TARHOKAR Engineering CO 
Contact: (+98 21) 28429513 - 28429831


The Human or urban wastewater is created through daily human activities such as washing, cooking, bathing, and so on, and it is very dangerous due to the high organic and microbial weight. The use of the sewerage is transferring the wastewater to the treatment.

The water can be recycled to the environment with the help of the sewerage and sewerage treatment plant. The slope and size of the pipeline and the manhole induction site have a great importance in designing gravity sewerage and calculating the discharge rate. In general, by accurately calculating these, the speed of the transfer of sewage into the sewerage can be controlled. The speed below the permissible limit causes the solid particles to settle and create a fetid smell and its high velocity creates a turbulent stream and releases gases in the wastewater.

The Design, implementation and installation of a variety of transmission lines, sewerage and pumping stations and wastewater sewer storage tanks is performed by the TARHOKAR engineering company in different sizes and in the form of an EPC contractor. The design of the sewerage is simulated with the CAD Sewer engineering software, as well as the regulations of the planning and budgeting organization.

Sewerage manhole

Early definitions of the design of Sewerage

Refer to the sewerage systems in residential complexes, including urban or rural, for example; sanitary wastewater, bathing, washing of utensils and clothes and kitchens, are called sanitary or human wastewater. The collection of sanitary and human wastewater is one of the most important problems of urban and rural life due to the high levels of contamination and pathogenic microorganisms. This waste water can lead to the transmission of many diseases to humans, and its proper disposal and treatment by the sewerage is considered as one of the basic infrastructure in every urban complex, today.

Basically, the sewerage is being constructed in order to transfer all human wastewater in cities to the wastewater treatment plant.
 Sanitary sewage has a lot of suspended solids, fats and particles due to its production nature. These particles and fats can cause clogging or blockage of the pipeline in the sewerage. In addition, there is the possibility of anaerobic conditions and the production of H2S gas, which is very stinky, because of the high organic content of sanitary wastewater.
 The most important issues to consider about the designing gravity sewerage include the following:

1 - Discharge or amount of sanitary wastewater which produced in each of the residential homes.
 2- The height difference between the treatment and the sewerage sites.
 3. The location of the city or village and the sites which considered for the sewerage pipeline.
 4. Calculating the amount of water discharged in the city or village.

A gravity sewerage can be designed with taking into account all of the above. In this network, the speed of sewage transfer within the pipeline is very important. This speed depends primarily on the flow rate and, secondly, on the slope of the line and the size of the pipe.
 The transmission speed of the sewage in the network should be designed in such a way that the solid particles contained therein do not have the time required to settle.
On the other hand, this speed should not be too high to convert the flow of fluid which is in the pipeline into turbulence, which causes the exhaust of fetid gases to flow through transmit and sewerage network.

Calculating the amount of discharge in the design of sewerage

 Initially, Discharge or the amount of sanitary wastewater which is produced in a transmission network depends on the city's population as well as on the population growth rate, because every person generates between 110 liters and 150 liters of sewage every day because of his daily works. We can calculate the discharge power of wastewater by using this number and taking into account the city's population rate in the coming years, for example, 21 to 31 coming years.

The table of sewage production in urban communities of Iran

Type of usage Liter for per person in a day Liter for per person in a day (average) 
Bathing 25 to 50 38 
Washing the clothes 10 to 20 15
Washing the dishes 5 to 15 10
Restroom (w.c and toilet) 20 to 30 25
Cooler and Air conditioner 2 to 5 3
Others 3 to 5 4
Collection 68 to 135  101
Source: Ministry of Energy Journal

In addition, the amount of runoff discharge caused by rainfall, ground water, or industrial and semi-industrial activities in the suburbs, as well as the amount of non-evaporated water which may be added to the sewerage must added to the amount of discharge.

In addition to the above, it should be taken into account that sewage which is produced in urban areas is at peak at some hour of the day and it comes at least at some hours.  For example, the maximum amount of wastewater production is from 07:00 to 9:00 in the early hours of the day in the morning or in the early hours of the night between19:00 and 22:00.

As a result, in order to accurately measure the maximum discharge flow rate, the peak of wastewater production is added and the sewerage is selected based on this.

The slope and size of the pipeline in the design of the sewerage

 The important issue in designing the sewerage and transportation network is its transmission speed. The choice of this speed is important because the sewerage is designed and implemented gravity and therefore the gradient of the ground is used to transfer. In some places where the gradient of the ground is not suitable, the pipeline is buried in greater depth. At the same time, the slope of the design of the sewerage should always be considered at run time.

 Another important parameter is the size of the pipeline in the sewerage. After the branches are collected from urban areas by pipelines, they enter the water main pipes and have transferred to the wastewater treatment plant.
Whatever the tube has a larger size, the greater flow rate can be transmitted by it. In this way, we can calculate the exact size of the pipe, by taking into account the slope of the line and the discharge of Sewage which collected in the network.

Sewerage pipe line

Wastewater sewerage road map

Due to the fact that residential areas are very tumultuous and gas, water and electricity cables, as well as metro and other channels are being excavated in the ground, the most appropriate route in the gravity sewerage should be carefully selected. In addition to the scheme  which mentioned above, a number of manholes should be designed and implemented at intervals along the transmission lines in the network so that they can be used for coiling or network drainage during  the operation. These manholes are also used where there is a difference in height or the angle difference between the inlet and outlet pipes.
The genus of pipelines in the sewerage:
 The economic components of the sewerage plan are also involved in choosing the pipe material in addition to the technical and engineering issues. The sewerage system in our country is being implemented as a polyethylene carotype pipeline, now. This pipe has a high pressure, so it is suitable for burial in urban areas. In addition, like all polyethylene pipes, it has excellent resistance to corrosion and acidic or alkaline conditions. Lightweight and easy to operate, are another advantage of this type of pipe.
Typically, the use of concrete or metal pipes is more cost-effective for large sizes or water main pipes.
In others, concrete channels have been collected due to the economic cost of replacing network pipes.

 Sewerage psiphon

The Results of using sewerage

 Today, due to the decrease in rainfall, the increase in urban population, as well as the growth of industry and agriculture, our country has faced drought more than before. One way of coping with droughts and lack of water experienced in many developed countries is to reuse wastewater or waste water and return it to the environmental cycle.

 In our country, there have been used absorbent wells for the purpose of wastewater discharge from the city. But these days research has shown that this method, in addition to causing severe soil contamination, has also damaged groundwater.

High concentrations of nitrate ions in many underground sources are proof of this:
1- Prevention of the contamination transmission and the growth of microorganisms in the urban environment
 2-No contamination the soil and water sources by sewage
 3 - Possibility of returning wastewater to the environment cycle and front the drought.
 4- Ability to generate electricity and fertilizer from sewage.