Desalination as a Clean Water Source in Indonesia

Indonesia as the world’s biggest archipelago has one of the longest coastlines in the world. Stretched from Sabang to Merauke, Indonesia’s coastline is measured at minimum of 54.000 km, with some claims it to be as long as 108.000 km. The number is high enough to make Indonesia at least among the top 4 countries with the longest coastline in the world. With such a high exposure to sea water, desalination becomes one of the feasible ways to produce clean water.

Desalination is a process of making saline water into fresh water by the simple means of removing the salt from the water body. The separation process from saline water will make a stream of fresh water, and a stream of brine (high concentrated salt water). A water is categorized as “saline“ if the concentration of salt or other minerals (quantified by the concentration of Cl-) is more than 1.000 ppm (parts per million), while sea water is approximately at 35.000 ppm. Fresh water, on the other hand is below 150 ppm salt concentration.

How to do desalination?

In principle we can obtain fresh water through desalination by two process, distillation and filtration. Distillation has been used for thousand years by Greek sailors to produce water from sea water, while the Roman used filter clays to separate the salt away from water. Until today, we can still find the modern approach to these two concepts of desalination.

In distillation-based process, fresh water obtained through methods of evaporation and trap the condensate as the fresh water product. One of the modern applications is the Multi-stage Flash (MSF). An MSF operates by “flashing” a portion of water into steam in multiple stages of what are essentially counter-current heat exchangers. MSF are widely used and contributes to about 26% of all desalinated waters in the world. The downside is that MSF operates on high cost and requires special conditions to achieve its economic feasibility, mainly compared to Reverse Osmosis (RO) technology. The other popular distillation-based technologies are MED (Multiple-effect Distillation) and VCD (Vapor Compression Distillation).

In filtration-based process, fresh water obtained through the means of “filtering” the salt from the water using membranes. The leading process for desalination in terms of installed capacity and yearly growth is filtration-based Reverse Osmosis (RO). Reverse Osmosis is the process of forcing a solvent from a region of high-solute concentration through semi-permeable membrane to a region of low-solute concentration by applying pressure in excess of the osmotic pressure. The application in desalination is the separation of pure water from sea water by pressuring the high salt concentration side, causing fresh water to emerge from the other side. This process requires high pressure and therefore high energy usage. But with the expanding market and improving technology, the efficiency of RO is getting better over time.

Why do we need desalination?

Desalination is a relatively high-cost way to produce clean water in comparison to collecting and treating from fresh water sources (rivers, lake, springs, groundwater, etc.), which Indonesia is very abundantly blessed with. However, lack of infrastructure for treating water makes a lot of households and even business to use groundwater. With the expanding population, especially in heavily dense area such as Jakarta, also plummets the quality of the groundwater used. In Jakarta, it is estimated that the ground level is sinking by 10 cm per year, part of it due to approximately 10 million deep wells for extracting groundwater all around Jakarta.

The other problem is the quality of the rivers which the clean water supply heavily relies on. Due to the low water quality of the rivers, the cost for treating raw water into clean water also increases. Adding to that fact is the expensive piping installation costs and maintenance to distribute especially to those regions far from the water treatment plants.
Geography is another problem for water distribution. Some small islands are too far to reach from the mainland islands with piping and therefore forced to buy water at a very high price. These leads to a dependant on surface waters, mostly collected from rain.

Currently, in addition to using WWTP (Wastewater Treatment Plant) technology as an effort to produce clean water, the desalination process itself is also widely used in factories throughout Indonesia to meet their clean water needs. This process is also used on many islands, albeit in a smaller capacity. Its use is still limited due to high-cost facilities and maintenance, although innovations in membranes and technology have made it cheaper over the years. But despite all these obstacles, desalination of seawater as a source of clean water is important to reduce pressure on the use of surface and ground water.

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