Assessing the Role of Desalination in Southern California’s Future Water Supply An investigation of economic & envir

1. Assessing the Role of Desalination in Southern California’s Future Water SupplyAn investigation of economic & environmental aspects Research Team: Jean-Daniel Saphores, CEE, Econ, & PPD; Tim Bradley, EEB; Sunny Jiang, CEE; Jan Scherfig, CEE.

2. Economic Questions (Jean-Daniel Saphores) • What is the current situation in Southern California? • What obstacles does desalination have to overcome to be viable? • What are the existing supply options? • What is the existing environment? • What is the value of desalination in the existing portfolio of water supply sources? • How does various types of uncertainty (technological, regulatory, economic) affect the decision to build a desalination plan? • Methodology: • 1) Perform simple benefit cost-analysis • 2) Build and analyze dynamic “real options” model • Application to a case study (Dana Point plant?)

3. Brine Disposal – Engineering aspects (Jan Scherfig) • Brine disposal = major environmental issue. Two options: • If a desalination plant is located within a reasonable distance from a sewage treatment plant with capacity in its ocean outfall: best solution = mix the brine and the treated sewage in the existing outfall. • If a separate outfall must be constructed: challenge = develop design tools (based on conventional sewage outfall design) so that: • Meet required discharge • No dense high salinity layer around outfall • No anaerobic conditions because of inadequate mixing. • Economical design • Methodology: 2-D simulation to develop design for a wide range of currents, salinity, and discharge criteria.

4. Environmental Impacts I (Sunny Jiang) Option 1: brine is discharged with secondary treated sewage. • Hypotheses: • 1) Mixing of brine with secondary treated sewage may alter the microbial community composition & diversity, facilitate evolution and adaptation of some microbial pathogens to marine water in discharge field; • 2) Direct discharge of desal to marine water may select a sub-group of microbial community that are more adaptable to higher salt concentration in discharge field. • Methodology: • 1) Investigate microbial community composition using molecular fingerprinting analysis in secondary sewage effluent and in secondary sewage effluent mixed with desal reject. • 2) Investigate occurrence & abundance of microbial pathogens in samples before and after mixing using both genome based and cultured based approaches. • 3) Investigate the impact of desal reject on marine microbial community in the discharge field by sampling marine bacterial community before & after mixing with desal reject.

5. Environmental Impacts II (Tim Bradley) Option 2: Separate outfall for brine. • Previous studies: different organisms have ≠hyper-saline tolerances: • Some organisms are very tolerant; others (e.g., fish) cannot breed at salinities >= 114% seawater. • However, fish can survive at salinities of 150% seawater if held steady. • Major gap: changing salinities; compared to steady salinity, changing salinity places much greater stress on cells as they swell & shrink. • Methodology: • Use sea urchin larvae because: • Comparatively sensitive to hyper-salinity; • Good model for planktonic organisms that cannot swim away from salt. • Examine salinities at which larvae cannot grow, & effects of rapid (~ minutes) salinity changes on survival. • Goal: determine parameters that adversely affect growth and survival; parameters then used to design outflow and to quantify the negative effects of placing brine into marine ecosystems.

6. Funding Sources • Water Resources Research – National Competitive Grants Program • Deadline = February 16, 2007 • 1-3 years & up to $250,000 • AWWA Research Foundation • Unsolicited Research • Others? • Industrial partner = MWDOC?