The City of Sweetwater, Texas, (population 12,000) shut down their surface water treatment
plant in December, 2001. Originally constructed in the 1920s, the conventional treatment plant
(rapid mix - flocculation - sedimentation - filtration) could not meet the finished water turbidity
requirements that became effective January 1, 2002. Additionally, monitoring at the plant
conducted prior to shutdown revealed an inability to meet a 25% reduction in total organic
carbon (TOC) as required under provisions of the Interim Enhanced Surface Water Treatment
Rules also effective for Sweetwater on January 1, 2002.
Planning for the future, the City of Sweetwater conducted pilot studies from October, 1999,
through March, 2000, to test the treatment capabilities of membrane technologies. Pilot
objectives included:
demonstrating organic removal performance;
demonstrating turbidity/particle removal capabilities;
demonstrating the overall treatment capability for feed water from three surface
water sources; and,
determining the design and operating parameters for a full-scale plant.
The size of natural organic matter present in surface waters is smaller than the pore size of
membranes. The pilot study focused on optimizing TOC removal by enhanced coagulation
upstream of the membranes. The goal was to generate pin-sized floc particles large enough to
be removed by ultrafiltration. The ZeeWeed Immersed Membrane System from ZENON
Environmental Systems, Inc. met all of the study objectives.
TOC reductions of over 32% were achieved when the ZENON pilot unit was operated for
enhanced coagulation. Design parameters developed from the pilot study included provisions
for rapid mixing of the coagulant, followed by a limited flocculation stage of 12.5 minutes prior to
entering the membrane tanks. By controlling system recovery and maintaining a high solids
concentration in the membrane process tanks, TOC reductions meeting or exceeding the
regulatory standards will be achievable in the full-scale plant.
The City of Sweetwater's new 8.0 MGD (30.28 MLD) surface water treatment plant is under
construction, with startup anticipated in August 2003. In addition to combining enhanced
coagulation for TOC removal with ultrafiltration, design of the full-scale plant includes a
secondary UF process tank to achieve a 99% recovery of feed water. These two design
characteristics (enhanced coagulation and 99% recovery) are key elements of the first
immersed, vacuum-driven membrane system in Texas. Includes 6 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 430 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 18 |
| Published : | 03/05/2003 |
