AWWA MTC57590

Low-pressure membrane systems depend on an automated backwash process to dislodge particulate build-up on the membrane surface. Although membrane manufacturers have different backwash procedures and intervals, all utilities are faced with disposal of this water. In many cases this backwash water can be re-treated through a separate membrane system to produce an effluent quality equal to that of the primary system. Additionally, by adding a secondary treatment system, the overall plant effectiveness is increased and costs for disposing backwash water are reduced. California's Department of Health Services (DHS) currently does not have regulations for processing membrane backwash water and relies on conventional treatment system criteria. The membrane process used at Carmichael Water District (CWD) does not require chemical addition to aid in filtration, which greatly differs from that found in conventional processes and permits re-treatment options. In June 2001, CWD embarked upon a program to demonstrate the viability of its treated backwash water as acceptable drinking water and aid the local regulatory agency in their decision to consider secondary filtrate for potable use. This paper examines the relationships of finished water quality parameters for the primary and secondary stage filtration under fullscale operational conditions. Includes 6 references, tables, figure.