AWWA REUSE52113

The City of McAllen, Texas, with the assistance of CH2M HILL and the co-sponsorship of the United States Bureau of Reclamation (BOR), Electric Power Research Institute, and the Texas Water Development Board, has pilot tested an integrated membrane bioreactor (MBR)/reverse osmosis (RO) treatment train to reclaim municipal wastewater to a quality suitable for use as a new drinking water supply in the process called indirect potable reuse. Previous testing by the City (Phase 1) demonstrated the applicability and cost of microfiltration (Memcor and ZeeWeed systems) to enhance the quality of secondary effluent for subsequent treatment by RO and the feasibility of a membrane bioreactor system (ZenoGem) to produce RO feedwater directly from minimally processed sewage. Phase 2 testing, reported on in this paper, is designed to demonstrate, when treating screened, degritted sewage, reliable operation of both the MBR and RO processes and that the effluent from such a train can meet all federal primary and state secondary drinking water regulations and comply with state requirements for indirect potable reuse. Results show the ZenoGem process to be reliable, require minimal operator attention and maintenance, produce an effluent that can be processed by RO with little fouling and that easily exceeds the City's current effluent discharge requirements relative to biological oxygen demand (BOD), total suspended solids (TSS), and ammonia. The ZenoGem permeate quality exceeds RO feedwater criteria for turbidity and silt density index and the RO system performance confirms minimal membrane fouling by particles. However, the high calcium hardness and phosphate levels in the City's wastewater (and ZenoGem permeate) caused mineral precipitation within the RO system when operated at higher recoveries. Precipitation can be controlled, however, by increased acidification of the RO feedwater. Includes 2 references, tables, figures.