City of Garland,
Duck Creek Wastewater Treatment Plant Expansion
- Retrofitted clarifier with a new bridge mechanism which included heavier bridge rails, a hydraulic drive system, and an improved sludge withdrawal system.
- Identification and evaluation or additional retrofit alternatives.
- Interactive O&M manual and digital library system implementation.
- Oso Wastewater Reclamation Plant Process Improvements.
Carollo, acting in conjunction with another national engineering firm, is providing preliminary design, final design, and construction management for expansion of the Duck Creek Wastewater Treatment Plant from 30 mgd to 40 mgd, City of Garland, Texas. In addition to increased plant capacity, the goals of the 10-mgd expansion are to rehabilitate the entire plant and to make sure nitrification (ammonia) discharge requirements are not exceeded. The existing plant has the following processes: flow equalization basin; coarse screening; aerated grit removal; raw sewage pumping; primary settling basins; trickling filters; solids contactor (aeration basin); secondary settling basins; tertiary filters; chlorine disinfection; and sulfur dioxide dechlorination. Design alternatives to achieve the expansion goal that were investigated during the preliminary design portion of the project included: increasing the size of the existing solids contactor; adding a nitrifying trickling tower (NTF); and adding a new activated sludge complex.
The existing plant has experienced exceedence of the ammonia discharge requirement during the winter months. To mitigate ammonia nitrogen excursions, the Wastewater Treatment Business Plan (completed by another consultant) recommended re-rating of the existing trickling filter/solids contact process to 25 mgd and addition of a 5-mgd activated sludge train. However, subsequent studies revealed that this was a more costly alternative than expansion of the existing solids contactors.
During preliminary design, it was determined that expansion to 40 mgd and rehabilitation of the existing facilities was the most appropriate path to assure permit compliance. Carollo was responsible for design of the following facilities: 116-mgd raw wastewater pumping station; fine step screens and vortex grit facilities; equalization basin improvements; trickling filter recycle pump station rehabilitation; trickling filter rehabilitation; snail removal basins; and a 72-mgd lift station expansion. This project is currently under construction and the team is providing contract administration, shop drawing review, and resident engineer services.