Salts removal from RO concentrate during NEWater production

• Main Author: Ng, Shiong Yong.
• Other Authors: Lim Teik Thye
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/53384
• Institution: Nanyang Technological University

In the process of NEWater production, one important step of producing NEWater involves the use of reverse osmosis (RO) to purify the water by removing the undesirable contaminants from the water. This process involves the use of a semi-permeable membrane with very small pores which only allow very small molecules like water molecules to pass through. As a result, contaminants such as bacteria, viruses, heavy metals, nitrate, chloride, sulphate, disinfection by-products, aromatic hydrocarbons, pesticides etc. cannot pass through the membrane. Hence, NEWater is RO water and is free from viruses, bacteria and contains negligible amount of salts and organic matters. However, the product water recovery rate from this process is far from the target of 93% as it is hindered by membrane fouling propensity and energy cost. This study will aim to help achieve that target by seeding the RO concentrate with calcium hydroxide, Ca(OH)2, or calcium carbonate, CaCO3. This step will precipitate the salts from the water before the RO process, helping reduce the potential of membrane fouling and in turn contribute to higher product water recovery rate. Experiments were set up to find out which chemical is the better seed material. Firstly with the use of a synthetic RO concentrate, it was found out that Ca(OH)2 was a better seed material due to its ability to raise the pH of the RO concentrate faster. Using Ca(OH)2 as seed material in the synthetic RO concentrate, tests like pH, conductivity, turbidity, total organic carbon (TOC), ICP and UV-Vis spectrophotometer were done to investigate if Ca(OH)2 did remove salts from RO concentrate. After that the experiments were carried out on actual RO concentrate collected from a NEWater Plant in Singapore. Results have shown that Ca(OH)2 is a relatively good seed material but there are still certainly some solutes which are unable to be remove.