The maximum Log Removal Value (LRV) that can be awarded to a membrane system has
traditionally been based on the primacy agency's interpretation of the Surface Water Treatment
Rule for devices considered Alternative Filtration Technologies (AFTs). Granted removal credits
are influenced by the demonstrated membrane disinfection capabilities, number of microbial
barriers, and water quality. The Long Term 2 Enhanced Surface Water Treatment Rule
(LT2ESWTR) will impose specific requirements and provide additional guidance for determining
the LRV. The Proposal Draft Version of LT2ESWTR and associated Membrane Filtration
Guidance Manual (MFGM) (USEPA, 2003), detail the impact of critical operating parameters on
LRVs.
Carollo Engineers recently completed the design of the Eastern Municipal Water District's
(EMWD) Hemet Water Filtration Plant (HWFP) (Hemet, California). The 10 million gallon per
day (mgd) plant (expandable to 40 mgd), includes prefilters, coagulation, single stage
flocculation, membrane filtration, chlorine contact time basin, and finished water pump station.
This manuscript describes design considerations that were necessary to operate the plant at
98% recovery while maintaining a membrane integrity test (MIT) sensitivity of 4 logs.
Due to an increasing need for water and a persistent drought, EMWD decided to construct a
new water treatment plant at Hemet with an initial capacity of 10 mgd.
Based on recent experiences at its recently commissioned Perris Water Treatment Plant,
EMWD selected Zenon 500d series membranes for disinfection and filtration at the HWFP.
Three main bodies of regulations were considered during process selection: the proposed
LT2ESWTR and its antecedents; the Stage 2 Disinfectants/Disinfection Byproducts Rule
(Stage 2 D/DBPR); and, the California Department of Health Services (DHS) requirements.
While the first two are Federal regulations, the specific requirements for LT2ESWTR are delegated to the State for membrane filtration. Therefore, California DHS has developed
requirements for membrane filtration, including credits for removals of pathogens such as
Giardia and Cryptosporidium. DHS has done this on a system-by-system basis.
The plant's source water, State Project Water (SPW), presents treatment challenges in three
areas:
relatively high levels of bromide, which contribute to the formation of disinfection
byproducts (DBPs);
taste and odor episodes resulting from algae growth and production of geosmin and
2-methylisoborneol (MIB); and,
levels of Total Organic Carbon (TOC) and Dissolved Organic Carbon (DOC), which
contribute to DBP formation, inhibit absorbance of ultraviolet light, and accelerate
membrane fouling.
The plant is not subject to the Stage 1 Disinfection/Disinfectants Byproducts Rule (Stage 1
D/DBPR) requirements for percentage TOC removal because this requirement applies only to
conventional treatment processes; membrane filtration is not a conventional treatment process.
In order to address these treatment challenges, the following additional processes were
selected for inclusion in the treatment train:
future taste and odor control process (granular activated carbon contactors);
coagulation/flocculation process (pump diffusion flash mix and single stage flocculation);
future UV disinfection process (closed channel reactors);
supplemental primary disinfection process (chlorination);
secondary disinfection with chloramines; and,
future wastewater recovery process (plate settler). Includes 2 references, table, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 780 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 11 |
| Published : | 03/01/2005 |
