Water Journal : Water Journal April 2011
conference reviews regular features 80 APRIL 2011 water feed salty water through a reversed RO membrane. The trick is to economically recycle compound X from the 'draw solution', leaving the fresh water as product. There are many possible compound Xs. The most studied has been ammonium bicarbonate, which can be decomposed by heat into the gases, which can then be recombined into the draw solution. However, there are practical problems. A list of 500 possibles has been filtered down to 13 for further investigation and organics, thermolytics and magnetics are being investigated. In concluding her address, Dr Childress acknowledged that it was unlikely that either technology could be applied in the same way as SWRO. However, both offer potential as hybrid systems. An example in reclamation of wastewater would be FO rather than microfiltration (MF) in a redesigned bioreactor as a pretreatment for RO. She drew attention to a pilot plant that has been operating for over a month but, to date, has needed only one backwash a week. FO is also being investigated in Reno for concentration of sludge dewatering centrate. Reconcentration of RO reject brine in inland sites where Zero Liquid Discharge is desirable is another possible application. Wherever scaling is a possibility, FO may be a better choice than MD. Commercial applications of forward osmosis are being pursued by Osmem, which has recently taken over Hydration Technology Innovations. Another in the field is Oasys, which is a spin-off from a Yale University research team, with innovative membranes. Professor Tony Fane is also working on FO-based systems in Singapore. In her second presentation on day two of the conference, Dr Childress introduced the audience to a very old concept, the idea of producing power from where the river meets the ocean. The theoretical difference in osmotic pressure is equivalent to a 225m waterfall (the opposite of the high pressure pump needed for SWRO). Could this be economically harvested by using RO in reverse, she asked. The system is called Pressure Retarded RO. However, between theory and practice there are numerous snags, not the least being concentration polarisation. After optimisation by mathematical modelling, they built a small plant, which on her photo seemed to be half the size of a container. It produced only enough power to boil up a cup of coffee, but caused frenzy in the media. However, a Norwegian company, Statkraft, is taking up the considerable challenge, which will necessitate the development of a tailored membrane. Emerging Trends and Technologies The second keynote presenter was Professor Gary Amy, Director of the Water Desalination Research Centre at the King Abdullah University of Science and Technology, Saudi Arabia, after being Professor of Water Supply Engineering at the UNESCO Institute in Delft. The title of his address neatly outlined the content: Emerging Trends and Emerging Technologies for Using Seawater and Wastewater to Produce Water that is Drinkable. He provided an overview of recent advances, drawing particular attention to the technologies previously discussed by Dr Childress. He also noted the increasing interest in direct potable re-use, though expressing a preference for indirect potable re-use, an easier option to "sell" to communities, especially those in the Middle East where cultural beliefs will influence acceptance. He alluded to his interest in soil aquifer treatment (SAT), a dimension of managed aquifer recovery where the soil is used as an environmental buffer capable of adsorbing chemical contaminants and microbial species. In his second address Professor Amy expanded on the nature of soil aquifer treatment and its application. He outlined the amount of work that has gone on in Europe and Australia in the EURECLAIM project as well as in other institutes, particularly in Israel. He argued that well-designed and maintained SAT can practically eliminate all pharmaceuticals, with the exception of the anti-epileptic carbamazepine, and can remove proteinaceous material, thus reducing bio-fouling of membranes. Professor Amy expressed ambivalence about the groundwater recharge and recovery process used at Water Factory 21, Orange County. In his opinion it would be better to inject the partially treated effluent into the aquifer, recover it by more distant tube-wells and then apply RO and disinfection before delivering it for potable use. He backed up this assertion by referring to the use of bank- and dune-filtration, practiced for over 50 years for the huge cities on the Rhine, which would once have been one of the most industrially polluted rivers in the world. In such systems, 5-log removal of micro-organisms is typical and there has been little problem with trace chemicals. In much the same vein, he recommended natural systems for pre-treatment of seawater, by ignoring open intakes in favour of beach wells or even sea-bed infiltration. Work has shown that the concentration of biopolymers is drastically reduced by even a few metres of suitable soil. For energy minimisation Professor Amy applauded the system being used in London, where the intake is from a tidal estuary and timed to make the most use of the outgoing tide where river PHOTO: NEIL PALMER PHOTO: NEIL PALMER First keynote speaker Professor Amy Childress. Second keynote speaker Professor Gary Amy.
Water Journal March 2011
Water Journal May 2011