A $300 million peak-flow treatment facility in Birmingham, Alabama that has been in operation since mid-2003 has dramatically improved wastewater quality in that community. But the Village Creek Wastewater Treatment Plant faced stern tests when hurricanes Ivan, Katrina and Rita dumped a total of about a foot-and-a-half of rain on the city in a short time span. The facility passed the test thanks to the TETRA ® deep bed filter technology and innovative new methods for ensuring consistent water flow.
Village Creek’s treatment plant’s 22 deep bed filters, each with 1160 ft.² filtration surface area, are laid out in two trains with room for expansion. The new control methods and innovative piping designs (a technology package referred to as StormMaster™) allow continuous, rolling execution of up to two simultaneous air-water backwashes and four water-only backwashes at the same time, divided among the two filter trains to control head loss and expel excess solids during wet weather events. These events peak at up to 360 mgd for four hours, with elevated flows persisting for as much as 24 hours. However, between storms the plant is successfully polishing 60 mgd of final effluent for discharge to Village Creek. A portion of the peak flow continues to be handled by the existing biological treatment plant. Dirty backwash water is sent to thickeners in the biological treatment plants.
A key feature of the filters is the 6-ft.-deep bed of large, rounded sand, which allows high flow rates, large storage capacity for heavy solids loadings and long run times. Self-flocculating mechanisms for solids lodged within the filter media reduce the need for chemical addition.
The filter underdrain includes rows of arched concrete blocks rest on the filter floor, leaving large passages for water to flow under and between rows. This “T-block™” design is extremely resistant to biological fouling, making it ideally suited for wastewater applications. The blocks also protect the backwash air-distribution system. A system of stainless-steel backwash air laterals under alternate rows of T-blocks precisely meter air under the entire bottom of the filter, allowing for even, effective backwashing. The design stands up well to heavy-duty conditions and provides zero maldistribution.
Adjacent to the new filter plant are 24 surge basins that hold the first flush of undiluted wastewater with the highest concentration of pollutants for later processing. This water may be applied directly to the filters at the operator’s discretion.
The new biological treatment plant also takes in some of the surge flow directly. All wastewater treated by the new facility also passes through the new filters. Final effluent is treated by UV disinfection before discharge to Village Creek.
On September 16, 2004, the plant received its first significant test when Hurricane Ivan roared through the state, dumping nearly 10 inches of rain on the area. The new facility handled the torrential rainfall as it was designed to. Rain infiltration into the collection system caused flows to rise rapidly. A 182 mgd flow was applied to the filters, which they handled without difficulty. The SpeedBump™ cycle was utilized, reducing head loss in the filters as planned.
Hurricanes Katrina and Rita, which wreaked havoc and record-setting damage along the Gulf Coast in 2005, were little more than rain events in Birmingham when compared to Hurricane Ivan. The storms combined to drop more than six additional inches of rain on the area during just a few hours. Again, the Village Creek facility handled the increased flow without any difficulties.
According to David Lee, plant manager at Village Creek, the system has provided multiple benefits. “The deep bed filters have worked exactly as intended,” Lee said. ”The system has proven its ability to handle significant water flow, so the bypass feature has never been required. All in all, the deep bed filter technology has helped the Village Creek plant to not only improve wastewater quality, but has benefited the Village Creek waterway and Bayview Lake, even during three hurricane events.”
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