Achieving Reduced-Cost Wet Weather Flow Treatment through Plant Operational Changes
Abstract:Despite documented I/I reductions in the collection system1, the dynamic hydraulic model for the Trinity River Authority of Texas' (TRA) Central Regional Wastewater System (CRWS) predicted an increase in the Q2-HR PEAK/QADF ratio at the WWTP from 2.5 to 3.30.2 The 2.5 ratio historical value was known to be artificially low, the result of unintended in-line storage created by hydraulic bottlenecks in the collection system. The 3.30 ratio is the year 2020 predicted value derived from the hydraulic model. This assumes the completion of the scheduled collection system improvements intended to remove the bottlenecks.
TRA intends to implement the collection system improvements and to treat all wastewater flows at the CRWS Wastewater Treatment Plant. The improvements recommended to handle the projected 3.30 ratio peak flows included 1) wet weather treatment facilities and 2) additional final clarifiers. Capital cost of the improvements to treat the peak flow was estimated at 21.1 million.3 The wet weather treatment facilities – High Rate Clarification – have been deferred pending final regulations/policy by the U.S. Environmental Protection Agency (USEPA) with regard to blended flows and the preparation of additional technical and economic data by the Authority. The final additional final clarifiers were budgeted for construction in 2010.
The Authority began investigating operational modifications at the plant to allow CRWS to handle increased peak flow until either or both of the planned improvements could be brought on line. The two operational modifications determined most feasible were the addition of step-feed capability for all of the secondary treatment basins and conversion of the existing in-line equalization basins to off-line peak storage basins. This paper describes these operational changes, the quantification of the increased peak flow capability of the CRWS plant and the associated capital cost reduction of 6.2 million.
Document Type: Research Article
Publication date: January 1, 2006
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