Diagnostic analysis of RO desalting treated wastewater

Abstract

Diagnostic analysis of reverse osmosis membranes that are fed with Western Treatment Plant (WTP) recycled water was investigated by both thermodynamic calculations and laboratory experiments, in order to predict the feasibility of RO desalting for WTP. The thermodynamic calculations suggested that RO recoveries of 80-85% were feasible with careful control of feed water pH and the use of chemical additives such as antiscalants and chelating agents, it also predicted the major minerals of concern to be silica, calcium fluoride, calcium carbonate, and calcium phosphate. Following the thermodynamic simulations, diagnostic laboratory experiments were undertaken. The experiments showed that the major contributor to scale formation was indeed calcium phosphate and possibly another calcium based compound, which was strongly suspected to be calcium carbonate. Based on previously published literature that indicated antiscalants did not substantially decrease the scaling effect of calcium phosphate and laboratory tests that indicated controlling the pH to 6.4 in the feed water dramatically reduced scaling formation, it was suggested that the feed water could be controlled by pH adjustments only. Inter-stage pH correction was suggested as an optional technique to enhance the overall water recovery to above 95%.

In situ structural and functional characterization of reverse osmosis membranes using electrical impedance spectroscopy

“…Therefore, the development of non-destructive real time monitoring for early detection of scale formation is vital for the successful management of membrane scaling. The industry practice for evaluating membrane performance or an anti-scalant is to compare permeate flow and salt passage under identical conditions, through standardising/normalizing industrial data [5][6][7][8][9][10]. The limitation associated with the permeate flux decline curve is the inability to distinguish between flow decline due to scaling and decline simply due to the increase in osmotic pressure [11].…”

Scaling and fouling in membrane distillation for desalination applications: A review

“…Calcium phosphate, another potential scale, is a non-alkaline scale that has frequently occurred in wastewater treatment and in RO membranes [19,66,67,68]. Phosphate often exists in water supplies as phosphoric acid, which is relatively weak and which dissociates through several stages; significant concentrations of phosphate ion do not occur until the pH becomes relatively basic.…”

Inorganic fouling control in reverse osmosis wastewater reclamation by purging carbon dioxide

“…There are many indices for predicting scale formation, but usually, the selection of saturation index depends upon the nature of feed water. The successful inhibition of inorganic scale at low pH was also determined by some other researchers with different saturation indices (Tzotzi et al 2007;Zach-Maor et al 2008;Tharamapalan and Duranceau 2014).…”