Category: WasteWater

Sludge Digestion Tank

The decomposition of complex organic matters in sludge by the biochemical reaction created by anaerobic bacteria is termed as sludge digestion. The sludge can be digested by a sludge digestion tank or an Imhoff tank.

⇛ The sludge digestion tanks are generally circular in shape with a flat or hopper-shaped bottom. The tanks are usually covered at the top to retain heat and odours and for collecting the sludge gas.

⇛ The floor of the tank is given a slope of about 1:1 to 1:3. Fresh raw sludge is usually introduced within the middle third section of the tank.

⇛ For taking out sludge liquor, two or more outlets are provided at different levels. One outlet is provided at the bottom to collect the digested sludge for its disposal. In some tanks, scum breaker arms are provided which brake scum.

⇛ Most of the tanks are provided with stirring equipment for thorough mixing of the sludge.

Read Also:

Sludge Volume Index (S.V.I)

Sludge Drying Bed

Combined Gravity And Pumping System

In this system, the treated water is pumped and stored in an elevated reservoir, from where it is supplied to the consumer by the action of gravity.

Thus, this method combines pumping as well as gravity flow. This system is fairly reliable.

Read more:

Function of Storage Reservoir

3 Types of Sewage Pumps And their advantages & Disadvantages

Separated Sewer System And Their Advantages and Disadvantages

5 Function Of Storage Reservoir

The storage reservoirs are generally provided in the distribution system to store clear treated water before it is distributed to the consumer.

The following 5 functions of the storage reservoir are:

1. They help the pump to run at a uniform rate.

2. They provide the facility of storage of water to meet the fluctuating demand for water.

3. They maintain constant pressure in the distribution mains.

4. They serve as storage for emergencies.

5. They make the design and construction of treatment units and distribution systems economical.

Read Also:

Dead End System

Grid Iron System

Grid Iron System- And their Advantages & Disadvantages

Grid Iron System

⇛ Grid iron system is one method of the layout of distribution pipes. This system is also known as interlaced system or reticulation system.

⇛ In this system, the mains, sub-mains, and branches are interconnected with each other. Thus, this system provides free circulation of water through the pipelines.

⇛ Cut-off valves are provided at each junction point. This is suitable for well-planned towns and cities.

Advantages of Grid Iron System

The advantages of grid iron system are:

1. In case of repairs, a very small portion of the distribution area will be affected.

2. This system provides free circulation of water through the pipelines. Hence, it is not liable for pollution due to stagnation of water.

3. The head loss is minimum.

4. It provides sufficient supply during fire fighting.

Disadvantages of Grid Iron System

Disadvantages of grid iron system are:

1. This system requires more length of pipelines and the greater number of cut-off valves.

2. Its construction is costlier.

3. The design calculations are complicated and difficult.

Read Also:

Dead End System

Ring System

Dead End System – And Their Advantages and Disadvantages

Dead End System

Dead end system is one method of the layout of distribution pipes. This method is also known as a tree system.

It consists of one supply main from which sub-mains are taken. From the sub-mains, the branch lines are provided from which service connections are given to the consumers.

The dead-end system of the layout is adopted in localities which have developed in a haphazard manner.

Advantages of Dead End System

The advantages of the dead-end system are:

1. The discharge and pressure at any point in the distribution system can be easily calculated.

2. The design calculation is simple and easy.

3. Lesser number of cut-off valves is required in this system.

4. Laying of pipes is easy and simple.

5. It is cheap and can be extended or expanded easily.

Read Also: Ring Water Distribution System.

Disadvantages of Dead End System

The disadvantages of the dead-end system are:

1. During repairs, a large portion of the distribution area is affected.

2. There is numerous dead end in this system, which prevent the free circulation of water.

3. The water may be polluted at the dead end due to its stagnation.

4. It gives limited supply during the fighting.

Read Also:

Grid Iron System

9 Steps Of Laying Of Sewer Pipes

7 Requirements of a Good Sewer Pipe

Rainfall Intensity And Their Formula

Rainfall Intensity

The rainfall intensity is the rate at which it is falling. It is expressed in cm/hr. It can be determined with the help of automatic rain gauges.

Formula Of Rainfall Intensity

The intensity of rainfall is greater when shorter periods are considered while it is lower when large periods are considered. The intensity of rainfall (p) in mm/hr is given by the following general formula:

p = 254a / (t+b) mm/hr Where, t = Duration of storm in minutes, a and b are constants.

The following value of a and b are considered adequate.

a = 30 and b = 10 when t is 5 to 20 minutes.
a = 40 and b = 20 when t is 20 to 100 minutes.

Duration of Rainfall

The duration of rainfall is the time for which rain falls with given intensity.

Frequency of Rainfall

The frequency of rainfall is the number of times it falls.

Determination of Quantity of Sanitary Sewage

What is Sanitary & Storm Sewage, Dry And Wet Weather Flow

2 Soil Fittings – Water Closets & Urinals

Soil Fittings

Soil fitting is one type of sanitary fittings. The following 2 soil fittings (water closets, urinals) are described below:

1) Water Closets(W.C)

A water closet is a sanitary fitting designed to receive human excreta directly. It is connected to the soil pipe by means of a trap.

Sometimes, the room in which it is installed is also referred by the term water closet. Two types of water closets are commonly used these days. They are:

Indian Type Water Closet.
European Type of Water Closet.

The Indian-type water closet (W.C) has a squatting pan 450mm to 675mm in overall length and 400mm to 500mm in height.

The pan is fitted with a P or S trap, which is then connected to the soil pipe. It is usually made of porcelain. The trap has an opening for fixing an anti siphonage pipe or a vent pipe.

