Overflow rate

= 40000 to 50000 lit/m^{2}day for plain sedimentation.

= 50000 to 60000 lit/m^{2}day for sedimentation with coagulation.

= 25000 to 35000 lit/m^{2}day for secondary sedimentation tank**(ii)**Depth ~ 2.4 to 3.6 m.**(iii)**Detention time = 1 to 2 hour.**(iv)**width = 6.0 m**(v)**Length = 4 to 5 times width.**(vi)**Velocity of flow Vf = 0.3 m/min.**(vii)**

Where,V = Flow velocity

B = Width of the Basin

H = Depth of sewage in the tank.**(viii)****(ix)****Detention Time****(i)**

For rectangular Tank**(ii)**

for circular tank

Where

d = Dia of the tank

H = Vertical depth of wall or side depth- Displacement Efficiency (η)

**Trickling Filter**

**Conventional Trickling Filter or Low Rate Trickling Filter**

Where,

η = The efficiency of the filter and its secondary clarifier, in terms of % of applied BOD

u = Organic loading in kg/ha-m/day applied to the filter (called unit organic loading)**High Rate Trickling Filter****(i)**

Where, F = Recirculation factor

Recirculation ratio**(ii)**

Where,

Y = Total organic loading in kg/day applied to the filter i.e. the total BOD in kg.

Y/VF = Unit organic loading in kg/Ha-m/day

V = Filter volume in Ha-m.

% efficiency of single-stage high rate trickling filter.

(iii)

Where,

n' = Final efficiency in the two-stage filter.

Y' = Total BOD in the effluent from the first stage in kg/day.

F' = Recirculation factor for second stage filter

V' = Volume in second stage filter in ha-m.

Dunbar Filter

Surface loading = 25000 MI/m^{2}/day.

BOD removed = 85%

Sludge and its Moisture Content

The volume of sludge at moisture content P_{1}%

The volume of sludge at moisture content P%

**Sludge Digestion Tank**

**When the change during digestion is linear.****(i)**

Where,

The volume of digestion in m^{3}.

Raw sludge added per day (m./day)

Equivalent digested sludge produced per day on completion of digestion, m^{3}/day.

Digestion period in the day.**(ii)**

with monsoon storage

Where,

T = Number of days for which digested sludge (V_{2}) is stored (monsoon) storage)**When the change during digestion is parabolic.****(i)**

without monsoon storage**(ii)**

without monsoon storage

**Destruction and Removal Efficiency (DRE)**

Where,

W_{in} = The mass fill rate of one POHC (Principal organic Hazardous constituent) in the waste stream.

W_{out} = Mass emission rate of the same POHC present in the exhaust emission prior to release to the atmosphere.

**Aeration Tank (ASP)**

- Detention period,

Where

V = Volume of the tank in m^{3}.

Q = Quantity of wastewater flow into the aeration tank excluding the quantity of recycled sludge (m^{3}/day) - Volumetric BOD Loading or Organic Loading, (U)

Where,

QY_{o}= Mass of BOD applied per day to the aeration tank through influent sewage in gm.

V = The volume of the aeration tank in m^{3}.

Q = Sewage flows into the aeration tank in m^{3}.

BOD_{5}in mg/lit (or gm/m^{3}) of the influent sewage.

Where,

F/M = Food (F) to Microorganism (M) ratio QY_{o}= Daily BOD applied to the aeration system in gm.

Y_{o}= 5 day BOD of the influent sewage in mg/lit.

Q = The flow of influent sewage in m3/day.

MLSS (Mixed liquor suspended solids) in mg/lit.

V = The volume of the Aeration Tank (lit).

M = X_{t}V = Total microbial mass in the system in gm.- Sludge Age (θ
_{c})

Where,

X_{T}= The concentration of solids in the influent of the Aeration Tank called the MLSS i.e. mixed liquor suspended solids in mg/lit.

V = Volume of Aerator

Q_{w}= The volume of waste sludge per day

The concentration of solids in the returned sludge or in the wasted sludge (both being equal) in mg/lit.

Q = Sewage inflow per day.

X_{E}= The concentration of solids in the effluent in mg/lit. - Sludge Volume Index (S.V.I)

Where,

X_{ab}= Concentration of suspended solids in the mixed liquor in mg/lit.

V_{ab}= Settled sludge volume in ml/lit.

S.V.I = Sludge volume index in ml/gm. - Sludge Recycle and Rate of Return Sludge

Q_{R}·X_{R}= (Q + Q_{R}) x R

Where,

Q_{R}= Sludge recirculation rate in m^{3}/day.

X_{t}= MLSS in the aeration tank in mg/lit.

X_{R}= MLSS in the returned or wasted sludge in mg/lit.

S.V.I = Sludge volume index in ml/gm.**(i) Specific substrate utilization rate**

α_{y}= 1 for MLSS and 0.6 for MLVSS, k_{e}= 0.66**(ii) Oxygen Requirement of the Aeration Tank****Where,****(iii) Oxygen Transfer Capacity (N)**

Where,

N = Oxygen transferred under field conditions in kg O_{2}/k.wh (Or MJ)

N_{s}= Oxygen transfer capacity under standard conditions in kg O_{2}/kwh (or MJ)

D_{s}= Dissolved oxygen-saturation value for sewage at operating temperature.

D_{L}= Operation D.O level in Areation tank usually 1 to 2 mg/lit.

T = Temperature in^{o}C

α = Correction factor for oxygen transfer for sewage usually 0.8 to 0.85.

**Oxidation Ponds**

- Depth → 1.0 to 1.8 m.
- Detention period → 2 to 6 weeks.
- Organic loading → 150 to 300 kg/ha/day.
- Under hot condition → 60 to 90 kg/ha/day.

Under cold conditions. - Length to width ratio = 2
- Sludge Accumulation = 2 to 5 cm/year
- Minimum depth to be kept = 0.3 m.

**For Inlet Pipe Design**

Assume V = 0.9 m/s

Assume flow for 8 hrs.

**For Outlet Pipe Design**

Dia of outlet = 1.5 dia of the inlet pipe

**Septic Tank**

- Detention time = 12 to 36 hr.
- Sludge accumulation rate = 30 lit/cap/year.
- Sewage flow = 90 to 150 lit/capita/day.
- Cleaning period = 6 to 12 months
- Length to width ratio = 2 to 3 m.
- Depth = 1.2 to 1.8 m
- Free board = 0.3 m.
**Volume of Septic Tank**= (Sewage flow x Detention time) + (Sludge accumulation rate) x Clearning rate

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