M.B. Kiaei, Roya Mansouri, Rahshahr Engineering, Tehran, Iran
Iran is among the world’s driest countries. This combined with increasing industrialization has led the country to turn to the private sector for the development of desalination plants to meet increasing demand for drinking water and quality industrial water.
With an average annual rainfall of 270mm (one third of the world’s average), Iran is classed as one of the arid and semi-arid regions of the world. The total rainfall in the country is estimated to be 416 billion m3 of which only 117 billion m3 is potentially available to use as surface and ground water. With another 13 billion m3 of surface water flowing into the country, this figure reaches 130 billion m3. Adding the recycled water and water exchanges, the final volume of resources is 159 billion m3.
Currently, the volume of regulated water in the country’s dam reservoirs is over 25 billion m3, but the total water uptake from surface resources is around 41 billion m3, and from ground water around 46 billion m3. The nation has a negative balance of 5 billion m3 of water, but with the possibility of tapping into lime and ground basins, it is possible to add 4 billion m3 of water to the country’s potential.
According to surveys, the population of Iran has increased from 19 million in 1956, to the present 65 million. Accordingly, the water availability per capita in Iran has decreased from 6800 m3 in the year 1956, to 2100 m3. According to estimates, the nation’s population, despite all the control measures, will reach 92 million by the year 2020. This will reduce the water per capita to 1410 m3 per year, putting Iran on the brink of a water stress situation.
The present share of urban water is 4.7 m3 billion, rural water accounts for 800 m3 million, industrial water 1 billion m3, and agricultural water is 80 billion m3. Since Iran faces the ever increasing problem of urban water supply, the government is implementing long distance water transfer plans; a trend which will continue in the future.
Examples of such plans are the water transfer line from Zayanderood to the city of Yazd, with a pipeline of 335 km and an annual capacity of 90 million m3 of water; and the Zarinerood to Tabriz line with a length of 177 km and annual capacity of 150 million m3.
Considering the water shortage problem, the difficulties of water transfers to satisfy urban demands, the spread of pollution to water resources – especially the present urban resources and also acute limitation of freshwater resources in many cities and reduction of per capita water in relation to population increase – it is necessary to take into account the proper methods of consumption management, water supply management and using desalination and water reuse technology. The role of the private sector also has to be considered.
Plants in Kish Island
In the southern parts of Iran and most Islands located in the Persian Gulf, the best available technology for supplying drinking water is desalination. Economic assessments show that for small capacities i.e. around 10 000 m3/day, the best desalination technology is seawater reverse osmosis (SWRO).
In recent times, most water and power projects in Iran have been undertaken by the private sector. The first private water supply project was implemented in Kish Island.
Kish Island is located in the Persian Gulf in the south of Iran. The island occupies an area of about 90 km2 with a population of 15 000. Seawater desalination plays a major role in the supply of drinking water to the Island. Therefore, a multi-effect distillation (MED) plant (with five units) with a nominal capacity of 10 000 m3/day (each unit has a capacity of 2000 m3/day) and a SWRO plant ( three units) with a nominal capacity of 3000 m3/day, desalinates the seawater from the Persian Gulf to reliable, quality drinking water allowing people to drink from the tap.
With water demand on the island increasing, in 2001 Kish Water and Power Company (KWPC) decided to invite contractors to implement a desalination project. Subsequently, KWPC agreed a SWRO BOT (build, operate and transfer) contract with the private sector to build a plant with a capacity of 5500 m3/day (one 500 m3/day unit + five 1000 m3/day units). Engineering and construction took two years and commissioning started in March 2003.
The plant consists of the following process sections:
- Pre-treatment, conventional raw water treatment and conditioning, fine filtration.
- Reverse osmosis process: Horizontal multistage centrifugal with turbine recovery and reverse osmosis unit in two stages.
- Post-treatment: Post chlorination and pH adjustment
After achieving successful privatization on Kish Island especially in operation and maintenance, other plants have started investigations in this field.
The price of water is 65.5 US cents per m3 (without power charge) and the plant is exempted from tax payments. After 15 years this plant will be transferred to KWPC.
In the southern parts of Iran and most Islands located in the Persian Gulf, the best available technology for supplying drinking water is desalination
SWRO in south Pars
The latest SWRO BOT contracts were carried out in the Assaluyeh region. Assaluyeh is located in the province of Bushehr, in the south of Iran. It is an arid area, where temperatures can reach 50ºC with a maximum relative humidity as high as 88 per cent. There is also very little rainfall – the average annual precipitation is 180 mm.
Also, Iran’s largest non-associated natural gas field is south Pars in Assaluyeh region. This gas field was first identified in 1988 and originally appraised at 128 trillion ft3 (tcf) in the early 1990s. Subsequent estimates were that south Pars contains around 280 tcf of gas, of which a large fraction and over 17 billion barrels of liquids would be recoverable.
Developments associated with this gas field means the Assaluyeh region is rapidly emerging as the largest industrial zone in Iran. In addition to south Pars, the 48 tcf north Pars development may also be part of Iran’s long-term gas utilization plans.
Development of south Pars is Iran’s largest energy project and has already attracted more than $20 billion in investment. Gas from south Pars could be exported by liquefied natural gas (LNG) tankers as well as by various planned pipelines.
Large scale projects including gas process industries, petrochemical plants such as olephine, aromatics, methanol, and other products such as polymer industries and relevant developments have created a vast growing market for utilities such as desalinated water in the area.
Based on estimations and current studies, the amount of desalinated water required will be around 180 000 m3/day for the next 10 years. According to feasibility studies, the best available technology for producing drinking and industrial water in Assaluyeh is through desalination.
In the first step of supplying drinking water, South Pars Economic Energy Zone (SPEEZ) held a bid for a SWRO BOT contract with capacity 10 000 m3/day.
After evaluation, SPEEZ selected two companies to install two plants, each with a capacity of 10 000m3 /day .
The contract was signed in March 2004 and the engineering and construction will take a total of 16 months. The first 5000 m3/day unit will come on line 10 months after contract close and the next unit, six months later. SWRO desalination units consist of the following main components:
- Sea water intake: the sea water will be pumped from the sea through transfer pumps.
- Pre-treatment packages for SWRO units consist of: chlorination, multimedia filtration (with backwash system and filtered water reservoir), activated carbon filtration (optional), acid dosing package, sodium metbisulphate dosing package, and an anti-scale dosing package.
- SWRO units with their accessories containing: cartridge filters, high pressure pumps, pressure vessels, membranes, CIP system and all pipes, valves, fittings, instruments and control.
- Post-treatment package for production of drinking water containing: chlorination as post-disinfection, chemical dosing for pH adjustment and chemical dosing for water hardness adjustment.
The average price of water from the desalination plant is expected to be 41 Euro cents /m3 (without power charge). The plant is exempted from tax payments. It was also agreed that after a period of 20 years these plants will be transferred to SPEEZ.
Following the successful privatization project on Kish Island and the second one underway at south Pars, other plants are being considered.
Kish Water and Power Company and Qeshm utility are contemplating further expansion projects with desalination capacities of 10 000 m3/day and 5000 m3/day, respectively.
Meanwhile, a further 16 000 m3/day is estimated to be needed at south Pars and this will likely be undertaken by the private sector.