Monitoring the membrane scaling propensity of retentate in reverse osmosis desalination plants, IDA Journal of Desalination and Water Reuse
Year : 2014
Author : A. J. Karabelas, S. Mitrouli, J. Gragopoulos, A. Karanasiou, N. P. Isaias and A. S. Al Rammah
Scaling appears first in the tail spiral wound membrane (SWM) elements of desalination plants due to increased salt concentration in the retentate; in particular, membrane scaling starts locally when supersaturation of sparingly soluble salts (commonly CaCO3 and CaSO4) is attained. Reliable determination of the onset ofmembrane scaling in the tail elements (as a function of the local retentate physico-chemical properties) provides a threshold condition serving a dual purpose; i.e., it imposes essentially an upper limit to the degree of permeate recovery, and guides the selection of an appropriate anti-scaling program involving additives. Judicious use of the latter is important for reduction of desalination cost and environmental impact. The current practices for estimating incipient scaling within the spacer filled reverse osmosis (RO) membrane elements involve a great deal of uncertainty. In this study, slightly supersaturated in CaCO3 brackish waters were desalinated in a test section comprising a narrow gap spacer filled channel simulating local (constant flux) conditions in SWM modules.