The pan has a flushing rim to spread the flush water. This W.C. requires at least 10 litres of water for proper flushing. This type of W.C. is largely used in Indian houses.

The European-type water closet (W.C) has a porcelain pan 500mm to 600mm in overall length and 350mm to 400mm in height.

It is one-piece construction in which the pan and trap are not separate. A cover is provided at its top.

The pan has a flushing rim to spread the flush water. This type of W.C. requires less area than the Indian type. This type of W.C. is largely used in the houses of Western countries and in high-class buildings and hotels in India.

2. Urinals

A urinal is a sanitary fitting designed for the collection and disposal
of urine. They are made of glazed earthenware or vitreous china clay. Two types of urinals are commonly used these days. They are:

Bowl or Basin Type Urinals
Stall or Slab Type Urinals

The bowl-type urinal is used in private buildings and the stall-type urinal is adopted for the public building.

A third type urinal, called squatting plate type is used specifically in ladies toilets. The usual centre to centre spacing of units is kept about 60 cm.

Read Also:

Ablution Fittings

Types of Trap

Pit Privy

Laying Of Sewer

4 Ablution Fittings -|| Flushing cisterns|| Wash Basin|| Bath Tube and Sinks

4 Ablution Fittings

Ablution fittings are a type of sanitary fitting. The following are the 4 ablution fittings(Flushing cisterns, Wash Basins, Bath Tube & Sinks).

1. Flushing Cisterns

Flushing cisterns are installed above the water closet or urinal for flushing them. It is usually made of cast iron or porcelain or plastic. It is operated by chain or handle. The discharge capacity of cisterns are usually 5, 10, or 15 liters.

A flushing cistern may either be of the siphonic type or flat-bottom type. The siphonic type of cisterns is widely used nowadays.

2. Wash Basin

A wash basin is a sanitary fitting used for washing hands or brushing teeth etc. It is made of glazed earthenware or vitreous china clay or steel or aluminium etc. In plan, the basins may have rectangular, square, circular, oblong, etc. shapes.

It is provided with one or two water taps. An outlet pipe with gratings is fitted with it for discharging wastewater. The wash basin may be supported either on brackets fixed on a wall or on pedestals.

3. Bath tube

It is a rectangular basin made of R.C.C. finished with marble chips or terrazzo. They may also be made of cast iron or steel. Bathtubs are provided in bathrooms for the purpose of bathing.

It is provided with one or two water taps, one outlet pipe and one overflow pipe. The wastewater from the bathtub is discharged into a waste pipe through a trap.

4. Sinks

A sink is a rectangular basin provided in kitchen or laboratory. It is used to clean utensils etc. It is usually made of glazed earthenware or marble or stainless steel etc.

The sink has an outlet pipe which is fitted with a waste pipe through a floor trap. The mouth of the outlet pipe is provided with grating of brass or nickel to prevent the entry of coarser materials into the waste pipe. The height of the top of the sink from the floor should be 90 cm.

Read Also:

Soil Fittings

Pit Privy

Laying Of Sewer

Sludge Drying Bed

Relation Between B.O.D (Biochemical Oxygen Demand) And Time

At certain temperature, the rate of deoxygenation is assumed to be directly proportional to the amount of organic matter present in the sewage at that time.

dLt / dt = – K.Lt ………….(1)

Relation Between B.O.D (Biochemical Oxygen Demand) And Time

Relation Between B.O.D And Time

[Note: Minus sign indicates that the with the passage of time the value Lt of decreases]

Where, Lt = Organic matter present in sewage after t day from the start of oxidation in mg/lit.

t = Time in days , K = Rate constant.

Now find out the relation between B.O.D and time?

Integrating equation (1), we get

ഽdLt / Lt = ഽ- K. dt

or,

log Lt = – K.t + C ………..(2)

Where C is constant of integration .

When t = 0, Lt = L (say)

Now, substituting these in equation (2) we have,

log L = – K. (0) + C

Or, C = log L

Substituting this value of C in equation (2) we get

log Lt = -K.t + log L

Or, log (Lt/ L) = -K.t

Or, 2.303 log10 (Lt/ L) = -K.t

Or, log10 (Lt/ L) = – 0.434 K.t

Or, (Lt/ L) = (10)^(-0.434 k.t)

If Yt represents the total amount of organic matter oxidized in t days (i.e B.O.D), then we have

Yt = L- Lt = L [1- (Lt/ L)]

Or, Yt /L = L- Lt = 1- (Lt/ L)

Or, Yt /L = L- Lt = 1- (10)^(-0.434 k.t)

Or, Yt = L [1- (10)^(-0.434 k.t) ]
Read Also:

Chemical Oxygen Demand (C.O.D) And Their Test
Laying Of Sewer
Sludge Drying Bed
Biochemical Oxygen Demand (B.O.D) And Their Test

3 Difference Between Biochemical (B.O.D) and Chemical (C.O.D) Oxygen Demand

3 Difference Between B.O.D & C.O.D

Following are the 3 differences between B.O.D (Biochemical oxygen demand) and C.O.D (Chemical oxygen demand) are described below:

B.O.D (Biochemical oxygen demand)	C.O.D (Chemical oxygen demand)
1. The amount of oxygen required to carry out the biological decomposition of dissolved solids in sewage under aerobic conditions at standard temperature is known as biochemical oxygen demand.	1. The amount of oxygen required to carry out the chemical decomposition of organic matters in sewage is known as chemical oxygen demand.
2. It is generally less than C.O.D.	2. In general, C.O.D of sewage is higher than B.O.D.
3. It indicates the amount of biologically active organic matter present in the sewage.	3. It indicates the amount of biologically active as well as biologically inactive organic matter present in the sewage.