The City of Wilmington's Sweeney Water Treatment Plant (SWTP) treats a challenging water
source (Cape Fear River) using a series of water treatment processes, including ozonation and
biofiltration. The biofiltration process serves the dual purpose of meeting the filtration
requirements for turbidity and production efficiency, and organics removal via adsorption
and biodegradation. The biofilters are dual-media filters with granular activated carbon (GAC)
over silica sand. GAC was chosen over anthracite because it provides an additional barrier
against chemicals that cause taste-and-odor (T&O) in the water.
The plant currently uses bituminous-based GAC that has been in place since 1997. The GAC has
performed well in both filtration and biological BOM removal. However, the City was interested
in determining whether other types of GAC material would perform as well as or better than the
bituminous GAC. If GAC made from other material performs as well, then the City's options for
GAC suppliers would increase substantially. NORIT supplies both lignite GAC and bituminous
GAC, but lignite GAC is their main product. NORIT was also interested in determining how well
lignite GAC would perform in a biofiltration role. NORIT contacted the staff of the Sweeney WTP
and jointly funded a side-by-side full-scale study to compare lignite GAC to bituminous GAC in a
biofiltration mode. One benefit of lignite GAC over bituminous GAC is its lower density. This
translates into a lower backwash water flow rate compared to bituminous GAC to achieve the
same backwashing efficiency, which in turn translates into savings in pumping energy and
wasted water.
This full-scale study was conducted between June 2001 and July 2002. The objectives of the
study were as follows:
compare the performance of lignite GAC to that of bituminous GAC for biofiltration;
determine whether lignite GAC filters can be backwashed at a lower rate than bituminous GAC filters without compromising performance; and,
collect long-term operational data on the performance of both GAC types for meeting
the filtration requirements for turbidity removal and filter runtimes.
Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 340 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 11 |
| Published : | 11/01/2002 |
