AWWA WKICO66065

Arsenic is a common trace inorganic contaminant present in many US drinking water supplies and its current MCL (maximum contaminant limit), based on concerns about the long-term health effects is 10 µg/L (USEPA, 2001). The Albuquerque Bernalillo County Water Utility Authority (the Authority) has 92 wells of which 41 have arsenic concentrations greater than 10 µg/L. With respect to the arsenic regulation, the Authority is one of the most severely impacted utilities in the US. Bench and pilot studies were performed at the University of Houston and at the West Mesa Pump Station in Albuquerque, respectively, to develop a ferric coagulation-direct microfiltration (C/MF) process. Process variables studied included arsenic speciation, initial arsenic concentration, pH, coagulant (ferric) dose, pre-formed vs. in situ coagulant use, coagulation time (prior to direct filtration), influence of co-occurring inorganic species (silica and sulfate), mixing intensity, filter pore size, filter flux and backwash interval. These studies proved the ability of the C/MF process to remove arsenic to meet the new MCL, and established design criteria for the full-scale 5.3-MGD Arsenic Removal Demonstration Facility (ARDF), which went into operation in July 2007. Design and operational details of the ARDF are described in this paper, along with a discussion of findings of the bench and pilot studies. Includes 4 references, tables, figures.