Water Journal : Water Journal April 2011
membranes & desalination refereed paper 100 APRIL 2011 water technical features Abstract Osmoflo has two operating reverse osmosis (RO) plants that treat hypersaline groundwater in remote mining sites. This type of water has proven more difficult compared to seawater, due to it containing problematic species. The feed water deviated from the design specifications during and after commissioning. Pre-treatment process changes were made to manage the deviations. The experience highlights the importance of continuously monitoring water quality to maintain plant availability. Introduction Over 30% of water used in Australia comes from groundwater sources (National Groundwater Commission 2008). Most of the groundwater consists of high total dissolved solids (TDS) and is not fit for human use. Some groundwater sources are classified as hypersaline, meaning the TDS is 35,000-100,000 mg/L. The high TDS areas are shown in Figure 1 (Plazinska, 2007). Figure 1: Groundwater basins in Australia. Osmoflo has two operating RO plants treating hypersaline groundwater to produce potable water and water for fire protection systems for remote mining operations. One site is the Ginkgo Mine, 40km west of Pooncarie in far west New South Wales (near Broken Hill), and the other is at the Jacinth-Ambrosia (JAA) Mine, 200km from the Port of Thevenard near Ceduna, South Australia. This paper discusses the challenges of desalinating hypersaline groundwater from a water quality perspective. Through hard work and persistence the challenges were overcome to deliver the proper solution for the clients. Background The Ginkgo RO plant is a build, own and operate (BOO) plant for Bemax Resources. It is capable of producing 2.1ML/d of treated water using two trains (plus one standby train) for site process water and potable water requirements. The plant was designed as direct feed from the borefield to prevent ferrous iron oxidation. Pre-treatment only included five micron cartridge filters for colloidal fouling mitigation and antiscalant dosing for sulfate scaling prevention. The design incorporates a horizontal multistage high pressure pump with energy recovery turbocharger and a single pass RO configuration capable of 40% recovery with 10 vessels by seven membranes for each train. Post-treatment includes pH adjustment via caustic dosing and chlorination via sodium hypochlorite. The plant was commissioned in November 2005 and was designed to be operated remotely with site attendance only for monthly preventative maintenance and ad hoc corrective maintenance. The JAA project for Iluka Resources was a design and construct contract and commenced in September 2008 with a temporary demonstration plant rated to 86kL/d, and then a permanent plant rated to 173kL/d of potable water. The original design of the temporary plant incorporated caustic dosing, aeration, chemical oxidation, coagulation, multimedia filtration (MMF), five and one micron cartridge filtration (CF) and antiscalant dosing as pretreatment. Through further laboratory-scale and on-site testing, the pre-treatment design was changed to direct feed (keeping feed water anoxic), acidification, coagulation (optional), MMF, five and one micron CF and antiscalant dosing. In addition, a high pH permeate flush on shutdown was also incorporated to ensure all iron particles are flushed off the membranes. The revised design was adopted on the permanent plant. The RO configuration included a horizontal multistage high pressure pump with energy recovery turbocharger and a two-pass RO with H Le, T Pritchard, N Palmer DESALINATION OF HYPERSALINE GROUNDWATER FOR REMOTE MINING SITES Figure 2: The Ginkgo plant in far west NSW.
Water Journal March 2011
Water Journal May 2011