**3. Environmental impact of desalination**

Fresh water shortage and demand are expected to increase in the coming few decades. The development and utilization of alternative water resources such as seawater desalination are becoming inevitable. On the other hand, desalination is very energy intensive process and has negative impact on the environment. The discharge of concentrated brine, hamper the life of marine eco systems. Waste discharge from desalination processes is considered to be a significant challenge that is becoming increasingly important. High energy consumption is considered the most influencing factor that inhibits growth of seawater desalination. Currently, most desalination processes are driven by energy obtained from fossil fuel. With such dependence on fossil fuel based energy sources, the increase in seawater desalination results in gas emissions that pollute the environment. Solar energy based desalination process is considered to be a promising method to alleviate the environmental impact of water desalination and also provide a sustainable source of potable water. This approach significantly mitigates the dependence on fossil fuel.

Large amount of concentrated brine discharge from saline water desalination plants is considered to be unpleasant waste. Marine life is strongly affected by the discharge of the concentrated brine. Concentrated brine is not only salt concentrated, but also contains chemicals such as anti-scaling agents from pre- and post-treatment. This results in high salt concentration in the area near brine discharge point. Brine disposal is a problem that challenges all desalination technologies. Brine discharged from membrane based desalination such as reversed osmosis is more concentrated than the brine discharged from thermal distillation plants. However, brine discharged from thermal distillation plants exits at a relatively high temperature compared with membrane based distillation. This influences the marine life such that only some plants or marine animal can withstand the high temperature near the outlet of thermal distillation plants. Marine life is also influenced by the intake of the seawater for the desalination plant. When a large amount of seawater is drawn from the sea, marine organisms and algae are sucked into the intake which cause a disturbance to the eco-system.

Many methods are currently used for brine disposal from desalination plants. Brine can be discharged to sea or river, discharged to solar ponds, or injected to deep saline aquifers. The discharge of brine to the sea or ocean is the least expensive method compared to other method. When brine is discharged to the sea, it tends to sink at the bottom of the sea because it has higher density than the seawater. A typical standard used in brine discharge is to diluted the brine with seawater to reduce its salinity before being discharged to sea. Furthermore, operating at lower recovery rates reduces the salinity of the brine. Brine is discharged at high depth of seawater which typically have a strong current. This reduces the detrimental effects of brine on the marine life. Brine discharges to a solar pond or the injection to a deep saline aquifer is more expensive method than sea discharge. These solar ponds and saline aquifers are typically located away from the desalination plant which require a long pipeline for transportation. This method has drawbacks because it may increase the salt in the soil and also increases the salinity of the ground water if linear is not used under the solar pond. The utilization of solar pond for brine disposal require a very large surface area, and it carries the risk of contaminating ground water.

technologies such as MSF, MED, and VC distillation. Although, this technology is still in the development stage, as demonstration plants have experienced operational difficulties. A labscale experimental investigation of an integrated solar pond of 70°C with 10 flash desalination

**Figure 12.** (a) Concentrated solar powered mechanical vapor compression unit coupled with MED, (b) concentrated

water [50]. Solar pond technology integrated with MSF desalination plant has potential to be more cost effective than any other solar powered desalination technology [51]. At present, additional research is required to demonstrate long-term reliability of solar pond powered

/d of distilled

units operating at 0.9 bar has been confirmed to produce approximately 15 m3

solar powered thermo vapor compression unit coupled with MED [47].

thermal desalination technologies.

144 Desalination and Water Treatment
