A massive project to collect wastewater is underway and it will collect effluents from central parts of Tehran and transfer it to the wastewater treatment center already constructed in the southwest of the capital.
More than 55% of the project has been completed and according to estimates it will be ready by the first quarter of the next year (starts March 21), said Masoud Reza Sameni, project executive director. The wastewater treatment center is the biggest in the country and has a capacity to treat sewage of residences comprising more than 3 million people.
So far only 20% of Tehran residences are connected to the wastewater network while the remaining goes underground or flows over the surface and creates environmental hazards including groundwater pollution, Alef News Agency reported.
The country’s average precipitation is one-third of the global average, while the per capita water consumption is three times greater than the world average per capita, said Mohammad Hosein Bazgir, general director of Tehran’s Department of Environment (DoE).
“At present the nation is facing a drought crisis and therefore measures should be taken to redress this problem. We should be able to treat wastewater and re-use it, which is a normal procedure all over the world. Sewage water is recycled even up to 16 times in some countries,” he noted.
Currently 50% of water consumed in Tehran comes from groundwater resources; and demand on groundwater is increasing day by day. “We should prevent water contamination,” he stressed. But as the water sources are mostly connected, therefore the contamination of groundwater spreads easily.”
Wastewater or sewage collection networks exist in eastern, southern and central parts of the city, but most parts of western and northern Tehran are not connected to the system.
If wastewater is not properly treated it can have dire consequences on the environment and human health. Other than drinking water contamination, it can cause harm to marine and wildlife habitats, oxygen depletion and restrictions on recreational water use as well as on fish harvesting.
Types of Treatment
Primary treatment of wastewater removes about 60 percent of suspended solids. This treatment also involves aerating (stirring up) the wastewater, to put oxygen back in.
Secondary (biological) treatment removes the dissolved organic matter that escapes primary treatment. This is achieved by microbes consuming the organic matter as food, and converting it to carbon dioxide, water, and energy for their own growth and reproduction.
Tertiary treatment can remove more than 99 percent of all the impurities from sewage, producing “an effluent of almost drinking-water quality.” The related technology can be very expensive, requiring a high level of technical know-how and well trained treatment plant operators.
Around the Country
Before the 1979 Islamic Revolution, wastewater treatment and reclamation was virtually non-existent in Iran. A strong effort was made in the 1990’s. In 2001, there were 39 wastewater treatment plants (WWTPs) with a total capacity of 712,000 m3 /day, treating the wastewater produced by a population of 3.8 million. The wastewater actually treated was around 130 million m3 (MCM) per year. Some 79 treatment plants with a total capacity of 1.917 MCM per day were under construction and 112 treatment plants with a total capacity of 1.590 MCM per day were being studied for completion by the year 2010, according to Massoud Tajrishy, Associate Professor, Environment and Water Research Center (EWRC) Department of Civil Engineering, Sharif University of Technology.
Now 129 municipal WWTPs cover 13 million inhabitants and generate more than 2.4 million cubic meters of treated wastewater per day. Municipal wastewater is mainly domestic and goes through secondary biological treatment. No further treatment is provided due to the high cost. Of the 129 plants, 51 are activated sludge, 41 facultative and 33 aerated ponds, 2 sequential batch reactor, 1 wetland, and 1 trickling filters.
Of the 3,547.8 MCM sewage produced in 2010, 1,162.3 MCM of wastewater was collected and only 820.7 MCM was treated. Of this treated effluent, 328.2 MCM was used for mainly irrigation. It is estimated that over 90% of the treated wastewater effluent from treatment plants across the country is reused in some way; however, much of it is mixed with freshwater before use, particularly in the suburban areas. The percentage of population served by drinking water systems, wastewater collection and wastewater treatment is now 99, 45 and 35 percent, respectively.
Rural Areas
For rural areas, the percentage of population served by drinking water system, wastewater collected and treated is 74 and 2 percent, respectively. These figures still have to improve dramatically before the end of the Fifth Five-Year Economic development Plan (2011-2016). There is no comprehensive national inventory of the extent of direct and indirect use of (un)treated urban wastewater, planned use of wastewater and even data regarding treated and non-treated wastewater used for irrigation.
Farmers have managed to use wastewater in irrigation for several decades. Since the early 1990s the general approach has been to treat the wastewater and either discharge it to the environment where it mixes with freshwater flows and is indirectly reused downstream, or merges with qanat’s or underground water systems, to irrigate restricted, relatively low-value crops. A significant number of indirect users of wastewater are unregulated and they withdraw treated wastewater from downstream points along a surface water source after discharge from the wastewater treatment plants. This volume is significant and will play an important role in meeting future demands for water in Iran.
