CSG Water Management
Where properly managed and treated, CSG water can be reused in a range of different ways including irrigation. Some of the uses for CSG Water includes:
- Coal washing
- Dust suppression
- Landscaping and re-vegetation
- Industrial and manufacturing operations
- Research and development
- Domestic, stock, stock intensive and incidental land management
Water Treatment and Management Systems
In order to fulfil the requirements of the CSG Water Management Policy, companies are required to investigate options for beneficial reuse of the CSG water and to treat the water so that it is fit for purpose.
While the level of salt in CSG water varies depending on the source location, CSG water treatment processes typically involve desalination, and the most commonly used desalination technique is reverse osmosis (RO).
Reverse Osmosis involves forcing the saline water under pressure against a semi-permeable membrane. The semi-permeable membrane allows water molecules to pass though, leaving larger molecules such as salt, behind in a higher concentration. The concentrated brine (called “reject”) is then collected for further processing (Figure 3).
Another way of conceptually thinking about a semi-permeable membrane is that it is like a flyscreen door. The screen will allow air to freely pass through the screen in both directions, but will reject larger objects, such as leaves and insects. RO is similar, in that the water passes through the very small holes of the membrane leaving behind the salt and other compounds.
What are the Water Treatment Steps?
There are a range of steps involved in the treatment of CSG water (Figure 4). Key steps involve the collection and storage of the raw CSG water, filtration to remove solids, removal of beneficial ions for later re-use, removal of the main salts through desalination and then water amendment and/or blending to ensure an appropriate final water quality for the intended use:
Raw Water Holding Ponds – primarily used for water storage prior to the processing of the water in the RO treatment plant. The ponds create a buffer for storing raw CSG water in the event that the water treatment plant is required to recirculate water for quality improvement, or if there is an issue with the beneficial use outlets (e.g. flood events). The ponds are also a starting point to monitor water quality parameters before water is sent to the RO plant.
Solids Removal – Prior to entering the RO plant, the raw water is first filtered to remove large particles and foreign material. This includes any soil and sediment that may be in the water as well as algae and other foreign material.
Ultra Filtration (UF) – The water is forced under pressure through fine filters. The water must be clean and free from all foreign material that would clog the RO membranes. At this stage the water is clean and free from all solids, but still is saline.
Ion Exchange (IX) – a process used to soften the water and remove calcium (Ca++) and magnesium (Mg++) before the water passes through the RO membranes. Calcium and magnesium extracted at this stage are often added back into the water after desalination to adjust the Sodium Adsorption Ratio (SAR) for compatibility with certain soil types, making the water more suitable for irrigation.
Reverse Osmosis (RO) – the main desalination process, responsible for the removal of the salts from the water. A reverse osmosis filter has a pore size of approximately 0.0001 micron and removes 90-99% of salt from the water.
VSEP or Vertical Separation Enhanced Process is an extremely simply and effective method of further dewatering the RO concentrate stream. With over 400 installations world wide, the VSEP systems are a simple but very effective brine squeezing system.
While small amounts of some chemical compounds may pass through the RO membranes, the DEHP has assessed the environmental and human health impacts and has placed limits on their release to the environment. The CSG companies have strict environmental reporting requirements and must report any non-compliance with the licensed release limits.