The use of speciation and X-ray techniques for determining pretreatment steps for desalination

A major cost factor in the construction of desalination plants is the feed water pretreatment section. Pretreatment is necessary to prevent fouling of membranes (in electrodialysis or reverse osmosis) or heat exchange surfaces (evaporation). Various laboratory techniques are described which enable small-scale tests to be undertaken in order to determine acceptable pretreatment sequences and feasible water recoveries. A variety of effluents were subjected to evaporation or small scale reverse osmosis tests. Precipitates produced were identified by X-ray techniques. In some cases, the identification of the precipitate was, in itself, sufficient to indicate the cause of fouling, in another, identification enabled various pretreatment sequences to be modelled using chemical equilibrium computer programmes. A combination of conventional chemical analysis, X-ray techniques and computer modelling has proved successful in determining acceptable pretreatment sequences.