A forced draft aeration (FDA) process has been in operation for approximately 18 months at the Keller Water Treatment Plant, Pinellas County Utilities (PCU), Florida. During this time, the system
has effectively removed sulfides, a major contaminant of concern because of long-standing impacts
associated with water disinfection, corrosion, turbidity and taste and odor in the Pinellas County Water
System (PCWS). However, increased turbidity levels in the FDA effluent were encountered within the
first few months of operation prompting further investigation. Turbidity has consistently exceeded 1
NTU with values exceeding 1.5 NTU within 3 months of operation. This represents a substantial increase
from the 0.2 NTU level commonly observed in the WTP raw water stream.
Visual inspection confirmed significant solids accumulation within the packing media and microbial
analysis performed for the County confirmed the presence of Thiothrix. This organism,
whose numbers greatly increase in the FDA process, is at least partly responsible for the turbidity
problem. The Floridan Aquifer appears to be the source of Thiothrix (Brigmon et al. 1994). Note that
while Thiothrix is not reported to pose a human health threat, the slime like substances (EPS, or
extrapolysaccharide) excreted by the bacterial biofilm could provide a protective matrix for a wide variety
of microorganisms to live and multiply, a condition which raises several fundamental concerns:
adverse water quality impacts caused by sloughing of biofilm material into the WTP process stream;
degradation of FDA treatment performance; and, mechanical failure of the FDA media support
structure. The information presented in this paper looks at low-cost filtration methods for removing
solids sloughed from the FDA media into the process water. Based on organism size, cartridge filters and backwashable
strainers were identified as sieving processes potentially capable of mitigating turbidity following FDA.
This study characterized the nature of solids accumulated/sloughed and evaluated turbidity
removal via either cartridge or strainer filtration techniques. Includes 2 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
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| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 20 |
| Published : | 11/02/2003 |
