Wastewater Treatment Plant and Raw Wastewater Force Main Rehabilitation

Town of Flower Mound, Texas

APAI designed facilities to increase the Town of Flower Mound’s Wastewater Treatment Plant’s design flow treatment capacity from 5 mgd to 10 mgd. The existing plant process included preliminary treatment, primary clarification, single-stage nitrification, effluent filtration and ultraviolet (UV) disinfection. The waste sludge was stored in sludge holding tanks, dewatered with a belt press, and lime stabilized to Class B biosolids. The expansion included a new preliminary treatment area, sequencing batch reactors (SBR), additional effluent filters, additional UV disinfection capacity, and a new effluent metering structure. APAI designed renovations to the existing secondary treatment system to remove the abandoned trickling filters, to incorporate additional piping flexibility ahead of the nitrification basins, and to replace the existing return activated sludge air lift pumps with non-clog centrifugal pumps.

Other improvements included the addition of a second belt press for sludge dewatering, two more wet-weather effluent pumps and odor control facilities for the preliminary treatment area. The new preliminary treatment area (PTA) treats the entire influent flow. Preliminary treatment includes fine screens, grit removal, influent metering, and flow splitting between the existing treatment train and the new sequencing batch reactors. The screenings are washed and compacted and combined with the dewatered grit in a screenings/grit container for disposal. APAI designed a building to store the screenings and grit and designed covers over the channels of the PTA to contain odorous air. The odorous air from the grit/screenings building and the PTA channels is routed to organic media biofilters for treatment. Normally, flow is split evenly between the existing treatment train and the new SBRs; however, the flow division weirs can be adjusted to split the flow, as the plant operators require. This operational flexibility allows the treatment plant to operate without primary clarifiers at flows less than 8.3 mgd. Since the completion of the SBR plant and taking the primary clarifiers offline, there have been no odor complaints regarding the wastewater treatment plant.

Subsequently, APAI contracted with the Town for the second phase of the rehabilitation of the wastewater treatment plant and the replacement of the raw wastewater force main, which included the evaluation of pipeline routes, hydraulics, and pipe sizing. APAI evaluated two pipeline routes from the existing raw wastewater lift station to the existing preliminary treatment unit as well as a topographic survey of the pipeline route and hydraulics to select pipe size to maintain lift station capacity. Throughout the construction phase, APAI provided assistance to the Town’s resident representative in conducting conferences; advising and making recommendations regarding materials and workmanship; reviewing samples, catalog data, schedules, show drawings, laboratory, shop and mill test of material and equipment, and other data; and interpreting the intent of the plans and specifications for the Town and contractor.

... because water is precious