Pilot Evaluation of Ceramic Membranes: An Emerging Reuse Treatment Technology

A skid-mounted portable ceramic membrane pilot unit (I. Krüger, Inc.) was installed at the Dallas (TX) Water Utilities (DWU) Southside WWTP (SWWTP) to demonstrate at a “proof of concept” level the capability of a monolithic pressurized ceramic membrane system to treat secondary effluent to reuse standards at high fluxes. The study was conducted at the SWWTP over a one-month period using two feed water sources: chlorinated secondary effluent and unchlorinated secondary effluent. Filtrate turbidity met Texas Commission on Environmental Quality (TCEQ) Type 1 reuse standards in all cases. The observed rise in transmembrane pressure (TMP) over 30 minute filtration cycles (i.e. 30 minutes between backwash events) at 100 gal/ft2-day (gfd) flux was within or below the expected range for both feed water sources, suggesting sustainable operation conditions. A ferric chloride dose of 50 mg/L (as Fe) was required to maintain operation under these conditions. While the use of an oxidant (hypochlorite) soak in addition to an acid soak to the chemical enhanced backwash acid (CEB) routine appeared to positively impact initial TMP recovery, the observed increases in initial TMP after CEB routines at 12-hour intervals suggest the possible need for more frequent recovery clean-in-place (CIP) procedures for wastewater reuse applications as well as the potential inherent limitations associated with use of the pilot-scale membrane element. Sustainable operation of ceramic membranes under these conditions requires optimization of coagulant dose and CEB/CIP protocols and frequencies through subsequent testing with a full scale 25 m2 module element. The cost competitiveness of ceramic membrane systems with polymeric membrane systems will be controlled by the ability to offset typically higher ceramic capital costs with lower ceramic operating, maintenance and life cycle costs.