Comparison of Existing Techniques

Advantages Disadvantages
Reverse Osmosis (RO) 1. Can separate dissolved substances and water at room temperature, helping avoid dirt accumulation and pipe erosion.

2. Uses electricity, which means there is no need for a heat source. Any electric power source can be used. Using RO with an energy recycling system can reduce energy consumption.

3. Uses pressure to help purify the water, meaning it is easy to operate.

4. Fast to construct and takes up little land mass.

1. Membranes become blocked easily. Pre-treatment of water is needed to ensure higher quality. 2. Membrane contamination occurs easily, which affects service life, meaning that frequent membrane replacements will increase costs.
Multi-stage Flash (MSF) 1. High capacity, multi-usage and easy to operate.

2. Not affected by the quality of raw seawater.

3. Avoids issues that traditional distillation methods encounter.

1. Maximum temperature is around 120oC.

2. Uses high amounts of energy.

3. Fresh water output low.

4. Expensive to construct.

Multi-effect Distillation (MED) 1. High heat transfer but small heat surface area.

2. Low water quality required.

3. Easily adaptable technology.

4. Heat efficiency high.

1. High amounts of energy and heat required.

2. Equipment is very complicated and becomes blocked very easily due to dirt, effecting the equipment’s lifespan.

3. Low-temperature distillation (less than 100℃) can be used to resolve issue of dirt but water quality is inferior.

 

Vapor Compression 1. Compressed vapor can be used to reduce costs.

2. High thermal efficiency with little pre-treatment and maintenance required.

3. Easily transportable.

4. Low construction and operational costs and does not require cooling water treatment.

5. High fresh water output.

1. High heat is required otherwise the water quality is low. However, the vapour compressor is not heat resistant and high heat leads to dirt build up.

2. Energy usage is very high.

 

 

Table 4-2 Comparison of water quality

Method Water quality (Total Dissolved Solids (TDS))
RO 250-500ppm
Electrodialysis 0-250ppm
MSF 100-250ppm
MED 50-250ppm
Vapor Compression 100-250ppm
Tap water 40-250ppm