Oasys forward osmosis concentrates in China

Massachusetts-based Oasys Water has claimed its recent contract to supply a forward osmosis brine concentrator to a fossil-fuelled power plant in China to be a world first.

The membrane brine concentrator (MBC) system will treat 650 m³/d of wastewater created in flue gas desulphurization (FGD) in which sulphur oxides are stripped chemically from smokestack gases at the 1,320 MW coal-fired Changxing Power Plant in China’s northern Zhejiang province. Oasys said the system was the first commercial zero liquid discharge (ZLD) system to apply an osmosis-driven process.

The MBC system incorporates Oasys’ forward osmosis process to further concentrate reverse osmosis reject from a total dissolved solids of 60,000 mg/l to about 280,000 mg/l. This is the first commercial power plant application of the technology in a ZLD project Oasys said. But Oasys’s forward osmosis process has been used to concentrate oil field brines in Texas’ Permian Basin and shale gas tracking liquid in Pennsylvania’s Marcellus shale.

FGD has become mandatory for coal-fired plant in China since the introduction of stricter air pollution regulations and estimates suggest the installed FGD capacity in the country could double by 2020. But with growing water scarcity the need for FGD wastewater treatment has grown Oasys said.

Oasys’ chief executive officer, Jim Matheson, said that he was excited about his company’s prospects for capturing a significant share of the resulting ZLD market. “The Changxing project is a promising model to showcase the merits of our MBC technology,” he said.

Oasys’ MBC uses a proprietary, high-salinity ammonia bicarbonate draw solution and a patented semi-permeable membrane,. The salinity gradient between the draw solution and the reverse osmosis concentrate generates the osmotic pressure to drive water across the membrane while rejecting up to 99% of the dissolved solids.

The diluted draw solution is re-concentrated continuously in a recovery system where draw solution solutes are removed by thermolysis at 70°C and the resultant low- TDS water is returned to the RO feedwater. This lowers the RO system’s operating pressure which reduces the treatment train’s energy consumption and capital cost.

The winning bid was evaluated against six other offers, including those from three of the largest brine concentrator evaporator suppliers said Oasys.