RO pre-treatment - injecting a little chemical control and management

Abstract

The successful longevity of RO plants and membranes depends critically upon both the design and operation of the pre-treatment systems and the optimisation of membrane management programmes especially in the larger plants. The construction of large RO plants by traditionally “Evaporation” orientated engineering companies has often resulted in a concentration on the engineering properties but with an underestimation of the fundamental importance of chemical and biological processes to the successful design and operation of RO plants treating both brackish and sea waters. The complex and often not well understood interactions between the modified chemical, physical and biological constituents of feed waters, which so often are the cause of membrane fouling episodes, lack the inherent robustness, accuracy and familiarity of the more accustomed engineering variables of pressure, flow and temperature. This paper describes how successful feed water pre-treatment design, control and membrane management depends on understanding the complex physical, chemical and biological interactions occurring at each plant unit process within an overall context of process water chemistry, to minimise fouling problems and prolong membrane longevity.