The Marin Municipal Water District (MMWD) Seawater Desalination Pilot
Program was a successful year-long desalination pilot study of advanced
pretreatment and seawater reverse osmosis (SWRO) technologies for desalting water from San Francisco
Bay (Bay) from June 2005 to May 2006. Based on the favorable outcome of the pilot program, seawater desalination can be a local, reliable drought-proof
source of drinking water supply for Marin, California. The MMWD Seawater
Desalination Pilot Program included:
determining that microfiltration (MF)/ultrafiltration (UF) is the recommended pretreatment for
North San Francisco Bay water;
developing preliminary design criteria and conceptual costs for a full
scale desalination facility;
demonstrating that the desalinated water is safe and meets all state and
federal requirements; and,
demonstrating that the brine discharge blended with CMSA effluent will
not adversely impact the San Francisco Bay environment. The
primary objective of the pilot testing program was to compare the
performance of high rejection SWRO membranes with two different pretreatment alternatives, MF/UF and conventional pretreatment. This
objective was accomplished through the concurrent operation of two parallel
SWRO pilot units of identical design, with Unit 1 treating MF/UF filtrate and
Unit 2 treating conventional filtrate.
The source water for the MMWD SWRO pilot plant, the North San Francisco
Bay, is a complex estuarine water body with influences from the ocean, rivers,
and bay discharges that affect water quality on a daily as well as seasonal
basis. Total dissolved solids (TDS) varied from approximately 25,000 mg/l in the summer to less than
5,000 mg/l in the winter. While both the conventional and MF/UF
pretreatment produced suitable quality RO feedwater, MF/UF filtrate was
lower in SDI and less impacted by source water variations. Four different
high rejection SWRO membranes were tested. All membranes provided
satisfactory performance, although differences were observed between
element types in both trains. No significant differences were observed in RO
performance between the two trains based on changes in normalized
permeate flow or salt passage. However, based on normalized differential
pressure and autopsy results, elements operated with conventional
pretreatment exhibited greater overall particulate, organic, protein and
carbohydrate fouling than those with MF/UF filtrate.
The pilot program also included analytical testing of over 100 regulated and
500 non-regulated constituents in the Bay water and RO permeate, as well as
an evaluation of second pass RO to meet MMWD's stringent finished water
boron and sodium requirements. Environmental studies conducted in
conjunction with the pilot testing included fish entrainment studies, bioassay
studies and California Toxics Rule analysis of the brine discharge and toxicity
analysis of the residuals from the pretreatment systems. Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 590 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 25 |
| Published : | 03/01/2007 |
