Fouling assessment in a municipal water reclamation reverse osmosis system as related to concentration factor

Abstract

A study was conducted to assess possible formation of inorganic scaling and organic fouling in a municipal wastewater reverse osmosis (MWRO) system with microfiltration membrane treated secondary effluent as feed water. Results indicate that reject from the MWRO process can be supersaturated with sparingly soluble phosphate salts and hydroxide compounds that may form scales on the reverse osmosis (RO) membrane. The degrees of saturation, however, are much less than that in the seawater RO (SWRO) process. Therefore, a concentration factor as high as 10 can be applied to the MWRO, reflecting a recovery of 90%. Such high recovery was demonstrated using RO design software and operating a two 3-elements-in-series RO pilot plant. As the recovery rate increases, organic substances from the feed water concentrate in membrane elements at locations where flowrate is substantially reduced. At CF 5, total organic carbon and total nitrogen in the reject can be greater than 40 g/m3. The challenge of high recovery in the MWRO process then is the design and configuration of an efficient RO process in which organic and bio-fouling can be effectively controlled and advanced technologies can be integrated for fouling minimization. Key words: wastewater reclamation, reverse osmosis, membrane inorganic scaling, organic fouling, concentration factor.